US20220340947A1 - Prokaryote-based cell-free system for the synthesis of glycoproteins - Google Patents

Abstract

The present invention is directed to a cell-free system for producing a glycosylated protein. This system comprises an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target, one or more isolated glycans, where each glycan is linked to a lipid carrier molecule, and a glycoprotein target comprising one or more glycan acceptor amino acid residues or a nucleic acid molecule encoding said glycoprotein target. The present invention further relates to kits and methods for producing a glycosylated protein in this cell-free system.

Description

• This application is a continuation of U.S. patent application Ser. No. 14/356,258, filed May 5, 2014, which is a national stage application under 35 U.S.C. § 371 of International Application No. PCT/US2012/063590, filed Nov. 5, 2012, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/555,854, filed Nov. 4, 2011, which are hereby incorporated by reference in their entirety.
FIELD OF THE INVENTION
• The present invention relates to cell-free systems, kits, and methods for producing a glycosylated protein or peptide.
BACKGROUND OF THE INVENTION
• Cell-free protein-synthesizing systems are emerging as an attractive alternative to conventional expression systems that rely on living cells (Katzen et al., “The Past, Present and Future of Cell-Free Protein Synthesis,” Trends Biotechnol. 23:150-156 (2005)). This is because, over the past decade, cell-free protein synthesis reactions: (i) can be completed in less than a day; (ii) use reagents whose costs are down; (iii) fold complex proteins by routinely forming disulfide bonds; and (iv) can be scaled to 100 L. Two main approaches have been used for in vitro transcription/translation: one is based on cell-free extracts (CFEs), often derived from Escherichia coli, rabbit reticulocytes or wheat germ, and the second is based on reconstituted protein synthesis from purified components (Shimizu et al., “Cell-Free Translation Reconstituted With Purified Components,” Nat. Biotechnol. 19:751-755 (2001)). Because of their ability to co-activate multiple biochemical networks in a single integrated platform (Jewett et al., “An Integrated Cell-Free Metabolic Platform for Protein Production and Synthetic Biology,” Mol. Syst. Biol. 4:220 (2008)), cell free systems are increasingly used in many important biotechnology and synthetic biology applications (Ryabova et al., “Functional Antibody Production Using Cell-Free Translation: Effects of Protein Disulfide Isomerase and Chaperones,” Nat. Biotechnol. 15:79-84 (1997); Noireaux et al., “Principles of Cell-Free Genetic Circuit Assembly,” Proc. Nat'l. Acad. Sci. U.S.A. 100:12672-12677 (2003); Yang et al., “Rapid Expression of Vaccine Proteins for B-Cell Lymphoma in a Cell-Free System,” Biotechnol. Bioeng. 89:503-511 (2005)).
• The ability to accurately and efficiently glycosylate proteins in a cell-free system would have advantages for many areas of basic and applied research, especially given the importance of N-linked glycosylation in protein folding, quality control, sorting, degradation, secretion and activity (Helenius & Aebi, “Roles of N-Linked Glycans in the Endoplasmic Reticulum,” Annu. Rev. Biochem. 73:1019-1049 (2004)). Unfortunately, the best characterized and most widely used cell-free translation systems based on E. coli are incapable of making glycoproteins because E. coli lack glycosylation machinery. Likewise, rabbit reticulocyte and wheat germ CFE systems cannot perform this post-translational modification because they lack microsomes (Tarui et al., “A Novel Cell-Free Translation/Glycosylation System Prepared From Insect Cells,” J. Biosci. Bioeng. 90:508-514 (2000)). This can be overcome by supplementing eukaryotic CFEs with microsomal vesicles (e.g., canine pancreas microsomes) (Lingappa et al., “Coupled Cell-Free Synthesis, Segregation, and Core Glycosylation of a Secretory Protein,” Proc. Nat'l. Acad. Sci. U.S.A. 75:2338-2342 (1978); Rothblatt & Meyer, “Secretion in Yeast: Reconstitution of the Translocation and Glycosylation of Alpha-Factor and Invertase in a Homologous Cell-Free System,” Cell 44:619-628 (1986)), but the resulting systems do not always faithfully process the target protein due to poor compatibility between some CFEs and microsomal vesicles (Rothblatt & Meyer, “Secretion in Yeast: Reconstitution of the Translocation and Glycosylation of Alpha-Factor and Invertase in a Homologous Cell-Free System,” Cell 44:619-628 (1986); Moreno et al., “An mRNA-Dependent in Vitro Translation System from Trypanosoma brucei,” Mol. Biochem. Parasitol. 46:265-274(1991)). An alternative strategy for creating a cell-free translation system that can execute N-linked glycosylation is to prepare CFEs from specialized cells such as hybridomas (Mikami et al., “A Hybridoma-Based in Vitro Translation System That Efficiently Synthesizes Glycoproteins,” J. Biotechnol. 127:65-78 (2006)), trypanosomes (Moreno et al., “An mRNA-Dependent in Vitro Translation System from Trypanosoma brucei,” Mol. Biochem. Parasitol. 46:265-274 (1991)), insect cells (Tarui et al., “A Novel Cell-Free Translation/Glycosylation System Prepared From Insect Cells,” J. Biosci. Bioeng. 90:508-514 (2000)) or mammalian cells (Shibutani et al., “Preparation of a Cell-Free Translation System From PC12 Cell,” Neurochem. Res. 21:801-807 (1996)). However, these systems are technically difficult to prepare and typically result in inefficient glycosylation and low product yields. Moreover, in all the above systems, the glycosylation process is effectively a “black-box” and thus difficult to control.
• The present invention is directed at overcoming these and other deficiencies in the art.
SUMMARY OF THE INVENTION
• A first aspect of the present invention is directed to a cell-free system for producing a glycosylated protein. This system comprises an isolated oligosaccharyltransferase (OST) capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target; one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule; and a glycoprotein target comprising one or more glycan acceptor amino acid residues, or a nucleic acid molecule encoding said glycoprotein target.
• Another aspect of the present invention is directed to a kit comprising an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target, and one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule.
• Another aspect of the present invention relates to a method for producing a glycosylated protein in a cell-free system. This method involves providing an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target, providing one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule, and providing a glycoprotein target comprising one or more glycan acceptor amino acid residues. This method further involves combining the oligosaccharyltransferase, one or more isolated glycans, and glycoprotein target to form a cell-free glycosylation reaction mixture, and subjecting the cell-free glycosylation reaction mixture to conditions effective for the oligosaccharyltransferase to transfer the glycan from the lipid carrier molecule to the one or more glycan acceptor residues of the glycoprotein target to produce a glycosylated protein.
• To address the failure of other cell-free systems to accurately and efficiently glycosylate proteins, two novel cell-free translation/glycosylation systems—termed “glycoCFE” and “glycoPURE”—were created as described herein. These systems combine existing in vitro translation systems with a reconstituted N-linked glycosylation pathway. Purified glycosylation components were derived from the protein glycosylation locus (pgl) present in the genome of the Gram-negative bacterium Campylobacter jejuni (FIG. 1A). This gene cluster encodes an N-linked glycosylation system that is functionally similar to that of eukaryotes and archaea, involving an oligosaccharyltransferase that catalyzes the en bloc transfer of preassembled oligosaccharides from lipid carriers onto asparagine residues in a conserved motif [N-X₁-S/T in eukaryotes and D/E-X₁-N-X₂-S/T (SEQ ID NO: 1) in bacteria (Kowarik et al., “Definition of the Bacterial N-Glycosylation Site Consensus Sequence,” EMBO J. 25:1957-1966 (2006), which is hereby incorporated by reference in its entirety), where X₁ and X₂ are any residues except proline] within polypeptides (FIG. 1B). C. jejuni glycosylation machinery is ideally suited for use in a cell-free translation/glycosylation system for the following reasons. First, E. coli transformed with the entire pgl gene cluster can perform N-linked protein glycosylation (Wacker et al., “N-Linked Glycosylation in Campylobacter jejuni and its Functional Transfer Into E. coli,” Science 298:1790-1793 (2002), which is hereby incorporated by reference in its entirety), thereby providing a convenient host for producing the necessary components in a pure and active form. Since E. coli lacks native glycosylation machinery, the potential for contamination from background N- or O-linked systems is eliminated. Second, C. jejuni OST, named PglB (CjPglB), is a single-subunit enzyme that is active when solubilized in detergent (Lizak et al., “X-ray Structure of a Bacterial Oligosaccharyltransferase,” Nature 474:350-355 (2011), which is hereby incorporated by reference in its entirety), and does not require any accessory components for its activity. Third, CjPglB can transfer sugars post-translationally to locally flexible structures in folded proteins (Kowarik et al., “N-Linked Glycosylation of Folded Proteins by the Bacterial Oligosaccharyltransferase,” Science 314:1148-1150 (2006), which is hereby incorporated by reference in its entirety), indicating that protein glycosylation can be achieved without supplementing a functional membrane system (e.g. microsomes).
BRIEF DESCRIPTION OF THE DRAWINGS
• FIGS. 1A-1B depict aspects of bacterial and eukaryotic N-linked glycosylation. FIG. 1A shows the 17-kb pgl locus of C. jejuni encoding the N-linked glycosylation machinery that has been fully reconstituted in E. coli. FIG. 1B shows a comparison of N-linked glycosylation in prokaryotes (left) and eukaryotes (right). In both systems, several glycosyltransferases synthesize the glycan by sequential addition of nucleotide-activated sugars on a lipid carrier on the cytoplasmic face of the inner membrane. Once assembled, a flippase transfers the lipid-linked glycans (also referred to as lipid-linked oligosaccharides or LLOs) across the membrane where the oligosaccharyltransferase catalyzes the transfer to Asn residues of periplasmic or endoplasmic reticulum substrate proteins. PglB is a single-subunit, integral membrane protein that is homologous to the catalytic subunit of the eukaryotic OST STT3 (note that PglB and STT3 complex are not drawn to scale). Whereas eukaryotes and archaea use an N-X-S/T acceptor sequence (where X is any amino acid but Pro), PglB requires an extended motif that includes an Asp or Glu residue in the −2 position (D/E-X₁-N-X₂-S/T (SEQ ID NO:1), where X₁ and X₂ can be any amino acid except Pro). PglB can transfer sugars post-translationally to locally flexible structures in folded proteins.
• FIGS. 2A-2B show the purification of bacterial OST. CjPglB was expressed in E. coli C43(DE3) cells and purified to near homogeneity. Elution fractions (as indicated) from gel filtration columns were examined by SDS-PAGE, and the Coomassie Blue-stained gel images (FIG. 2B) are shown together with the elution profiles (FIG. 2A). MW, molecular weight standard.
• FIGS. 3A-3C show reconstituted glycosylation with defined components. In FIG. 3A, the in vitro glycosylation assay was carried out using purified OST, extracted LLOs and purified acceptor proteins produced in E. coli. The immunoblots of FIG. 3A show the detection of acceptor protein AcrA and scFv13-R4-GT (both anti-His) or glycans (anti-glycan). Reactions included 3 μg wild-type CjPglB, 5 (+) or 10 (++) μL of LLOs and 5 μg of acceptor protein. Controls included the omission of different components (−), inactivated PglB (mut) and LLOs from SCM6 cells with empty pACYC (+/−). Glycosylation yields a mobility shift from the unmodified (g0) to the glycosylated forms (g1 and g2). FIG. 3B is the same assay as described in FIG. 3A but with purified PglB from Campylobacter lari (ClPglB).
• FIG. 3C shows immunoblots detecting AcrA following in vitro glycosylation using 3-month-old freeze thawed components.
• FIGS. 4A-4B demonstrate the cell-free translation/glycosylation of AcrA. FIG. 4A is an immunoblot detecting different AcrA constructs (anti-AcrA) produced by in vitro translation using either E. coli CFEs or purified translation components (PURE). AcrA concentration was estimated by comparing band intensities to that of purified AcrA loaded in lane 1. FIG. 4B is an immunoblot detecting ΔssAcrA expression (anti-AcrA) and glycosylation (anti-glycan). ΔssAcrAwas produced by cell-free translation/glycosylation using either the CFE or the PURE systems that were primed with pET24(AcrA-cyt). Controls included the omission of different components (−) or LLOs from SCM6 cells with empty pACYC (+/−).
• FIGS. 5A-5B depict the cell-free translation/glycosylation of scFv 13-R4-GT. FIG. 5A is an immunoblot detecting different scFv13-R4-GT (anti-FLAG) produced by in vitro translation using either E. coli cell-free extracts (CFE) or purified translation components (PURE). Estimates of the scFv13-R4-GT concentration were determined by comparison of band intensities to that of the purified scFv13-R4-GT sample loaded in lane 1. FIG. 5B is an immunoblot detecting scFv13-R4-GT expression (anti-FLAG) and glycosylation (anti-glycan). The scFv13-R4-GT protein was produced by cell-free translation/glycosylation using either the CFE or PURE systems that were primed with pET24-ssDsbAscFv13-R4-GT. Controls included omission of different components (−).
• FIGS. 6A-6C show an amino acid sequence alignment of various Campylobacter PglB proteins that are suitable for use in the systems, kits, and methods of the present invention. The PglB amino acid sequences are derived from C. jejuni (SEQ ID NO: 2), C. lari (SEQ ID NO:4), C. coli (SEQ ID NO: 6), and C. upsaliensis (SEQ ID NO: 8). An (*) indicates positions which have a single, fully conserved residue; (:) indicates conservation between groups of strongly similar properties; and (.) indicates conservation between groups of weakly similar properties. A PglB consensus sequence based on the alignment of Campylobacter PglB sequences is presented as SEQ ID NO: 10. Residues that are not fully conserved between the four Campylobacter sequences are depicted as X, where X can be any amino acid residue. Alternatively, X is selected from an amino acid residue at that corresponding position in one of the four depicted Campylobacter sequences.
• FIGS. 7A-7E shows an amino acid sequence alignment of various Pyrococcus OST STT3 subunit proteins that are suitable for use in the systems, kits, and methods of the present invention. The OST amino acid sequences are derived from P. furiosus (SEQ ID NO: 11), Pyrococcus sp. ST04 (SEQ ID NO: 13), Pyrococcus sp. (strain NA2) (SEQ ID NO: 14), P. horikoshii (SEQ ID NO:15), P. abyssi (SEQ ID NO: 16), and P. yayanosii (SEQ ID NO: 17). An (*) indicates positions which have a single, fully conserved residue; (:) indicates conservation between groups of strongly similar properties; and (.) indicates conservation between groups of weakly similar properties. A STT3 consensus sequence based on the alignment of Pyrococcus STT3 sequences is presented as SEQ ID NO: 18. Residues that are not fully conserved between the six Pyrococcus sequences are depicted as X, where X can be any amino acid residue. Alternatively, X is selected from an amino acid residue at the corresponding position in one of the six depicted Pyrococcus sequences.
• FIGS. 8A-8D shows an amino acid sequence alignment of various Leishmania OST STT3 subunit related proteins that are suitable for use in the systems, kits, and methods of the present invention. The OST amino acid sequences are derived from L. major (SEQ ID NO: 19), L. donovani (SEQ ID NO: 21), L. infantum (SEQ ID NO: 22), L. mexicana (SEQ ID NO: 23), and L. braziliensis (SEQ ID NO: 24). An (*) indicates positions which have a single, fully conserved residue; (:) indicates conservation between groups of strongly similar properties; and (.) indicates conservation between groups of weakly similar properties. A STT3 consensus sequence based on the alignment of Leishmania STT3 sequences is presented as SEQ ID NO: 25. Residues that are not fully conserved between the five Leishmania sequences are depicted as X, where X can be any amino acid residue. Alternatively, X is selected from an amino acid residue at the corresponding position in one of the five depicted Leishmania sequences.
• FIGS. 9A-9J contain a listing of eukaryotic STT3 oligosaccharyltransferases that are suitable for use in the methods, systems, and kits of the present invention. The oligosaccharyltransferases are identified by UniProtKB Entry number (col. 1), which provides the amino acid sequence of the protein, UniProtKB Entry name (col. 2), protein name (col. 3), gene name (col. 4), organism (col. 5) and European Molecular Biology Laboratory (EMBL) database accession number (col. 6) which provides the encoding nucleotide sequence of the protein.
DETAILED DESCRIPTION OF THE INVENTION
• A first aspect of the present invention is directed to a cell-free system for producing a glycosylated protein. This system comprises an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target; one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule; and a glycoprotein target comprising one or more glycan acceptor amino acid residue, or a nucleic acid molecule encoding said glycoprotein target.
• In accordance with this and all aspects of the present invention, “oligosaccharyltransferase” (“OST”) refers generally to a glycosylation enzyme or subunit of a glycosylation enzyme complex that is capable of transferring a glycan, i.e., an oligosaccharide or polysaccharide, from a donor substrate to a particular acceptor substrate. The donor substrate is typically a lipid carrier molecule linked to the glycan, and the acceptor substrate is typically a particular amino acid residue of a target glycoprotein. Suitable OSTs include those enzymes that transfer a glycan to an asparagine residue, i.e., an OST involved in N-linked glycosylation, and those enzymes that transfer a glycan or activated sugar moiety to a hydroxyl oxygen molecule of an amino acid residue, i.e., an OST involved in O-linked glycosylation. An isolated OST of the present invention can be a single-subunit enzyme, a multi-subunit enzyme complex, or a single subunit derived from a multi-subunit enzyme complex. While a number of exemplary OST enzymes are described below, one of skill in the art readily appreciates that any oligosaccharyltransferase enzyme known in the art is suitable for use in the present invention.
• In accordance with this and all aspects of the present invention, the OST can be a prokaryotic OST. By way of example only, PglB, a single, integral membrane OST protein derived from Campylobacter jejuni is suitable for use in the present invention. PglB attaches a heptasaccharide to an asparagine residue of a glycoprotein target (Kowarik et al., “Definition of the Bacterial N-glycosylation Site Consensus Sequence,” Embo J. 25:1957-66 (2006), which is hereby incorporated by reference in its entirety). The amino acid sequence encoding C. jejuni PglB (UniProtKB Accession No. Q9S4V7) is shown below as SEQ ID NO: 2:

• Ile Ile Ser Asn Asp Gly Tyr Ala Phe Ala Glu Gly Ala Arg Asp Met
  1               5                   10                  15
  Ile Ala Gly Phe His Gln Pro Asn Asp Leu Ser Tyr Tyr Gly Ser Ser
  20                  25                  30
  Leu Ser Thr Leu Thr Tyr Trp Leu Tyr Lys Ile Thr Pro Phe Ser Phe
  35                  40                  45
  Glu Ser Ile Ile Leu Tyr Met Ser Thr Phe Leu Ser Ser Leu Val Val
  50                  55                  60
  Ile Pro Ile Ile Leu Leu Ala Asn Glu Tyr Lys Arg Pro Leu Met Gly
  65                  70                  75                  80
  Phe Val Ala Ala Leu Leu Ala Ser Ile Ala Asn Ser Tyr Tyr Asn Arg
  85                  90                  95
  Thr Met Ser Gly Tyr Tyr Asp Thr Asp Met Leu Val Ile Val Leu Pro
  100                 105                 110
  Met Phe Ile Leu Phe Phe Met Val Arg Met Ile Leu Lys Lys Asp Phe
  115                 120                 125
  Phe Ser Leu Ile Ala Leu Pro Leu Phe Ile Gly Ile Tyr Leu Trp Trp
  130                 135                 140
  Tyr Pro Ser Ser Tyr Thr Leu Asn Val Ala Leu Ile Gly Leu Phe Leu
  145                 150                 155                 160
  Ile Tyr Thr Leu Ile Phe His Arg Lys Glu Lys Ile Phe Tyr Ile Ala
  165                 170                 175
  Val Ile Leu Ser Ser Leu Thr Leu Ser Asn Ile Ala Trp Phe Tyr Gln
  180                 185                 190
  Ser Thr Ile Ile Val Ile Leu Phe Ala Leu Phe Ala Leu Glu Gln Lys
  195                 200                 205
  Arg Leu Asn Phe Val Ile Ile Gly Ile Leu Ala Ser Val Thr Leu Ile
  210                 215                 220
  Phe Leu Ile Leu Ser Gly Gly Val Asp Pro Ile Leu Tyr Gln Leu Lys
  225                 230                 235                 240
  Phe Tyr Ile Phe Arg Ser Asp Glu Ser Ala Asn Leu Thr Gln Gly Phe
  245                 250                 255
  Met Tyr Phe Asn Val Asn Gln Thr Ile Gln Glu Val Glu Asn Val Asp
  260                 265                 270
  Leu Ser Glu Phe Met Arg Arg Ile Ser Gly Ser Glu Ile Val Phe Leu
  275                 280                 285
  Phe Ser Leu Phe Gly Phe Val Trp Leu Leu Arg Lys His Lys Ser Met
  290                 295                 300
  Ile Met Ala Leu Pro Ile Leu Val Leu Gly Phe Leu Ala Leu Lys Gly
  305                 310                 315                 320
  Gly Leu Arg Phe Thr Ile Tyr Ser Val Pro Val Met Ala Leu Gly Phe
  325                 330                 335
  Gly Phe Leu Leu Ser Glu Phe Lys Ala Ile Leu Val Lys Lys Tyr Ser
  340                 345                 350
  Gln Leu Thr Ser Asn Val Cys Ile Val Phe Ala Thr Ile Leu Thr Leu
  355                 360                 365
  Ala Pro Val Phe Ile His Ile Tyr Asn Tyr Lys Ala Pro Thr Val Phe
  370                 375                 380
  Ser Gln Asn Glu Ala Ser Leu Leu Asn Gln Leu Lys Asn Ile Ala Asn
  385                 390                 395                 400
  Arg Glu Asp Tyr Val Val Thr Trp Trp Asp Tyr Gly Tyr Pro Val Arg
  405                 410                 415
  Tyr Tyr Ser Asp Val Lys Thr Leu Val Asp Gly Gly Lys His Leu Gly
  420                 425                 430
  Lys Asp Asn Phe Phe Pro Ser Phe Ala Leu Ser Lys Asp Glu Gln Ala
  435                 440                 445
  Ala Ala Asn Met Ala Arg Leu Ser Val Glu Tyr Thr Glu Lys Ser Phe
  450                 455                 460
  Tyr Ala Pro Gln Asn Asp Ile Leu Lys Thr Asp Ile Leu Gln Ala Met
  465                 470                 475                 480
  Met Lys Asp Tyr Asn Gln Ser Asn Val Asp Leu Phe Leu Ala Ser Leu
  485                 490                 495
  Ser Lys Pro Asp Phe Lys Ile Asp Thr Pro Lys Thr Arg Asp Ile Tyr
  500                 505                 510
  Leu Tyr Met Pro Ala Arg Met Ser Leu Ile Phe Ser Thr Val Ala Ser
  515                 520                 525
  Phe Ser Phe Ile Asn Leu Asp Thr Gly Val Leu Asp Lys Pro Phe Thr
  530                 535                 540
  Phe Ser Thr Ala Tyr Pro Leu Asp Val Lys Asn Gly Glu Ile Tyr Leu
  545                 550                 555                 560
  Ser Asn Cly Val Val Leu Ser Asp Asp Phe Arg Ser Phe Lys Ile Gly
  565                 570                 575
  Asp Asn Val Val Ser Val Asn Ser Ile Val Glu Ile Asn Ser Ile Lys
  580                 585                 590
  Gln Cly Glu Tyr Lys Ile Thr Pro Ile Asp Asp Lys Ala Gln Phe Tyr
  595                 600                 605
  Ile Phe Tyr Leu Lys Asp Ser Ala Ile Pro Tyr Ala Gln Phe Ile Leu
  610                 615                 620
  Met Asp Lys Thr Met Phe Asn Ser Ala Tyr Val Gln Met Phe Phe Leu
  625                 630                 635                 640
  Gly Asn Tyr Asp Lys Asn Leu Phe Asp Leu Val Ile Asn Ser Arg Asp
  645                 650                 655
  Ala Lys Val Phe Lys Leu Lys Ile
  660

• The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 2 is provided below as SEQ ID NO: 3 (EMBL Nucleotide Sequence Database No. AAD51383):

• atcatttcaa acgatggtta tgcttttgct gagggtgcaa gagatatgat agcaggtttt   60
  catcagccta atgatttgag ttattatgga tcttctttat ctacgcttac ttattggctt  120
  tataaaatca cacctttttc tttcgaaagt attattttat atatgagtac ttttttatct  180
  tctttggtgg tgattcctat tattttacta gctaatgaat acaaacgtcc tttaatgggc  240
  tttgtagctg ctcttttagc aagtatagca aacagttatt ataatcgcac tatgagtggg  300
  tattatgata cggatatgct ggtaattgtt ttacctatgt ttattttatt ttttatggta  360
  agaatgattt taaaaaaaga ctttttttca ttgattgcct taccgttatt tataggaatt  420
  tatctttggt ggtatccttc aagctatact ttaaatgtag ctttaattgg acttttttta  480
  atttatacac ttatttttca tagaaaagaa aagatttttt atatagctgt gattttgtct  540
  tctcttactc tttcaaatat agcatggttt tatcaaagta ctattatagt aatacttttt  600
  gctttatttg ctttagagca aaaacgctta aattttgtaa ttataggaat tttagctagt  660
  gtaactttga tatttttgat tttaagtgga ggggttgatc ctatacttta tcagcttaaa  720
  ttttatattt ttagaagtga tgaaagtgcg aatttaacgc agggttttat gtattttaat  780
  gtcaatcaaa ccatacaaga agttgaaaat gtagatctta gcgaatttat gcgaagaatt  840
  agtggtagtg aaattgtttt tttgttttct ttgtttggtt ttgtatggct tttgagaaaa  900
  cataaaagta tgattatggc tttacctata ttggtgcttg ggtttttagc cttaaaaggg  960
  gggcttagat ttaccattta ttctgtacct gtaatggcct taggatttgg ttttttattg 1020
  agcgagttta aggctatatt ggttaaaaaa tatagccaat taacttcaaa tgtttgtatt 1080
  gtttttgcaa ctattttgac tttagctcca gtatttatcc atatttacaa ctataaagca 1140
  ccaacagttt tttctcaaaa tgaagcatca ttattaaatc aattaaaaaa tatagccaat 1200
  agagaagatt atgtggtaac ttggtgggat tatggttatc ctgtgcgtta ttatagtgat 1260
  gtgaaaactt tagtagatgg tggaaagcat ttaggtaagg ataatttttt cccttctttt 1320
  gctttaagca aagatgaaca agctgcagct aatatggcaa gacttagtgt agaatataca 1380
  gaaaaaagct tttatgctcc gcaaaatgat attttaaaaa cagacatttt acaagccatg 1440
  atgaaagatt ataatcaaag caatgtggat ttgtttctag cttcattatc aaaacctgat 1500
  tttaaaatcg atacaccaaa aactcgtgat atttatcttt atatgcccgc tagaatgtct 1560
  ttgatttttt ctacggtggc tagtttttct tttattaatt tagatacagg agttttggat 1620
  aaacctttta cctttagcac agcttatcca cttgatgtta aaaatggaga aatttatctt 1680
  agcaacggag tggttttaag cgatgatttt agaagtttta aaataggtga taatgtggtt 1740
  tctgtaaata gtatcgtaga gattaattct attaaacaag gtgaatacaa aatcactcca 1800
  attgatgata aggctcagtt ttatattttt tatttaaagg atagtgctat tccttacgca 1860
  caatttattt taatggataa aaccatgttt aatagtgctt atgtgcaaat gtttttttta 1920
  ggaaattatg ataagaattt atttgacttg gtgattaatt ctagagatgc taaggttttt 1980
  aaacttaaaa tttaa                                                  1995

• The amino acid and nucleotide sequences of SEQ ID NOs: 2 and 3, respectively, are representative C. jejuni PglB protein and nucleic acid sequences. It is appreciated by one of skill in the art that there are at least 70 subspecies of C. jejuni having a PglB protein that may vary in sequence identity from the amino acid sequence of SEQ ID NO: 2, but retain the same function. Accordingly, homologous PglB protein sequences from other subspecies and strains of C. jejuni that are characterized by an amino acid sequence identity of at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the C. jejuni amino acid sequence of SEQ ID NO: 2 are also suitable for use in the present invention. The amino acid sequences of related C. jejuni PglB proteins and nucleotide sequences encoding the same are known and readily available to one of skill in the art.
• OSTs from other species of Campylobacter that share sequence identity to C. jejuni PglB and/or are capable of transferring an oligosaccharide moiety to a target glycoprotein are also suitable for use in this and all aspects of the present invention. For example, as demonstrated herein, PglB from Campylobacter lari (ClPglB), which shares only 56% sequence identity to the amino acid sequence of C. jejuni (Schwarz et al., “Relaxed Acceptor Site Specificity of Bacterial Oligosaccharyltransferase in Vivo,” Glycobiology 21:45-54 (2011), which is hereby incorporated by reference in its entirety), is capable of transferring a glycan to an acceptor amino acid residue (i.e., asparagine) of a target glycoprotein in the cell-free glycosylation system of the present invention. The amino acid sequence encoding C. lari PglB (UniProtKB Accession No. B9KDD4) is shown below as SEQ ID NO: 4:

• Met Lys Leu Gln Gln Asn Phe Thr Asp Asn Asn Ser Ile Lys Tyr Thr
  1               5                   10                  15
  Cys Ile Leu Ile Leu Ile Ala Phe Ala Phe Ser Val Leu Cys Arg Leu
  20                  25                  30
  Tyr Trp Val Ala Trp Ala Ser Glu Phe Tyr Glu Phe Phe Phe Asn Asp
  35                  40                  45
  Gln Leu Met Ile Thr Thr Asn Asp Gly Tyr Ala Phe Ala Glu Gly Ala
  50                  55                  60
  Arg Asp Met Ile Ala Gly Phe His Gln Pro Asn Asp Leu Ser Tyr Phe
  65                  70                  75                   80
  Gly Ser Ser Leu Ser Thr Leu Thr Tyr Trp Leu Tyr Ser Ile Leu Pro
  85                  90                  95
  Phe Ser Phe Glu Ser Ile Ile Leu Tyr Met Ser Ala Phe Phe Ala Ser
  100                 105                 110
  Leu Ile Val Val Pro Ile Ile Leu Ile Ala Arg Glu Tyr Lys Leu Thr
  115                 120                 125
  Thr Tyr Gly Phe Ile Ala Ala Leu Leu Gly Ser Ile Ala Asn Ser Tyr
  130                 135                 140
  Tyr Asn Arg Thr Met Ser Gly Tyr Tyr Asp Thr Asp Met Leu Val Leu
  145                 150                 155                 160
  Val Leu Pro Met Leu Ile Leu Leu Thr Phe Ile Arg Leu Thr Ile Asn
  165                 170                 175
  Lys Asp Ile Phe Thr Leu Leu Leu Ser Pro Val Phe Ile Met Ile Tyr
  180                 185                 190
  Leu Trp Trp Tyr Pro Ser Ser Tyr Ser Leu Asn Phe Ala Met Ile Gly
  195                 200                 205
  Leu Phe Gly Leu Tyr Thr Leu Val Phe His Arg Lys Glu Lys Ile Phe
  210                 215                 220
  Tyr Leu Thr Ile Ala Leu Met Ile Ile Ala Leu Ser Met Leu Ala Trp
  225                 230                 235                 240
  Gln Tyr Lys Leu Ala Leu Ile Val Leu Leu Phe Ala Ile Phe Ala Phe
  245                 250                 255
  Lys Glu Glu Lys Ile Asn Phe Tyr Met Ile Trp Ala Leu Ile Phe Ile
  260                 265                 270
  Ser Ile Leu Ile Leu His Leu Ser Gly Gly Leu Asp Pro Val Leu Tyr
  275                 280                 285
  Gln Leu Lys Phe Tyr Val Phe Lys Ala Ser Asp Val Gln Asn Leu Lys
  290                 295                 300
  Asp Ala Ala Phe Met Tyr Phe Asn Val Asn Glu Thr Ile Met Glu Val
  305                 310                 315                 320
  Asn Thr Ile Asp Pro Glu Val Phe Met Gln Arg Ile Ser Ser Ser Val
  325                 330                335
  Leu Val Phe Ile Leu Ser Phe Ile Gly Phe Ile Leu Leu Cys Lys Asp
  340                 345                 350
  His Lys Ser Met Leu Leu Ala Leu Pro Met Leu Ala Leu Gly Phe Met
  355                 360                 365
  Ala Leu Arg Ala Gly Leu Arg Phe Thr Ile Tyr Ala Val Pro Val Met
  370                 375                 380
  Ala Leu Gly Phe Gly Tyr Phe Leu Tyr Ala Phe Phe Asn Phe Leu Glu
  385                 390                 395                 400
  Lys Lys Gln Ile Lys Leu Ser Leu Arg Asn Lys Asn Ile Leu Leu Ile
  405                 410                 415
  Leu Ile Ala Phe Phe Ser Ile Ser Pro Ala Leu Met His Ile Tyr Tyr
  420                 425                 430
  Tyr Lys Ser Ser Thr Val Phe Thr Ser Tyr Glu Ala Ser Ile Leu Asn
  435                 440                 445
  Asp Leu Lys Asn Lys Ala Gln Arg Glu Asp Tyr Val Val Ala Trp Trp
  450                 455                 460
  Asp Tyr Gly Tyr Pro Ile Arg Tyr Tyr Ser Asp Val Lys Thr Leu Ile
  465                 470                 475                 480
  Asp Cly Gly Lys His Leu Gly Lys Asp Asn Phe Phe Ser Ser Phe Val
  485                 490                 495
  Leu Ser Lys Glu Gln Ile Pro Ala Ala Asn Met Ala Arg Leu Ser Val
  500                 505                 510
  Glu Tyr Thr Glu Lys Ser Phe Lys Glu Asn Tyr Pro Asp Val Leu Lys
  515                 520                 525
  Ala Met Val Lys Asp Tyr Asn Lys Thr Ser Ala Lys Asp Phe Leu Glu
  530                 535                 540
  Ser Leu Asn Asp Lys Asp Phe Lys Phe Asp Thr Asn Lys Thr Arg Asp
  545                 550                 555                 560
  Val Tyr Ile Tyr Met Pro Tyr Arg Met Leu Arg Ile Met Pro Val Val
  565                 570                 575
  Ala Gln Phe Ala Asn Thr Asn Pro Asp Asn Gly Glu Gln Glu Lys Ser
  580                 585                 590
  Leu Phe Phe Ser Gln Ala Asn Ala Ile Ala Gln Asp Lys Thr Thr Gly
  595                 600                 605
  Ser Val Met Leu Asp Asn Gly Val Glu Ile Ile Asn Asp Phe Arg Ala
  610                 615                620
  Leu Lys Val Glu Gly Ala Ser Ile Pro Leu Lys Ala Phe Val Asp Ile
  625                 630                 635                 640
  Glu Ser Ile Thr Asn Gly Lys Phe Tyr Tyr Asn Glu Ile Asp Ser Lys
  645                 650                 655
  Ala Gln Ile Tyr Leu Leu Phe Leu Arg Glu Tyr Lys Ser Phe Val Ile
  660                 665                 670
  Leu Asp Glu Ser Leu Tyr Asn Ser Ser Tyr Ile Gln Met Phe Leu Leu
  675                 680                 685
  Asn Gln Tyr Asp Gln Asp Leu Phe Glu Gln Ile Thr Asn Asp Thr Arg
  690                 695                 700
  Ala Lys Ile Tyr Arg Leu Lys
  705                 710

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the C. lari amino acid sequence of SEQ ID NO: 4 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 4 is provided below as SEQ ID NO: 5 (EMBL Nucleotide Sequence Database No. ACM64573.1):

• atgaaactac aacaaaattt cacggataat aattctataa aatatacctg tattttaatc   60
  cttatagcct ttgcttttag tgttttgtgt agattatact gggtagcttg ggcaagtgag  120
  ttttatgagt ttttctttaa tgatcaactc atgattacta ctaatgatgg ctatgctttt  180
  gcagaaggtg caagagatat gatagcaggt tttcatcaac ctaatgactt atcttatttt  240
  ggaagctcac tttctacttt gacttattgg ctttatagta ttttgccttt tagctttgaa  300
  agtattattt tatatatgag tgcttttttt gcttctttga ttgttgtgcc tattatatta  360
  atcgcaagag agtataaact cactacctat ggctttatag cagctttact tggaagcatt  420
  gcaaatagtt attataaccg cactatgagt gggtattacg atacagatat gctagtgtta  480
  gttttaccaa tgcttatttt gcttaccttt atacgcttaa ctattaataa agacattttc  540
  accctacttt taagtccggt ttttatcatg atttatttgt ggtggtatcc atcaagttat  600
  tctttaaatt ttgctatgat aggacttttt ggactttata ctttagtatt tcatagaaaa  660
  gaaaagattt tttatctaac tattgctttg atgatcatag ctttaagtat gctagcatgg  720
  caatataagc ttgctttgat tgtattatta tttgctattt ttgcttttaa agaagaaaaa  780
  atcaattttt atatgatttg ggctttgatt tttattagca ttttgatatt gcatttaagt  840
  ggcggcttag atcctgtttt ataccaactt aaattttatg tatttaaagc ttctgatgtg  900
  caaaatttaa aagatgctgc ctttatgtat tttaatgtca atgaaaccat tatggaagta  960
  aatactatcg atcctgaagt atttatgcaa agaattagct ctagtgtttt agtatttatc 1020
  ctttctttta taggttttat cttactttgc aaagatcaca aaagcatgct tttggctcta 1080
  cctatgcttg cactaggttt tatggcttta agagctggac ttagatttac catttatgca 1140
  gttcctgtga tggctttggg ttttgggtat tttttatatg cattttttaa ttttttagaa 1200
  aaaaaacaaa tcaaacttag cctaagaaat aaaaatatct tacttatact cattgcattt 1260
  tttagtataa gccctgcttt gatgcatatt tattattata aatcctctac tgtttttact 1320
  tcttatgaag ctagtatttt aaatgattta aaaaataaag ctcaaagaga agattatgtt 1380
  gttgcttggt gggattatgg ttatccaata cgctattata gcgatgtaaa aaccttaatc 1440
  gatggtggaa aacacctagg aaaagataat tttttctcat cttttgtctt aagcaaagaa 1500
  caaattccag cagccaatat ggcaagactt agcgtagaat acactgaaaa atctttcaaa 1560
  gaaaactatc ctgatgtttt aaaagctatg gttaaagatt ataataaaac aagtgctaaa 1620
  gattttttag aaagtttaaa tgataaagat tttaaatttg ataccaataa aactagagat 1680
  gtatacattt atatgcctta tagaatgttg cgtatcatgc ctgtggtggc acaatttgca 1740
  aatacaaatc ctgataatgg agagcaagaa aaaagtttat ttttctccca agctaatgcc 1800
  atagctcaag ataaaaccac aggttctgtt atgcttgata atggagtaga aattattaat 1860
  gattttagag ccttaaaagt agaaggtgca agcatacctt taaaagcttt tgtggatata 1920
  gaatccatta ctaatggcaa attttattac aatgaaattg attcaaaagc tcaaatttat 1980
  ttgctctttt taagagaata taaaagcttt gtgattttag atgaaagtct ttataatagt 2040
  tcttatatac aaatgttttt gttaaatcaa tacgatcaag atttatttga acaaattact 2100
  aatgatacaa gagcaaaaat ttataggcta aaaagatga                        2139

• Another N-linked OST from Campylobacter that is suitable for use in this and all aspects of the present invention is PglB from C. Coli. The amino acid sequence encoding PglB from C. coli (UniProtKB Accession No. H7W16), which is 81% identical to that of C. jejuni, is provided below as SEQ ID NO: 6

• Met Leu Lys Lys Glu Tyr Phe Lys Asn Pro Thr Phe Ile Leu Leu Ala
  1               5                   10                  15
  Phe Ile Ile Leu Ala Tyr Val Phe Ser Val Leu Cys Arg Phe Tyr Trp
  20                  25                  30
  Ile Phe Trp Ala Ser Glu Phe Asn Glu Tyr Phe Phe Asn Asn Glu Leu
  35                  40                  45
  Met Ile Ile Ser Asn Asp Gly Tyr Ala Phe Ala Glu Gly Ala Arg Asp
  50                  55                  60
  Met Ile Ala Gly Phe His Gln Pro Asn Asp Leu Ser Tyr Tyr Gly Ser
  65                  70                  75                   80
  Ser Leu Ser Thr Leu Thr Tyr Trp Phe Tyr Lys Ile Thr Pro Phe Ser
  85                  90                  95
  Leu Glu Ser Ile Phe Ile Tyr Ile Ser Thr Phe Leu Ser Ser Leu Val
  100                 105                 110
  Val Ile Pro Leu Ile Leu Ile Ala Asn Glu Tyr Lys Arg Pro Leu Met
  115                 120                 125
  Gly Phe Val Ala Ala Leu Leu Ala Ser Ile Ala Asn Ser Tyr Tyr Asn
  130                 135                 140
  Arg Thr Met Ser Gly Tyr Tyr Asp Thr Asp Met Leu Val Ile Val Leu
  145                 150                 155                 160
  Ala Met Met Ile Val Phe Phe Met Ile Arg Leu Ile Leu Lys Lys Asp
  165                 170                 175
  Leu Leu Ser Leu Ile Thr Leu Pro Leu Phe Val Gly Ile Tyr Leu Trp
  180                 185                 190
  Trp Tyr Pro Ser Ser Tyr Thr Leu Asn Val Ala Leu Leu Gly Leu Phe
  195                 200                 205
  Phe Ile Tyr Thr Leu Val Phe His Ile Lys Glu Lys Thr Leu Tyr Met
  210                 215                 220
  Ala Ile Ile Leu Ala Ser Ile Thr Leu Ser Asn Ile Ala Trp Phe Tyr
  225                 230                 235                 240
  Gln Ser Ala Ile Ile Val Ile Leu Phe Ser Leu Phe Val Leu Gln Asn
  245                 250                 255
  Lys Arg Phe Ser Phe Ala Leu Leu Gly Ile Leu Gly Leu Ala Thr Leu
  260                 265                 270
  Val Phe Leu Ile Leu Ser Gly Gly Ile Asp Pro Ile Leu Tyr Gln Leu
  275                 280                 285
  Lys Phe Tyr Ile Phe Arg Ser Asp Glu Ser Ala Asn Leu Ala Gln Gly
  290                 295                 300
  Phe Met Tyr Phe Asn Val Asn Gln Thr Ile Gln Glu Val Glu Ser Ile
  305                 310                 315                 320
  Asp Leu Ser Ile Phe Met Gln Arg Ile Ser Gly Ser Glu Leu Val Phe
  325                 330                335
  Phe Val Ser Leu Ile Gly Phe Ile Phe Leu Val Arg Lys His Lys Ser
  340                 345                 350
  Met Ile Leu Ala Leu Pro Met Leu Ala Leu Gly Phe Leu Ala Leu Lys
  355                 360                 365
  Ser Gly Leu Arg Phe Thr Ile Tyr Ala Val Pro Val Leu Ala Leu Gly
  370                 375                 380
  Phe Gly Phe Leu Met Ser Leu Leu Gln Glu Arg Lys Gln Lys Asn Asn
  385                 390                 395                 400
  Asn Thr Tyr Trp Trp Ala Asn Ile Gly Val Phe Ile Phe Thr Phe Leu
  405                 410                 415
  Ser Leu Ile Pro Met Phe Tyr His Ile Asn Asn Tyr Lys Ala Pro Thr
  420                 425                 430
  Val Phe Ser Gln Asn Glu Ala Thr Lys Leu Asp Glu Leu Lys Lys Ile
  435                 440                 445
  Ala Gln Arg Glu Asp Tyr Val Val Thr Trp Trp Asp Tyr Gly Tyr Pro
  450                 455                 460
  Ile Arg Tyr Tyr Ser Asp Val Lys Thr Leu Ala Asp Gly Gly Lys His
  465                 470                 475                 480
  Leu Gly Lys Asp Asn Phe Phe Pro Ser Phe Val Leu Ser Lys Asp Gln
  485                 490                 495
  Val Ala Ala Ala Asn Met Ala Arg Leu Ser Val Glu Tyr Thr Glu Lys
  500                 505                 510
  Ser Phe Tyr Ala Pro Leu Asn Asp Ile Leu Lys Asn Asp Leu Leu Gln
  515                 520                 525
  Ala Met Met Lys Asp Tyr Asn Gln Asn Asn Val Asp Leu Phe Leu Ala
  530                 535                 540
  Ser Leu Ser Lys Pro Asp Phe Lys Ile Asn Thr Pro Lys Thr Arg Asp
  545                 550                 555                 560
  Val Tyr Ile Tyr Met Pro Ala Arg Met Ser Leu Ile Phe Ser Thr Val
  565                 570                 575
  Ala Per Phe Ser Phe Val Asp Leu Glu Thr Gly Glu Ile Asn Lys Pro
  580                 585                 590
  Phe Thr Phe Ser Ala Ala Tyr Pro Leu Asp Val Lys Asn Gly Glu Ile
  595                 600                 605
  Tyr Leu Ser Asn Cly Ile Ala Leu Ser Asp Asp Phe Arg Ser Phe Lys
  610                 615                620
  Ile Asn Asn Ser Thr Ile Ser Val Asn Ser Ile Ile Glu Ile Asn Ser
  625                 630                 635                 640
  Ile Lys Gln Gly Glu Tyr Lys Ile Thr Pro Ile Asp Asp Met Ala Gln
  645                 650                 655
  Phe Tyr Ile Phe Tyr Leu Lys Asp Ser Thr Ile Pro Tyr Ala Gln Phe
  660                 665                 670
  Ile Leu Met Asp Lys Thr Met Phe Asn Ser Ala Tyr Val Gln Met Phe
  675                 680                 685
  Phe Leu Gly Asn Tyr Asp Lys Asn Leu Tyr Asp Leu Val Ile Asn Ala
  690                 695                 700
  Arg Asp Ala Lys Val Phe Lys Leu Lys Ile
  705                 710

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the C. coli amino acid sequence of SEQ ID NO: 6 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 6 is provided below as SEQ ID NO: 7 (EMBL Nucleotide Sequence Database No. EIB14175):

• atgttaaaaa aagaatactt taaaaaccca acttttattt tattggcttt tataatttta   60
  gcgtatgtct ttagtgtttt atgtaggttt tattggattt tttgggcaag tgagtttaat  120
  gaatattttt tcaataacga gcttatgatt atctcaaatg atggatatgc ttttgcagag  180
  ggtgcaagag atatgatagc gggttttcat caacctaatg atttgagtta ttatggttct  240
  tcgctttcaa cgctcacata ttggttttat aaaataactc ctttttcttt agaaagcatt  300
  tttatatata tcagtacttt tttatcttct ttggtggtta tacctttgat tttgattgct  360
  aatgaataca aacgcccttt aatggggttt gttgcagcat tgctagccag tatagctaat  420
  agctattata atcgcacgat gagcggatat tatgatactg atatgcttgt tatagttctt  480
  gcaatgatga tagttttctt tatgataagg ctgattttga aaaaagattt attatcttta  540
  ataacactgc ctttgtttgt aggaatttat ctttggtggt atccatcaag ctatacttta  600
  aatgttgctt tactaggact tttctttatt tataccttgg tttttcatat aaaagaaaaa  660
  acgctttata tggctattat cctagcttct atcacacttt caaatatagc ttggttttat  720
  caaagcgcca tcattgtcat actttttagt ctttttgttt tgcaaaataa gcgttttagc  780
  tttgctttgc ttggaatttt aggtttggca actttggtat ttttgatact aagcggtgga  840
  attgatccta tactctatca acttaaattt tatattttta gaagtgatga gagtgcaaat  900
  ttggctcaag gttttatgta ttttaatgta aatcaaacca tacaagaggt agaaagtata  960
  gatttaagta tttttatgca aaggattagc ggaagcgagc ttgtattttt tgtatcttta  1020
  atcggcttta ttttccttgt tagaaaacat aaaagtatga ttttggcttt gccgatgtta  1080
  gctttaggat ttttagcact taagagtgga cttcgtttta ctatttatgc agtacctgtt  1140
  ttagcacttg gatttggttt tttaatgagt cttttgcaag aaagaaaaca aaaaaacaat  1200
  aatacctatt ggtgggccaa tataggcgtt tttattttta cttttttaag tttaattcct  1260
  atgttctatc atatcaacaa ttataaagca ccaactgttt tttctcaaaa tgaggctacg  1320
  aaattagatg agcttaaaaa aattgcacaa agagaagatt atgtagtaac ttggtgggat  1380
  tatggatatc ctattaggta ttacagcgat gttaaaactt tggctgatgg gggtaagcat  1440
  ttaggcaagg ataatttttt cccatotttt gttctaagta aagatcaagt ggctgctgca  1500
  aatatggcaa gacttagtgt agaatacaca gaaaaaagtt tttacgcccc tttaaatgat  1560
  attttaaaaa atgatctttt acaagccatg atgaaagatt ataatcaaaa taatgtggat  1620
  ttgtttttag cttcgctttc caagcctgat tttaaaatca atacgccaaa aacacgcgat  1680
  gtgtatatct atatgccagc tagaatgtct ttgatttttt caactgtggc tagtttttct  1740
  tttgtggatt tggagacagg tgagataaat aaacctttta cttttagtgc agcttatcca  1800
  cttgatgtta aaaatggaga aatttatctt agcaatggta ttgcattaag tgatgatttt  1860
  agaagtttta aaataaataa tagtactata tccgtaaata gtatcataga gattaattct  1920
  atcaaacaag gtgaatataa aatcactcct attgatgata tggctcaatt ttatattttt  1980
  tatcttaaag atagcaccat accttatgct cagtttattt taatggataa aactatgttt  2040
  aatagtgctt atgtgcaaat gtttttcctt ggaaattatg ataaaaattt gtatgattta  2100
  gtgattaatg ctagagatgc aaaagttttt aaactcaaaa tttaa                  2145

• Another Campylobacter OST that is suitable for use in this and all aspects of the present invention is PglB from C. upsaliensis. The amino acid sequence encoding PglB from C. upsaliensis (UniProtKB Accession No. E6LAJ2), which is 57% identical to that of C. jejuni, is provided below as SEQ ID NO: 8:

• Met Lys Asn Glu Ala Val Lys Asn Ala Asn Leu Arg Leu Val Phe Phe
  1               5                   10                  15
  Ile Leu Leu Ala Phe Gly Phe Ser Val Leu Cys Arg Phe Tyr Trp Ile
  20                  25                  30
  Tyr Trp Ala Ser Asp Phe Asn Glu Tyr Phe Phe Asn Asn Gln Leu Met
  35                  40                  45
  Ile Ser Ser Asn Asp Gly Tyr Thr Phe Ala Glu Gly Ala Arg Asp Lys
  50                  55                  60
  Ile Ala Gly Phe His Gln Glu Asn Asp Leu Ser Phe Ile Asn Ser Ser
  65                  70                  75                   80
  Leu Ser Ile Leu Thr Tyr Val Leu Tyr Lys Ile Thr Pro Phe Ser Phe
  85                  90                  95
  Glu Ser Ile Ile Leu Tyr Met Ser Val Phe Phe Ser Ser Leu Ile Val
  100                 105                 110
  Val Pro Leu Ile Leu Ile Ala Asn Glu Leu Lys Arg Pro Leu Met Gly
  115                 120                 125
  Leu Phe Ala Ala Phe Leu Ala Ser Ile Ala Lys Ser Tyr Tyr Asn Arg
  130                 135                 140
  Thr Met Ala Gly Tyr Tyr Asp Thr Asp Met Leu Ala Ile Val Leu Pro
  145                 150                 155                 160
  Met Phe Ile Leu Tyr Phe Phe Ile Arg Leu Ile Leu Arg Lys Asp Asp
  165                 170                 175
  Phe Ser Leu Leu Ala Leu Pro Phe Phe Met Gly Leu Tyr Leu Trp Trp
  180                 185                 190
  Tyr Pro Ser Ser Tyr Thr Leu Asn Val Ala Phe Ile Ala Leu Phe Thr
  195                 200                 205
  Leu Tyr Val Leu Ile Tyr His Arg Lys Glu Arg Ser Phe Tyr Met Ala
  210                 215                 220
  Ala Leu Leu Cys Ala Ile Thr Leu Ser Asn Ile Ala Trp Phe Tyr Gln
  225                 230                 235                 240
  Ser Ala Ile Ile Val Leu Leu Phe Ala Leu Phe Met Leu Lys Asn Ser
  245                 250                 255
  Phe Phe Asn Phe Lys Phe Ile Ala Leu Leu Ala Leu Gly Val Leu Val
  260                 265                 270
  Phe Leu Ala Leu Ser Gly Gly Ile Asp Pro Ile Leu Tyr Gln Leu Lys
  275                 280                 285
  Phe Tyr Leu Leu Arg Ser Asp Glu Ser Ala Ser Leu Ala Arg Gly Phe
  290                 295                 300
  Ala Tyr Phe Asn Val Asn Leu Thr Ile Gln Glu Val Glu Ser Ile Asp
  305                 310                 315                 320
  Leu Ser Thr Phe Met Gln Arg Ile Ser Gly Ser Glu Leu Val Phe Leu
  325                 330                335
  Leu Ser Leu Phe Gly Phe Leu Trp Leu Leu Lys Lys His Lys Val Met
  340                 345                 350
  Leu Leu Thr Leu Pro Met Leu Leu Leu Gly Phe Leu Ala Leu Arg Gly
  355                 360                 365
  Gly Leu Arg Phe Thr Ile Tyr Ala Val Pro Ile Met Ala Leu Gly Phe
  370                 375                 380
  Gly Phe Leu Ser Val Gln Ile Leu Ser Leu Ile Gln Lys Met Arg Pro
  385                 390                 395                 400
  Leu Lys Glu Thr Arg Lys Leu Arg Ile Phe Phe Tyr Gly Ile Phe Pro
  405                 410                 415
  Leu Phe Val Leu Val Leu Gly Ala Tyr Phe Tyr Phe Ser Gln Ser Ala
  420                 425                 430
  Ile Tyr Glu Ser Met Gly Val Glu Phe Gln Lys Asn Phe Val Ser Phe
  435                 440                 445
  Phe Val Glu Asp Thr Leu Leu Phe Ser Leu Leu Ile Leu Ala Ile Phe
  450                 455                 460
  Thr Pro Leu Ile Phe Glu Leu Leu Trp Arg Lys Lys Asp Ile Arg Phe
  465                 470                 475                 480
  Val Cys Ser Phe Tyr Ile Val Gly Val Leu Leu Phe Ser Leu Trp Ala
  485                 490                 495
  Asn Leu Ser His Ile Tyr Asn Tyr Arg Ala His Thr Val Phe Ser Tyr
  500                 505                 510
  Asn Glu Ala Ser Ile Leu Asp Asn Leu Lys Ala Asn Val Ser Arg Glu
  515                 520                 525
  Asp Tyr Ile Val Ala Trp Trp Asp Tyr Gly Tyr Pro Ile Arg Tyr Tyr
  530                 535                 540
  Ser Asp Val Lys Thr Leu Ala Asp Gly Gly Lys His Leu Gly Lys Asp
  545                 550                 555                 560
  Asn Phe Phe Pro Ser Phe Val Leu Ser Gln Asn Pro Arg Ala Ala Ala
  565                 570                 575
  Asn Met Ala Arg Leu Ser Val Glu Tyr Thr Glu Lys Gly Phe Lys Thr
  580                 585                 590
  Pro Tyr Asn Asp Leu Leu Glu Ala Met Met Lys Asp Tyr Asn Tyr Ser
  595                 600                 605
  Asn Val Asn Leu Phe Leu Ala Ala Leu Ser Lys Glu Asp Phe Thr Leu
  610                 615                620
  Gln Thr Pro Lys Thr Arg Asp Ile Tyr Ile Tyr Met Pro Ser Arg Met
  625                 630                 635                 640
  Ala Ala Ile Phe Gly Thr Val Ala Ser Phe Ser Tyr Met Ser Leu Glu
  645                 650                 655
  Thr Gly Glu Leu Glu Asn Pro Phe Val Tyr Ser Val Ala Tyr Tyr Leu
  660                 665                 670
  Gly Asn Glu Asp Gly Lys Leu Val Leu Ser Asn Asn Met Leu Leu His
  675 680 685
  Ser Asp Phe Arg Ser Phe Asp Leu Asn Gly Lys Asn Tyr Ala Ile Asn
  690                 695                 700
  Ser Leu Val Glu Phe Thr Ser Val Gln Gln Lys Tyr Tyr Ser Val Val
  705                 710                 715                 720
  Glu Ile Asp Lys Asn Ala Lys Tyr Tyr Leu Phe His Ile Lys Asp Ala
  725                 730                 735
  Asn Ile Pro Asn Val Gln Phe Ile Leu Met Asp Lys Ala Met Tyr Glu
  740                 745                 750
  Ser Ala Phe Val Gln Met Phe Phe Phe Gly Lys Tyr Asp Glu Ser Leu
  755                 760                 765
  Tyr Glu Leu Ile Val Asp Ser Lys Glu Ala Lys Val Tyr Lys Leu Lys
  770                 775                 780
  Leu
  785

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the C. upsaliensis amino acid sequence of SEQ ID NO: 8 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 8 is provided below as SEQ ID NO: 9 (EMBL Nucleotide Sequence Database No. EFU71695):

• atgaaaaacg aggctgtgaa aaatgcgaat ttgaggctag tattttttat cttactagct   60
  tttggtttta gtgttttatg tcgcttttat tggatttatt gggcgagtga ttttaacgaa  120
  tattttttta ataatcagct tatgataagc tcaaatgacg gctacacttt tgcagagggt  180
  gctagagata agatagcggg ctttcatcag gaaaatgatt LaagcLLLaL taattcctct  240
  ctttctattt tgacttatgt gctttataaa atcacgcctt ttagttttga aagcattatt  300
  ttatatatga gtgtattttt ttcttcactt atagttgtgc cgcttatttt aattgcaaac  360
  gagcttaaac gccctttaat gggacttttt gcggcatttt tagcaagtat tgcaaaaagc  420
  tattataacc gcactatggc aggatattat gatacagata tgttagccat tgtgcttcct  480
  atgtttattt tatatttttt catcaggctt attttaagaa aagatgattt ttctttactt  540
  gccttgccgt tttttatggg actttatctt tggtggtatc catcaagcta tactctaaat  600
  gtcgctttta tcgcactttt taccctttat gttttgattt atcatagaaa agaaagatct  660
  ttttatatgg cagcactttt gtgtgccatt accctttcaa atattgcttg gttttatcaa  720
  agtgctatta ttgttttact ttttgctctt tttatgctta aaaattcgtt ttttaatttt  780
  aaatttatcg cacttttagc cttaggagtt ttagtttttt tggctttaag tggggggata  840
  gaccccatac tttatcagct taaattttat cttttaagaa gtgatgaaag tgcaagttta  900
  gcgcgtggtt ttgcgtattt taatgtaaat ttaaccatac aagaggttga aagtatcgat  960
  ttaagcactt ttatgcaaag aattagcgga agtgagcttg tgtttttact ttctcttttt 1020
  ggctttttat ggcttttaaa aaagcataag gtgatgcttt taaccctacc tatgcttttg 1080
  ctcggttttt tagcacttag aggtgggctt agatttacta tttatgctgt gcctattatg 1140
  gcgcttggct ttggcttttt aagcgttcaa attttaagct taatccaaaa aatgcgtccc 1200
  ttaaaagaaa ctcgaaaatt aagaatattt ttttatggaa tctttccgct ttttgtgctt 1260
  gttttggggg cttattttta ttttagtcaa agtgctattt atgagagtat gggagtggaa 1320
  tttcaaaaga actttgtgag cttttttgta gaagatactt tgcttttttc tttgctgatt 1380
  ttggctattt ttacgccttt aatttttgag cttttgtgga gaaaaaagga cattcgtttt 1440
  gtgtgtagct tttatattgt gggggttttg cttttttctt tatgggcaaa tttaagtcat 1500
  atttataatt atagagcaca caccgttttt agctacaatg aagcgagtat tttggataat 1560
  cttaaagcta atgtttctag ggaagattat attgtggctt ggtgggatta tggctatcct 1620
  attcgttatt atagcgatgt gaaaacctta gctgatgggg gtaagcattt gggtaaggat 1680
  aattttttcc cttcttttgt tttaagtcaa aatccacgcg cagcggcaaa tatggcaaga 1740
  cttagcgtag aatacacaga aaaaggcttt aaaacgcctt ataatgatct tttagaagcg 1800
  atgatgaagg attataatta tagcaatgta aatttatttt tagcggcact ttctaaggag 1860
  gattttactc ttcaaacgcc caaaactaga gatatttaca tctatatgcc ttctcgtatg 1920
  gcggcgattt ttggcacggt ggcaagtttt tcttatatga gcttagaaac gggtgagctt 1980
  gaaaatcctt ttgtttatag tgtggcgtat tatttgggaa atgaggacgg caaactcgtc 2040
  ttaagtaata atatgctcct tcatagcgac tttagaagct ttgaccttaa tggcaagaat 2100
  tatgctatta attctttggt tgaatttact tcggtgcagc aaaaatatta tagtgttgtg 2160
  gagattgata aaaacgctaa atattatctc tttcacatca aagacgctaa tatccctaat 2220
  gtgcaattta tcctaatgga taaggcgatg tatgagagtg ctttcgtgca aatgtttttc 2280
  tttggtaagt atgatgagag tttgtatgaa ttaattgtag atagtaaaga agcaaaggtg 2340
  tataaattaa aattatga                                               2358

• An alignment of the Campylobacter PglB sequences is provided in FIGS. 6A-6C, and a PglB consensus sequence based on this alignment is presented as SEQ ID NO: 10 of FIG. 6. Residues that are not fully conserved between the four Campylobacter sequences are depicted as X, where X can be any amino acid residue. Alternatively, X is selected from one of the four depicted amino acid residue at the corresponding position in the depicted Campylobacter sequences.
• In another embodiment of the present invention, the OST is an archaea oligosaccharyltransferase. For example, the OST STT3 subunit from Pyrococcus furiosus which is capable of transferring a glycan to an asparagine residue of a target glycoprotein is suitable for use in this and all aspects of the present invention. The amino acid sequence of P. furiosus (UniProtKB Accession No. Q8U4D2) is provided below as SEQ ID NO: 11:

• Met Val Lys Thr Gln Ile Lys Glu Lys Lys Lys Asp Glu Lys Val Thr
  1               5                   10                  15
  Ile Pro Leu Pro Gly Lys Ile Lys Thr Val Leu Ala Phe Leu Val Val
  20                  25                  30
  Leu Ala Phe Ala Ala Tyr Gly Phe Tyr Ile Arg His Leu Thr Ala Gly
  35                  40                  45
  Lys Tyr Phe Ser Asp Pro Asp Thr Phe Tyr His Phe Glu Ile Tyr Lys
  50                  55                  60
  Leu Val Leu Lys Glu Gly Leu Pro Arg Tyr Tyr Pro Met Ala Asp Ala
  65                  70                  75                   80
  Pro Phe Gly Ser Leu Ile Gly Glu Pro Leu Gly Leu Tyr Ile Leu Pro
  85                  90                  95
  Ala Ile Phe Tyr Lys Ile Ile Ser Ile She Gly Tyr Asn Glu Leu Glu
  100                 105                 110
  Ala Phe Leu Leu Trp Pro Pro She Val Gly Phe Leu Ser Val Ile Gly
  115                 120                 125
  Val Tyr Leu Leu Gly Arg Lys Val Leu Asn Glu Trp Ala Gly Met Trp
  130                 135                 140
  Gly Ala Ile Ile Leu Ser Val Leu Thr Ala Asn Phe Ser Arg Thr Phe
  145                 150                 155                 160
  Ser Gly Asn Ala Arg Gly Asp Gly Pro Phe Met Met Leu Phe Thr Phe
  165                 170                 175
  Ser Ala Val Leu Met Leu Tyr Tyr Leu Thr Glu Clu Asn Lys Asn Lys
  180                 185                 190
  Lys Ile Ile Trp Gly Thr Leu Phe Val Leu Leu Ala Gly Ile Ser Thr
  195                 200                 205
  Ala Ala Trp Asn Gly Ser Pro Phe Gly Leu Met Val Leu Leu Gly Phe
  210                 215                 220
  Ala Ser Phe Gln Thr Ile Ile Leu Phe Ile Phe Gly Lys Ile Asn Glu
  225                 230                 235                 240
  Leu Arg Glu Phe Ile Lys Glu Tyr Tyr Pro Ala Tyr Leu Gly Ile Leu
  245                 250                 255
  Ala Ile Ser Tyr Leu Leu Thr Ile Pro Gly Ile Gly Lys Ile Gly Gly
  260                 265                 270
  Phe Val Arg Phe Ala Phe Glu Val Phe Leu Gly Leu Val Phe Leu Ala
  275                 280                 285
  Ile Val Met Leu Tyr Gly Gly Lys Tyr Leu Asn Tyr Ser Asp Lys Lys
  290                 295                 300
  His Arg Phe Ala Val Val Ala Val Ile Val Ile Ala Gly Phe Ala Gly
  305                 310                 315                 320
  Ala Tyr Ile Tyr Val Gly Pro Lys Leu Phe Thr Leu Met Gly Gly Ala
  325                 330                335
  Tyr Gln Ser Thr Gln Val Tyr Glu Thr Val Gln Glu Leu Ala Lys Thr
  340                 345                 350
  Asp Trp Gly Asp Val Lys Val Tyr Tyr Gly Val Glu Lys Pro Asn Gly
  355                 360                 365
  Ile Val Phe Phe Leu Gly Leu Val Gly Ala Met Ile Val Thr Ala Arg
  370                 375                 380
  Tyr Leu Tyr Lys Leu Phe Lys Asp Gly Arg Arg Pro His Glu Glu Leu
  385                 390                 395                 400
  Phe Ala Ile Thr Phe Tyr Val Met Ser Ile Tyr Leu Leu Trp Thr Ala
  405                 410                 415
  Ala Arg Phe Lou Phe Leu Ala Ser Tyr Ala Ile Ala Leu Met Ser Gly
  420                 425                 430
  Val Phe Ala Gly Tyr Val Leu Glu Thr Val Glu Lys Met Lys Glu Ser
  435                 440                 445
  Ile Pro Ile Lys Ala Ala Leu Gly Gly Val Ile Ala Ile Met Leu Leu
  450                 455                 460
  Leu Ile Pro Leu Thr His Gly Pro Leu Leu Ala Gln Ser Ala Lys Ser
  465                 470                 475                 480
  Met Arg Thr Thr Glu Ile Glu Thr Ser Gly Trp Glu Asp Ala Leu Lys
  485                 490                 495
  Trp Leu Arg Glu Asn Thr Pro Glu Tyr Ser Thr Ala Thr Ser Trp Trp
  500                 505                 510
  Asp Tyr Gly Tyr Trp Ile Glu Ser Ser Leu Leu Gly Gln Arg Arg Ala
  515                 520                 525
  Ser Ala Asp Gly Gly His Ala Arg Asp Arg Asp His Ile Leu Ala Leu
  530                 535                 540
  Phe Leu Ala Arg Asp Gly Asn Ile Ser Glu Val Asp Phe Glu Ser Trp
  545                 550                 555                 560
  Glu Leu Asn Tyr Phe Leu Val Tyr Leu Asn Asp Trp Ala Lys Phe Asn
  565                 570                 575
  Ala Ile Ser Tyr Leu Gly Gly Ala Ile Thr Arg Arg Glu Tyr Asn Gly
  580                 585                 590
  Asp Glu Ser Gly Arg Gly Ala Val Thr Thr Leu Leu Pro Leu Pro Arg
  595                 600                 605
  Tyr Gly Glu Lys Tyr Val An Leu Tyr Ala Lys Val Ile Val Asp Val
  610                 615                620
  Ser Asn Ser Ser Val Lys Val Thr Val Gly Asp Arg Glu Cys Asp Pro
  625                 630                 635                 640
  Leu Met Val Thr Phe Thr Pro Ser Gly Lys Thr Ile Lys Gly Thr Gly
  645                 650                 655
  Thr Cys Ser Asp Gly Asn Ala Phe Pro Tyr Val Leu His Leu Thr Pro
  660                 665                 670
  Thr Ile Gly Val Leu Ala Tyr Tyr Lys Val Ala Thr Ala Asn Phe Ile
  675                 680                 685
  Lys Leu Ala Phe Gly Val Pro Ala Ser Thr Ile Pro Gly Phe Ser Asp
  690                 695                 700
  Lys Leu Phe Ser Asn Phe Glu Pro Val Tyr Glu Ser Gly Asn Val Ile
  705                 710                 715                 720
  Val Tyr Arg Phe Thr Pro Phe Gly Ile Tyr Lys Ile Glu Glu Asn Ile
  725                 730                 735
  Asn Gly Thr Trp Lys Gln Val Tyr Asn Leu Thr Pro Gly Lys His Glu
  740                 745                 750
  Leu Lys Leu Tyr Ile Ser Ala Phe Gly Arg Asp Ile Glu Asn Ala Thr
  755                 760                 765
  Leu Tyr Ile Tyr Ala Ile Asn Asn Glu Lys Ile Ile Glu Lys Ile Lys
  770                 775                 780
  Ile Ala Glu Ile Ser His Met Asp Tyr Leu Asn Glu Tyr Pro Ile Ala
  785                 790                 795                 800
  Val Asn Val Thr Leu Pro Asn Ala Thr Ser Tyr Arg Phe Val Leu Val
  805                 810                 815
  Gln Lys Gly Pro Ile Gly Val Leu Leu Asp Ala Pro Lys Val Asn Gly
  820                 825                 830
  Glu Ile Arg Ser Pro Thr Asn Ile Leu Arg Glu Gly Glu Ser Gly Glu
  835                 840                 845
  Ile Glu Leu Lys Val Gly Val Asp Lys Asp Tyr Thr Ala Asp Leu Tyr
  850                 855                 860
  Leu Arg Ala Thr Phe Ile Tyr Leu Val Arg Lys Ser Gly Lys Asp Asn
  865                 870                 875                 880
  Glu Asp Tyr Asp Ala Ala Phe Glu Pro Gln Met Asp Val Phe Phe Ile
  885                 890                 895
  Thr Lys Ile Gly Glu Asn Ile Gln Leu Lys Glu Gly Glu Asn Thr Val
  900                 905                 910
  Lys Val Arg Ala Glu Leu Pro Glu Gly Val Ile Ser Ser Tyr Lys Asp
  915                 920                 925
  Glu Leu Gln Arg Lys Tyr Gly Asp Lys Leu Ile Ile Arg Gly Ile Arg
  930                 935                 940
  Val Glu Pro Val Phe Ile Ala Glu Lys Glu Tyr Leu Met Leu Glu Val
  945                 950                 955                 960
  Ser Ala Ser Ala Pro His His
  965

• Amino acid sequences sharing at least about 70 percent more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the P. furiosus amino acid 50 sequence of SEQ ID NO: 11 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 11 is provided below as SEQ ID NO: 12 (EMBL Nucleotide Sequence Database No. AAL80280):

• atggtgaaaa cccaaataaa ggagaaaaag aaagatgaaa aagttactat tccacttcct   60
  gggaagataa aadctgtttt ggccttccta gtcgttttgg catttgccgc atatggattt  120
  tacattagac atttaacagc cggaaagtat ttctcagatc cagatacctt ctaccatttc  180
  gaaatttata agctagtcct caaagagggc cttcctaggt attacccaat ggcagatgct  240
  ccatttggaa gtctcatagg agaacctctt ggactataca tccttccagc aatattctac  300
  aaaatdatct cadtatttgg gtacaatgag ctagaggcat ttcttctttg gcccccattc  360
  gtaggatttc tcagtgttat aggtgtttac ttactcggaa gaaaagttct gaacgaatgg  420
  gcagggatgt ggggtgctat aattctctca gtcctcacgg caaacttttc aagaacattc  480
  tcaggcaacg caagaggcga cggcccattc atgatgttgt ttacgttttc agcagtccta  540
  atgctcLatt atctaaccga ggadaataaa aacadgaaaa taatctgggg aacactgttt  600
  gtactcttgg caggaatatc aactgcagca tggaacggtt caccatttgg actaatggtt  660
  ctccttggat tcgcatcgtt ccagacaata atcctcttta tttttggaaa gatcaatgag  720
  cttagagaat tcataaagga atactaccca gcatacctgg gaattttagc tataagctac  780
  cttctdacga toccaggaat tggdaaadta ggaggatttg taagatttgc atttgaggLt  840
  ttcttagggt tagttttctt agccatcgtc atgctctatg gaggaaaata cttgaactat  900
  tctgacaaga agcacaggtt cgcagtggtt gcagttatag ttattgcggg gttcgcagga  960
  gcttatattt acgttggtcc aaaactcttc actctaatgg gtggagctta tcagtcaacg 1020
  cdagtttatg aaacagtaca ggagctcgca aaaactgatt ggggagatgt aaaagtctat 1080
  tatggagtag aaaagccaaa cggaatagtc ttcttccttg gattagttgg agcaatgatt 1140
  gttacagcta ggtacctcta caaattattt aaagatggaa ggcgcccaca cgaagagtta 1200
  tttgcaataa ctttctatgt aatgtcaatt tacctcctct ggacagctgc tagattccta 1260
  ttcctagcga gttatgcgat agcdttgatg tcaggtgtct ttgcaggatd cgtcctagag 1320
  actgtagaaa agatgaaaga gagtatacca ataaaagcag cactaggagg agtaattgct 1380
  attatgcttc ttctaatacc cttaactcat ggcccactct tagctcaaag cgctaaaagt 1440
  atgagaacaa ccgagatcga gactagtgga tgggaagatg cgctcaaatg gctcagagaa 1500
  adcactccag aatattcgac cgcdacctct tggtgggact atggatattg gatagagtca 1560
  agcctcctag gacagagaag ggccagtgct gatggtggac atgcaagaga tagagatcat 1620
  atcttagccc tatttctagc cagagacggt aacattagtg aagtagactt tgagagttgg 1680
  gagcttaact acttcctagt ttaccttaat gattgggcaa agttcaatgc aatcagctat 1740
  ctaggcgggg ctataacgag gagagaatac aatggagatg aaagtggaag aggagccgta 1800
  actacgctac ttcctctccc aaggtatgga gagaaatacg tcaacctcta tgccaaagtt 1860
  atagttgatg tttcaaactc gagcgtaaag gttactgtag gagacagaga gtgtgatcca 1920
  ctaatggtta cgtttactcc aagtggaaag acgataaaag gaactggaac ctgtagtgat 1980
  ggcaacgcct tcccatatgt tttacactta actccaacaa ttggagtact tgcatactac 2040
  aaagtagcaa ctgcaaactt cattaagtta gccttcggtg ttccagcttc aacaattcca 2100
  ggattctctg ataagctatt ctcaaacttt gagccagtgt atgagtcagg aaacgtaata 2160
  gtatatcgct tcacaccatt tggaatatac aaaattgagg aaaacattaa cggaacttgg 2220
  aagcaagttt ataacctaac tcctggaaaa cacgagctca aactgtacat ttcagcattc 2280
  ggaagagaca tcgaaaatgc aacgctgtac atttacgcca taaacaacga gaagatcata 2340
  gagaaaatta agattgccga gatatcccac atggactatc tdaatgaata cccgatagca 2400
  gtgaacgtaa ccctaccaaa tgctacaagc tacaggtttg tactagttca aaaaggccca 2460
  ataggtgttc ttctagatgc accaaaagtc aatggtgaga taagaagtcc aaccaacata 2520
  ctaagggaag gagaaagtgg agaaatagag cttaaagttg gggttgataa agactacact 2580
  gccgatctat acttaagggc tacgttcata tatttagtca gaaaaagtgg aaaggataac 2640
  gaagattatg acgcagcgtt tgagccccaa atggatgttt tctttatcac aaagatcgga 2700
  gaaaacattc aacttaaaga aggagagaat acagtaaagg ttagggcgga gcttccagaa 2760
  ggagttatat ctagctacaa agatgaacta cagagaaaat acggagacaa gttgataatc 2820
  agaggaataa gagtagagcc agtgttcata gcagaaaaag agtacctaat gctcgaggtc 2880
  agtgcatcgg ctcctcatca ctaa                                        2904

• OSTs from other Pyrococcus species or strains that share sequence identity to P. furiosus OST STT3 subunit related protein and/or are capable of transferring a glycan moiety to a target glycoprotein are also suitable for use in the present invention. For example, homologous OSTs derived from Pyrococcus sp. ST04 (SEQ ID NO: 13; UniProtKB No. I3RCF1), Pyrococcus sp. (strain NA2) (SEQ ID NO: 14; UniProtKB No. F4HM23). P. horikoshii (SEQ ID NO: 15; UniProtKB No. 074088), P. abyssi (SEQ ID NO: 16; UniProtKB No. Q9V250), and P. yayanosii (SEQ ID NO: 17; UniProtKB No. F8AIG3) each share greater than 70% sequence identity with the amino acid sequence of P. furiosus OST (see alignment of FIG. 7), and are suitable for use in this and all aspects of the present invention. The nucleotide sequences encoding the aforementioned Pyrococcus OSTs are known and readily available in the art. A STT3 consensus sequence based on the alignment of Pyrococcus STT3 sequences is presented as SEQ ID NO: 18 in FIG. 7. Residues that are not fully conserved between the six Pyrococcus sequences are depicted as X, where X can be any amino acid residue. Alternatively, X is selected from an amino acid residue at the corresponding position in one of the six depicted Pyrococcus sequences.
• In another embodiment of the present invention, the OST is a eukaryotic oligosaccharyltransferase. For example, the OST STT3subunit from Leishmania major, which is capable of transferring a glycan to an asparagine residue of a target glycoprotein is suitable for use in this and all aspects of the present invention. The amino acid sequence of L. major (UniProtKB Accession No. Q9U5N8) is provided below as SEQ ID NO: 19.

• Met Ala Ala Ala Ser Asn Val Asn Ala Pro Glu Ser Asn Val Met Thr
  1               5                   10                  15
  Thr Arg Ser Ala Val Ala Pro Pro Ser Thr Ala Ala Pro Lys Glu Ala
  20                  25                  30
  Ser Ser Glu Thr Leu Leu Ile Gly Leu Tyr Lys Met Pro Ser Gln Thr
  35                  40                  45
  Arg Ser Leu Ile Tyr Ser Ser Cys Phe Ala Val Ala Met Ala Ile Ala
  50                  55                  60
  Leu Pro Ile Ala Tyr Asp Met Arg Val Arg Ser Ile Gly Val Tyr Gly
  65                  70                  75                   80
  Tyr Leu Phe His Ser Ser Asp Pro Trp Phe Asn Tyr Arg Ala Ala Glu
  85                  90                  95
  Tyr Met Ser Thr His Gly Trp Ser Ala Phe Phe Ser Trp Phe Asp Tyr
  100                 105                 110
  Met Ser Trp Tyr Pro Leu Gly Arg Pro Val Gly Ser Thr Thr Tyr Pro
  115                 120                 125
  Gly Leu Gln Leu Thr Ala Val Ala Ile His Arg Ala Leu Ala Ala Ala
  130                 135                 140
  Gly Met Pro Met Ser Leu Asn Asn Val Cys Val Leu Met Pro Ala Trp
  145                 150                 155                 160
  Phe Ser Leu Val Ser Ser Ala Met Ala Ala Leu Leu Ala His Glu Met
  165                 170                 175
  Ser Gly Asn Met Ala Val Ala Ser Ile Ser Ser Ile Leu Phe Ser Val
  180                 185                 190
  Val Pro Ala His Leu Met Arg Ser Met Ala Gly Glu Phe Asp Asn Glu
  195                 200                 205
  Cys Ile Ala Val Ala Ala Met Leu Leu Thr Phe Tyr Cys Trp Val Arg
  210                 215                 220
  Ser Leu Arg Thr Arg Ser Ser Trp Pro Ile Gly Val Leu Thr Gly Val
  225                 230                 235                 240
  Ala Tyr Gly Tyr Met Ala Ala Ala Trp Gly Gly Tyr Ile Phe Val Leu
  245                 250                 255
  Asn Met Val Ala Met His Ala Gly Ile Ser Ser Met Val Asp Trp Ala
  260                 265                 270
  Arg Asn Thr Tyr Asn Pro Ser Leu Leu Arg Ala Tyr Thr Leu Phe Tyr
  275                 280                 285
  Val Val Gly Thr Ala Ile Ala Val Cys Val Pro Pro Val Gly Met Ser
  290                 295                 300
  Pro Phe Lys Ser Leu Glu Gln Leu Gly Ala Leu Leu Val Leu Val Phe
  305                 310                 315                 320
  Ile Phe Gly Gln Ser Val Cys Glu Ala Gln Arg Arg Arg Leu Gly Ile
  325                 330                335
  Ala Arg Leu Ser Lys Glu Gly Val Ala Leu Leu Ile Arg Ile Asp Ala
  340                 345                 350
  Ala Phe Phe Val Gly Ile Val Ala Val Ala Thr Ile Ala Pro Ala Gly
  355                 360                 365
  Phe Phe Lys Pro Leu Ser Leu Gln Ala Asn Ala Ile Ile Thr Gly Val
  370                 375                 380
  Ser Arg Thr Gly Asn Thr Leu Val Asp Ile Leu Leu Ala Gln Asp Ala
  385                 390                 395                 400
  Ser Asn Leu Leu Met Val Trp Gln Leu Phe Leu Phe Pro Phe Leu Gly
  405                 410                 415
  Trp Val Ala Gly Met Ser Ala Phe Leu Arg Glu Leu Ile Arg Asn Tyr
  420                 425                 430
  Thr Tyr Ala Lys Ser Phe Ile Leu Met Tyr Gly Val Val Gly Met Tyr
  435                 440                 445
  Phe Ala Ser Gln Ser Val Arg Met Met Val Met Met Ala Pro Val Ala
  450                 455                 460
  Cys Ile Phe Thr Ala Leu Leu Phe Arg Trp Ala Leu Asp Tyr Leu Leu
  465                 470                 475                 480
  Gly Ser Leu Phe Trp Ala Glu Met Pro Pro Ser Phe Asp Thr Asp Ala
  485                 490                 495
  Gln Arg Gly Arg Gln Gln Gln Thr Ala Glu Glu Ser Glu Ala Glu Thr
  500                 505                 510
  Lys Arg Lys Glu Glu Glu Tyr Asn Thr Met Gln Val Lys Lys Met Ser
  515                 520                 525
  Val Arg Met Leu Pro Phe Met Leu Leu Leu Leu Leu Phe Arg Leu Ser
  530                 535                 540
  Gly Phe Ile Glu Asp Val Ala Ala Ile Ser Arg Lys Met Glu Ala Pro
  545                 550                 555                 560
  Gly Ile Val Phe Pro Ser Glu Gln Val Gln Gly Val Ser Glu Lys Lys
  565                 570                 575
  Val Asp Asp Tyr Tyr Ala Gly Tyr Leu Tyr Leu Arg Asp Ser Thr Pro
  580                 585                 590
  Glu Asp Ala Arg Val Leu Ala Trp Trp Asp Tyr Gly Tyr Gln Ile Thr
  595                 600                 605
  Gly Ile Gly Asn Arg Thr Ser Leu Ala Asp Gly Asn Thr Trp Asn His
  610                 615                620
  Glu His Ile Ala Thr Ile Gly Lys Met Leu Thr Ser Pro Val Ala Glu
  625                 630                 635                 640
  Ala His Ser Leu Val Arg His Met Ala Asp Tyr Val Leu Ile Ser Ala
  645                 650                 655
  Gly Asp Thr Tyr Phe Ser Asp Leu Asn Arg Ser Pro Met Met Ala Arg
  660                 665                 670
  Ile Gly Asn Ser Val Tyr His Asp Ile Cys Pro Asp Asp Pro Leu Cys
  675                 680                 685
  Ser Gln Phe Val Leu Gln Lys Arg Pro Lys Ala Ala Ala Ala Lys Arg
  690                 695                 700
  Ser Arg His Val Ser Val Asp Ala Leu Glu Glu Asp Asp Thr Ala Glu
  705                 710                 715                 720
  His Met Val Tyr Glu Pro Ser Ser Leu Ile Ala Lys Ser Leu Ile Tyr
  725                 730                 735
  His Leu His Ser Thr Gly Val Val Thr Gly Val Thr Leu Asn Glu Thr
  740                 745                 750
  Leu Phe Gln His Val Phe Thr Ser Pro Gln Gly Leu Met Arg Ile Phe
  755                 760                 765
  Lys Val Met Asn Val Ser Thr Glu Ser Lys Lys Trp Val Ala Asp Ser
  770                 775                 780
  Ala Asn Arg Val Cys His Pro Pro Gly Ser Trp Ile Cys Pro Gly Gln
  785                 790                 795                 800
  Tyr Pro Pro Ala Lys Glu Ile Gln Glu Met Leu Ala His Gln His Thr
  805                 810                 815
  Asn Phe Lys Asp Leu Leu Asp Pro Arg Thr Thr Trp Ser Gly Ser Arg
  820                 825                 830
  Arg

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the L. major amino acid sequence of SEQ ID NO: 19 are also suitable for use in the present invention. The nucleic acid 50 sequence encoding the amino acid sequence of SEQ ID NO: 19 (L. major STT3) is provided below as SEQ ID NO: 20 (EMBL Nucleotide Sequence Database No. CAB61569):

• atggcggcag cgtcaaacgt gaatgccccc gaaagcaacg tgatgacaac gagaagtgcc	60
  gttgcaccac cgtcgacggc tgcacccaaa gaggcttcaa gtgaaacgct gctcattggc	120
  ctatacaaga tgccctcgca aactcgtagc ctcatctact cctcctgctt tgeggtggcc	180
  atggccattg ccctccctat cgcgtacgac atgcgtgtcc gctccatcgg cgtgtacggg	240
  tacctcttcc acagcagtga cccgtggttc aactaccgcg ctgccgagta catgtccacg	300
  cacggctggt ccgccttctt cagctggttc gactacatga gctggtaccc gctgggccgc	360
  cccgtcggct ccaccacgta cccgggcctg cagctcactg ccgtcgccat tcaccgcgca	420
  ctggcggctg ccggcatgcc gatgtctctc aacaacgtgt gcgtgctgat gccagcgtgg	480
  ttttcacttg tctcttcagc gatggcggca ctgctggcgc atgagatgag cggcaatatg	540
  gcggtagcca gcatctcgtc tatcttattc agtgtggttc cagcccacct gatgcggtcc	600
  atggcgggtg agttcgacaa cgagtgtatc gccgtcgcag ccatgctcct caccttctac	660
  tgctgggtgc gctcgctgcg cacgcggtcc tcgtggccca tcggtgtcct caccggtgtc	720
  gcctacggct acatggcggc ggcgtggggc ggctacattt tcgtgctcaa catggttgcc	780
  atgcatgccg gcatatcatc gatggtggac tgggcccgca acacgtacaa cccgtcgctg	840
  ctgcgtgcat acacgctgtt ctacgtcgtg ggcaccgcca tcgccgtgtg cgtgccgcca	900
  gtggggatgt cgcccttcaa gtcgctggag cagctgggtg cgctgctggt gcttgtcttc	960
  attttcggtc agtctgtgtg tgaggcccag cgcagacgat tgggaatcgc gcgcctttca	1020
  aaggagggcg tggcgctgct catccgcatc gacgcagcct tcttcgtcgg tatcgttgcc	1080
  gtggccacca ttgccccggc tggattcttc aagccgctct ccctgcaagc gaacgcgata	1140
  atcactggcg tatctcgtac cggaaacaca ctcgtagaca ttctgcttgc gcaagacgcg	1200
  tccaacctac tcatggtgtg gcagcttttt ctctttccct tcttaggttg ggtggcgggc	1260
  atgagcgcct tccttagaga gttgatccgg aactacacct acgcgaagag tttcatcctg	1320
  atgtacggcg tggtcggtat gtacttcgcc agccagtctg tccgaatgat ggtgatgatg	1380
  gcccccgtgg cgtgcatctt tactgccctc ttgttccgct gggcactgga ctacctcctc	1440
  gggtctttgt tttgggctga gatgccacct tcctttgaca ccgacgcaca gcgtgggcgg	1500
  cagcaacaga ccgccgagga gtcggaggca gagaccaagc gtaaggagga agagtacaac	1560
  accatgcagg tcaagaagat gtcggtgcgc atgttgccct tcatgctgtt gctcttactg	1620
  tttcgtcttt cggggttcat cgaagatgtg gcggcgatat cgcgcaagat ggaggcgccg	1680
  ggtatagttt ttcccagtga acaggtgcaa ggcgtgtcgg agaaaaaggt cgacgactac	1740
  tatgcggggt acctgtatct gcgcgacagc acgccagagg acgcgcgcgt tttggcctgg	1800
  tgggactacg gctaccagat cacaggcatc ggcaaccgca cctcgctggc cgatggcaac	1860
  acctggaacc acgagcacat cgccacgatc ggcaagatgc tgacgtcgcc cgtggcggag	1920
  gcgcactcgc tggtgcgcca catggccgac tatgttctga tttctgctgg agacacatat	1980
  ttttccgacc tgaatcgctc accgatgatg gcgcgcatcg gcaacagcgt gtaccacgac	2040
  atctgccccg acgacccact ttgtagtcag ttcgtgttgc agaaaagacc gaaagctgct	2100
  gcagcgaagc gcagtcggca cgtcagcgtt gacgcactag aggaggatga cactgcagag	2160
  catatggtat acgagccgtc atcactcata gccaagtcgc tcatatatca cctgcactcc	2220
  acaggggtgg tgacgggggt cacgctgaat gagacgctct tccagcacgt cttcacctca	2280
  ccgcagggtc tcatgcgcat cttcaaggtc atgaacgtga gcacggagag caaaaagtgg	2340
  gttgctgact cggcaaaccg cgtgtgccac ccgcctgggt cgtggatctg ccccgggcag	2400
  tacccgccgg cgaaggagat ccaggagatg ctggcacacc aacacaccaa cttcaaggac	2460
  cttcttgatc ccagaacgac ttggagcggg agcaggcgct ga	2502

• OSTs from other Leishmania species or strains that share sequence identity to L. major OST STT3 subunit related protein and/or are capable of transferring a glycan moiety to a target glycoprotein are also suitable for use in the present invention. For example, homologous OSTs derived from L. donovani (SEQ ID NO: 21; UniProtKB No. E9BRZ2), L. infantum (SEQ ID NO: 22; UniProtKB No. A4IB10), L. mexicana (SEQ ID NO: 23; UniProtKBKB No. E9B5Z4), and L. braziliensis (SEQ ID NO: 24; UniProtKB No. A4HMD6), which each share greater than 70% sequence identity with the amino acid sequence of L. major OST (see alignment of FIG. 8), are also suitable for use in the this and all aspects of the present invention. A STT3 consensus sequence based on the alignment of Leishmania STT3 sequences is presented as SEQ ID NO: 25 in FIG. 8. Residues that are not fully conserved between the five Leishmania sequences are depicted as X, where X can be any amino acid residue. Alternatively, X is selected from an amino acid residue at the corresponding position in one of the five depicted Leishmania sequences.
• In another embodiment of the present invention, the eukaryotic oligosaccharyltransferase is STT3 from Saccharomyces cerevisiae. The amino acid sequence of S. cerevisiae (UniProtKB Accession No. P39007) is provided below as SEQ ID NO: 26.

• Met Gly Ser Asp Arg Ser Cys Val Leu Ser Val Phe Gln Thr Ile Leu
  1               5                   10                  15
  Lys Leu Val Ile Phe Val Ala Ile Phe Gly Ala Ala Ile Ser Ser Arg
  20                  25                  30
  Leu Phe Ala Val Ile Lys Phe Glu Ser Ile Ile His Glu Phe Asp Pro
  35                  40                  45
  Trp Phe Asn Tyr Arg Ala Thr Lys Tyr Leu Val Asn Asn Ser Phe Tyr
  50                  55                  60
  Lys Phe Leu Asn Trp Phe Asp Asp Arg Thr Trp Tyr Pro Leu Gly Arg
  65                  70                  75                  80
  Val Thr Gly Gly Thr Leu Tyr Pro Gly Leu Met Thr Thr Ser Ala Phe
  85                  90                  95
  Ile Trp His Ala Leu Arg Asn Trp Leu Gly Leu Pro Ile Asp Ile Arg
  100                 105                 110
  Asn Val Cys Val Leu Phe Ala Pro Leu Phe Ser Gly Val Thr Ala Trp
  115                 120                 125
  Ala Thr Tyr Glu Phe Thr Lys Glu Ile Lys Asp Ala Ser Ala Gly Leu
  130                 135                 140
  Leu Ala Ala Gly Phe Ile Ala Ile Val Pro Gly Tyr Ile Ser Arg Ser
  145                 150                 155                 160
  Val Ala Gly Ser Tyr Asp Asn Glu Ala Ile Ala Ile Thr Leu Leu Met
  165                 170                 175
  Val Thr Phe Met Phe Trp Ile Lys Ala Gln Lys Thr Gly Ser Ile Met
  180                 185                 190
  His Ala Thr Cys Ala Ala Leu Phe Tyr Phe Tyr Met Val Ser Ala Trp
  195                 200                 205
  Gly Gly Tyr Val Phe Ile Thr Asn Leu Ile Pro Leu His Val Phe Leu
  210                 215                 220
  Leu Ile Leu Met Gly Arg Tyr Ser Ser Lys Leu Tyr Ser Ala Tyr Thr
  225                 230                 235                 240
  Thr Trp Tyr Ala Ile Gly Thr Val Ala Ser Met Gln Ile Pro Phe Val
  245                 250                 255
  Gly Phe Leu Pro Ile Arg Ser Asn Asp His Met Ala Ala Leu Gly Val
  260                 265                 270
  Phe Gly Leu Ile Gln Ile Val Ala Phe Gly Asp Phe Val Lys Gly Gln
  275                 280                 285
  Ile Ser Thr Ala Lys Phe Lys Val Ile Met Met Val Ser Leu Phe Leu
  290                 295                 300
  Ile Leu Val Leu Gly Val Val Gly Leu Ser Ala Leu Thr Tyr Met Gly
  305                 310                 315                 320
  Leu Ile Ala Pro Trp Thr Gly Arg Phe Tyr Ser Leu Trp Asp Thr Asn
  325                 330                 335
  Tyr Ala Lys Ile His Ile Pro Ile Ile Ala Ser Val Ser Glu His Gln
  340                 345                 350
  Pro Val Ser Trp Pro Ala Phe Phe Phe Asp Thr His Phe Leu Ile Trp
  355                 360                 365
  Leu Phe Pro Ala Gly Val Phe Leu Leu Phe Leu Asp Leu Lys Asp Glu
  370                 375                 380
  His Val Phe Val Ile Ala Tyr Ser Val Leu Cys Ser Tyr Phe Ala Gly
  385                 390                 395                 400
  Val Met Val Arg Leu Met Leu Thr Leu Thr Pro Val Ile Cys Val Ser
  405                 410                 415
  Ala Ala Val Ala Leu Ser Lys Ile Phe Asp Ile Tyr Leu Asp Phe Lys
  420                 425                 430
  Thr Ser Asp Arg Lys Tyr Ala Ile Lys Pro Ala Ala Leu Leu Ala Lys
  435                 440                 445
  Leu Ile Val Ser Gly Ser Phe Ile Phe Tyr Leu Tyr Leu Phe Val Phe
  450                 455                 460
  His Ser Thr Trp Val Thr Arg Thr Ala Tyr Ser Ser Pro Ser Val Val
  465                 470                 475                 480
  Leu Pro Ser Gln Thr Pro Asp Gly Lys Leu Ala Leu Ile Asp Asp Phe
  485                 490                 495
  Arg Glu Ala Tyr Tyr Trp Leu Arg Met Asn Ser Asp Glu Asp Ser Lys
  500                 505                 510
  Val Ala Ala Trp Trp Asp Tyr Gly Tyr Gln Ile Gly Gly Met Ala Asp
  515                 520                 525
  Arg Thr Thr Leu Val Asp Asn Asn Thr Trp Asn Asn Thr His Ile Ala
  530                 535                 540
  Ile Val Gly Lys Ala Met Ala Ser Pro Glu Glu Lys Ser Tyr Glu Ile
  545                 550                 555                 560
  Leu Lys Glu His Asp Val Asp Tyr Val Leu Val Ile Phe Gly Gly Leu
  565                 570                 575
  Ile Gly Phe Gly Gly Asp Asp Ile Asn Lys Phe Leu Trp Met Ile Arg
  580                 585                 590
  Ile Ser Glu Gly Ile Trp Pro Glu Glu Ile Lys Glu Arg Tyr Phe Tyr
  595                 600                 605
  Thr Ala Glu Gly Glu Tyr Arg Val Asp Ala Arg Ala Ser Glu Thr Met
  610                 615                 620
  Arg Asn Ser Leu Leu Tyr Lys Met Ser Tyr Lys Asp Phe Pro Gln Leu
  625                 630                 635                 640
  Phe Asn Gly Gly Gln Ala Thr Asp Arg Val Arg Gln Gln Met Ile Thr
  645                 650                 655
  Pro Leu Asp Val Pro Pro Leu Asp Tyr Phe Asp Glu Val Phe Thr Ser
  660                 665                 670
  Glu Asn Trp Met Val Arg Ile Tyr Gln Leu Lys Lys Asp Asp Ala Gln
  675                 680                 685
  Gly Arg Thr Leu Arg Asp Val Gly Glu Leu Thr Arg Ser Ser Thr Lys
  690                 695                 700
  Thr Arg Arg Ser Ile Lys Arg Pro Glu Leu Gly Leu Arg Val
  705                 710                 715

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the S. cerevisiae amino acid sequence of SEQ ID NO: 26 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 26 (S. cerevisiae STT3) is provided below as SEQ ID NO: 27 (EMBL Nucleotide Sequence Database No. BAA06079).

• atgggatccg accggtcgtg tgttttgtct gtgtttcaga ccatcctcaa gctcgtcatc	60
  ttcgtggcga tttttggggc tgccatatca tcacgtttgt ttgcagtcat caaatttgag	120
  tctattatcc atgaattcga cccctggttc aattataggg ctaccaaata tctcgtcaac	180
  aattcgtttt acaagttttt gaactggttt gacgaccgta cctggtaccc cctcggaagg	240
  gttactggag ggactttata tcctggtttg atgacgacta gtgcgttcat ctggcacgcc	300
  ctgcgcaact ggtUgggctt gcccattgac atcagaaacg tttgtgtgct atttgcgcca	360
  ctattttctg gggtcaccgc ctgggcgact tacgaattta cgaaagagat taaagatgcc	420
  agcgctgggc ttttggctgc tggttttata gccattgtcc ccggttatat atctagatca	480
  gtggcggggt cctacgataa tgaggccatt gccattacac tattaatggt cactttcatg	540
  ttttggatta aggcccaaaa gactggctct atcatgcacg caacgtgtgc agctttattc	600
  tacttctaca tggtgtcggc ttggggtgga tacgtgttca tcaccaactt gatcccactc	660
  catgtctttt tgctgatttt gatgggcaga tattcgtcca aactgtattc tgcctacacc	720
  acttggtacg ctattggaac tgttgcatcc atgcagatcc catttgtcgg tttcctacct	780
  atcaggtcta acgaccacat ggccgcattg ggtgttttcg gtttgattca gattgtcgcc	840
  ttcggtgact tcgtgaaggg ccaaatcagc acagctaagt ttaaagtcat catgatggtt	900
  tctctgtttt tgatcttggt ccttggtgtg gtcggacttt ctgccttgac ctatatgggg	960
  ttgattgccc cttggactgg tagattttat tcgttatggg ataccaacta cgcaaagatc	1020
  cacattccta tcattgcctc cgtttccgaa catcaacccg tttcgtggcc cgctttcttc	1080
  tttgataccc actttttgat ctggctattc cccgccggtg tattcctact attcctcgac	1140
  ttgaaagacg agcacgtttt tgtcatcgct tactccgttc tgtgttcgta ctttgccggt	1200
  gttatggtta gattgatgtt gactttgaca ccagtcatct gtgtgtccgc cgccgtcgca	1260
  ttgtccaaga tatttgacat ctacctggat ttcaagacaa gtgaccgcaa aLacgccatc	1320
  aaacctgcgg cactactggc caaattgatt gtttccggat cattcatctt ttatttgtat	1380
  cttttcgtct tccattctac ttgggtaaca agaactgcat actcttctcc ttctgttgtt	1440
  ttgccatcac aaaccccaga tggtaaattg gcgttgatcg acgacttcag ggaagcgtac	1500
  tattggttaa gaatgaactc tgatgaggac agtaaggttg cagcgtggtg ggattacggt	1560
  taccaaattg gtggcatggc agacagaacc actttagtcg ataacaacac gtggaacaat	1620
  actcacatcg ccatcgttgg taaagccatg gcttcccctg aagagaaatc ttacgaaatt	1680
  ctaaaagagc atgatgtcga ttatgtcttg gtcatctttg gtggtctaat tgggtttggt	1740
  ggtgatgaca tcaacaaatt cttgtggatg atcagaatta gcgagggaat ctggccagaa	1800
  gagataaaag agcgttattt ctataccgca gagggagaat acagagtaga tgcaagggct	1860
  tctgagacca tgaggaactc gctactttac aagatgtcct acaaagattt cccacaatta	1920
  ttcaatggtg gccaagccac tgacagagtg cgtcaacaaa tgatcacacc attagacgtc	1980
  ccaccattag actacttcga cgaagttttt acttccgaaa actggatggt tagaatatat	2040
  caattgaaga aggatgatgc ccaaggtaga actttgaggg acgttggtga gttaaccagg	2100
  tcttctacga aaaccagaag gtccataaag agacctgaat taggcttgag agtctaa	2157

• In another embodiment of the present invention, the eukaryotic oligosaccharyltransferase is STT3 from Schizosaccharomyces pombe. The amino acid sequence of S. pombe (UniProtKB Accession No. O94335) is provided below as SEQ ID NO: 28.

• Met Ala Asn Ser Ala Thr Ile Thr Ser Lys Lys Gly Val Lys Ser His
  1               5                   10                  15
  Gln Lys Asp Trp Lys Ile Pro Leu Lys Val Leu Ile Leu Ile Cys Ile
  20                  25                  30
  Ala Val Ala Ser Val Ser Ser Arg Leu Phe Ser Val Ile Arg Tyr Glu
  35                  40                  45
  Ser Ile Ile His Glu Phe Asp Pro Trp Phe Asn Phe Arg Ala Ser Lys
  50                  55                  60
  Ile Leu Val Glu Gln Gly Phe Tyr Asn Phe Leu Asn Trp Phe Asp Glu
  65                  70                  75                  80
  Arg Ser Trp Tyr Pro Leu Gly Arg Val Ala Gly Gly Thr Leu Tyr Pro
  85                  90                  95
  Gly Leu Met Val Thr Ser Gly Ile Ile Phe Lys Val Leu His Leu Leu
  100                 105                 110
  Arg Ile Asn Val Asn Ile Arg Asp Val Cys Val Leu Leu Ala Pro Ala
  113                 120                 125
  Phe Ser Gly Ile Thr Ala Ile Ala Thr Tyr Tyr Leu Ala Arg Glu Leu
  130                 135                 140
  Lys Ser Asp Ala Cys Gly Leu Leu Ala Ala Ala Phe Met Gly Ile Ala
  145                 150                 155                 160
  Pro Gly Tyr Thr Ser Arg Ser Val Ala Gly Ser Tyr Asp Asn Glu Ala
  165                 170                 175
  Ile Ala Ile Thr Leu Leu Met Ser Thr Phe Ala Leu Trp Ile Lys Ala
  180                 185                 190
  Val Lys Ser Gly Ser Ser Phe Trp Gly Ala Cys Thr Gly Leu Leu Tyr
  195                 200                 205
  Phe Tyr Met Val Thr Ala Trp Gly Gly Tyr Val Phe Ile Thr Asn Met
  210                 215                 220
  Ile Pro Leu His Val Phe Val Leu Leu Leu Met Gly Arg Tyr Thr Ser
  225                 230                 235                 240
  Lys Leu Tyr Ile Ala Tyr Thr Thr Tyr Tyr Val Ile Gly Thr Leu Ala
  245                 250                 255
  Per Met Gln Val Pro Phe Val Gly Phe Gln Pro Val Ser Thr Ser Glu
  260                 265                 270
  His Met Ser Ala Leu Gly Val Phe Gly Leu Leu Gln Leu Phe Ala Phe
  275                 280                 285
  Tyr Asn Tyr Val Lys Gly Leu Val Ser Per Lys Gln Phe Gln Ile Leu
  290                 295                 300
  Ile Arg Phe Ala Leu Val Cys Leu Val Gly Leu Ala Thr Val Val Leu
  305                 310                 315                 320
  Phe Ala Leu Ser Ser Thr Gly Val Ile Ala Pro Trp Thr Gly Arg Phe
  325                 330                 335
  Tyr Ser Leu Trp Asp Thr Asn Tyr Ala Lys Ile His Ile Pro Ile Ile
  340                 345                 350
  Ala Ser Val Ser Glu His Gln Pro Pro Thr Trp Ser Ser Leu Phe Phe
  355                 360                 365
  Asp Leu Gln Phe Leu Ile Trp Leu Leu Pro Val Gly Val Tyr Leu Cys
  370                 375                 380
  Phe Lys Glu Leu Arg Asn Glu His Val Phe Ile Ile Ile Tyr Pro Val
  385                 390                 395                 400
  Leu Gly Thr Tyr Phe Cys Gly Val Met Val Arg Leu Val Leu Thr Leu
  405                 410                 415
  Thr Pro Cys Val Cys Ile Ala Ala Ala Val Ala Ile Ser Thr Leu Leu
  420                 425                 430
  Asp Thr Tyr Met Gly Pro Glu Val Glu Glu Asp Lys Val Ser Glu Glu
  435                 440                 445
  Ala Ala Ser Ala Lys Ser Lys Asn Lys Lys Gly Ile Per Ser Ile Leu
  450                 455                 460
  Ser Phe Phe Thr Ser Gly Ser Lys Asn Ile Gly Ile Tyr Ser Leu Leu
  465                 470                 475                 480
  Ser Arg Val Leu Val Ile Ser Ser Thr Ala Tyr Phe Leu Ile Met Phe
  485                 490                 495
  Val Tyr His Ser Ser Trp Val Thr Ser Asn Ala Tyr Ser Ser Pro Thr
  500                 505                 510
  Val Val Leu Ser Thr Val Leu Asn Asp Gly Ser Leu Met Tyr Ile Asp
  515                 520                 525
  Asp Phe Arg Glu Ala Tyr Asp Trp Leu Arg Arg Asn Thr Pro Tyr Asp
  530                 535                 540
  Thr Lys Val Met Ser Trp Trp Asp Tyr Gly Tyr Gln Ile Ala Gly Met
  545                 550                 555                 560
  Ala Asp Arg Ile Thr Leu Val Asp Asn Asn Thr Trp Asn Asn Thr His
  565                 570                 575
  Ile Ala Thr Val Gly Lys Ala Met Ser Ser Pro Glu Glu Lys Ala Tyr
  580                 585                 590
  Pro Ile Leu Arg Lys His Asp Val Asp Tyr Ile Leu Ile Ile Tyr Gly
  595                 600                 605
  Gly Thr Leu Gly Tyr Ser Ser Asp Asp Met Asn Lys Phe Leu Trp Met
  610                 615                 620
  Ile Arg Ile Ser Gln Gly Leu Trp Pro Asp Glu Ile Val Glu Arg Asn
  625                 630                 635                 640
  Phe Phe Thr Pro Asn Gly Glu Tyr Arg Thr Asp Asp Ala Ala Thr Pro
  645                 650                 655
  Thr Met Arg Glu Ser Leu Leu Tyr Lys Met Ser Tyr His Gly Ala Trp
  660                 665                 670
  Lys Leu Phe Pro Pro Asn Gln Gly Tyr Asp Arg Ala Arg Asn Gln Lys
  675                 680                 685
  Leu Pro Ser Lys Asp Pro Gln Leu Phe Thr Ile Glu Glu Ala Phe Thr
  690                 695                 700
  Thr Val His His Leu Val Arg Leu Tyr Lys Val Lys Lys Pro Asp Thr
  705                 710                 715                 720
  Leu Gly Arg Asp Leu Lys Gln Val Thr Leu Phe Glu Glu Gly Lys Arg
  725                 730                 735
  Lys Lys Ser Ala Val Leu Gln Lys Leu Thr Lys Phe Leu
  740                 745

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the S. pombe amino acid sequence 55 of SEQ ID NO: 28 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 28 (S. pombe STT3) is provided below as SEQ ID NO: 29 (EMBL Nucleotide Sequence Database No. BAA76479).

• atggctaatt ctgctacaat tacgagtaaa aaaggcgtga agtctcatca gaaggactgg	60
  aaaattccac ttaaagtgct cattcttata tgtattgctg tggcttctgt ctcttcgagg	120
  cttttttctg tcattcgtta cgagtccatt attcatgaat ttgatccttg gttcaatttc	180
  cgagcttcca aaatattggt ggaacaaggt ttttataact ttttaaattg gtttgatgaa	240
  agaagttggt acccgttggg tcgtgtagcg ggtggtactt tgtacccagg acttatggtc	300
  acgtctggta ttattttcaa agttttacat cttttaagaa ttaacgtgaa catccgtgat	360
  gtatgtgttt tacttgcccc tgctttctct ggaatcactg cgattgctac ctattatctg	420
  gctagagaat tgaaaagtga tgcatgtggc cttttagctg ccgcatttat gggtattgct	480
  cctggataca cctcccgttc cgtcgctggt tcttacgata atgaagcaat tgctattacc	540
  cttttgatgt caacgtttgc tttgtggatc aaggcagtga agtctggctc ctctttctgg	600
  ggtgcctgca caggattgct ctacttctat atggtaactg cgtggggtgg ttatgtattc	660
  atcacaaaca tgataccttt acacgtattt gttcttctac ttatgggtog ctatactagc	720
  aaattataca ttgcttacac aacatactat gttattggaa cgctggcttc tatgcaagtt	780
  ccgtttgttg gtttccaacc cgtgtcgact agtgagcata tgtccgcttt aggagtgttt	840
  ggcctgttac agctttttgc attctacaat tatgttaaag gtctagtttc atccaagcaa	900
  ttccaaatac ttattcgttt tgccttggtt tgcttagtgg gtctagcaac agtcgtcctt	960
  tttgctttat cttcaacagg tgttatcgct ccttggacag gacgtttcta ttctctttgg	1020
  gatacaaact acgccaagat tcatattcct atcattgctt cggtatcaga acatcagcct	1080
  cctacttgga gttcgttgtt ctttgatctt caatttttga tttggttatt gccagttggt	1140
  gtttacttgt gtttcaagga acttcgtaat gaacatgtct ttattattat atatcctgtc	1200
  ttaggaacat atttttgtgg tgtgatggtt cgtttggttt taaccttaac tccttgtgtt	1260
  tgcatagctg ctgctgtagc aatttccact cttttagaca catatatggg tcctgaagtt	1320
  gaagaggaca aagtgagcga agaagccgct tcagccaaat ctaagaacaa gaaaggtatt	1380
  tcctctattc ttagtttctt cacttctggc tcaaaaaata ttggaattta cagtttgctt	1440
  tccagagtat tagtcatttc ctctaccgca tatttcctaa taatgtttgt ttatcattcc	1500
  agttgggtga cttctaatgc ttactcttcc cctaccgtgg ttttgtctac cgtgttaaac	1560
  gatggtagtt taatgtatat tgatgacttc cgtgaagctt atgactggct tcgtagaaac	1620
  actccttatg acacaaaggt tatgaglAgg tgggattatg gttaccaaat tgctggtatg	1680
  gctgatcgta ttactttagt cgacaacaat acgtggaaca acacacatat tgccacagtt	1740
  ggaaaagcca tgtcttcacc tgaagaaaaa gcttacccta tcctccgtaa acacgatgtt	1800
  gattatattc ttattatata tggtggtact cttggataca gcagcgacga catgaacaag	1860
  ttcctttgga tgatccgaat ttctcaggga ttatggcccg atgaaatagt agagcgtaac	1920
  ttttttactc ctaatggaga atatcgaact gacgatgcgg ctactcccac tatgcgtgag	1980
  tctttattat ataagatgtc atatcacggt gcttggaaac ttttccctcc caatcaagga	2040
  tatgaccgtg ctcgcaatca aaaactacca tcgaaagatc ctcaactatt tactatcgaa	2100
  gaagcattca ctaccgttca tcatttagtt cgtttgtata aggttaagaa accggataca	2160
  cttggacgcg atttgaaaca agtgacatta tttgaagaag gcaaaagaaa gaagtccgcc	2220
  gtcctgcaaa aactaacgaa attcctttga	2250

• In another embodiment of the present invention, the eukaryotic oligosaccharyltransferase is STT3 from Dictyostelium discoideum. The amino acid sequence of D. discoideum (UniProtKB Accession No. Q54NM9) is provided below as SEQ ID NO: 30.

• Met Lys Arg Ser Glu Lys Ser Ser Thr Ser Val Val Ser Asn Asn Lys
  1               5                   10                  15
  Gln Gln Asp Val Asn Ile Ile Ser Ser Asn Glu Val Gly Val Lys Glu
  20                  25                  30
  Glu Asn Lys Gly His Gln Glu Phe Leu Leu Lys Val Leu Ile Leu Ser
  35                  40                  45
  Val Ile Tyr Val Leu Ala Phe Ser Thr Arg Leu Phe Ser Val Leu Arg
  50                  55                  60
  Tyr Glu Ser Val Ile His Glu Phe Asp Pro Tyr Phe Asn Tyr Arg Ser
  65                  70                  75                  80
  Thr Ile Tyr Leu Val Gln Glu Gly Phe Tyr Asn Phe Leu Asn Trp Phe
  85                  90                  95
  Asp Glu Arg Ala Trp Tyr Pro Leu Gly Arg Ile Val Gly Gly Thr Ile
  100                 105                 110
  Tyr Pro Gly Leu Met Ala Thr Ala Ser Leu Val His Trp Ser Leu Asn
  115                 120                 125
  Ser Leu Asn Ile Thr Val Asn Ile Arg Asn Val Cys Val Leu Leu Ser
  130                 135                 140
  Pro Trp Phe Ala Ser Asn Thr Ala Met Val Thr Tyr Lys Phe Ala Lys
  145                 150                 155                 160
  Glu Val Lys Asp Thr Gln Thr Gly Leu Val Ala Ala Ala Met Ile Ala
  165                 170                 175
  Ile Val Pro Gly Tyr Ile Ser Arg Ser Val Ala Gly Ser Phe Asp Asn
  180                 185                 190
  Glu Gly Ile Ala Ile Phe Ala Leu Ile Phe Thr Tyr Tyr Cys Trp Ile
  195                 200                 205
  Lys Ser Val Asn Thr Gly Ser Leu Met Trp Ala Ala Ile Cys Ser Leu
  210                 215                 220
  Ala Tyr Phe Tyr Met Ala Ser Ala Trp Gly Gly Tyr Val Phe Ile Ile
  225                 230                 235                 240
  Asn Leu Ile Pro Leu His Ala Phe Phe Leu Leu Leu Thr Gly Arg Tyr
  245                 250                 255
  Ser His Arg Leu Tyr Ile Ala Tyr Ser Thr Met Phe Val Ile Gly Thr
  260                 265                 270
  Ile Leu Ser Met Gln Ile Thr Phe Ile Ser Phe Gln Pro Val Gln Ser
  275                 280                 285
  Ser Glu His Leu Ala Ala Ile Gly Ile Phe Gly Leu Leu Gln Leu Tyr
  290                 295                 300
  Ala Gly Leu Ser Trp Val Lys Ser His Leu Thr Asn Glu Ala Phe Lys
  305                 310                 315                 320
  Lys Leu Gln Arg Leu Thr Val Leu Phe Val Leu Ser Cys Ala Ala Ala
  325                 330                 335
  Val Leu Val Val Gly Thr Leu Thr Gly Tyr Ile Ser Pro Phe Asn Gly
  340                 345                 350
  Arg Phe Tyr Ser Leu Leu Asp Pro Thr Tyr Ala Arg Asp His Ile Pro
  355                 360                 365
  Ile Ile Ala Ser Val Ser Glu His Gln Pro Thr Thr Trp Ala Ser Tyr
  370                 375                 380
  Phe Phe Asp Leu His Ile Leu Val Phe Leu Phe Pro Ala Gly Leu Tyr
  385                 390                 395                 400
  Phe Cys Phe Gln Lys Leu Thr Asp Ala Asn Ile Phe Leu Ile Leu Tyr
  405                 410                 415
  Gly Val Thr Ser Ile Tyr Phe Ser Gly Val Met Val Arg Leu Met Leu
  420                 425                 430
  Val Leu Ala Pro Val Ala Cys Ile Leu Ala Ala Val Ala Val Ser Ala
  435                 440                 445
  Thr Leu Thr Thr Tyr Met Lys Lys Leu Lys Ala Pro Ser Ser Pro Ser
  450                 455                 460
  Asp Ala Asn Asn Ser Lys Glu Ser Gly Gly Val Met Val Ala Val Leu
  465                 470                 475                 480
  Thr Val Leu Leu Ile Leu Tyr Ala Phe His Cys Thr Trp Val Thr Ser
  485                 490                 495
  Glu Ala Tyr Ser Ser Pro Ser Ile Val Leu Ser Ala Lys Gln Asn Asp
  500                 505                 510
  Gly Ser Arg Val Ile Phe Asp Asp Phe Arg Glu Ala Tyr Arg Trp Ile
  515                 520                 525
  Gly Gln Asn Thr Ala Asp Asp Ala Arg Ile Met Ser Trp Trp Asp Tyr
  530                 535                 540
  Gly Tyr Gln Leu Ser Ala Met Ala Asn Arg Thr Val Leu Val Asp Asn
  545                 550                 555                 560
  Asn Thr Trp Asn Asn Ser His Ile Ala Gln Val Gly Lys Ala Phe Ala
  565                 570                 575
  Ser Thr Glu Glu Asp Ala Tyr Ile Gln Met Lys Ala Leu Asp Val Asp
  580                 585                 590
  Tyr Val Leu Val Ile Phe Gly Gly Leu Thr Gly Tyr Ser Ser Asp Asp
  595                 600                 605
  Ile Asn Lys Phe Leu Trp Met Val Arg Ile Gly Gly Ser Cys Asp Pro
  610                 615                 620
  Asn Ile Lys Glu Gln Asp Tyr Leu Thr Asn Gly Gln Tyr Arg Ile Asp
  625                 630                 635                 640
  Lys Gly Ala Ser Pro Thr Met Leu Asn Ser Leu Met Tyr Lys Leu Ser
  645                 650                 655
  Tyr Tyr Arg Phe Ser Glu Val His Thr Asp Tyr Gln Arg Pro Thr Gly
  660                 665                 670
  Phe Asp Arg Val Arg Asn Val Glu Ile Gly Asn Lys Asn Phe Asp Leu
  675                 680                 685
  Thr Tyr Leu Glu Glu Ala Phe Thr Ser Val His Trp Leu Val Arg Val
  690                 695                 700
  Tyr Lys Val Lys Asp Phe Asp Asn Arg Ala
  705                 710

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the D. discoideum amino acid sequence of SEQ ID NO: 30 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 30 (D. discoideum STT3) is provided below as SEQ ID NO: 31 (EMBL Nucleotide Sequence Database No. EAL64892).

• atgaaaagat cagaaaaatc aagtacatct gttgttagta ataacaaaca acaagatgta	60
  aatatcatca gttcaaatga agttggtgtt aaagaagaaa ataaaggaca tcaagaattc	120
  ttattaaaag ttttaattct atcagtcatt tatgttttag cattttcaac tcgtttattc	180
  tcagtattac gttatgaaag tgttattcat gaatttgatc catattttaa ttatagatca	240
  acaatatatc ttgttcaaga aggtttttat aattttttaa attggtttga tgaaagagca	300
  tggtatccat taggacgtat tgtaggtggt acaatttacc caggtttaat ggcaacagca	360
  agtttagttc attggtcatt gaattcattg aatattacag ttaatattag aaatgtatgt	420
  gtattgttat caccatggtt tgcatcaaat acagcaatgg taacctataa atttgccaaa	480
  gaagttaagg atacacaaac tggtttggtt gcagcagcca tgattgcaat tgttccaggt	540
  tatatttcac gttcagtagc aggttcattc gataatgaag gtattgcaat ctttgcattg	600
  attttcacat attattgttg gattaagtca gtaaacacag gctcattgat gtgggctgcc	660
  atctgttcat tggcctactt ttatatggca agtgcctggg gtggttatgt attcatcatt	720
  aatttaatcc cattgcatgc ctttttcttg cttttgacag gccgttattc acatcgtctc	780
  tacatagcct acagcacaat gtttgtcatt ggtacaatcc tctctatgca aattacattc	840
  attagtttcc aaccagttca atcatctgaa catttggctg ccattggtat ctttggtctc	900
  ctccaattgt acgctggttt gtcatgggta aagagtcacc tcaccaatga agccttcaag	960
  aaacttcaac gtttgacagt gttattcgtt ttatcttgtg ctgctgccgt acttgtcgtt	1020
  ggtacattaa ctggttacat ctcaccattc aatggtcgtt tctattcatt gttggatcca	1080
  acctatgctc gtgaccacat tccaatcatt gcatcagtat cagagcatca accaaccact	1140
  tgggcatcat actttttcga tctccatatc ttggtattcc ttttcccagc cggtttatac	1200
  ttttgtttcc aaaaattaac cgatgctaat attttcctca ttctctacgg tgtcacctcc	1260
  atttatttct ctggtgtaat ggtacgtctt atgttggttt tagcaccagt tgcatgtatt	1320
  ttagccgccg ttgccgtcag tgcaaccctc accacctata tgaagaagtt aaaggctcca	1380
  tcatcaccaa gtgatgctaa taattccaaa gagagtggtg gtgttatggt tgcagtctta	1440
  actgttcttt taattctcta cgctttccat tgtacttggg tcactagtga agcctactca	1500
  tctccatcca ttgtactctc tgccaaacaa aacgatggta gtcgtgtgat tttcgatgat	1560
  ttccgtgaag cctaccgttg gattggtcaa aatactgccg acgacgctcg tattatgtct	1620
  tggtgggatt atggttatca attatctgca atggccaatc gtaccgtatt ggttgataat	1680
  aacacttgga acaatagtca tatcgctcaa gttggtaaag catttgcatc cactgaagaa	1740
  gatgcttaca tacaaatgaa agcattggat gtcgattatg ttttagttat ttttggtggt	1800
  ttaactggtt acagttctga tgatatcaat aaattccttt ggatggttag aattggtggt	1860
  agttgtgatc caaatattaa agaacaagat tatctcacca atggtcaata tagaatagat	1920
  aaaggtgcct caccaacaat gttaaattct ctcatgtaca aacttagtta ctatcgtttc	1980
  tctgaagttc acactgacta tcaaagacca acaggtttcg atcgtgtaag aaatgttgaa	2040
  attggtaata aaaatttcga tttaacttat ttagaagaag ctttcacatc tgttcattgg	2100
  ttagttagag tttataaagt taaagatttt gataatagag cttaa	2145

• Other eukaryotic oligosaccharyltransferases that can be utilized in this and all aspects of the present invention are listed in the table of FIGS. 9A-9G. This table identifies each oligosaccharyltransferase by its UniProtKB entry number, which provides the amino acid sequence of the protein, and the EMBL database accession number, which provides the encoding nucleotide sequence. The UniProtKB and EMBL accession numbers, along with the corresponding amino acid and nucleotide sequence information for each oligosaccharyltransferase listed in FIG. 9 is hereby incorporated by reference in its entirety.
• In another embodiment of the present invention, the oligosaccharyltransferase is an O-linked oligosaccharyltransferase. An exemplary O-linked OST is PilO from Pseudomonas aeruginosa. PilO is responsible for the en bloc transfer of an oligosaccharide from a lipid-linked donor to an oxygen atom of serine and threonine residues (Faridmoayer et al., “Functional Characterization of Bacterial Oligosaccharyltransferases Involved in O-Linked Protein Glycosylation,” J. Bacteriol. 189(22): 8088-8098 (2007), which is hereby incorporated by reference in its entirety). The amino acid sequence of P. aeruginosa (UniProtKB Accession No. Q51353) is provided below as SEQ ID NO: 32

• Met Ser Leu Ala Ser Ser Leu Glu Ser Leu Arg Lys Ile Asp Ile Asn
  1               5                   10                  15
  Asp Leu Asp Leu Asn Asn Ile Gly Ser Trp Pro Ala Ala Val Lys Val
  20                  25                  30
  Ile Val Cys Val Leu Leu Thr Ala Ala Val Leu Ala Leu Gly Tyr Asn
  35                  40                  45
  Phe His Leu Ser Asp Met Gln Ala Gln Leu Glu Gln Gln Ala Ala Glu
  50                  55                  60
  Glu Glu Thr Leu Lys Gln Gln Phe Ser Thr Lys Ala Phe Gln Ala Ala
  65                  70                  75                  80
  Asn Leu Glu Ala Tyr Lys Ala Gln Met Lys Glu Met Glu Glu Ser Phe
  85                  90                  95
  Gly Ala Leu Leu Arg Gln Leu Pro Ser Asp Thr Glu Val Pro Gly Leu
  100                 105                 110
  Leu Glu Asp Ile Thr Arg Thr Gly Leu Gly Ser Gly Leu Glu Phe Glu
  115                 120                 125
  Glu Ile Lys Leu Leu Pro Glu Val Ala Gln Gln Phe Tyr Ile Glu Leu
  130                 135                 140
  Pro Ile Gln Ile Ser Val Val Gly Gly Tyr His Asp Leu Ala Thr Val
  145                 150                 155                 160
  Ser Gly Val Ser Ser Leu Pro Arg Ile Val Thr Leu His Asp Phe Glu
  165                 170                 175
  Ile Lys Pro Val Ala Pro Gly Ser Thr Ser Lys Leu Arg Met Ser Ile
  180                 185                 190
  Leu Ala Lys Thr Tyr Arg Tyr Asn Asp Lys Gly Leu Lys Lys
  195                 200                 205

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the P. aeruginosa amino acid sequence of SEQ ID NO: 32 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 33 (P. aeruginosa PilO) is provided below as SEQ ID NO: 33 (EMBL Nucleotide Sequence Database No. AAA87404).

• atgagtctgg ccagttccct ggaaagtctg cgcaagatcg atatcaacga tctcgacctg	60
  aacaacatcg gttcctggcc ggcggcggtc aaggtcatcg tctgcgtgct gctgaccgcg	120
  gcggtcctgg cgctgggcta caacttccat ctgagtgaca tgcaggctca gctcgaacag	180
  caggccgcgg aagaggagac gctcaagcag cagttctcca ccaaggcctt ccaggccgcg	240
  aacctggaag cctacaaggc acagatgaag gagatggaag agtcctttgg cgccttgctg	300
  cggcagttgc ccagcgacac cgaggtaccc gggctgctcg aggacatcac tcgtaccggc	360
  ctgggcagcg gcctggagtt cgaggaaatc aagctgcttc ccgaggttgc ccagcagttc	420
  tacatcgagc tgccgatcca gatcagcgtg gtcggcggct accacgactt ggcgaccttc	480
  gtcagcggcg tgtccagcct gccgcggatc gtcaccctgc atgacttcga gatcaagccg	540
  gtcgcgcccg gcagcacgtc caagctgcgc atgagcatcc tggccaagac ctatcgctac	600
  aacgacaagg ggctgaagaa atga	624

• Another exemplary O-linked OST suitable for use in all aspects of the present invention is PglL from Neisseria meningitidis (Faridmoayer et al., “Functional Characterization of Bacterial Oligosaccharyltransferases Involved in O-Linked Protein Glycosylation,” J. Bacteriol. 189(22): 8088-8098 (2007), which is hereby incorporated by reference in its entirety). The amino acid sequence of N. meningitidis (UniProtKB Accession No. GIFG65) is provided below as SEQ ID NO: 34:

• Met Pro Ala Glu Thr Thr Val Ser Gly Ala His Pro Ala Ala Lys Leu
  1               5                   10                  15
  Pro Ile Tyr Ile Leu Pro Cys Phe Leu Trp Ile Gly Ile Val Pro Phe
  20                  25                  30
  Thr Phe Ala Leu Lys Leu Lys Pro Ser Pro Asp Phe Tyr His Asp Ala
  35                  40                  45
  Ala Ala Ala Ala Gly Leu Ile Val Leu Leu Phe Leu Thr Ala Gly Lys
  50                  55                  60
  Lys Leu Phe Asp Val Lys Ile Pro Ala Ile Ser Phe Leu Leu Phe Ala
  65                  70                  75                  80
  Met Ala Ala Phe Trp Tyr Leu Gln Ala Arg Leu Met Asn Leu Ile Tyr
  85                  90                  95
  Pro Gly Met Asn Asp Ile Val Ser Trp Ile Phe Ile Leu Leu Ala Val
  100                 105                 110
  Ser Ala Trp Ala Cys Arg Ser Leu Val Ala His Phe Gly Gln Glu Arg
  115                 120                 125
  Ile Val Thr Leu Phe Ala Trp Ser Leu Leu Ile Gly Ser Leu Leu Gln
  130                 135                 140
  Ser Cys Ile Val Val Ile Gln Phe Ala Gly Trp Glu Asp Thr Pro Leu
  145                 150                 155                 160
  Phe Gln Asn Ile Ile Val Tyr Ser Gly Gln Gly Val Ile Gly His Ile
  165                 170                 175
  Gly Gln Arg Asn Asn Leu Gly His Tyr Leu Met Trp Gly Ile Leu Ala
  180                 185                 190
  Ala Ala Tyr Leu Asn Gly Gln Arg Lys Ile Pro Ala Ala Leu Gly Val
  195                 200                 205
  Ile Cys Leu Ile Met Gln Thr Ala Val Leu Gly Leu Val Asn Ser Arg
  210                 215                 220
  Thr Ile Leu Thr Tyr Ile Ala Ala Ile Ala Leu Ile Leu Pro Phe Trp
  225                 230                 235                 240
  Tyr Phe Arg Ser Asp Lys Ser Asn Arg Arg Thr Met Leu Gly Ile Ala
  245                 250                 255
  Ala Ala Val Phe Leu Thr Ala Leu Phe Gln Phe Ser Met Asn Thr Ile
  260                 265                 270
  Leu Glu Thr Phe Thr Gly Ile Arg Tyr Glu Thr Ala Val Glu Arg Val
  275                 280                 285
  Ala Asn Gly Gly Phe Thr Asp Leu Pro Arg Gln Ile Glu Trp Asn Lys
  290                 295                 300
  Ala Leu Ala Ala Phe Gln Ser Ala Pro Ile Phe Gly His Gly Trp Asn
  305                 310                 315                 320
  Ser Phe Ala Gln Gln Thr Phe Leu Ile Asn Ala Glu Gln His Asn Ile
  325                 330                 335
  Tyr Asp Asn Leu Leu Ser Asn Leu Phe Thr His Ser His Asn Ile Val
  340                 345                 350
  Leu Gln Leu Leu Ala Glu Met Gly Ile Ser Gly Thr Leu Leu Val Ala
  355                 360                 365
  Ala Thr Leu Leu Thr Gly Ile Ala Gly Leu Leu Lys Arg Pro Leu Thr
  370                 375                 380
  Pro Ala Ser Leu Phe Leu Ile Cys Thr Leu Ala Val Ser Met Cys His
  385                 390                 395                 400
  Ser Met Leu Glu Tyr Pro Leu Trp Tyr Val Tyr Phe Leu Ile Pro Phe
  405                 410                     415
  Gly Leu Met Leu Phe Leu Ser Pro Ala Glu Ala Ser Asp Gly Ile Ala
  420                 425                     430
  Phe Lys Lys Ala Ala Asn Leu Gly Ile Leu Thr Ala Ser Ala Ala Ile
  435                 440                     445
  Phe Ala Gly Leu Leu His Leu Asp Trp Thr Tyr Thr Arg Leu Val Asn
  450                 455                     460
  Ala Phe Ser Pro Ala Thr Asp Asp Ser Ala Lys Thr Leu Asn Arg Lys
  465                 470                 475                 480
  Ile Asn Glu Leu Arg Tyr Ile Ser Ala Asn Ser Pro Met Leu Ser Phe
  485                 490                 495
  Tyr Ala Asp Phe Ser Leu Val Asn Phe Ala Leu Pro Glu Tyr Pro Glu
  500                 505                 510
  Thr Gln Thr Trp Ala Glu Glu Ala Thr Leu Lys Ser Leu Lys Tyr Arg
  515                 520                 525
  Pro His Ser Ala Thr Tyr Arg Ile Ala Leu Tyr Leu Met Arg Gln Gly
  530                 535                 540
  Lys Val Ala Glu Ala Lys Gln Trp Met Arg Ala Thr Gln Ser Tyr Tyr
  545                 550                 555                 560
  Pro Tyr Leu Met Pro Arg Tyr Ala Asp Glu Ile Arg Lys Leu Pro Val
  565                 570                 575
  Trp Ala Pro Leu Leu Pro Glu Leu Leu Lys Asp Cys Lys Ala Phe Ala
  580                 585                 590
  Ala Ala Pro Gly His Pro Glu Ala Lys Pro Cys Lys
  595                 600

• Amino acid sequences sharing at least about 70 percent, more preferably at least about 75 percent or 80 percent, most preferably at least about 85 percent or 90 percent or 95 percent as compared to the N. menigitidis amino acid sequence of SEQ ID NO: 34 are also suitable for use in the present invention. The nucleic acid sequence encoding the amino acid sequence of SEQ ID NO: 34 (N. menigitidis PglL) is provided below as SEQ ID NO: 35 (EMBL Nucleotide Sequence Database No. AEK98518).

• atgcccgctg aaacgaccgt atccggcgcg caccccgccg ccaaactgcc gatttacatc	60
  ctgccctgct tcctttggat aggcatcgtc ccctttacct tcgcgctcaa actgaaaccg	120
  tcgcccgact tttaccacga tgccgccgcc gcagccggcc tgattgtcct gttgttcctc	180
  acggcaggaa aaaaactgtt tgatgtcaaa atccccgcca tcagcttcct tctgtttgca	240
  atggcggcgt tttggtatct tcaggcacgc ctgatgaacc tgatttaccc cggtatgaac	300
  gacatcgtct cttggatttt catcttgctc gccgtcagcg cgtgggcctg ccggagcttg	360
  gtcgcacact tcggacaaga acgcatcgtg accctgtttg cctggtcgct gcttatcggc	420
  tccctgcttc aatcctgcat cgtcgtcatc cagtttgccg gctgggaaga cacccctctg	480
  tttcaaaaca tcatcgttta cagcgggcaa ggcgtaatcg gacacatcgg gcagcgcaac	540
  aacctcggac actacctcat gtggggcata ctcgccgccg cctacctcaa cggacaacga	600
  aaaatccccg ccgccctcgg cgtaatctgc ctgattatgc agaccgccgt tttaggtttg	660
  gtcaactcgc gcaccatctt gacctacata gccgccatcg ccctcatcct tcccttctgg	720
  tatttccgtt cggacaaatc caacaggcgg acgatgctcg gcatagccgc agccgtattc	780
  cttaccgcgc tgttccaatt ttccatgaac accattctgg aaacctttac tggcatccgc	840
  tacgaaactg ccgtcgaacg cgtcgccaac ggcggtttca cagacttgcc gcgccaaatc	900
  gaatggaata aagcccttgc cgccttccag tccgccccga tattcgggca cggctggaac	960
  agttttgccc aacaaacctt cctcatcaat gccgaacagc acaacatata cgacaacctc	1020
  ctcagcaact tgttcaccca ttcccacaac atcgtcctcc aactccttgc agagatggga	1080
  atcagcggca cgcttctggt tgccgcaacc ctgctgacgg gcattgccgg gctgcttaaa	1140
  cgccccctga cccccgcatc gcttttccta atctgcacgc ttgccgtcag tatgtgccac	1200
  agtatgctcg aatatccttt gtggtatgtc tatttcctca tccctttcgg actgatgctc	1260
  ttcctgtccc ccgcagaggc ttcagacggc atcgccttca aaaaagccgc caatctcggc	1320
  atactgaccg cctccgccgc catattcgca ggattgctgc acttggactg gacatacacc	1380
  cggctggtta acgccttttc ccccgccact gacgacagtg ccaaaaccct caaccggaaa	1440
  atcaacgagt tgcgctatat ttccgcaaac agtccgatgc tgtcctttta tgccgacttc	1500
  tccctcgtaa acttcgccct gccggaatac cccgaaaccc agacttgggc ggaagaagca	1560
  accctcaaat cactaaaata ccgcccccac tccgccacct accgcatcgc cctctacctg	1620
  atgoggcaag gcaaagttgc agaagcaaaa caatggatgc gggcgacaca gtcctattac	1680
  ccctacctga tgccccgata cgccgacgaa atccgcaaac tgcccgtatg ggcgccgctg	1740
  ctacccgaac tgctcaaaga ctgcaaagcc ttcgccgccg cgcccggtca tccggaagca	1800
  aaaccctgca aatga	1815

• As used herein, an “isolated” oligosaccharyltransferase refers to an oligosaccharyltransferase that is substantially pure or substantially separated from other cellular components that naturally accompany the native protein in its natural host cell. Typically, the isolated oligosaccharyltransferase of the present invention is at about 80% pure, usually at least about 90% pure, and preferably at least about 95% pure. Purity can be assessed using any method known in the art, e.g., polyacrylamide gel electrophoresis, HPLC, etc. The isolated oligosaccharyltransferase can be obtained from the organism from which it is derived directly, or it can be recombinantly produced and purified from a host cell as described in the Examples herein or using techniques readily known in the art as described below.
• Generally, the use of recombinant expression systems to produce and isolate a protein of interest involves inserting a nucleic acid molecule encoding the amino acid sequence of the desired protein into an expression system to which the molecule is heterologous (i.e., not normally present). One or more desired nucleic acid molecules encoding one or more proteins may be inserted into the vector. When multiple nucleic acid molecules are inserted, the multiple nucleic acid molecules may encode the same or different enzymes. The heterologous nucleic acid molecule is inserted into the expression system or vector in proper sense (5′→3′) orientation relative to the promoter and any other 5′ regulatory molecules, and correct reading frame.
• The preparation of the nucleic acid constructs can be carried out using standard cloning procedures well known in the art as described by Joseph Sambrook et al., MOLECULAR CLONING: A LABORATORY MANUAL (Cold Springs Harbor 1989) and U.S. Pat. No. 4,237,224 to Cohen and Boyer, which are hereby incorporated by reference in its entirety. These recombinant plasmids are then introduced by means of transformation and replicated in a suitable host cell.
• A variety of genetic signals and processing events that control many levels of gene expression (e.g., DNA transcription and messenger RNA (“mRNA”) translation) can be incorporated into the nucleic acid construct to maximize enzyme production. For the purposes of expressing a cloned nucleic acid sequence encoding one or more desired enzymes, it is advantageous to use strong promoters to obtain a high level of transcription. Depending upon the host system utilized, any one of a number of suitable promoters may be used. For instance, when cloning in E. coli, its bacteriophages, or plasmids, promoters such as the 17 phage promoter, lac promoter, trp promoter, recA promoter, ribosomal RNA promoter, the P_R and P_L promoters of coliphage lambda and others, including but not limited, to lacUV5, ompF, bla, lpp, and the like, may be used to direct high levels of transcription of adjacent DNA segments. Additionally, a hybrid trp-lacUV5 (tac) promoter or other E. coli promoters produced by recombinant DNA or other synthetic DNA techniques may be used to provide for transcription of the inserted gene. Common promoters suitable for directing expression in mammalian cells include, without limitation, SV40, MMTV, metallothionein-1, adenovirus Ela, CMV, immediate early, immunoglobulin heavy chain promoter and enhancer, and RSV-LTR.
• There are other specific initiation signals required for efficient gene transcription and translation in prokaryotic cells that can be included in the nucleic acid construct to maximize peptide production, e.g., the Shine-Dalgarno ribosome binding site. Depending on the vector system and host utilized, any number of suitable transcription and/or translation elements, including constitutive, inducible, and repressible promoters, as well as minimal 5′ promoter elements, enhancers or leader sequences may be used. For a review on maximizing gene expression see Roberts and Lauer, “Maximizing Gene Expression on a Plasmid Using Recombination In Vitro,” Methods in Enzymology 68:473-82 (1979), which is hereby incorporated by reference in its entirety.
• A nucleic acid molecule encoding an oligosaccharyltransferase or other protein component of the present invention (e.g., glycoprotein target, enzymes involved in glycan production), a promoter molecule of choice, including, without limitation, enhancers, and leader sequences, a suitable 3′ regulatory region to allow transcription in the host, and any additional desired components, such as reporter or marker genes, are cloned into the vector of choice using standard cloning procedures in the art, such as described in Joseph Sambrook et al., MOLECULAR CLONING: A LABORATORY MANUAL (Cold Springs Harbor 1989); Frederick M. Ausubel, SHORT PROTOCOLS IN MOLECULAR BIOLOGY (Wiley 1999), and U.S. Pat. No. 4,237,224 to Cohen and Boyer, which are hereby incorporated by reference in their entirety.
• Once the nucleic acid molecule encoding the protein or proteins has been cloned into an expression vector, it is ready to be incorporated into a host. Recombinant molecules can be introduced into cells, without limitation, via transfection (if the host is a eukaryote), transduction, conjugation, mobilization, electroporation, lipofection, protoplast fusion, calcium chloride transformation, mobilization, transfection using bacteriophage, or particle bombardment, using standard cloning procedures known in the art, as described by JOSEPH SAMBROOK et al., MOLECULAR CLONING: A LABORATORY MANUAL (Cold Springs Harbor 1989), which is hereby incorporated by reference in its entirety.
• Suitable host cells for recombinant protein production include both prokaryotic and eukaryotic cells. Suitable prokaryotic host cells include, without limitation, E. coli and other Enterobacteriaceae, Escherichia sp., Campylobacter sp., Wolinella sp., Desulfovibrio sp. Vibrio sp., Pseudomonas sp. Bacillus sp., Listeria sp., Staphylococcus sp., Streptococcus sp., Peptostreptococcus sp., Megasphaera sp., Pectinatus sp., Selenomonas sp., Zymophilus sp., Actinomyces sp., Arthrobacter sp., Frankia sp., Micromonospora sp., Nocardia sp., Propionibacterium sp., Streptomyces sp., Lactobacillus sp., Lactoocccus sp., Leuconostoc sp., Pediococcus sp., Acetobacterium sp., Eubacterium sp., Heliobacterium sp., Heliospirillum sp., Sporomusa sp., Spiroplasma sp., Ureaplasma sp., Erysipelothrix, sp., Corynebacterium sp. Enterococcus sp., Clostridium sp., Mycoplasma sp., Mycobacterium sp., Actinobacteria sp., Salmonella sp., Shigella sp., Moraxella sp., Helicobacter sp. Stenotrophomonas sp., Micrococcus sp., Neisseria sp., Bdellovibrio sp., Hemophilus sp., Klebsiella sp., Proteus mirabilis, Enterobacter cloacae, Serratia sp., Citrobacter sp., Proteus sp., Serratia sp., Yersinia sp., Acinetobacter sp., Actinobacillus sp. Bordetella sp., Brucella sp., Capnocytophaga sp., Cardiobacterium sp., Eikenella sp., Francisella sp., Haemophilus sp., Kingella sp., Pasteurella sp., Flavobacterium sp. Xanthomonas sp., Burkholderia sp., Aeromonas sp., Plesiomonas sp., Legionella sp. and alpha-proteobacteria such as Wolbachia sp., cyanobacteria, spirochaetes, green sulfur and green non-sulfur bacteria, Gram-negative cocci, Gram negative bacilli which are fastidious, Enterobacteriaceae-glucose-fermenting gram-negative bacilli, Gram negative bacilli-non-glucose fermenters, Gram negative bacilli-glucose fermenting, oxidase positive. In addition to bacteria cells, eukaryotic cells such as mammalian, insect, and yeast systems are also suitable host cells for transfection/transformation of the expression vector for recombinant protein production. Mammalian cell lines available in the art for expression of a heterologous protein or polypeptide include Chinese hamster ovary cells, HeLa cells, baby hamster kidney cells, COS cells and many others.
• Purified proteins may be obtained from the host cell by several methods readily known in the art, including ion exchange chromatography, hydrophobic interaction chromatography, affinity chromatography, gel filtration, and reverse phase chromatography. The peptide is preferably produced in purified form (preferably at least about 70 to about 75% pure, or about 80% to 85% pure, more preferably at least about 90% or 95% pure) by conventional techniques. Depending on whether the recombinant host cell is made to secrete the protein into growth medium (see U.S. Pat. No. 6,596,509 to Bauer et al., which is hereby incorporated by reference in its entirety), the protein can be isolated and purified by centrifugation (to separate cellular components from supernatant containing the secreted protein) followed by sequential ammonium sulfate precipitation of the supernatant. The fraction containing the protein can be subjected to gel filtration in an appropriately sized dextran or polyacrylamide column to separate the protein from other cellular components and proteins. If necessary, the protein fraction may be further purified by HPLC.
• The oligosaccharyltransferase catalyzes the transfer of a glycan from a lipid donor to an acceptor protein, peptide, or polypeptide. In one embodiment of the present invention, the lipid donor or carrier molecule is a prokaryotic lipid donor, i.e., it is made in a prokaryote or native to the prokaryote. Examples of prokaryotic lipid donors include an undecaprenyl-phosphate and an undecaprenyl phosphate-linked bacillosamine (Weerapana et al., “Investigating Bacterial N-Linked Glycosylation: Synthesis and Glycosyl Acceptor Activity of the Undecaprenyl Pyrophosphate-linked Bacillosamine,” J. Am. Chem. Soc. 127: 13766-67 (2005), which is hereby incorporated by reference in its entirety). In another embodiment of the present invention, the lipid donor is a eukaryotic lipid donor, i.e., it is made in a eukaryotic cell or native to the eukaryotic cell. An exemplary eukaryotic lipid donor is dolichylpyrophosphate
• In accordance with this and all aspects of the present invention, the glycan comprises an oligosaccharide or polysaccharide that is linked to a lipid donor molecule. The composition of the glycan component varies in number and type of monosaccharide units that make up the oligosaccharide or polysaccharide chain. The monosaccharide components of a glycan include, but are not limited to, one or more of glucose (Glc), galactose (Gal), mannose (Man), fucose (Fuc), N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), glucorionic acid, xylose, sialic acid (e.g., N-acetyl-neuraminic acid (NeuAc), 6-deoxy-talose, and rhamnose monosaccharides.
• In accordance with this and all aspects of the present invention, the glycan can be a prokaryotic, archaea, or eukaryotic glycan. Alternatively, the glycan may comprise a completely unnatural glycan composition.
• In one embodiment of the present invention, the glycan is a prokaryotic glycan that is produced by one or more prokaryotic glycosyltransferases. In another embodiment of the present invention, the prokaryotic glycan is produced using a combination of prokaryotic and eukaryotic glycosyltransferases, but has a monosaccharide composition that mimics a prokaryotic glycan structure. In another embodiment of the present invention, the prokaryotic glycan is synthetically produced (Seeberger et al., Chemical and Enzymatic Synthesis of Glycans and Glycoconjugates, in ESSENTIALS OF GLYCOBIOLOGY (A. Varki et al. eds., 2009), which is hereby incorporated by reference in its entirety).
• An exemplary prokaryotic glycan is a glycan produced by the glycosyltransferases of the C. jejuni, C. Coli, C. lari, or C. upsaliensis Pgl gene clusters or a modified C. jejuni, C. Coli, C. lari, or C. upsaliensis Pgl gene cluster. Genes of the Pgl cluster include wlaA, galE, wlaB, pglH, pglI, pglJ, pglB, pglA, pglC, pglD, wlaJ, pglE, pglF, and pglG (Szymanski and Wren, “Protein Glycosylation in Bacterial Mucosal Pathogens,” Nature Microbiol. 3:225-237 (2005), which is hereby incorporated by reference in its entirety). A prokaryotic glycan typically comprises the diacetamido-trideoxy-sugar, bacillosamine (Bac; 2,4-diacetamido-2,4,6-trideoxyglucose). A suitable prokaryotic glycan of this and all aspects of the present invention is a heptasaccharide comprising glucose, N-acetylgalactosamine, and bacillosamine, i.e., GlcGalNAc₅Bac.
• As described in the Examples herein, the glycan of this and all aspects of the present invention can be recombinantly produced. For example, a modified or unmodified C. jejuni pgl gene cluster encoding the enzymes that carry out the biosynthesis of the GlcGalNac₅Bac heptasaccharide and other glycan structures can be isolated and transferred to a suitable host cell for production of a lipid-linked glycan (see also Wacker et al., “N-Linked Glycosylation in Campylobacter jejuni and its Functional Transfer into E. coli,” Science 298(5599): 1790-93 (2002), which is hereby incorporated by reference in its entirety). Pgl gene clusters from other Campylobacter species, e.g., C. coli, C. lari, and C. upsaliensis, are also suitable for recombinant production of glycans for use in all aspects of the present invention (Szymanski and Wren, “Protein Glycosylation in Bacterial Mucosal Pathogens,” Nature Microbiol. 3:225-237 (2005), which is hereby incorporated by reference in its entirety). Additionally, similar Pgl-like glycosylation gene loci have been identified in Wolinella succinogens, Desulfovibrio desulfuricans, and D. vulgaris that are also suitable for recombinant production of glycans for the present invention (Baar et al., “Complete Genome Sequence and Analysis of Wolinella succinogenes,” Proc. Natl. Acad. Sci. USA 100: 11690-11695 (2003) and Szymanski and Wren, “Protein Glycosylation in Bacterial Mucosal Pathogens,” Nature Microbiol. 3:225-237 (2005), which are hereby incorporated by reference in their entirety).
• The Pgl gene cluster may be modified to enhance lipid-linked glycan production, accumulation, and isolation in the host cell. For example, inactivation of the oligosaccharyltransferase component of the gene cluster (e.g., the pglB gene in the pgl gene cluster) is desirable to prevent transfer of the lipid-linked glycan to a glycoprotein target of the host cell. Additionally, in some embodiments of the present invention, it may be desirable to attenuate, disrupt, or delete competing glycan biosynthesis reactions of the host cell. In particular, inactivation of host cell glycosyltransferase enzymes (N-linked or O-linked reaction enzymes) or other enzymes involved in the transfer or ligation of a glycan to acceptor moieties of the host cell may also be desirable. For instance, when E. coli is utilized as the host cell, deletion of the WaaL enzyme which transfers glycans from the undecaprenyl lipid carrier onto lipid A, which in turn shuttles the oligosaccharides to the outer leaflet of the outer membrane, will ensure that the recombinantly produced lipid-linked glycans accumulate in the inner membrane. Other E. coli host cell glycosylation related enzymes that may be deleted, disrupted, or modified include, without limitation, wecA, wbbL, glcT, glf, gafT, wzx, wzy, and enzymes of the O16 antigen biosynthesis pathway.
• In another embodiment of the present invention, the glycan is a eukaryotic glycan, i.e., a glycan produced by one or more eukaryotic glycosyltransferases. In one embodiment, of the present invention, a eukaryotic glycan is produced by only eukaryotic glycosyltransferases. In another embodiment of the present invention, the eukaryotic glycan is produced using a combination of both eukaryotic and prokaryotic glycosyltransferase enzymes, but mimics eukaryotic glycan structure. In another embodiment of the present invention, the eukaryotic glycan is synthetically produced (Seeberger et al., Chemical and Enzymatic Synthesis of Glycans and Glycoconjugates, in ESSENTIALS OF GLYCOBIOLOGY (A. Varki et al. eds., 2009), which is hereby incorporated by reference in its entirety).
• In one embodiment, the eukaryotic glycan comprises a GlcNAc₂ core. The GlcNac₂ core may further comprise at least one mannose residue. Suitable eukaryotic glycan structures may comprise, but are not limited to, Man₁GlcNAc₂, Man₂GlcNAc₂, and Man₃GlcNAc₂.
• As described above, the eukaryotic lipid-linked glycan can be recombinantly produced by introducing one or more eukaryotic glycosyltransferase enzymes in a suitable host cell. A eukaryotic glycosyltransferase as used herein refers to an enzyme that catalyzes the transfer of a sugar reside from a donor substrate, e.g., from an activated nucleotide sugar, to an acceptor substrate, e.g., a growing lipid-linked oligosaccharide chain. Suitable glycosyltransferase enzyme that can be utilized in host cells to facilitate the recombinant production of a eukaryotic lipid-linked glycan of the system include, without limitation, galactosyltransferases (e.g., β1,4-galactosyltransferase, β1,3-galactosyltransferase), fucosyltransferases, glucosyltransferases, N-acetylgalactosaminyltransferases (e.g., GalNAcT, GalNAc-T1, GalNAc-T2, GalNAc-T3), N-acetylglucosaminyltransferases (e.g., β-1,2-N-acetylglucosaminyltransferase I (GnTI-), GnT-II, GnT-III, GnT-IV, GnT-V, GnT-VI, and GvT-IVH), glucuronyltransferases, sialyltransferases (e.g., α(2,3)sialyltransferase, α-N-acetylgalactosaminide α-2,6-sialyltransferase I, Galβ1,3GalNAc α2,3-sialyltransferase, β galactoside-α-2,6-sialyltransferase, and α2,8-sialyltransferase), mannosyltransferases (e.g., α-1,6-mannosyltransferase, α-1,3-mannosyltransferase, β-1,4-mannosyltransferase), glucuronic acid transferases, galacturonic acid transferases, and the like. The aforementioned glycosyltransferase enzymes have been extensively studied in a variety of eukaryotic systems. Accordingly, the nucleic acid and amino acid sequences of these enzymes are known and readily available to one of skill in the art. Additionally, many of these enzymes are commercially available (e.g., Sigma-Aldrich, St. Louis, Mo.).
• Suitable host cells for the production of a prokaryotic or eukaryotic lipid-linked glycan include both prokaryotic host cells and eukaryotic cells. An exemplary list of suitable host cells is provided supra. When utilizing eukaryotic glycosyltransferases in prokaryotic host cells, the nucleotide sequences of the eukaryotic glycosyltransferases can be codon optimized to overcome limitations associated with the codon usage bias between E. coli (and other bacteria) and higher organisms, such as yeast and mammalian cells. Codon usage bias refers to differences among organisms in the frequency of occurrence of codons in protein-coding DNA sequences (genes). A codon is a series of three nucleotides (triplets) that encodes a specific amino acid residue in a polypeptide chain. Codon optimization can be achieved by making specific transversion nucleotide changes, i.e. a purine to pyrimidine or pyrimidine to purine nucleotide change, or transition nucleotide change, i.e. a purine to purine or pyrimidine to pyrimidine nucleotide change.
• In accordance with this and all aspects of the present invention, a “glycoprotein target” includes any peptide, polypeptide, or protein that comprise one or more glycan acceptor amino acid residues. Typically glycan acceptor residues comprise an asparagine (N or Asn) to form an N-linked glycoprotein, or hydroxyl oxygen on the side chain of hydroxylysine, hydroxyproline, serine, threonine, or tyrosine to form an O-linked glycoprotein. A wide variety of glycoprotein targets exist including, without limitation, structural molecules (e.g., collagens), lubricant and protective agents (e.g., mucins), transport proteins (e.g., transferrin), immunological proteins (immunoglobulins, histocompatibility antigens), hormones, enzymes, cell attachment recognition sites, receptors, protein folding chaperones, developmentally regulated proteins, and proteins involved in hemostasis and thrombosis. Therapeutic proteins, such as antibodies are important glycoprotein targets of the system of the present invention.
• According to this and all aspect of the present invention, the one or more oligosaccharide acceptor residues of the glycoprotein target may be an asparagine (N or Asn) residue. The asparagine residue is positioned within a glycosylation consensus sequence comprising N-X₁-S/T (eukaryotic consensus sequence) or D/E-X₁-N-X₂-S/T (SEQ ID NO: 1) (prokaryotic consensus sequence) where D is aspartic acid, X₁ and X₂ are any amino acid other than proline, N is asparagine, and T is threonine.
• The glycoprotein target according to this and all aspects of the present invention can be a purified protein, peptide, or polypeptide comprising the requisite glycan acceptor residues. Alternatively, the glycoprotein target can be in the form of an isolated nucleic acid molecule encoding the glycoprotein target. In accordance with this embodiment of the present invention, the system further includes reagents suitable for synthesizing the glycoprotein target from said nucleic acid molecule, i.e., translation reagents.
• Reagents for synthesizing proteins from nucleic acid molecules in vitro (i.e., in a cell-free environment) are well known in the art. These reagents or systems typically consist of extracts from rabbit reticulocytes, wheat germ, and E. coli. The extracts contain all the macromolecule components necessary for translation of an exogenous RNA molecule, including, for example, ribosomes, tRNAs, aminoacyl-tRNA synthetases, initiation, elongation, and termination factors. The other required components of the system include amino acids, energy sources (e.g., ATP, GTP), energy regenerating systems (creatine phosphate and creatine phosphokinase for eukaryote systems, and phosphoenol pyruvate and pyruvate kinase for prokaryote systems), and other cofactors (e.g., Mg²⁺, K⁺, etc.). If the nucleic acid molecule encoding the glycoprotein target is a DNA molecule, the cell-free translation reaction is coupled or linked to an initial transcription reaction that utilizes a RNA polymerase.
• Another aspect of the present invention is directed to a kit comprising an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target, and one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule.
• In accordance with this aspect of the present invention, the isolated oligosaccharyltransferase of the kit may be a purified protein or may be in the form of a nucleic acid encoding the oligosaccharyltransferase. The nucleic acid molecule can be a DNA or RNA molecule, and it can be linearized (naked) or circularized (housed in an expression vector). Exemplary prokaryotic, archaea, and eukaryotic oligosaccharyltransferases are described supra.
• As described supra, the one or more glycans are linked to a lipid carrier molecule (e.g., an undecaprenol-pyrophosphate, an undecaprenyl pyrophosphate-linked bacillosamine, or a dolichylpyrophosphate). The glycan may comprise a prokaryotic, archaea, eukaryotic, or completely unnatural synthetic glycan as also described supra. Suitable prokaryotic core glycan structures comprise a heptasaccharide containing glucose, N-acetylgalactosamine, and optionally bacillosamine (e.g., GlcGalNAc₅Bac). Suitable eukaryotic glycan core structures comprises N-acetylglucosamine and mannose (e.g., Man₁GlcNAc₂, Man₂GlcNAc₂, and Man₃GlcNAc₂).
• In one embodiment of this aspect of the present invention, the one or more isolated glycans linked to a lipid carrier molecule of the kit are in an assembled and purified form. Alternatively, the kit of the present invention comprises one or more nucleic acid molecules encoding one or more eukaryotic and/or prokaryotic glycosyltransferase enzymes, and host cells (eukaryotic or prokaryotic) that contain a polyisoprenyl pyrophosphate glycan carrier and are capable of expressing the one or more nucleic acid molecules. In accordance with this embodiment, the kit may further contain instructions for recombinantly producing and isolating the lipid-linked glycan in the host cells prior to use with the other kit components.
• The kit of the present invention may further include in vitro or cell-free transcription and/or translation reagents for synthesizing the oligosaccharyltransferase and/or a glycoprotein, peptide or polypeptide of choice.
• Another aspect of the present invention relates to a method for producing a glycosylated protein in a cell-free system. This method involves providing an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target, providing one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule, and providing a glycoprotein target comprising one or more glycan acceptor amino acid residues. This method further involves combining the oligosaccharyltransferase, one or more isolated glycans, and glycoprotein target to form a cell-free glycosylation reaction mixture, and subjecting the cell-free glycosylation reaction mixture to conditions effective for the oligosaccharyltransferase to transfer the glycan from the lipid carrier molecule to the one or more glycan acceptor residues of the glycoprotein target to produce a glycosylated protein.
• The components of the method of the present invention. i.e., the oligosaccharyltransferase, isolated glycans linked to a lipid carrier molecule, and glycoprotein target are described in detail supra.
• The method of the present invention may comprise one or more additional steps. For example, glycoprotein target translation may be coupled with glycosylation by providing reagents suitable for synthesizing a glycoprotein target from a nucleic acid molecule. In this embodiment of the present invention, the nucleic acid molecule encoding the glycoprotein target, the translation reagents, oligosaccharyltransferase, isolated glycans are all combined to form a translation-glycosylation reaction mixture. The glycoprotein target is then synthesized from the target nucleic acid molecule prior to or concurrent with the glycosylation reaction.
EXAMPLES Materials and Methods for Examples 1-4
• Protein purification. For the purification of CjPglB, E. coli strain C43(DE3) (Lucigen, Middleton, Wis.) was freshly transformed with plasmid pSN18 (Kowarik et al., “N-Linked Glycosylation of Folded Proteins by the Bacterial Oligosaccharyltransferase,” Science 314:1148-1150 (2006), which is hereby incorporated by reference in its entirety), a modified pBAD expression plasmid encoding C. jejuni pglB with a C-terminal decahistidine affinity tag. Cells were grown in 1.5 L of terrific Broth supplemented with 100 μg/mL of ampicillin at 37° C. When the optical density (A600) of the culture reached ˜1.0, cells were induced by the addition of 0.02% arabinose (w/v) for 4.5 h at 30° C. All following steps were performed at 4° C. unless specified differently. Cells were harvested by centrifugation, resuspended in 25 mM Tris, pH 8.0, and 250 mM NaCl and lysed by three passages through a French press (SLM-Aminco; 10,000 PSI, SLM Instruments, Inc., Urbana, Ill.). Following the removal of cell debris by centrifugation, the membrane fraction was isolated by ultracentrifugation at 100,000×g for 1 h. Membranes containing PglB were resuspended in 25 mM Tris-HCl, pH 8.0, 250 mM NaCl. 10% glycerol (v/v) and 1% DDM (w/v) (DDM, Anatrace, Affymetrix, Inc., Santa Clara, Calif.) and incubated for 2 h. The insoluble fraction was removed by ultracentrifugation at 100,000×g for 1 h. All subsequent buffers contained DDM as the detergent. The solubilized membranes were supplemented with 10 mM imidazole, loaded onto a Ni-NTA superflow affinity column (Qiagen, Valencia, Calif.) and washed with 60 mM imidazole before PglB was eluted with 200 mM imidazole. The purified protein was then injected onto a SUPERDEX® 200 gel filtration column using AKTA-FPLC (GE Healthcare, Waukesha, Wis.). Eluate fractions were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and stained with Coomassie blue to identify the fractions containing PglB (FIG. 2). The protein was desalted with a PD10 desalting column (GE Healthcare) into 20 mM Tris, pH 7.5, 100 mM NaCl, 5% glycerol (w/v) and 0.05% DDM (w/v) and concentrated to 5-10 mg/mL in an Amicon centricon with a molecular mass cutoff of 100 kDa. Expression and purification of the inactive CjPglB mutant was performed identically except C43(DE3) cells carrying plasmid pSN18.1, which encodes an inactive copy of pglB subcloned from pACYCpglmut (see below) were used. ClPglB was purified from BL2-Gold(DE3) cells (Stratagene, La Jolla, Calif.) carrying plasmid pSF2 as described elsewhere (Lizak et al., “X-ray Structure of a Bacterial Oligosaccharyltransferase,” Nature 474:350-355 (2011), which is hereby incorporated by reference in its entirety). For long-term storage at −20° C., the glycerol content in PglB samples was increased to 10% (w/v). Purification of AcrA and scFv13-R4-GT was from periplasmic fractions isolated from BL21(DE3) cells carrying plasmid pET24(AcrA-per) (Nita-Lazar et al., “The N-X-S/T Consensus Sequence is Required but not Sufficient for Bacterial N-Linked Protein Glycosylation,” Glycobiology 15:361-367 (2005), which is hereby incorporated by reference in its entirety) or pET24-ssDsbAscFv13-R4-GT (see below). Periplasmic extracts were prepared as described previously (Schwarz et al., “Relaxed Acceptor Site Specificity of Bacterial Oligosaccharyltransferase in Vivo,” Glycobiology 21:45-54 (2011), which is hereby incorporated by reference in its entirety), supplemented with imidazole to reach a final concentration of 10 mM, sterile filtered (0.22 μm), and purified by nickel affinity chromatography using Ni-NTA superflow affinity column (Qiagen, Valencia, Calif.).
• Isolation of Lipid-linked Glycans. Escherichia coli SCM6 cells transformed with pACYCpglmut (Wacker et al., “N-Linked Glycosylation in Campylobacter jejuni and its Functional Transfer Into E. coli,” Science 298:1790-1793 (2002), which is hereby incorporated by reference in its entirety), which codes for the biosynthesis of the C. jejuni LLO and an inactivated C. jejuni pglB gene (W458A and D459A), were grown in 1 L of Luria-Burtani supplemented with 25 μg/mL of chloramphenicol at 37° C. When the A600 reached−1.0, cells were harvested by centrifugation and the pellet was lyophilized to dryness for 20 h at −80° C. and 0.04 mbar. All subsequent steps were performed using glass tubes and glass pipettes. Homogenized pellets were extracted in 25 mL of 10:20:3 CHCl₃:MeOH:H₂O followed by centrifugation at 3000×g for 30 min. The supernatants were evaporated using a rotary evaporator (Büchi, Flawil, Sankt Gallen, Switzerland), after which the resulting pellet was resuspended in 1 mL of 10:20:3 CHCl₃:MeOH:H₂O and sonicated until homogenous. The sample was dried under nitrogen gas at 37° C., dissolved in 10 mM HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid), pH 7.5, 1 mM MnCl2 and 0.1% DDM (w/v) and stored at −20° C. An identical procedure was followed to extract lipids from SCM6 cells carrying empty pACYC.
• Cell-Free Translation and Glycosylation. For in vitro glycosylation of purified acceptor proteins, a 50 μL solution containing 3 μg of purified PglB, 5-10 μL of extracted LLOs and 5 μg of purified AcrA or scFv13-R4-GT in 10 mM HEPES, pH 7.5, 1 mM MnCl₂ and 0.1% DDM (w/v) was incubated for 12 h at 30° C. For in vitro translation of AcrA and scFv13-R4-GT in the absence of glycosylation, a 50 μL reaction was prepared using the S30 T7 High-Yield Expression System (Promega, Fitchburg, Wis.) or PUREXPRESS® (New England Biolabs, Ipswich, Mass.) according to the manufacturer's instructions. A total of 1 μg of the following plasmids were added to each reaction: pET24b (Novagen, Madison, Wis.); pET24-AcrA encoding full-length C. jejuni AcrA with a C-terminal hexahistidine tag (Nita-Lazar et al., “The N-X-S/T Consensus Sequence is Required but not Sufficient for Bacterial N-Linked Protein Glycosylation,” Glycobiology 15:361-367 (2005), which is hereby incorporated by reference in its entirety); pET24(AcrA-per) encoding a version of AcrA with an N-terminal PelB signal peptide in place of its native export signal (Nita-Lazar et al., “The N-X-S/T Consensus Sequence is Required but not Sufficient for Bacterial N-Linked Protein Glycosylation,” Glycobiology 15:361-367 (2005), which is hereby incorporated by reference in its entirety); pET24(AcrA-cyt) encoding a version of AcrA without an N-terminal export signal (ΔssAcrA) (Nita-Lazar et al., “The N-X-S/T Consensus Sequence is Required but not Sufficient for Bacterial N-Linked Protein Glycosylation,” Glycobiology 15:361-367 (2005), which is hereby incorporated by reference in its entirety), and pET24-ssDsbA-scFv13-R4-GT encoding the expression-optimized scFv13-R4 intrabody gene (Martineau et al., “Expression of an Antibody Fragment at High Levels in the Bacterial Cytoplasm,” J. Mol. Biol. 280:117-127 (1998), which is hereby incorporated by reference in its entirety) with an N-terminal signal peptide from E. coli DsbA for secretion and a C-terminal GT (Fisher et al., “Production of Secretory and Extracellular N-Linked Glycoproteins in Escherichia coli,” Appl. Environ. Microbiol. 77:871-881 (2011), which is hereby incorporated by reference in its entirety) followed by a FLAG and a hexahistidine epitope tag. For in vitro translation/glycosylation reactions, 50 μL of translation reactions was supplemented with 3 μg purified PglB, 5 μL extracted LLOs, 1 μg purified plasmid DNA, 1 mM MnCl₂ and 0.1% DDM (w/v) and incubated for 12 h at 30° C. DDM was chosen for in vitro translation/glycosylation because it was previously observed to be well tolerated in an E. coli-derived CFE system (Klammt et al., “Evaluation of Detergents for the Soluble Expression of Alpha-Helical and Beta-Barrel-Type Integral Membrane Proteins by a Preparative Scale Individual Cell-Free Expression System,” Febs J. 272:6024-6038 (2005), which is hereby incorporated by reference in its entirety).
• Western blot analysis. Expression and glycosylation of AcrA and scFv13-R4-GT was analyzed by immunoblot following SDS-PAGE. Immunodetection was performed with monoclonal anti-His antibody (Qiagen, Valencia, Calif.), monoclonal anti-FLAG antibody (Abcam, Cambridge, Mass.), polyclonal anti-AcrA serum (Wacker et al., “N-Linked Glycosylation in Campylobacter jejuni and its Functional Transfer Into E. coli,” Science 298:1790-1793 (2002), which is hereby incorporated by reference in its entirety) and polyclonal anti-glycan serum hR6. All in vitro translation samples were treated with RNase A (Roche Diagnostics GmbH, Mannheim, Germany) prior to SDS-PAGE to reduce the irregularity of gel electrophoresis due to excess RNA. All experiments were performed at least in triplicate, and representative samples are shown.
Example 1—Preparation of N-linked Glycosylation Components
• To begin, functional reconstitution of bacterial N-linked glycosylation in vitro was attempted. Minimally, this required three components: an OST, a lipid-linked oligosaccharide (LLO) (i.e., a lipid-linked glycan) and an acceptor protein carrying the D/E-X₁-N-X₂-S/T motif. For the OST, CjPglB was expressed in the membrane fraction of E. coli cells, solubilized with 1% N-dodecyl-β-D-maltopyranoside (DDM) and purified to near homogeneity by nickel affinity chromatography followed by gel filtration (FIG. 2B). Separately, E. coli cells carrying the C. jejuni pgl locus were used for producing the oligosaccharide donor. This gene cluster encodes enzymes that carry out the biosynthesis of a GlcGalNAc5Bac heptasaccharide (where Bac is bacillosamine) and its transfer from membrane-anchored undecaprenylpyrophosphate (UndPP) to asparagine residues. Here, a modified version of this cluster that carried an inactivated pglB gene (Wacker et al., “N-Linked Glycosylation in Campylobacter jejuni and its Functional Transfer Into E. coli,” Science 298:1790-1793 (2002), which is hereby incorporated by reference in its entirety) was transferred to E. coli SCM6 cells and used to prepare LLOs. SCM6 cells were chosen for several reasons. First, these cells lack the WaaL enzyme that naturally transfers oligosaccharides (e.g. O-antigens, glycans) from the lipid carrier undecaprenyl onto lipid A, which in turn shuttles the oligosaccharides to the outer leaflet of the outer membrane (Feldman et al., “Engineering N-Linked Protein Glycosylation With Diverse O Antigen Lipopolysaccharide Structures in Escherichia coli,” Proc. Nat'l. Acad. Sci. U.S.A. 102:3016-3021 (2005), which is hereby incorporated by reference in its entirety). Thus, in the absence of WaaL, the desired lipid-linked glycans accumulate in the inner membrane. Second, the lipopolysaccharide and enterobacterial common antigen initiating GlcNAc transferase, WecA, is removed. Thus, this strain should only produce LLOs with GlcGalNAc5Bac at the reducing end. In support of this notion, previous mass spectrometry analysis of LLOs extracted from an E. coli strain similar to the one used here (i.e. ΔwaaL ΔwecA) revealed that only LLOs containing GlcGalNAc5Bac heptasaccharide were detected (Reid et al., “Affinity-Capture Tandem Mass Spectrometric Characterization of Polyprenyl-Linked Oligosaccharides: Tool to Study Protein N-Glycosylation Pathways,” Anal. Chem. 80:5468-5475 (2008), which is
Example 1—Preparation of N-linked Glycosylation Components
• To begin, functional reconstitution of bacterial N-linked glycosylation in vitro was attempted. Minimally, this required three components: an OST, a lipid-linked oligosaccharide (LLO) (i.e., a lipid-linked glycan) and an acceptor protein carrying the D/E-X₁-N-X₂-S/T motif. For the OST. CjPglB was expressed in the membrane fraction of E. coli cells, solubilized with 1% N-dodecyl-s-D-maltopyranoside (DDM) and purified to near homogeneity by nickel affinity chromatography followed by gel filtration (FIG. 2B). Separately, E. coli cells carrying the C. jejuni pgl locus were used for producing the oligosaccharide donor. This gene cluster encodes enzymes that carry out the biosynthesis of a GlcGalNAc5Bac heptasaccharide (where Bac is bacillosamine) and its transfer from membrane-anchored undecaprenylpyrophosphate (UndPP) to asparagine residues. Here, a modified version of this cluster that carried an inactivated pglB gene (Wacker et al., “N-Linked Glycosylation in Campylobacter jejuni and its Functional Transfer Into E. coli,” Science 298:1790-1793 (2002), which is hereby incorporated by reference in its entirety) was transferred to E. coli SCM6 cells and used to prepare LLOs. SCM6 cells were chosen for several reasons. First, these cells lack the WaaL enzyme that naturally transfers oligosaccharides (e.g. O-antigens, glycans) from the lipid carrier undecaprenyl onto lipid A, which in turn shuttles the oligosaccharides to the outer leaflet of the outer membrane (Feldman et al., “Engineering N-Linked Protein Glycosylation With Diverse O Antigen Lipopolysaccharide Structures in Escherichia coli,” Proc. Nat'l. Acad. Sci. U.S.A. 102:3016-3021 (2005), which is hereby incorporated by reference in its entirety). Thus, in the absence of WaaL, the desired lipid-linked glycans accumulate in the inner membrane. Second, the lipopolysaccharide and enterobacterial common antigen initiating GlcNAc transferase, WecA, is removed. Thus, this strain should only produce LLOs with GlcGalNAc5Bac at the reducing end. In support of this notion, previous mass spectrometry analysis of LLOs extracted from an E. coli strain similar to the one used here (i.e. ΔwaaL ΔwecA) revealed that only LLOs containing GlcGalNAc5Bac heptasaccharide were detected (Reid et al., “Affinity-Capture Tandem Mass Spectrometric Characterization of Polyprenyl-Linked Oligosaccharides: Tool to Study Protein N-Glycosylation Pathways,” Anal. Chem. 80:5468-5475 (2008), which is hereby incorporated by reference in its entirety). For the oligosaccharide acceptor, the model glycoprotein AcrA from C. jejuni (Nita-Lazar et al., “The N-X-S/T Consensus Sequence is Required but not Sufficient for Bacterial N-Linked Protein Glycosylation,” Glycobiology 15:361-367 (2005), which is hereby incorporated by reference in its entirety) was purified from the periplasm. AcrA presents two consensus D/E-X₁-N-X₂-S/T sites that are glycosylated by CjPglB (Kowarik et al., “Definition of the Bacterial N-Glycosylation Site Consensus Sequence,” EMBO J. 25:1957-1966 (2006), which is hereby incorporated by reference in its entirety). Alternatively, a glycoengineered single-chain variable fragment (scFv) called scFv13-R4-GT, which carried a C-terminal glycosylation tag (GT) consisting of four consecutive DQNAT motifs separated from one another by consecutive glycine residues (Fisher et al., “Production of Secretory and Extracellular N-Linked Glycoproteins in Escherichia coli,” App. Environ. Microbiol. 77:871-881 (2011), which is hereby incorporated by reference in its entirety), was similarly purified.
Example 2—Functional Reconstitution In Vitro of the C. jejuni Protein Glycosylation Pathway
• To evaluate the reconstituted glycosylation pathway, CjPgIB OST was combined with LLOs extracted from E. coli cells and purified AcrA. This reaction resulted in efficient glycosylation of both AcrA sites as evidenced by the mobility shift of nearly all of the AcrA from the unmodified (g0) to the fully glycosylated (g2) form (FIG. 3A). This activity was dependent on PglB and LLOs. Doubling the LLO concentration resulted in the appearance of the g0 and g1 forms of AcrA, in addition to g2, suggesting slightly less efficient glycosylation. Importantly, glycosylation activity was lost when lipid extracts from cells lacking the pgl cluster or an inactive CjPglB mutant was used (FIG. 3A). These results were corroborated by detecting glycosylated AcrA with serum specific for the C. jejuni N-glycan (FIG. 3A). Nearly identical results were observed when the glycoengineered scFv13-R4-GT protein was used as the oligosaccharide acceptor (FIG. 3A). It should be noted that g2, g3 and g4 were the predominant glycoforms detected here, with barely detectable levels of g1. To demonstrate that other OSTs could be used in this system, in vitro glycosylation of AcrA was also performed using Campylobacter lari PglB (ClPglB), which is 56% identical to that of C. jejuni (Schwarz et al., “Relaxed Acceptor Site Specificity of Bacterial Oligosaccharyltransferase in Vivo,” Glycobiology 21:45-54 (2011), which is hereby incorporated by reference in its entirety). This resulted in nearly equal amounts of the g0, g1 and g2 forms of AcrA under the conditions tested (FIG. 3B). To be useful for translation/glycosylation reactions, the purified glycosylation components must tolerate long-term storage and freeze-thaw cycles. To test this, the components were stored separately at −20° C. for 3 months. No changes were made to the storage buffers except that the final concentration of glycerol in the PglB samples was increased to 10%. Each of the components was thawed and refrozen 5-10 times during this period, after which an in vitro reaction with ClPglB was performed. This reaction yielded the glycosylation of AcrA that appeared to be only slightly less efficient than the glycosylation observed with freshly purified components (compare FIGS. 3B and 3C).
Example 3—Cell-Free Translation of Protein Targets
• To determine whether existing cell-free translation systems could synthesize protein targets of interest, both an E. coli CFE-based protein synthesis system and the PURE (protein synthesis using recombinant elements) system that uses purified translation components and T7 RNA polymerase (Shimizu et al., “Cell-Free Translation Reconstituted With Purified Components,” Nat. Biotechnol. 19:751-755 (2001), which is hereby incorporated by reference in its entirety) were evaluated. This involved priming the CFE and PURE systems with three different AcrA DNA sequences cloned in a T7 promoter-driven pET vector. Using the CFE system, ˜150-250 μg/mL of each AcrA variant was produced as a full-length polypeptide in 1 h (FIG. 4A). AcrA carrying its native signal peptide accumulated to the highest level but also experienced the greatest amount of degradation. In contrast, AcrA carrying a PelB signal peptide in place of the native signal and AcrA lacking a signal peptide each accumulated to a slightly lower concentration but experienced no visible degradation. The PURE system similarly produced all three AcrA variants as full-length polypeptides albeit at a slightly lower level (˜100 μg/mL/h of each) than the CFE-based system (FIG. 4A). Both systems were also able to generate appreciable amounts of scFv13-R4-GT (FIG. 5A). It should be noted that this scFv was previously optimized for expression under nonoxidizing conditions (i.e., in the absence of disulfide bonds) (Martineau et al., “Expression of an Antibody Fragment at High Levels in the Bacterial Cytoplasm,” J. Mol. Biol. 280:117-127 (1998), which is hereby incorporated by reference in its entirety) and thus did not require special transcription/translation conditions.
Example 4—Cell-Free Translation and Glycosylation of Target Glycoproteins
• Encouraged by these results, the glycoCFE and glycoPURE translation/glycosylation systems were constructed by combining the purified glycosylation components (minus the acceptor protein) with one of the ccll-free translation systems. The plasmid pET24(AcrA-cyt) that encodes AcrA without an N-terminal signal peptide was chosen to evaluate these systems because it gave rise to significant amounts of target protein in both translation systems with no detectable degradation. When either the CFE or the PURE system were primed with this plasmid along with CjPglB and LLOs, AcrA was produced primarily as the doubly glycosylated g2 glycoform with lesser amounts of g1 and virtually no detectable unmodified AcrA (FIG. 4B). It was estimated that ˜100-150 μg of glycosylated AcrA was produced in a 1 mL reaction volume after 12 h. Likewise, scFv13-R4-GT was efficiently produced by both the glycoCFE and glycoPURE systems, with ˜50% of the protein in the fully glycosylated g4 form and 50% in the g3 form (FIG. 5B). Both systems produced ˜50-100 μg/mL of glycosylated scFv13-R4-GT in 12 h. Thus, the glycoCFE and glycoPURE systems contain all the components essential for efficiently translating N-linked glycoproteins.
Discussion of Examples 1-4
• A major advantage of the open prokaryote-based translation/glycosylation systems developed here is that the supply of purified glycosylation components as well as their substrates and cofactors (Lizak et al., “X-ray Structure of a Bacterial Oligosaccharyltransferase,” Nature 474:350-355 (2011), which is hereby incorporated by reference in its entirety) can be provided at precise ratios. Likewise, the concentration of inhibitory substances such as proteases and glycosidases that catalyze the hydrolysis of glycosidic linkages can be reduced or eliminated entirely. Additionally, the in vitro systems permit the introduction of components that may be incompatible with in vivo systems such as certain LLOs that cannot be produced or flipped in vivo. This level of controllability is unavailable in any previous translation/glycosylation system and is significant for several reasons. First, it helps to avoid glycoprotein heterogeneity, which is particularly bothersome in fundamental studies to assess the contribution of specific glycan structures or in pharmaceutical glycoprotein production. Along these lines, the glycoCFE and glycoPURE systems should allow the examination of factors that interact with or stimulate the glycosylation machinery and promote increased acceptor site occupancy. While the glycosylation efficiency observed here with CjPglB exceeded the level typically observed in vivo (Kowarik et al., “N-Linked Glycosylation of Folded Proteins by the Bacterial Oligosaccharyltransferase,” Science 314:1148-1150 (2006); Kowarik et al., “Definition of the Bacterial N-Glycosylation Site Consensus Sequence,” EMBO J. 25:1957-1966 (2006); Fisher et al., “Production of Secretory and Extracellular N-Linked Glycoproteins in Escherichia coli,” Appl. Environ. Microbiol. 77:871-881 (2011), which are hereby incorporated by reference in their entirety), it should be pointed out that further study of the reaction conditions should lead to increases in productivity and glycosylation efficiency. Second, it facilitates the integration/co-activation of multiple complex metabolic systems and pathways in vitro including transcription, translation, protein folding and glycosylation. Therefore, the glycoCFE and glycoPURE systems should provide a unique opportunity for studying the interplay of these important mechanisms under conditions where system complexity is reduced and structural barriers are removed. For instance, since the bacterial OST can glycosylate locally flexible structures in folded proteins (Kowarik et al., “N-Linked Glycosylation of Folded Proteins by the Bacterial Oligosaccharyltransferase,” Science 314:1148-1150 (2006), which is hereby incorporated by reference in its entirety) and also structured domains of some proteins, these systems should help to decipher the influence of protein structure on glycosylation efficiency. Also, since bacterial and eukaryotic glycosylation mechanisms display significant similarities, these bacterial systems could provide a simplified model framework for understanding the more complex eukaryotic process. Third, it allows for further customization of the system by reconstituting additional or alternative steps (both natural and unnatural) in the glycosylation pathway. For instance, the sequential activities of the glycosyltransferases in the pgl pathway have been reconstituted in vitro (Glover et al., “In Vitro Assembly of the Undecaprenylpyrophosphate-Linked Heptasaccharide for Prokaryotic N-Linked Glycosylation.” Proc. Nat'l. Acad. Sci. U.S.A. 102:14255-14259 (2005), which is hereby incorporated by reference in its entirety) and could easily be integrated with the translation/glycosylation reactions into a single integrated platform. While glycoengineered E. coli have the potential to provide a wide array of UndPP-linked glycans (Feldman et al., “Engineering N-Linked Protein Glycosylation With Diverse O Antigen Lipopolysaccharide Structures in Escherichia coli,” Proc. Nat'l. Acad. Sci. U.S.A. 102:3016-3021 (2005); Yavuz et al., “Glycomimicry: Display of Fucosylation on the Lipo-Oligosaccharide of Recombinant Escherichia coli K12.” Glycoconj. J. 28:39-47 (2011), which are hereby incorporated by reference in their entirety), the ability to extend beyond bacterial glycans can be achieved by supplementation with specific glycosyltransferases and the requisite activated sugars. This approach can be used for making eukaryotic glycan mimetics (Schwarz et al., “A Combined Method for Producing Homogeneous Glycoproteins With Eukaryotic N-Glycosylation,” Nat. Chem. Biol. 6:264-266 (2010), which is hereby incorporated by reference in its entirety) and will allow finer control over the diversity of glycoforms that can be used for modifying target proteins in vitro. Since CjPglB has relaxed specificity toward the glycan structure (Feldman et al., “Engineering N-Linked Protein Glycosylation With Diverse O Antigen Lipopolysaccharide Structures in Escherichia coli,” Proc. Nat'l. Acad. Sci. U.S.A. 102:3016-3021 (2005), which is hereby incorporated by reference in its entirety), all of these UndPP-linked glycans are likely to be suitable substrates. Even if CjPglB should prove insufficient, the demonstration here that two different OSTs could be used interchangeably suggests that virtually any single-subunit OST including those from other bacteria, archaea and even some eukaryotes (Nasab et al., “All in One: Leishmania Major STT3 Proteins Substitute for the Whole Oligosaccharyltransferase Complex in Saccharomyces cerevisiae,” Mol. Biol. Cell 19:3758-3768 (2008), which is hereby incorporated by reference in its entirety) could be used in these systems. In support of this notion, the Leishmania major and Pyrococcus furiosus single-subunit OSTs can be functionally expressed in E. coli membranes (Igura & Kohda, “Selective Control of Oligosaccharide Transfer Efficiency for the N-Glycosylation Sequon by a Point Mutation in Oligosaccharyltransferase,” J. Biol. Chem. 286:13255-13260 (2011), which is hereby incorporated by reference in its entirety). Finally, because one is not limited to natural glycans, the glycoCFE and glycoPURE systems should permit synthesis of hybrid natural/unnatural or even completely artificial glycans. For example, the addition of synthetic sugar-nucleotide donor substrates and/or mutant glycosyltransferases and OSTs having new specificities will enable the construction of a glycosylation system founded on a noncanonical glycan code. For all of these reasons, the glycoCFE and glycoPURE systems are useful additions to the cell-free translation and glycobiology toolkits alike.
• Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the claims which follow.

Claims (34)

What is claimed is:

1. A cell-free system for producing a glycosylated protein comprising:

an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target;

one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule; and

a glycoprotein target comprising one or more glycan acceptor amino acid residue, or a nucleic acid molecule encoding said glycoprotein target.

2. The system of claim 1, wherein the oligosaccharyltransferase is a prokaryotic oligosaccharyltransferase.

3. The system of claim 2, wherein the prokaryotic oligosaccharyltransferase is derived from Campylobacter.

4. The system of claim 1, wherein the oligosaccharyltransferase is an archaea oligosaccharyltransferase.

5. The system of claim 1, wherein the oligosaccharyltransferase is a eukaryotic oligosaccharyltransferase.

6. The system of claim 1, wherein the lipid carrier molecule comprises undecaprenyl-phosphate.

7. The system of claim 1, wherein the one or more isolated glycans comprise a prokaryotic glycan.

8. The system of claim 1, wherein the prokaryotic glycan comprises GlcGalNAc₅Bac.

9. The system of claim 1, wherein the one or more isolated glycans comprise a eukaryotic glycan.

10. The system of claim 9, wherein the eukaryotic glycan comprises GlcNAc₂.

11. The system of claim 10, wherein the eukaryotic glycan further comprises at least one mannose residue.

12. The system of claim 9, wherein the eukaryotic glycan comprises a composition selected from Man₁GlcNAc₂, Man₂GlcNAc₂, and Man₃GlcNAc₂.

13. The system of claim 1, wherein the one or more glycan acceptor amino acid residues of the glycoprotein target is an asparagine residue.

14. The system of claim 13, wherein glycoprotein target further comprising an N-X₁-S/T or a D/E-X₁-N-X₂-S/T (SEQ ID NO: 1) glycan acceptor amino acid sequence motif wherein D is aspartic acid, X₁ and X₂ are any amino acid other than proline, N is asparagine, and T is threonine.

15. The system of claim 1 further comprising:

reagents suitable for synthesizing the glycoprotein target from said nucleic acid molecule.

16. The system of claim 1, wherein the glycoprotein target comprises an antibody.

17. A kit comprising:

an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target and

one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule.

18. The kit of claim 17 further comprising:

reagents suitable for synthesizing a glycoprotein target from a nucleic acid molecule encoding said glycoprotein target.

19. A method for producing a glycosylated protein in a cell-free system comprising:

providing an isolated oligosaccharyltransferase capable of transferring a glycan from a lipid carrier molecule to a glycoprotein target;

providing one or more isolated glycans, wherein each glycan is linked to a lipid carrier molecule;

providing a glycoprotein target comprising one or more glycan acceptor amino acid residues;

combining the oligosaccharyltransferase, one or more isolated glycans and glycoprotein target to form a cell-free glycosylation reaction mixture; and

subjecting the cell-free glycosylation reaction mixture to conditions effective for the oligosaccharyltransferase to transfer the glycan from the lipid carrier molecule to the one or more glycan acceptor residues of the glycoprotein target to produce a glycosylated protein.

20. The method of claim 19, wherein the oligosaccharyltransferase is a prokaryotic oligosaccharyltransferase.

21. The method of claim 20, wherein the prokaryotic oligosaccharyltransferase is derived from Campylobacter.

22. The method of claim 19, wherein the oligosaccharyltransferase is an archaea oligosaccharyltransferase.

23. The method of claim 19, wherein the oligosaccharyltransferase is a eukaryotic oligosaccharyltransferase.

24. The method of claim 19, wherein the lipid carrier molecule comprises undecaprenyl phosphate.

25. The method of claim 19, wherein the one or more isolated glycans comprise a prokaryotic glycan.

26. The method of claim 25, wherein the one or more prokaryotic glycans comprise GlcGalNAc₅Bac.

27. The method of claim 19, wherein one or more isolated glycans comprise a eukaryotic glycan.

28. The method of claim 27, wherein the one or more eukaryotic glycans comprise GlcNAc₂.

29. The method of claim 28, wherein the one or more eukaryotic glycans further comprise at least one mannose residue.

30. The method of claim 28, wherein the one or more eukaryotic glycans comprise a composition selected from Man₁GlcNAc₂, Man₂GlcNAc₂, and Man₃GlcNAc₂.

31. The method of claim 19, wherein said providing a glycoprotein target comprises providing a nucleic acid molecule encoding the glycoprotein, said method further comprising:

providing reagents suitable for synthesizing a glycoprotein target from said nucleic acid molecule and

blending the reagents with the glycosylation reaction under conditions effective to synthesize the glycoprotein target from the nucleic acid molecule prior to, or concurrent with, said subjecting.

32. The method of claim 19, wherein the one or more glycan acceptor amino acid residues of the glycoprotein target is an asparagine residue.

33. The method of claim 32, wherein the glycoprotein target further comprising an N-X₁-S/T or a D/E-X₁-N-X₂-S/T (SEQ ID NO: 1) glycan acceptor amino acid sequence motif wherein D is aspartic acid, X₁ and X₂ are any amino acid other than proline, N is asparagine, and T is threonine.

34. The method of claim 19, wherein the protein comprises an antibody.

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