Oligosaccharide Moieties Research Articles

Nosokomycins, new antibiotics discovered in an in vivo-mimic infection model using silkworm larvae. II: Structure elucidation

The structures of nosokomycins A, B, C and D, new anti-methicillin-resistant Staphylococcus aureus antibiotics produced by Streptomyces sp. K04-0144, were elucidated by spectroscopic studies including various NMR experiments. Nosokomycins A, B, C and D are new members of the moenomycin family consisting of an oligosaccharide moiety, a 2,3-dihydroxypropionic acid and an unusual sesterterpenoid moiety. All nosokomycins lack the cyclopentenone moiety in the oligosaccharide moiety of moenomycin A.

Synthesis of the glycosylated polypeptide chain of an inducible costimulator on T-cells

The glycoprotein AILIM/ICOS (Activation inducible lymphocyte immunomediately molecule/Inducible co-stimulator) on T-cells was identified in 1998 as a member of the CD28/CTLA4 family. The three-dimensional structure of the AILIM/ICOS extracellular domain has not been solved, and therefore we have examined the preparation of homogeneous glycosylated polypeptide chains of this domain having two homogeneous N-linked complex type oligosaccharides for use in folding experiments. To synthesize the glycosylated whole polypeptide chain of the AILIM/ICOS extracellular domain, the target polypeptide chain was divided into four segments, each containing a cysteine residue. Those peptide segments were synthesized by conventional SPPS, followed by thioesterification of the C-terminus. The oligosaccharide moiety, a biantennary complex type disialyloligosaccharide, was attached to the cysteine thiol in the peptide backbone using the haloacetamide method. These peptides, as well as a glycosylated peptide, were sequentially coupled by use of native chemical ligation. This process successfully afforded the desired polypeptide chain having homogeneous oligosaccharides.

Prediction of the In‐vivo Biological Activity of Human Recombinant Follicle‐stimulating Hormone Using Quantitative Isoelectric Focusing. Optimization of the Model

Follicle-stimulating hormone (FSH) is a glycoprotein consisting of two non-covalently linked subunits, α and β. FSH exists as multiple isoforms due to the attachment of oligosaccharides. The oligosaccharide moiety of these isohormones differs in branching pattern as well as in the sialic acid (N-acetyl neuraminic acid) content. The isohormone-related inherent microheterogeneity can be easily visualized using charge-based separation methods such as isoelectric focusing (IEF). Isohormones of recombinant FSH (rFSH, follitropin-β) display largely differing and isoelectric point (pI)-dependent in-vivo bioactivity. This has formed the basis for correlation between the charge distribution as determined by IEF (amount of isohormones focusing below pI 5) and the in-vivo bioactivity. Here we show that the sialic acid content is responsible for the differences in the in-vivo bioactivity. Gradual removal of sialic acid by in-vitro neuraminidase treatment of rFSH reduces the in-vivo bioactivity and results in a more basic IEF profile. The data allowed the refinement of the IEF in-vivo bioactivity model especially for samples with low in-vivo bioactivity (less than 5000 IU mg−1). In the optimized model the average pI was found to be a better parameter than the percentage of isohormones below pI 5. The average pI model for the in-vivo bioactivity was subsequently used to predict the in-vivo bioactivity of 27 production batches. The mean difference between the experimental and predicted in-vivo bioactivity was—1% (95% confidence interval—13 to 11%). These data further substantiate the use of IEF to accurately predict in-vivo bioactivity and offers an attractive alternative for the in-vivo bioassay currently in use for the potency declaration of rFSH. Similarly, since there is a strong correlation between sialic-acid content and the in-vivo bioactivity, this parameter may also be used to determine the potency of rFSH.

Construction of an Expression System for Human α1-Acid Glycoprotein in E. coli: the Roles of Oligosaccharide Moieties in Structural and Functional Properties

Unglycosylated recombinant human alpha(1)-acid glycoprotein (hAGP) variants (rF1(*)S and rA) were prepared in an E. coli expression system using the Origami B strain and pET-3c vector. Thioredoxin was co-expressed to promote the appropriate folding of hAGP. SDS-PAGE under reducing conditions showed that rF1(*)S and rA migrate as single bands after purification. However, several bands derived from rA were observed under non-reducing conditions because of the high reactivity of a free cystein residue (C149). We therefore prepared a mutant of A variant (C149R-A), and confirmed that this mutant maintained homogeneity. Circular dichroism and intrinsic tryptophan fluorescence spectroscopic analyses indicated that rF1(*)S and C149R-A have almost the same conformational structures as F1(*)S and A purified from serum. Ligand binding experiments using propranolol as a F1(*)S ligand and disopyramide as an A specific ligand indicated that the capacity of rF1(*)S and C149R-A is equivalent to those ligands as well as F1(*)S and A from serum. These results suggest that the oligosaccharide moieties of hAGP have negligible effects on the structural and ligand binding properties of hAGP. Thus, rF1(*)S and C149R-A promise to be useful in studies on the drug binding sites of hAGP.

N- and O-linked oligosaccharides completely lack galactose residues in the gms1och1 mutant of Schizosaccharomyces pombe

Unlike their counterparts in budding yeast Saccharomyces cerevisiae, the glycoproteins of Schizosaccharomyces pombe contain, in addition to alpha-D-mannose (Man), a large number of alpha-D-galactose (Gal) residues. In both yeasts, large outer chains are attached to the oligosaccharide cores of glycoproteins during export via Golgi. Formation of the yeast-specific large outer chain is initiated by alpha-1,6-mannosylatransferase encoded by the och1+ gene, the disruption of which blocked outer chain elongation. We previously reported that N-linked oligosaccharide structures of S. pombe och1Delta mutant consisted of Gal(2-6)Man(9)GlcNAc(2) with alpha-linked Gal residues attached to the core oligosaccharide moiety. The disruption of gms1+, a gene encoding the UDP-galactose transporter required for the synthesis of galactomannan, abolished cell surface galactosylation in S. pombe. In this study, we constructed a gms1Deltaoch1Delta double mutant and determined the N- and O-linked oligosaccharide structures present on the cell surface. Oligosaccharides were liberated from glycoproteins by hydrazinolysis and labeled with the fluorophore, 2-aminopyridine. The pyridylaminated N-linked oligosaccharides were analyzed by high-performance liquid chromatography in combination with alpha1,2-mannosidase digestion and partial acetolysis. These analyses revealed that the N-linked oligosaccharides of gms1Deltaoch1Delta cells consisted of alpha1,2-linked Man-extended core oligosaccharides (Man(8-12)GlcNAc2) from which the fission yeast-specific alpha-linked Gal residues were completely absent.

Mannose binding lectin and lung collectins interact with Toll-like receptor 4 and MD-2 by different mechanisms

Background We have previously shown that lung collectins, surfactant protein A (SP-A) and surfactant protein D, interact with Toll-like receptor (TLR) 2, TLR4, or MD-2. Bindings of lung collectins to TLR2 and TLR4/MD-2 result in the alterations of signaling through these receptors, suggesting the immunomodulatory functions of lung collectins. Mannose binding lectin (MBL) is another collectin molecule which has structural homology to SP-A. The interaction between MBL and TLRs has not yet been determined. Methods We prepared recombinant MBL, and analyzed its bindings to recombinant soluble forms of TLR4 (sTLR4) and MD-2. Results MBL bound to sTLR4 and MD-2. The interactions were Ca 2+-dependent and inhibited by mannose or monoclonal antibody against the carbohydrate-recognition domain of MBL. Treatment of sTLR4 or MD-2 by peptide N-glycosidase F significantly decreased the binding of MBL. SP-A bound to deglycosylated sTLR4, and this property did not change in chimeric molecules of SP-A/MBL in which Glu 195–Phe 228 or Thr 174–Gly 194 of SP-A were replaced with the corresponding MBL sequences. General Significance These results suggested that MBL binds to TLR4 and MD-2 through the carbohydrate-recognition domain, and that oligosaccharide moieties of TLR4 and MD-2 are important for recognition by MBL. Since our previous studies indicated that lung collectins bind to the peptide portions of TLRs, MBL and lung collectins interact with TLRs by different mechanisms. These direct interactions between MBL and TLR4 or MD-2 suggest that MBL may modulate cellular responses by altering signals through TLRs.

Synthesis of Glycosyltransferase Inhibitors

Glycosyltransferases and glycosidases work together to constructthe oligosaccharide moieties of biologically active glycoconjugates.Although many excellent glycosidase inhibitors have been developed,some of which are in clinical use, there are relatively few promisingcandidates of glycosyltransferase inhibitors. In this review, wesummarize the current state of the development of glycosyltransferaseinhibitors. 1 Introduction 2 Basic Strategy for Designing Glycosyltransferase Inhibitors 3 Sugar Nucleotide Analogues 4 Analogues of Acceptor Oligosaccharides (Acceptor [nl]Analogues) 5 Bisubstrate Inhibitors 6 High-Throughput Screening: Discovering Structurally [nl]SimpleInhibitors 7 Antisense Inhibitors 8 Questions and Future Directions

Biosynthesis and Structure of the Burkholderia cenocepacia K56-2 Lipopolysaccharide Core Oligosaccharide: TRUNCATION OF THE CORE OLIGOSACCHARIDE LEADS TO INCREASED BINDING AND SENSITIVITY TO POLYMYXIN B

Burkholderia cenocepacia is an opportunistic pathogen that displays a remarkably high resistance to antimicrobial peptides. We hypothesize that high resistance to antimicrobial peptides in these bacteria is because of the barrier properties of the outer membrane. Here we report the identification of genes for the biosynthesis of the core oligosaccharide (OS) moiety of the B. cenocepacia lipopolysaccharide. We constructed a panel of isogenic mutants with truncated core OS that facilitated functional gene assignments and the elucidation of the core OS structure in the prototypic strain K56-2. The core OS structure consists of three heptoses in the inner core region, 3-deoxy-d-manno-octulosonic acid, d-glycero-d-talo-octulosonic acid, and 4-amino-4-deoxy-l-arabinose linked to d-glycero-d-talo-octulosonic acid. Also, glucose is linked to heptose I, whereas heptose II carries a second glucose and a terminal heptose, which is the site of attachment of the O antigen. We established that the level of core truncation in the mutants was proportional to their increased in vitro sensitivity to polymyxin B (PmB). Binding assays using fluorescent 5-dimethylaminonaphthalene-1-sulfonyl-labeled PmB demonstrated a correlation between sensitivity and increased binding of PmB to intact cells. Also, the mutant producing a heptoseless core OS did not survive in macrophages as compared with the parental K56-2 strain. Together, our results demonstrate that a complete core OS is required for full PmB resistance in B. cenocepacia and that resistance is due, at least in part, to the ability of B. cenocepacia to prevent binding of the peptide to the bacterial cell envelope.

O‐Glycosylated 24 kDa human growth hormone has a mucin‐like biantennary disialylated tetrasaccharide attached at Thr‐60

MS was used to characterize the 24 kDa human growth hormone (hGH) glycoprotein isoform and determine the locus of O-linked oligosaccharide attachment, the oligosaccharide branching topology, and the monosaccharide sequence. MALDI-TOF/MS and ESI-MS/MS analyses of glycosylated 24 kDa hGH tryptic peptides showed that this hGH isoform is a product of the hGH normal gene. Analysis of the glycoprotein hydrolysate by high-performance anion-exchange chromatography with pulsed amperometric detection and HPLC with fluorescent detection for N-acetyl neuraminic acid (NeuAc) yielded the oligosaccharide composition (NeuAc(2), N-acetyl galactosamine(1), Gal(1)). After beta-elimination to release the oligosaccharide from glycosylated 24 kDa hGH, collision-induced dissociation of tryptic glycopeptide T6 indicated that there had been an O-linked oligosaccharide attached to Thr-60. The sequence and branching structure of the oligosaccharide were determined by ESI-MS/MS analysis of tryptic glycopeptide T6. The mucin-like O-oligosaccharide sequence linked to Thr-60 begins with N-acetyl galactosamine and branches in a bifurcated topology with one appendage consisting of galactose followed by NeuAc and the other consisting of a single NeuAc. The oligosaccharide moiety lies in the high-affinity binding site 1 structural epitope of hGH that interfaces with both the growth hormone and the prolactin receptors and is predicted to sterically affect receptor interactions and alter the biological actions of hGH.

Identification of a novel lipopolysaccharide core biosynthesis gene cluster in Bordetella pertussis, and influence of core structure and lipid A glucosamine substitution on endotoxic activity.

Lipopolysaccharide (LPS), also known as endotoxin, is one of the main constituents of the gram-negative bacterial outer membrane. Whereas the lipid A portion of LPS is generally considered the main determinant for endotoxic activity, the oligosaccharide moiety plays an important role in immune evasion and the interaction with professional antigen-presenting cells. Here we describe a novel four-gene cluster involved in the biosynthesis of the Bordetella pertussis core oligosaccharide. By insertionally inactivating these genes and studying the resulting LPS structures, we show that at least two of the genes encode active glycosyltransferases, while a third gene encodes a deacetylase also required for biosynthesis of full-length oligosaccharide. In addition, we demonstrate that mutations in the locus differentially affect LPS and whole-cell endotoxic activities. Furthermore, while analyzing the mutant LPS structures, we confirmed a novel modification of the lipid A phosphate with glucosamine and found that inactivation of the responsible glycosyltransferase reduces the endotoxic activity of the LPS.

2,3-Anhydrosugars in Glycoside Bond Synthesis. Application to 2,6-Dideoxypyranosides

We describe here the first use of 2,3-anhydrosugars as glycosylating agents for the preparation of 2-deoxypyranosides. In particular, the methodology was used to assemble 2,6-dideoxysugar glycosides. Glycosylation of a panel of alcohols with one of two 6-deoxy-2,3-anhydrosugar thioglycosides (8 and 9) in the presence of a Lewis acid afforded 2,6-dideoxy-2-thiotolyl glycoside products in generally excellent yields with an exclusively syn relationship between the aglycon and the C-3 hydroxyl group. Removal of the 2-thiotolyl group can be achieved upon reaction with tri-n-butyltin hydride and AIBN to give the corresponding 2,6-dideoxy pyranosides. Once developed, the method was applied to the synthesis of oligosaccharide moieties in the natural products apoptolidin and olivomycin A.

Leucospilotaside C, a new sulfated triterpene glycoside from sea cucumber Holothuria leucospilota

A new triterpene glycoside, leucospilotaside C, along with two known saponin, was isolated from sea cucumber Holothuria leucospilota collected from the South China Sea, and its structure was elucidated as 3- O-{4′- O-sodiumsulfate- β- d-xylopyranosyl}-holosta-22,25-epoxy-9-ene-3 β,12 α,17 α-triol ( 1) by extensive spectroscopic analysis and chemical methods. The glycosides have the same triterpene aglycone, but differ in the oligosaccharide moieties.

Role of N-linked oligosaccharides in the biosynthetic processing of the cystic fibrosis membrane conductance regulator

The epithelial chloride channel CFTR is a glycoprotein that is modified by two N-linked oligosaccharides. The most common mutant CFTR protein in patients with cystic fibrosis, DeltaF508, is misfolded and retained by ER quality control. As oligosaccharide moieties of glycoproteins are known to mediate interactions with ER lectin chaperones, we investigated the role of N-linked glycosylation in the processing of wild-type and DeltaF508 CFTR. We found that N-glycosylation and ER lectin interactions are not major determinants of trafficking of wild-type and DeltaF508 from the ER to the plasma membrane. Unglycosylated CFTR, generated by removal of glycosylation sites or treatment of cells with the N-glycosylation inhibitor tunicamycin, did not bind calnexin, but did traffic to the cell surface and exhibited chloride channel activity. Most importantly, unglycosylated DeltaF508 CFTR still could not escape quality control in the early secretory pathway and remained associated with the ER. However, the absence of N-linked oligosaccharides did reduce the stability of wild-type CFTR, causing significantly more-rapid turnover in post-ER compartments. Surprisingly, the individual N-linked carbohydrates do not play equivalent roles and modulate the fate of the wild-type protein in different ways in its early biosynthetic pathway.

Evaluation of glycosylation for quality assurance of antibody pharmaceuticals by capillary electrophoresis

The development of monoclonal antibody (mAb) pharmaceuticals has rapidly generated in this decade, and there are currently 23 FDA-approved mAb pharmaceuticals. Carbohydrate chains in mAb pharmaceuticals play important roles for the expression of their biological activities such as antibody-dependent cellular cytotoxicity, whereas the oligosaccharide profile is easily changed depending on the manufacturing conditions. Therefore, the evaluation of carbohydrate chains in detail is quite important for quality control in the development of mAb from early phases, but oligosaccharides in mAb have high heterogeneity and full characterization of oligosaccharide moiety in mAb has been a challenging target. Capillary electrophoresis (CE) is a powerful tool for the evaluation of glycan occupancy and oligosaccharide profile. This review focuses mainly on the application of CE to the analytical studies on glycosylation in mAb pharmaceuticals developed in our laboratory. The related techniques including the full-image microchip isoelectric focusing and the newly developed mass spectrometry technologies are also shown. The combination of the techniques described in this review will be a good guide for the evaluation of glycosylation for quality assurance of antibody pharmaceuticals by CE from the early stage of the development to the marketing stage.

High-throughput screening of cell lysates for ganglioside synthesis

A high-throughput screen to detect the synthesis of natural and non-natural gangliosides by cell lysates has been developed and automated. Utilizing the binding specificity of cholera toxin B-subunit for the oligosaccharide moiety of the ganglioside G M1, the synthesis of sugar–sphingolipid glycosidic linkages was detected using a modified enzyme-linked immunosorbent assay (ELISA)/enzyme-linked lectin assay (ELLA). The screen was optimized and validated for high-throughput screening of cell lysates by evaluating different vectors, promoters, substrates and detection strategies. The extent of ganglioside synthesis was found to be proportional to enzyme concentration and length of incubation time. As a test of the finalized screen efficacy, individual colonies from a saturation mutagenesis library of nucleophile mutants of an endoglycoceramidase were screened to identify the most active enzyme for ganglioside synthesis. This screen should find general application in assaying both glycolipid biosynthesis and glycolipid hydrolysis, as it is highly sensitive and can be used with crude cell extracts.

Rapid identification of triterpenoid saponins in the roots of Codonopsis lanceolata by liquid chromatography–mass spectrometry

Liquid chromatography coupled with sequential mass spectrometry (LC-MS(n)) has been used to identify 3,28-bidesmosidic triterpenoid saponins, lancemaside A (1), foetidissimoside A (2), aster saponin Hb (3), lancemaside E (4), lancemaside B (5), lancemaside F (6), lancemaside G (7), lancemaside C (8), and lancemaside D (9) in the roots of Codonopsis lanceolata. Structural information about both the aglycone and the sugar moiety at the C-3 position of saponins was obtained in the negative-ion mode. On the other hand, positive-ion spectra mainly provide structural information about the sugar chains of saponins, especially the oligosaccharide moiety at the C-28 position. During subsequent fragmentation of the product ions derived from the oligosaccharide moiety at the C-28 position, fragments produced by sequential loss of a monosaccharide unit were observed. Furthermore, the structural features of two unknown saponins in the roots of C. lanceolata were assigned on the basis of the fragmentation patterns of the known saponins. These studies demonstrate that LC-MS(n) analysis has great potential for the identification and characterization of triterpenoid saponins in plant extracts.

New variants of polar glycopeptidolipids detected inMycobacterium simiae, includinghabanastrains, as evidenced by electrospray ionization-ion trap-mass spectrometry

To determine the composition of polar glycopeptidolipids (pGPLs) of Mycobacterium simiae and, particularly, those of 'habana' strains, in a search for specific markers given the immunogenic potential of 'habana' TMC 5135 in experimental tuberculosis. pGPLs were determined in free lipid extracts using electrospray ionization-ion trap-mass spectrometry (ESI-IT-MS), working in both negative- and positive-ion mode. In the case of TMC 5135, the presence of the previously characterized GPL-II (containing 2,4-di-O-CH(3) glucuronic acid as distal sugar in the oligosaccharide antigenic moiety) and GPL-III (containing 4-O-CH(3) glucuronic acid as distal sugar) was confirmed using MS/MS and MS/MS/MS approaches. Interestingly, some 'habana' strains presented variants of GPL-II, designated GPL-II'-A and GPL-II'-B. A di-O-CH(3)-deoxy-hexose (tentatively, 2,3-di-O-CH(3)-fucose) was identified as the penultimate sugar in the oligosaccharide moiety of GPL-II'-A, whereas in GPL-II'-B the penultimate sugar was fucose (tentative identification). On the contrary, the distal sugar of the oligosaccharide chain of pGPLs of Myco. simiae ATCC 25275(T) was identified as tri-O-CH(3)-glucuronic acid (designated GPL-sim(T)-I, with two variants: GPL-sim(T)-I-A and GPL-sim(T)-I-B), O-CH(3)-glucuronic acid (designated GPL-sim(T)-II) and di-O-CH(3)-glucuronic acid (GPL-II'-A and GPL-II'-B). The penultimate sugar of the oligosaccharide chain of GPL-sim(T)-I-A and GPL-sim(T)-II was identified as di-O-CH(3)-deoxy-hexose (tentatively, 2,3-di-O-CH(3) fucose), and that of GPL-sim(T)-I-B as deoxy-hexose (tentatively, fucose). In all strains studied, each [M-H](-) and [M+Na](+) ion was revealed as a mixture of homologous compounds varying in the number of -O-CH(3) groups present in the oligosaccharide moiety and in the length of the fatty acyl linked to the peptide. The present work indicates that, within a similar general pattern of pGPLs, different strains of Myco. simiae present some variations, so that new compounds (GPL-II'-A, GPL-II'-B, GPL-sim(T)-I-A, GPL-sim(T)-I-B and GPL-sim(T)-II) were defined. Noteworthy was the fact that the 'habana' strains clearly differed from the type strain of Myco. simiae. The data obtained can be used in the delineation of the 'habana' group of Myco. simiae, including the quality control of the immunogenic strain 'habana' TMC 5135.

Characterization of Na,K-ATPase and H,K-ATPase Enzymes with Glycosylation-Deficient β-Subunit Variants by Voltage-Clamp Fluorometry in Xenopus Oocytes

The role of N-linked glycosylation of beta-subunits in the functional properties of the oligomeric P-type ATPases Na,K- and H,K-ATPase has been examined by expressing glycosylation-deficient Asn-to-Gln beta-variants in Xenopus oocytes. For both ATPases, the absence of the huge N-linked oligosaccharide moiety on the beta-subunit does not affect alpha/beta coassembly, plasma membrane delivery or functional activity of the holoenzyme. Whereas this is in line with several previous glycosylation studies on Na,K-ATPase, this is the first report showing that the cell surface delivery and enzymatic activity of the gastric H,K-ATPase is unaffected by the lack of N-linked glycosylation. Sulfhydryl-specific labeling of introduced cysteine reporter sites with the environmentally sensitive fluorophore tetramethylrhodamine-6-maleimide (TMRM) upon expression in Xenopus oocytes enabled us to further investigate potential effects of the N-glycans on more subtle enzymatic properties, like the distribution between E 1P/E 2P states of the catalytic cycle and the kinetics of the E 1P/E 2P conformational transition under presteady state conditions. For both Na,K-ATPase and H,K-ATPase, we observed differences in neither the voltage-dependent E 1P/E 2P ratio nor the kinetics of the E 1P/E 2P transition between holoenzymes comprising glycosylated and glycosylation-deficient beta-subunits. We conclude that the N-linked glycans on these essential accessory subunits of oligomeric P-type ATPases are dispensable for proper folding, membrane stabilization of the alpha-subunit and transport function itself. Glycosylation is rather important for other cellular functions not relevant in the oocyte expression system, such as intercellular interactions or basolateral versus apical targeting in polarized cells, as demonstrated in other expression systems.

Efficient synthesis of α- and β-chacotriosyl glycosides using appropriate donors, and their cytotoxic activity

Natural steroidal glycosides containing α- l-rhamnopyranosyl-(1→4)-[α- l-rhamnopyranosyl-(1→2)]-β- d-glucopyranose (chacotriose) at the oligosaccharide moiety exhibit anti-cancer and anti-herpes activities. To investigate the structure–activity relationships of the aglycone parts of chacotriosides, we developed a synthesis method for chacotriosyl glycosides having various aglycones. In the process, it was revealed that α-chacotriosyl glycosides could be obtained mainly by using a trichloroacetimidate donor, while β-chacotriosyl glycosides were afforded by using phosphite and phosphate donors. In cytotoxicity tests using the A549 and HepG2 cell lines, naturally occurring β-chacotriosyl diosgenin and cholestanol exhibited higher activities than the corresponding α-chacotriosyl glycosides.

Proteomics Reveals N-Linked Glycoprotein Diversity in Caenorhabditis elegans and Suggests an Atypical Translocation Mechanism for Integral Membrane Proteins

Protein glycosylation is one of the most common post-translational modifications in eukaryotes and affects various aspects of protein structure and function. To facilitate studies of protein glycosylation, we paired glycosylation site-specific stable isotope tagging of lectin affinity-captured N-linked glycopeptides with mass spectrometry and determined 1,465 N-glycosylated sites on 829 proteins expressed in Caenorhabditis elegans. The analysis shows the diversity of protein glycosylation in eukaryotes in terms of glycosylation sites and oligosaccharide structures attached to polypeptide chains and suggests the substrate specificity of oligosaccharyltransferase, a single multienzyme complex in C. elegans that incorporates an oligosaccharide moiety en bloc to newly synthesized polypeptides. In addition, topological analysis of 257 N-glycosylated proteins containing a putative single transmembrane segment that were identified based on the relative positions of glycosylation sites and transmembrane segments suggests that an atypical non-cotranslational mechanism translocates large N-terminal segments from the cytosol to the endoplasmic reticulum lumen in the absence of signal sequence function.