Fluorescence method for the structural analysis of oligomannose-type sugar chains by partial acetolysis

Separation of 2-aminobenzoic acid-derivatized glycosaminoglycans and asparagine-linked glycans by capillary electrophoresis

A capillary electrophoresis method was developed for the analysis of oligosaccharides combined with derivatization with 2-aminobenzoic acid. Glycosaminoglycan delta-disaccharides were effectively resolved on a fused-silica capillary tube using 150 mM borate, pH 8.5, as a running electrolyte solution. This analytical method was applied to the identification of glycosaminoglycan in combination with enzymatic digestion. The separation of N-glycans or glucose-oligomers was performed with a phosphate buffer containing polyethylene glycol or borate as an electrolyte solution. This method is expected to be useful in the determination of oligosaccharide structures in a glycoprotein.

Structural analysis of free N-glycans occurring in soybean seedlings and dry seeds

The structures of unconjugated or free N-glycans in stems of soybean seedlings and dry seeds have been identified. The free N-glycans were extracted from the stems of seedlings or defatted dry seeds. After desalting by two kinds of ion-exchange chromatography and a gel filtration, the free N-glycans were coupled with 2-aminopyridine. The resulting fluorescence-labeled (PA-) N-glycans were purified by gel filtration, Con A affinity chromatography, reverse-phase HPLC, and size-fractionation HPLC. The structures of the PA-sugar chains purified were analyzed by the combination of two-dimensional sugar chain mapping, jack bean alpha-mannosidase digestion, alpha-1,2-mannosidase digestions, partial acetolysis, and ESI-MS/MS. The free N-glycan structures found showed that two categories of free N-glycans occur in the stems of soybean seedlings. One is a high-mannose type structure having one GlcNAc residue at the reducing end (Man 9 approximately 5 GlcNAc1, 93%), that would be derived by endo-GM (Kimura, Y. et al., Biochim. Biophys. Acta, 1381, 27-36 (1998)). The other small component is a xylose-containing type one having two GlcNAc residues at the reducing end (Man3Xyl1GlcNAc2, 7%), which would be derived by PNGase-GM (Kimura, Y. and Ohno, A., Biosci. Biotechnol. Biochem., 62, 412-418 (1998)). The detailed structural analysis of free glycans showed that high-mannose type free N-glycans (Man 9 approximately 5 GlcNAc1) in the soybean seedlings have a common core structural unit; Manalpha1-6(Man1-3)Manalpha1-6(Manalpha1-3)Ma nbeta1-4GlcNAc. Comparing the amount of free N-glycans in the seedling stems and dry seeds, the amount in the stems of seedlings was much higher than that in the dry seeds; approximately 700 pmol per one stem, 8 pmol in one dry seed. This fact suggested that free N-glycans in soybean seedlings could be produced by two kinds of N-glycan releasing enzymes during germination or seedling-development.

A pyridylamination method aimed at automatic oligosaccharide analysis of N-linked sugar chains

The procedure for preparation of pyridylaminated sugar chains from glycoproteins was improved with a view to its eventual automation. Following on the coupling reaction improvement already reported [N. Kuraya and S. Hase (1992) J. Biochem. 112, 122-126], two further aspects were improved in this study. Instead of sodium bicarbonate-acetic anhydride, volatile reagents were adopted for the re-N-acetylation of hexosamine residues after hydrazinolysis to give rapid removal of excess reagents. Subsequent to the pyridylamination reaction, excess reagents were removed by cation-exchange to isolate the pyridylaminated oligosaccharides in place of gel filtration. These alterations rendered a one-pot reaction possible and resulted in a large reduction in the amount of time needed compared with other methods so far reported. The procedure was successfully applied to the detection of sugar chains from Taka-amylase A and human erythrocyte membranes.

Characterization of oligosaccharides from an antigenic mannan of Saccharomyces cerevisiae

Mannans of the yeast Saccharomyces cerevisiae have been implicated as containing the allergens to which bakers and brewers are sensitive and also the antigen recognized by patients with Crohn's disease. A fraction of S. cerevisiae mannan, Sc500, having high affinity for antibodies in Crohn's patients has been characterized by NMR spectroscopy followed by fragmentation using alkaline elimination, partial acid hydrolysis and acetolysis. The released oligosaccharides were separated by gel filtration on a Biogel P4 column and analyzed by fluorescence labeling, HPLC and methylation analysis. The relationship between structure and antigen activity was measured by competitive ELISA. The antigenic activity of the original high molecular weight mannan could be ascribed to terminal Manalpha1-->3Manalpha1-->2 sequences which are rarely found in human glycoproteins but were over-represented in Sc500 compared to other yeast mannans.

Structural analysis of N-linked carbohydrate chains of funnel web spider (Agelenopsis aperta) venom peptide isomerase

The structure of the N-linked carbohydrate chains of peptide isomerase from the venom of the funnel web spider (Agelenopsis aperta) has been analyzed. Carbohydrates were released from peptide isomerase by hydrazinolysis and reductively aminated with 2-aminopyridine. The fluorescent derivatives were purified by phenol/chloroform extraction, followed by size-exclusion HPLC. The structure of the purified pyridylamino (PA-) carbohydrate chains were analyzed by a combination of two-dimensional HPLC mapping, sugar composition analysis, sequential exoglycosidase digestions, and mass spectrometry. The peptide isomerase contains six kinds of N-linked carbohydrate chains of truncated high-mannose type, with a fucose alpha 1-6 linked to the reducing N-acetylglucosamine in approximately 80% of them.

Structures of the N-linked sugar chains in the PAS-6 glycoprotein from the bovine milk fat globule membrane

The structures of the N-linked sugar chains in the PAS-6 glycoprotein (PAS-6) from the bovine milk fat globule membrane were determined. The sugar chains were liberated from PAS-6 by hydrazinolysis, and the pyridylaminated sugar chains were separated into a neutral (6N) and two acidic chains (6M and 6D), the acidic sugar chains then being converted to neutral sugar chains (6MN and 6DN). 6N was separated into two neutral fractions (6N13 and 6N5.5), while 6MN and 6DN each gave a single fraction (6MN13 and 6DN13). The structure of 6N5.5, which was the major sugar chain in PAS-6, is proposed to be Man alpha1 --> 6 (Man alpha1 --> 3) Man beta1 --> 4GlcNAc beta1 --> 4GlcNAc-PA; 6N13, 6MN13 and 6DN13 are proposed to be Gal beta1 --> 3Gal beta1 --> 4GlcNAc beta1 --> 2Man alpha1 --> 6 (Gal beta1 --> 3Gal beta1 --> 4GlcNAc beta1 --> 2Man alpha1 --> 3) Man beta1 --> 4GlcNAc beta1 --> 4 (Fuc alpha1 --> 6)GlcNAc-PA; 6M and 6D had 1 or 2 additional NeuAc residues at the non-reducing ends of 6MN13 and 6DN13, respectively.

Processing of asparagine-linked oligosaccharides in insect cells: evidence for alpha-mannosidase II

The occurrence of alpha-D-mannosidase II activity in insect cells was studied using pyridylaminated oligosaccharides as substrates and two-dimensional HPLC and glycosidase digestion for the analysis of products. GlcNAcMan5GlcNAc2 was converted to GlcNAcMan3GlcNAc2 by each of the three cell lines investigated (Bm-N, Sf-21, and Mb-0503). The respective activity was highest in Bm-N cells which were used for further experiments. Man5GlcNAc2 was not degraded by the Bm-N cell homogenate. Thus, this alpha-mannosidase essentially exhibits the same substrate specificity as mammalian and plant Golgi alpha-mannosidase II. The alpha-mannosidase II-like activity from Bm-N cells exhibits a pH optimum of 6.0-6.5, has no requirement for divalent metal ions, and is highly sensitive to swainsonine. The alpha 1,6-linked mannosyl residue is removed first as deduced from the elution time on reversed phase HPLC of the intermediate product. The same branch preference was found with alpha-mannosidase II from mung bean seedlings and Xenopus liver. Upon ultracentrifugation of Bm-N cell homogenate, 72% of the mannosidase acting on the GlcNAcMan5GlcNAc2 substrate was found in the microsomal pellet indicating the enzyme to be membrane-bound.

The carbohydrate moiety of the acid carboxypeptidase from Aspergillus saitoi

Acid carboxypeptidase from Aspergillus saitoi is a glycoprotein that contains both N- and O-linked sugar chains. The N-glycanase released high-mannose type oligosaccharides that were separated into eight components on HPLC. One, which had a unique structure of Man11GlcNAc2, was characterized. Mild alkali treatment of the carboxypeptidase, under conditions that effect beta-elimination, yielded D-mannose. Deglycosylation of the carboxypeptidase with endo-beta-N-acetylglucosaminidase and alpha-mannosidase effected the reduction of the molecular mass from 72 kDa to 60 kDa. Partial changes of CD spectra of the native and the deglycosylated enzymes indicate that some conformational changes on the peptide of the enzyme occurred after deglycosylation. Other enzymatic properties, such as catalytic activity, pH, and thermal stability and resistivity to protease digestion, did not appear to change. Tunicamycin halted secretion of the carboxypeptidase extracellularly.

Post-translational modifications of the Dictyostelium discoideum glycoprotein PsA. Glycosylphosphatidylinositol membrane anchor and composition of O-linked oligosaccharides

Prespore-specific antigen (PsA) is a cell-surface glycoprotein isolated from Dictyostelium discoideum, which is post-translationally modified by addition of carbohydrate to threonine residues of the carboxy-terminal peptide domain, and a glycosylphosphatidylinositol (GPI) anchor which attaches the glycoprotein to the cell membrane. The GPI anchor was isolated by proteolytic cleavage of the protein, and the structure of the lipid and glycan portions of the anchor were determined. The lipid moiety of the anchor is an inositolphosphoceramide which contains C18:0 phytosphingosine as a long chain base, and a mixture of fatty acids with a C18:1 mono-unsaturated fatty acid as the major component. The purified GPI anchor was susceptible to digestion by a bacterial phosphatidylinositol-specific phospholipase-C enzyme. The glycan of the GPI anchor consisted of two molecular species present in the ratio 55:45, the structures of which were determined by exoglycosidase sequencing and found to be Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcNH2 and Man alpha 1-2Man alpha 1-2Man alpha 1-6Man alpha 1-4GlcNH2. The glucosamine in both structures is glycosidically linked to the inositol ring of the inositolphosphoceramide. The GPI glycan structures are consistent with the conserved core structure of all characterised GPI anchors, and the structure of the D. discoideum GPI moiety has features in common with structures from yeast, protozoa and higher eukaryotes. Compositional analysis of the carbohydrate attached to threonine residues in the carboxy-terminal peptide domain is also presented. The oligosaccharides bind to wheat germ agglutinin, and contain glucosamine and fucose as the major constituents.

Molecular characterization of Limulus polyphemus C-reactive protein. II. Asparagine-linked oligosaccharides

The N-linked oligosaccharides of C-reactive protein (CRP) from the arachnid Limulus polyphemus, the horseshoe crab, were characterized after their release by hydrazinolysis, re-N-acetylation, and reduction with NaB3H4. High-voltage paper electrophoresis of the reduced oligosaccharides revealed only neutral species. Gel-permeation chromatography on Bio-Gel P4 yielded five fractions. The oligosaccharide fractions were further fractionated using high-voltage borate paper electrophoresis and Dionex BioLC ion-exchange chromatography. The oligosaccharides were structurally characterized by sequential exoglycosidase digestion, fragmentation by acetolysis and methylation analysis. Three major structures were found, of which two were the biantennary oligomannose type with compositions Man5GlcNAc2 (B-1), Man4GlcNAc2 (C-3) and one was the monoantennary structure Man3GlcNAc2 (D-1). The biantennary oligomannose structures B-1 and C-3 contained the structural unit Man alpha 6Man alpha 6R. This unusual arrangement of mannose linkages suggests a biosynthetic pathway in Limulus which differs from that reported in mammals, plants and the parasitic protozoa.

Primary structures of the N-linked carbohydrate chains from honeybee venom phospholipase A2

The N-linked carbohydrate chains of phospholipase A2 from honeybee (Apis mellifera) were released from glycopeptides with peptide-N-glycanase A and reductively aminated with 2-aminopyridine. The fluorescent derivatives were separated by size-fractionation and reverse-phase HPLC, yielding 14 fractions. Structural analysis was accomplished by compositional and methylation analyses, by comparison of the HPLC elution patterns with reference oligosaccharides, by stepwise exoglycosidase digestions which were monitored by HPLC, and, where necessary, by 500-MHz 1H-NMR spectroscopy. Ten oligosaccharides consisted of mannose, N-acetylglucosamine and fucose alpha 1-6 and/or alpha 1-3 linked to the innermost N-acetylglucosamine. Four compounds, which comprised 10% of the oligosaccharide pool from phospholipase A2, contained a rarely found terminal element with N-acetylgalactosamine. The structures of the 14 N-glycans from honeybee phospholipase A2 can be arranged into the following three series: [formula: see text]

Separation of oligomannose-type sugar chains having one to five mannose residues by high-performance liquid chromatography as their pyridylamino derivatives

Ten oligomannose-type sugar chains (ManGlcNAc2-Man5GlcNAc2) were prepared from various glycoproteins and fluorescence labeled with 2-aminopyridine. The fluorescent pyridylamino (PA)-sugar chains were first separated into five fractions according to their molecular sizes by HPLC on a TSK gel Amide-80 column. Each fraction was then separated into the component PA-sugar chains by reversed-phase HPLC on a Capcell Pak C18 column according to their chemical structures. The method is useful for studying the substrate specificities of alpha-mannosidases with Man5GlcNAc2-PA as a substrate.

Characterisation of the asparagine-linked oligosaccharides from Trypanosoma brucei type-I variant surface glycoproteins

The complete primary structures of the Asn-linked oligosaccharides from the conserved glycosylation site of the type-I variant surface glycoproteins of Trypanosoma brucei MITat 1.4 and MITat 1.6 were determined using a combination of exoglycosidase digestions, permethylation analysis, acetolysis and 1H NMR. Both variants contained almost exclusively oligomannose-type oligosaccharides, identical in structure to those of mammalian glycoproteins. The oligosaccharides ranged in size from (Man)9(GlcNAc)2 to (Man)5(GlcNAc)2. The relative abundance of each component was similar in both variants. The major components were (Man)8(GlcNAc)2 and (Man)7(GlcNAc)2 with slightly less (Man)9(GlcNAc)2 and (Man)6(GlcNAc)2 and much less (Man)5(GlcNAc)2. Both variants also contained the same structural isomers. The close similarity of the oligomannose series indicates identical processing at the conserved site in both variants.

Analysis of tissue glycoprotein sugar chains by two-dimensional high-performance liquid chromatographic mapping

Excellent separation of 45 pyridylamino derivatives of oligosaccharides were achieved by the two-dimensional combination of reversed-phase and size-fractionation high-performance liquid chromatography. The sugar chains of brain glycoproteins were derivatized into a mixture of pyridylamino-oligosaccharides from lyophilized brain tissue without any purification steps, and they were well separated by the system used. The pattern obtained was reproducible, and inter-individual variation was negligible. This finding demonstrated the possibility that this method could be applied to the detection of differences in the structure of glycoprotein sugar chains in crude preparations.

Identification method for twelve oligomannose-type sugar chains thought to be processing intermediates of glycoproteins

A mixture of the pyridylamino (PA) derivatives of 12 oligomannose-type sugar chains was fractionated into five fractions (mannose5N-acetylglucosamine2-PA approximately mannose9N-acetylglucosamine2-PA) by size-fractionation HPLC with a MicroPak AX-5 column. Each fraction thus obtained was then analyzed by reversed-phase HPLC with a Cosmosil 5C18-P column. In this way, the 12 PA-oligomannose-type sugar chains were completely separated from each other. The method was used to identify the structures of oligomannose-type sugar chains of human C3, the third component of human complement.