Methylation techniques in the structural analysis of glycoproteins and glycolipids

Fibrinolytic compounds isolated from a brown alga, Sargassum fulvellum

Two of bioactive natural products were founded in a brown alga, Sargassum fulvellum. After isolation and purification, the molecular structures of these two products were investigated by NMR spectroscopy and GC-mass spectroscopy. The two compounds were identified to be 1-O-palmitoyl-2-O-oleoyl-3-O-(alpha-D-glucopyranosyl)-glycerol (POGG) and 1-O-myristoyl-2-O-oleoyl-3-O-(alpha-D-glucopyranosyl)-glycerol (MOGG) which were obtained from Sargassum fulvellum for the first time. POGG and MOGG showed fibrinolytic activity in the reaction system of pro-u-PA and plasminogen.

NMR spectroscopy in the structural elucidation of oligosaccharides and glycosides

The potential of one- and two-dimensional NMR techniques for the identification of individual sugar residues, their anomeric configuration, interglycosidic linkages, sequencing and the site of any appended group, in establishing the structures of naturally occurring oligosaccharides and glycosides is presented.

Analysis of glycoprotein-derived oligosaccharides by high-pH anion-exchange chromatography

The technique of high-pH anion-exchange chromatography with pulsed amperometric detection has recently been shown to be a powerful method for resolving closely related oligosaccharides [M. R. Hardy and R. R. Townsend, Proc. Natl. Acad. Sci. U.S.A., 85 (1988) 3289-3293]. This report describes separations involving a total of nineteen different high-mannose, hybrid and complex-type oligosaccharides isolated after peptide: N-glycosidase F (PNGase F) or endo-beta-N-acetylglucosaminidase H digestion of glycoproteins. Separations were carried out at a constant base concentration (0.1 M NaOH) using linear gradients from 0 to 0.2 M sodium acetate. The applicability of this chromatography for profiling the N-linked oligosaccharides of glycoproteins was demonstrated by generating "oligosaccharide maps" of PNGase F-liberated oligosaccharides from recombinant human tissue plasminogen activator, ribonuclease b, human transferrin, and bovine fetuin. Methods for recovering salt-free oligosaccharides after this chromatography were also investigated. On-line ion suppression with an anionic micromembrane suppressor cartridge was found to be capable of effective desalting up to a total sodium ion concentration of 0.15-0.2 M at a flow-rate of 1 ml/min. After high-pH anion-exchange chromatography with ion suppression, collected oligosaccharides were analyzed by fast-atom bombardment mass spectrometry after conversion to permethyl derivatives or after reductive amination with rho-aminobenzoic acid ethyl ester.

Separation of neutral reducing oligosaccharides derived from glycoproteins by HPLC on a hydroxylated polymeric support

A prototype hydroxylated polymeric support, Glyco-PAK N, was employed to separate a number of neutral reducing oligosaccharides derived from various glycoproteins by the hydrazinolysis/re-N-acetylation/mild acid hydrolysis procedure. General features of the separation properties of the matrix are described. A major advantage of the packing over silica-based supports is its stability, a property which is advantageous both in repetitive analytical chromatography and in the preparative isolation and spectroscopic identification of pure compounds, free of column breakdown products.

Structural studies on sialylated and sulphated O-glycosidic mannose-linked oligosaccharides in the chondroitin sulphate proteoglycan of brain

We have previously described the structures of neutral and sialylated O-glycosidic mannose-linked tetrasaccharides and keratan sulphate polysaccharide chains in the chondroitin sulphate proteoglycan of brain. The present paper provides information on a series of related sialylated and/or sulphated tri- to penta-saccharides released by alkaline-borohydride treatment of the proteoglycan glycopeptides. The oligosaccharides were fractionated by ion-exchange chromatography and gel filtration, and their structural properties were studied by methylation analysis and fast-atom-bombardment mass spectrometry. Five fractions containing [35S]sulphate-labelled oligosaccharides were obtained by ion-exchange chromatography, each of which was eluted from Sephadex G-50 as two well-separated peaks. The apparent Mr values of both the large- and small-molecular-size fractions increased with increasing acidity (and sulphate labelling) of the oligosaccharides. The larger-molecular-size fractions contained short mannose-linked keratan sulphate chains of Mr 3000-4500, together with some asparagine-linked oligosaccharides. The smaller tri- to penta-saccharides, of Mr 800-1400, appear to have a common GlcNac(beta 1-3)Manol core, and to contain one to two residues of sialic acid and/or sulphate.

Efficient HPLC separation of N-p-nitrophenylglycosylamines derived from complex oligosaccharide mixtures. Human orosomucoid as a model

With human orosomucoid as model compound, a new method was developed to separate neutral oligosaccharides as N-p-nitro-phenylglycosylamines. Asialo orosomucoid was prepared by treatment with neuraminidase and purified by size exclusion HPLC on TSK 2000 SW. Oligosaccharides were isolated by reversed phase HPLC on Hamilton PRP-1 after hydrazinolysis and re-N-acetylation. Glycosylamination was performed with p-nitroaniline in DMSO-formic acid-water, where the whole mixture of oligosaccharide derivatives was isolated by reversed phase HPLC on Hamilton PRP-1 and separated into single glycosylamines on Shandon Hypersil ODS. The purified glycosylamines could be methylated by a new rapid method with sodium hydroxide and methyl iodide in DMSO, isolation and purification were carried out on Hamilton PRP-1 and Spherisorb ODS 2, respectively, as described for the glycosylamines. Preparative scale HPLC separations were performed on analytical columns using repetitive collection mode and automatic sample loading by means of a peristaltic pump operated by the HPLC controller. The purified glycosylamines can be used for sugar analyses or, after permethylation, for methylation analyses or related procedures.

Structural analysis of the major urinary oligosaccharides in feline alpha-mannosidosis

Two homologous series of urinary oligosaccharides were identified by h.p.l.c. and fast-atom-bombardment mass spectrometry in feline alpha-mannosidosis. The predominant series has the composition Man2-8GlcNAc2 and a minor series the composition Man2-9GlcNAc. The structure of the most abundant oligosaccharide, which accounts for over 80% of the urinary oligosaccharide, was shown to be alpha-D-Manp(1----3)[alpha-D-Manp-(1----6)]beta-D-Manp -(1----4)-beta-D-GlcpNA c-(1----4)-D-GlcNAc by gas chromatography and mass spectrometry. Such a structure is consistent with the incomplete catabolism of complex N-linked glycans due to a deficiency of alpha-D-mannosidase in tissue lacking an endohexosaminidase activity.

Enrichment of high mannose-type glycans in nervous tissue glycoproteins in neuronal ceroid-lipofuscinosis

In view of the hypothesis that a biochemical abnormality in the childhood forms of neuronal ceroid-lipofuscinosis may lie in the utilization of dolichols in glycoprotein synthesis, we analyzed the oligosaccharide structures of brain glycoproteins in infantile neuronal ceroid-lipofuscinosis (INCL). Lectin affinity chromatography of purified glycopeptides and of oligosaccharides prepared by hydrazinolysis showed an increase in high mannose-type glycopeptides and a decrease in tri- and tetra-antennary glycopeptides in INCL brain when compared with control brain. These changes were more pronounced in the storage cytosomes than in whole brain. Methylation analysis of the isolated glycopeptide fractions did not reveal differences in substitution patterns of the individual sugar residues between INCL and control brain. In INCL the core disaccharide of the O-glycosidically-linked oligosaccharides was sialylated to a higher degree than in control brain indicating that the structural changes were not confined only to N-glycosidically-linked carbohydrate chains. The observed structural changes in the carbohydrate chains of brain glycopeptides in INCL could be explained by a defect in the biosynthesis of glycoproteins. Alternatively, the changes may reflect the increased glial cell population in the degenerating brain. In fact, the elution profiles in lectin chromatography of oligosaccharides prepared from cultured rat glioma cells resembled those from INCL brain.

Separation of partially methylated mannitols by liquid chromatography

To facilitate the methylation linkage analysis of complex carbohydrates containing radioactively labeled mannose residues, an HPLC micromethylation technique has been developed which effectively resolves all of the partially methylated mannitol standards prepared using an under-methylation protocol. The method was applied to the linkage analysis of the nine mannose residues of the dolichol-derived oligosaccharide Glc3Man9GlcNAc2 isolated from BHK-21 fibroblasts. This technique should prove widely applicable to the methylation linkage analysis of radiolabeled complex carbohydrates.

High-mannose structure of apolipoprotein-B from low-density lipoproteins of human plasma

Human plasma low-density lipoproteins were purified by flotation followed by gel filtration. The protein moiety of the lipoproteins, apolipoprotein-B, which was detected by polyacrylamide gel electrophoresis as the only protein component, contained 4.4% (by weight) carbohydrate. Glycopeptides liberated from apolipoprotein-B by pronase were fractionated by affinity chromatography on concanavalin-A--Sepharose. The results indicated that high-mannose glycopeptides interacting strongly with the lectin comprise about 37% of the total monosaccharides of apolipoprotein-B. Thus, as compared to the total serum glycoproteins having about 5% of their monosaccharides in high-mannose glycopeptides, low-density lipoproteins are relatively enriched in these structures amounting up to about 10% of the total high-mannose oligosaccharides in serum. The rest of the carbohydrates in low-density lipoproteins are suggested to be mainly biantennary acidic oligosaccharides interacting weakly with concanavalin A. The oligomannosidic chains from native low-density lipoproteins and isolated glycopeptides were released by digestion with endo-beta-N-acetylglucosaminidase H. Thin-layer chromatography of the released oligosaccharides indicated that apolipoprotein-B contains five different oligomannosidic structures varying in the number of the mannose residues from Man5GlcNAc to Man9GlcNAc. Separation of the per-O-benzoylated high-mannose oligosaccharides by high-pressure liquid chromatography revealed the same polymeric structures in a molar ratio (from Man5 to Man9) of 10:2:3:2:3. Apolipoprotein-B in low-density lipoproteins was calculated to contain five high-mannose chains in total. The different high-mannose oligosaccharides liberated by endo-beta-N-acetylglucosaminidase H were isolated with high-pressure liquid chromatography after reduction with NaBH4, and subjected to methylation analysis with gas-liquid chromatography--mass spectrometry. The data of these studies and the results of exoglycosidase treatment suggest the following structure for the main high-mannose oligosaccharide: (formula: see text) The higher polymeric structures are composed of chains in which the Man5GlcNAc structure is continued by one to four Man(alpha 1-2) residues.

Enhancement of structural information in FAB ionized carbohydrate samples by neutral gas collision

Fast atom bombardment (FAB) ionization and two coupled analyzers (BE-EB) have been combined with neutral gas collision (C) to enhance structural information in the mass spectra of oligosaccharides. (B and E are abbreviations for magnetic and electric sectors respectively.) FAB ionization and the first analysers (BE) have provided parent ions free from biological and liquid matrix contaminants. Structural detail of these products were observed after collision and daughter ion analysis in a second coupled analyser (EB). Starting from complex mixtures, this instrumental approach, BE-C-EB, has provided specific oligomeric sequence information which was not observed in the normal FAB mass spectra. Collision spectra obtained from isomeric linear and branched oligosaccharides show unique fragments that can be directly related to structure.

Methylation analysis in glycoprotein chemistry: a comparative study of the carbohydrate structures of three hormone-binding glycoproteins from human serum

The structures of the carbohydrate moieties of three hormone-binding glycoproteins from human serum, namely, thyroxine-binding globulin, transcortin, and sex hormone-binding globulin, have been characterised using quantitative g.l.c. of the methylated monosaccharide derivatives obtained after methanolysis of the methylated glycoproteins.

An improved procedure for the methylation analysis of oligosaccharides and polysaccharides

An improved procedure for the methylation analysis of oligosaccharides and polysaccharides is described. Steps in the procedure were examined and optimised for quantitative recovery and speed. Methylation was shown to be complete by using [14C]methyl iodide. All operations were performed in the same tube and the need to concentrate solutions containing acetylated alditols of methylated sugars was eliminated, thus minimising losses due to volatilization. The method is convenient, gives high recoveries of acetylated alditols of methylated sugars, and allows analysis of the glycosyl linkages of oligo- or poly-saccharides to be completed within a working day. A wide range of oligo- and poly-saccharides were methylated by this procedure.

Structural studies on glycoprotein oligosaccharides of chromaffin granule membranes and dopamine beta-hydroxylase

Dopamine beta-hydroxylase present in the soluble matrix of bovine adrenal medullary chromaffin granules contains biantennary complex oligosaccharides and high-mannose oligosaccharides in a molar ratio of approximately 2:1. The high-mannose oligosaccharides contain an average of six mannose residues. The largest biantennary oligosaccharides (40% of the total) have two complete peripheral branches consisting of sialic acid-galactose-N-acetylglucosamine, but an equal proportion lack sialic acid on one branch and the remainder lack N-acetylglucosamine and/or galactose. Affinity chromatography on lentil lectin-agarose demonstrated that 84% of the dopamine beta-hydroxylase biantennary oligosaccharides are substituted by fucose on the core N-acetylglucosamine which is linked to asparagine. Based on carbohydrate concentration and the proportions of biantennary and high-mannose oligosaccharides, it would appear that the four dopamine beta-hydroxylase subunits of Mr congruent to 75,000 are not identical with respect to their oligosaccharide moieties. In chromaffin granule membranes, high-mannose and biantennary oligosaccharides comprise 20 and 35%, respectively, of the glycoprotein carbohydrate. Almost 40% is present in the form of large complex oligosaccharides with three or more antennas, less than 3% of which have both a core fucose residue and a 2,6-substituted alpha-linked mannose residue. Chromaffin granule membranes also contain a small proportion (approximately 6%) of O-glycosidically linked glycoprotein oligosaccharides which are predominantly monosialyl derivatives of galactosyl-N-acetylgalactosamine. The ratio of N-acetyl- to N-glycolylneuraminic acid in dopamine beta-hydroxylase and the glycoproteins of chromaffin granule membranes is approximately 1.5:1, which is within the same range as that previously found in membrane gangliosides and in the chromogranins isolated from the soluble granule matrix.