Analytical and semi-preparative high-performance liquid chromatography of oligosaccharides obtained by hydrazinolysis of hen ovomucoid

A new fungal lectin recognizing alpha(1-6)-linked fucose in the N-glycan

In this report, we describe a new lectin from the fungus Rhizopus stolonifer that agglutinates rabbit red blood cells. Agglutinating activity was detected in the extract of mycelium-forming spores cultured on agar plates but not in the mycelium-forming no spores from liquid medium. This lectin, which we designated R. stolonifer lectin (RSL), was isolated by affinity chromatography with porcine stomach mucin-Sepharose. SDS-polyacrylamide gel electrophoresis and mass spectral analysis showed that RSL is approximately 4.5 kDa, whereas gel filtration indicated a mass of 28 kDa. This indicates that the lectin is a hexamer of noncovalently associated RSL monomers. RSL activity was very stable, since it was insensitive to heat treatment at 70 degrees C for 10 min. Analysis of RSL binding specificity by both microtiter plate and precipitation assays showed that N-glycans with l-fucose linked to the reducing terminal GlcNAc residues are the most potent inhibitors of RSL binding, whereas N-glycans without alpha(1-6)-linked fucose residues are approximately 100-fold weaker inhibitors of binding. Oligosaccharides with alpha(1-2, -3, and -4) linkages showed no inhibition of binding in these assays. In a mirror resonance biosensor assay, high affinity binding was observed between RSL and the glycopeptide of bovine gamma-globulin, which has N-glycans with alpha(1-6)-linked fucose residues. However, RSL showed only a weak interaction with the glycopeptide of quail ovomucoid, which lacks fucose residues. Finally, capillary affinity electrophoresis studies indicated that RSL binds strongly to N-glycans with alpha(1-6)-linked fucose residues. Together, these results show that RSL recognizes the core structure of N-glycans with alpha(1-6)-linked l-fucose residues. This specificity could make RSL a valuable tool for glycobiological studies.

HPLC of oligosaccharides in glycobiology

Carbohydrate chains of glycoproteins are extremely varied and are a wide variety of different biological processes. Determination of their structures is therefore of great interest in both research and clinical fields. HPLC has proved to be the ideal tool for mono- and oligosaccharide purification and analysis. A wide range of adsorbent and solvent systems are available and we describe in this mini-review the main methods used for the separation and detection of oligosaccharides.

The biosynthesis of highly branched N-glycans: studies on the sequential pathway and functional role of N-acetylglucosaminyltransferases I, II, III, IV, V and VI

At least 6 N-acetylglucosaminyltransferases (GlcNAc-T I, II, III, IV, V and VI) are involved in initiating the synthesis of the various branches found in complex asparagine-linked oligosaccharides (N-glycans), as indicated below: GlcNAc beta 1-6 GlcNAc-T V GlcNAc beta 1-4 GlcNAc-T VI GlcNAc beta 1-2Man alpha 1-6 GlcNAc-T II GlcNAc beta 1-4Man beta 1-4-R GlcNAc T III GlcNAc beta 1-4Man alpha 1-3 GlcNAc-T IV GlcNAc beta 1-2 GlcNAc-T I where R is GlcNAc beta 1-4(+/- Fuc alpha 1-6)GlcNAcAsn-X. HPLC was used to study the substrate specificities of these GlcNAc-T and the sequential pathways involved in the biosynthesis of highly branched N-glycans in hen oviduct (I. Brockhausen, J.P. Carver and H. Schachter (1988) Biochem. Cell Biol. 66, 1134-1151). The following sequential rules have been established: GlcNAc-T I must act before GlcNAc-T II, III and IV; GlcNAc-T II, IV and V cannot act after GlcNAc-T III, i.e., on bisected substrates; GlcNAc-T VI can act on both bisected and non-bisected substrates; both Glc-NAc-T I and II must act before GlcNAc-T V and VI; GlcNAc-T V cannot act after GlcNAc-T VI. GlcNAc-T V is the only enzyme among the 6 transferases cited above which can be essayed in the absence of Mn2+. In studies on the possible functional role of N-glycan branching, we have measured GlcNAc-T III in pre-neoplastic rat liver nodules (S. Narasimhan, H. Schachter and S. Rajalakshmi (1988) J. Biol. Chem. 263, 1273-1281). The nodules were initiated by administration of a single dose of carcinogen 1,2-dimethyl-hydrazine.2 HCl 18 h after partial hepatectomy and promoted by feeding a diet supplemented with 1% orotic acid for 32-40 weeks. The nodules had significant GlcNAc-T III activity (1.2-2.2 nmol/h/mg), whereas the surrounding liver, regenerating liver 24 h after partial hepatectomy and control liver from normal rats had negligible activity (0.02-0.03 nmol/h/mg). These results suggest that GlcNAc-T III is induced at the pre-neoplastic stage in liver carcinogenesis and are consistent with the reported presence of bisecting GlcNAc residues in N-glycans from rat and human hepatoma gamma-glutamyl transpeptidase and their absence in enzyme from normal liver of rats and humans (A. Kobata and K. Yamashita (1984) Pure Appl. Chem. 56, 821-832).

Microheterogeneity and structures of neutral glycans present in quail ovomucoid

Anionic chromatography of oligosaccharide-alditols obtained by alkaline hydrolysis of quail ovomucoid glycopeptides resulted in the isolation of a major neutral fraction (83%) which was separated into 14 fractions by high-performance liquid chromatography on an alkylamine silica column. The structures of nine oligosaccharide-alditols were determined. By the identification of mannobiosido-, and mannotriosido-di-N-acetylchitobiose mixed with N-acetyl-lactosaminic and oligomannosidic-types oligosaccharides, we demonstrate the high microheterogeneity of the glycans presents in the neutral fraction of this glycoprotein and suggest that ovomucoid glycosylation uses several pathways.

A solid phase assay for galactosyl transferases. Evidence for an active site of less than 14 kDa

Galactosyltransferase (GalTase) prepared from human milk was found to exist as a complex with alpha-lactalbumin as demonstrated by crossed immunoelectrophoresis against specific antibodies raised against the complex. GalTase activity was stable to proteolysis and, when subjected to gel filtration on Ultrogel AcA54, the enzyme activity eluted as a single peak. A second peak of activity was found to be adsorbed to the column matrix and was eluted with buffer containing 1 M NaCl. The hydrophobic fraction represented 5% of the total GalTase activity in human milk. After polyacrylamide gel electrophoresis the main enzyme activity peak was represented by polypeptides of 67 kDa molecular weight and of 14 kDa molecular weight. Electroblotting of these peptides onto a nitrocellulose membrane followed by determination of GalTase activity showed activity for 45-55 kDa and for 14 kDa peptides. The hydrophobic fraction from the AcA54 column was resolved into polypeptides of 110 kDa-45 kDa molecular weight, all of which contained GalTase activity after blotting. It is supposed that the GalTase from non-proteolyzed milk is composed of a 14 kDa polypeptide containing the active site together with another part of the polypeptide backbone which is involved in the regulation of GalTase activity by alpha-lactalbumin, a third part of the polypeptide is responsible for the membrane insertion.

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.

A convenient method for methylation of glycoprotein glycans in small amounts by using lithium methylsulfinyl carbanion

Treatment of dimethyl sulfoxide with butyllithium leads to rapid formation of lithium methylsulfinyl carbanion. The reaction products tend to be significantly freer from impurities when lithium methylsulfinyl carbanion is used rather than sodium or potassium methylsulfinyl carbanion. This reagent gives less background in g.l.c. and thus may be used to methylate micro-quantities of glycoprotein glycans (down to 10 micrograms) without the necessity of identifying methyl ethers by mass spectrometry.

High-pressure liquid chromatography of neutral oligosaccharides: effects of structural parameters

Sixty-five neutral oligosaccharides were analyzed by high-pressure liquid chromatography on an amine-modified silica column (Lichrosorb-NH2). By systematic comparison of the retention times, it was possible to attribute chromatographic behavior to specific structural features. It appeared that retention times increase with the number of sugar residues. The presence of a fucose or an N-acetylglucosamine residue results in a decreased retention time, in particular when the latter sugar is at the reducing end. A dramatic increase in retention time is shown by oligosaccharides having a 1----6 linkage, regardless of whether this linkage is involved in a branch. Less important features are the nature of the component sugars other than N-acetylglucosamine and fucose, the anomeric configuration of the sugars, and the presence of a reduced terminal sugar.

Separation of sialyl-oligosaccharides by high-performance liquid chromatography. Application to analysis of carbohydrate units of acidic oligosaccharides obtained by hydrazinolysis of hen ovomucoid

Sialyl- oligossacharides derived from hen ovomucoid by hydrazinolysis have been separated by liquid chromatography on quaternary amine bonded silica and alkylamine modified silicas . By using a mobile phase consisting of a mixture of acetonitrile and potassium dihydrogen phosphate with 0.01% of 1,4- diaminobutane , effective resolution of high-molecular-weight monosialylated oligossacharides was achieved in less than 2 h.

Carbohydrate structures of hen ovomucoid. A mass spectrometric analysis

The apparently homogenous N-glycosidically-linked glycans 1, 7, 11 and 14 released by hydrazinolysis from hen ovomucoid were analysed by fast atom bombardment and electron-impact mass spectrometry after reduction and permethylation. The spectra support the primary structures established independently [FEBS Letters (1983) 152, 145-152] using methylation analysis, partial acid hydrolysis and 500 MHz 1H NMR spectroscopy. In addition to the major constituents present in fractions 1, 7, 11 and 14, four minor components not detected by other methods could be characterized with the aid of the mass spectrometry data as: Man2GlcNAcGlcNAc-o1, GlcNAc4Man3GlcNAc-o1, GlcNAc6Man3GlcNAc-o1 and GalGlcNAc6-Man3GlcNAc-o1. Our results show that the physical techniques used provide valuable data on the structure of complex glycans. In addition they can be employed to ascertain the homogeneity of the compounds examined as well as to detect trace amounts of homologs that might not be noticed by other methods.

Primary structure of a novel N-glycosidic carbohydrate unit, derived from hen ovomucoid. A 500-MHz 1H-NMR study

The N-glycosidic carbohydrate chains of hen beta-ovomucoid were released from the protein by hydrazinolysis, and separated by HPLC. Primary structural analysis of 3 major fractions was conducted by applying 500-MHz 1H-NMR spectroscopy in combination with methylation analysis. One of the fractions investigated appeared to consist of an intersected penta-antennary structure extended with one Gal residue. The location of the latter in a certain branch could be established unambiguously by NMR. This structure is a novel member of the family of N-glycosidic carbohydrates of glycoproteins.