Characterisation of minor tetra- to hepta-saccharides O-linked to human meconium glycoproteins by t.l.c.-m.s. microsequencing of neoglycolipid derivatives in conjunction with conventional m.s. and 1H-n.m.r. spectroscopy

Structure and Immune Recognition of the HIV Glycan Shield

Vaccine design efforts against the human immunodeficiency virus (HIV) have been greatly stimulated by the observation that many infected patients eventually develop highly potent broadly neutralizing antibodies (bnAbs). Importantly, these bnAbs have evolved to recognize not only the two protein components of the viral envelope protein (Env) but also the numerous glycans that form a protective barrier on the Env protein. Because Env is heavily glycosylated compared to host glycoproteins, the glycans have become targets for the antibody response. Therefore, considerable efforts have been made in developing and validating biophysical methods to elucidate the complex structure of the Env-spike glycoprotein, with its combination of glycan and protein epitopes. We illustrate here how the application of robust biophysical methods has transformed our understanding of the structure and function of the HIV Env spike and stimulated innovation in vaccine design strategies that takes into account the essential glycan components.

On-line overpressure thin-layer chromatographic separation and electrospray mass spectrometric detection of glycolipids

On-line thin-layer chromatographic separation and electrospray mass spectrometry (TLC/ESI-MS) has been accomplished by direct linking of a commercial overpressure TLC instrument, OPLC 50, and a Q-TOF mass spectrometer. Mass spectrometric detection sensitivity and chromatographic resolution achieved by this configuration were assessed using acidic glycolipids as examples. Under the optimized conditions, a sensitivity of 5 pmol of glycosphingolipid was readily demonstrated for TLC/ESI-MS and 20 pmol for TLC/ESI-MS/MS production scanning to derive the saccharide sequence and long chain base/fatty acid composition of the ceramide. Initial preconditioning of TLC plates is necessary to achieve high sensitivity detection by reducing chemical background noise. Plates can be used repeatedly (at least 10 times) for analysis, although this may result in a minor reduction in TLC resolution. Following solvent development, separated components on the TLC plates can be detected in the conventional way by nondestructive staining or UV absorption or fluorescence and can be stored for on-line TLC/ESI-MS analysis at a later stage without reduction in mass spectrometric detection sensitivity and chromatographic resolution. Aspects for further improvement of OPLC instrumentation include use of narrower TLC plate dimensions and refined design of the eluate exit system.

Core-branching pattern and sequence analysis of mannitol-terminating oligosaccharides by neoglycolipid technology

The occurrence of mannitol-terminating oligosaccharides (2-substituted or 2,6-disubstituted) among the O-glycans released by alkaline borohydride treatment from glycoproteins of the nervous system has prompted the development of a microscale method to analyze the core-branching pattern and sequence by the neoglycolipid (NGL) technology, analogous to a method previously described for GalNAcol-terminating oligosaccharides (M. S. Stoll, E. F. Hounsell, A. M. Lawson, W. Chai, and T. Feizi, Eur. J. Biochem. 189, 499-507, 1990). The approach involves the selective cleavage at the core mannitol by mild periodate treatment and analysis of the reaction products as NGLs by in situ TLC/liquid secondary ion mass spectrometry. Oxidation conditions have been optimized using as reference compounds 2-, 3-, 4-, or 6-monosubstituted mannobi-itols, 3,6-disubstituted mannitol-terminating pentasaccharides, and 2-mono- and 2,6-disubstituted mannitol-terminating neutral and sialylated oligosaccharides isolated from brain glycopeptides. When a 2:1 molar ratio of periodate to alditol is used, the core mannitol is cleaved at the C3-C4 threo-diol bond and in the absence of a threo-diol cleavage occurs to a lesser extent at erythro-diols. Saccharide ring diols are not cleaved under these conditions, and it is also shown that the side chain of sialic acid on the oligosaccharide is largely unaffected. Substituents at 2- and 6-positions of the core mannitol can be identified, and the method is applicable to neutral and sialylated oligosaccharide alditols. Typically, the starting material is 5 nmol of oligosaccharide and 0.5-1 nmol of derivatives is applied for analysis. By this strategy, the core-branching pattern and position of sialic acid of two branched monosialylated mannitol-terminating oligosaccharide isomers have been determined.

Second Jenner international glycoimmunology meeting

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Neutral oligosaccharides of bovine submaxillary mucin. A combined mass spectrometry and 1H-NMR study

Twenty-two neutral O-linked oligosaccharides ranging from monosaccharides to octasaccharides were identified in bovine submaxillary-gland-mucin glycoprotein by a combination of liquid secondary-ion mass spectrometry, methylation analysis and 1H-NMR. Only five of these have been previously detected in bovine submaxillary-gland mucin although several have been described from other sources of mucin. The structures include short linear sequences 3-linked to N-acetylgalactosaminitol (GalNAcol) and branched structures based on either a GlcNAc(beta 1-6) [Gal(beta 1-3)]GalNAcol or GlcNAc(beta 1-6)[GlcNAc(beta 1-3)]GalNAcol core region. Oligosaccharides not previously characterised from any source were the disaccharide GalNAc alpha 1-6GalNAcol (GalNAc, N-acetylgalactosamine and the hexasaccharide GlcNAc(beta 1-6) [GalNAc(alpha 1-3)( Fuc (alpha 1-2)]Gal(beta 1-4)GlcNAc(beta 1-3)]GalNAcol (Fuc, L-fucose). Oligosaccharides of the blood-group-A type have not been detected previously in bovine submaxillary-gland mucin although their occurrence on bovine gastric-mucosal glycoproteins has been established by classical immunochemical studies.