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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Multidimensional and heteronuclear NMR investigations of oligosaccharides in the free and protein bound states

Milton, Mark John January 1997 (has links)
The three dimensional structure and dynamics of three biologically important oligosaccharides were probed using a range of NMR techniques. The solution structure of oligosaccharide moiety of was solved using conventional 1H - 1H ROESY data in conjunction with molecular dynamics simulations. It was evident from this study that the dominant conformation in free solution is similar to the structure of oligo-GM1 in complex with the B-subunit of the enteropathogenic cholera toxin. The solution dynamics of an analogue of globoside (Gb4-OEtTMS), a cellular receptor for an E. coli verotoxin, was also elucidated using conventional 1H - 1H ROESY data. However, it was not clear that these data alone could adequately model the structure. Additional distance restraints were derived from 1H - 1H NOE contacts between exchangeable and non-exchangeable protons measured in H2O/acetone-d6 solutions at low temperature (-15 °C). It was concluded on the basis of these studies that Gb4-OEtTMS is an extremely flexible sugar, however, the time- averaged conformation was similar to the proposed conformation of Gb4 in complex with a verotoxin (VT2e). In order to increase the structural information which may be measured from NMR spectroscopy, carbon-13 enriched carbohydrate moieties, commonly found in glycolipids and glycoproteins, were synthesised. Isotopically labelled N-acetyl neuraminic acid, a2,3 sialyl N-acetyl lactosamine (required for the synthesis of sialyl Lewis antigen) and a2,3 sialyl lactose (oligo-GM3), the core ganglioside which is required for the synthesis of more complex gangliosides (e.g. GM1), was accomplished using a mixture of enzymatic and synthetic methods. To test the applicability of heteronuclear NMR spectroscopy in the study of oligosaccharides, the solution structure and dynamics of [U-13C] oligo- GM3 was probed by recording three dimensional 13C-edited ROESY spectra, and long-range carbon-carbon and carbon-proton spin-coupling constants. Inter-residue ROEs could be unambiguously assigned from the 3D experiment, and these assignments contradict previous inter-residue ROE contacts published in the literature (based only on homonuclear data). Two additional inter-residue ROE contacts could be measured across the Gaibeta1-4Glc linkage. The solution conformation of [U-13C] oligo-GM3 in complex with wheat germ agglutinin was solved on the basis of 3D TRNOESY-HSQC data. Theoretical TRNOE intensities back-calculated from full relaxation matrix calculations performed on the X-ray crystal structures of the complex were consistent with experimentally measured values and confirmed the flexible nature of the Galbeta1-4Glc linkage when bound to the protein. Finally, carbon-13 enriched N-acetyl neuraminic acid and galactose were introduced into the glycan chains of an intact glycoprotein FcREA. 13C-1H HSQC data suggest that the two arms of the biantennary glycan experience two distinct magnetic environments.

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