Conformational analysis of two xylose-containing N-glycans in aqueous solution by using 1H NMR ROESY and NOESY spectroscopy in combination with MD simulations

The conformational behavior of the synthetic hexa- and heptasaccharide methyl P-glycosides alpha-D-Manp-(1 --> 6)-[alpha-D-Manp(1 --> 3)-][beta-D-Xylp-(1 --> 2)-]beta-D-Manp-(1 --> 4)-beta-D-GlepNAc-(1 --> 4)-beta-D-GlcpNAc-(1 --> OMe and alpha-D-Manp-(1 --> 6)-[alpha-D-Manp(1 --> 3)-][beta-D-Xylp-(1 --> 2)-]beta-D-Manp-(1 --> 4)-beta-D-GlcpNAc-(1 --> 4)-[alpha-L-Fucp-(1 --> 6)-]beta-D-GlcpNAc-(1 --> OMe, representing the xylosylated and the xylosylated alpha-(1 --> 6)-fucosylated core structures of N-glycans in alpha(D)-hemocyanin of the snail Helix pomatia, respectively, were investigated by H-1 NMR spectroscopy in combination with molecular dynamics (MD) simulations in water. H-1 and C-13 chemical shifts of the oligosaccharides were assigned using H-1-H-1 COSY, TOCSY, and NOESY, and H-1-C-13 HMQC techniques. Experimental 2D H-1 cross-peak intensities from one series of NOESY and one series of ROESY experiments of the two oligosaccharides were compared with calculated values derived from MD trajectories using the CROSPEL program. yielding information about the conformation of each glycosidic linkage of the methyl glycosides. The flexibility of the linkages was described by generalized order parameters and internal rotation correlation times. Analysis of the data indicated that several conformations are likely to exist for the alpha-D-Man-(1 --> 6)-beta-D-Man. the alpha-L-Fuc-(1 --> 6)-beta-D-GlcNAc, and the alpha-D-Man-(1 --> 3)-beta-D-Man linkage, whereas the beta-D-Xyl-(1 --> 2)-beta-D-Man-(1 --> 4)-beta-D-GleNAc-(1 --> 4)-beta-D-GlcNAc fragment occurs in one rigid conformation. No significant differences were found between the corresponding structural elements in both methyl glycosides. NOESY and ROESY experiments proved to be suitable for providing the experimental data required, however, due to more overlap within the ROESY spectra. reducing the accuracy of the analysis, NOESY spectral analysis is preferred. (C) 2002 Elsevier Science Ltd. All rights reserved.