THE LACTOSYLCERAMIDE BINDING-SPECIFICITY OF HELICOBACTER-PYLORI

The possible role of glycosphingolipids as adhesion receptors for the human gastric pathogen Helicobacter pylori was examined by use of radi olabeled bacteria, or protein extracts from the bacterial cell surface , in the thin-laver chromatogram binding assay, Of several binding spe cificities found, the binding to lactosylceramide is described in deta il here, the others being reported elsewhere, By autoradiography a pre ferential binding to lactosylceramide having sphingosine/phytosphingos ine and 2-D hydroxy fatty acids was detected, whereas lactosylceramide having sphingosine and nonhydroxy fatty acids was consistently nonbin ding, A selective binding of H. pylori to lactosylceramide with phytos phingosine and 2-D hydroxy fatty acid was obtained when the different lactosylceramide species were incorporated into liposomes, but only in the presence of cholesterol, suggesting that this selectivity may be present also in vivo, Importantly, lactosylceramide with sphingosine a nd hydroxy fatty acids does not bind in this assay, Furthermore, a lac tosylceramide-based binding pattern obtained for different trisacchari de glycosphingolipids is consistent with the assumption that this sele ctivity is due to binding of a conformation of lactosylceramide in whi ch the oxygen of the 2-D fatty acid hydroxyl group forms a hydrogen bo nd with the Glc hydroxy methyl group, yielding an epitope presentation different from other possible conformers, An alternative conformation that may come into consideration corresponds to the crystal structure found for cerebroside, in which the fatty acid hydroxyl group is free to interact directly with the adhesin, By isolating glycosphingolipid s from epithelial cells of human stomach from seven individuals, a bin ding of H. pylori to the diglycosylceramide region of the non-acid fra ction could be demonstrated in one of these cases, Mass spectrometry s howed that the binding-active sample contained diglycosylceramides wit h phytosphingosine and 2-D hydroxy fatty acids with 16-24 carbon atoms in agreement with the results related above.