Conformational differences among mono- and oligosaccharide fragments of the O-specific polysaccharides of Vibrio cholerae O1 revealed by circular dichroism

The circular dichroism (CD) of synthetic mono- and oligosaccharides that re present the terminal, non-reducing group of O-antigens of Vibrio choler ne O1 from the subtypes Ogawa and Inaba was measured in various solvents. We f ound differences in the CD of the monosaccharides of these subtypes that de crease with increasing chain lengths of the oligosaccharides. The differenc es can be explained by different orientations of the N-acyl side chain of t he terminal monosaccharides. The linear relationship of ellipticity versus the number of residues in an oligosaccharide chain follows the principle of optical superposition. This, together with a similar contribution by inter nal units to the overall ellipticity, suggests an identical, regular confor mation of oligosaccharide fragments of both Ogawa and Inaba series. (C) 199 8 Elsevier Science Ltd. All rights reserved.