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Prebiotic isomaltooligosaccharide preparations contain α-D-glucooligosaccharides comprising isomaltooligosaccharides (IMOs) and non-prebiotic maltooligosaccharides (MOs). They are both glucose oligosaccharides characterized by their degree of polymerization (DP) value (from 2 to ∼10), linkages types and positions (IMOs: α-(1→2, 3, 6 and in a lower proportion internal 1→4) linkages, MOs: α-(1→4) linkages). Their structure is the key factor for their prebiotic potential. In order to determine and elucidate the exact structure of unknown IMOs and MOs, unambiguous assignments of 13 C and 1 H chemical shifts of commercial standards, representative of IMOs and MOs diversity, have been determined using optimized standard one and two-dimensional experiments such as 1 H NMR, 13 C NMR, APT and 1 H- 1 H COSY, TOCSY, NOESY and 1 H- 13 C heteronuclear HSQC, HSQC-TOCSY, and HMBC. Here we point out the differential effect of substitution by a glucose residue at different positions on chemical shifts of anomeric as well as ring carbons together with the effect of the reducing end configuration for low DP oligosaccharides and diasteroisotopic effect for H-6 protons. From this study, structural 13 C specific spectral features can be identified as tools for structural analysis of isomaltooligosaccharides.

Background In V. cholerae, the biogenesis of capsule polysaccharide is poorly understood. The elucidation of capsule structure and biogenesis is critical to understanding the evolution of surface polysaccharide and the internal relationship between the capsule and LPS in this species. V. cholerae serogroup O31 NRT36S, a human pathogen that produces a heat-stable enterotoxin (NAG-ST), is encapsulated. Here, we report the covalent structure and studies of the biogenesis of the capsule in V. cholerae NRT36S. Results The structure of the capsular (CPS) polysaccharide was determined by high resolution NMR spectroscopy and shown to be a complex structure with four residues in the repeating subunit. The gene cluster of capsule biogenesis was identified by transposon mutagenesis combined with whole genome sequencing data (GenBank accession DQ915177). The capsule gene cluster shared the same genetic locus as that of the O-antigen of lipopolysaccharide (LPS) biogenesis gene cluster. Other than V. cholerae O139, this is the first V. cholerae CPS for which a structure has been fully elucidated and the genetic locus responsible for biosynthesis identified. Conclusion The co-location of CPS and LPS biosynthesis genes was unexpected, and would provide a mechanism for simultaneous emergence of new O and K antigens in a single strain. This, in turn, may be a key element for V. cholerae to evolve new strains that can escape immunologic detection by host populations.