Structural and interaction studies of polysaccharides by NMR spectroscopy

Abstract: In this thesis, polysaccharides of different origins have been investigated by NMR spectroscopy with regard to structures and interactions. In paper I, hydrogen bonding interactions in kappa- (κ) and kappa/mu- (κ/μ) hybrid carrageenan oligosaccharides were studied by NMR spectroscopy of hydroxy protons. Weak hydrogen bonding over the 1→4 glycosidic linkage of μ-carrabiose was observed in the κ/μ oligosaccharides. In the hexasaccharide κμκ and octasaccharide κμμκ, one and two hydrogen bonds respectively were found over the 1→4 glycosidic linkage. In the decasaccharide κμμμκ, a loss of a hydrogen bond in the inner μ-unit was observed, suggesting higher flexibility in a μ-unit having other μ-units as neighbors. In papers II and III, the activities and substrate specificities of three new alginate lyases were characterized. The alginate lyase from the marine bacteria Pseudomonas alginovora showed an endo-cleaving activity with a strict specificity for M-block alginates. The AlyA1 lyase from the marine bacteria Zobellia galactanivorans, showed an endo-cleaving activity with a strict specificity for G-block alginates, whereas AlyA5 showed an exo-cleaving activity with a broad substrate tolerance, degrading oligosaccharides down to monosaccharides. Paper IV describes the elucidation of the primary structure of the O-specific polysaccharide and core oligosaccharide from the lipopolysaccharide produced by the Gram-negative bacteria Plesiomonas shigelloides strain CNCTC 92/89 (O24:H8). The O-specific polysaccharide was composed of a tetrasaccharide repeating unit: →3) α FucpNAc-(1→3)-α-GalpNAcA-(1→3)-α-QuipNAc-(1→, with α-RhapNAc linked (1→4) to α-GalpNAcA. The core oligosaccharide was composed of a decasaccharide.