title: Structural and conformational features of the Escherichia coli K92 capsular polysaccharide.
abstract: Escherichia coli K92 polysaccharide, an alternating (2----8)-alpha- and (2----9)-alpha-linked heteropolymer of sialic acid, undergoes lactonisation (10-20%) at low pH or on treatment with a water-soluble carbodi-imide (greater than 90%). Under the latter conditions, the formation of O-acylisourea is a minor pathway. The antigenicity of the K92 polysaccharide is unaffected by lactonisation of approximately 10% of the residues, but is abolished by lactonisation of approximately 90% of the residues. The unexpected, relative resistance of the K92 polysaccharide to periodate oxidation contrasts with the behaviour of the meningococcal non-O-acetylated (O-Ac-) C polysaccharide, a (2----9)-alpha-linked homopolymer of sialic acid. Two-dimensional 13C-1H-n.m.r. correlation spectroscopy has been used to assign 1H chemical shifts which have aided the interpretation of a resolution-enhanced one-dimensional spectrum. This has led to a determination of conformational features of the K92 polysaccharide in solution. The side-chain adopts a conformation such that H-7 and H-8 are gauche in the (2----8)-alpha-linked residues (1a or 1b), but antiperiplanar in the (2----9)-alpha-linked residues (2). Molecular correlation times have been calculated and some aspects of internal motion elucidated.
mesh_terms: D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D004926:Escherichia coli / Q000276:immunology*; D009682:Magnetic Resonance Spectroscopy; D009345:Neisseria meningitidis / Q000276:immunology; D011135:Polysaccharides, Bacterial; D013045:Species Specificity
chemical_list: D011135:Polysaccharides, Bacterial