Structure of the Escherichia coli O24 and O56 O-specific sialic-acid-containing polysaccharides and linkage of these structures to the core region in lipopolysaccharides.

The lipopolysaccharides from Escherichia coli O24 and O56 could be separated into higher-molecular-mass and lower-molecular-mass fractions. Mild acid hydrolysis of lipopolysaccharides of both serotypes released an O-specific polysaccharide and a tetrasaccharide repeating unit. Oligomers of the repeating unit, the core and the oligosaccharide that contains a fragment of the repeating unit linked to the core region were also obtained according to hydrolysis conditions. On the basis of sugar and methylation analyses, Smith degradation, fast-atom-bombardment mass spectrometry and NMR spectroscopy of the hydrolysis products, the biological repeating units of the O-specific polysaccharides were shown to be the following tetrasaccharides: [formula: see text] The structures differ from the structures proposed previously by Kogan et al. [Kogan, G., Shashkov, A. S., Jann, B. & Jann, K. (1993) Carbohydr. Res. 238, 261-270; Kogan, G., Jann, B. & Jann, K. (1993) Carbohydr. Res. 238, 335-338]. The O-specific repeating unit in E. coli O24 lipopolysaccharide is linked to O6 of the terminal D-galactose in the core region, whereas in O56 LPS the repeating unit is linked to O4 of a subterminal D-glucose residue in an R2 type core.