The structure of the sialic acid-containing Escherichia coli O104 O-specific polysaccharide and its linkage to the core region in lipopolysaccharide.

Mild acid hydrolysis of Escherichia coli O104 lipopolysaccharide released an O-specific polysaccharide, a tetrasaccharide repeating unit, the corresponding dimer, and a disaccharide fragment of the repeating unit. Complete and incomplete cores, and oligosaccharides comprising fragments of the repeating unit and the core region, were also obtained. On the basis of sugar and methylation analysis, FAB-mass spectrometry and NMR spectroscopy of the hydrolysis products, the repeating unit of the O-specific polysaccharide was shown to be the tetrasaccharide:-->4)-alpha-D-Galp-(1-->4)-alpha-Neup5,7,9Ac3++ +-(2-->3)-beta-D- Galp-(1-->3)-beta-D-GalpNAc (1-->. The linkage between the O-specific polysaccharide chain and the core region, which appeared to be of the R2 type, was established. These results indicate that N-acetylneuraminic acid, located in the O-specific polysaccharide, is an inherent lipopolysaccharide component.