Structural and genetic studies of the O-antigen of Escherichia coli O163

An acidic O-polysaccharide (O-antigen) of Escherichia coli O163 was obtained by mild acid hydrolysis of the lipopolysaccharide and studied by sugar analysis and Smith degradation along with 1D and 2D (1)H and (13)C NMR spectroscopy. The following structure of the linear tetrasaccharide repeating unit was established, which is unique among known structures of bacterial polysaccharides: -->2)-β-D-Manp-(1-->4)-β-D-GlcpA-(1-->3)-α-L-QuipNAc-(1-->3)-α-D-GlcpNAc-(1-->. Functions of genes in the O-antigen gene cluster of E. coli O163 were tentatively assigned by comparison with sequences in the available databases and found to be in agreement with the O-polysaccharide structure. Relationships between O-antigen structures and gene clusters of E. coli O163 and Salmonella enterica O41 are discussed.