Structure and biosynthesis gene cluster of the O-antigen of Escherichia coli O12

Abstract

Two polysaccharides were isolated from Escherichia coli O12, the major being identified as the O12-antigen and the minor as the K5-antigen. The polysaccharides were studied by sugar analysis, Smith degradation, and one- and twodimensional ¹H and ¹³C NMR spectroscopy. As a result, the following structure of the O12-polysaccharide was elucidated, which, to our knowledge, has not been hitherto found in bacterial carbohydrates: →2)-β-D-Glcp-(1→6)-α-D-GlcpNAc(1→3)-α-L-FucpNAc-(1→3)-β-D-GlcpNAc-(1→. The →4)-β-D-GlcpA-(1→4)-α-D-GlcpNAc-(1→ structure established for the K5-polysaccharide (heparosan) is previously known. Functions of genes in the O-antigen biosynthesis gene cluster of E. coli O12 were assigned by comparison with sequences in the available databases and found to be consistent with the O12-polysaccharide structure.