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Structure and gene cluster of the O-antigen of Escherichia coli O165 containing 5-N-acetyl-7-N-[(R)-3-hydroxybutanoyl]pseudaminic acid.
Upon mild acid degradation of the lipopolysaccharide of Escherichia coli O165, the O-polysaccharide chain was cleaved at the glycosidic linkage of 5-N-acetyl-7-N-[(R)-3-hydroxybutanoyl]pseudaminic acid (Pse5Hb7Ac). Analysis of the resulting linear tetrasaccharide and alkali-treated lipopolysaccharide by (1)H/(13)C 1D and 2D nuclear magnetic resonance spectroscopy enabled elucidation of the following structure of the O-polysaccharide: →8)-α-Psep5Hb7Ac-(2 → 6)-β-d-Galp-(1 → 4)-β-d-Glсp-(1 → 3)-α-d-GlсpNAc-(1→. The β-d-Galp-(1 → 4)-β-d-Glсp-(1 → 3)-d-GlсpNAc structural element is also present in the O-polysaccharide of E. coli O82. The content of the O-antigen gene cluster of E. coli O165 was found to be consistent with the O-polysaccharide structure established. Functions of proteins encoded in the gene cluster, including enzymes involved in the Pse5Hb7Ac biosynthesis and glycosyltransferases, were putatively assigned by comparison with sequences in available databases.
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