Structural and genetic characterization of the O-antigen of Escherichia coli O161 containing a derivative of a higher acidic diamino sugar, legionaminic acid.

The O-antigen is an essential component of lipopolysaccharide on the surface of Gram-negative bacteria and plays an important role in its pathogenicity. Composition and structure of the O-antigens of Escherichia coli are highly diverse mainly due to genetic variations in the O-antigen gene cluster. In this work, the chemical structure and the gene cluster of the O-antigen of E. coli O161 were studied. Chemical degradations, sugar analyses, and NMR spectroscopy showed that the O161 antigen possesses a trisaccharide O-repeating unit containing a 5-N-acetyl-7-N-(d-alanyl) derivative of 5,7-diamino-3,5,7,9-tetradeoxy-d-glycero-d-galacto-non-2-ulosonic (legionaminic) acid (Leg5Ac7Ala) and having the following structure: The O-antigen gene cluster of E. coli O161 was sequenced. In addition to the genes encoding sugar transferases, O-repeating unit flippase (Wzx) and O-antigen polymerase (Wzy), the genes involved in the biosynthesis of a legionaminic acid derivative were identified based on database similarities.