Structure and genetics of the O-antigen of Enterobacter cloacae C6285 containing di-N-acetyllegionaminic acid

• Enterobacter cloacae is a pathogen causing various human diseases.
• No systematic structural studies on the OPSs of E. cloacae were performed earlier.
• The OPS structure of E. cloacae C6285 was established.
• The O-antigen gene cluster of E. cloacae C6285 was sequenced and genes were annotated.

On mild acid degradation of the lipopolysaccharide of Enterobacter cloacae C6285, the O-polysaccharide was cleaved at residues of 5,7-diacetamido-3,5,7,9-tetradeoxy-d-glycero-d-galacto-non-2-ulosonic acid (di-N-acetyllegionaminic acid, Leg5Ac7Ac) in the main chain. The resultant oligosaccharide and an alkali-treated lipopolysaccharide were studied by sugar analysis along with 1H and 13C NMR spectroscopy, and the following structure of the tetrasaccharide repeating unit of the linear O-polysaccharide was established:→4)-α-d-Galp-(1→4)-α-Legp5Ac7Ac-(2→3)-β-d-Galp-(1→3)-β-d-GalpNAc-(1→The O-antigen gene cluster of E. cloacae C6285 was sequenced, the gene functions were tentatively assigned by comparison with sequences in the available databases and found to be in agreement with the O-polysaccharide structure.

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