STRUCTURE AND CHARACTERIZATION OF THE GENE CLUSTER OF THE O-ANTIGEN OF <i>Escherichia coli </i>O49 CONTAINING 4,6-DIDEOXY-4-[(<i>S</i>)-3-HYDROXYBUTANOYLAMINO] -D-GLUCOSE
An O-polysaccharide was isolated by mild acid degradation of the lipopolysaccharide of an enteropathogenic bacterium Escherichia coli O49 and studied by sugar analysis along with one- and two-dimensional 1H and 13C NMR spectroscopy. The following structure of the linear tetrasaccharide repeating unit of the O-polysaccharide was established: →2)-α-D-Quip4N(S3HOBut)-(1→4)-β-D-GalpNAc-(1→4)-α-L-Rhap-(1→3)-β-D-GlcpNAc6Ac-(1→, where D-Qui4N(S3HOBut) stands for 4,6-dideoxy-4-[(S)-3-hydroxybutanoylamino]-D-glucose and O-acetylation of GlcNAc is partial (~30%). To our knowledge no N-(3-hydroxybutanoyl) derivative of Qui4N has been hitherto found in bacterial polysaccharides. Gene functions of the O-antigen gene cluster of E. coli O49 were assigned by bioinformatics analysis and found to correspond to the O-polysaccharide structure. Two new genes were revealed and suggested to be responsible for synthesis and transfer of the 3-hydroxybutanoyl group.