Structure and characterization of the gene cluster of the O-antigen of Escherichia coli O49 containing 4,6-dideoxy-4-[(S-3-hydroxybutanoylamino]-D-glucose

An O-polysaccharide was isolated by mild acid degradation of the lipopolysaccharide of enteropathogenic 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: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \to 2) - \alpha - D - Quip4N(S3HOBut) - (1 \to 4) - \beta - D - GalpNAc - (1 \to 4) - \alpha - L - Rhap - (1 \to 3) - \beta - D - GlcpNAc6Ac - (1 \to , $$\end{document} 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.