Structural studies and biosynthetic aspects of the O-antigen polysaccharide from Escherichia coli O174

The structure of the repeating unit of the O-antigenic polysaccharide (PS) from Escherichia coli O174 has been determined. Component analysis together with 1H and 13C NMR spectroscopy experiments were employed to elucidate the structure. Inter-residue correlations were determined by 1H,13C-heteronuclear multiple-bond correlation and 1H,1H-NOESY experiments. The PS is composed of tetrasaccharide repeating units with the following structure:Cross-peaks of low intensity were present in the NMR spectra consistent with a β-d-GlcpNAc-(1→2)-β-d-GlcpA(1→ structural element at the terminal part of the polysaccharide, which on average is composed of ∼15 repeating units. Consequently the biological repeating unit has a 3-substituted N-acetyl-d-galactosamine residue at its reducing end.