Structure of the O-polysaccharide of Proteus vulgaris O44: a new O-antigen that contains an amide of d-glucuronic acid with l-alanine

The O-polysaccharide of Proteus vulgaris O44, strain PrK 67/57 was studied by 1H and 13C NMR spectroscopy, including 2D COSY, TOCSY, ROESY, H-detected 1H, 13C HMQC, HMQC–TOCSY and HMBC experiments. The polysaccharide was found to contain an amide of d-glucuronic acid with l-alanine [d-GlcA6(l-Ala)], and the following structure of the linear pentasaccharide repeating unit was established:→4)-β-d-GlcpA6(l-Ala)-(1→3)-β-d-GalpNAc-(1→4)-β-d-Glcp-(1→3)-α-d-Galp-(1→4)-β-d-GalpNAc-(1→.The structural data of the O-polysaccharide and the results of serological studies with P. vulgaris O44 O-antiserum showed that the strain studied is unique among Proteus bacteria, which is in agreement with its classification in a separate Proteus serogroup, O44.