THE O-18-ANTIGENS (LIPOPOLYSACCHARIDES) OF ESCHERICHIA-COLI - STRUCTURAL CHARACTERIZATION OF THE O18A-SPECIFIC, O18A1-SPECIFIC, O18B-SPECIFIC AND O18B1-SPECIFIC POLYSACCHARIDES

The 0-specific polysaccharide moieties (PS) of the O18A, O18AI, O18B, and O18B1 antigens (lipopolysaccharides, LPS) consist Of L-rhamnose (Rha), N-acetyl-D-glucosamine, D-galactose, and D-glucose in different molar ratios. By using chemical fragmentation, methylation, as well as one- and two-dimensional NMR spectroscopy, the structures of these polysaccharides were found to be [GRAPHICS] In O18A-PS and O18A1-PS x = 2, whereas in O18B-PS and in O18B11-PS x = 3. In all four polysaccharides alpha-D-Galp (residue D) is substituted at 0-3. This substituent L (residue E) is beta-1-GlcpNAc-(l in O18A-PS and O18A1-PS and it is alpha-D-Glcp-(l in O18B-PS and O18B1-PS. Whereas there is no further substituent on the main chain of the O18A and O18B polysaccharides, in O18A1-PS and O18B1-PS the alpha-D-GlcpNAc residue A is substituted with alpha-Glcp-(l (residue F), which is linked to 0-6 in O18A1-PS and to 0-4 in O18B1-PS. These results show that the 018 antigen comprises a group of four related LPS (O18A and O18B, with their glucosylated forms, O18A1 and O18B1). The results are discussed with respect to epitope definition and biochemical implications.