STRUCTURE OF THE CAPSULAR ANTIGEN OF ESCHERICHIA-COLI 08-K50-H

The primary structure of the acidic capsular antigen of Escherichia co li O8:K50:H- was shown by glycose analysis, methylation analysis, and one- and two-dimensional H-1 and C-13 NMR spectroscopy to be composed of repeating linear tetrasaccharide units having the structure: [GRAPH ICS] cetamido-4,6-dideoxy-D-galactose (Fuc4NAc), and 2-amino-2-deoxy-D -glucose which is partially N- and partially 6-O-acetylated. The struc ture of the trisaccharide repeating unit was established by analyses o f LMP and the completely N-acetylated LMP (LMP-NAc) using H-1 and C-13 NMR spectroscopy, including 2D COSY and 1D NOE spectroscopy. Deaminat ion of LMP with nitrous acid gave a set of oligomers terminated with 2 ,5-anhydromannose and ranging from tri- to dodeca-saccharides, thus in dicating a random distribution of free amino groups. FABMS analyses of LMP and LMP-NAc showed that LMP consists mainly of the cyclic tetrame r of the trisaccharide repeating unit together with a small amount of the cyclic trimer and a very small amount of the cyclic pentamer and h as, thus, the following structure: [GRAPHICS] where R is Ac or H (simi lar to 1:1), R' is Ac or H(similar to 1:4), and n = 4 (major), 3, 5 (m inor). Small proportions of the linear trimer and the linear tetramer were also detected in the preparations. The high molecular weight poly saccharide is linear and has the same (or a very similar) repeating un it as LMP.