STRUCTURAL STUDIES ON THE SHIGELLA-LIKE ESCHERICHIA-COLI O121 O-SPECIFIC POLYSACCHARIDE

The O-specific polysaccharide isolated from the lipopolysaccharide (LP S) of Escherichia coli O121 by mild acid hydrolysis has been studied u sing mainly NMR spectroscopy. The polysaccharide was treated with mild base to yield a O-deacetylated polysaccharide which contained D-GlcNA c, D-GalNAcA, D-GalNAcAN (2-acetamido-2-deoxy-D-galacturonamide) and D -Qui4NAcGly (where D-Qui4N is 4-amino-4,6-dideoxy-D-glucose) in equimo lar proportions. The presence of the amide was confirmed by recording the H-1 NMR spectrum of the O-deacetylated polysaccharide at different pH values. The O-acetyl group was located on O-3 of the GalNAcAN and the structure of the polysaccharide can be written as [GRAPHICS] This structure is almost identical to that previously reported for the O-sp ecific polysaccharide of Shigella dysenterine type 7 LPS, the only dif ference being that O-acetylation is stoichiometric in the latter. (C) 1997 Elsevier Science Ltd.