Structures of the O-antigens of Escherichia coli O13, O129, and O135 related to the O-antigens of Shigella flexneri

Abstract

O-Polysaccharides (O-antigens) were isolated from Escherichia coli O13, O129, and O135 and studied by chemical analyses along with 2D (1)H and (13)C NMR spectroscopy. They were found to possess a common -->2)-l-Rha-(alpha1-->2)-l-Rha-(alpha1-->3)-l-Rha-(alpha1-->3)-d-GlcNAc-(beta1--> backbone, which is a characteristic structural motif of the O-polysaccharides of Shigella flexneri types 1-5. In both the bacterial species, the backbone is decorated with lateral glucose residues or/and O-acetyl groups. In E. coli O13, a new site of glycosylation on 3-substituted Rha was revealed and the following O-polysaccharide structure was established: The structure of the E. coli O129 antigen was found to be identical to the O-antigen structure of S. flexneri type 5a specified in this work and that of E. coli O135 to S. flexneri type 4b reported earlier.