Structural investigations on the core polysaccharide of Escherichia coli 0100.

In order to investigate the core structure of the lipopolysaccharide from an Escherichia coli 0100 strain, two derivatives were prepared from this strain by introducing genetic material from Salmonella abony. One, an SR hybrid, contained a lipopolysaccharide with short side chains consisting of simple repeating units of Salmonella group B specificity attached to the E. coli core. The other, an R form, contained only the E. coli core and no O side chains, due to a mutation in the Salmonella rfb chromosomal region, which determines the synthesis of the O repeating units. By partial acid hydrolysis of the SR and R lipopolysaccharides, oligosaccharide fragments were obtained which made it possible to reconstruct the hexose region of the core (see formula below). Methylation studies performed on the dephosphorylated polysaccharides confirmed and extended these results. It was found that only about 60% of the distal glucose units of the core chains were substituted by N-acetylglucosamine residues. Further, the heptose region was shown to form a branched trisaccharide. On mild acid hydrolysis of both lipopolysaccharide preparations a Gal-α1,7(8)-KDO disaccharide was formed, indicating that a galactose unit is linked to the 2-keto-3-deoxyoctonate (KDO) portion of the lipopolysaccharide. After Smith degradation of the SR lipopolysaccharide, the oligosaccharide Gal-β1,4-Glc-glycerol was identified which derived from the linkage region between the Salmonella type repeating unit and the E. coli core. Only the core stubs substituted by N-acetylglucosamine residues carried an O-specific unit. On the basis of the these findings the partial structure of the E. coli 0100 core polysaccharide with a Salmonella group B-specific unit attached to it is proposed as given below. The relationships to core structures identified in lipopolysaccharides of other representatives of Enterobacteriaceae are discussed.