The cell-wall lipopolysaccharide of Escherichia coli K-12. Structure and acceptor site for O-antigen and other substituents.

The lipopolysaccharides of two wild-type Escherichia coli K-12 strains, two core-deficient mutants and one SR recombinant with Salmonella typhimurium specificity were analyzed. The respective oligosaccharides were dephosphorylated and methylated. Chemical analysis of the oligosaccharides and mass spectrometric analysis of their methylated derivatives indicated the presence of core structures with different degrees of completion. In different strains of E. coli K-12 the complete core is substituted at the non-reducing end with N-acetylglucosamine or with another substituent. There are indications that the latter may be N-acetylmannosaminuronic acid. In the SR recombinant the complete (N-acetylglucosamine-free) K-12 core is substituted with one S-specific oligosaccharide of S. typhimurium. The attachment site for all these substituents is the 6-position of the non-reducing core-terminal glucose. The heterogeneity of the K-12 core preparations and mode and nature of their substitution are discussed.