Lipopolysaccharides of Helicobacter pylori serogroups O:3 and O:6--structures of a class of lipopolysaccharides with reference to the location of oligomeric units of D-glycero-alpha-D-manno-heptose residues.

Lipopolysaccharides (LPS) from antigenically different strains assigned to serogroups O:3 and O:6 of Helicobacter pylori were isolated as water-soluble material of high Mr and as water-insoluble gels of low Mr. Chemical and spectroscopic analyses of the soluble LPS and oligosaccharides liberated from the water-insoluble gels led to proposed structures with Lewis (Le) antigen determinants terminating regular repeating units of different types, linked in turn to inner core regions of invariable structure. The O:6 LPS has two populations of related molecules with chains of 3-linked D-glycero-alpha-D-manno-heptose residues similar to those in the MO19 strain, one with and the other without a single terminal Lewis (Le(y)) epitope. In contrast, in the O:3 LPS, Lewis (Le(x) and Le(y)) epitopes terminate a partially fucosylated N-acetyllactosaminoglycan, but a heptan chain similar to that in the O:6 LPS was shown to connect the outer chains to the inner core. These LPS provide examples of the molecular mimicry of cell-surface glycoconjugates. Structural variations of LPS between strains, and differences in some aspects of structure within strains, between high Mr and low Mr LPS indicate a class of LPS whose mechanisms of biosynthesis lead to overall architectures different from those characteristic of most LPS from enteric bacteria.