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.

Chemical structures of the core region of Campylobacter jejuni O:3 lipopolysaccharide and an associated polysaccharide.

The complete structure for the core oligosaccharide region of the water-insoluble low-M(r) lipopolysaccharide of Campylobacter jejuni serotype O:3 from phenol/water extraction of bacterial cells was assigned through studies on derivatives of the liberated oligosaccharide. Structure determinations were performed using 1H-NMR and 31P-NMR spectroscopies, methylation analysis supported by fast-atom-bombardment mass spectrometry, and Smith degradation experiments. It was concluded that the complete chains in the core oligosaccharide had the following structure in which a proportion of the terminal residues were phosphorylated: [formula: see text] From a similar series of experiments, it was concluded that an associated polysaccharide, which was isolated from the water phase of the phenol/water extracts, had the following repeating unit in which a proportion of the previously unknown L-glycero-D-ido-heptose (L-alpha-D-ido-Hep) residues were present as 3-hydroxypropanoyl esters, and were not covalently linked to the lipopolysaccharide: [formula see: text]