Structure of Cell Wall Lipopolysaccharide from Salmonella typhimurium

Lipopolysaccharide of wild type Salmonella typhimurium is believed to contain O side chains, whose reducing terminal sugar, galactose, is linked to the R core. Two oligosaccharides were isolated by periodate oxidation, NaBH4 reduction, and mild acid hydrolysis of such a lipopolysaccharide. They were also isolated from the lipopolysaccharide of a mutant synthesizing very short O side chains each containing only one repeat unit, but not from that of a mutant totally lacking O side chains. The degradation of a lipopolysaccharide, which was synthesized partially in vitro and contained 14C only in the reducing terminal galactose residue of the O side chain, also resulted in the isolation of these two oligosaccharides, labeled with 14C. These results indicate that the oligosaccharides were derived from the linkage region between the O side chain and R core. Moreover, one of the oligosaccharides was identified as O-d-galactosyl-O-d-glucosyl-(1 → 2)-glyceraldehyde; the other appeared to be a cyclic acetal formed from the former oligosaccharide and glycerol. These and other results show that the reducing terminal galactose of O side chains is not linked to the nonreducing terminal sugar of the R core, i.e. N-acetyl-d-glucosamine, but to a glucose residue within the R core, through a 1 → 4 linkage if the sugars are in pyranose forms. This glucose in turn is linked, through a 1 → 2 linkage, to a galactose residue in the R core.