Chemical structure of the lipid A component of the lipopolysaccharide from a Proteus mirabilis Re-mutant.

The chemical structure of the lipid A component from the lipopolysaccharide of a Proteus mirabilis Re-mutant (strain R45) was analysed. It consists of a beta(1-6)-linked D-glucosamine disaccharide which carries two phosphate groups, one being ester-linked to position 4' of the nonreducing glucosaminyl residue and the other being bound to the glycosidic hydroxyl group of the reducing glucosaminyl residue. The ester-bound phosphate group is quantitatively substituted by a 4-amino-4-deoxy-L-arabinopyranosyl residue, the glycosidic phosphoryl group appears to be unsubstituted. Two available hydroxyl groups of the disaccharadide (probably at positions 3 and 3') are acylated by approximately 1 mol each of (R)-3-tetradecanoyloxytetradecanoic and (R)-3-hydroxytetradecanoic acid/mol. The amino group of the nonreducing glucosaminyl residue carries (R)-3-tetradecanoyloxytetradecanoic and that of the reducing residue (R)-3-hydroxytetradecanoic acid. In addition smaller amounts of (R)-3-hexadecanoyloxytetradecanoic acid are present in amide linkage. The attachment site of the oligosaccharide portion to lipid A was also investigated. It was found that the hydroxyl group at position 6' of the nonreducing glucosaminyl residue carries 3-deoxy-D-manno-octulosonic acid. This indicates that the saccharide portion in this Proteus lipopolysaccharide is linked to lipid A via the primary hydroxyl group in position 6'.