Nature and location of amide-bound (R)-3-acyloxyacyl groups in lipid A of lipopolysaccharides from various gram-negative bacteria.

It has previously been demonstrated [Eur. J. Biochem. 124, 191-198 (1982) and 137, 15-22 (1983)] that the lipid A component of Salmonella and Proteus lipopolysaccharides contains amide-linked (R)-3-acyloxyacyl residues. In the present study lipid A of other gram-negative bacteria was analysed for the presence of amide-bound 3-acyloxyacyl residues. It was found that such residues are constituents of all lipid A tested (Agrobacterium tumefaciens, Chromobacterium violaceum, Pseudomonas aeruginosa, Xanthomonas sinensis, Bacteroides fragilis, Vibrio cholerae, Fusobacterium nucleatum, Rhodospirillum tenue, Acinetobacter calcoaceticus, and Escherichia coli). Amide-linked (R)-3-acyloxyacyl groups, therefore, represent common and ubiquitous structural elements of bacterial lipid A. The composition of 3-acyloxyacyl groups differed considerably among different bacteria. As amide-bound (R)-3-hydroxy fatty acids straight chain and isobranched acyl groups with 10-17 carbon atoms were identified. The most frequently encountered fatty acids, substituting the 3-hydroxyl group of 3-hydroxy fatty acids, were nonhydroxylated straight chain and isobranched acyl residues with 10-17 carbon atoms as well as (S)-2-hydroxy fatty acids with 12 carbon atoms. In some cases, using laser desorption mass spectrometry, the distribution of 3-acyloxyacyl residues over the two available glucosamine amino groups of the lipid A backbone was investigated.