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

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Abstract
The lipid A component of Salmonella and Proteus lipopolysaccharides contains amide-linked (R)-3-acyloxyacyl residues. Lipid A of other gram-negative bacteria was analyzed for the presence of amide-bound 3-acyloxyacyl residues. 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-acyloxacyl 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 C 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 C atoms as well as (S)-2-hydroxy fatty acids with 12 C atoms. In some cases, using laser desorption mass spectrometry, the distribution of 3-acyloxyacyl residues over the 2 available glucosamine amino groups of the lipid A backbone was investigated.