Identification of a broad family of lipid A late acyltransferases with non-canonical substrate specificity.

LIPOPOLYSACCHARIDES; LIPIDS; ACYLTRANSFERASES; ORGANIC synthesis; BIOCHEMICAL templates

Most Gram-negative organisms produce lipopolysaccharide ( LPS), a complex macromolecule anchored to the bacterial membrane by the lipid A moiety. Lipid A is synthesized via the Raetz pathway, a conserved nine-step enzymatic process first characterized in E scherichia coli. The Epsilonproteobacterium H elicobacter pylori uses the Raetz pathway to synthesize lipid A; however, only eight of nine enzymes in the pathway have been identified in this organism. Here, we identify the missing acyltransferase, Jhp0255, which transfers a secondary acyl chain to the 3′-linked primary acyl chain of lipid A, an activity similar to that of E . coli LpxM. This enzyme, reannotated as LpxJ due to limited sequence similarity with LpxM, catalyses addition of a C12:0 or C14:0 acyl chain to the 3′-linked primary acyl chain of lipid A, complementing an E . coli LpxM mutant. Enzymatic assays demonstrate that LpxJ and homologues in C ampylobacter jejuni and W olinella succinogenes can act before the 2′ secondary acyltransferase, LpxL, as well as the 3-deoxy- d- manno-octulosonic acid ( Kdo) transferase, KdtA. Ultimately, LpxJ is one member of a large class of acyltransferases found in a diverse range of organisms that lack an E . coli LpxM homologue, suggesting that LpxJ participates in lipid A biosynthesis in place of an LpxM homologue. [ABSTRACT FROM AUTHOR]