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UDP-3-O-acyl-glucosamine N-acyltransferase (LpxD): The enzyme catalyzes the transfer of 3-hydroxymyristic acid or 3-hydroxy-arachidic acid, depending on the organism, from the acyl carrier protein (ACP) to UDP-3-O-acyl-glucosamine to produce UDP-2,3-diacyl-GlcNAc. This constitutes the third step in the lipid A biosynthetic pathway in Gram-negative bacteria. LpxD is a homotrimer, with each subunit consisting of a novel combination of an N-terminal uridine-binding domain, a core lipid-binding left-handed parallel beta helix (LbH) domain, and a C-terminal alpha-helical extension. The LbH domain contains 9 turns, each containing three imperfect tandem repeats of a hexapeptide repeat motif (X-[STAV]-X-[LIV]-[GAED]-X).
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