Hydrocarbon rulers in UDP-N-acetylglucosamine acyltransferases

UDP-GlcNAc acyltransferase (LpxA), the first enzyme of lipid A biosynthesis , catalyzes the transfer of an acyl chain activated on acyl carrier protein (ACP) to UDP-GlcNAc. LpxAs are very selective for the lengths of their acy l donor substrates. Escherichia coli LpxA prefers R-3-hydroxymyristoyl-ACP to R-3-hydroxydecanoyl-ACP by a factor of similar to 1000, whereas Pseudomo nas aeruginosa LpxA prefers the opposite. E. coil G173M LpxA and the recipr ocal P. aeruginosa M169G LpxA show reversed substrate selectivity in vitro and in vivo, demonstrating the existence of precise hydrocarbon rulers in L pxAs.