SHORTENED HYDROXYACYL CHAINS ON LIPID-A OF ESCHERICHIA-COLI-CELLS EXPRESSING A FOREIGN UDP-N-ACETYLGLUCOSMAINE O-ACYLTRANSFERASE

The first reaction of lipid A biosynthesis in Gram-negative bacteria i s catalyzed by UDP-N-acetylglucosamine (UDP-GlcNAc) O-acyltransferase, the product of the lpxA gene. The reaction involves the transfer of a n acyl chain from hydroxyacyl-acyl carrier protein (ACP) to the glucos amine 3-OH position of UDP-GlcNAc. The lipid A isolated from Escherich ia coli contains (R)-3-hydroxymyristate at the 3 and 3' positions. Acc ordingly, LpxA of E. coli is highly selective for (R)-3-hydroxymyristo yl-ACP over ACP thioesters of longer or shorter acyl chains. We now de monstrate that the lpxA gene from Neisseria meningitidis encodes a sim ilar acyltransferase that selectively utilizes 3-hydroxylauroyl-ACP. S trains of E. coli harboring the temperature-sensitive lpxA2 mutation m ake very little lipid A and lose viability rapidly at 42 degrees C. We have created an E. coli strain in which the chromosomal lpxA2 mutatio n is complemented by the N. meningitidis lpxA gene introduced on a pla smid. This strain, RO138/pTO6, grows similarly to wild type cells at 4 2 degrees C and produces wild type levels of lipid A. However, the lip id A isolated from RO138/pTO6 contains mostly hydroxylaurate and hydro xydecanoate in the 3 and 3' positions. The strain RO138/pTO6 is more s usceptible than wild type to certain antibiotics at 42 degrees C. This is the first report of an E. coli strain growing with shortened hydro xyacyl chains on its lipid A. The lpxA gene product appears to be a cr itical determinant of the length of the ester-linked hydroxyacyl chain s found on lipid A in living cells.