Effect of cold shock on lipid A biosynthesis in Escherichia coli - Induction at 12 degrees C of an acyltransferase specific for palmitoleoyl-acyl carrier protein

Palmitoleate is not present in lipid A isolated from Escherichia coli grown at 30 degrees C or higher, but it comprises similar to 11% of the fatty ac yl chains of lipid A in cells grown at 12 degrees C. The appearance of palm itoleate at 12 degrees C is accompanied by a decline in laurate from -18% t o similar to 5.5%. We now report that wild-type E. coli shifted from 30 deg rees C to 12 degrees C acquire a novel palmitoleoyl-acyl carrier protein (A CP)-dependent acyltransferase that acts on the key lipid A precursor Kdo(2) -lipid IVA. The palmitoleoyl transferase is induced more than 30-fold upon cold shock, as judged by assaying extracts of cells shifted to 12 degrees C . The induced activity is maximal after 2 h of cold shock, and then gradual ly declines but does not disappear. Strains harboring an insertion mutation in the lpxL(htrB) gene, which encodes the enzyme that normally transfers l aurate from lauroyl-ACP to Kdo(2)-lipid IVA (Clementz, T., Bednarski, J. J. , and Raetz, C. R. H. (1996) J. Biol. Chem. 271, 12095-12102) are not defec tive in the cold-induced palmitoleoyl transferase. Recently, a gene display ing 54% identity and 73% similarity at the protein level to lpxL was found in the genome off. coli. This lpxL homologue, designated lpxP, encodes the cold shock-induced palmitoleoyl transferase. Extracts of cells containing l pxP on the multicopy plasmid pSK57 exhibit a 10-fold increase in the specif ic activity of the cold-induced palmitoleoyl transferase compared with cell s lacking the plasmid. The elevated specific activity of the palmitoleoyl t ransferase under conditions of cold shock is attributed to greatly increase d levels of lpxP mRNA. The replacement of laurate with palmitoleate in lipi d A may reflect the desirability of maintaining the optimal outer membrane fluidity at 12 degrees C.