Transfer of fatty acids from the 1-position of phosphatidylethanolamine to the major outer membrane lipoprotein of Escherichia coli.

The utilization of exogenous fatty acids for phospholipid synthesis via the sn-glycerol-3-phosphate acyltransferase was blocked in Escherichia coli mutants lacking acyl-CoA synthetase activity (fadD) resulting in the selective esterification of the 1-position of phosphatidylethanolamine by extracellular fatty acids (Rock, C. O., and Jackowski, S. (1985) J. Biol. Chem. 260, 12720-12724). The incorporation of exogenous [1-14C]palmitate into phosphatidylethanolamine in fadD mutants was inhibited by chloramphenicol and was depressed by preventing the acylation of the amino terminus of the lipoproteins with the antibiotic globomycin. Lipoprotein acylation was directly examined in fadD mutants harboring hybrid plasmids containing either the major outer membrane lipoprotein gene or a lipoprotein-beta-lactamase gene fusion transcriptionally regulated by the lacUV5 promoter-operator region. Induction of lipoprotein synthesis in the presence of extracellular [1-14C]palmitate increased the amount of radioactivity entering the 1-position of phosphatidylethanolamine and efficiently labeled lipoprotein acyl moieties. Labeling of the 1-position of phosphatidylethanolamine prior to the induction of lipoprotein biosynthesis resulted in the transfer of fatty acid from phosphatidylethanolamine to the lipoprotein. Lipoprotein fatty acids derived from the 1-position of phosphatidylethanolamine were resistant to hydroxylamine hydrolysis, and globomycin reduced the incorporation of exogenous [1-14C]palmitate into lipoproteins by 80% suggesting that this fatty acid is primarily attached to the amino terminus of the lipoprotein. These data illustrate that fatty acid turnover in phosphatidylethanolamine is initiated by the transfer of 1-position acyl moieties to the major outer membrane lipoprotein.