Biosynthesis of lipid A precursors in Escherichia coli. A membrane-bound enzyme that transfers a palmitoyl residue from a glycerophospholipid to lipid X.

摘要: Certain phosphatidylglycerol-deficient mutants of Escherichia coli accumulate two fatty acylated monosaccharides related to lipid A biosynthesis that have been identified as 2,3-diacylglucosamine 1-phosphate (lipid X) and triacylglucosamine Y) (Raetz, C. R. H. (1984) Rev. Infect. Dis. 6, 463-472). Lipid Y has the same structure X, except it bears an additional palmitoyl moiety, esterified 3-OH N-linked R-3-hydroxymyristoyl residue. We now describe a membrane-associated system for enzymatic conversion X Y. Removal glycerophospholipids form such membranes by washing with cold ethanol abolishes activity. The can be reactivated addition exogenous phospholipids dispersed mixed micelles Triton X-100. When reconstituted in this manner, formation is strictly dependent upon glycerophospholipid donor bearing residue sn-1 position. enzyme does not utilize coenzyme or acyl carrier protein. It catalyze efficient transfer acids differing from palmitate only one carbon atom. In contrast, relatively little specificity polar headgroup phospholipid donor, also appears disaccharide precursor alternative acceptor. Since vitro synthesis proceeds high yield, we isolated product verified its 1H NMR spectroscopy mass spectrometry. transesterification reaction converts may model other acyloxyacyl structures, known occur mature A.