The Wax Ester Synthase/Acyl Coenzyme A:Diacylglycerol Acyltransferase from Acinetobacter sp. Strain ADP1: Characterization of a Novel Type of Acyltransferase

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Abstract
The wax ester synthase/acyl coenzyme A (acyl-CoA):diacylglycerol acyltransferase (WS/DGAT) catalyzes the final steps in triacylglycerol (TAG) and wax ester (WE) biosynthesis in the gram-negative bacterium Acinetobacter sp. strain ADP1. It constitutes a novel class of acyltransferases which is fundamentally different from acyltransferases involved in TAG and WE synthesis in eukaryotes. The enzyme was purified by a three-step purification protocol to apparent homogeneity from the soluble fraction of recombinant Escherichia coli Rosetta (DE3)pLysS (pET23a::atfA). Purified WS/DGAT revealed a remarkably low substrate specificity, accepting a broad range of various substances as alternative acceptor molecules. Besides having DGAT and WS activity, the enzyme possesses acyl-CoA:monoacylglycerol acyltransferase (MGAT) activity. The sn-1 and sn-3 positions of acylglycerols are accepted with higher specificity than the sn-2 position. Linear alcohols ranging from ethanol to triacontanol are efficiently acylated by the enzyme, which exhibits highest specificities towards medium-chain-length alcohols. The acylation of cyclic and aromatic alcohols, such as cyclohexanol or phenylethanol, further underlines the unspecific character of this enzyme. The broad range of possible substrates may lead to biotechnological production of interesting wax ester derivatives. Determination of the native molecular weight revealed organization as a homodimer. The large number of WS/DGAT-homologous genes identified in pathogenic mycobacteria and their possible importance for the pathogenesis and latency of these bacteria makes the purified WS/DGAT from Acinetobacter sp. strain ADP1 a valuable model for studying this group of proteins in pathogenic mycobacteria.