The Arabidopsis thaliana lysophospholipid acyltransferase At1g78690p acylates lysocardiolipins.

The Arabidopsis thaliana lysophospholipid acyltransferase At1g78690 acylates a variety of lysophospholipids such as lyso phosphatidylglycerol, lyso phosphatidylethanolamine and lyso phosphatidylserine. Despite di-acylate phosphatidylglycerol being a substrate, overexpression of At1g78690 in Escherichia coli leads to the accumulation of acyl-PG. Here we show that cardiolipin also accumulates in cells overexpressing At1g78690. To help try and explain this observation, we show, using a liquid chromatography mass spectrometry (LC-MS) based assay, that At1g78690 utilizes both mono- and di-lyso cardiolipin as an acyl acceptor. Because At1g78690 shares high homology (∼40%) with the cardiolipin remodeling enzyme tafazzin, we also tested whether At1g78690 was able to catalyze a tafazzin-like transacylation reaction. Di-linoleoyl phosphatidylcholine was used as the acyl donor and mono-lyso cardiolipin was used as the acyl acceptor in a reaction and the reaction was monitored by LC-MS. No transfer of the linoleoyl chains was detected in an At1g78690 dependent manner suggesting that, despite the strong homology, these enzymes catalyze unique reactions.

The Arabidopsis thaliana lysophospholipid acyltransferase At1g78690p acylates a variety of lysophospholipids including bis(monoacylglycero)phosphate.

When the lysoglycerophospholipid (GPL) acyltransferase At1g78690 from Arabidopsis thaliana is over-expressed in Escherichiacoli a headgroup acylated GPL, acyl phosphatidylglycerol (PG), accumulates despite that in vitro this enzyme catalyzes the transfer of an acyl chain from acyl-CoA to the sn-2 position of 1-acyl phosphatidylethanolamine (PE) or 1-acyl PG to form the sn-1, sn-2, di acyl PE and PG respectively; it does not acylate PG to form acyl PG. To begin to understand why the overexpression of a lyso GPL acyltransferase leads to the accumulation of a headgroup acylated GPL in E. coli we investigated the headgroup specificity of At1g78690. Using membranes prepared from E. coli overexpressing At1g78690, we assessed the ability of At1g78690 to catalyze the transfer of acyl chains from acyl-coenzyme A to a variety of lyso GPL acyl acceptors including lyso-phosphatidic acid (PA), -phosphatidylcholine (PC), -phosphatidylserine (PC), -phosphatidylinositol (PI) and three stereoisoforms of bis(monoacylglycero)phosphate (BMP). The predicted products were formed when lyso PI and lyso PC were used as the acyl acceptor but not with lyso PC or lyso PA. In addition, At1g78690 robustly acylates two BMP isoforms with sn-2 and/or sn-2' hydroxyls in the R-stereoconfiguration, but not the BMP isoform with the sn-2 and sn-2' hydroxyls in the S-stereoconfiguration. This strongly suggests that At1g78690 is stereoselective for hydroxyls with R-stereochemistry. In addition, this robust acylation of BMPs by At1g78690, which yields acyl PG like molecules, may explain the mechanism by which At1g78690 so strikingly alters the lipid composition of E. coli.