Abstract
To what extent fatty acyltransferases control fatty acid composition in glycerolipids is largely unknown. To gain some insight into this process, we characterized a membrane-bound glycerol-3-phosphate acyltransferase (GPAT), designated TpGPAT, from the marine diatom Thalassiosira pseudonana Hasle & Heim. The glycerolipids from T. pseudonana consist predominantly of 16:0, 16:1ω7, and 20:5ω3 fatty acids. Heterologous expression of TpGPAT in a yeast GPAT-deficient mutant (gat1) demonstrated that TpGPAT could effectively use glycerol-3-phosphate, but not dihydroxyacetone phosphate, as fatty acyl acceptor. This enzyme highly preferred 16:0 in an in vitro enzyme assay, and discriminated against the monounsaturated 16-carbon fatty acid. Accordingly, expression of TpGPAT in gat1 resulted in approximately 18% and 12% increases of 16:0 in triacylglycerols and phospholipids, respectively. The unsaturated fatty acids, 16:1 and 18:1, on the other hand, were reduced by 15% and 21% in these two lipid species. Collectively, the results demonstrate that TpGPAT possesses a high substrate preference for 16:0-CoA and it exerts a large effect on the fatty-acid composition of glycerolipids.
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