A membrane-bound glycerol-3-phosphate acyltransferase from Thalassiosira pseudonana regulates acyl composition of glycerolipids

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 T_pGPAT, from the marine diatom Thalassiosira pseudonana Hasle & Heim. The glycerolipids from T. pseudonana consist predominantly of 16:0, 16:1ω7, and 20:5u3 fatty acids. Heterologous expression of T _pGPAT in a yeast GPAT-deficient mutant (gat1) demonstrated that T_pGPAT 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 T_pGPAT 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 T_pGPAT possesses a high substrate preference for 16:0-CoA and it exerts a large effect on the fatty-acid composition of glycerolipids.