Cloning of human choline / ethanolaminephospho - transferases; synthesis of phosphatidyl - choline, phosphatidyle - thanolamine, and platelet activating factor

摘要

We report the first cloning and expression, from a mammalian source, of proteins capable of catalyzing choline- and ethanolaminephosphotransferase reactions (hCEPT1 and hCEPT2). Both coding regions predict highly hydrophobic proteins of 43-46.5 kDa with several predicted membrane spanning domains. A CDP-alcohol phosphotransferase motif, DG(x)2AR(x)8G(x)3D(x)3D, has been identified in both hCEPT1 and hCEPT2 choline- and ethanolamine-phosphotransferases (and several other lipid synthesizing enzymes that catalyze the formation of a phosphoester bond by the displacement of CMP from a CDP-alcohol by a second alcohol). Site-directed mutagenesis was used to differentiate the residues responsible for choline- versus ethanolamine-phosphotransferase activity. Mutation of glycine 156 of hCEPT1 abolished ethanolaminephosphotransferase activity, while cholinephosphotransferase activity remained intact.