CLONING OF HUMAN CHOLINE/ETHANOLAMINEPHOSPHOTRANSFERASES; SYNTHESIS OF PHOSPHATIDYLCHOLINE, PHOSPHATIDYLETHANOLAMINE, AND PLATELET ACTIVATING FACTOR

摘要

We report the first cloning and expression, from a mammalian source, ofproteins capable of catalyzing choline- and ethanolaminephosphotransferasereactions (hCEPT1 and hCEPT2). Both coding regions predict highly hydrophobicproteins of 43-46.5 kDa with several predicted membrane spanning domains. ACDP-alcohol phosphotransferase motif, DG(x)2AR(x)8G(x)3D(x)3D, has beenidentified in both hCEPT1 and hCEPT2 choline- and ethanolamine-phosphotransferases (and several other lipid synthesizing enzymes thatcatalyze the formation of a phosphoester bond by the displacement of CMP froma CDP-alcohol by a second alcohol). Site-directed mutagenesis was used todifferentiate the residues responsible for choline- versus ethanolamine-phosphotransferase activity. Mutation of glycine 156 of hCEPT1 abolishedethanolaminephosphotransferase activity, while cholinephosphotransferaseactivity remained intact.