IDENTIFICATION OF A GENE ENCODING AN ACYL COA-DIACYLGLYCEROL ACYLTRANSFERASE, A KEY ENZYME IN TRIACYLGLYCEROL SYNTHESIS

Triacylglycerols are quantitatively the most important storage form of energy for eukaryotic cells. Acyl CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the terminal and only committed step in triacylglycerol synthesis, by using diacylglycerol and fatty acyl CoA as substrates. DGAT plays a fundamental role in the metabolism of cell ular diacylglycerol and is important in higher eukaryotes for physiolo gic processes involving triacylglycerol metabolism such as intestinal fat absorption, lipoprotein assembly, adipose tissue formation, and la ctation. DGAT is an integral membrane protein that has never been puri fied to homogeneity, nor has its gene been cloned, We identified an ex pressed sequence tag clone that shared regions of similarity with acyl CoA:cholesterol acyltransferase, an enzyme that also uses fatty acyl CoA as a substrate. Expression of a mouse cDNA for this expressed sequ ence tag in insect cells resulted in high levels of DGAT activity in c ell membranes. No other acyltransferase activity was detected when a v ariety of substrates, including cholesterol, were used as acyl accepte rs. The gene was expressed in all tissues examined; during differentia tion of NIH 3T3-L1 cells into adipocytes, its expression increased mar kedly in parallel with increases in DGAT activity. The identification of this cDNA encoding a DGAT will greatly facilitate studies of cellul ar glycerolipid metabolism and its regulation.