出版社：American Society for Biochemistry and Molecular Biology
摘要：Acyl-coenzyme A:monoacylglycerol acyltransferase 3 (MGAT3) isa member of the MGAT family of enzymes that catalyze the synthesisof diacylglycerol (DAG) from monoacylglycerol (MAG), a committedstep in dietary fat absorption. Although named after the initialidentification of its MGAT activity, MGAT3 shares higher sequencehomology with acyl-coenzyme A:diacylglycerol acyltransferase2 (DGAT2) than with other MGAT enzymes, suggesting that MGAT3may also possess significant DGAT activity. This study comparedthe catalytic properties of MGAT3 with those of MGAT1 and MGAT2enzymes using both MAG and DAG as substrates. Our results showedthat in addition to the expected MGAT activity, the recombinantMGAT3 enzyme expressed in Sf-9 insect cells displayed a strongDGAT activity relative to that of MGAT1 and MGAT2 enzymes inthe order MGAT3 > MGAT1 > MGAT2. In contrast, none ofthe three MGAT enzymes recognized biotinylated acyl-CoA or MAGas a substrate. Although MGAT3 possesses full DGAT activity,it differs from DGAT1 in catalytic properties and subcellularlocalization. The MGAT3 activity was sensitive to inhibitionby the presence of 1% CHAPS, whereas DGAT1 activity was stimulatedby the detergent. Consistent with high sequence homology withDGAT2, the MGAT3 enzyme demonstrated a similar subcellular distributionpattern to that of DGAT2, but not DGAT1, when expressed in COS-7cells. Our data suggest that MGAT3 functions as a novel triacylglycerol(TAG) synthase that catalyzes efficiently the two consecutiveacylation steps in TAG synthesis.Supplementary key words acyl-coenzyme A:monoacylglycerol acyltransferase • acyltransferase • monoacylglycerol
Abbreviations: DAG, diacylglycerol; DGAT, acyl-coenzyme A:diacylglycerol acyltransferase; ER, endoplasmic reticulum; G3P, glycerol-3-phosphate; MAG, monoacylglycerol; MGAT, acyl-coenzyme A:monoacylglycerol acyltransferase; TAG, triacylglycerol
