Catalytic properties of MGAT3, a putative triacylgycerol synthase

Abstract

Acyl-coenzyme A:monoacylglycerol acyltransferase 3 (MGAT3) is a member of the MGAT family of enzymes that catalyze the synthesis of diacylglycerol (DAG) from monoacylglycerol (MAG), a committed step in dietary fat absorption. Although named after the initial identification of its MGAT activity, MGAT3 shares higher sequence homology with acyl-coenzyme A:diacylglycerol acyltransferase 2 (DGAT2) than with other MGAT enzymes, suggesting that MGAT3 may also possess significant DGAT activity. This study compared the catalytic properties of MGAT3 with those of MGAT1 and MGAT2 enzymes using both MAG and DAG as substrates. Our results showed that in addition to the expected MGAT activity, the recombinant MGAT3 enzyme expressed in Sf-9 insect cells displayed a strong DGAT activity relative to that of MGAT1 and MGAT2 enzymes in the order MGAT3 . MGAT1 . MGAT2. In contrast, none of the three MGAT enzymes recognized biotinylated acyl-CoA or MAG as a substrate. Although MGAT3 possesses full DGAT activity, it differs from DGAT1 in catalytic properties and subcellular localization. The MGAT3 activity was sensitive to inhibition by the presence of 1% CHAPS, whereas DGAT1 activity was stimulated by the detergent. Consistent with high sequence homology with DGAT2, the MGAT3 enzyme demonstrated a similar subcellular distribution pattern to that of DGAT2, but not DGAT1, when expressed in COS-7 cells. Our data suggest that MGAT3 functions as a novel triacylglycerol (TAG) synthase that catalyzes efficiently the two consecutive acylation steps in TAG synthesis.-Cao, J., L. Cheng, and Y. Shi. Catalytic properties of MGAT3, a putative triacylgycerol synthase. J. Lipid Res. 2007. 48: 583-591.

Evidence for regulated monoacylglycerol acyltransferase expression and activity in human liver

“…5 ) as assessed by incorporation of [ 14 C]decanoyl CoA into DAG, TAG, or total incorporation into both DAG and TAG. This fi nding is consistent with MGAT3 acting as both an MGAT and DGAT enzyme ( 13 ). In contrast, MOGAT2 expression was not correlated with MGAT activity ( Fig.…”

“…The murine Mogat3 gene arose from duplication of Mogat2 , whereas the human MOGAT3 gene may have arisen from duplication of the gene encoding DGAT2 ( 12 ). Human MGAT3 also possesses signifi cant DGAT activity and can catalyze both reactions required to convert monoacylglycerol to TAG ( 13 ). In fact, the amino acid sequence of all the MGATs exhibits homology to that of DGAT enzymes, and the two principal DGATs also possess modest MGAT activity ( 4,14,15 ).…”

“…Although MGAT3 can utilize both sn-1-monoacylglycerol (MAG) and sn -2-MAG as substrate, in the presence of sn -1-MAG, it also effi ciently functions as a DGAT ( 11,13 ). To specifi cally examine MGAT activity, sn -2-monooleoylglycerol (200 M) was used as the acyl acceptor and [ 14 C]decanoyl CoA (20 M) as the acyl donor.…”

Usefulness of Obese Animal Models in Antiobesity Drug Development

“…The genes encoding three MGATs, MGAT1, MGAT2, and MGAT3 have been identified [102][103][104]. MGAT1 is mainly expressed in the heart, lung, skeletal muscle, and pancreas, but not in the small intestine.…”

Diacylglycerol Acyltransferase-2 (DGAT2) and Monoacylglycerol Acyltransferase-2 (MGAT2) Interact to Promote Triacylglycerol Synthesis

“…7A). MGAT2 may account for the majority of MGAT activity in McArdle cells as other MGAT isoforms have yet to be identified in rat liver (15,(31)(32)(33).…”