Monoacylglycerol acyltransferase-2 is a tetrameric enzyme that selectively heterodimerizes with diacylglycerol acyltransferase-1 [Lipids]

February 25th, 2014 by Zhang, J., Xu, D., Nie, J., Cao, J., Zhai, Y., Tong, D., Shi, Y.

Acyl-CoA:monoacylglycerol acyltransferases (MGATs) and diacylglycerol acyltransferases (DGATs) catalyze the two consecutive steps in the synthesis of triacylglycerol, a key process required for dietary fat absorption into the enterocytes of the small intestine. In this report, we investigated tenacity of MGAT2 to form an enzyme complex with DGAT1 and DGAT2 in intact cells. We demonstrated that in addition to the 38 kDa monomer of the MGAT2 enzyme predicted by its peptide sequence, a 76 kDa moiety was detected in SDS/PAGE without reducing agent and heat inactivation. The 76 kDa MGAT2 moiety was greatly enhanced by treatment with a cross-linking reagent in intact cells. Additionally, the cross-linking reagent dose-dependently yielded a band corresponding to the tetramer (152 kDa) in SDS/PAGE, suggest that the MGAT2 enzyme primarily functions as a homotetrameric protein as a tetrameric protein. Likewise, DGAT1 also forms a homodimer under nondenaturing condition. When co-expressed in COS-7 cells, MGAT2 heterodimerized with DGAT1 without treatment with a cross-linking reagent. MGAT2 also co-eluted with DGAT1 on a gel-filtration column, suggesting the two enzymes form a complex in intact cells. In contrast, MGAT2 did not heterodimerize with DGAT2 when co-expressed in COS-7 cells, despite of high sequence homology between the two enzymes. Furthermore, systematic deletion analysis demonstrates that N-terminal amino acids 35-80 of DGAT1, but not a signal peptide at the N-terminus of MGAT2, is required for the heterodimerization. Finally, co-expression of MGAT2 with DGAT1 significantly increased lipogenesis in Cos-7 cells, implicating functional importance of the dimerization.