A novel phosphatidylglycerol-selective phospholipase A2 from macrophages

Abstract

In our recent studies on the synthesis of bis(monoacylglycero)phosphate (BMP), we postulated that the first step involved a PLA2 that cleaved the 2-acyl group from phosphatidylglycerol (PG). In the present study, a novel lysosomal PLA2 was partially purified and characterized from RAW 264.7, macrophage like cells. Cells were homogenized and delipidated, and the PLA2 activity in the soluble fraction was purified by Sephacryl S100 and DEAE Sephacel. Further purification was performed using Con-A Sepharose, Phenyl Sepharose, DEAE Sephacel, and Superdex 75 FPLC. The enzyme at this stage of purification showed a dominant band around 45 kDa plus several minor bands on SDS-PAGE. The molecular mass determined by Superdex 75 column FPLC was about 45 kDa. The highly purified fraction hydrolyzed at the sn-1 position, implying that this PLA2 also has some intrinsic PLA1 activity. This enzyme preferentially hydrolyzed PG, has an acidic pH optima, and does not require divalent metal ions. Comparison using PG with various acyl chains on the sn-2 position showed that oleate and linoleate were preferred relative to arachidonate. MAFP, a known cytosolic PLA2 inhibitor, strongly inhibited this PLA2 activity. MJ33, AACOCF3, DENP, and Amiodarone also gave moderate inhibition. The characteristics of this enzyme showed this to be a new type of PLA, and the overwhelming preference for PG as substrate suggests its physiological role is in the biosynthesis of BMP.