Conodipine-M, a novel phospholipase A2 isolated from the venom of the marine snail Conus magus.

We describe the purification and first biochemical characterization of an enzymatic activity in venom from the marine snail Conus magus. This enzyme, named conodipine-M, is a novel phospholipase A2 with a molecular mass of 13.6 kDa and is comprised of two polypeptide chains linked by one or more disulfide bonds. The amino acid sequence of conodipine-M shows little if any homology to other previously sequenced phospholipase A2 enzymes (PLA2s). Conodipine-M thus represents a new group of PLA2s. This is remarkable, since conodipine-M displays a number of properties that are similar to those of previously characterized 14-kDa PLA2s. The enzyme shows little, if any, phospholipase A1, diacyglycerol lipase, triacylglycerol lipase, or lysophospholipase activities. Conodipine-M hydrolyzes the sn-2 ester of various preparations of phospholipid only in the presence of calcium and with specific activities that are comparable to those of well known 14-kDa snake venom and pancreatic PLA2s. The Conus enzyme binds tightly to vesicles of the negatively charged phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphomethanol and catalyzes the hydrolysis of this substrate in a processive fashion. Conodipine-M does not significantly discriminate against phospholipids with unsaturated versus saturated fatty acids at the sn-2 position or with different polar head groups. Linoleoyl amide and a phospholipid analog containing an alkylphosphono group at the sn-2 position are potent inhibitors of conodipine-M. We suggest that the functional resemblance of conodipine-M to other PLA2s might be explained by the utilization of similar catalytic residues.