CONODIPINE-M, A NOVEL PHOSPHOLIPASE-A(2) 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. Thi s enzyme, named conodipine-M, is a novel phospholipase A(2) with a mol ecular mass of 13.6 kDa and is comprised of two polypeptide chains lin ked by one or more disulfide bonds. The amino acid sequence of conodip ine-M shows little if any homology to other previously sequenced phosp holipase A(2) enzymes (PLA(2)s). Conodipine-M thus represents a new gr oup of PLA(2)s. This is remarkable, since conodipine-M displays a numb er of properties that are similar to those of previously characterized 14-kDa PLA(2)s. The enzyme shows little, if any, phospholipase A(1), diacylglycerol lipase, triacylglycerol lipase, or lysophospholipase ac tivities. Conodipine-M hydrolyzes the sn-2 ester of various preparatio ns of phospholipid only in the presence of calcium and with specific a ctivities that are comparable to those of well known 14-kDa snake veno m and pancreatic PLA(2)s. The Conus enzyme binds tightly to vesicles o f the negatively charged phospholipid 1,2-dimyristoyl-sn-glycero-3-pho sphomethanol and catalyzes the hydrolysis of this substrate in a proce ssive fashion. Conodipine-M does not significantly discriminate agains t phospholipids with unsaturated versus saturated fatty acids at the s n-2 position or with different polar head groups. Linoleoyl amide and a phospholipid analog containing an alkylphosphono group at the sn-2 p osition are potent inhibitors of conodipine-M. We suggest that the fun ctional resemblance of conodipine-M to other PLA(2)s might be explaine d by the utilization of similar catalytic residues.