NATIVE PEPTIDE INHIBITION - SPECIFIC-INHIBITION OF TYPE-II PHOSPHOLIPASES A(2) BY SYNTHETIC PEPTIDES DERIVED FROM THE PRIMARY SEQUENCE

The binding of low molecular weight type II phospholipase A(2) (EC 3.1 .1.4) to membrane surfaces and hydrolysis of phospholipid are thought to involve the formation of a hydrophobic channel into which a single substrate molecule diffuses before cleavage, The floor and right side of the channel are provided by hydrophobic residues 2, 5, and 9 of an amphipathic amino-terminal helix, The channel is postulated to form vi a a conformational change in this helix and inward movement of a hydro phobic flap (residue 69 side chain). We show that the amino-terminal t ryptic peptide of human type II phospholipase A(2) forms a noncovalent complex with the tryptic peptide from residues 70-74 of the enzyme, F urther, the 70-74-peptide sequence (FLSYK) dose-dependently inhibits p hospholipid hydrolysis in a mixed micelle assay. This native peptide i nhibition also occurred with type II enzymes from Crotalus durissus an d Crotalus atrox, which have different amino acid sequences at the ami no terminus as well as different 70-74 regions of the molecules. Despi te significant conservation of tertiary structure among the enzymes, i nhibition by each peptide is specific to the enzyme from which the pep tide sequence is derived, We propose that these native peptides inhibi t enzyme activity via a sequence-specific, noncovalent interaction wit h the amino-terminal residues of the enzyme, thereby preventing the co nformational change on binding to the micelle interface, These experim ents demonstrate a new method for specific inhibition of phospholipase A(2) which, in principle, would be applicable to other biologically a ctive polypeptides and proteins.