IDENTIFICATION OF A SPECIFIC REGION OF LOW-MOLECULAR-WEIGHT PHOSPHOLIPASES-A(2) (RESIDUES-21-40) AS A POTENTIAL TARGET FOR STRUCTURE-BASED DESIGN OF INHIBITORS OF THESE ENZYMES

We have identified a specific region of porcine pancreatic phospholipa se A2 (residues 21-40) which interacts with a neutralizing antibody ca using a dramatic inhibition of its enzymatic activity (K(i) in the ord er of 10(-8)M). The binding equilibrium of the antibody-phospholipase A2 complex is reached in <3 min at 37-degrees-C. Fab fragments are equ ally effective phospholipase A2 inhibitors, as are intact IgG molecule s. The inhibition is virtually complete and noncompetitive with respec t to phosphatidylcholine substrate. The formation of precipitating imm unocomplexes is not involved in the inhibition. The region of phosphol ipase A2 (residues 21-40) recognized by this antibody includes a highl y conserved sequence which contains several functionally important res idues of both group I and group II phospholipases A2. These data sugge st that amino acid residues in this region of porcine pancreatic phosp holipase A2 are accessible for interaction with inhibitors such as neu tralizing antibodies and that agents specifically interacting with thi s region may have potent phospholipase A2 inhibitory activity. Thus, t his conserved region of low molecular weight, extracellular phospholip ases A2 is a potential target for structure-based design of specific n oncompetitive inhibitors of these enzymes. Since these extracellular p hospholipases A2 are suggested to play a pathogenic role in several im portant human diseases, the development of such pharmacologic inhibito rs is of potential clinical importance.