Specificity of two types of phospholipase A2 inhibitors from the plasma of venomous snakes.

Specificity of two different types of phospholipase A2 (PLA2) inhibitory proteins from the blood plasma of venomous snakes was investigated. Two Crotalidae inhibitors, having a carbohydrate recognition domain (CRD) in their sequences, inhibited specifically the group-II acidic PLA2s of their own snake venom. On the other hand, Elapidae inhibitor, having two tandem patterns of cysteine residues found in proteins of the Ly-6 superfamily, inhibited not only the group-I PLA2 from its own snake venom but also the group-I, -II, and -III PLA2s from other snake venom. Amino acid sequences of PLA2s that were specifically inhibited by the inhibitors were compared with those of the other PLA2s. A unique aromatic patch structure appeared on the group-II acidic PLA2s was suggested to be involved in the binding to the Crotalidae inhibitors; and residues located in or close to the Ca2+ binding loop of PLA2, in the binding to the Elapidae inhibitor.