Interaction of the neurotoxic and nontoxic secretory phospholipases A(2) with the crotoxin inhibitor from Crotalus serum

Crotalus durissus terrificus snakes possess a protein in their blood, named crotoxin inhibitor from Crotalus serum (CICS), which protects them against crotoxin, the main toxin of their venom. CICS neutralizes the lethal poten cy of crotoxin and inhibits its phospholipase A(2) (PLA(2)) activity. The a im of the present study is to investigate the specificity of CICS towards s nake venom neurotoxic PLA(2)s (beta-neurotoxins) and nontoxic mammalian PLA (2)s. This investigation shows that CICS does not affect the enzymatic acti vity of pancreatic and nonpancreatic PLA(2)s, bee venom PLA(2) and Elapidae beta-neurotoxins but strongly inhibits the PLA(2) activity of Viperidae be ta-neurotoxins. Surface plasmon resonance and PAGE studies further demonstr ated that CICS makes complexes with monomeric and multimeric Viperidae beta -neurotoxins but does not interact with nontoxic PLA(2)s. In the case of di meric beta-neurotoxins from Viperidae venoms (crotoxin, Mojave toxin and Cb ICbII), which are made by the noncovalent association of a PLA(2) with a no nenzymatic subunit, CICS does not react with the noncatalytic subunit, inst ead it binds tightly to the PLA(2) subunit and induces the dissociation of the heterocomplex. In vitro assays performed with Torpedo synaptosomes show ed a protective action of CICS against Viperidae beta-neurotoxins but not a gainst other PLA(2) neurotoxins, on primary and evoked liberation of acetyl choline. In conclusion, CICS is a specific PLA(2) inhibitor of the beta-neu rotoxins from the Viperidae family.