Effect of sulfhydryl group modification on the neurotoxic action of a sea snake toxin

Pelamis toxin a is a major neurotoxin isolated from the venom of Pelamis platurus (yellow-bellied sea snake). The effect of sulfhydryl group modification by NN’-1,4-phenylenedimaleimide on the neurotoxic action of Pelamis toxin a has been investigated. The cross-linked toxin having a molecular weight of 11 000 was formed without significant structural changes in the toxin. Lethality tests on the modified toxin indicated that it retained considerable toxicity, although its potency was weaker than that of the native toxin. Binding studies with the acetylcholine receptor isolated from the electroplax of Torpedo californica indicated that the modified toxin binds to the receptor but less effectively than the native toxin. These results suggest that the decreases in toxicity and binding to the receptor are due to a decrease in accessibility of cross-linked neurotoxin to the receptor. This leads us to the conclusion that the region of the neurotoxin containing the sulfhydryl group is not essential for its biological activity. Analysis of the structure and function relationships of the modified toxin suggests that the neurotoxin-acetylcholine receptor interaction requires the proper orientation of the neurotoxin molecule.