An NMR study of the interaction of cardiotoxin gamma from Naja nigricollis with perdeuterated dodecylphosphocholine micelles.

We investigated the interaction of toxin gamma, a cardiotoxin from the venom of the elapid Naja nigricollis, with perdeuterated dodecylphosphocholine (DodPCho) micelles using standard two-dimensional proton NMR spectroscopy. The proton spectrum resonances of the micelle-bound toxin gamma were assigned, and the chemical shifts of the backbone and side-chain protons were compared with those determined in the absence of DodPCho. We observed that DodPCho induced large chemical shift changes on residues localized on the hydrophobic face of the toxin. These changes are not associated with conformational changes of the toxin. However, the micellar environment may induce some stabilization of the triple-stranded beta sheet, the major component of the protein structural core. Since the proton NMR spectrum of toxin alpha, a structurally related neurotoxin extracted from the same venom, was unaffected by the presence of the micelles, we came to the conclusion that the observed effects are specific to cardiotoxins. The present results give direct evidence of the contribution of the hydrophobic face of the toxin to the toxic site and further suggest a possible mechanism of action of cardiotoxin on biological bilayers.