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 dodecylphosp hocholine (DodPCho) micelles using standard two-dimensional proton NMR spectroscopy. The proton spectrum resonances of the micelle-bound tox in gamma were assigned, and the chemical shifts of the backbone and si de-chain protons were compared with those determined in the absence of DodPCho. We observed that DodPCho induced large chemical shift change s on residues localized on the hydrophobic face of the toxin. These ch anges an not associated with conformational changes of the toxin. Howe ver, the micellar environment may induce some stabilization of the tri ple-stranded beta sheet, the major component of the protein structural core. Since the proton NMR spectrum of toxin alpha, a structurally re lated 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 contibution of the hydrophobic face of the toxin to th e toxic site and further suggest a possible mechanism of action of car diotoxin on biological bilayers.