HYDROXYL GROUP OF TYR(13) IS ESSENTIAL FOR THE ACTIVITY OF OMEGA-CONOTOXIN GVIA, A PEPTIDE TOXIN FOR N-TYPE CALCIUM-CHANNEL

A series of analogs of omega-conotoxin GVIA, a peptide neurotoxin having 27 amino acid residues with three disulfide bridges, were synthesized by replacing each amino acid residue except for Cys and Hyp with Ala. CD spectra were virtually identical between native and all of the analogs, indicating the overall conformations were not changed by the substitutions. The inhibitory effects of these analogs on I-125-omega-conotoxin GVIA binding to chick brain synaptic plasma membranes showed that replacement of Tyr(13) with Ala drastically lowered the affinity of the toxin to the N-type Ca2+ channel. Substitution of Tyr(13) with Phe also showed reduction of the affinity, indicating that the hydroxyl group of Tyr(13) is critical for binding. Since Lys(2) is also important for binding (Sato, K. Park, N.-G., Kohno, T. Maeda, T., Kim, J.-I., Kato, R., and Takahashi, M. (1993) Biochem. Biophys. Res. Commun. 194, 1292-1296), we propose a two-point binding model in which Tyr(13) and Lys(2) interact with specific amino acid residues of the Ca2+ channel through hydrogen bonding and ionic interaction, respectively.