3-DIMENSIONAL STRUCTURE IN SOLUTION OF THE CALCIUM-CHANNEL BLOCKER OMEGA-CONOTOXIN MVIIA

The three-dimensional solution structure of omega-conotoxin MVIIA, a 2 5-mer peptide antagonist of N-type calcium channels, was determined by two-dimensional H-1 NMR spectroscopy with simulated annealing calcula tions, A total of 13 converged structures of omega-conotoxin MVIIA wer e obtained on the basis of 273 experimental constraints, including 232 distance constraints obtained from nuclear Overhauser effect (NOE) co nnectivities, 22 torsion angle (phi, chi(1)) constraints, and 19 const raints associated with hydrogen bonds and disulfide bonds. The atomic root mean square difference about the averaged coordinate positions is 0.47 +/- 0.08 Angstrom for the backbone atoms (N, C-alpha, C) and 1.2 7 +/- 0.14 Angstrom for all heavy atoms of the entire peptide. The mol ecular structure of omega-conotoxin MVIIA is composed of a short tripl e-stranded antiparallel beta-sheet, The overall beta-sheet topology is +2x, -1, which is the same as that reported for omega-conotoxin GVIA, another N-type calcium channel blocker. The orientation of beta-stran ded structure is similar to each other, suggesting that the conserved disulfide bond combination is essential for the molecular folding. We have recently determined by using alanine substitution analyses that T yr 13 is essential for the activity of both toxins. On the basis of fu nctional and structural analysis, it is shown that both omega-conotoxi n MVIIA and GVIA retain a similar conformation to locate Tyr 13 in the appropriate position to allow binding to N-type calcium channels. The se results provide a molecular basis for understanding the mechanism o f calcium channel modulation through the toxin-channel interaction and insight into the discrimination of different subtypes of calcium chan nels.