The three-dimensional solution structure of delta-conotoxin TxVIA, a 27-mer peptide agonist/antagonist of sodium channels, was determined by two-dimensional (1)H NMR spectroscopy with simulated annealing calculations. A total of 20 converged structures of delta-conotoxin TxVIA were obtained on the basis of 360 distance constraints obtained from nuclear Overhauser effect connectivities, 28 torsion angle constraints, and 27 constraints associated with hydrogen bonds and disulfide bonds. The atomic root mean square difference about the averaged coordinate positions is 0.35 +/- 0.07 A for the backbone atoms (N, C(alpha), C) and 0.98 +/- 0.14 A for all heavy atoms of the entire peptide. The molecular structure of delta-conotoxin TxVIA is composed of a short triple-stranded antiparallel beta-sheet. The overall beta-sheet topology is +2x, -1, which is the same as those for other conotoxins. However, the three-dimensional structure of delta-conotoxin TxVIA has an unusual hydrophobic patch on one side of the molecule, which may play an important role in the sodium channel binding. These results provide a molecular basis for understanding the mechanism of sodium channel modulation through the toxin-channel interaction and insight into the discrimination of different ion channels.