From the venom of scorpion Buthus martensii Karsch, a short peptide (BmP01, 29 amino acid residues) was isolated and characterized as previously reported (Lebren, R., R., et al. (1997) Eur. J. Biochem. 245, 457-464). It was shown to reduce 33% outward HC channel (hippocampal neurons) currents at 10 mu M The solution structure of BmP01 was determined by 2D H-1 NMR spectroscopy. The NOEs, coupling constants, and H-D exchange obtained from NMR spectroscopy were used in structural calculations. The conformation of BmP01 is composed of a short alpha-helix (Cys 3-Thr 12) and a two-stranded antiparalleI beta-sheet (Ala IB-Asp 20 and Lys 23-Pro 28). There are three disulfide bridges (Cys S-Cys 19, Cys 6-Cys 24 and Cys 10-Cys 26) connecting the alpha-helix and beta-sheet. Asp 20 to Lys 23 form a type II turn linking the two strands. Structural and electrostatic potential comparison between BmP01 and its analogues are also presented.