Molecular characterization of a K+ channel blocker in the scorpion Buthus martensii Karsch

K+ channel blockers of scorpion venoms are of important value in studying p harmacology and physiology of specific K+ channel of cells. Based on the am ino acid sequences of BmP01 previously characterized as a small-conductance Ca2+-activated K+ channel blocker, two "back to back" degenarate primers h ave been designed and synthesized for inverse PCR strategy, its full-length cDNA has been cloned from the venom gland of the Chinese scorpion Buthus m artensii. The cDNA is composed of 3 parts: 5' UTR, ORF and 3' UTR. The flan king sequence of translation initiation codon ATG is AAAATGA, which is high ly conserved in scorpion Na+ channel toxin and protozoan genes, suggesting that these genes may have followed a common mechanism for translation initi ation. The 3' UTR contains poly(A) signal AATAAA. The open reading frame en codes a precursor of 57 residues with a signal peptide of 28 residues and a mature peptide of 29 residues. The signal peptide is rich in hydrophobic a mino acid residues and its length is significantly different from that of t he determined scorpion Na+ channel toxin. The deduced amino acid sequence o f mature peptide is completely consistent with BmP01 previously determined by primary structure analysis.