EVIDENCE FOR A NEW CLASS OF SCORPION TOXINS ACTIVE AGAINST K+ CHANNELS

cDNAs encoding novel long-chain scorpion toxins (64 amino acid residue s, including only six cysteines) were isolated from cDNA libraries pro duced from the venom glands of the scorpions Androctonus australis fro m Old World and Tityus serrulatus from New World. The encoded peptides were very similar to a recently identified toxin from T. serrulatu, w hich is active against the voltage-sensitive 'delayed-rectifier' potas sium channel, but they were completely different from the long-chain a nd short-chain scorpion toxins already characterised. However, there w as some sequence similarity (42%) between these new toxins, Aa TX KP a nd Ts TX KP, and scorpion defensins purified from the hemolymph of But hidae scorpions Leiurus quinquestriatus and A. australis. Thus, accord ing to a multiple sequence alignment using CLUSTAL, these new toxins s eem to be related to the scorpion defensins. (C) 1998 Federation of Eu ropean Biochemical Societies.