CHEMICAL SYNTHESIS AND CHARACTERIZATION OF MAUROTOXIN, A SHORT SCORPION TOXIN WITH 4 DISULFIDE BRIDGES THAT ACTS ON K+ CHANNELS

Maurotoxin is a toxin isolated from the venom of the Tunisian chactoid scorpion Scorpio maurus. It is a 34-amino-acid peptide cross-linked b y four disulfide bridges; Maurotoxin competes with radiolabeled apamin and kaliotoxin for binding to rat-brain synaptosomes. Due to its very low concentration in venom (0.6% of the proteins), maurotoxin was che mically synthesized by means of an optimized solid-phase technique. Th e synthetic maurotoxin was characterized. It was lethal to mice follow ing intracerebroventricular injection (LD(50), 80 ng/mouse). The synth etic maurotoxin competed with I-125-apamin and I-125-kalio-toxin for b inding to rat-brain synaptosomes with half-maximal effects at concentr ations of 5 nM and 0.2 nM, respectively. Synthetic maurotoxin was test ed on K+ channels and was found to block the Kv1.1, Kv1.2, and Kv1.3 c urrents with half-maximal blockage (IC50) at 37, 0.8 and 150 nM, respe ctively. Thus, maurotoxin is a scorpion toxin with four disulfide brid ges that acts on K+ channels. The half-cystine pairings of synthetic m aurotoxin were identified by enzymatic cleavage. The pairings were Cys 3-Cys24, Cys9-Cys29, Cys13-Cys19 and Cys31-Cys34. This disulfide organ ization is unique among known scorpion toxins. The physicochemical and pharmacological properties of synthetic maurotoxin were indistinguish able from those of natural maurotoxin, which suggests that natural mau rotoxin adopts the same half-cystine pairing pattern. The conformation of synthetic maurotoxin was investigated by means of circular dichroi sm spectroscopy and molecular modeling. In spite of its unusual half-c ystine pairings, the synthetic-maurotoxin conformation appears to be s imilar to that of other short scorpion toxins.