ISOLATION, CHARACTERIZATION AND COMPARISON OF A NOVEL CRUSTACEAN TOXIN WITH A MAMMALIAN TOXIN FROM THE VENOM OF THE SCORPION CENTRUROIDES NOXIUS HOFFMANN

A novel crustacean-specific toxin, Cn5, containing 66 amino acid resid ues was isolated from the venom of the scorpion Centruroides noxius Ho ffmann. It is stabilized by four disulfide bridges, formed between Cys 12-Cys65, Cys16-Cys41, Cys25-Cys46 and Cys29-Cys48. Toxicity tests rev ealed that Cn5 is a toxin that affects arthropods but not mammals. How ever, at high concentrations, Cn5 does displace the mammal-specific to xin Cn2 from rat brain synaptosomes. The concentration of Cn5 that pro duces half-maximal inhibition (IC50) was estimated to be 100 mu M. Seq uence comparison of Cn5 with toxin Cn2, a mammal-specific toxin from t he same scorpion, showed the presence of two sequence stretches, at po sitions 30 to 38 and 49 to 58, where the majority of the differences a re concentrated. On the three-dimensional structure of Cn5 it is demon strated that these two sequence stretches form a continuous surface re gion near the site thought to bind to the sodium channel. We assume th at this region might be implicated in determining species specificity: (C) 1997 Elsevier Science Inc.