Isolation and primary structure of a potent toxin from the venom of the scorpion Centruroides sculpturatus Ewing

A potent toxin has been purified from the venom of the scorpion Centruroides sculpturatus Ewing using the ion‐exchange resin CM‐Sepharose CL‐6B at basic pH. The toxin, designated CsE M₁, comprised 65 amino acid residues and its primary structure was established as: Lys‐Glu‐Gly‐Tyr‐Leu‐Val‐Asn‐Ser‐Tyr‐Thr¹⁰‐Gly‐Cys‐Lys‐Tyr‐Glu‐Cys‐Leu‐Lys‐Leu‐Gly²⁰‐Asp‐Asn‐Asp‐Tyr‐Cys‐Leu‐Arg‐Glu‐Cys‐Arg³⁰‐Gln‐Gln‐Tyr‐Gly‐Lys‐Ser‐Gly‐Gly‐Tyr‐Cys⁴⁰‐Tyr‐Ala‐Phe‐Ala‐Cys‐Trp‐Cys‐Thr‐His‐Leu⁵⁰‐Tyr‐Glu‐Gln‐Ala‐Val‐Val‐Trp‐Pro‐Leu‐Pro⁶⁰‐Asn‐Lys‐Thr‐Cys‐Asn. CsE M₁ is the most lethal protein to be identified in C. sculpturatus venom and the LD₅₀ of the toxin, determined by subcutaneous injection into Swiss mice, is 87 μg/kg. CsE M₁ shows strong structural similarity (92% positional identity) to the most potent β‐toxin, Css II, from the Mexican scorpion, Centruroides suffusus suffusus but is quite dissimilar to the previously characterized toxins with low potency isolated from C. sculpturarus Ewing.