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.