Structural Determination of Bl-3, an Insecticidal Peptide from the <i>Buthacus leptochelys</i> Scorpion Venom

Scorpion venoms contain a variety of peptides that exhibit toxicity toward insects or mammals by acting on ion channels. We previously isolated four insecticidal peptides (Bl-1, Bl-2, Bl-3, and Bl-4) from the venom of <i>Buthacus leptochelys</i>. Among these, the complete amino acid sequence of Bl-1 was determined, whereas only N-terminal partial sequences were obtained for the others. In the present study, we determined the complete sequence of Bl-3 through <i>de novo</i> sequencing of enzymatically digested fragments. The discrimination between Leu and Ile was achieved based on side-chain fragmentation observed under high-energy collision-induced dissociation conditions. Bl-3 was identified as a 65-residue peptide containing four disulfide bonds. During the sequencing analysis, deamidation of the Asn residue at position 30 was observed, which is likely to have occurred after the purification step. Sequence comparison revealed that Bl-3 shares high similarity with α-toxins that act on sodium channels and exhibit nonselective toxicity toward both insects and mammals. These findings suggest that Bl-3 is likely to exert nonselective toxicity through a mechanism similar to that of α-toxins.