Isolation and characterization of a novel non-selective β-toxin from the venom of the scorpion Isometrus maculatus.

Scorpion venom is composed of a number of peptides, many of which show neurotoxicity. The Isometrus maculatus scorpion, belonging to the Buthidae family, is found in many tropical regions, including the southern islands of Japan, but there have been no reports on the isolation of toxins from its venom affecting sodium channels. We isolated in this study a novel toxin, Im-2, from the I. maculatus venom. Im-2 induced paralysis in crickets after injecting 20 µg/g of body weight. Im-2 also induced lethality in mice after an intracerebroventricular injection, indicating that Im-2 had non-selective toxicity between insects and mammals. Im-2 consists of 68 amino acids cross-linked by 4 disulfide bonds, and has sequence similarity to scorpion β-toxins that have been reported to affect the sodium channels of both insects and mammals. The toxic symptoms caused by Im-2 suggest that it acted on the nervous system and shared the action mechanism(s) with sequence-homologous β-toxins.