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Characterization of Am IT, an anti-insect β-toxin isolated from the venom of scorpion Androctonus mauretanicus

Naoual Oukkache, Rachid ElJaoudi, Fatima Chgoury, Marisa Teixeira Rocha, Jean-Marc Sabatier

Laboratory of Venoms and Toxins, Pasteur Institute of Morocco, Casablanca 20360, Morocco； Laboratory of Venoms-Herpetology, Institute Butantan, Sao Paulo 05503-900, Brazil； Laboratory of Pharmacology and Toxicology, Faculty of Medicine and Pharmacy, Rabat-Institus, Rabat, Morocco； Laboratory INSERM UMRs 1097, Aix-Marseille University, Science and Technology Park of Luminy, Marseille 13288, France

Abstract

In the present study, a ‘novel’ toxin, called Am IT from the venom of scorpion Androctonus mauretanicus is isolated and characterized. A detailed analysis of the action of Am IT on insect axonal sodium currents is reported. Am IT was purified through gel filtration followed by C18 reversed-phase HPLC. Toxicity of Am IT in vivo was assessed on male German cockroach (Blattella germanica) larvae and C57/BL6 mice. Cross-reactivity of Am IT with two β-toxins was evidenced using 125I-iodinated toxin-based radioimmunoassays with synaptosomal preparations from rat brain. The complete amino acid sequence of Am IT was finally determined by Edman sequencing. Am IT was observed to compete with AaH IT4 purified from the venom of scorpion Androctonus australis in binding assays. It was recognized by an antibody raised against a β-type toxin, which indicated some structural similarity with β-toxins (or related toxin family). The ‘novel’ toxin exhibited dual activity since it competed with anti-mammal toxins in binding assays as well as showed contracting activity to insect. The toxin competed with radio-labeled β-toxin Css IV by binding to Na+ channels of rat brain synaptosomes. Analysis of toxin amino acid sequences showed that Am IT shares high structural identity (92%) with AaH IT4. In conclusion, Am IT not only reveals an anti-insect compound properties secreted by ‘Old World’ scorpions, paralyzing insect larvae by binding to Na+ channels on larvae’s nerve-cell membranes, but also exerts toxic activity in mice, which is similar to anti-mammal toxins from ‘New World’ scorpions (North and South Americas). Therefore, Am IT appears to be structurally and functionally similar to AaH IT4.

Key words: Androctonus mauretanicus venom; scorpion toxin; Am IT; β-toxin; anti-mammal toxin; anti-insect toxin; sodium channel; toxicity; de novo sequencing; Edman degradation

Received: 2015-01-06　　Accepted: 2015-05-04

Corresponding author: Naoual Oukkache　　E-mail: oukkache.naoual@gmail.com

Citing This Article：

Naoual Oukkache, Rachid ElJaoudi, Fatima Chgoury, Marisa Teixeira Rocha, Jean-Marc Sabatier. Characterization of Am IT, an anti-insect β-toxin isolated from the venom of scorpion Androctonus mauretanicus. Acta Physiol Sin 2015; 67 (3): 295-304 (in Chinese with English abstract).