A scorpion venom neurotoxin paralytic to insects that affects sodium current inactivation: purification, primary structure, and mode of action

Abstract

A new toxin, Lqh alpha IT, which caused a unique mode of paralysis of blowfly larvae, was purified from the venom of the scorpion Leiurus quinquestriatus hebraeus, and its structural and pharmacological properties were compared to those of three other groups of neurotoxins found in Buthinae scorpion venoms. Like the excitatory and depressant insect-selective neurotoxins, Lqh alpha IT was highly toxic to insects, but it differed from these toxins in two important characteristics: (a) Lqh alpha IT lacked strict selectivity for insects; it was highly toxic to crustaceans and had a measurable but low toxicity to mice. (b) It did not displace an excitatory insect toxin, 125I-AaIT, from its binding sites in the insect neuronal membrane; this indicates that the binding sites for Lqh alpha IT are different from those shared by the excitatory and depressant toxins. However, in its primary structure and its effect on excitable tissues, Lqh alpha IT strongly resembled the well-characterized alpha scorpion toxins, which affect mammals. The amino acid sequence was identical with alpha toxin sequences in 55%-75% of positions. This degree of similarity is comparable to that seen among the alpha toxins themselves. Voltage- and current-clamp studies showed that Lqh alpha IT caused an extreme prolongation of the action potential in both cockroach giant axon and rat skeletal muscle preparations as a result of the slowing and incomplete inactivation of the sodium currents. These observations indicate that Lqh alpha IT is an alpha toxin which acts on insect sodium channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional expression of an alpha anti‐insect scorpion neurotoxin in insect cells and lepidopterous larvae

“…Sustained contraction paralysis at 5 min post-injection indicated the presence of active alpha insect toxin [3].…”

“…The dried material was subjected to three successive chromatography steps: (a) gel filtration on Sephadex G-50 fine (Pharmacia); (b) cation-exchange chromatography on CM-52 cellulose (Whatman); and (c) reverse-phase HPLC on RP-C,s column (4.6 x 250 mm, Vydac). The amino acid sequence was performed by automated Edman degradation using an Applied Biosystem gas-phase sequencer connected to its corresponding PTH-analyzer and data system according to a previously described [3] method.…”

“…The alpha toxins are responsible for human envenomation by scorpion venoms [2] but they affect insects as well [1]. An alpha toxin, Lqh~IT, recently isolated from the venom of the Israeli yellow scorpion Leiurus quinquestriatus hebraeus [3] was shown to affect insects strongly and to possess weak toxicity towards mammals. LqhcdT, resembles alpha mammal toxins in its primary structure and ability to slow or even block the sodium current inactivation process in an insect axonal preparation [3].…”

“…An alpha toxin, Lqh~IT, recently isolated from the venom of the Israeli yellow scorpion Leiurus quinquestriatus hebraeus [3] was shown to affect insects strongly and to possess weak toxicity towards mammals. LqhcdT, resembles alpha mammal toxins in its primary structure and ability to slow or even block the sodium current inactivation process in an insect axonal preparation [3]. However, LqhcdT has been shown to bind with high affinity to an insect but not to a mammal neuronal preparation [4].…”

“…Thus, Lqh~IT is able to distinguish between insect and mammalian sodium channels [3,4] and hence it may serve as an excellent model for the clarification of structural elements that confer high anti-insect specificity. This demands the expression of the corresponding cDNA to enable a genetic approach for its structure-activity relationships.…”