OdTx12/GNA, a chimeric variant of a β excitatory toxin from Odontobuthus doriae, reveals oral toxicity towards Locusta migratoria and Tenebrio molitor.

OdTx12, a beta excitatory toxin from Odontobothus doriae had previously been identified and characterized. It had been shown that OdTx12 causes significant lethal effects on insects by injection but does not show any toxicity on mice. Due to the natural ineffectiveness of scorpion toxins to act as oral toxins, OdTx12 was fused to Galanthus nivalis agglutinin (GNA), a protein with the potential to cross the insect gut. The sequence of OdTx1 2/GNA gene was chemically synthesized, cloned in Escherichia coli , and expressed. The effect of the purified fusion protein (OdTx12/GNA) was assessed on the insect and mammalian cell lines, insect larvae and mice. Toxicity assay on insect cell culture (SF9 cell line) showed comparable toxicity between OdTx12 and OdTx12/GNA (LD50 of 0.0030 and 0.0048 μM, respectively). Also very similar mortality rates were observed by injecting OdTx12 and OdTx12/GNA to Locusta migratoria and Tenebrio molitor. Oral administration of OdTx12/GNA, after five days of feeding, resulted in 96.6% and 98.3% mortality of L. migratoria and T. molitor larvae with an LC50 of 0.69 and 0.43 nmol/g of insect food, respectively, while OdTx12 alone did not cause any toxic effects on the larvae orally, suggesting the role of GNA in delivering the toxin to the insect's haemolymph. No toxicity or mortality was observed after toxicity testing of OdTx12/GNA on a mammalian cell line (HEP-2) or any mortality in vivo, by testing the protein in the laboratory mouse. Herein, we demonstrated that the fusion protein OdTx12/GNA could be considered an effective toxin for the biological control of insects. [Display omitted] • OdTx12, a toxin from Odontobothus doriae scorpion was recombinantly fused to the snowdrop lectin (GNA). • The fusion protein (OdTx12/GNA) and OdTx12 showed similar toxic effects on the model insects by injection. • OdTx12/GNA caused high mortality in the insects orally but OdTx12 itself showed no toxicity effects by the same route. • GNA caused the toxin to pass through the gut epithelium and reach the insect haemolymph. • OdTx12/GNA may be considered as a biological insecticide candidate. [ABSTRACT FROM AUTHOR]