Cloning and expression of OdTx12, a β excitatory toxin from Odontobuthus doriae, in Escherichia coli and evaluation of its bioactivity in Locusta migratoria

Evaluation of recombinant toxin JFTX-23, an oral-effective anti-insect peptide from the spider Selenocosmia jiafu venom gland proteome

Excessive utilization of chemical pesticides for pest control can lead to adverse consequences for the health of humans and other organisms and may also cause irreversible ecological changes; therefore, the use of biologically derived insecticides can be a safe alternate strategy. Transcriptomic studies have shown JFTX- 23,a small peptide from the spider Selenocosmia jiafuis highly similar to U1-TRTX-Sp1, a well-characterized oral-effective insecticide toxin from the Australian tarantula Selenotypus plumipes. First, we evaluated the JFTX-23 peptide sequence using bioinformatics tools and modeling studies. Preliminary results showed a high similarity of JFTX-23 to JZTX-58 (91.67%) and U1-TRTX-Sp1 (86.11%). Superimposition of the α-carbons of the modeled JFTX-23 and U1-TRTX-Sp1 demonstrated a very high similarity of the 3-D structure of the two peptides (RMSD of 0.02 Å).The injection assay of JFTX-23 in Helicoverpa armigera indicated an LD50 of 0.077 and 0.423 nmol/insect after 24 and 120 h, respectively. JFTX-23 was toxic to H. armigera via oral administration with an LC50 of 1.16 nmol/g food after 5 days, which was comparable to the toxicity of the oral-effective toxin U1-TRTX-Sp1. Our studies have shown that JFTX-23 is a potent oral-effective toxin that can be considered an attractive candidate for the biological control of insect pests.

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 OdTx12/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.

Expression and purification of recombinant alpha-toxin AnCra1 from the scorpion Androctonus crassicauda and its functional characterization on mammalian sodium channels

BACKGROUND

Alpha-scorpion toxins with long-chain peptide and four disulfide bonds represent diverse pharmacological profiles for various subtypes of voltage-gated sodium channels. Obtaining the natural toxins are difficult and time-consuming process, which represents the major difficulty to interpreting analysis of their structural and functional properties.

METHODS AND RESULTS

This study describes the toxin peptide and plasmid construct containing the gene coding for mammalian toxin AnCra1 from the scorpion Androctonus crassicauda venom. We have established genetic construction of fusion protein in pET32a + vector containing thioredoxin (Trx-tag), enterokinase cleavage site and 6xhistidine-tag for efficient expression in Escherichia coli strain RG2 (DE3). The soluble expressed peptide, then purified by Ni-NTA resin affinity chromatography and its purity was confirmed by reverse-phase HPLC and mass spectrometry (7433.54 Da.). The electrophysiological data showed that recombinant AnCra1 selectively inhibits the fast inactivation of hNav1.7 channel (EC₅₀ = 136.7 ± 6.6 nM).

CONCLUSIONS

Our findings demonstrate that the AnCra1 is structurally and functionally analogous to alpha excitatory toxins; furthermore, expression and purification of bioactive scorpion toxins in bacterial cells can be a practicable and efficient way to obtain a novel source of toxin peptides as tools to study the function and physiological responses of ion channels.