Recombinant expression, purification, and characterization of scorpion toxin BmαTX14

Similar neurotoxin expression profiles of traditional Chinese scorpion medicine material between juvenile and adult Mesobuthus martensii scorpions revealed by multiple strategic proteomics

ETHNOPHARMACOLOGICAL RELEVANCE

The Mesobuthus martensii scorpions, called as "Quanxie", are known Chinese medicinal material base on the "Combat poison with poison" strategy for more than one thousand years, and still widely used to treat various diseases according to the Pharmacopoeia of the People's Republic of China nowadays.

AIM OF STUDY

The study aims to investigate the similarity of scorpion neurotoxins at the protein level between the juvenile and adult Mesobuthus martensii scorpions as Chinese medicine materials.

MATERIALS AND METHODS

The second-, third- and fourth-instar, and adult Mesobuthus martensii scorpions were collected for the characterization of neurotoxin expression through multiple strategic proteomics, including undigested scorpion venom, endopeptidase-digested, and undigested scorpion telson extract for the sample analysis.

RESULTS

Based on the known 107 scorpion neurotoxins from the genomic and transcriptomic analysis of adult Mesobuthus martensii scorpions, the multiple strategic proteomics first revealed that neurotoxins exhibited more stability in telson extract than secreted venom. In the reported transcripts of scorpion neurotoxins, approximately 53%, 56%, 66% and 78% of neurotoxins were detected through undigested scorpion venom, the endopeptidase Arg-C-, Lys-C-digested telson extract, and undigested telson extract strategies, respectively. Nearly 79% of scorpion neurotoxins detected in third-instar Mesobuthus martensii scorpions represent the largest number of scorpion neurotoxins from proteomic analysis to date. Moreover, a total of 84% of scorpion neurotoxins were successfully identified at the protein level, and similar neurotoxin expression profiles in second-, third- and fourth-instar, and adult Mesobuthus martensii scorpions were first revealed by the multiple strategic proteomics.

CONCLUSION

These findings for the first time demonstrate the similar neurotoxin expression profiles between the juvenile and adult Mesobuthus martensii scorpions as Chinese medicinal material, which would serve as a paradigm for further toxin analysis from different venomous animals.

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.

Production of recombinant venom peptides as tools for ion channel research

Animal venom is a rich source for peptide toxins that bind and modulate the function of ion channels. Owing to their ability to bind receptor sites on the channel protein with high affinity and specificity, peptide neurotoxins have become an indispensable tool for ion channel research. Recent breakthroughs in structural biology and advances in computer simulations of biomolecules have sparked a new interest in animal toxins as probes of channel protein structure and function. Here, we focus on methods used to produce animal toxins for research purposes using recombinant expression. The specific challenges associated with heterologous production of venom peptides are discussed, and several methods targeting these issues are presented with an emphasis on E. coli based systems. An efficient protocol for the bacterial expression, folding, and purification of recombinant venom peptides is described.

Cytotoxic and lethal effects of recombinant β-BUTX-Lqq1a peptide against Lepidopteran insects and cell lines

Extensive usage of synthetic chemical pesticides have collateral effect in harming the health, environment and development of resistance in insect pests. Scorpion produces variety of molecules that are specific to insects, mammals and to both. Insect specific molecules act as potential candidature as an alternative to synthetic chemical pesticides. We have successfully expressed and purified recombinant Scorpion Leiurus quinquestriatus quinquestriaus β-BUTX-Lqq1a toxin in bacterial system. Cytotoxic activity assay with the help of insect cell line Sf-21 from Spodoptera frugiperda reveals that mean IC₅₀ 1.72-3.0 μg ml ^-1 significantly reduced the cell proliferation when compared with control. Microscopic examination of treated Sf-21 cell lines also showed changes in the cell morphology such as cell membrane blebbing, cell shrinkage and granulated apoptotic bodies. When β-BUTX-Lqq1a was hemocoelly injected with various doses, significant reduction in survival of Helicoverpa armigera (LC₅₀ = 0.13 μg insect^-1) and Spodoptera litura (LC₅₀ = 0.147 μg insect ^-1) were noticeable with immediate paralysis, and reduced feeding when compared with control. Toxicity with purified recombinant β-BUTX-Lqq1a protein towards insect cell line Sf-21 and major agricultural pest was demonstrated by various bioassays. Cytotoxicity and insect bioassay demonstrated the potential use of β-BUTX-Lqq1a protein as an effective insecticide against lepidopteran insects. These results strongly suggest that the development of rational insecticidal molecule against with significant promise.

Microbial production of toxins from the scorpion venom: properties and applications

Scorpion venom are composed mainly of bioactive proteins and peptides that may serve as lead compounds for the design of biotechnological tools and therapeutic drugs. However, exploring the therapeutic potential of scorpion venom components is mainly impaired by the low yield of purified toxins from milked venom. Therefore, production of toxin-derived peptides and proteins by heterologous expression is the strategy of choice for research groups and pharmaceutical industry to overcome this limitation. Recombinant expression in microorganisms is often the first choice, since bacteria and yeast systems combine high level of recombinant protein expression, fast cell growth and multiplication and simple media requirement. Herein, we present a comprehensive revision, which describes the scorpion venom components that were produced in their recombinant forms using microbial systems. In addition, we highlight the pros and cons of performing the heterologous expression of these compounds, regarding the particularities of each microorganism and how these processes can affect the application of these venom components. The most used microbial system in the heterologous expression of scorpion venom components is Escherichia coli (85%), and among all the recombinant venom components produced, 69% were neurotoxins. This review may light up future researchers in the choice of the best expression system to produce scorpion venom components of interest.

Expression of recombinant α-toxin BmKM9 from scorpion Buthus martensii Karsch and its functional characterization on sodium channels

Scorpion toxins are invaluable pharmacological tools for studying ion channels and potential drugs for channelopathies. The long-chain toxins from scorpion venom with four disulfide bridges exhibit their unusual bioactivity or biotoxicity by acting on the sodium channels. However, the functional properties of most toxins are still unclear due to their tiny amounts in crude venom and their challenging production by chemical and gene engineering techniques. Here, we expressed one of the long-chain α-toxins, BmKM9, found in the venom of the scorpion Buthus martensii Karsch and characterized its pharmacological properties on sodium channels. Unlike previous toxin production, the recombinant BmKM9 (rBmKM9) possessed no additional amino acid residues such as the His-tag and thrombin cleavage site. The refolded toxin could inhibit the inactivation of rNa_v1.4, hNa_v1.5 and hNa_v1.7 sodium channels. Dose-response experiments were further conducted on these channels. The calculated EC₅₀ values were 131.7±6.6nM for rNa_v1.4, 454.2±50.1nM for hNa_v1.5 and 30.9±10.3μM for hNa_v1.7. The channel activation experiments indicated that the rBmKM9 toxin could shift the activation curves of rNa_v1.4 and hNa_v1.5 channels toward a more negative direction and present the typical features of a β-toxin. However, instead of the same activation property on sodium channels, the rBmKM9 toxin could result in different inactivation shift capabilities on rNa_v1.4 and hNa_v1.5 channels. The V_1/2 values of the steady-state inactivation were altered to be more positive for rNa_v1.4 and more negative for hNa_v1.5. Moreover, the recovery of the hNa_v1.5 channel from inactivation was more significantly delayed than that of the rNa_v1.4 channel by exposure to rBmKM9. Together, these findings highlighted that the rBmKM9 toxin presents the pharmacological properties of both α- and β-toxins, which would increase the challenge to the classical classification of scorpion toxins. Furthermore, the expression method and functional information on sodium channels would promote the potential application of toxins and contribute to further channel structural and functional studies.

Adaptive evolution of insect selective excitatory β-type sodium channel neurotoxins from scorpion venom

Insect selective excitatory β-type sodium channel neurotoxins from scorpion venom (β-NaScTxs) are composed of about 70-76 amino acid residues and share a common scaffold stabilized by four unique disulfide bonds. The phylogenetic analysis of these toxins was hindered by limited sequence data. In our recent study, two new insect selective excitatory β-NaScTxs, LmIT and ImIT, were isolated from Lychas mucronatus and Isometrus maculatus, respectively. With the sequences previously reported, we examined the adaptive molecular evolution of insect selective excitatory β-NaScTxs by estimating the nonsynonymous-to-synonymous rate ratio (ω=d_N/d_S). The results revealed 12 positively selected sites in the genes of insect selective excitatory β-NaScTxs. Moreover, these positively selected sites match well with the sites important for interacting with sodium channels, as demonstrated in previous mutagenesis study. These results reveal that adaptive evolution after gene duplication is one of the most important genetic mechanisms of scorpion neurotoxin diversification.

Toxin Fused with SUMO Tag: A New Expression Vector Strategy to Obtain Recombinant Venom Toxins with Easy Tag Removal inside the Bacteria

Many animal toxins may target the same molecules that need to be controlled in certain pathologies; therefore, some toxins have led to the formulation of drugs that are presently used, and many other drugs are still under development. Nevertheless, collecting sufficient toxins from the original source might be a limiting factor in studying their biological activities. Thus, molecular biology techniques have been applied in order to obtain large amounts of recombinant toxins into Escherichia coli. However, most animal toxins are difficult to express in this system, which results in insoluble, misfolded, or unstable proteins. To solve these issues, toxins have been fused with tags that may improve protein expression, solubility, and stability. Among these tags, the SUMO (small ubiquitin-related modifier) has been shown to be very efficient and can be removed by the Ulp1 protease. However, removing SUMO is a labor- and time-consuming process. To enhance this system, here we show the construction of a bicistronic vector that allows the expression of any protein fused to both the SUMO and Ulp1 protease. In this way, after expression, Ulp1 is able to cleave SUMO and leave the protein interest-free and ready for purification. This strategy was validated through the expression of a new phospholipase D from the spider Loxosceles gaucho and a disintegrin from the Bothrops insularis snake. Both recombinant toxins showed good yield and preserved biological activities, indicating that the bicistronic vector may be a viable method to produce proteins that are difficult to express.

Scorpion toxin peptide action at the ion channel subunit level

This review categorizes functionally validated actions of defined scorpion toxin (SCTX) neuropeptides across ion channel subclasses, highlighting key trends in this rapidly evolving field. Scorpion envenomation is a common event in many tropical and subtropical countries, with neuropharmacological actions, particularly autonomic nervous system modulation, causing significant mortality. The primary active agents within scorpion venoms are a diverse group of small neuropeptides that elicit specific potent actions across a wide range of ion channel classes. The identification and functional characterisation of these SCTX peptides has tremendous potential for development of novel pharmaceuticals that advance knowledge of ion channels and establish lead compounds for treatment of excitable tissue disorders. This review delineates the unique specificities of 320 individual SCTX peptides that collectively act on 41 ion channel subclasses. Thus the SCTX research field has significant translational implications for pathophysiology spanning neurotransmission, neurohumoral signalling, sensori-motor systems and excitation-contraction coupling. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

rBmαTX14 Increases the Life Span and Promotes the Locomotion of Caenorhabditis Elegans

The scorpion has been extensively used in various pharmacological profiles or as food supplies. The exploration of scorpion venom has been reported due to the presence of recombinant peptides. rBmαTX14 is an α-neurotoxin extracted from the venom gland of the East Asian scorpion Buthus martensii Karsch and can affect ion channel conductance. Here, we investigated the functions of rBmαTX14 using the Caenorhabditis elegans model. Using western blot analysis, rBmαTX14 was shown to be expressed both in the cytoplasm and inclusion bodies in the E.coli Rosetta (DE3) strain. Circular dichroism spectroscopy analysis demonstrated that purified rBmαTX14 retained its biological structures. Next, feeding nematodes with E.coli Rosetta (DE3) expressing rBmαTX14 caused extension of the life span and promoted the locomotion of the nematodes. In addition, we identified several genes that play various roles in the life span and locomotion of C. elegans through microarray analysis and quantitative real-time PCR. Furthermore, if the amino acid site H₁₅ of rBmαTX14 was mutated, rBmαTX14 no longer promoted the C. elegans life span. In conclusion, the results not only demonstrated the functions and mechanism of rBmαTX14 in C. elegans, but also provided the new sight in the utility of recombinant peptides from scorpion venom.

Wheat germ in vitro translation to produce one of the most toxic sodium channel specific toxins

Envenoming following scorpion sting is a common emergency in many parts of the world. During scorpion envenoming, highly toxic small polypeptides of the venom diffuse rapidly within the victim causing serious medical problems. The exploration of toxin structure-function relationship would benefit from the generation of soluble recombinant scorpion toxins in Escherichia coli. We developed an in vitro wheat germ translation system for the expression of the highly toxic Aah (Androctonus australis hector)II protein that requires the proper formation of four disulphide bonds. Soluble, recombinant N-terminal GST (glutathione S-transferase)-tagged AahII toxin is obtained in this in vitro translation system. After proteolytic removal of the GST-tag, purified rAahII (recombinant AahII) toxin, which contains two extra amino acids at its N terminal relative to the native AahII, is highly toxic after i.c.v. (intracerebroventricular) injection in Swiss mice. An LD₅₀ (median lethal dose)-value of 10 ng (or 1.33 pmol), close to that of the native toxin (LD₅₀ of 3 ng) indicates that the wheat germ in vitro translation system produces properly folded and biological active rAahII. In addition, NbAahII10 (Androctonus australis hector nanobody 10), a camel single domain antibody fragment, raised against the native AahII toxin, recognizes its cognate conformational epitope on the recombinant toxin and neutralizes the toxicity of purified rAahII upon injection in mice.

A wheat germ embryo derived cell-free translation system expresses a biologically active, highly toxic scorpion venom protein that is fully neutralized by a camel single domain antibody fragment raised against the native scorpion toxin.

Overview of scorpion species from China and their toxins

Scorpions are one of the most ancient groups of terrestrial animals. They have maintained a steady morphology over more than 400 million years of evolution. Their venom arsenals for capturing prey and defending against predators may play a critical role in their ancient and conservative appearance. In the current review, we present the scorpion fauna of China: 53 species covering five families and 12 genera. We also systematically list toxins or genes from Chinese scorpion species, involving eight species covering four families. Furthermore, we review the diverse functions of typical toxins from Chinese scorpion species, involving Na⁺ channel modulators, K⁺ channel blockers, antimicrobial peptides and protease inhibitors. Using scorpion species and their toxins from China as an example, we build the bridge between scorpion species and their toxins, which helps us to understand the molecular and functional diversity of scorpion venom arsenal, the dynamic and functional evolution of scorpion toxins, and the potential relationships of scorpion species and their toxins.

Characterization of a novel BmαTX47 toxin modulating sodium channels: the crucial role of expression vectors in toxin pharmacological activity

Long-chain scorpion toxins with four disulfide bridges exhibit various pharmacological features towards the different voltage-gated sodium channel subtypes. However, the toxin production still remains a huge challenge. Here, we reported the effects of different expression vectors on the pharmacological properties of a novel toxin BmαTX47 from the scorpion Buthus martensii Karsch. The recombinant BmαTX47 was obtained using the expression vector pET-14b and pET-28a, respectively. Pharmacological experiments showed that the recombinant BmαTX47 was a new α-scorpion toxin which could inhibit the fast inactivation of rNa_v1.2, mNa_v1.4 and hNa_v1.5 channels. Importantly, the different expression vectors were found to strongly affect BmαTX47 pharmacological activities while toxins were obtained by the same expression and purification procedures. When 10 µM recombinant BmαTX47 from the pET-28a vector was applied, the values of I_5ms/I_peak for rNa_v1.2, mNa_v1.4 and hNa_v1.5 channels were 44.12% ± 3.17%, 25.40% ± 4.89% and 65.34% ± 3.86%, respectively, which were better than those values of 11.33% ± 1.46%, 15.96% ± 1.87% and 5.24% ± 2.38% for rNa_v1.2, mNa_v1.4 and hNa_v1.5 channels delayed by 10 µM recombinant BmαTX47 from the pET-14b vector. The dose-response experiments further indicated the EC₅₀ values of recombinant BmαTX47 from the pET-28a vector were 7262.9 ± 755.9 nM for rNa_v1.2 channel and 1005.8 ± 118.6 nM for hNav1.5 channel, respectively. Together, these findings highlighted the important role of expression vectors in scorpion toxin pharmacological properties, which would accelerate the understanding of the structure-function relationships of scorpion toxins and promote the potential application of toxins in the near future.

Gene construction, expression and functional testing of an inotropic peptide from the venom of the black scorpion Hottentotta judaicus

Anti-insect depressant toxins represent a subfamily of scorpion venom-derived β-toxins that are polypeptides composed of 61-65 amino acid residues stabilized by four disulfide bridges. These toxins affect the activation of voltage-sensitive sodium channels (NaScTx) and exhibit the preferential ability to induce flaccid paralysis in insect larvae. Here we demonstrate the recombinant expression of the novel cardiac inotropic peptide (Bj-IP) that was classified as an anti-insect depressant βNaScTx isolated from the venom of Hottentotta judaicus. By using "splicing by overlap extension" (SOE)-PCR, allowing for the first time one step de novo synthesis of long-chain scorpion toxin genes, we generated a codon-optimized DNA fragment of Bj-IP for cloning into the Escherichia coli vector pQE30. Moreover, the gene of interest was fused to a 6xHis coding DNA sequence. Subsequent recombinant expression was performed in E. coli KRX. The purification of the polypeptide was achieved by a combination of NiNTA agarose columns and RP (C(18)) high-performance liquid chromatography. The purified fusion protein was digested with factor Xa resulting in the elution of Bj-IP. The yield of recombinant Bj-IP expression was approximately 4.5 mg per liter of culture. Mass spectrometry confirmed the theoretical total mass of Bj-IP (6608 Da). Tag-free Bj-IP was refolded in guanidine chloride buffer with a glutathione redox system which was supplemented with different additives at 16 °C. Supplementation with 10% glycerol produced Bj-IP folding forms that exhibited reproducible biological activity in mouse cardiomyocytes. Cell contractility was increased by almost 3-fold and decay kinetics were hasten by 47% after administration of Bj-IP. Taken together, here we show the recombinant expression of the functionally active cardiac inotropic peptide Bj-IP, a new βNaScTx from H. judaicus, for promising pharmacological applications. Furthermore, our data suggest that the use of SOE-PCR may help to facilitate in future the high throughput of cloning and/or modification of scorpion toxin genes.