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

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.

Ts17, a Tityus serrulatus β-toxin structurally related to α-scorpion toxins

Ts17 was purified from the venom of the scorpion Tityus serrulatus, the most dangerous scorpion species in Brazil. The activity on Na_v1.1-Na_v1.7 channels was electrophysiologically characterized by patch-clamp technique. Ts17 amino acid sequence indicated high similarity to alpha-scorpion toxins; however, it presented beta-toxin activity, altering the kinetics of the Na⁺-channels. The most affected subtypes during activation (with and without prepulse) and inactivation phases were Na_v1.2 and Na_v1.5, respectively. For recovery from inactivation, the most affected voltage-gated sodium channel was Na_v1.5. Circular dichroism spectra showed that Ts17 presents mainly β-sheet and unordered structures at all analyzed pHs, and the maximum value of α-helix was found at pH 4.0 (13.3 %). Based on the results, Ts17 might be used as a template to develop a new cardiac drug. Key contribution Purification of Ts17 from Tityus serrulatus, electrophysiological characterization of Ts17 on voltage-gated sodium channel subtypes, β-toxin classification.

Mouse β-Defensin 3, A Defensin Inhibitor of Both Its Endogenous and Exogenous Potassium Channels

The human defensins are recently discovered to inhibit potassium channels, which are classical targets of the animal toxins. Whether other vertebrate defensins are potassium channel inhibitors remains unknown. In this work, we reported that the mouse β-defensin 3 (mBD3) was a novel inhibitor of both endogenous and exogenous potassium channels. The structural analysis showed that mBD3 is the most identical to human Kv1.3 channel-sensitive human β-defensin 2 (hBD2). However, the pharmacological profiles indicated that the recombinant mBD3 (rmBD3) weakly inhibited the mouse and human Kv1.3 channels. Different from the pharmacological features of human β-defensins, mBD3 more selectively inhibited the mouse Kv1.6 and human KCNQ1/KCNE1 channels with IC₅₀ values of 0.6 ± 0.4 μM and 1.2 ± 0.8 μM, respectively. The site directed mutagenesis experiments indicated that the extracellular pore region of mouse Kv1.6 channel was the interaction site of rmBD3. In addition, the minor effect on the channel conductance-voltage relationship curves implied that mBD3 might bind the extracellular transmembrane helices S1-S2 linker and/or S3-S4 linker of mouse Kv1.6 channel. Together, these findings not only revealed mBD3 as a novel inhibitor of both endogenous and exogenous potassium channels, but also provided a clue to investigate the role of mBD3-Kv1.6 channel interaction in the physiological and pathological field in the future.

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.

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.'

Voltage-Gated Sodium Channels: Structure, Function, Pharmacology, and Clinical Indications

The tremendous therapeutic potential of voltage-gated sodium channels (Na(v)s) has been the subject of many studies in the past and is of intense interest today. Na(v)1.7 channels in particular have received much attention recently because of strong genetic validation of their involvement in nociception. Here we summarize the current status of research in the Na(v) field and present the most relevant recent developments with respect to the molecular structure, general physiology, and pharmacology of distinct Na(v) channel subtypes. We discuss Na(v) channel ligands such as small molecules, toxins isolated from animal venoms, and the recently identified Na(v)1.7-selective antibody. Furthermore, we review eight characterized ligand binding sites on the Na(v) channel α subunit. Finally, we examine possible therapeutic applications of Na(v) ligands and provide an update on current clinical studies.