A depressant insect toxin with a novel analgesic effect from scorpion Buthus martensii Karsch

Scorpion venom peptides: Molecular diversity, structural characteristics, and therapeutic use from channelopathies to viral infections and cancers

Animal venom is an important evolutionary innovation in nature. As one of the most representative animal venoms, scorpion venom contains an extremely diverse set of bioactive peptides. Scorpion venom peptides not only are 'poisons' that immobilize, paralyze, kill, or dissolve preys but also become important candidates for drug development and design. Here, the review focuses on the molecular diversity of scorpion venom peptides, their typical structural characteristics, and their multiple therapeutic or pharmaceutical applications in channelopathies, viral infections and cancers. Especially, the group of scorpion toxin TRPTx targeting transient receptor potential (TRP) channels is systematically summarized and worthy of attention because TRP channels play a crucial role in the regulation of homeostasis and the occurrence of diseases in human. We also further establish the potential relationship between the molecular characteristics and functional applications of scorpion venom peptides to provide a research basis for modern drug development and clinical utilization of scorpion venom resources.

Scorpion Venom: Detriments and Benefits

Scorpion venom may cause severe medical complications and untimely death if injected into the human body. Neurotoxins are the main components of scorpion venom that are known to be responsible for the pathological manifestations of envenoming. Besides neurotoxins, a wide range of other bioactive molecules can be found in scorpion venoms. Advances in separation, characterization, and biotechnological approaches have enabled not only the development of more effective treatments against scorpion envenomings, but have also led to the discovery of several scorpion venom peptides with interesting therapeutic properties. Thus, scorpion venom may not only be a medical threat to human health, but could prove to be a valuable source of bioactive molecules that may serve as leads for the development of new therapies against current and emerging diseases. This review presents both the detrimental and beneficial properties of scorpion venom toxins and discusses the newest advances within the development of novel therapies against scorpion envenoming and the therapeutic perspectives for scorpion toxins in drug discovery.

BmK AEP, an Anti-Epileptic Peptide Distinctly Affects the Gating of Brain Subtypes of Voltage-Gated Sodium Channels

BmK AEP, a scorpion peptide purified form the venom of Buthus martensii Karsch, has been reported to display anti-epileptic activity. Voltage-gated sodium channels (VGSCs) are responsible for the rising phase of action potentials (APs) in neurons and, therefore, controlling neuronal excitability. To elucidate the potential molecular mechanisms responsible for its anti-epileptic activity, we examined the influence of BmK AEP on AP firing in cortical neurons and how BmK AEP influences brain subtypes of VGSCs (Na_v1.1–1.3 and Na_v1.6). BmK AEP concentration-dependently suppresses neuronal excitability (AP firing) in primary cultured cortical neurons. Consistent with its inhibitory effect on AP generation, BmK AEP inhibits Na⁺ peak current in cortical neurons with an IC₅₀ value of 2.12 µM by shifting the half-maximal voltage of activation of VGSC to hyperpolarized direction by ~7.83 mV without affecting the steady-state inactivation. Similar to its action on Na⁺ currents in cortical neurons, BmK AEP concentration-dependently suppresses the Na⁺ currents of Na_v1.1, Na_v1.3, and Na_v1.6, which were heterologously expressed in HEK-293 cells, with IC₅₀ values of 3.20, 1.46, and 0.39 µM with maximum inhibition of 82%, 56%, and 93%, respectively. BmK AEP shifts the voltage-dependent activation in the hyperpolarized direction by ~15.60 mV, ~9.97 mV, and ~6.73 mV in Na_v1.1, Na_v1.3, and Na_v1.6, respectively, with minimal effect on steady-state inactivation. In contrast, BmK AEP minimally suppresses Na_v1.2 currents (~15%) but delays the inactivation of the channel with an IC₅₀ value of 1.69 µM. Considered together, these data demonstrate that BmK AEP is a relatively selective Na_v1.6 gating modifier which distinctly affects the gating of brain subtypes of VGSCs.

BotAF, a new Buthus occitanus tunetanus scorpion toxin, produces potent analgesia in rodents

This work reports the purification of new potent scorpion neuropeptide, named BotAF, by an activity-guided screening approach. BotAF is a 64-residue long-chain peptide that shares very high similarity with the original β-like scorpion toxin group, in which several peptides have been characterized to be anti-nociceptive in rodents. BotAF administration to rodents does not produce any toxicity or motor impairment, including at high doses. In all models investigated, BotAF turned out to be an efficient peptide in abolishing acute and inflammatory (both somatic and visceral) pain in rodents. It performs with high potency compared to standard analgesics tested in the same conditions. The anti-nociceptive activity of BotAF depends on the route of injection: it is inactive when tested by i.c.v. or i.v. routes but gains in potency when pre-injected locally (in the same compartment than the irritant itself) or by i.t. root 40 to 60 min before pain induction, respectively. BotAF is not an AINS-like compound as it fails to reduce inflammatory edema. Also, it does not activate the opioidergic system as its activity is not affected by naloxone. BotAF does also not bind onto RyR and has low activity towards DRG ion channels (particularly TTX sensitive Na⁺ channels) and does not bind onto rat brain synaptosome receptors. In somatic and visceral pain models, BotAF dose-dependently inhibited lumbar spinal cord c-fos/c-jun mRNA up regulation. Altogether, our data favor a spinal or peripheral anti-nociceptive mode of action of BotAF.

Scorpion β-toxin interference with NaV channel voltage sensor gives rise to excitatory and depressant modes

Scorpion β toxins, peptides of ∼70 residues, specifically target voltage-gated sodium (Na_V) channels to cause use-dependent subthreshold channel openings via a voltage–sensor trapping mechanism. This excitatory action is often overlaid by a not yet understood depressant mode in which Na_V channel activity is inhibited. Here, we analyzed these two modes of gating modification by β-toxin Tz1 from Tityus zulianus on heterologously expressed Na_V1.4 and Na_V1.5 channels using the whole cell patch-clamp method. Tz1 facilitated the opening of Na_V1.4 in a use-dependent manner and inhibited channel opening with a reversed use dependence. In contrast, the opening of Na_V1.5 was exclusively inhibited without noticeable use dependence. Using chimeras of Na_V1.4 and Na_V1.5 channels, we demonstrated that gating modification by Tz1 depends on the specific structure of the voltage sensor in domain 2. Although residue G658 in Na_V1.4 promotes the use-dependent transitions between Tz1 modification phenotypes, the equivalent residue in Na_V1.5, N803, abolishes them. Gating charge neutralizations in the Na_V1.4 domain 2 voltage sensor identified arginine residues at positions 663 and 669 as crucial for the outward and inward movement of this sensor, respectively. Our data support a model in which Tz1 can stabilize two conformations of the domain 2 voltage sensor: a preactivated outward position leading to Na_V channels that open at subthreshold potentials, and a deactivated inward position preventing channels from opening. The results are best explained by a two-state voltage–sensor trapping model in that bound scorpion β toxin slows the activation as well as the deactivation kinetics of the voltage sensor in domain 2.

BmK-YA, an enkephalin-like peptide in scorpion venom

By screening extracts of venom from the Asian scorpion Buthus martensii Karsch (BmK) for their abilities to activate opioid receptors, we have identified BmK-YA, an amidated peptide containing an enkephalin-like sequence. BmK-YA is encoded by a precursor that displays a signal sequence and contains four copies of BmK-YA sequences and four of His⁴-BmK-YA, all flanked by single amino acid residues. BmK-YA and His⁴-BmK-YA are amidated and thus fulfill the characteristics expected of bioactive peptides. BmK-YA can activate mammalian opioid receptors with selectivity for the δ subtype while His⁴-BmK-YA is inactive at opioid receptors. The discovery of BmK-YA suggests that scorpion venom may represent a novel source of bioactive molecules targeting G protein-coupled receptors (GPCRs) and reveal additional insights on the evolution of the opioid precursors.

Purification, characterization and functional expression of a new peptide with an analgesic effect from Chinese scorpion Buthus martensii Karsch (BmK AGP-SYPU1)

In this study, a new peptide named BmK AGP-SYPU1 with an analgesic effect was purified from the venom of Chinese scorpion Buthus martensi Karsch (BmK) through a four-step chromatographic process. The mouse twisting test was used to identify the target peptides in every separation step. The purified BmK AGP-SYPU1 was further qualified by RP-HPLC and HPCE. The molecular mass determined by the MALDI-4800-TOF/TOF MS for BmK AGP-SYPU1 was 7544 Da. Its primary structure of the N-terminal was obtained using Edman degradation. The gene sequence of BmK AGP-SYPU1 was cloned from the cDNA pool and genomic of scorpion glands, respectively, and then expressed in Escherichia coli. The sequence determination showed that BmK AGP-SYPU1 was composed of 66 amino acid residues with a new primary structure. The metal chelating affinity column and cation exchange chromatography were used to purify the recombinant BmK AGP-SYPU1. Consequently, the native and recombinant BmK AGP-SYPU1 showed similar analgesic effects on mice as assayed using a mouse twisting model. These results suggested that BmK AGP-SYPU1 is a new analgesic component found in the Chinese scorpion Buthus martensi Karsch.

Location of the analgesic domain in Scorpion toxin BmK AGAP by mutagenesis of disulfide bridges

An increasing number of analgesic peptides have been found in the tail toxicyst, but there has been little research into their analgesic domains. Where are the analgesic domains in a conservative betaalphabetabeta topology conformation of the analgesic peptides? We have carried out research to address this question. On account of the importance of disulfide bonds in the study of protein structure, the conformational stability, catalytic activity and folding, and site-directed mutagenesis in disulfide bridges have been used to look for the analgesic domain in a mature antitumor-analgesic peptide from the venom of the Chinese scorpion Buthus martensii Karsch (BmK AGAP). The mouse-twisting assay was used to examine the analgesic activity of 12 mutants, in which two mutants (C22S, C46S) and (C16S, C36S), exhibited lower relative activity. Following the conformational analysis, one domain, called the "core domain", was found to be the key to the analgesic activity.

Potent Modulation of the Voltage-Gated Sodium Channel Nav1.7 by OD1, a Toxin from the Scorpion Odonthobuthus doriae

Voltage-gated sodium channels are essential for the propagation of action potentials in nociceptive neurons. Nav1.7 is found in peripheral sensory and sympathetic neurons and involved in short-term and inflammatory pain. Nav1.8 and Nav1.3 are major players in nociception and neuropathic pain, respectively. In our effort to identify isoform-specific and high-affinity ligands for these channels, we investigated the effects of OD1, a scorpion toxin isolated from the venom of the scorpion Odonthobuthus doriae. Nav1.3, Nav1.7, and Nav1.8 channels were coexpressed with beta1-subunits in Xenopus laevis oocytes. Na+ currents were recorded with the two-electrode voltage-clamp technique. OD1 modulates Nav1.7 at low nanomolar concentrations: 1) fast inactivation is dramatically impaired, with an EC50 value of 4.5 nM; 2) OD1 substantially increases the peak current at all voltages; and 3) OD1 induces a substantial persistent current. Nav1.8 was not affected by concentrations up to 2 microM, whereas Nav1.3 was sensitive only to concentrations higher than 100 nM. OD1 impairs the inactivation process of Nav1.3 with an EC50 value of 1127 nM. Finally, the effects of OD1 were compared with a classic alpha-toxin, AahII from Androctonus australis Hector and a classic alpha-like toxin, BmK M1 from Buthus martensii Karsch. At a concentration of 50 nM, both toxins affected Nav1.7. Nav1.3 was sensitive to AahII but not to BmK M1, whereas Nav1.8 was affected by neither toxin. In conclusion, the present study shows that the scorpion toxin OD1 is a potent modulator of Nav1.7, with a unique selectivity pattern.

Accurate prediction of scorpion toxin functional properties from primary structures

Scorpion toxins are common experimental tools for studies of biochemical and pharmacological properties of ion channels. The number of functionally annotated scorpion toxins is steadily growing, but the number of identified toxin sequences is increasing at much faster pace. With an estimated 100,000 different variants, bioinformatic analysis of scorpion toxins is becoming a necessary tool for their systematic functional analysis. Here, we report a bioinformatics-driven system involving scorpion toxin structural classification, functional annotation, database technology, sequence comparison, nearest neighbour analysis, and decision rules which produces highly accurate predictions of scorpion toxin functional properties.

Molecular cloning of a novel putative potassium channel-blocking neurotoxin from the venom of the North African scorpion, Androctonus amoreuxi

Scorpion venoms are a particularly rich source of neurotoxic proteins/peptides that interact in a highly specific fashion with discrete subtypes of ion channels in excitable and non-excitable cells. Here we have employed a recently developed technique to effect molecular cloning and structural characterization of a novel putative potassium channel-blocking toxin from the same sample of venom from the North African scorpion, Androctonus amoreuxi. The deduced precursor open-reading frame is composed of 59 amino acid residues that consists of a signal peptide of approximately 22 amino acid residues followed by a mature toxin of 37 amino acid residues. The mature toxin contains two functionally important residues (Lys27 and Tyr36), constituting a functional dyad motif that may be critical for potassium channel-blocking activity that can be affirmed from structural homologs as occurring in the venoms from other species of Androctonus scorpions. Parallel proteomic/transcriptomic studies can thus be performed on the same scorpion venom sample without sacrifice of the donor animal.

Toxins in anti-nociception and anti-inflammation

The use of toxins as novel molecular probes to study the structure-function relationship of ion-channels and receptors as well as potential therapeutics in the treatment of wide variety of diseases is well documented. The high specificity and selectivity of these toxins have attracted a great deal of interest as candidates for drug development. This review highlights the involvement of the proteins and peptide toxins as well as non-proteinaceous compounds derived from both venomous and non-venomous animals, in anti-nociception and anti-inflammation. The possible mechanisms of these potential therapeutic agents and possible clinical applications in the treatment of pain and inflammation are also summarized.

NMR solution structure of Cn12, a novel peptide from the Mexican scorpion Centruroides noxius with a typical beta-toxin sequence but with alpha-like physiological activity

Cn12 isolated from the venom of the scorpion Centruroides noxius has 67 amino-acid residues, closely packed with four disulfide bridges. Its primary structure and disulfide bridges were determined. Cn12 is not lethal to mammals and arthropods in vivo at doses up to 100 microg per animal. Its 3D structure was determined by proton NMR using 850 distance constraints, 36 phi angles derived from 36 coupling constants obtained by two different methods, and 22 hydrogen bonds. The overall structure has a two and half turn alpha-helix (residues 24-32), three strands of antiparallel beta-sheet (residues 2-4, 37-40 and 45-48), and a type II turn (residues 41-44). The amino-acid sequence of Cn12 resembles the beta scorpion toxin class, although patch-clamp experiments showed the induction of supplementary slow inactivation of Na(+) channels in F-11 cells (mouse neuroblastoma N18TG-2 x rat DRG2), which means that it behaves more like an alpha scorpion toxin. This behaviour prompted us to analyse Na(+) channel binding sites using information from 112 Na(+) channel gene clones available in the literature, focusing on the extracytoplasmic loops of the S5-S6 transmembrane segments of domain I and the S3-S4 segments of domain IV, sites considered to be responsible for binding alpha scorpion toxins.

Isolation of scorpion (Androctonus amoreuxi) putative alpha neurotoxins and parallel cloning of their respective cDNAs from a single sample of venom

The venoms of buthid scorpions are known to contain basic, single-chain protein toxins (alpha toxins) consisting of 60-70 amino acid residues that are tightly folded by four disulfide bridges. Here we describe isolation and sequencing of three novel putative alpha toxins (AamH1-3) from the venom of the North African scorpion, Androctonus amoreuxi, and subsequent cloning of their precursor cDNAs from the same sample of venom. This experimental approach can expedite functional genomic analyses of the protein toxins from this group of venomous animals and does not require specimen sacrifice for cloning of protein toxin precursor cDNAs.

Expression of an antitumor-analgesic peptide from the venom of Chinese scorpion Buthus martensii karsch in Escherichia coli

The gene encoding a putative mature antitumor-analgesic peptide (AGAP) from the venom of the Chinese scorpion Buthus martensii Karsch was obtained by polymerase chain reaction (PCR) according to its cDNA sequence and expressed in Escherichia coli. While most of the recombinant AGAP was expressed in the form of insoluble inclusion body. The recombinant AGAP was purified to homogeneity by metal chelating affinity chromatography. Pharmaceutical tests showed that the recombinant AGAP has both analgesic and antitumor activities on mice.

An overview of toxins and genes from the venom of the Asian scorpion Buthus martensi Karsch

Among the different scorpion species, Buthus martensi Karsch (BmK), a widely distributed scorpion species in Asia, has received a lot of attention. Indeed, over the past decade, more than 70 different peptides, toxins or homologues have been isolated and more peptides are probably still to be revealed. This review is focusing on the many peptides isolated from the venom of this scorpion, their targets, their genes and their structures. The aim is to give both a 'state of the art' view of the research on BmK venom and an illustration of the complexity of this scorpion venom. In the present manuscript, we have listed the different ion channel toxins and homologues isolated from the venom of BmK, either from the literature or from databases. We have described here 51 long-chain peptides related to the Na(+) channel toxins family: 34 related to the alpha-toxin family, four related to the excitatory insect toxin family, 10 related to the depressant insect toxin, one beta-like toxin plus two peptides, BmK AS and AS1, that act on ryanodine receptors. We also listed 18 peptides related to the K(+) channel toxin family: 14 short chain toxins or homologues, two long chain K(+) toxin homologues and two putative K(+) toxin precursors. Additionally, two chlorotoxin like peptides (Bm-12 and 12 b) have been isolated in the venom of BmK. Besides these ion channels toxins, two peptides without disulfide bridges (the bradykinin-potentiating peptide BmK bpp and BmK n1) and three peptides with no known functions have also been discovered in this venom. We have also taken the opportunity of this review to update the classification of scorpion K(+) toxins () which now presents 17 subfamilies instead of the 12 described earlier. The work on the venom of BmK led to the discovery of two new subfamilies, alpha-KT x 14 and alpha-KT x 17.