Isolation and characterization of two novel scorpion toxins: The alpha-toxin-like CeII8, specific for Na(v)1.7 channels and the classical anti-mammalian CeII9, specific for Na(v)1.4 channels

Design of antinociceptive peptide by grafting domains between scorpion β-neurotoxins

Neurotoxic peptides from venomous animals have been pointed out as antinociceptive therapeutic leads. Venom peptides have modulation properties on isoforms of voltage-gated sodium channels (VGSC), associated with pathologies such as neuropathic or inflammatory pain. The β-neurotoxins obtained from scorpion venoms are peptides that can alter the kinetics of VGSC by binding to its receptor site 4. CeII8 is a non-lethal scorpion β-neurotoxin that has been reported to interact with hNaV1.7, a VGSC isoform related to the codification and processing of painful stimulus (nociception), and it is involved in pain pathologies. On the other hand, CssII is a lethal scorpion β-neurotoxin that binds mainly to site 4 of hNav1.6. Because of this, we used computational methods and the amino acid sequence of the novo recombinant neurotoxin rCssII-RCR to graft in some of its domains existing amino acids from the non-lethal CeII8 to generate a chimeric peptide with antinociceptive activity, named rCssII-Del-D23A-TCD. This peptide variant was found to have antinociceptive activity in inflammatory and neuropathic pain models with an effect comparable to the mu-opioid receptor agonists DAMGO (H-Tyr-D-Ala-Gly-N(Me) Phe-Gly-ol).

State of the art on the development of a recombinant antivenom against Mexican scorpion stings

Around 2,750 species of scorpions have been recorded worldwide and classified into 21 families and 208 genera. Of these, the family Buthidae stands out as one of the largest, comprising several genera including the genus Centruroides with 102 recorded species. This genus is home to the largest number of species dangerous to humans as described in Mexico, where there are 55 species of the genus Centruroides, of which more than 24 are of medical importance. Envenoming in humans is caused by the presence of peptides (toxins) in the venom that modify the gating mechanism of Na+ voltage dependent ionic channels. Therefore, a rational approach to generate a new antivenom is to obtain neutralizing antibodies against these toxins, whose average abundance in venom is 10%. In this review paper, we document that from the characterization of the lethal venoms of Mexican scorpions, 30 lethal components have been identified, so their neutralization represents an enormous challenge. Thanks to phage display and directed evolution technologies, it has been possible to generate specific antibody fragments against several of these toxins, some of which exhibit broad cross-neutralization. Currently, progress has been made in neutralizing the venoms of 9 species with the use of recombinant antibody fragments, mainly of human origin. One of them has the potential to neutralize approximately 20 toxins.

Short Peptides from Asian Scorpions: Bioactive Molecules with Promising Therapeutic Potential

Scorpion venom peptides, particularly those derived from Asian species, have garnered significant attention, offering therapeutic potential in pain management, cancer, anticoagulation, and infectious diseases. This review provides a comprehensive analysis of scorpion venom peptides, focusing on their roles as voltage-gated sodium (Nav), potassium (Kv), and calcium (Cav) channel modulators. It analyzed Nav1.7 inhibition for analgesia, Kv1.3 blockade for anticancer activity, and membrane disruption for antimicrobial effects. While the low targeting specificity and high toxicity of some scorpion venom peptides pose challenges to their clinical application, recent research has made strides in overcoming these limitations. This review summarizes the latest progress in scorpion venom peptide research, discussing their mechanisms of action, therapeutic potential, and challenges in clinical translation. This work aims to provide new insights and directions for the development of novel therapeutic drugs.

Spider and scorpion knottins targeting voltage-gated sodium ion channels in pain signaling

In sensory neurons that transmit pain signals, whether acute or chronic, voltage-gated sodium channels (VGSCs) are crucial for regulating excitability. NaV1.1, NaV1.3, NaV1.6, NaV1.7, NaV1.8, and NaV1.9 have been demonstrated and defined their functional roles in pain signaling based on their biophysical properties and distinct patterns of expression in each subtype of sensory neurons. Scorpions and spiders are traditional Chinese medicinal materials, belonging to the arachnid class. Most of the studied species of them have evolved venom peptides that exhibit a wide variety of knottins specifically targeting VGSCs with subtype selectivity and conformational specificity. This review provides an overview on the exquisite knottins from scorpion and spider venoms targeting pain-related NaV channels, describing the sequences and the structural features as well as molecular determinants that influence their selectivity on special subtype and at particular conformation, with an aim for the development of novel research tools on NaV channels and analgesics with minimal adverse effects.

Development of a human antibody fragment cross-neutralizing scorpion toxins

Previously, it was demonstrated that from the single chain fragment variable (scFv) 3F it is possible to generate variants capable of neutralizing the Cn2 and Css2 toxins, as well as their respective venoms (Centruroides noxius and Centruroides suffusus). Despite this success, it has not been easy to modify the recognition of this family of scFvs toward other dangerous scorpion toxins. The analysis of toxin-scFv interactions and in vitro maturation strategies allowed us to propose a new maturation pathway for scFv 3F to broaden recognition toward other Mexican scorpion toxins. From maturation processes against toxins CeII9 from C. elegans and Ct1a from C. tecomanus, the scFv RAS27 was developed. This scFv showed an increased affinity and cross-reactivity for at least 9 different toxins while maintaining recognition for its original target, the Cn2 toxin. In addition, it was confirmed that it can neutralize at least three different toxins. These results constitute an important advance since it was possible to improve the cross-reactivity and neutralizing capacity of the scFv 3F family of antibodies.

Structural and Functional Characterization of a Novel Scorpion Toxin that Inhibits NaV1.8 via Interactions With the DI Voltage Sensor and DII Pore Module

Voltage-gated sodium channel Na_V1.8 regulates transmission of pain signals to the brain. While Na_V1.8 has the potential to serve as a drug target, the molecular mechanisms that shape Na_V1.8 gating are not completely understood, particularly mechanisms that couple activation to inactivation. Interactions between toxin producing animals and their predators provide a novel approach for investigating Na_V structure-function relationships. Arizona bark scorpions produce Na⁺ channel toxins that initiate pain signaling. However, in predatory grasshopper mice, toxins inhibit Na_V1.8 currents and block pain signals. A screen of synthetic peptide toxins predicted from bark scorpion venom showed that peptide NaTx36 inhibited Na⁺ current recorded from a recombinant grasshopper mouse Na_V1.8 channel (OtNa_V1.8). Toxin NaTx36 hyperpolarized OtNa_V1.8 activation, steady-state fast inactivation, and slow inactivation. Mutagenesis revealed that the first gating charge in the domain I (DI) S4 voltage sensor and an acidic amino acid (E) in the DII SS2 – S6 pore loop are critical for the inhibitory effects of NaTx36. Computational modeling showed that a DI S1 – S2 asparagine (N) stabilizes the NaTx36 – OtNa_V1.8 complex while residues in the DI S3 – S4 linker and S4 voltage sensor form electrostatic interactions that allow a toxin glutamine (Q) to contact the first S4 gating charge. Surprisingly, the models predicted that NaTx36 contacts amino acids in the DII S5 – SS1 pore loop instead of the SS2 – S6 loop; the DII SS2 – S6 loop motif (QVSE) alters the conformation of the DII S5 – SS1 pore loop, enhancing allosteric interactions between toxin and the DII S5 – SS1 pore loop. Few toxins have been identified that modify Na_V1.8 gating. Moreover, few toxins have been described that modify sodium channel gating via the DI S4 voltage sensor. Thus, NaTx36 and OtNa_V1.8 provide tools for investigating the structure-activity relationship between channel activation and inactivation gating, and the connection to alternative pain phenotypes.

From the PnTx2-6 Toxin to the PnPP-19 Engineered Peptide: Therapeutic Potential in Erectile Dysfunction, Nociception, and Glaucoma

The venom of the “armed” spider Phoneutria nigriventer comprises several potent toxins. One of the most toxic components from this venom is the neurotoxin PnTx2-6 (LD50 = ∼ 0.7 μg/mouse, 48 residues, five disulfide bridges, MW = 5,289.31 Da), which slows down the inactivation of various Na+ channels. In mice and rats, this toxin causes priapism, an involuntary and painful erection, similar to what is observed in humans bitten by P. nigriventer. While not completely elucidated, it is clear that PnTx2-6 potentiates erectile function via NO/cGMP signaling, but it has many off-target effects. Seeking to obtain a simpler and less toxic molecule able to retain the pharmacological properties of this toxin, we designed and synthesized the peptide PnPP-19 (19 residues, MW = 2,485.6 Da), representing a discontinuous epitope of PnTx2-6. This synthetic peptide also potentiates erectile function via NO/cGMP, but it does not target Na+ channels, and therefore, it displays nontoxic properties in animals even at high doses. PnPP-19 effectively potentiates erectile function not only after subcutaneous or intravenous administration but also following topical application. Surprisingly, PnPP-19 showed central and peripheral antinociceptive activity involving the opioid and cannabinoid systems, suggesting applicability in nociception. Furthermore, considering that PnPP-19 increases NO availability in the corpus cavernosum, this peptide was also tested in a model of induced intraocular hypertension, characterized by low NO levels, and it showed promising results by decreasing the intraocular pressure which prevents retinal damage. Herein, we discuss how was engineered this smaller active non-toxic peptide with promising results in the treatment of erectile dysfunction, nociception, and glaucoma from the noxious PnTx2-6, as well as the pitfalls of this ongoing journey.

Pain-related toxins in scorpion and spider venoms: a face to face with ion channels

Pain is a common symptom induced during envenomation by spiders and scorpions. Toxins isolated from their venom have become essential tools for studying the functioning and physiopathological role of ion channels, as they modulate their activity. In particular, toxins that induce pain relief effects can serve as a molecular basis for the development of future analgesics in humans. This review provides a summary of the different scorpion and spider toxins that directly interact with pain-related ion channels, with inhibitory or stimulatory effects. Some of these toxins were shown to affect pain modalities in different animal models providing information on the role played by these channels in the pain process. The close interaction of certain gating-modifier toxins with membrane phospholipids close to ion channels is examined along with molecular approaches to improve selectivity, affinity or bioavailability in vivo for therapeutic purposes.

Identification and Characterization of Novel Proteins from Arizona Bark Scorpion Venom That Inhibit Nav1.8, a Voltage-Gated Sodium Channel Regulator of Pain Signaling

The voltage-gated sodium channel Nav1.8 is linked to neuropathic and inflammatory pain, highlighting the potential to serve as a drug target. However, the biophysical mechanisms that regulate Nav1.8 activation and inactivation gating are not completely understood. Progress has been hindered by a lack of biochemical tools for examining Nav1.8 gating mechanisms. Arizona bark scorpion (Centruroides sculpturatus) venom proteins inhibit Nav1.8 and block pain in grasshopper mice (Onychomys torridus). These proteins provide tools for examining Nav1.8 structure–activity relationships. To identify proteins that inhibit Nav1.8 activity, venom samples were fractioned using liquid chromatography (reversed-phase and ion exchange). A recombinant Nav1.8 clone expressed in ND7/23 cells was used to identify subfractions that inhibited Nav1.8 Na⁺ current. Mass-spectrometry-based bottom-up proteomic analyses identified unique peptides from inhibitory subfractions. A search of the peptides against the AZ bark scorpion venom gland transcriptome revealed four novel proteins between 40 and 60% conserved with venom proteins from scorpions in four genera (Centruroides, Parabuthus, Androctonus, and Tityus). Ranging from 63 to 82 amino acids, each primary structure includes eight cysteines and a “CXCE” motif, where X = an aromatic residue (tryptophan, tyrosine, or phenylalanine). Electrophysiology data demonstrated that the inhibitory effects of bioactive subfractions can be removed by hyperpolarizing the channels, suggesting that proteins may function as gating modifiers as opposed to pore blockers.

Venom characterization of the bark scorpion Centruroides edwardsii (Gervais 1843): Composition, biochemical activities and in vivo toxicity for potential prey

In this study, we characterize the venom of Centruroides edwardsii, one of the most abundant scorpions in urban and rural areas of Costa Rica, in terms of its biochemical constituents and their biological activities. C. edwardsii venom is rich in peptides but also contains some higher molecular weight protein components. No phospholipase A₂, hemolytic or fibrinogenolytic activities were found, but the presence of proteolytic and hyaluronidase enzymes was evidenced by zymography. Venom proteomic analysis indicates the presence of a hyaluronidase, several cysteine-rich secretory proteins, metalloproteinases and a peptidylglycine α-hydroxylating monooxygenase like-enzyme. It also includes peptides similar to the K⁺-channel blocker margatoxin, a dominant toxin in the venom of the related scorpion C. margaritatus. MS and N-terminal sequencing analysis also reveals the presence of Na⁺-channel-modulating peptides with sequence similarity to orthologs present in other scorpion species of the genera Centruroides and Tityus. We purified the hyaluronidase (which co-eluted with an allergen 5-like CRiSP) and sequenced ~60% of this enzyme. We also sequenced some venom gland transcripts that include other cysteine-containing peptides and a Non-Disulfide Bridged Peptide (NDBP). Our in vivo experiments characterizing the effects on potential predators and prey show that C. edwardsii venom induces paralysis in several species of arthropods and geckos; crickets being the most sensitive and cockroaches and scorpions the most resistant organisms tested. Envenomation signs were also observed in mice, but no lethality was reached by intraperitoneal administration of this venom up to 120 μg/g body weight.

Structural and functional characterization of toxic peptides purified from the venom of the Colombian scorpion Tityus macrochirus

The soluble venom of the scorpion Tityus macrochirus was separated by chromatographic procedures and three homogeneous peptides were obtained and their primary structures were determined. They were called: Tma1-Tma3, from the abbreviated name of the scorpion. Tma1 is a peptide containing 65 amino acids with four disulfide linkages and a molecular weight of 7386.2 Da. It is a mammalian toxin, shown to affect human sodium-channels sub-types hNav1.6 and hNav1.4. Tma2 and Tma3 are peptides containing 69 amino acids linked by four disulfide bonds, molecular weights 7819.7 and 7830.0 Da, respectively. They do not affect human sodium-channels but are lethal to insects (crickets). A phylogenic analysis of the three peptides and those of other toxic peptides isolated from the genus Tityus and Centruroides were grouped together and analyzed, permitting to obtain a topology with two main clades, one includes most sodium-channel anti-insect scorpion toxins and others includes mostly sodium-channel scorpion toxins anti-mammalian. Tma1 segregates among a group of well-studied β-class toxins of other Tityus species such as T. discrepans, T. obscurus and T. pachyurus. Tma2 and Tma3 are associated with anti-insect toxins, particularly with one of T. obscurus. This phylogenetic analysis confirms and enforces our experimental results obtained with these three new sodium-channel scorpion toxins.

Animal toxins for channelopathy treatment

Ion channels are transmembrane proteins that allow passive flow of ions inside and/or outside of cells or cell organelles. Except mutations lead to nonfunctional protein production or abolished receptor entrance on the membrane surface an altered channel may have two principal conditions that can be corrected. The channel may conduct fewer ions through (loss-of-function mutations) or too many ions (gain-of-function mutations) compared to a normal channel. Toxins from animal venoms are specialised molecules that are generally oriented toward interactions with ion channels. This is a result of long coevolution between predators and their prey. On the molecular level, toxins activate or inhibit ion channels, so they are ideal molecules for restoring conductance in mutated channels. Another aspect of this long coevolution is that a broad variety of toxins have been fine tuned to recognize the channels of different species, keeping many amino acids substitution among sequences. Many peptide ligands with high selectivity to specific receptor subtypes have been isolated from animal venoms, some of which are absolutely non-toxic to humans and mammalians. It is expected that molecules that are selective to each known receptor can be found in animal venoms, but the pool of toxins currently does not override all receptors described as being involved in channelopathies. Modern investigating methods have enhanced the search process for selective ligands. One prominent method is a site-directed mutagenesis of existing toxins to change the selectivity or/and affinity to the selected receptor, which has shown positive results. This article is part of the Special Issue entitled 'Channelopathies.'

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.'

Activation of sodium channels by α-scorpion toxin, BmK NT1, produced neurotoxicity in cerebellar granule cells: an association with intracellular Ca2+ overloading

Voltage-gated sodium channels (VGSCs) are responsible for the action potential generation in excitable cells including neurons and involved in many physiological and pathological processes. Scorpion toxins are invaluable tools to explore the structure and function of ion channels. BmK NT1, a scorpion toxin from Buthus martensii Karsch, stimulates sodium influx in cerebellar granule cells (CGCs). In this study, we characterized the mode of action of BmK NT1 on the VGSCs and explored the cellular response in CGC cultures. BmK NT1 delayed the fast inactivation of VGSCs, increased the Na⁺ currents, and shifted the steady-state activation and inactivation to more hyperpolarized membrane potential, which was similar to the mode of action of α-scorpion toxins. BmK NT1 stimulated neuron death (EC₅₀ = 0.68 µM) and produced massive intracellular Ca²⁺ overloading (EC₅₀ = 0.98 µM). TTX abrogated these responses, suggesting that both responses were subsequent to the activation of VGSCs. The Ca²⁺ response of BmK NT1 was primary through extracellular Ca²⁺ influx since reducing the extracellular Ca²⁺ concentration suppressed the Ca²⁺ response. Further pharmacological evaluation demonstrated that BmK NT1-induced Ca²⁺ influx and neurotoxicity were partially blocked either by MK-801, an NMDA receptor blocker, or by KB-R7943, an inhibitor of Na⁺/Ca²⁺ exchangers. Nifedipine, an L-type Ca²⁺ channel inhibitor, slightly suppressed both Ca²⁺ response and neurotoxicity. A combination of these three inhibitors abrogated both responses. Considered together, these data ambiguously demonstrated that activation of VGSCs by an α-scorpion toxin was sufficient to produce neurotoxicity which was associated with intracellular Ca²⁺ overloading through both NMDA receptor- and Na⁺/Ca²⁺ exchanger-mediated Ca²⁺ influx.

Scorpions from Mexico: From Species Diversity to Venom Complexity

Scorpions are among the oldest terrestrial arthropods, which are distributed worldwide, except for Antarctica and some Pacific islands. Scorpion envenomation represents a public health problem in several parts of the world. Mexico harbors the highest diversity of scorpions in the world, including some of the world's medically important scorpion species. The systematics and diversity of Mexican scorpion fauna has not been revised in the past decade; and due to recent and exhaustive collection efforts as part of different ongoing major revisionary systematic projects, our understanding of this diversity has changed compared with previous assessments. Given the presence of several medically important scorpion species, the study of their venom in the country is also important. In the present contribution, the diversity of scorpion species in Mexico is revised and updated based on several new systematic contributions; 281 different species are recorded. Commentaries on recent venomic, ecological and behavioral studies of Mexican scorpions are also provided. A list containing the most important peptides identified from 16 different species is included. A graphical representation of the different types of components found in these venoms is also revised. A map with hotspots showing the current knowledge on scorpion distribution and areas explored in Mexico is also provided.

Subtype specificity interaction of bactridines with mammalian, insect and bacterial sodium channels under voltage clamp conditions

The present work demonstrates that bactridines (Bacts) possess different selectivities for neuronal and muscular voltage-dependent sodium (Na(V) ) channels, with subtle differences on channel isoforms. Bacts 2, 3, 4, 5 and 6 (100 nm) reduced the peak current of several skeletal and neuronal channel isoforms selectively. Bacts 2 and 3 were more potent on Na(V) 1.4, Bacts 4 and 6 on Na(V) 1.3 and Bact 5 on Na(V) 1.7. Bactridines (except Bacts 1 and 5) caused a hyperpolarizing shift in the V(1/2) of activation and inactivation of Na(V) 1.3, Na(V) 1.4 and Na(V) 1.6. Voltage shifts of Boltzmann curves fitted to activation and inactivation occurred with a decrease in κ. Since the slope is proportional to κ = RT/zF, changes in κ probably express changes in z, the valence, in a voltage-dependent manner. Changes in z may express toxin-induced changes in the channel ionic environment, perhaps due to surface charges of the molecules. Bact 2 induced a Na(V) 1.2 voltage shift of the activation curves but no shift of the mutant Na(V) 1.2 IFM/QQQ; peak I(N) (a) was reduced in both channel forms, suggesting that channel blockage resulted from toxin binding to a site partially distinct from the α subunit binding site 4. Bactridines emerge as potential research tools to understand sodium channel isoform structure-function relationships and also as pharmacologically interesting peptides.

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.

Isolation and characterization of CvIV4: a pain inducing α-scorpion toxin

Background

Among scorpion species, the Buthidae produce the most deadly and painful venoms. However, little is known regarding the venom components that cause pain and their mechanism of action. Using a paw-licking assay (Mus musculus), this study compared the pain-inducing capabilities of venoms from two species of New World scorpion (Centruroides vittatus, C. exilicauda) belonging to the neurotoxin-producing family Buthidae with one species of non-neurotoxin producing scorpion (Vaejovis spinigerus) in the family Vaejovidae. A pain-inducing α-toxin (CvIV4) was isolated from the venom of C. vittatus and tested on five Na⁺ channel isoforms.

Principal Findings

C. vittatus and C. exilicauda venoms produced significantly more paw licking in Mus than V. spinigerus venom. CvIV4 produced paw licking in Mus equivalent to the effects of whole venom. CvIV4 slowed the fast inactivation of Na_v1.7, a Na⁺ channel expressed in peripheral pain-pathway neurons (nociceptors), but did not affect the Na_v1.8-based sodium currents of these neurons. CvIV4 also slowed the fast inactivation of Na_v1.2, Na_v1.3 and Na_v1.4. The effects of CvIV4 are similar to Old World α-toxins that target Na_v1.7 (AahII, BmK MI, LqhIII, OD1), however the primary structure of CvIV4 is not similar to these toxins. Mutant Na_v1.7 channels (D1586A and E1589Q, DIV S3–S4 linker) reduced but did not abolish the effects of CvIV4.

Conclusions

This study: 1) agrees with anecdotal evidence suggesting that buthid venom is significantly more painful than non-neurotoxic venom; 2) demonstrates that New World buthids inflict painful stings via toxins that modulate Na⁺ channels expressed in nociceptors; 3) reveals that Old and New World buthids employ similar mechanisms to produce pain. Old and New World α-toxins that target Na_v1.7 have diverged in sequence, but the activity of these toxins is similar. Pain-inducing toxins may have evolved in a common ancestor. Alternatively, these toxins may be the product of convergent evolution.