Australian funnel-web spiders: master insecticide chemists

Drosophila X virus-like particles as delivery carriers for improved oral insecticidal efficacy of scorpion Androctonus australis peptide against the invasive fruit fly, Drosophila suzukii

Insect-specific neurotoxic peptides derived from the venoms of scorpions and spiders can cause acute paralysis and death when injected into insects, offering a promising insecticidal component for insect pest control. However, effective delivery systems are required to help neurotoxic peptides pass through the gut barrier into the hemolymph, where they can act. Here, we investigated the potential of a novel nanocarrier, Drosophila X virus-like particle (DXV-VLP), for delivering a neurotoxin from the scorpion Androctonus australis Hector (AaIT) against the invasive pest fruit fly, Drosophila suzukii. Our results show that the fusion proteins of DXV polyproteins with AaIT peptide at their C-termini could be sufficiently produced in Lepidoptera Hi5 cells in a soluble form using the recombinant baculovirus expression system, and could self-assemble into VLPs with similar particle morphology and size to authentic DXV virions. In addition, the AaIT peptides displayed on DXV-VLPs retained their toxicity, as demonstrated in injection bioassays that resulted in severe mortality (72%) in adults after 72 h. When fed to adults, mild mortality was observed in the group treated with DXV-AaIT (38%), while no mortality occurred in the group treated with AaIT peptide, thus indicating the significant role of DXV-VLPs in delivering AaIT peptides. Overall, this proof-of-concept study demonstrates for the first time that VLPs can be exploited to enhance oral delivery of insect-specific neurotoxic peptides in the context of pest control. Moreover, it provides insights for further improvements and potentially the development of neurotoxin-based bioinsecticides and/or transgenic crops for insect pest control.

Spider venom neurotoxin based bioinsecticides: A novel bioactive for the control of the Asian citrus psyllid Diaphorina citri (Hemiptera)

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is a key vector of the phloem-limited bacteria Candidatus Liberibacter asiaticus (CLas) associated with huanglongbing (HLB), the most serious and currently incurable disease of citrus worldwide. Here we report the first investigation into the potential use of a spider venom-derived recombinant neurotoxin, ω/κ-HxTx-Hv1h (hereafter HxTx-Hv1h) when delivered alone or when fused to snowdrop lectin (Galanthus nivalis agglutinin; GNA) to control D. citri. Proteins, including GNA alone, were purified from fermented transformed yeast Pichia pastoris cultures. Recombinant HxTx-Hv1h, HxTx-Hv1h/GNA and GNA were all orally toxic to D. citri, with Day 5 median lethal concentrations (LC50) derived from dose-response artificial diet assays of 27, 20 and 52 μM, respectively. Western analysis of whole insect protein extracts confirmed that psyllid mortality was attributable to protein ingestion and that the fusion protein was stable to cleavage by D. citri proteases. When applied topically (either via droplet or spray) HxTx-Hv1h/GNA was the most effective of the proteins causing >70 % mortality 5 days post treatment, some 2 to 3-fold higher levels of mortality as compared to the toxin alone. By contrast, no significant mortality or phenotypic effects were observed for bumble bees (Bombus terrestris L.) fed on the recombinant proteins in acute toxicity assays. This suggests that HxTx-Hv1h/GNA has potential as a novel bioinsecticide for the management of D. citri offering both enhanced target specificity as compared to chemical pesticides and compatibility with integrated pest management (IPM) strategies.

A ShK-like Domain from Steinernema carpocapsae with Bioinsecticidal Potential

Entomopathogenic nematodes are used as biological control agents against a broad range of insect pests. We ascribed the pathogenicity of these organisms to the excretory/secretory products (ESP) released by the infective nematode. Our group characterized different virulence factors produced by Steinernema carpocapsae that underlie its success as an insect pathogen. A novel ShK-like peptide (ScK1) from this nematode that presents high sequence similarity with the ShK peptide from a sea anemone was successfully produced recombinantly in Escherichia coli. The secondary structure of ScK1 appeared redox-sensitive, exhibiting a far-UV circular dichroism spectrum consistent with an alpha-helical secondary structure. Thermal denaturation of the ScK1 allowed estimating the melting temperature to 59.2 ± 0.1 °C. The results from toxicity assays using Drosophila melanogaster as a model show that injection of this peptide can kill insects in a dose-dependent manner with an LD₅₀ of 16.9 µM per adult within 24 h. Oral administration of the fusion protein significantly reduced the locomotor activity of insects after 48 h (p < 0.05, Tukey's test). These data show that this nematode expresses insecticidal peptides with potential as next-generation insecticides.

The bee venom active compound melittin protects against bicuculline-induced seizures and hippocampal astrocyte activation in rats

Epilepsy is a chronic neuropathology characterized by an abnormal hyperactivity of neurons that generate recurrent, spontaneous, paradoxical and synchronized nerve impulses, leading or not to seizures. This neurological disorder affects around 70 million individuals worldwide. Pharmacoresistance is observed in about 30% of the patients and long-term use of antiepileptics may induce serious side effects. Thus, there is an interest in the study of the therapeutic potential of bioactive substances isolated from natural products in the treatment of epilepsy. Arthropod venoms contain neurotoxins that have high affinity for molecular structures in the neural tissue such as receptors, transporters and ion channels both in glial and neuronal membranes. This study evaluated the potential neuroprotective effect of melittin (MEL), an active compound of bee venom, in the bicuculline-induced seizure model (BIC) in rats. Male Wistar rats (3 months, 250-300 g) were submitted to surgery for the implantation of a unilateral cannula in the lateral ventricle. After the recovery period, rats received a microinjection of saline solution or MEL (0.1 mg per animal). Firstly, rats were evaluated in the open field (20 min) and in the elevated plus maze (5 min) tests after received microinjection of saline or MEL. After, 30 min later animals received BIC (100 mg/ml) or saline, and their behaviors were analyzed for 20 min in the open field according to a seizure scale. At the end, rats were euthanized, brains collected and processed to glial fibrillary acidic protein (GFAP) immunohistochemistry evaluation. No changes were observed in MEL-treated rats in the open field and elevated plus maze. However, 90% of MEL-treated animals were protected against seizures induced by BIC. There was an increase in the latency for the onset of seizures, accompanied by a reduction of GFAP-immunoreactivity cells in the dentate gyrus and CA1. Thus, our study suggests that MEL has an anticonvulsant potential, and further studies are needed to elucidate the mechanisms involved in this action.

Assessing the Single and Combined Toxicity of the Bioinsecticide Spear and Cry3Bb1 Protein Against Susceptible and Resistant Western Corn Rootworm Larvae (Coleoptera: Chrysomelidae)

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), poses a serious threat to maize (Zea mays L.) growers in the U.S. Corn Belt. Transgenic corn expressing Bacillus thuringiensis (Bt) Berliner is the major management tactic along with crop rotation. Bt crops targeting WCR populations have been widely planted throughout the Corn Belt. Rootworms have developed resistance to nearly all management strategies including Bt corn. Therefore, there is a need for new products that are not cross-resistant with the current Bt proteins. In this study, we evaluated the susceptibility of WCR strains resistant and susceptible to Cry3Bb1 to the biological insecticide Spear-T (GS-omega/kappa-Hexatoxin-Hv1a) alone and combined with Cry3Bb1 protein. The activity of Hv1a alone was similar between Cry3Bb1-resistant and susceptible strains (LC50s = 0.95 mg/cm2 and 1.50 mg/cm2, respectively), suggesting that there is no cross-resistance with Cry3Bb1 protein. Effective concentration (EC50), molt inhibition concentration (MIC50), and inhibition concentration (IC50) values of Hv1a alone were also similar between both strains, based on non-overlapping confidence intervals. Increased mortality (64%) was observed on resistant larvae exposed to Hv1a (0.6 mg/cm2) + Cry3Bb1 protein (170.8 µg/cm2) compared to 0% mortality when exposed to Cry3Bb1 alone and 34% mortality to Hv1a alone (0.3 mg/cm2). The time of larval death was not significantly different between Hv1a alone (3.79 mg/cm2) and Hv1a (0.6 mg/cm2) + Cry3Bb1 (170.8 µg/cm2). New control strategies that are not cross-resistant with current insecticides and Bt proteins are needed to better manage the WCR, and Hv1a together with Cry3Bb1 may fit this role.

The insecticidal activity of recombinant nemertide toxin α-1 from Lineus longissimus towards pests and beneficial species

The nemertide toxins from the phylum Nemertea are a little researched family of neurotoxins with potential for development as biopesticides. Here we report the recombinant production of nemertide α-1 (α-1), a 65-residue inhibitor cystine knot (ICK) peptide from Lineus longissimus, known to target insect voltage-gated sodium channels. The insecticidal activity of α-1 was assessed and compared with the well characterised ICK venom peptide, ω-atracotoxin/hexatoxin-Hv1a (Hv1a). α-1 elicited potent spastic paralysis when injected into cabbage moth (Mamestra brassicae) larvae; conferring an ED₅₀ 3.90 μg/larva (10.30 nmol/g larva), followed by mortality (60% within 48 h after 10 μg injection). By comparison, injection of M. brassicae larvae with recombinant Hv1a produced short-lived flaccid paralysis with an ED₅₀ over 6 times greater than that of α-1 at 26.20 μg/larva (64.70 nmol/g larva). Oral toxicity of α-1 was demonstrated against two aphid species (Myzus persicae and Acyrthosiphon pisum), with respective LC₅₀ values of 0.35 and 0.14 mg/mL, some 6-fold lower than those derived for recombinant Hv1a. When delivered orally to M. brassicae larvae, α-1 caused both paralysis (ED₅₀ 11.93 μg/larva, 31.5 nmol/g larva) and mortality. This contrasts with the lack of oral activity of Hv1a, which when fed to M. brassicae larvae had no effect on feeding or survival. Hv1a has previously been shown to be non-toxic by injection to the beneficial honeybee (Apis mellifera). By contrast, rapid paralysis and 100% mortality was observed following injection of α-1 (31.6 nmol/g insect). These results demonstrate the great potential of naturally occurring non-venomous peptides, such as α-1, for development as novel effective biopesticides, but equally highlights the importance of understanding the phyletic specificity of a given toxin at an early stage in the quest to discover and develop safe and sustainable pesticides.

Variation in venom composition in the Australian funnel-web spiders Hadronyche valida

Mygalomorph venom properties and active components, which have importance in medicine, agronomy, venomics, ecology and evolution, have been widely studied, but only a small fraction have been characterised. Several studies have shown inter-individual variation in the composition of venom peptides based on ontogeny, sexual dimorphism, season and diet. However, intra-individual variation in venom composition, which could play a key role in the evolution, diversification and function of toxins, is poorly understood. In this study, we demonstrate significant intra- and inter-individual variation in venom composition in the Australian funnel-web spider Hadronyche valida, highlighting that individuals show different venom profiles over time. Fourteen (four juvenile and ten adult females) funnel-web spiders, maintained under the same environmental conditions and diet, were milked a total of four times, one month apart. We then used reversed-phase high performance liquid chromatography/electrospray ionisation mass spectrometry to generate venom fingerprints containing the retention time and molecular weights of the different toxin components in the venom. Across all individuals, we documented a combined total of 83 individual venom components. Only 20% of these components were shared between individuals. Individuals showed variation in the composition of venom peptides, with some components consistently present over time, while others were only present at specific times. When individuals were grouped using the Jaccard clustering index and Kernel Principal Component Analysis, spiders formed two distinct clusters, most likely due to their origin or time of collection. This study contributes to the understanding of variation in venom composition at different levels (intra-individual, and intra- and inter-specific) and considers some of the mechanisms of selection that may contribute to venom diversification within arachnids. In addition, inter-specific variation in venom composition can be highly useful as a chemotaxonomic marker to identify funnel-web species.

Animal toxins - Nature's evolutionary-refined toolkit for basic research and drug discovery

Venomous animals have evolved toxins that interfere with specific components of their victim's core physiological systems, thereby causing biological dysfunction that aids in prey capture, defense against predators, or other roles such as intraspecific competition. Many animal lineages evolved venom systems independently, highlighting the success of this strategy. Over the course of evolution, toxins with exceptional specificity and high potency for their intended molecular targets have prevailed, making venoms an invaluable and almost inexhaustible source of bioactive molecules, some of which have found use as pharmacological tools, human therapeutics, and bioinsecticides. Current biomedically-focused research on venoms is directed towards their use in delineating the physiological role of toxin molecular targets such as ion channels and receptors, studying or treating human diseases, targeting vectors of human diseases, and treating microbial and parasitic infections. We provide examples of each of these areas of venom research, highlighting the potential that venom molecules hold for basic research and drug development.

Conformational ensembles of non-peptide ω-conotoxin mimetics and Ca+2 ion binding to human voltage-gated N-type calcium channel Cav2.2

Chronic neuropathic pain is the most complex and challenging clinical problem of a population that sets a major physical and economic burden at the global level. Ca²⁺-permeable channels functionally orchestrate the processing of pain signals. Among them, N-type voltage-gated calcium channels (VGCC) hold prominent contribution in the pain signal transduction and serve as prime targets for synaptic transmission block and attenuation of neuropathic pain. Here, we present detailed in silico analysis to comprehend the underlying conformational changes upon Ca²⁺ ion passage through Ca_v2.2 to differentially correlate subtle transitions induced via binding of a conopeptide-mimetic alkylphenyl ether-based analogue MVIIA. Interestingly, pronounced conformational changes were witnessed at the proximal carboxyl-terminus of Ca_v2.2 that attained an upright orientation upon Ca⁺² ion permeability. Moreover, remarkable changes were observed in the architecture of channel tunnel. These findings illustrate that inhibitor binding to Ca_v2.2 may induce more narrowing in the pore size as compared to Ca²⁺ binding through modulating the hydrophilicity pattern at the selectivity region. A significant reduction in the tunnel volume at the selectivity filter and its enhancement at the activation gate of Ca⁺²-bound Ca_v2.2 suggests that ion binding modulates the outward splaying of pore-lining S6 helices to open the voltage gate. Overall, current study delineates dynamic conformational ensembles in terms of Ca⁺² ion and MVIIA-associated structural implications in the Ca_v2.2 that may help in better therapeutic intervention to chronic and neuropathic pain management.

A review of progress toward field application of transgenic mosquitocidal entomopathogenic fungi

In Africa, adult mosquito populations are primarily controlled with insecticide-impregnated bed nets and residual insecticide sprays. This coupled with widespread applications of pesticides in agriculture has led to increasing insecticide resistance in mosquito populations. We have developed multiple alternative strategies for exploiting transgenic Metarhizium spp. directed at: (i) shortening the lifespan of adult mosquitoes; (ii) reducing transmission potential of Plasmodium spp.; (iii) reducing vector competence via pre-lethal effects. The present challenge is to convert this promising strategy into a validated public health intervention by resolving outstanding issues related to the release of genetically modified organisms. © 2019 Society of Chemical Industry.

Tying pest insects in knots: the deployment of spider-venom-derived knottins as bioinsecticides

Spider venoms are complex chemical arsenals that contain a rich variety of insecticidal toxins. However, the major toxin class in many spider venoms is disulfide-rich peptides known as knottins. The knotted three-dimensional fold of these mini-proteins provides them with exceptional chemical and thermal stability as well as resistance to proteases. In contrast with other bioinsecticides, which are often slow-acting, spider knottins are fast-acting neurotoxins. In addition to being potently insecticidal, some knottins have exceptional taxonomic selectivity, being lethal to key agricultural pests but innocuous to vertebrates and beneficial insects such as bees. The intrinsic oral activity of these peptides, combined with the ability of aerosolized knottins to penetrate insect spiracles, has enabled them to be developed commercially as eco-friendly bioinsecticides. Moreover, it has been demonstrated that spider-knottin transgenes can be used to engineer faster-acting entomopathogens and insect-resistant crops. © 2019 Society of Chemical Industry.

Demonstrating the potential of a novel spider venom-based biopesticide for target-specific control of the small hive beetle, a serious pest of the European honeybee

The parasitic small hive beetle (Aethina tumida) feeds on pollen, honey and brood of the European honey bee (Apis mellifera); establishment in North America and Australia has resulted in severe economic damage to the apiculture industry. We report potential for the "in-hive" use of a novel biopesticide that is toxic to this invasive beetle pest but harmless to honeybees. Constructs encoding the spider venom neurotoxin ω-hexatoxin-Hv1a (Hv1a) linked to the N- or C-terminus of snowdrop lectin (GNA) were used to produce recombinant Hv1a/GNA and GNA/Hv1a fusion proteins. Both were similarly toxic to beetles by injection (respective LD₅₀s 1.5 and 0.9 nmoles/g larvae), whereas no effects on adult honeybee survival were observed at injection doses of > 200 nmoles/g insect. When fed to A. tumida larvae, GNA/Hv1a was significantly more effective than Hv1a/GNA (LC₅₀s of 0.52 and 1.14 mg/ml diet, respectively), whereas both proteins were similarly toxic to adults. Results suggested that the reduced efficacy of Hv1a/GNA against larvae was attributable to differences in the susceptibility of the fusion proteins to cleavage by gut serine proteases. In laboratory assays, A. tumida larval survival was significantly reduced when brood, inoculated with eggs, was treated with GNA/Hv1a.

Peptidomic characterization and bioactivity of Protoiurus kraepelini (Scorpiones: Iuridae) venom

Protoiurus kraepelini is a scorpion species found in parts of Turkey and Greece. In this study, the peptide profile of its venom was determined for the first time. The electrophoretic profile of the crude venom showed a protein distribution from 2 to 130 kDa. MALDI-TOF MS analysis of the venom peptide fraction yielded 27 peptides between 1059 and 4623 Da in mass. Several ion channelblocking and antimicrobial peptides were identified by peptide mass fingerprinting analysis. Cytotoxic and antimicrobial effects of the venom were also demonstrated on Jurkat cells and Escherichia coli, respectively. As the first peptidomic characterization study on P. kraepelini venom, this report lays the foundation for detailed future studies that may lead to the discovery of novel bioactive peptides.

Computational and biological characterization of fusion proteins of two insecticidal proteins for control of insect pests

Sucking pests pose a serious agricultural challenge, as available transgenic technologies such as Bacillus thuringiensis crystal toxins (Bt) are not effective against them. One approach is to produce fusion protein toxins for the control of these pests. Two protein toxins, Hvt (ω-atracotoxin from Hadronyche versuta) and onion leaf lectin, were translationally fused to evaluate the negative effects of fusion proteins on Phenacoccus solenopsis (mealybug), a phloem-feeding insect pest. Hvt was cloned both N-terminally (HL) and then C-terminally (LH) in the fusion protein constructs, which were expressed transiently in Nicotiana tabacum using a Potato Virus X (PVX) vector. The HL fusion protein was found to be more effective against P. solenopsis, with an 83% mortality rate, as compared to the LH protein, which caused 65% mortality. Hvt and lectin alone caused 42% and 45%, respectively, under the same conditions. Computational studies of both fusion proteins showed that the HL protein is more stable than the LH protein. Together, these results demonstrate that translational fusion of two insecticidal proteins improved the insecticidal activity relative to each protein individually and could be expressed in transgenic plants for effective control of sucking pests.

Phylogenomic reclassification of the world's most venomous spiders (Mygalomorphae, Atracinae), with implications for venom evolution

Here we show that the most venomous spiders in the world are phylogenetically misplaced. Australian atracine spiders (family Hexathelidae), including the notorious Sydney funnel-web spider Atrax robustus, produce venom peptides that can kill people. Intriguingly, eastern Australian mouse spiders (family Actinopodidae) are also medically dangerous, possessing venom peptides strikingly similar to Atrax hexatoxins. Based on the standing morphology-based classification, mouse spiders are hypothesized distant relatives of atracines, having diverged over 200 million years ago. Using sequence-capture phylogenomics, we instead show convincingly that hexathelids are non-monophyletic, and that atracines are sister to actinopodids. Three new mygalomorph lineages are elevated to the family level, and a revised circumscription of Hexathelidae is presented. Re-writing this phylogenetic story has major implications for how we study venom evolution in these spiders, and potentially genuine consequences for antivenom development and bite treatment research. More generally, our research provides a textbook example of the applied importance of modern phylogenomic research.

Successful refolding and NMR structure of rMagi3: A disulfide-rich insecticidal spider toxin

The need for molecules with high specificity against noxious insects leads the search towards spider venoms that have evolved highly selective toxins for insect preys. In this respect, spiders as a highly diversified group of almost exclusive insect predators appear to possess infinite potential for the discovery of novel insect-selective toxins. In 2003, a group of toxins was isolated from the spider Macrothele gigas and the amino acid sequence was reported. We obtained, by molecular biology techniques in a heterologous system, one of these toxins. Purification process was optimized by chromatographic methods to determine the three-dimensional structure by nuclear magnetic resonance in solution, and, finally, their biological activity was tested. rMagi3 resulted to be a specific insect toxin with no effect on mice.

Silk gene expression of theridiid spiders: implications for male-specific silk use

Spiders (order Araneae) rely on their silks for essential tasks, such as dispersal, prey capture, and reproduction. Spider silks are largely composed of spidroins, members of a protein family that are synthesized in silk glands. As needed, silk stored in silk glands is extruded through spigots on the spinnerets. Nearly all studies of spider silks have been conducted on females; thus, little is known about male silk biology. To shed light on silk use by males, we compared silk gene expression profiles of mature males to those of females from three cob-web weaving species (Theridiidae). We de novo assembled species-specific male transcriptomes from Latrodectus hesperus, Latrodectus geometricus, and Steatoda grossa followed by differential gene expression analyses. Consistent with their complement of silk spigots, male theridiid spiders express appreciable amounts of aciniform, major ampullate, minor ampullate, and pyriform spidroin genes but not tubuliform spidroin genes. The relative expression levels of particular spidroin genes varied between sexes and species. Because mature males desert their prey-capture webs and become cursorial in their search for mates, we anticipated that major ampullate (dragline) spidroin genes would be the silk genes most highly expressed by males. Indeed, major ampullate spidroin genes had the highest expression in S. grossa males. However, minor ampullate spidroin genes were the most highly expressed spidroin genes in L. geometricus and L. hesperus males. Our expression profiling results suggest species-specific adaptive divergence of silk use by male theridiids.

Venom Profiling of a Population of the Theraphosid Spider Phlogius crassipes Reveals Continuous Ontogenetic Changes from Juveniles through Adulthood

Theraphosid spiders (tarantulas) are venomous arthropods found in most tropical and subtropical regions of the world. Tarantula venoms are a complex cocktail of toxins with potential use as pharmacological tools, drugs and bioinsecticides. Although numerous toxins have been isolated from tarantula venoms, little research has been carried out on the venom of Australian tarantulas. We therefore investigated the venom profile of the Australian theraphosid spider Phlogius crassipes and examined whether there are ontogenetic changes in venom composition. Spiders were divided into four ontogenic groups according to cephalothorax length, then the venom composition of each group was examined using gel electrophoresis and mass spectrometry. We found that the venom of P. crassipes changes continuously during development and throughout adulthood. Our data highlight the need to investigate the venom of organisms over the course of their lives to uncover and understand the changing functions of venom and the full range of toxins expressed. This in turn should lead to a deeper understanding of the organism’s ecology and enhance the potential for biodiscovery.

Sublethal effects of the insecticidal fusion protein ω-ACTX-Hv1a/GNA on the parasitoid Eulophus pennicornis via its host Lacanobia oleracea

BACKGROUND

The neurotoxin peptide ω-ACTX-Hv1a, fused to the carrier molecule GNA, presents potential for insect control as a biopesticide, being orally toxic to insect pests from different orders. However, thorough evaluation is required to assure its safety towards non-target invertebrates. Effects of this novel biopesticide on the parasitoid Eulophus pennicornis via its host Lacanobia oleracea are presented.

RESULTS

Hv1a/GNA did not cause mortality when injected or fed to fifth-stage L. oleracea, but caused up to 39% reduction in mean larval weight (P < 0.05) and increased developmental time when injected. When fed, GNA, but not Hv1a/GNA, caused ∼35% reduction in larval weight, indicating that host quality was not affected by the fusion protein. Although GNA and Hv1a/GNA were internalised by the hosts following ingestion, and thus were available to higher trophic levels, no significant changes in the rate of E. pennicornis parasitism occurred. Number of parasitoid pupae per host, adult emergence and sex ratio were unaffected by GNA- or Hv1a/GNA-treated hosts (P > 0.05). The fusion protein was degraded by parasitoid larvae, rendering it non-toxic.

CONCLUSION

Hv1a/GNA has negligible effects on the parasitoid, even under worst-case scenarios. This low toxicity to these insects is of interest in terms of biopesticide specificity and safety to non-target organisms.

The Cystine Knot Is Responsible for the Exceptional Stability of the Insecticidal Spider Toxin ω-Hexatoxin-Hv1a

The inhibitor cystine knot (ICK) is an unusual three-disulfide architecture in which one of the disulfide bonds bisects a loop formed by the two other disulfide bridges and the intervening sections of the protein backbone. Peptides containing an ICK motif are frequently considered to have high levels of thermal, chemical and enzymatic stability due to cross-bracing provided by the disulfide bonds. Experimental studies supporting this contention are rare, in particular for spider-venom toxins, which represent the largest diversity of ICK peptides. We used ω-hexatoxin-Hv1a (Hv1a), an insecticidal toxin from the deadly Australian funnel-web spider, as a model system to examine the contribution of the cystine knot to the stability of ICK peptides. We show that Hv1a is highly stable when subjected to temperatures up to 75 °C, pH values as low as 1, and various organic solvents. Moreover, Hv1a was highly resistant to digestion by proteinase K and when incubated in insect hemolymph and human plasma. We demonstrate that the ICK motif is essential for the remarkable stability of Hv1a, with the peptide’s stability being dramatically reduced when the disulfide bonds are eliminated. Thus, this study demonstrates that the ICK motif significantly enhances the chemical and thermal stability of spider-venom peptides and provides them with a high level of protease resistance. This study also provides guidance to the conditions under which Hv1a could be stored and deployed as a bioinsecticide.

A Comparative Analysis of the Venom Gland Transcriptomes of the Fishing Spiders Dolomedes mizhoanus and Dolomedes sulfurous

Dolomedes sulfurous and Dolomedes mizhoanus are predaceous arthropods catching and feeding on small fish. They live in the same area and have similar habits. Their venoms exhibit some similarities and differences in biochemical and electrophysiological properties. In the present work, we first performed a transcriptomic analysis by constructing the venom gland cDNA library of D. sulfurous and 127 novel putative toxin sequences were consequently identified, which were classified into eight families. This venom gland transcriptome was then compared with that of D. mizhoanus, which revealed that the putative toxins from both spider venoms might have originated from the same gene ancestors although novel toxins were evolved independently in the two spiders. The putative toxins from both spiders contain 6-12 cysteine residues forming seven cysteine patterns. As revealed by blast search, the two venoms are rich in neurotoxins targeting ion channels with pharmacological and therapeutic significance. This study provides insight into the venoms of two closely related species of spider, which will be of use for future investigations into the structure and function of their toxins.

Isolation and preliminary characterization of proteinaceous toxins with insecticidal and antibacterial activities from black widow spider (L. tredecimguttatus) eggs

The eggs of black widow spider (L. tredecimguttatus) have been demonstrated to be rich in toxic proteinaceous components. The study on such active components is of theoretical and practical importance. In the present work, using a combination of multiple biochemical and biological strategies, we isolated and characterized the proteinaceous components from the aqueous extract of the black widow spider eggs. After gel filtration of the egg extract, the resulting main protein and peptide peaks were further fractionated by ion exchange chromatography and reversed-phase high performance liquid chromatography. Two proteinaceous components, named latroeggtoxin-III and latroeggtoxin-IV, respectively, were purified to homogeneity. Latroeggtoxin-III was demonstrated to have a molecular weight of about 36 kDa. Activity analysis indicated that latroeggtoxin-III exhibited neurotoxicity against cockroaches but had no obvious effect on mice, suggesting that it is an insect-specific toxin. Latroeggtoxin-IV, with a molecular weight of 3.6 kDa, was shown to be a broad-spectrum antibacterial peptide, showing inhibitory activity against all five species of bacteria tested, with the highest activity against Staphylococcus aureus. Finally, the implications of the proteinaceous toxins in egg protection and their potential applications were analyzed and discussed.

The insecticidal spider toxin SFI1 is a knottin peptide that blocks the pore of insect voltage-gated sodium channels via a large β-hairpin loop

Spider venoms contain a plethora of insecticidal peptides that act on neuronal ion channels and receptors. Because of their high specificity, potency and stability, these peptides have attracted much attention as potential environmentally friendly insecticides. Although many insecticidal spider venom peptides have been isolated, the molecular target, mode of action and structure of only a small minority have been explored. Sf1a, a 46-residue peptide isolated from the venom of the tube-web spider Segesteria florentina, is insecticidal to a wide range of insects, but nontoxic to vertebrates. In order to investigate its structure and mode of action, we developed an efficient bacterial expression system for the production of Sf1a. We determined a high-resolution solution structure of Sf1a using multidimensional 3D/4D NMR spectroscopy. This revealed that Sf1a is a knottin peptide with an unusually large β-hairpin loop that accounts for a third of the peptide length. This loop is delimited by a fourth disulfide bond that is not commonly found in knottin peptides. We showed, through mutagenesis, that this large loop is functionally critical for insecticidal activity. Sf1a was further shown to be a selective inhibitor of insect voltage-gated sodium channels, consistent with its 'depressant' paralytic phenotype in insects. However, in contrast to the majority of spider-derived sodium channel toxins that function as gating modifiers via interaction with one or more of the voltage-sensor domains, Sf1a appears to act as a pore blocker.

Construction of a hypervirulent and specific mycoinsecticide for locust control

Locusts and grasshoppers (acridids) are among the worst pests of crops and grasslands worldwide. Metarhizium acridum, a fungal pathogen that specifically infects acridids, has been developed as a control agent but its utility is limited by slow kill time and greater expense than chemical insecticides. We found that expression of four insect specific neurotoxins improved the efficacy of M. acridum against acridids by reducing lethal dose, time to kill and food consumption. Coinoculating recombinant strains expressing AaIT1(a sodium channel blocker) and hybrid-toxin (a blocker of both potassium and calcium channels), produced synergistic effects, including an 11.5-fold reduction in LC₅₀, 43% reduction in LT₅₀ and a 78% reduction in food consumption. However, specificity was retained as the recombinant strains did not cause disease in non-acridids. Our results identify a repertoire of toxins with different modes of action that improve the utility of fungi as specific control agents of insects.

Transgenic plants expressing ω-ACTX-Hv1a and snowdrop lectin (GNA) fusion protein show enhanced resistance to aphids

Recombinant fusion proteins containing arthropod toxins have been developed as a new class of biopesticides. The recombinant fusion protein Hv1a/GNA, containing the spider venom toxin ω-ACTX-Hv1a linked to snowdrop lectin (GNA) was shown to reduce survival of the peach-potato aphid Myzus persicae when delivered in artificial diet, with survival <10% after 8 days exposure to fusion protein at 1 mg/ml. Although the fusion protein was rapidly degraded by proteases in the insect, Hv1a/GNA oral toxicity to M. persicae was significantly greater than GNA alone. A construct encoding the fusion protein, including the GNA leader sequence, under control of the constitutive CaMV 35S promoter was transformed into Arabidopsis; the resulting plants contained intact fusion protein in leaf tissues at an estimated level of 25.6 ± 4.1 ng/mg FW. Transgenic Arabidopsis expressing Hv1a/GNA induced up to 40% mortality of M. persicae after 7 days exposure in detached leaf bioassays, demonstrating that transgenic plants can deliver fusion proteins to aphids. Grain aphids (Sitobion avenae) were more susceptible than M. persicae to the Hv1a/GNA fusion protein in artificial diet bioassays (LC50 = 0.73 mg/ml after 2 days against LC50 = 1.81 mg/ml for M. persicae), as they were not able to hydrolyze the fusion protein as readily as M. persicae. Expression of this fusion protein in suitable host plants for the grain aphid is likely to confer higher levels of resistance than that shown with the M. persicae/Arabidopsis model system.

Novel biopesticide based on a spider venom peptide shows no adverse effects on honeybees

Evidence is accumulating that commonly used pesticides are linked to decline of pollinator populations; adverse effects of three neonicotinoids on bees have led to bans on their use across the European Union. Developing insecticides that pose negligible risks to beneficial organisms such as honeybees is desirable and timely. One strategy is to use recombinant fusion proteins containing neuroactive peptides/proteins linked to a 'carrier' protein that confers oral toxicity. Hv1a/GNA (Galanthus nivalis agglutinin), containing an insect-specific spider venom calcium channel blocker (ω-hexatoxin-Hv1a) linked to snowdrop lectin (GNA) as a 'carrier', is an effective oral biopesticide towards various insect pests. Effects of Hv1a/GNA towards a non-target species, Apis mellifera, were assessed through a thorough early-tier risk assessment. Following feeding, honeybees internalized Hv1a/GNA, which reached the brain within 1 h after exposure. However, survival was only slightly affected by ingestion (LD50>100 µg bee(-1)) or injection of fusion protein. Bees fed acute (100 µg bee(-1)) or chronic (0.35 mg ml(-1)) doses of Hv1a/GNA and trained in an olfactory learning task had similar rates of learning and memory to no-pesticide controls. Larvae were unaffected, being able to degrade Hv1a/GNA. These tests suggest that Hv1a/GNA is unlikely to cause detrimental effects on honeybees, indicating that atracotoxins targeting calcium channels are potential alternatives to conventional pesticides.

Diversification of a single ancestral gene into a successful toxin superfamily in highly venomous Australian funnel-web spiders

BACKGROUND

Spiders have evolved pharmacologically complex venoms that serve to rapidly subdue prey and deter predators. The major toxic factors in most spider venoms are small, disulfide-rich peptides. While there is abundant evidence that snake venoms evolved by recruitment of genes encoding normal body proteins followed by extensive gene duplication accompanied by explosive structural and functional diversification, the evolutionary trajectory of spider-venom peptides is less clear.

RESULTS

Here we present evidence of a spider-toxin superfamily encoding a high degree of sequence and functional diversity that has evolved via accelerated duplication and diversification of a single ancestral gene. The peptides within this toxin superfamily are translated as prepropeptides that are posttranslationally processed to yield the mature toxin. The N-terminal signal sequence, as well as the protease recognition site at the junction of the propeptide and mature toxin are conserved, whereas the remainder of the propeptide and mature toxin sequences are variable. All toxin transcripts within this superfamily exhibit a striking cysteine codon bias. We show that different pharmacological classes of toxins within this peptide superfamily evolved under different evolutionary selection pressures.

CONCLUSIONS

Overall, this study reinforces the hypothesis that spiders use a combinatorial peptide library strategy to evolve a complex cocktail of peptide toxins that target neuronal receptors and ion channels in prey and predators. We show that the ω-hexatoxins that target insect voltage-gated calcium channels evolved under the influence of positive Darwinian selection in an episodic fashion, whereas the κ-hexatoxins that target insect calcium-activated potassium channels appear to be under negative selection. A majority of the diversifying sites in the ω-hexatoxins are concentrated on the molecular surface of the toxins, thereby facilitating neofunctionalisation leading to new toxin pharmacology.

Spit and venom from scytodes spiders: a diverse and distinct cocktail

Spiders from the family Scytodidae have a unique prey capturing technique: they spit a zig-zagged silken glue to tether prey to a surface. Effectiveness of this sticky mixture is based on a combination of contraction and adhesion, trapping prey until the spider immobilizes it by envenomation and then feeds. We identify components expressed in Scytodes thoracica venom glands using combined transcriptomic and proteomic analyses. These include homologues of toxic proteins astacin metalloproteases and potentially toxic proteins including venom allergen, longistatin, and translationally controlled tumor protein (TCTP). We classify 19 distinct groups of candidate peptide toxins; 13 of these were detected in the venom, making up 35% of the proteome. Six have significant similarity to toxins from spider species spanning mygalomorph and nonhaplogyne araneomorph lineages, suggesting their expression in venom is phylogenetically widespread. Twelve peptide toxin groups have homologues in venom gland transcriptomes of other haplogynes. Of the transcripts, approximately 50% encode glycine-rich peptides that may contribute to sticky fibers in Scytodes spit. Fifty-one percent of the identified venom proteome is a family of proteins that is homologous to sequences from Drosophila sp. and Latrodectus hesperus with uncharacterized function. Characterization of these components holds promise for discovering new functional activity.

The insecticidal potential of venom peptides

Pest insect species are a burden to humans as they destroy crops and serve as vectors for a wide range of diseases including malaria and dengue. Chemical insecticides are currently the dominant approach for combating these pests. However, the de-registration of key classes of chemical insecticides due to their perceived ecological and human health risks in combination with the development of insecticide resistance in many pest insect populations has created an urgent need for improved methods of insect pest control. The venoms of arthropod predators such as spiders and scorpions are a promising source of novel insecticidal peptides that often have different modes of action to extant chemical insecticides. These peptides have been optimized via a prey-predator arms race spanning hundreds of millions of years to target specific types of insect ion channels and receptors. Here we review the current literature on insecticidal venom peptides, with a particular focus on their structural and pharmacological diversity, and discuss their potential for deployment as insecticides.

Isolation of an orally active insecticidal toxin from the venom of an Australian tarantula

Many insect pests have developed resistance to existing chemical insecticides and consequently there is much interest in the development of new insecticidal compounds with novel modes of action. Although spiders have deployed insecticidal toxins in their venoms for over 250 million years, there is no evolutionary selection pressure on these toxins to possess oral activity since they are injected into prey and predators via a hypodermic needle-like fang. Thus, it has been assumed that spider-venom peptides are not orally active and are therefore unlikely to be useful insecticides. Contrary to this dogma, we show that it is possible to isolate spider-venom peptides with high levels of oral insecticidal activity by directly screening for per os toxicity. Using this approach, we isolated a 34-residue orally active insecticidal peptide (OAIP-1) from venom of the Australian tarantula Selenotypus plumipes. The oral LD50 for OAIP-1 in the agronomically important cotton bollworm Helicoverpa armigera was 104.2±0.6 pmol/g, which is the highest per os activity reported to date for an insecticidal venom peptide. OAIP-1 is equipotent with synthetic pyrethroids and it acts synergistically with neonicotinoid insecticides. The three-dimensional structure of OAIP-1 determined using NMR spectroscopy revealed that the three disulfide bonds form an inhibitor cystine knot motif; this structural motif provides the peptide with a high level of biological stability that probably contributes to its oral activity. OAIP-1 is likely to be synergized by the gut-lytic activity of the Bacillus thuringiensis Cry toxin (Bt) expressed in insect-resistant transgenic crops, and consequently it might be a good candidate for trait stacking with Bt.

Spider peptide toxins as leads for drug development

Venomous animals use a highly complex cocktails of proteins, peptides and small molecules to subdue and kill their prey. As such, venoms represent highly valuable combinatorial peptide libraries, displaying an extensive range of pharmacological activities, honed by natural selection. Modern analytical technologies enable us to take full advantage of this vast pharmacological cornucopia in the hunt for novel drug leads. Spider venoms represent a resource of several million peptides, which selectively target specific subtypes of ion channels. Structure-function studies of spider toxins are leading not only to the discovery of novel molecules, but also to novel therapeutic routes for cardiovascular diseases, cancer, neuromuscular diseases, pain and to a variety of other pathological conditions. This review presents an overview of spider peptide toxins as candidates for therapeutics and focuses on their applications in the discovery of novel mechanisms of analgesia.

The insecticidal neurotoxin Aps III is an atypical knottin peptide that potently blocks insect voltage-gated sodium channels

One of the most potent insecticidal venom peptides described to date is Aps III from the venom of the trapdoor spider Apomastus schlingeri. Aps III is highly neurotoxic to lepidopteran crop pests, making it a promising candidate for bioinsecticide development. However, its disulfide-connectivity, three-dimensional structure, and mode of action have not been determined. Here we show that recombinant Aps III (rAps III) is an atypical knottin peptide; three of the disulfide bridges form a classical inhibitor cystine knot motif while the fourth disulfide acts as a molecular staple that restricts the flexibility of an unusually large β hairpin loop that often houses the pharmacophore in this class of toxins. We demonstrate that the irreversible paralysis induced in insects by rAps III results from a potent block of insect voltage-gated sodium channels. Channel block by rAps III is voltage-independent insofar as it occurs without significant alteration in the voltage-dependence of channel activation or steady-state inactivation. Thus, rAps III appears to be a pore blocker that plugs the outer vestibule of insect voltage-gated sodium channels. This mechanism of action contrasts strikingly with virtually all other sodium channel modulators isolated from spider venoms that act as gating modifiers by interacting with one or more of the four voltage-sensing domains of the channel.

Spider-venom peptides: structure, pharmacology, and potential for control of insect pests

Spider venoms are an incredibly rich source of disulfide-rich insecticidal peptides that have been tuned over millions of years to target a wide range of receptors and ion channels in the insect nervous system. These peptides can act individually, or as part of larger toxin cabals, to rapidly immobilize envenomated prey owing to their debilitating effects on nervous system function. Most of these peptides contain a unique arrangement of disulfide bonds that provides them with extreme resistance to proteases. As a result, these peptides are highly stable in the insect gut and hemolymph and many of them are orally active. Thus, spider-venom peptides can be used as stand-alone bioinsecticides, or transgenes encoding these peptides can be used to engineer insect-resistant crops or enhanced entomopathogens. We critically review the potential of spider-venom peptides to control insect pests and highlight their advantages and disadvantages compared with conventional chemical insecticides.

The lethal toxin from Australian funnel-web spiders is encoded by an intronless gene

Australian funnel-web spiders are generally considered the most dangerous spiders in the world, with envenomations from the Sydney funnel-web spider Atrax robustus resulting in at least 14 human fatalities prior to the introduction of an effective anti-venom in 1980. The clinical envenomation syndrome resulting from bites by Australian funnel-web spiders is due to a single 42-residue peptide known as δ-hexatoxin. This peptide delays the inactivation of voltage-gated sodium channels, which results in spontaneous repetitive firing and prolongation of action potentials, thereby causing massive neurotransmitter release from both somatic and autonomic nerve endings. Here we show that δ-hexatoxin from the Australian funnel-web spider Hadronyche versuta is produced from an intronless gene that encodes a prepropeptide that is post-translationally processed to yield the mature toxin. A limited sampling of genes encoding unrelated venom peptides from this spider indicated that they are all intronless. Thus, in distinct contrast to cone snails and scorpions, whose toxin genes contain introns, spiders may have developed a quite different genetic strategy for evolving their venom peptidome.

Fusion to snowdrop lectin magnifies the oral activity of insecticidal ω-Hexatoxin-Hv1a peptide by enabling its delivery to the central nervous system

Background

The spider-venom peptide ω-hexatoxin-Hv1a (Hv1a) targets insect voltage-gated calcium channels, acting directly at sites within the central nervous system. It is potently insecticidal when injected into a wide variety of insect pests, but it has limited oral toxicity. We examined the ability of snowdrop lectin (GNA), which is capable of traversing the insect gut epithelium, to act as a “carrier” in order to enhance the oral activity of Hv1a.

Methodology/Principal Findings

A synthetic Hv1a/GNA fusion protein was produced by recombinant expression in the yeast Pichia pastoris. When injected into Mamestra brassicae larvae, the insecticidal activity of the Hv1a/GNA fusion protein was similar to that of recombinant Hv1a. However, when proteins were delivered orally via droplet feeding assays, Hv1a/GNA, but not Hv1a alone, caused a significant reduction in growth and survival of fifth stadium Mamestra brassicae (cabbage moth) larvae. Feeding second stadium larvae on leaf discs coated with Hv1a/GNA (0.1–0.2% w/v) caused ≥80% larval mortality within 10 days, whereas leaf discs coated with GNA (0.2% w/v) showed no acute effects. Intact Hv1a/GNA fusion protein was delivered to insect haemolymph following ingestion, as shown by Western blotting. Immunoblotting of nerve chords dissected from larvae following injection of GNA or Hv1a/GNA showed high levels of bound proteins. When insects were injected with, or fed on, fluorescently labelled GNA or HV1a/GNA, fluorescence was detected specifically associated with the central nerve chord.

Conclusions/Significance

In addition to mediating transport of Hv1a across the gut epithelium in lepidopteran larvae, GNA is also capable of delivering Hv1a to sites of action within the insect central nervous system. We propose that fusion to GNA provides a general mechanism for dramatically enhancing the oral activity of insecticidal peptides and proteins.

Expression and characterization of a recombinant Cry1Ac crystal protein fused with an insect-specific neurotoxin ω-ACTX-Hv1a in Bacillus thuringiensis

In order to assess possible enhancement of biopesticide activity, the fusion gene of crystal protein gene cry1Ac with the insect-specific neurotoxin ω-ACTX-Hv1a gene and egfp was expressed in Bacillus thuringiensis acrystalliferous strain Cry-B under the control of the native gene expression system. The fusion recombinant Cry-B(1Ac-ACTX-EGFP) generally produced two or three small crystal-like inclusion bodies in each cell and the GFP signal could be clearly observed. A 166 kDa full-length fusion protein was identified by immunoblot analysis. Virulence of the fusion inclusions was at least fivefold higher toward larvae of Spodoptera exigua. These results demonstrated that a foreign protein could be expressed and accumulate as parasporal inclusions in B. thuringiensis by C-terminal fusion with the native endotoxin while retaining partial insecticidal activity.

Spider-venom peptides as bioinsecticides

Over 10,000 arthropod species are currently considered to be pest organisms. They are estimated to contribute to the destruction of ~14% of the world's annual crop production and transmit many pathogens. Presently, arthropod pests of agricultural and health significance are controlled predominantly through the use of chemical insecticides. Unfortunately, the widespread use of these agrochemicals has resulted in genetic selection pressure that has led to the development of insecticide-resistant arthropods, as well as concerns over human health and the environment. Bioinsecticides represent a new generation of insecticides that utilise organisms or their derivatives (e.g., transgenic plants, recombinant baculoviruses, toxin-fusion proteins and peptidomimetics) and show promise as environmentally-friendly alternatives to conventional agrochemicals. Spider-venom peptides are now being investigated as potential sources of bioinsecticides. With an estimated 100,000 species, spiders are one of the most successful arthropod predators. Their venom has proven to be a rich source of hyperstable insecticidal mini-proteins that cause insect paralysis or lethality through the modulation of ion channels, receptors and enzymes. Many newly characterized insecticidal spider toxins target novel sites in insects. Here we review the structure and pharmacology of these toxins and discuss the potential of this vast peptide library for the discovery of novel bioinsecticides.

Molecular Cloning and Sequence Analysis of the cDNAs Encoding Toxin-Like Peptides from the Venom Glands of Tarantula Grammostola rosea

Tarantula venom glands produce a large variety of bioactive peptides. Here we present the identification of venom components obtained by sequencing clones isolated from a cDNA library prepared from the venom glands of the Chilean common tarantula, Grammostola rosea. The cDNA sequences of about 1500 clones out of 4000 clones were analyzed after selection using several criteria. Forty-eight novel toxin-like peptides (GTx1 to GTx7, and GTx-TCTP and GTx-CRISP) were predicted from the nucleotide sequences. Among these peptides, twenty-four toxins are ICK motif peptides, eleven peptides are MIT1-like peptides, and seven are ESTX-like peptides. Peptides similar to JZTX-64, aptotoxin, CRISP, or TCTP are also obtained. GTx3 series possess a cysteine framework that is conserved among vertebrate MIT1, Bv8, prokineticins, and invertebrate astakines. GTx-CRISP is the first CRISP-like protein identified from the arthropod venom. Real-time PCR revealed that the transcripts for TCTP-like peptide are expressed in both the pereopodal muscle and the venom gland. Furthermore, a unique peptide GTx7-1, whose signal and prepro sequences are essentially identical to those of HaTx1, was obtained.

Venoms as a platform for human drugs: translating toxins into therapeutics

INTRODUCTION

An extraordinarily diverse range of animals have evolved venoms for predation, defence, or competitor deterrence. The major components of most venoms are peptides and proteins that are often protease-resistant due to their disulfide-rich architectures. Some of these toxins have become valuable as pharmacological tools and/or therapeutics due to their extremely high specificity and potency for particular molecular targets. There are currently six FDA-approved drugs derived from venom peptides or proteins.

AREAS COVERED

This article surveys the current pipeline of venom-derived therapeutics and critically examines the potential of peptide and protein drugs derived from venoms. Emerging trends are identified, including an increasing industry focus on disulfide-rich venom peptides and the use of a broader array of molecular targets in order to develop venom-based therapeutics for treating a wider range of clinical conditions.

EXPERT OPINION

Key technical advances in combination with a renewed industry-wide focus on biologics have converged to provide a larger than ever pipeline of venom-derived therapeutics. Disulfide-rich venom peptides obviate some of the traditional disadvantages of therapeutic peptides and some may be suitable for oral administration. Moreover, some venom peptides can breach the blood brain barrier and translocate across cell membranes, which opens up the possibility of exploiting molecular targets not previously accessible to peptide drugs.

Zootoxic effects of reduviid Rhynocoris marginatus (Fab.) (Hemiptera: Reduviidae) venomous saliva on Spodoptera litura (Fab.)

Rhynocoris marginatus is a predominant and potential reduviid predator of many economically important pests in India. The venomous saliva (VS) was collected by milking method and diluted with HPLC grade water to prepare different concentrations (200, 400, 600, 800 and 1000ppm). The VS from R. marginatus was found to be toxic and the LD(50) of the VS in Spodoptera litura third instar were 768 and 929ppm at 48 and 96h for microinjection and oral toxicity studies, respectively. Level of hydrolase and detoxification enzymes significantly decreased in a dose-dependent manner after treating the host with VS for 96h. A decrease in carbohydrate (21%) and lipid (46%) contents and an increase in the protein content (50%) were prominent in the experimental category. The VS reduced the relative growth rate, approximate digestibility, efficiency of conversion of ingested and digested food of S. litura in the oral toxicity study. Salivary venom inhibits the haemocytes from aggregation and affects spreading behavior of haemocytes separated from the fifth stadium larvae of S. litura. The result showed that VS toxins caused mortality, changed the nutritional indices, and altered the levels of macromolecule quantity and digestive enzymes of S. litura. We concluded that the VS of R. marginatus is venomous to a prey species, S. litura.

Characterization of voltage-dependent calcium channel blocking peptides from the venom of the tarantula Grammostola rosea

Voltage-dependent calcium channel blocking peptides were purified and sequenced from the venom of the tarantula, Grammostola rosea. cDNAs encoding the peptide sequences were cloned from the venom gland cDNA library. The electrophysiological effects of the peptides on several types of voltage-dependent calcium channels were evaluated using a Xenopus laevis oocyte expression system. A peptide contained in one of the HPLC peak fractions inhibited P/Q type voltage-dependent calcium channels (Ca(v)2.1). The amino acid sequence of this peptide is identical to that of ω-grammotoxin SIA. A peptide from another discrete peak, which is identical to GsAFII except for one tryptophan residue in the C-terminus, inhibited L-type voltage-dependent calcium channels (Ca(v)1.2). A novel peptide, named GTx1-15 (Accession number, AB201016), shows 76.5% sequence homology with the sodium channel blocker phrixotoxin 3, however, GTx1-15 preferentially inhibited T-type voltage-dependent calcium channels (Ca(v)3.1). In silico secondary and tertiary structure prediction revealed that GTx1-15 and sodium channel blockers such as hainantoxin-IV, phrixotoxin 3, and ceratotoxin 2 show very similar β-strand composition, distribution of Optimal Docking Areas (continuous surface patches likely to be involved in protein-protein interactions), and surface electrostatic potential. These findings suggest that these peptide toxins evolved from common ancestors by gene duplication to maintain surface atmospheres appropriate for interaction with low-voltage-dependent ion channels.

Unique scorpion toxin with a putative ancestral fold provides insight into evolution of the inhibitor cystine knot motif

The three-disulfide inhibitor cystine knot (ICK) motif is a fold common to venom peptides from spiders, scorpions, and aquatic cone snails. Over a decade ago it was proposed that the ICK motif is an elaboration of an ancestral two-disulfide fold coined the disulfide-directed β-hairpin (DDH). Here we report the isolation, characterization, and structure of a novel toxin [U(1)-liotoxin-Lw1a (U(1)-LITX-Lw1a)] from the venom of the scorpion Liocheles waigiensis that is the first example of a native peptide that adopts the DDH fold. U(1)-LITX-Lw1a not only represents the discovery of a missing link in venom protein evolution, it is the first member of a fourth structural fold to be adopted by scorpion-venom peptides. Additionally, we show that U(1)-LITX-Lw1a has potent insecticidal activity across a broad range of insect pest species, thereby providing a unique structural scaffold for bioinsecticide development.

Brown spider (Loxosceles genus) venom toxins: tools for biological purposes

Venomous animals use their venoms as tools for defense or predation. These venoms are complex mixtures, mainly enriched of proteic toxins or peptides with several, and different, biological activities. In general, spider venom is rich in biologically active molecules that are useful in experimental protocols for pharmacology, biochemistry, cell biology and immunology, as well as putative tools for biotechnology and industries. Spider venoms have recently garnered much attention from several research groups worldwide. Brown spider (Loxosceles genus) venom is enriched in low molecular mass proteins (5–40 kDa). Although their venom is produced in minute volumes (a few microliters), and contain only tens of micrograms of protein, the use of techniques based on molecular biology and proteomic analysis has afforded rational projects in the area and permitted the discovery and identification of a great number of novel toxins. The brown spider phospholipase-D family is undoubtedly the most investigated and characterized, although other important toxins, such as low molecular mass insecticidal peptides, metalloproteases and hyaluronidases have also been identified and featured in literature. The molecular pathways of the action of these toxins have been reported and brought new insights in the field of biotechnology. Herein, we shall see how recent reports describing discoveries in the area of brown spider venom have expanded biotechnological uses of molecules identified in these venoms, with special emphasis on the construction of a cDNA library for venom glands, transcriptome analysis, proteomic projects, recombinant expression of different proteic toxins, and finally structural descriptions based on crystallography of toxins.

Spider-venom peptides as therapeutics

Spiders are the most successful venomous animals and the most abundant terrestrial predators. Their remarkable success is due in large part to their ingenious exploitation of silk and the evolution of pharmacologically complex venoms that ensure rapid subjugation of prey. Most spider venoms are dominated by disulfide-rich peptides that typically have high affinity and specificity for particular subtypes of ion channels and receptors. Spider venoms are conservatively predicted to contain more than 10 million bioactive peptides, making them a valuable resource for drug discovery. Here we review the structure and pharmacology of spider-venom peptides that are being used as leads for the development of therapeutics against a wide range of pathophysiological conditions including cardiovascular disorders, chronic pain, inflammation, and erectile dysfunction.

Novel class of spider toxin: active principle from the yellow sac spider Cheiracanthium punctorium venom is a unique two-domain polypeptide

Venom of the yellow sac spider Cheiracanthium punctorium (Miturgidae) was found unique in terms of molecular composition. Its principal toxic component CpTx 1 (15.1 kDa) was purified, and its full amino acid sequence (134 residues) was established by protein chemistry and mass spectrometry techniques. CpTx 1 represents a novel class of spider toxin with modular architecture. It consists of two different yet homologous domains (modules) each containing a putative inhibitor cystine knot motif, characteristic of the widespread single domain spider neurotoxins. Venom gland cDNA sequencing provided precursor protein (prepropeptide) structures of three CpTx 1 isoforms (a-c) that differ by single residue substitutions. The toxin possesses potent insecticidal (paralytic and lethal), cytotoxic, and membrane-damaging activities. In both fly and frog neuromuscular preparations, it causes stable and irreversible depolarization of muscle fibers leading to contracture. This effect appears to be receptor-independent and is inhibited by high concentrations of divalent cations. CpTx 1 lyses cell membranes, as visualized by confocal microscopy, and destabilizes artificial membranes in a manner reminiscent of other membrane-active peptides by causing numerous defects of variable conductance and leading to bilayer rupture. The newly discovered class of modular polypeptides enhances our knowledge of the toxin universe.