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

Peptide NCTX15 derived from spider toxin gland effectively relieves hyperuricemia in mice

Hyperuricemia is a clinical disease characterized by a continuous increase in uric acid (UA) due to purine metabolism disorder. As current drug treatments are limited, it is imperative to explore new drugs that offer better safety and efficacy. In this study, Nephila clavata toxin gland homogenates were isolated and purified by exclusion chromatography and high-performance liquid chromatography, resulting in the identification and isolation of a short peptide (NCTX15) with the sequence 'QSGHTFK'. Analysis showed that NCTX15 exhibited no cytotoxicity in mouse macrophages or toxic and hemolytic activity in mice. Notably, NCTX15 inhibited UA production by down-regulating urate transporter 1 and glucose transporter 9 and up-regulating organic anion transporter 1, thus promoting UA excretion. In addition, NCTX15 alleviated the inflammatory response and renal injury by inhibiting the expression of inflammatory factors interleukin-6, interleukin-1β, tumor necrosis factor alpha, NLR family, pyrin domain-containing 3, and pyroptosis-related factor gasdermin D. These results indicate that NCTX15 displayed urate-lowering, anti-inflammatory, and analgesic effects. As the first urate-reducing short peptide isolated from a spider toxin gland homogenate, NCTX15 exhibits considerable potential as a novel drug molecule for anti-gout and hyperuricemia treatment.

Domain Shuffling and Site-Saturation Mutagenesis for the Enhanced Inhibitory Potential of Amaranthaceae α-Amylase Inhibitors

Amaranthaceae α-amylase inhibitors (AAIs) are knottin-type proteins with selective inhibitory potential against coleopteran α-amylases. Their small size and remarkable stability make them exciting molecules for protein engineering to achieve superior selectivity and efficacy. In this report, we have designed a set of AAI pro- and mature peptides chimeras. Based on in silico analysis, stable AAI chimeras having a stronger affinity with target amylases were selected for characterization. In vitro studies validated that chimera of the propeptide from Chenopodium quinoa α-AI and mature peptide from Beta vulgaris α-AI possess 3, 7.6, and 4.26 fold higher inhibition potential than parental counterparts. Importantly, recombinant AAI chimera retained specificity towards target coleopteran α-amylases. In addition, to improve the inhibitory potential of AAI, we performed in silico site-saturation mutagenesis. Computational analysis followed by experimental data showed that substituting Asparagine at the 6th position with Methionine had a remarkable increase in the specific inhibition potential of Amaranthus hypochondriacus α-AI. These results provide structural-functional insights into the vitality of AAI propeptide and a potential hotspot for mutagenesis to enhance the AAI activity. Our investigation will be a toolkit for AAI's optimization and functional differentiation for future biotechnological applications.

Analysis of NGS data from Peruvian Loxosceles laeta spider venom gland reveals toxin diversity

Accidents involving spiders from the genus Loxosceles cause medical emergencies in several countries of South America. The species Loxosceles laeta is ubiquitously present in Peru and is responsible for severe accidents in this country. To further characterize L. laeta venom components and to unveil possible variations in the Peruvian population, we provide an overview of the toxins-related transcripts present in the venom gland of Peruvian L. laeta. A dataset from a cDNA library previously sequenced by MiSeq sequencer (Illumina) was re-analyzed and the obtained data was compared with available sequences from Loxosceles toxins. Phospholipase-D represent the majority (69,28 %) of the transcripts related to venom toxins, followed by metalloproteases (20,72 %), sicaritoxins (6,03 %), serine-proteases (2,28 %), hyaluronidases (1,80 %) and Translationally Controlled Tumor Protein (TCTP) (0,56 %). New sequences of phospholipases D,sicaritoxins, hyaluronidase, TCTP and serine proteinases were described. Differences between the here-described toxin sequences and others, previously identified in venom glands from other spiders, were visualized upon sequence alignments. In addition, an in vitro hyaluronidase activity assay was also performed to complement comparisons between Peruvian and Brazilian L. laeta venom enzymatic activities, revealing a superior activity in the venom from Brazilian specimens. These new data provide a molecular basis that can help to explain the difference in toxicity among L. laeta venoms from different countries in South America.

Improving the Annotation of the Venom Gland Transcriptome of Pamphobeteus verdolaga, Prospecting Novel Bioactive Peptides

Spider venoms constitute a trove of novel peptides with biotechnological interest. Paucity of next-generation-sequencing (NGS) data generation has led to a description of less than 1% of these peptides. Increasing evidence supports the underestimation of the assembled genes a single transcriptome assembler can predict. Here, the transcriptome of the venom gland of the spider Pamphobeteus verdolaga was re-assembled, using three free access algorithms, Trinity, SOAPdenovo-Trans, and SPAdes, to obtain a more complete annotation. Assembler’s performance was evaluated by contig number, N50, read representation on the assembly, and BUSCO’s terms retrieval against the arthropod dataset. Out of all the assembled sequences with all software, 39.26% were common between the three assemblers, and 27.88% were uniquely assembled by Trinity, while 27.65% were uniquely assembled by SPAdes. The non-redundant merging of all three assemblies’ output permitted the annotation of 9232 sequences, which was 23% more when compared to each software and 28% more when compared to the previous P. verdolaga annotation; moreover, the description of 65 novel theraphotoxins was possible. In the generation of data for non-model organisms, as well as in the search for novel peptides with biotechnological interest, it is highly recommended to employ at least two different transcriptome assemblers.

Revealing the Venomous Secrets of the Spider's Web

Orb-weaving spiders use a highly strong, sticky and elastic web to catch their prey. These web properties alone would be enough for the entrapment of prey; however, these spiders may be hiding venomous secrets in the web, which current research is revealing. Here, we provide strong proteotranscriptomic evidence for the presence of toxin/neurotoxin-like proteins, defensins, and proteolytic enzymes on the web silk from Nephila clavipes spider. The results from quantitative-based transcriptomic and proteomic approaches showed that silk-producing glands produce an extensive repertoire of toxin/neurotoxin-like proteins, similar to those already reported in spider venoms. Meanwhile, the insect toxicity results demonstrated that these toxic components can be lethal and/or paralytic chemical weapons used for prey capture on the web, and the presence of fatty acids in the web may be a responsible mechanism opening the way to the web toxins for accessing the interior of prey's body, as shown here. Comparative phylogenomic-level evolutionary analyses revealed orthologous genes among two spider groups, Araneomorphae and Mygalomorphae, and the findings showed protein sequences similar to toxins found in the taxa Scorpiones and Hymenoptera in addition to Araneae. Overall, these data represent a valuable resource to further investigate other spider web toxin systems and also suggest that N. clavipes web is not a passive mechanical trap for prey capture, but it exerts an active role in prey paralysis/killing using a series of neurotoxins.

Structural venomics reveals evolution of a complex venom by duplication and diversification of an ancient peptide-encoding gene

Spiders are one of the most successful venomous animals, with more than 48,000 described species. Most spider venoms are dominated by cysteine-rich peptides with a diverse range of pharmacological activities. Some spider venoms contain thousands of unique peptides, but little is known about the mechanisms used to generate such complex chemical arsenals. We used an integrated transcriptomic, proteomic, and structural biology approach to demonstrate that the lethal Australian funnel-web spider produces 33 superfamilies of venom peptides and proteins. Twenty-six of the 33 superfamilies are disulfide-rich peptides, and we show that 15 of these are knottins that contribute >90% of the venom proteome. NMR analyses revealed that most of these disulfide-rich peptides are structurally related and range in complexity from simple to highly elaborated knottin domains, as well as double-knot toxins, that likely evolved from a single ancestral toxin gene.

Targeting Trypanosoma evansi with disulphide-rich peptides derived from a phage display library

A phage-display library was generated using a Bus thalamus scorpion toxin (BTK-2) as a peptide scaffold. BTK-2 belongs to the disulfide-rich family of proteins with pronounced structural stability due to the presence of three disulfide bridges that connects antiparallel beta-sheets and one alpha helix. Using BTK-2 as a phage display scaffold, we introduced mutations in five residues located in the alpha-helix and two residues located in the smaller loop, keeping intact the disulfide bridges to create a peptide phage-displayed library with disulfide-rich family properties. The library was subjected to in vivo and in vitro phage display selections against Trypanosoma evansi, the etiological agent of "Surra", a disease that affects a wide range of mammals. The development of T. evansi specific biomarkers is essential to improve diagnostic methods and epidemiological studies leading to a more accurate clinical decision for the treatment of this disease of economic impact for commercial livestock production. In this study, we identified two disulfide-rich peptides targeting T. evansi parasites. Further specificity studies are necessary to investigate the potential of selected peptides as new biomarkers to aid diagnostic and treatment procedures of T. evansi infections.

The Place for Enzymes and Biologically Active Peptides from Marine Organisms for Application in Industrial and Pharmaceutical Biotechnology

Since the beginning of written history, diverse texts have reported the use of enzymatic preparations in food processing and have described the medicinal properties of crude and fractionated venoms to treat various diseases and injuries. With the biochemical characterization of enzymes from distinct sources and bioactive polypeptides from animal venoms, the last sixty years have testified the advent of industrial enzymology and protein therapeutics, which are currently applicable in a wide variety of industrial processes, household products, and pharmaceuticals. Bioprospecting of novel biocatalysts and bioactive peptides is propelled by their unsurpassed properties that are applicable for current and future green industrial processes, biotechnology, and biomedicine. The demand for both novel enzymes with desired characteristics and novel peptides that lead to drug development, has experienced a steady increase in response to the expanding global market for industrial enzymes and peptidebased drugs. Moreover, although largely unexplored, oceans and marine realms, with their unique ecosystems inhabited by a large variety of species, including a considerable number of venomous animals, are recognized as untapped reservoirs of molecules and macromolecules (enzymes and bioactive venom-derived peptides) that can potentially be converted into highly valuable biopharmaceutical products. In this review, we have focused on enzymes and animal venom (poly)peptides that are presently in biotechnological use, and considering the state of prospection of marine resources, on the discovery of useful industrial biocatalysts and drug leads with novel structures exhibiting selectivity and improved performance.

Not so Dangerous After All? Venom Composition and Potency of the Pholcid (Daddy Long-Leg) Spider Physocyclus mexicanus

Pholcid spiders (Araneae: Pholcidae), officially "cellar spiders" but popularly known as "daddy long-legs," are renown for the potential of deadly toxic venom, even though venom composition and potency has never formally been studied. Here we detail the venom composition of male Physocyclus mexicanus using proteomic analyses and venom-gland transcriptomes ("venomics"). We also analyze the venom's potency on insects, and assemble available evidence regarding mammalian toxicity. The majority of the venom (51% of tryptic polypeptides and 62% of unique tryptic peptides) consists of proteins homologous to known venom toxins including enzymes (astacin metalloproteases, serine proteases and metalloendopeptidases, particularly neprilysins) and venom peptide neurotoxins. We identify 17 new groups of peptides (U1-17-PHTX) most of which are homologs of known venom peptides and are predicted to have an inhibitor cysteine knot fold; of these, 13 are confirmed in the proteome. Neprilysins (M13 peptidases), and astacins (M12 peptidases) are the most abundant venom proteins, respectively representing 15 and 11% of the individual proteins and 32 and 20% of the tryptic peptides detected in crude venom. Comparative evidence suggests that the neprilysin gene family is expressed in venoms across a range of spider taxa, but has undergone an expansion in the venoms of pholcids and may play a central functional role in these spiders. Bioassays of crude venoms on crickets resulted in an effective paralytic dose of 3.9 µg/g, which is comparable to that of crude venoms of Plectreurys tristis and other Synspermiata taxa. However, crickets exhibit flaccid paralysis and regions of darkening that are not observed after P. tristis envenomation. Documented bites on humans make clear that while these spiders can bite, the typical result is a mild sting with no long-lasting effects. Together, the evidence we present indicates pholcid venoms are a source of interesting new peptides and proteins, and effects of bites on humans and other mammals are inconsequential.

High-yield production of spider short-chain insecticidal neurotoxin Tx4(6-1) in Pichia pastoris and bioactivity assays in vivo

Short-chain insecticidal neurotoxin Tx4(6-1) from the spider Phoneutria nigriventer can be prepared by reversed-phase high-performance liquid-chromatography (HPLC) fractionation of PhTx4, but this is difficult and represents an obstacle preventing analyses of its insecticidal activity against agricultural insect pests. Herein, we performed secretory expression of recombinant Tx4(6-1) using Pichia pastoris strain X33 as the host, and screened transformants using enzyme-linked immunosorbent assay (ELISA). In flasks, ∼5 mg/l rTx4(6-1) was expressed as a secreted protein following induction with methanol, and this was increased to 45 mg/l rTx4(6-1) in a fed-batch reactor. Approximately 4 mg of high-purity rTx4(6-1) was purified from a 400 ml fed-batch culture supernatant by Ni⁺-nitriloacetic acid affinity chromatography, followed by carboxymethyl (CM) sepharose ion-exchange chromatography. Purified rTx4(6-1) was determined by mass spectrometry (MS) analysis, revealing a molecular weight (MW) of 7660.5 Da, larger than the expected size due to O-linked glycosylation. Insect bioactivity tests of rTx4(6-1)-treated fifth-instar silkworm larvae (Bombyx mori Linnaeus) showed neurotoxin symptoms such as contraction paralysis, abdominal contraction, and mouth movement syndrome, with a half lethal dose at 12 h post-injection of ∼4.5-8.5 μg/g body weight. Dietary toxicity was not observed in silkworm larvae.

Purification and Characterization of a Novel Insecticidal Toxin, μ-sparatoxin-Hv2, from the Venom of the Spider Heteropoda venatoria

The venom of the spider Heteropoda venatoria produced lethal effect to cockroaches as reported in our previous study, and could be a resource for naturally-occurring insecticides. The present study characterized a novel cockroach voltage-gated sodium channels (Na_Vs) antagonist, μ-sparatoxin-Hv2 (μ-SPRTX-Hv2 for short), from this venom. μ-SPRTX-Hv2 is composed of 37 amino acids and contains six conserved cysteines. We synthesized the toxin by using the chemical synthesis method. The toxin was lethal to cockroaches when intraperitoneally injected, with a LD₅₀ value of 2.8 nmol/g of body weight. Electrophysiological data showed that the toxin potently blocked Na_Vs in cockroach dorsal unpaired median (DUM) neurons, with an IC₅₀ of 833.7 ± 132.2 nM, but it hardly affected the DUM voltage-gated potassium channels (K_Vs) and the DUM high-voltage-activated calcium channels (HVA Ca_Vs). The toxin also did not affect Na_Vs, HVA Ca_Vs, and Kvs in rat dorsal root ganglion (DRG) neurons, as well as Na_V subtypes Na_V1.3–1.5, Na_V1.7, and Na_V1.8. No envenomation symptoms were observed when μ-SPRTX-Hv2 was intraperitoneally injected into mouse at the dose of 7.0 μg/g. In summary, μ-SPRTX-Hv2 is a novel insecticidal toxin from H. venatoria venom. It might exhibit its effect by blocking the insect Na_Vs and is a candidate for developing bioinsecticide.

Insect-Active Toxins with Promiscuous Pharmacology from the African Theraphosid Spider Monocentropus balfouri

Many chemical insecticides are becoming less efficacious due to rising resistance in pest species, which has created much interest in the development of new, eco-friendly bioinsecticides. Since insects are the primary prey of most spiders, their venoms are a rich source of insect-active peptides that can be used as leads for new bioinsecticides or as tools to study molecular receptors that are insecticidal targets. In the present study, we isolated two insecticidal peptides, µ/ω-TRTX-Mb1a and -Mb1b, from venom of the African tarantula Monocentropus balfouri. Recombinant µ/ω-TRTX-Mb1a and -Mb1b paralyzed both Lucilia cuprina (Australian sheep blowfly) and Musca domestica (housefly), but neither peptide affected larvae of Helicoverpa armigera (cotton bollworms). Both peptides inhibited currents mediated by voltage-gated sodium (Na_V) and calcium channels in Periplaneta americana (American cockroach) dorsal unpaired median neurons, and they also inhibited the cloned Blattella germanica (German cockroach) Na_V channel (BgNa_V1). An additional effect seen only with Mb1a on BgNa_V1 was a delay in fast inactivation. Comparison of the Na_V channel sequences of the tested insect species revealed that variations in the S1–S2 loops in the voltage sensor domains might underlie the differences in activity between different phyla.

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

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

Insecticidal activity of a recombinant knottin peptide from Loxosceles intermedia venom and recognition of these peptides as a conserved family in the genus

Loxosceles intermedia venom comprises a complex mixture of proteins, glycoproteins and low molecular mass peptides that act synergistically to immobilize envenomed prey. Analysis of a venom-gland transcriptome from L. intermedia revealed that knottins, also known as inhibitor cystine knot peptides, are the most abundant class of toxins expressed in this species. Knottin peptides contain a particular arrangement of intramolecular disulphide bonds, and these peptides typically act upon ion channels or receptors in the insect nervous system, triggering paralysis or other lethal effects. Herein, we focused on a knottin peptide with 53 amino acid residues from L. intermedia venom. The recombinant peptide, named U₂ -sicaritoxin-Li1b (Li1b), was obtained by expression in the periplasm of Escherichia coli. The recombinant peptide induced irreversible flaccid paralysis in sheep blowflies. We screened for knottin-encoding sequences in total RNA extracts from two other Loxosceles species, Loxosceles gaucho and Loxosceles laeta, which revealed that knottin peptides constitute a conserved family of toxins in the Loxosceles genus. The insecticidal activity of U₂ -SCTX-Li1b, together with the large number of knottin peptides encoded in Loxosceles venom glands, suggests that studies of these venoms might facilitate future biotechnological applications of these toxins.

Gene design, fusion technology and TEV cleavage conditions influence the purification of oxidized disulphide-rich venom peptides in Escherichia coli

Background

Animal venoms are large, complex libraries of bioactive, disulphide-rich peptides. These peptides, and their novel biological activities, are of increasing pharmacological and therapeutic importance. However, recombinant expression of venom peptides in Escherichia coli remains difficult due to the significant number of cysteine residues requiring effective post-translational processing. There is also an urgent need to develop high-throughput recombinant protocols applicable to the production of reticulated peptides to enable efficient screening of their drug potential. Here, a comprehensive study was developed to investigate how synthetic gene design, choice of fusion tag, compartment of expression, tag removal conditions and protease recognition site affect levels of solubility of oxidized venom peptides produced in E. coli.

Results

The data revealed that expression of venom peptides imposes significant pressure on cysteine codon selection. DsbC was the best fusion tag for venom peptide expression, in particular when the fusion was directed to the bacterial periplasm. While the redox activity of DsbC was not essential to maximize expression of recombinant fusion proteins, redox activity did lead to higher levels of correctly folded target peptides. With the exception of proline, the canonical TEV protease recognition site tolerated all other residues at its C-terminus, confirming that no non-native residues, which might affect activity, need to be incorporated at the N-terminus of recombinant peptides for tag removal.

Conclusions

This study reveals that E. coli is a convenient heterologous host for the expression of soluble and functional venom peptides. Using the optimal construct design, a large and diverse range of animal venom peptides were produced in the µM scale. These results open up new possibilities for the high-throughput production of recombinant disulphide-rich peptides in E. coli.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0618-0) contains supplementary material, which is available to authorized users.

A Strategy for Production of Correctly Folded Disulfide-Rich Peptides in the Periplasm of E. coli

Recombinant expression of disulfide-reticulated peptides and proteins is often challenging. We describe a method that exploits the periplasmic disulfide-bond forming machinery of Escherichia coli and combines this with a cleavable, solubility-enhancing fusion tag to obtain higher yields of correctly folded target protein than is achievable via cytoplasmic expression. The protocols provided herein cover all aspects of this approach, from vector construction and transformation to purification of the cleaved target protein and subsequent quality control.

Isolation of two insecticidal toxins from venom of the Australian theraphosid spider Coremiocnemis tropix

Sheep flystrike is caused by parasitic flies laying eggs on soiled wool or open wounds, after which the hatched maggots feed on the sheep flesh and often cause large lesions. It is a significant economic problem for the livestock industry as infestations are difficult to control due to ongoing cycles of larval development into flies followed by further egg laying. We therefore screened venom fractions from the Australian theraphosid spider Coremiocnemis tropix to identify toxins active against the sheep blowfly Lucilia cuprina, which is the primary cause of flystrike in Australia. This screen led to isolation of two insecticidal peptides, Ct1a and Ct1b, that are lethal to blowflies within 24 h of injection. The primary structure of these peptides was determined using a combination of Edman degradation and sequencing of a C. tropix venom-gland transcriptome. Ct1a and Ct1b contain 39 and 38 amino acid residues, respectively, including six cysteine residues that form three disulfide bonds. Recombinant production in bacteria (Escherichia coli) resulted in low yields of Ct1a whereas solid-phase peptide synthesis using native chemical ligation produced sufficient quantities of Ct1a for functional analyses. Synthetic Ct1a had no effect on voltage-gated sodium channels from the American cockroach Periplanata americana or the German cockroach Blattella germanica, but it was lethal to sheep blowflies with an LD₅₀ of 1687 pmol/g.

The Whitefly Bemisia tabaci Knottin-1 Gene Is Implicated in Regulating the Quantity of Tomato Yellow Leaf Curl Virus Ingested and Transmitted by the Insect

The whitefly Bemisia tabaci is a major pest to agricultural crops. It transmits begomoviruses, such as Tomato yellow leaf curl virus (TYLCV), in a circular, persistent fashion. Transcriptome analyses revealed that B. tabaci knottin genes were responsive to various stresses. Upon ingestion of tomato begomoviruses, two of the four knottin genes were upregulated, knot-1 (with the highest expression) and knot-3. In this study, we examined the involvement of B. tabaci knottin genes in relation to TYLCV circulative transmission. Knottins were silenced by feeding whiteflies with knottin dsRNA via detached tomato leaves. Large amounts of knot-1 transcripts were present in the abdomen of whiteflies, an obligatory transit site of begomoviruses in their circulative transmission pathway; knot-1 silencing significantly depleted the abdomen from knot-1 transcripts. Knot-1 silencing led to an increase in the amounts of TYLCV ingested by the insects and transmitted to tomato test plants by several orders of magnitude. This effect was not observed following knot-3 silencing. Hence, knot-1 plays a role in restricting the quantity of virions an insect may acquire and transmit. We suggest that knot-1 protects B. tabaci against deleterious effects caused by TYLCV by limiting the amount of virus associated with the whitefly vector.

Molecular basis of the remarkable species selectivity of an insecticidal sodium channel toxin from the African spider Augacephalus ezendami

The inexorable decline in the armament of registered chemical insecticides has stimulated research into environmentally-friendly alternatives. Insecticidal spider-venom peptides are promising candidates for bioinsecticide development but it is challenging to find peptides that are specific for targeted pests. In the present study, we isolated an insecticidal peptide (Ae1a) from venom of the African spider Augacephalus ezendami (family Theraphosidae). Injection of Ae1a into sheep blowflies (Lucilia cuprina) induced rapid but reversible paralysis. In striking contrast, Ae1a was lethal to closely related fruit flies (Drosophila melanogaster) but induced no adverse effects in the recalcitrant lepidopteran pest Helicoverpa armigera. Electrophysiological experiments revealed that Ae1a potently inhibits the voltage-gated sodium channel BgNa_V1 from the German cockroach Blattella germanica by shifting the threshold for channel activation to more depolarized potentials. In contrast, Ae1a failed to significantly affect sodium currents in dorsal unpaired median neurons from the American cockroach Periplaneta americana. We show that Ae1a interacts with the domain II voltage sensor and that sensitivity to the toxin is conferred by natural sequence variations in the S1–S2 loop of domain II. The phyletic specificity of Ae1a provides crucial information for development of sodium channel insecticides that target key insect pests without harming beneficial species.

Characterization of Three Venom Peptides from the Spitting Spider Scytodes thoracica

We present the solution-state NMR structures and preliminary functional characterizations of three venom peptides identified from the spitting spider Scytodes thoracica. Despite little sequence identity to other venom peptides, structural characterization reveals that these peptides contain an inhibitor cystine knot motif common to many venom peptides. These are the first structures for any peptide or protein from spiders of the Scytodidae family. Many venom peptides target neuronal ion channels or receptors. However, we have not been able to determine the target of these Scytodes peptides so we can only state with certainty the channels and receptors that they do not target.