Inhibition of insect calcium channels by huwentoxin-V, a neurotoxin from Chinese tarantula Ornithoctonus huwena venom

Insecticidal toxicity of ω-Atypitoxin-Cs1a and its inhibitory effects on insect voltage-gated calcium channels

BACKGROUND

Excessive use of chemical insecticides raises concerns about insecticide resistance, urging the development of novel insecticides. Peptide neurotoxins from spider venom are an incredibly rich source of ion channel modulators with potent insecticidal activity. A neurotoxin U1-Atypitoxin-Cs1a from the spider Calommata signata was annotated previously. It was of interest to investigate its insecticidal activity and potential molecular targets.

RESULTS

Cs1a was heterologously expressed, purified and pharmacologically characterized here. The recombinant neurotoxin inhibited high-voltage-activated calcium channel currents with an median inhibitory concentration (IC50 ) value of 0.182 ± 0.026 μm on cockroach DUM neurons and thus was designated as ω-Atypitoxin-Cs1a. The recombinant Cs1a was toxic to three insect pests of agricultural importance, Nilaparvata lugens, Spodoptera frugiperda and Plutella xylostella with median lethal concentration (LD50 ) values of 0.121, 0.172 and 0.356 nmol g-1 , respectively, at 24 h postinjection. Cs1a was equivalently toxic to both insecticide-susceptible and -resistant insects. Cs1a exhibited low toxicity to Danio rerio with an LD50 of 2.316 nmol g-1 .

CONCLUSION

Our results suggest that ω-Atypitoxin-Cs1a is a potent CaV channel inhibitor and an attractive candidate reagent for pest control and resistance management. © 2023 Society of Chemical Industry.

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.

The Venom of Ornithoctonus huwena affect the electrophysiological stability of neonatal rat ventricular myocytes by inhibiting sodium, potassium and calcium current

Spider venoms are known to contain various toxins that are used as an effective means to capture their prey or to defend themselves against predators. An investigation of the properties of Ornithoctonus huwena (O.huwena) crude venom found that the venom can block neuromuscular transmission of isolated mouse phrenic nerve-diaphragm and sciatic nerve-sartorius preparations. However, little is known about its electrophysiological effects on cardiac myocytes. In this study, electrophysiological activities of ventricular myocytes were detected by 100 μg/mL venom of O.huwena, and whole cell patch-clamp technique was used to study the acute effects of the venom on action potential (AP), sodium current (I_Na), potassium currents (I_Kr, I_Ks, I_to1 and I_K1) and L-type calcium current (I_CaL). The results indicated that the venom prolongs APD₉₀ in a frequency-dependent manner in isolated neonatal rat ventricular myocytes. 100 μg/mL venom inhibited 72.3 ± 3.6% I_Na current, 58.3 ± 4.2% summit current and 54 ± 6.1% the end current of I_Kr, and 65 ± 3.3% I_CaL current, yet, didn't have obvious effect on I_Ks, I_to1 and I_K1 currents. In conclusion, the O.huwena venom represented a multifaceted pharmacological profile. It contains abundant of cardiac channel antagonists and might be valuable tools for investigation of both channels and anti- arrhythmic therapy development.

Characterization of ion channels on subesophageal ganglion neurons from Chinese tarantula Ornithoctonus huwena: Exploring the myth of the spider insensitive to its venom

Chinese tarantula Ornithoctonus huwena is one of the most venomous spiders distributing in the hilly areas of southern China. In this study, using whole-cell patch-clamp technique we investigated electrophysiological and pharmacological properties of ion channels from tarantula subesophageal ganglion neurons. It was found that the neurons express multiple kinds of ion channels at least including voltage-gated calcium channels, TTX-sensitive sodium channels and two types of potassium channels. They exhibit pharmacological properties similar to mammalian subtypes. Spider calcium channels were sensitive to ω-conotoxin GVIA and diltiazem, two well-known inhibitors of mammalian neuronal high-voltage-activated (HVA) subtypes. 4-Aminopyridine and tetraethylammonium could inhibit spider outward transient and delayed-rectifier potassium channels, respectively. Huwentoxin-I and huwentoxin-IV are two abundant toxic components in the venom of Ornithoctonus huwena. Interestingly, although in our previous work they inhibit HVA calcium channels and TTX-sensitive sodium channels from mammalian sensory neurons, respectively, they fail to affect the subtypes from spider neurons. Moreover, the crude venom has no effect on delayed-rectifier potassium channels and only slightly reduces transient outward potassium channels with an IC50 value of ∼51.3 mg/L. Therefore, our findings provide important evidence for ion channels from spiders having an evolution as self-defense and prey mechanism.

ω-Tbo-IT1-New Inhibitor of Insect Calcium Channels Isolated from Spider Venom

Novel disulfide-containing polypeptide toxin was discovered in the venom of the Tibellus oblongus spider. We report on isolation, spatial structure determination and electrophysiological characterization of this 41-residue toxin, called ω-Tbo-IT1. It has an insect-toxic effect with LD50 19 μg/g in experiments on house fly Musca domestica larvae and with LD50 20 μg/g on juvenile Gromphadorhina portentosa cockroaches. Electrophysiological experiments revealed a reversible inhibition of evoked excitatory postsynaptic currents in blow fly Calliphora vicina neuromuscular junctions, while parameters of spontaneous ones were not affected. The inhibition was concentration dependent, with IC50 value 40 ± 10 nM and Hill coefficient 3.4 ± 0.3. The toxin did not affect frog neuromuscular junctions or glutamatergic and GABAergic transmission in rat brains. Ca(2+) currents in Calliphora vicina muscle were not inhibited, whereas in Periplaneta americana cockroach neurons at least one type of voltage gated Ca(2+) current was inhibited by ω-Tbo-IT1. Thus, the toxin apparently acts as an inhibitor of presynaptic insect Ca(2+) channels. Spatial structure analysis of the recombinant ω-Tbo-IT1 by NMR spectroscopy in aqueous solution revealed that the toxin comprises the conventional ICK fold containing an extended β-hairpin loop and short β-hairpin loop which are capable of making "scissors-like mutual motions".

Structural and Functional Diversity of Peptide Toxins from Tarantula Haplopelma hainanum (Ornithoctonus hainana) Venom Revealed by Transcriptomic, Peptidomic, and Patch Clamp Approaches

Spider venom is a complex mixture of bioactive peptides to subdue their prey. Early estimates suggested that over 400 venom peptides are produced per species. In order to investigate the mechanisms responsible for this impressive diversity, transcriptomics based on second generation high throughput sequencing was combined with peptidomic assays to characterize the venom of the tarantula Haplopelma hainanum. The genes expressed in the venom glands were identified, and the bioactivity of their protein products was analyzed using the patch clamp technique. A total of 1,136 potential toxin precursors were identified that clustered into 90 toxin groups, of which 72 were novel. The toxin peptides clustered into 20 cysteine scaffolds that included between 4 and 12 cysteines, and 14 of these groups were newly identified in this spider. Highly abundant toxin peptide transcripts were present and resulted from hypermutation and/or fragment insertion/deletion. In combination with variable post-translational modifications, this genetic variability explained how a limited set of genes can generate hundreds of toxin peptides in venom glands. Furthermore, the intraspecies venom variability illustrated the dynamic nature of spider venom and revealed how complex components work together to generate diverse bioactivities that facilitate adaptation to changing environments, types of prey, and milking regimes in captivity.

Toxin diversity revealed by a transcriptomic study of Ornithoctonus huwena

Spider venom comprises a mixture of compounds with diverse biological activities, which are used to capture prey and defend against predators. The peptide components bind a broad range of cellular targets with high affinity and selectivity, and appear to have remarkable structural diversity. Although spider venoms have been intensively investigated over the past few decades, venomic strategies to date have generally focused on high-abundance peptides. In addition, the lack of complete spider genomes or representative cDNA libraries has presented significant limitations for researchers interested in molecular diversity and understanding the genetic mechanisms of toxin evolution. In the present study, second-generation sequencing technologies, combined with proteomic analysis, were applied to determine the diverse peptide toxins in venom of the Chinese bird spider Ornithoctonus huwena. In total, 626 toxin precursor sequences were retrieved from transcriptomic data. All toxin precursors clustered into 16 gene superfamilies, which included six novel superfamilies and six novel cysteine patterns. A surprisingly high number of hypermutations and fragment insertions/deletions were detected, which accounted for the majority of toxin gene sequences with low-level expression. These mutations contribute to the formation of diverse cysteine patterns and highly variable isoforms. Furthermore, intraspecific venom variability, in combination with variable transcripts and peptide processing, contributes to the hypervariability of toxins in venoms, and associated rapid and adaptive evolution of toxins for prey capture and defense.

Molecular cloning, bioinformatics analysis and functional characterization of HWTX-XI toxin superfamily from the spider Ornithoctonus huwena

Spider venom contains a very valuable repertoire of natural resources to discover novel components for molecular diversity analyses and therapeutic applications. In this study, HWTX-XI toxins from the spider venom glands of Ornithoctonus huwena which are Kunitz-type toxins (KTTs) and were directly cloned, analyzed and functionally characterized. To date, the HWTX-XI superfamily consists of 38 members deduced from 121 high-quality expressed sequence tags, which is the largest spider KTT superfamily with significant molecular diversity mainly resulted from cDNA tandem repeats as well as focal hypermutation. Among them, HW11c40 and HW11c50 may be intermediate variants between native Kunitz toxins and sub-Kunitz toxins based on evolutionary analyses. In order to elucidate their biological activities, recombinant HW11c4, HW11c24, HW11c27 and HW11c39 were successfully expressed, further purified and functionally characterized. Both HW11c4 and HW11c27 display inhibitory activities against trypsin, chymotrypsin and kallikrein. Moreover, HW11c4 is also an inhibitor relatively specific for Kv1.1 channels. HW11c24 and HW11c39 are found to be inactive on chymotrysin, trypsin, kallikrein, thrombin and ion channels. These findings provide molecular evidence for toxin diversification of the HWTX-XI superfamily and useful molecular templates of serine protease inhibitors and ion channel blockers for the development of potentially clinical applications.

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.

Expression and characterization of jingzhaotoxin-34, a novel neurotoxin from the venom of the tarantula Chilobrachys jingzhao

Jingzhaotoxin-34 (JZTX-34) is a 35-residue polypeptide from the venom of Chinese tarantula Chilobrachys jingzhao. Our previous work reported its full-length cDNA sequence encoding a precursor with 87 residues. In this study we report the protein expression and biological function characterization. The toxin was efficiently expressed by the secretary pathway in yeast. Under whole-cell patch-clamp mode, the expressed JZTX-34 was able to inhibit tetrodotoxin-sensitive (TTX-S) sodium currents (IC(50) approximately 85 nM) while having no significant effects on tetrodotoxin-resistant (TTX-R) sodium currents on rat dorsal root ganglion neurons. The inhibition of TTX-S sodium channels was completely reversed by strong depolarization (+120 mV). Toxin treatment altered neither channel activation and inactivation kinetics nor recovery rate from inactivation. However, it is interesting to note that in contrast to huwentoxin-IV, a recently identified receptor site-4 toxin from Ornithoctonus huwena venom, 100 nM JZTX-34 caused a negative shift of steady-state inactivation curve of TTX-S sodium channels by approximately 10 mV. The results indicated that JZTX-34 might inhibit mammalian sensory neuronal sodium channels through a mechanism similar to HWTX-IV by trapping the IIS4 voltage sensor in the resting conformation, but their binding sites should not overlay completely.

Expression, purification and characterization of a group of lectin-like peptides from the spider Ornithoctonus huwena

By sequencing random clones from the venom gland cDNA library of the spider Ornithoctonus huwena, a transcript, named SHL-Ib1, encoding a lectin-like peptide was cloned. The amino acid sequence of the putative mature peptide of SHL-Ib1 is identical, except for seven different residues, with that of SHL-I, a lectin found in the venom of O. huwena. The mature peptides of SHL-Ib1b and SHL-Ib1c are the mutants of SHL-Ib1 with two or three amino acid residues truncated at the C-terminal. The recombinant SHL-Ib1b and SHL-Ib1c were expressed successfully by the yeast expression system and purified by using a combination of ion-exchange and reverse phase high performance liquid chromatography (HPLC). The molecular masses of the two expressed peptides were identified by mass spectrometry, indicating that the C-terminals of the two peptides were not amidated. The two peptides can agglutinate human erythrocytes at minimal concentrations of 0.75 and 1.475mg/ml, respectively. Structure modeling of SHL-Ib1 has given a clue to the low agglutination bioactivities of these recombinant toxins. These lectin-like peptides, due to the small molecular sizes, may have the advantage to investigate the binding mechanism of the lectin and have the potential to be the carrier for drug delivery.