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Zhu Q, Du Y, Nomura Y, Gao R, Cang Z, Wei GW, Gordon D, Gurevitz M, Groome J, Dong K. Charge substitutions at the voltage-sensing module of domain III enhance actions of site-3 and site-4 toxins on an insect sodium channel. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2021; 137:103625. [PMID: 34358664 PMCID: PMC9376739 DOI: 10.1016/j.ibmb.2021.103625] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2021] [Revised: 07/29/2021] [Accepted: 07/29/2021] [Indexed: 06/13/2023]
Abstract
Scorpion α-toxins bind at the pharmacologically-defined site-3 on the sodium channel and inhibit channel inactivation by preventing the outward movement of the voltage sensor in domain IV (IVS4), whereas scorpion β-toxins bind at site-4 on the sodium channel and enhance channel activation by trapping the voltage sensor of domain II (IIS4) in its outward position. However, limited information is available on the role of the voltage-sensing modules (VSM, comprising S1-S4) of domains I and III in toxin actions. We have previously shown that charge reversing substitutions of the innermost positively-charged residues in IIIS4 (R4E, R5E) increase the activity of an insect-selective site-4 scorpion toxin, Lqh-dprIT3-c, on BgNav1-1a, a cockroach sodium channel. Here we show that substitutions R4E and R5E in IIIS4 also increase the activity of two site-3 toxins, LqhαIT from Leiurusquinquestriatus hebraeus and insect-selective Av3 from Anemonia viridis. Furthermore, charge reversal of either of two conserved negatively-charged residues, D1K and E2K, in IIIS2 also increase the action of the site-3 and site-4 toxins. Homology modeling suggests that S2-D1 and S2-E2 interact with S4-R4 and S4-R5 in the VSM of domain III (III-VSM), respectively, in the activated state of the channel. However, charge swapping between S2-D1 and S4-R4 had no compensatory effects on gating or toxin actions, suggesting that charged residue interactions are complex. Collectively, our results highlight the involvement of III-VSM in the actions of both site 3 and site 4 toxins, suggesting that charge reversing substitutions in III-VSM allosterically facilitate IIS4 or IVS4 voltage sensor trapping by these toxins.
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Affiliation(s)
- Qing Zhu
- Key Lab of Food Quality and Safety of Jiangsu Province-State Key Laboratory Breeding Base, Key Laboratory of Control Technology and Standard for Agro-product Safety and Quality, Ministry of Agriculture, Institute of Food Safety and Nutrition, Jiangsu Academy of Agricultural Sciences, Nanjing, China; Department of Entomology, Michigan State University, East Lansing, MI, USA
| | - Yuzhe Du
- Department of Entomology, Michigan State University, East Lansing, MI, USA
| | - Yoshiko Nomura
- Department of Entomology, Michigan State University, East Lansing, MI, USA
| | - Rong Gao
- Department of Hygienic Analysis and Detection, School of Public Health, Nanjing Medical University, 818 Tianyuan East Road, Nanjing, Jiangsu, China
| | - Zixuan Cang
- Department of Mathematics, Michigan State University, East Lansing, MI, USA
| | - Guo-Wei Wei
- Department of Mathematics, Michigan State University, East Lansing, MI, USA
| | - Dalia Gordon
- Department of Plant Molecular Biology & Ecology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv, Israel
| | - Michael Gurevitz
- Department of Plant Molecular Biology & Ecology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel Aviv, Israel.
| | - James Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID, USA
| | - Ke Dong
- Department of Entomology, Michigan State University, East Lansing, MI, USA; Department of Biology, Duke University, Durham, NC, USA.
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Zhorov BS, Dong K. Elucidation of pyrethroid and DDT receptor sites in the voltage-gated sodium channel. Neurotoxicology 2017; 60:171-177. [PMID: 27567732 PMCID: PMC5730328 DOI: 10.1016/j.neuro.2016.08.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 08/20/2016] [Accepted: 08/23/2016] [Indexed: 12/19/2022]
Abstract
DDT and pyrethroid insecticides were among the earliest neurotoxins identified to act on voltage-gated sodium channels. In the 1960s, equipped with, at the time, new voltage-clamp techniques, Professor Narahashi and associates provided the initial evidence that DDT and allethrin (the first commercial pyrethroid insecticide) caused prolonged flow of sodium currents in lobster and squid giant axons. Over the next several decades, continued efforts by Prof. Narahashi's group as well as other laboratories led to a comprehensive understanding of the mechanism of action of DDT and pyrethroids on sodium channels. Fast forward to the 1990s, genetic, pharmacological and toxicological data all further confirmed voltage-gated sodium channels as the primary targets of DDT and pyrethroid insecticides. Modifications of the gating kinetics of sodium channels by these insecticides result in repetitive firing and/or membrane depolarization in the nervous system. This mini-review focuses on studies from Prof. Narahashi's pioneer work and more recent mutational and computational modeling analyses which collectively elucidated the elusive pyrethroid receptor sites as well as the molecular basis of differential sensitivities of insect and mammalian sodium channels to pyrethroids.
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Affiliation(s)
- Boris S Zhorov
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada; Sechenov Institute of Evolutionary Physiology & Biochemistry, Russian Academy of Sciences, St. Petersburg 194223, Russia
| | - Ke Dong
- Department of Entomology, Genetics and Neuroscience Programs, Michigan State University, East Lansing, MI 48824, USA.
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β/δ-PrIT1, a highly insecticidal toxin from the venom of the Brazilian spider Phoneutria reidyi (F.O. Pickard-Cambridge, 1897). Toxicon 2015. [DOI: 10.1016/j.toxicon.2015.07.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Dong K, Du Y, Rinkevich F, Nomura Y, Xu P, Wang L, Silver K, Zhorov BS. Molecular biology of insect sodium channels and pyrethroid resistance. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2014; 50:1-17. [PMID: 24704279 PMCID: PMC4484874 DOI: 10.1016/j.ibmb.2014.03.012] [Citation(s) in RCA: 296] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 03/24/2014] [Accepted: 03/24/2014] [Indexed: 05/06/2023]
Abstract
Voltage-gated sodium channels are essential for the initiation and propagation of the action potential in neurons and other excitable cells. Because of their critical roles in electrical signaling, sodium channels are targets of a variety of naturally occurring and synthetic neurotoxins, including several classes of insecticides. This review is intended to provide an update on the molecular biology of insect sodium channels and the molecular mechanism of pyrethroid resistance. Although mammalian and insect sodium channels share fundamental topological and functional properties, most insect species carry only one sodium channel gene, compared to multiple sodium channel genes found in each mammalian species. Recent studies showed that two posttranscriptional mechanisms, alternative splicing and RNA editing, are involved in generating functional diversity of sodium channels in insects. More than 50 sodium channel mutations have been identified to be responsible for or associated with knockdown resistance (kdr) to pyrethroids in various arthropod pests and disease vectors. Elucidation of molecular mechanism of kdr led to the identification of dual receptor sites of pyrethroids on insect sodium channels. Many of the kdr mutations appear to be located within or close to the two receptor sites. The accumulating knowledge of insect sodium channels and their interactions with insecticides provides a foundation for understanding the neurophysiology of sodium channels in vivo and the development of new and safer insecticides for effective control of arthropod pests and human disease vectors.
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Affiliation(s)
- Ke Dong
- Department of Entomology, Neuroscience and Genetics Programs, Michigan State University, East Lansing, MI, USA.
| | - Yuzhe Du
- Department of Entomology, Neuroscience and Genetics Programs, Michigan State University, East Lansing, MI, USA
| | - Frank Rinkevich
- Department of Entomology, Neuroscience and Genetics Programs, Michigan State University, East Lansing, MI, USA
| | - Yoshiko Nomura
- Department of Entomology, Neuroscience and Genetics Programs, Michigan State University, East Lansing, MI, USA
| | - Peng Xu
- Department of Entomology, Neuroscience and Genetics Programs, Michigan State University, East Lansing, MI, USA
| | - Lingxin Wang
- Department of Entomology, Neuroscience and Genetics Programs, Michigan State University, East Lansing, MI, USA
| | - Kristopher Silver
- Department of Anatomy and Physiology, Kansas State University, Manhattan, KS, USA
| | - Boris S Zhorov
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada; Sechenov Institute of Evolutionary Physiology & Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
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Panditrao MM, Panditrao MM, Sunilkumar V, Panditrao AM. Effect of previous scorpion bite(s) on the action of intrathecal bupivacaine: A case control study. Indian J Anaesth 2013; 57:236-40. [PMID: 23983280 PMCID: PMC3748676 DOI: 10.4103/0019-5049.115593] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Background: During the routine practice in the institution, it was observed that there were persistent incidents of inadequate/failed spinal anaesthesia in patients with a history of single or multiple scorpion bite/s. To test any possible correlation between scorpion bite and the altered response to spinal anaesthesia, a case control study was conducted involving patients with a history of scorpion bite/s and without such a history. Methods: Randomly selected 70 (n=70) patients of either sex and age range of 18-80 years, were divided into two equal groups, giving past history of one or multiple scorpion bites and giving no such a history. The anaesthetic management was identical inclusive of subarachnoid block with 3.5 ml. 0.5% bupivacaine heavy. The onsets of sensory, motor and peaks of sensory and motor blocks were observed with the pin-prick method and Bromage scale. After waiting for 20 min, if the block was inadequate, then balanced general anaesthesia was administered. The analysis of the data and application of various statistical tests was carried out using Chi-square test, percentages, independent sample t-test and paired t-test. Results: Demographically both groups were comparable. In scorpion bite group, the time of onsets of both sensory and motor blocks and time for the peak of sensory and motor blocks were significantly prolonged, 4 patients had failed/inadequate sensory block and 5 patients had failed/inadequate motor block while all the patients in non-bite group had adequate intra-operative block. Conclusion: We conclude that there appears to be a direct correlation between the histories of old, single or multiple scorpion bites and development of resistance to effect of local anaesthetics administered intra-thecally.
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Affiliation(s)
- Mridul M Panditrao
- Department of Anaesthesiology and Intensive Care, Padmashree Dr. Vithalrao Vikhe Patil Foundation's Medical College and Hospital, Vilad Ghat, Ahmednagar, Maharashtra, India
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Song W, Du Y, Liu Z, Luo N, Turkov M, Gordon D, Gurevitz M, Goldin AL, Dong K. Substitutions in the domain III voltage-sensing module enhance the sensitivity of an insect sodium channel to a scorpion beta-toxin. J Biol Chem 2011; 286:15781-8. [PMID: 21454658 DOI: 10.1074/jbc.m110.217000] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Scorpion β-toxins bind to the extracellular regions of the voltage-sensing module of domain II and to the pore module of domain III in voltage-gated sodium channels and enhance channel activation by trapping and stabilizing the voltage sensor of domain II in its activated state. We investigated the interaction of a highly potent insect-selective scorpion depressant β-toxin, Lqh-dprIT(3), from Leiurus quinquestriatus hebraeus with insect sodium channels from Blattella germanica (BgNa(v)). Like other scorpion β-toxins, Lqh-dprIT(3) shifts the voltage dependence of activation of BgNa(v) channels expressed in Xenopus oocytes to more negative membrane potentials but only after strong depolarizing prepulses. Notably, among 10 BgNa(v) splice variants tested for their sensitivity to the toxin, only BgNa(v)1-1 was hypersensitive due to an L1285P substitution in IIIS1 resulting from a U-to-C RNA-editing event. Furthermore, charge reversal of a negatively charged residue (E1290K) at the extracellular end of IIIS1 and the two innermost positively charged residues (R4E and R5E) in IIIS4 also increased the channel sensitivity to Lqh-dprIT(3). Besides enhancement of toxin sensitivity, the R4E substitution caused an additional 20-mV negative shift in the voltage dependence of activation of toxin-modified channels, inducing a unique toxin-modified state. Our findings provide the first direct evidence for the involvement of the domain III voltage-sensing module in the action of scorpion β-toxins. This hypersensitivity most likely reflects an increase in IIS4 trapping via allosteric mechanisms, suggesting coupling between the voltage sensors in neighboring domains during channel activation.
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Affiliation(s)
- Weizhong Song
- Department of Entomology, Michigan State University, East Lansing, Michigan 48824, USA
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Petricevich VL. Scorpion venom and the inflammatory response. Mediators Inflamm 2010; 2010:903295. [PMID: 20300540 PMCID: PMC2838227 DOI: 10.1155/2010/903295] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2009] [Accepted: 01/04/2010] [Indexed: 02/06/2023] Open
Abstract
Scorpion venoms consist of a complex of several toxins that exhibit a wide range of biological properties and actions, as well as chemical compositions, toxicity, and pharmacokinetic and pharmacodynamic characteristics. These venoms are associated with high morbility and mortality, especially among children. Victims of envenoming by a scorpion suffer a variety of pathologies, involving mainly both sympathetic and parasympathetic stimulation as well as central manifestations such as irritability, hyperthermia, vomiting, profuse salivation, tremor, and convulsion. The clinical signs and symptoms observed in humans and experimental animals are related with an excessive systemic host inflammatory response to stings and stings, respectively. Although the pathophysiology of envenomation is complex and not yet fully understood, venom and immune responses are known to trigger the release of inflammatory mediators that are largely mediated by cytokines. In models of severe systemic inflammation produced by injection of high doses of venom or venoms products, the increase in production of proinflammatory cytokines significantly contributes to immunological imbalance, multiple organ dysfunction and death. The cytokines initiate a cascade of events that lead to illness behaviors such as fever, anorexia, and also physiological events in the host such as activation of vasodilatation, hypotension, and increased of vessel permeability.
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Affiliation(s)
- Vera L Petricevich
- Laboratorio de Inflamación y Toxicología, Facultad de Medicina de la Universidad Autónoma del Estado de Morelos, Avenida Universidad 1001, Cuernavaca, Morelos 62209, Mexico.
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Yamaji N, Little MJ, Nishio H, Billen B, Villegas E, Nishiuchi Y, Tytgat J, Nicholson GM, Corzo G. Synthesis, solution structure, and phylum selectivity of a spider delta-toxin that slows inactivation of specific voltage-gated sodium channel subtypes. J Biol Chem 2009; 284:24568-82. [PMID: 19592486 DOI: 10.1074/jbc.m109.030841] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Magi 4, now renamed delta-hexatoxin-Mg1a, is a 43-residue neurotoxic peptide from the venom of the hexathelid Japanese funnel-web spider (Macrothele gigas) with homology to delta-hexatoxins from Australian funnel-web spiders. It binds with high affinity to receptor site 3 on insect voltage-gated sodium (Na(V)) channels but, unlike delta-hexatoxins, does not compete for the related site 3 in rat brain despite being previously shown to be lethal by intracranial injection. To elucidate differences in Na(V) channel selectivity, we have undertaken the first characterization of a peptide toxin on a broad range of mammalian and insect Na(V) channel subtypes showing that delta-hexatoxin-Mg1a selectively slows channel inactivation of mammalian Na(V)1.1, Na(V)1.3, and Na(V)1.6 but more importantly shows higher affinity for insect Na(V)1 (para) channels. Consequently, delta-hexatoxin-Mg1a induces tonic repetitive firing of nerve impulses in insect neurons accompanied by plateau potentials. In addition, we have chemically synthesized and folded delta-hexatoxin-Mg1a, ascertained the bonding pattern of the four disulfides, and determined its three-dimensional solution structure using NMR spectroscopy. Despite modest sequence homology, we show that key residues important for the activity of scorpion alpha-toxins and delta-hexatoxins are distributed in a topologically similar manner in delta-hexatoxin-Mg1a. However, subtle differences in the toxin surfaces are important for the novel selectivity of delta-hexatoxin-Mg1a for certain mammalian and insect Na(V) channel subtypes. As such, delta-hexatoxin-Mg1a provides us with a specific tool with which to study channel structure and function and determinants for phylum- and tissue-specific activity.
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Affiliation(s)
- Nahoko Yamaji
- Suntory Institute for Bioorganic Research, Mishima-gun, Shimamoto-cho, Osaka 618-8503, Japan
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10
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Gordon D, Karbat I, Ilan N, Cohen L, Kahn R, Gilles N, Dong K, Stühmer W, Tytgat J, Gurevitz M. The differential preference of scorpion α-toxins for insect or mammalian sodium channels: Implications for improved insect control. Toxicon 2007; 49:452-72. [PMID: 17215013 DOI: 10.1016/j.toxicon.2006.11.016] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2006] [Accepted: 11/17/2006] [Indexed: 11/19/2022]
Abstract
Receptor site-3 on voltage-gated sodium channels is targeted by a variety of structurally distinct toxins from scorpions, sea anemones, and spiders whose typical action is the inhibition of sodium current inactivation. This site interacts allosterically with other topologically distinct receptors that bind alkaloids, lipophilic polyether toxins, pyrethroids, and site-4 scorpion toxins. These features suggest that design of insecticides with specificity for site-3 might be rewarding due to the positive cooperativity with other toxins or insecticidal agents. Yet, despite the central role of scorpion alpha-toxins in envenomation and their vast use in the study of channel functions, molecular details on site-3 are scarce. Scorpion alpha-toxins vary greatly in preference for sodium channels of insects and mammals, and some of them are highly active on insects. This implies that despite its commonality, receptor site-3 varies on insect vs. mammalian channels, and that elucidation of these differences could potentially be exploited for manipulation of toxin preference. This review provides current perspectives on (i) the classification of scorpion alpha-toxins, (ii) their mode of interaction with sodium channels and pharmacological divergence, (iii) molecular details on their bioactive surfaces and differences associated with preference for channel subtypes, as well as (iv) a summary of the present knowledge about elements involved in constituting receptor site-3. These details, combined with the variations in allosteric interactions between site-3 and the other receptor sites on insect and mammalian sodium channels, may be useful in new strategies of insect control and future design of anti-insect selective ligands.
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Affiliation(s)
- Dalia Gordon
- Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv 69978, Tel-Aviv, Israel.
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11
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Gurevitz M, Karbat I, Cohen L, Ilan N, Kahn R, Turkov M, Stankiewicz M, Stühmer W, Dong K, Gordon D. The insecticidal potential of scorpion β-toxins. Toxicon 2007; 49:473-89. [PMID: 17197009 DOI: 10.1016/j.toxicon.2006.11.015] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2006] [Accepted: 11/20/2006] [Indexed: 11/28/2022]
Abstract
Voltage-gated sodium channels are a major target for toxins and insecticides due to their central role in excitability, but due to the conservation of these channels in Animalia most insecticides do not distinguish between those of insects and mammals, thereby imposing risks to humans and livestock. Evidently, as long as modern agriculture depends heavily on the use of insecticides there is a great need for new substances capable of differentiating between sodium channel subtypes. Such substances exist in venomous animals, but ways for their exploitation have not yet been developed due to problems associated with manufacturing, degradation, and delivery to the target channels. Engineering of plants for expression of anti-insect toxins or use of natural vectors that express toxins near their target site (e.g. baculoviruses) are still problematic and raise public concern. In this problematic reality a rational approach might be to learn from nature how to design highly selective anti-insect compounds preferably in the form of peptidomimetics. This is a complex task that requires the elucidation of the face of interaction between insect-selective toxins and their sodium channel receptor sites. This review delineates current progress in: (i) elucidation of the bioactive surfaces of scorpion beta-toxins, especially the excitatory and depressant groups, which show high preference for insects and bind insect sodium channels with high affinity; (ii) studies of the mode of interaction of scorpion beta-toxins with receptor site-4 on voltage-gated sodium channels; and (iii) clarification of channel elements that constitute receptor site-4. This information may be useful in future attempts to mimic the bioactive surface of the toxins for the design of anti-insect selective peptidomimetics.
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Affiliation(s)
- Michael Gurevitz
- Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv 69978, Tel-Aviv, Israel.
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12
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Nicholson GM. Insect-selective spider toxins targeting voltage-gated sodium channels. Toxicon 2007; 49:490-512. [PMID: 17223149 DOI: 10.1016/j.toxicon.2006.11.027] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Accepted: 11/17/2006] [Indexed: 12/21/2022]
Abstract
The voltage-gated sodium (Na(v)) channel is a target for a number of drugs, insecticides and neurotoxins. These bind to at least seven identified neurotoxin binding sites and either block conductance or modulate Na(v) channel gating. A number of peptide neurotoxins from the venoms of araneomorph and mygalomorph spiders have been isolated and characterized and determined to interact with several of these sites. These all conform to an 'inhibitor cystine-knot' motif with structural, but not sequence homology, to a variety of other spider and marine snail toxins. Of these, spider toxins several show phyla-specificity and are being considered as lead compounds for the development of biopesticides. Hainantoxin-I appears to target site-1 to block Na(v) channel conductance. Magi 2 and Tx4(6-1) slow Na(v) channel inactivation via an interaction with site-3. The delta-palutoxins, and most likely mu-agatoxins and curtatoxins, target site-4. However, their action is complex with the mu-agatoxins causing a hyperpolarizing shift in the voltage-dependence of activation, an action analogous to scorpion beta-toxins, but with both delta-palutoxins and mu-agatoxins slowing Na(v) channel inactivation, a site-3-like action. In addition, several other spider neurotoxins, such as delta-atracotoxins, are known to target both insect and vertebrate Na(v) channels most likely as a result of the conserved structures within domains of voltage-gated ion channels across phyla. These toxins may provide tools to establish the molecular determinants of invertebrate selectivity. These studies are being greatly assisted by the determination of the pharmacophore of these toxins, but without precise identification of their binding site and mode of action their potential in the above areas remains underdeveloped.
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Affiliation(s)
- Graham M Nicholson
- Neurotoxin Research Group, Department of Medical and Molecular Biosciences, University of Technology, Sydney P.O. Box 123, Broadway, NSW 2007, Australia.
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Corzo G, Sabo JK, Bosmans F, Billen B, Villegas E, Tytgat J, Norton RS. Solution structure and alanine scan of a spider toxin that affects the activation of mammalian voltage-gated sodium channels. J Biol Chem 2006; 282:4643-4652. [PMID: 17148449 DOI: 10.1074/jbc.m605403200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Magi 5, from the hexathelid spider Macrothele gigas, is a 29-residue polypeptide containing three disulfide bridges. It binds specifically to receptor site 4 on mammalian voltage-gated sodium channels and competes with scorpion beta-toxins, such as Css IV from Centruroides suffusus suffusus. As a consequence, Magi 5 shifts the activation voltage of the mammalian rNav1.2a channel to more hyperpolarized voltages, whereas the insect channel, DmNav1, is not affected. To gain insight into toxin-channel interactions, Magi 5 and 23 analogues were synthesized. The three-dimensional structure of Magi 5 in aqueous solution was determined, and its voltage-gated sodium channel-binding surfaces were mapped onto this structure using data from electrophysiological measurements on a series of Ala-substituted analogues. The structure clearly resembles the inhibitor cystine knot structural motif, although the triple-stranded beta-sheet typically found in that motif is partially distorted in Magi 5. The interactive surface of Magi 5 toward voltage-gated sodium channels resembles in some respects the Janus-faced atracotoxins, with functionally important charged residues on one face of the toxin and hydrophobic residues on the other. Magi 5 also resembles the scorpion beta-toxin Css IV, which has distinct nonpolar and charged surfaces that are critical for channel binding and has a key Glu involved in voltage sensor trapping. These two distinct classes of toxin, with different amino acid sequences and different structures, may utilize similar groups of residues on their surface to achieve the common end of modifying voltage-gated sodium channel function.
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Affiliation(s)
- Gerardo Corzo
- Instituto de Biotecnologi´a, Universidad Nacional Auto´noma de México, Apartado Postal 510-3, Cuernavaca, Morelos 61500, Mexico; Suntory Institute for Bioorganic Research, Mishima-gun, Shimamoto-cho, Wakayamadai 1-1-1, Osaka 618-8503, Japan
| | - Jennifer K Sabo
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia
| | - Frank Bosmans
- Laboratory of Toxicology, University of Leuven, Campus Gasthuisberg, O&N2, 3000 Leuven, Belgium, and the
| | - Bert Billen
- Laboratory of Toxicology, University of Leuven, Campus Gasthuisberg, O&N2, 3000 Leuven, Belgium, and the
| | - Elba Villegas
- Centro de Investigacion en Biotecnologia Universidad Auto´noma del Estado de México, Avenida Universidad 2001, Cuernavaca, Morelos 62210, Mexico
| | - Jan Tytgat
- Laboratory of Toxicology, University of Leuven, Campus Gasthuisberg, O&N2, 3000 Leuven, Belgium, and the
| | - Raymond S Norton
- Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, Victoria 3050, Australia.
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Abstract
Voltage-gated Na(+) channels are integral membrane proteins that function as a gateway for a selective permeation of sodium ions across biological membranes. In this way, they are crucial players for the generation of action potentials in excitable cells. Voltage-gated Na(+) channels are encoded by at least nine genes in mammals. The different isoforms have remarkably similar functional properties, but small changes in function and pharmacology are biologically well-defined, as underscored by mutations that cause several diseases and by modulation of a myriad of compounds, respectively. This review will stress on the modulation of voltage-gated Na(+) channels by scorpion alpha-toxins. Nature has designed these two classes of molecules as if they were predestined to each other: an inevitable 'encounter' between a voltage-gated Na(+) channel isoform and an alpha-toxin from scorpion venom indeed results in a dramatically changed Na(+) current phenotype with clear-cut consequences on electrical excitability and sometimes life or death. This fascinating aspect justifies an overview on scorpion venoms, their alpha-toxins and the Na(+) channel targets they are built for, as well as on the molecular determinants that govern the selectivity and affinity of this 'inseparable duo'.
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Affiliation(s)
- Frank Bosmans
- Laboratory of Toxicology, University of Leuven, O and N 2, Postbus 922, Herestraat 49, 3000 Leuven, Belgium
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Cohen L, Lipstein N, Gordon D. Allosteric interactions between scorpion toxin receptor sites on voltage‐gated Na channels imply a novel role for weakly active components in arthropod venom. FASEB J 2006; 20:1933-5. [PMID: 16877526 DOI: 10.1096/fj.05-5545fje] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Scorpion beta and alpha-toxins modify the activation and inactivation of voltage-gated sodium channels. Although the two types of toxin bind at two distinct receptor sites on the same sodium channel, they exhibit synergic effects when coinjected into insects. To clarify the basis of this synergism we examined the mutual effects of alpha and beta toxin representatives in radio-ligand binding assays. We found positive allosteric interactions between receptor site-4 of the excitatory Bj-xtrIT and the depressant LqhIT2 beta toxins and receptor site-3 of the alpha toxin LqhalphaIT, on locust neuronal membranes. Unexpectedly, a nontoxic mutant Bj-xtrIT-E15R, which binds with high affinity to receptor site-4, was able to enhance LqhalphaIT binding and toxicity similarly to the unmodified Bj-xtrIT. This result indicates that mere binding of a nontoxic ligand to receptor site-4 ("silent binding") induces a conformational change that does not alter channel gating, but influences toxin binding at receptor site-3 leading to enhanced toxicity. This finding suggests a new functional role for weakly toxic polypeptides in that they enhance the effect of other active neurotoxins in the arthropod venom. Such silent binding may have also valuable implications in attempts to improve drug efficacy by combining potent drugs with nonactive allosteric enhancers.
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Affiliation(s)
- Lior Cohen
- Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv, Tel-Aviv 69978, Israel
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16
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17
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Bel Haj Rhouma R, Cérutti-Duonor M, Benkhadir K, Goudey-Perrière F, El Ayeb M, Lopez-Ferber M, Karoui H. Insecticidal effects of Buthus occitanus tunetanus BotIT6 toxin expressed in Escherichia coli and baculovirus/insect cells. JOURNAL OF INSECT PHYSIOLOGY 2005; 51:1376-83. [PMID: 16216259 DOI: 10.1016/j.jinsphys.2005.08.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Revised: 08/24/2005] [Accepted: 08/26/2005] [Indexed: 05/04/2023]
Abstract
BotIT6 is a neurotoxin polypeptide derived from the venom of the scorpion Buthus occitanus tunetanus (Bot). Its mature form is composed of 62 amino acids. BotIT6 has been reported to be the most potent toxin from Bot venom that has a strict selectivity for insects. Such toxin may have potential as a potent animal-harmless tool against insects. Using RT-PCR, we isolated and sequenced a cDNA encoding 62 amino acid residues corresponding to the known amino acid sequence of BotIT6. We have expressed a recombinant active form of BotIT6 in significantly high amounts in Escherichia coli. We have also engineered the cDNA into the Autographa californica Nuclear Polyhedrosis Virus (AcMNPV) genome and expressed the protein under control of the polyhedrin promoter. Supernatants of AcIT6-virus infected Sf9 insect cells exhibit a typical intoxication effect when injected to Spodoptera littoralis larvae. Moreover, injection of the recombinant virus showed enhanced insecticidal potency against S. littoralis larvae compared with wild type AcMNPV.
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Affiliation(s)
- Rahima Bel Haj Rhouma
- Laboratoire des Venins et Toxines, Institut Pasteur de Tunis, Tunis-Belvedère, Tunisia
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18
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Abstract
Voltage-gated sodium channels open (activate) when the membrane is depolarized and close on repolarization (deactivate) but also on continuing depolarization by a process termed inactivation, which leaves the channel refractory, i.e., unable to open again for a period of time. In the “classical” fast inactivation, this time is of the millisecond range, but it can last much longer (up to seconds) in a different slow type of inactivation. These two types of inactivation have different mechanisms located in different parts of the channel molecule: the fast inactivation at the cytoplasmic pore opening which can be closed by a hinged lid, the slow inactivation in other parts involving conformational changes of the pore. Fast inactivation is highly vulnerable and affected by many chemical agents, toxins, and proteolytic enzymes but also by the presence of β-subunits of the channel molecule. Systematic studies of these modulating factors and of the effects of point mutations (experimental and in hereditary diseases) in the channel molecule have yielded a fairly consistent picture of the molecular background of fast inactivation, which for the slow inactivation is still lacking.
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Affiliation(s)
- Werner Ulbricht
- Psychologisches Institut, University of Kiel, Hermann-Rodewald-Strasse 5, D-24118 Kiel, Germany.
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19
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Arnon T, Potikha T, Sher D, Elazar M, Mao W, Tal T, Bosmans F, Tytgat J, Ben-Arie N, Zlotkin E. BjalphaIT: a novel scorpion alpha-toxin selective for insects--unique pharmacological tool. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2005; 35:187-195. [PMID: 15705498 DOI: 10.1016/j.ibmb.2004.11.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2004] [Revised: 10/21/2004] [Accepted: 11/01/2004] [Indexed: 05/24/2023]
Abstract
Long-chain neurotoxins derived from the venom of the Buthidae scorpions, which affect voltage-gated sodium channels (VGSCs) can be subdivided according to their toxicity to insects into insect-selective excitatory and depressant toxins (beta-toxins) and the alpha-like toxins which affect both mammals and insects. In the present study by the aid of reverse-phase HPLC column chromatography, RT-PCR, cloning and various toxicity assays, a new insect selective toxin designated as BjalphaIT was isolated from the venom of the Judean Black Scorpion (Buthotus judaicus), and its full primary sequence was determined: MNYLVVICFALLLMTVVESGRDAYIADNLNCAYTCGSNSYCNTECTKNGAVSGYCQWLGKYGNACWCINLPDKVPIRIPGACR (leader sequence is underlined). Despite its lack of toxicity to mammals and potent toxicity to insects, BjalphaIT reveals an amino acid sequence and an inferred spatial arrangement that is characteristic of the well-known scorpion alpha-toxins highly toxic to mammals. BjalphaITs sharp distinction between insects and mammals was also revealed by its effect on sodium conductance of two cloned neuronal VGSCs heterloguously expressed in Xenopus laevis oocytes and assayed with the two-electrode voltage-clamp technique. BjalphaIT completely inhibits the inactivation process of the insect para/tipE VGSC at a concentration of 100 nM, in contrast to the rat brain Na(v)1.2/beta1 which is resistant to the toxin. The above categorical distinction between mammal and insect VGSCs exhibited by BjalphaIT enables its employment in the clarification of the molecular basis of the animal group specificity of scorpion venom derived neurotoxic polypeptides and voltage-gated sodium channels.
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Affiliation(s)
- Tal Arnon
- Department of Cell and Animal biology, Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
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20
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Karbat I, Cohen L, Gilles N, Gordon D, Gurevitz M, Izhar K, Lior C, Nicholas G, Dalia G, Michael G. Conversion of a scorpion toxin agonist into an antagonist highlights an acidic residue involved in voltage sensor trapping during activation of neuronal Na
+
channels. FASEB J 2004; 18:683-9. [PMID: 15054090 DOI: 10.1096/fj.03-0733com] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Gating modifiers constitute a large group of polypeptide toxins that interact with the voltage-sensing module of ion channels. Among them, scorpion beta-toxins induce a negative shift in the voltage dependence of sodium channel activation. To explain their effect, a "voltage sensor trapping" model has been proposed in which the voltage sensor of domain-II (DIIS4) is trapped in an outward, activated position by a prebound beta-toxin upon membrane depolarization. Whereas toxin effect on channel activation was enhanced upon neutralization of the two outermost arginines in DIIS4, toxin residues involved in sensor trapping have not been identified. Using the scorpion excitatory beta-toxin, Bj-xtrIT, we found two conserved acidic residues, Glu15 and Glu30, mandatory for toxin action. Whereas mutagenesis of Glu30 affected both toxicity and binding affinity, substitutions E15A/F abolished activity but had minor effects on binding. Complete uncoupling of activity from binding was obtained with mutant E15R, acting as an efficient antagonist of Bj-xtrIT. On the basis of the voltage sensor trapping model and our results, we propose that Glu15 interacts with the emerging gating charges of DIIS4 upon membrane depolarization. Conserved acidic residues found in a variety of gating modifiers from scorpions and spiders may interact similarly with the voltage sensor.
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Affiliation(s)
- Izhar Karbat
- Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv 69978, Tel-Aviv, Israel
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21
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Nicholson GM, Little MJ, Birinyi-Strachan LC. Structure and function of δ-atracotoxins: lethal neurotoxins targeting the voltage-gated sodium channel. Toxicon 2004; 43:587-99. [PMID: 15066415 DOI: 10.1016/j.toxicon.2004.02.006] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Delta-atracotoxins (delta-ACTX), isolated from the venom of Australian funnel-web spiders, are responsible for the potentially lethal envenomation syndrome seen following funnel-web spider envenomation. They are 42-residue polypeptides with four disulfides and an "inhibitor cystine-knot" motif with structural but not sequence homology to a variety of other spider and marine snail toxins. Delta-atracotoxins induce spontaneous repetitive firing and prolongation of action potentials resulting in neurotransmitter release from somatic and autonomic nerve endings. This results from a slowing of voltage-gated sodium channel inactivation and a hyperpolarizing shift of the voltage-dependence of activation. This action is due to voltage-dependent binding to neurotoxin receptor site-3 in a similar, but not identical, fashion to scorpion alpha-toxins and sea anemone toxins. Unlike other site-3 neurotoxins, however, delta-ACTX bind with high affinity to both cockroach and mammalian sodium channels but low affinity to locust sodium channels. At present the pharmacophore of delta-ACTX is unknown but is believed to involve a number of basic residues distributed in a topologically similar manner to scorpion alpha-toxins and sea anemone toxins despite distinctly different protein scaffolds. As such, delta-ACTX provide us with specific tools with which to study sodium channel structure and function and determinants for phyla- and tissue-specific actions of neurotoxins interacting with site-3.
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Affiliation(s)
- Graham M Nicholson
- Neurotoxin Research Group, Department of Heath Sciences, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia.
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22
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Cohen L, Karbat I, Gilles N, Froy O, Corzo G, Angelovici R, Gordon D, Gurevitz M. Dissection of the Functional Surface of an Anti-insect Excitatory Toxin Illuminates a Putative “Hot Spot” Common to All Scorpion β-Toxins Affecting Na+ Channels. J Biol Chem 2004; 279:8206-11. [PMID: 14672947 DOI: 10.1074/jbc.m307531200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Scorpion beta-toxins affect the activation of voltage-sensitive sodium channels (NaChs). Although these toxins have been instrumental in the study of channel gating and architecture, little is known about their active sites. By using an efficient system for the production of recombinant toxins, we analyzed by point mutagenesis the entire surface of the beta-toxin, Bj-xtrIT, an anti-insect selective excitatory toxin from the scorpion Buthotus judaicus. Each toxin mutant was purified and analyzed using toxicity and binding assays, as well as by circular dichroism spectroscopy to discern the differences among mutations that caused structural changes and those that specifically affected bioactivity. This analysis highlighted a functional discontinuous surface of 1405 A(2), which was composed of a number of non-polar and three charged amino acids clustered around the main alpha-helical motif and the C-tail. Among the charged residues, Glu(30) is a center of a putative "hot spot" in the toxin-receptor binding-interface and is shielded from bulk solvent by a hydrophobic "gasket" (Tyr(26) and Val(34)). Comparison of the Bj-xtrIT structure with that of other beta-toxins that are active on mammals suggests that the hot spot and an adjacent non-polar region are spatially conserved. These results highlight for the first time structural elements that constitute a putative "pharmacophore" involved in the interaction of beta-toxins with receptor site-4 on NaChs. Furthermore, the unique structure of the C-terminal region most likely determines the specificity of excitatory toxins for insect NaChs.
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Affiliation(s)
- Lior Cohen
- Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Ramat-Aviv 69978, Tel-Aviv, Israel
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23
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Distinct primary structures of the major peptide toxins from the venom of the spider Macrothele gigas that bind to sites 3 and 4 in the sodium channel. FEBS Lett 2003; 547:43-50. [PMID: 12860384 DOI: 10.1016/s0014-5793(03)00666-5] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Six peptide toxins (Magi 1-6) were isolated from the Hexathelidae spider Macrothele gigas. The amino acid sequences of Magi 1, 2, 5 and 6 have low similarities to the amino acid sequences of known spider toxins. The primary structure of Magi 3 is similar to the structure of the palmitoylated peptide named PlTx-II from the North American spider Plectreurys tristis (Plectreuridae). Moreover, the amino acid sequence of Magi 4, which was revealed by cloning of its cDNA, displays similarities to the Na+ channel modifier delta-atracotoxin from the Australian spider Atrax robustus (Hexathelidae). Competitive binding assays using several 125I-labelled peptide toxins clearly demonstrated the specific binding affinity of Magi 1-5 to site 3 of the insect sodium channel and also that of Magi 5 to site 4 of the rat sodium channel. Only Magi 6 did not compete with the scorpion toxin LqhalphaIT in binding to site 3 despite high toxicity on lepidoptera larvae of 3.1 nmol/g. The K(i)s of other toxins were between 50 pM for Magi 4 and 1747 nM for Magi 1. In addition, only Magi 5 binds to both site 3 in insects (K(i)=267 nM) and site 4 in rat brain synaptosomes (K(i)=1.2 nM), whereas it showed no affinities for either mammal binding site 3 or insect binding site 4. Magi 5 is the first spider toxin with binding affinity to site 4 of a mammalian sodium channel.
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24
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Gilles N, Gurevitz M, Gordon D. Allosteric interactions among pyrethroid, brevetoxin, and scorpion toxin receptors on insect sodium channels raise an alternative approach for insect control. FEBS Lett 2003; 540:81-5. [PMID: 12681487 DOI: 10.1016/s0014-5793(03)00226-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Intensive pyrethroid use in insect control has led to resistance buildup among various pests. One alternative to battle this problem envisions the combined use of synergistically acting insecticidal compounds. Pyrethroids, scorpion alpha- and beta-toxins, and brevetoxins bind to distinct receptor sites on voltage-gated sodium channels (NaChs) and modify their function. The binding affinity of scorpion alpha-toxins to locust, but not rat-brain NaChs, is allosterically increased by pyrethroids and by brevetoxin-1. Brevetoxin-1 also increases the binding of an excitatory beta-toxin to insect NaChs. These results reveal differences between insect and mammalian NaChs and may be exploited in new strategies of insect control.
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Affiliation(s)
- Nicolas Gilles
- CEA, Département d'Ingénierie et d'Etudes des Protéines, CE Saclay, 91191 Gif-sur-Yvette, France
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25
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Regev A, Rivkin H, Inceoglu B, Gershburg E, Hammock BD, Gurevitz M, Chejanovsky N. Further enhancement of baculovirus insecticidal efficacy with scorpion toxins that interact cooperatively. FEBS Lett 2003; 537:106-10. [PMID: 12606040 DOI: 10.1016/s0014-5793(03)00104-2] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have studied whether the cooperative insecticidal effect of certain scorpion toxin pairs, namely either a combination of excitatory and depressant, or alpha and depressant scorpion toxins, would improve the efficacy of Autographa californica nucleopolyhedrovirus (AcMNPV) over a virus expressing only a single toxin, towards Heliothis virescens, Helicoverpa armigera, and Spodoptera littoralis larvae. The best result was achieved by combined expression of the excitatory toxin, LqhIT1, and the depressant toxin, LqhIT2, that provided an ET(50) value of 46.9 h on H. virescens neonates, an improvement of 40% over the efficacy of wild-type AcMNPV, and of 18% and 22% over baculoviruses that express each of the toxins independently. These results demonstrate that significant improvement in efficacy of recombinant baculoviruses is obtainable with toxins that exhibit a cooperative effect, and may contribute to employ baculoviruses to replace hazardous chemicals in insect control.
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Affiliation(s)
- Avital Regev
- Entomology Department, Institute of Plant Protection, ARO, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
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26
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Domain 2 of Drosophila para voltage-gated sodium channel confers insect properties to a rat brain channel. J Neurosci 2002. [PMID: 12040042 DOI: 10.1523/jneurosci.22-11-04364.2002] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The ability of the excitatory anti-insect-selective scorpion toxin AahIT (Androctonus australis hector) to exclusively bind to and modify the insect voltage-gated sodium channel (NaCh) makes it a unique tool to unravel the structural differences between mammalian and insect channels, a prerequisite in the design of selective pesticides. To localize the insect NaCh domain that binds AahIT, we constructed a chimeric channel composed of rat brain NaCh alpha-subunit (rBIIA) in which domain-2 (D2) was replaced by that of Drosophila Para (paralytic temperature-sensitive). The choice of D2 was dictated by the similarity between AahIT and scorpion beta-toxins pertaining to both their binding and action and the essential role of D2 in the beta-toxins binding site on mammalian channels. Expression of the chimera rBIIA-ParaD2 in Xenopus oocytes gave rise to voltage-gated and TTX-sensitive NaChs that, like rBIIA, were sensitive to scorpion alpha-toxins and regulated by the auxiliary subunit beta(1) but not by the insect TipE. Notably, like Drosophila Para/TipE, but unlike rBIIA/beta(1), the chimera gained sensitivity to AahIT, indicating that the phyletic selectivity of AahIT is conferred by the insect NaCh D2. Furthermore, the chimera acquired additional insect channel properties; its activation was shifted to more positive potentials, and the effect of alpha-toxins was potentiated. Our results highlight the key role of D2 in the selective recognition of anti-insect excitatory toxins and in the modulation of NaCh gating. We also provide a methodological approach to the study of ion channels that are difficult to express in model expression systems.
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27
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Bouhaouala-Zahar B, Benkhalifa R, Srairi N, Zenouaki I, Ligny-Lemaire C, Drevet P, Sampieri F, Pelhate M, El Ayeb M, Ménez A, Karoui H, Ducancel F. A chimeric scorpion alpha-toxin displays de novo electrophysiological properties similar to those of alpha-like toxins. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:2831-41. [PMID: 12071945 DOI: 10.1046/j.1432-1033.2002.02918.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BotXIV and LqhalphaIT are two structurally related long chain scorpion alpha-toxins that inhibit sodium current inactivation in excitable cells. However, while LqhalphaIT from Leiurus quinquestriatus hebraeus is classified as a true and strong insect alpha-toxin, BotXIV from Buthus occitanus tunetanus is characterized by moderate biological activities. To assess the possibility that structural differences between these two molecules could reflect the localization of particular functional topographies, we compared their sequences. Three structurally deviating segments located in three distinct and exposed loops were identified. They correspond to residues 8-10, 19-22, and 38-43. To evaluate their functional role, three BotXIV/LqhalphaIT chimeras were designed by transferring the corresponding LqhalphaIT sequences into BotXIV. Structural and antigenic characterizations of the resulting recombinant chimera show that BotXIV can accommodate the imposed modifications, confirming the structural flexibility of that particular alpha/beta fold. Interestingly, substitution of residues 8-10 yields to a new electrophysiological profile of the corresponding variant, partially comparable to that one of alpha-like scorpion toxins. Taken together, these results suggest that even limited structural deviations can reflect functional diversity, and also that the structure-function relationships between insect alpha-toxins and alpha-like scorpion toxins are probably more complex than expected.
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28
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Gilles N, Harrison G, Karbat I, Gurevitz M, Nicholson GM, Gordon D. Variations in receptor site-3 on rat brain and insect sodium channels highlighted by binding of a funnel-web spider delta-atracotoxin. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:1500-10. [PMID: 11874465 DOI: 10.1046/j.1432-1033.2002.02799.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Delta-atracotoxins (delta-ACTXs) from Australian funnel-web spiders differ structurally from scorpion alpha-toxins (Sc(alpha)Tx) but similarly slow sodium current inactivation and compete for their binding to sodium channels at receptor site-3. Characterization of the binding of 125I-labelled delta-ACTX-Hv1a to various sodium channels reveals a decrease in affinity for depolarized (0 mV; Kd=6.5 +/- 1.4 nm) vs.polarized (-55 mV; Kd=0.6 +/- 0.2 nm) rat brain synaptosomes. The increased Kd under depolarized conditions correlates with a 4.3-fold reduction in the association rate and a 1.8-increase in the dissociation rate. In comparison, Sc(alpha)Tx binding affinity decreased 33-fold under depolarized conditions due to a 48-fold reduction in the association rate. The binding of 125I-labelled delta-ACTX-Hv1a to rat brain synaptosomes is inhibited competitively by classical Sc(alpha)Txs and allosterically by brevetoxin-1, similar to Sc(alpha)Tx binding. However, in contrast with classical Sc(alpha)Txs, 125I-labelled delta-ACTX-Hv1a binds with high affinity to cockroach Na+ channels (Kd=0.42 +/- 0.1 nm) and is displaced by the Sc(alpha)Tx, Lqh(alpha)IT, a well-defined ligand of insect sodium channel receptor site-3. However, delta-ACTX-Hv1a exhibits a surprisingly low binding affinity to locust sodium channels. Thus, unlike Sc(alpha)Txs, which are capable of differentiating between mammalian and insect sodium channels, delta-ACTXs differentiate between various insect sodium channels but bind with similar high affinity to rat brain and cockroach channels. Structural comparison of delta-ACTX-Hv1a to Sc(alpha)Txs suggests a similar putative bioactive surface but a 'slimmer' overall shape of the spider toxin. A slimmer shape may ease the interaction with the cockroach and mammalian receptor site-3 and facilitate its association with different conformations of the rat brain receptor, correlated with closed/open and slow-inactivated channel states.
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Affiliation(s)
- Nicolas Gilles
- CEA, Dèpartement d'Ingènierie et d'Etudes des Protèines, Gif-sur-Yvette, France
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29
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Jiang G, Xu Y, Zhu X, Su Y, Zhu Y. Prokaryotically expressed Buthus martensii Karsch insect depressant toxin has insecticidal effects. Toxicon 2001; 39:469-76. [PMID: 11024486 DOI: 10.1016/s0041-0101(00)00115-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
An insect depressant toxin Buthus martensii Karsch insect toxin 4 (BmK IT(4)) cDNA was cloned into the prokaryotic expression vector pSW202 and expressed in HB101 host cells. The authenticity of this in vitro expressed peptide was confirmed by Western blotting, mass spectrometry and N-terminal peptide sequencing. Bioassays using growth media supplemented with BmK IT(4) demonstrated that, at the end of the 5-day experimental period, about 77% of the testing cotton bollworm larvae were killed. Furthermore, the average weight picked up by larvae grown on BmK IT(4) containing media amounts only to 0.7% of that of control group. Our results indicate that BmK IT(4) may be used for biological control of insect damages in place of other traditional insecticides.
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Affiliation(s)
- G Jiang
- The National Laboratory of Protein Engineering and Plant Genetic Engineering, College of Life Sciences, Peking University, 100871, Beijing, People's Republic of China
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30
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Abstract
AaIT is a single chain neurotoxic polypeptide derived from the venom of the Buthid scorpion Androctonus australis Hector, composed of 70 amino acids cross-linked by four disulfide bridges. Its strict selectivity for insects has been documented by toxicity, electrophysiological and ligand receptor binding assays. These last have shown that various insect neuronal membranes possess a single class of non-interacting AaIT binding sites of high affinity (K(D) = 1-3(n)M) and low capacity (0.5-2.0 pmol/mg prot.). The fast excitatory paralysis induced by AaIT is a result of a presynaptic effect, namely the induction of a repetitive firing in the terminal branches of the insect's motor nerves resulting in a massive and uncoordinated stimulation of the respective skeletal muscles. The neuronal repetitive activity is attributed to an exclusive and specific perturbation of sodium conductance as a consequence of toxin binding to external loops of the insect voltage-dependent sodium channel and modification of its gating mechanism. From a strictly agrotechnical point of view AaIT involvement in plant protection has taken the following two complementary forms: firstly, as a factor for the genetic engineering of insect infective baculoviruses resulting in potent and selective bio-insecticides. The efficacy of the AaIT-expressing, recombinant baculovirus is attributed mainly to its ability to continuously provide and translocate the gene of the expressed toxin to the insect central nervous system; secondly, based on the pharmacological flexibility of the voltage-gated sodium channel, as a device for insecticide resistance management. Channel mutations conferring resistance to a given class of insecticidal agents (such as the KDR phenomenon) may greatly increase susceptibility to the AaIT expressing bioinsecticides. Thus the AaIT is a pharmacological tool for the study of insect neuronal excitability and chemical ecology and the development of new approaches to insect control.
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Affiliation(s)
- E Zlotkin
- Department of Animal and Cell Biology, Institute of Life Sciences, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel.
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