title: Lethal effects of an insecticidal spider venom peptide involve positive allosteric modulation of insect nicotinic acetylcholine receptors.
abstract: κ-Hexatoxins (κ-HXTXs) are a family of excitotoxic insect-selective neurotoxins from Australian funnel-web spiders that are lethal to a wide range of insects, but display no toxicity towards vertebrates. The prototypic κ-HXTX-Hv1c selectively blocks native and expressed cockroach large-conductance calcium-activated potassium (BKCaor KCa1.1) channels, but not their mammalian orthologs. Despite this potent and selective action on insect KCa1.1 channels, we found that the classical KCa1.1 blockers paxilline, charybdotoxin and iberiotoxin, which all block insect KCa1.1 channels, are not lethal in crickets. We therefore used whole-cell patch-clamp analysis of cockroach dorsal unpaired median (DUM) neurons to study the effects of κ-HXTX-Hv1c on sodium-activated (KNa), delayed-rectifier (KDR) and 'A-type' transient (KA) K+channels. 1 μM κ-HXTX-Hv1c failed to significantly inhibit cockroach KNaand KDRchannels, but did cause a 30 ± 7% saturating inhibition of KAchannel currents, possibly via a Kv4 (Shal-like) action. However, this modest action at such a high concentration of κ-HXTX-Hv1c would indicate a different lethal target. Accordingly, we assessed the actions of κ-HXTX-Hv1c on neurotransmitter-gated ion channels in cockroach DUM neurons. We found that κ-HXTX-Hv1c failed to produce any major effects on GABAAor glutamate-Cl receptors but dramatically slowed nicotine-evoked ACh receptor (nAChR) current decay and reversed nAChR desensitization. These actions occurred without any alterations to nAChR current amplitude or the nicotine concentration-response curve, and are consistent with a positive allosteric modulation of nAChRs. κ-HXTX-Hv1c therefore represents the first venom peptide that selectively modulates insect nAChRs with a mode of action similar to the excitotoxic insecticide spinosyn A. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
authors.affiliation: School of Life Sciences, University of Technology Sydney, Broadway, NSW 2007, Australia.
authors.forename: Monique J
authors.initials: MJ
authors.lastname: Windley
authors.affiliation: Institute for Molecular Bioscience, University of Queensland, Brisbane St. Lucia, QLD 4072, Australia; School of Pharmacy, University of Queensland, Brisbane St. Lucia, QLD 4072, Australia.
authors.forename: Irina
authors.initials: I
authors.lastname: Vetter
authors.affiliation: Institute for Molecular Bioscience, University of Queensland, Brisbane St. Lucia, QLD 4072, Australia.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lewis
authors.affiliation: School of Life Sciences, University of Technology Sydney, Broadway, NSW 2007, Australia. Electronic address: Graham.Nicholson@uts.edu.au.
authors.forename: Graham M
authors.initials: GM
authors.lastname: Nicholson
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects; D000495:Allosteric Site / Q000187:drug effects; D000704:Analysis of Variance; D000818:Animals; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006135:Gryllidae; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D009447:Neuroblastoma / Q000473:pathology; D009474:Neurons / Q000187:drug effects; D009498:Neurotoxins / Q000633:toxicity*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000187:drug effects*; D013111:Spider Venoms / Q000633:toxicity*; D050994:Voltage-Dependent Anion Channels / Q000502:physiology
chemical_list: D007211:Indoles; D009498:Neurotoxins; D026902:Potassium Channel Blockers; D011978:Receptors, Nicotinic; D013111:Spider Venoms; D050994:Voltage-Dependent Anion Channels; C048220:paxilline
keywords: Bioinsecticide; Insect-selective; Peptide toxins; Spider toxins; nAChR PAM