title: The omega-atracotoxins: selective blockers of insect M-LVA and HVA calcium channels.
abstract: The omega-atracotoxins (omega-ACTX) are a family of arthropod-selective peptide neurotoxins from Australian funnel-web spider venoms (Hexathelidae: Atracinae) that are candidates for development as biopesticides. We isolated a 37-residue insect-selective neurotoxin, omega-ACTX-Ar1a, from the venom of the Sydney funnel-web spider Atrax robustus, with high homology to several previously characterized members of the omega-ACTX-1 family. The peptide induced potent excitatory symptoms, followed by flaccid paralysis leading to death, in acute toxicity tests in house crickets. Using isolated smooth and skeletal nerve-muscle preparations, the toxin was shown to lack overt vertebrate toxicity at concentrations up to 1 microM. To further characterize the target of the omega-ACTXs, voltage-clamp analysis using the whole-cell patch-clamp technique was undertaken using cockroach dorsal unpaired median neurons. It is shown here for the first time that omega-ACTX-Ar1a, and its homolog omega-ACTX-Hv1a from Hadronyche versuta, reversibly block both mid-low- (M-LVA) and high-voltage-activated (HVA) insect calcium channel (Ca(v)) currents. This block occurred in the absence of alterations in the voltage-dependence of Ca(v) channel activation, and was voltage-independent, suggesting that omega-ACTX-1 family toxins are pore blockers rather than gating modifiers. At a concentration of 1 microM omega-ACTX-Ar1a failed to significantly affect global K(v) channel currents. However, 1 microM omega-ACTX-Ar1a caused a modest 18% block of insect Na(v) channel currents, similar to the minor block of Na(v) channels reported for other insect Ca(v) channel blockers such as omega-agatoxin IVA. These findings validate both M-LVA and HVA Ca(v) channels as potential targets for insecticides.
authors.affiliation: Neurotoxin Research Group, Department of Medical & Molecular Biosciences, University of Technology, Sydney, Broadway, NSW 2007, Australia.
authors.forename: Youmie
authors.initials: Y
authors.lastname: Chong
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Hayes
authors.forename: Brianna
authors.initials: B
authors.lastname: Sollod
authors.forename: Suping
authors.initials: S
authors.lastname: Wen
authors.forename: David T
authors.initials: DT
authors.lastname: Wilson
authors.forename: Peter G
authors.initials: PG
authors.lastname: Hains
authors.forename: Wayne C
authors.initials: WC
authors.lastname: Hodgson
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Broady
authors.forename: Glenn F
authors.initials: GF
authors.lastname: King
authors.forename: Graham M
authors.initials: GM
authors.lastname: Nicholson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism*; D002645:Chickens; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005260:Female; D006135:Gryllidae / Q000187:drug effects; D007928:Lethal Dose 50; D008297:Male; D008969:Molecular Sequence Data; D008970:Molecular Weight; D018482:Muscle, Skeletal / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D009498:Neurotoxins / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D010526:Periplaneta / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013111:Spider Venoms / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D013112:Spiders; D018675:Toxicity Tests / Q000379:methods; D014649:Vas Deferens / Q000187:drug effects / Q000473:pathology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009498:Neurotoxins; D013111:Spider Venoms