title: Mapping the interaction site for a β-scorpion toxin in the pore module of domain III of voltage-gated Na(+) channels.
abstract: Activation of voltage-gated sodium (Na(v)) channels initiates and propagates action potentials in electrically excitable cells. β-Scorpion toxins, including toxin IV from Centruroides suffusus suffusus (CssIV), enhance activation of Na(V) channels. CssIV stabilizes the voltage sensor in domain II in its activated state via a voltage-sensor trapping mechanism. Amino acid residues required for the action of CssIV have been identified in the S1-S2 and S3-S4 extracellular loops of domain II. The extracellular loops of domain III are also involved in toxin action, but individual amino acid residues have not been identified. We used site-directed mutagenesis and voltage clamp recording to investigate amino acid residues of domain III that are involved in CssIV action. In the IIISS2-S6 loop, five substitutions at four positions altered voltage-sensor trapping by CssIV(E15A). Three substitutions (E1438A, D1445A, and D1445Y) markedly decreased voltage-sensor trapping, whereas the other two substitutions (N1436G and L1439A) increased voltage-sensor trapping. These bidirectional effects suggest that residues in IIISS2-S6 make both positive and negative interactions with CssIV. N1436G enhanced voltage-sensor trapping via increased binding affinity to the resting state, whereas L1439A increased voltage-sensor trapping efficacy. Based on these results, a three-dimensional model of the toxin-channel interaction was developed using the Rosetta modeling method. These data provide additional molecular insight into the voltage-sensor trapping mechanism of toxin action and define a three-point interaction site for β-scorpion toxins on Na(V) channels. Binding of α- and β-scorpion toxins to two distinct, pseudo-symmetrically organized receptor sites on Na(V) channels acts synergistically to modify channel gating and paralyze prey.
authors: Department of Pharmacology, University of Washington, Seattle, WA 98195-7280, USA.
authors: Joel Z
authors: JZ
authors: Zhang
authors: Vladimir
authors: V
authors: Yarov-Yarovoy
authors: Todd
authors: T
authors: Scheuer
authors: Izhar
authors: I
authors: Karbat
authors: Lior
authors: L
authors: Cohen
authors: Dalia
authors: D
authors: Gordon
authors: Michael
authors: M
authors: Gurevitz
authors: William A
authors: WA
authors: Catterall
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D015640:Ion Channel Gating / Q000187:drug effects* / Q000235:genetics; D020125:Mutation, Missense; D062551:NAV1.2 Voltage-Gated Sodium Channel / Q000235:genetics / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D012604:Scorpion Venoms / Q000494:pharmacology*
chemical_list: C035413:Centruroides toxin; D062551:NAV1.2 Voltage-Gated Sodium Channel; C568253:Scn2A protein, rat; D012604:Scorpion Venoms