title: Structure-function map of the receptor site for β-scorpion toxins in domain II of voltage-gated sodium channels.
abstract: Voltage-gated sodium (Na(v)) channels are the molecular targets of β-scorpion toxins, which shift the voltage dependence of activation to more negative membrane potentials by a voltage sensor-trapping mechanism. Molecular determinants of β-scorpion toxin (CssIV) binding and action on rat brain sodium channels are located in the S1-S2 (IIS1-S2) and S3-S4 (IIS3-S4) extracellular linkers of the voltage-sensing module in domain II. In IIS1-S2, mutations of two amino acid residues (Glu(779) and Pro(782)) significantly altered the toxin effect by reducing binding affinity. In IIS3-S4, six positions surrounding the key binding determinant, Gly(845), define a hot spot of high-impact residues. Two of these substitutions (A841N and L846A) reduced voltage sensor trapping. The other three substitutions (N842R, V843A, and E844N) increased voltage sensor trapping. These bidirectional effects suggest that the IIS3-S4 loop plays a primary role in determining both toxin affinity and efficacy. A high resolution molecular model constructed with the Rosetta-Membrane modeling system reveals interactions of amino acid residues in sodium channels that are crucial for toxin action with residues in CssIV that are required for its effects. In this model, the wedge-shaped CssIV inserts between the IIS1-S2 and IIS3-S4 loops of the voltage sensor, placing key amino acid residues in position to interact with binding partners in these extracellular loops. These results provide new molecular insights into the voltage sensor-trapping model of toxin action and further define the molecular requirements for the development of antagonists that can prevent or reverse toxicity of scorpion toxins.
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, Washington 98195-7280, USA.
authors.forename: Joel Z
authors.initials: JZ
authors.lastname: Zhang
authors.forename: Vladimir
authors.initials: V
authors.lastname: Yarov-Yarovoy
authors.forename: Todd
authors.initials: T
authors.lastname: Scheuer
authors.forename: Izhar
authors.initials: I
authors.lastname: Karbat
authors.forename: Lior
authors.initials: L
authors.lastname: Cohen
authors.forename: Dalia
authors.initials: D
authors.lastname: Gordon
authors.forename: Michael
authors.initials: M
authors.lastname: Gurevitz
authors.forename: William A
authors.initials: WA
authors.lastname: Catterall
mesh_terms: D000818:Animals; D015640:Ion Channel Gating; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism*; D012604:Scorpion Venoms / Q000737:chemistry* / Q000378:metabolism*; D015222:Sodium Channels / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D050505:Mutant Proteins; D062551:NAV1.2 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; C568253:Scn2A protein, rat; D012604:Scorpion Venoms; D015222:Sodium Channels