title: Common features in the functional surface of scorpion beta-toxins and elements that confer specificity for insect and mammalian voltage-gated sodium channels.
abstract: Scorpion beta-toxins that affect the activation of mammalian voltage-gated sodium channels (Navs) have been studied extensively, but little is known about their functional surface and mode of interaction with the channel receptor. To enable a molecular approach to this question, we have established a successful expression system for the anti-mammalian scorpion beta-toxin, Css4, whose effects on rat brain Navs have been well characterized. A recombinant toxin, His-Css4, was obtained when fused to a His tag and a thrombin cleavage site and had similar binding affinity for and effect on Na currents of rat brain sodium channels as those of the native toxin isolated from the scorpion venom. Molecular dissection of His-Css4 elucidated a functional surface of 1245 A2 composed of the following: 1) a cluster of residues associated with the alpha-helix, which includes a putative "hot spot" (this cluster is conserved among scorpion beta-toxins and contains their "pharmacophore"); 2) a hydrophobic cluster associated mainly with the beta2 and beta3 strands, which is likely to confer the specificity for mammalian Navs; 3) a single bioactive residue (Trp-58) in the C-tail; and 4) a negatively charged residue (Glu-15) involved in voltage sensor trapping as inferred from our ability to uncouple toxin binding from activity upon its substitution. This study expands our understanding about the mode of action of scorpion beta-toxins and illuminates differences in the functional surfaces that may dictate their specificities for mammalian versus insect sodium channels.
authors.affiliation: Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Sackler School of Medicine, Tel-Aviv University, Ramat-Aviv 69978, Tel-Aviv, Israel.
authors.forename: Lior
authors.initials: L
authors.lastname: Cohen
authors.forename: Izhar
authors.initials: I
authors.lastname: Karbat
authors.forename: Nicolas
authors.initials: N
authors.lastname: Gilles
authors.forename: Nitza
authors.initials: N
authors.lastname: Ilan
authors.forename: Morris
authors.initials: M
authors.lastname: Benveniste
authors.forename: Dalia
authors.initials: D
authors.lastname: Gordon
authors.forename: Michael
authors.initials: M
authors.lastname: Gurevitz
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D016466:CHO Cells; D002942:Circular Dichroism; D006224:Cricetinae; D004247:DNA / Q000737:chemistry; D004594:Electrophysiology; D004926:Escherichia coli / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D051381:Rats; D017208:Rats, Wistar; D012604:Scorpion Venoms / Q000737:chemistry* / Q000378:metabolism; D012605:Scorpions; D017386:Sequence Homology, Amino Acid; D015222:Sodium Channels / Q000737:chemistry*; D013574:Synaptosomes / Q000378:metabolism
chemical_list: C498553:Css4 protein, Centruroides suffusus suffusus; D012604:Scorpion Venoms; D015222:Sodium Channels; D004247:DNA