title: Substitutions in the domain III voltage-sensing module enhance the sensitivity of an insect sodium channel to a scorpion beta-toxin.
abstract: Scorpion β-toxins bind to the extracellular regions of the voltage-sensing module of domain II and to the pore module of domain III in voltage-gated sodium channels and enhance channel activation by trapping and stabilizing the voltage sensor of domain II in its activated state. We investigated the interaction of a highly potent insect-selective scorpion depressant β-toxin, Lqh-dprIT(3), from Leiurus quinquestriatus hebraeus with insect sodium channels from Blattella germanica (BgNa(v)). Like other scorpion β-toxins, Lqh-dprIT(3) shifts the voltage dependence of activation of BgNa(v) channels expressed in Xenopus oocytes to more negative membrane potentials but only after strong depolarizing prepulses. Notably, among 10 BgNa(v) splice variants tested for their sensitivity to the toxin, only BgNa(v)1-1 was hypersensitive due to an L1285P substitution in IIIS1 resulting from a U-to-C RNA-editing event. Furthermore, charge reversal of a negatively charged residue (E1290K) at the extracellular end of IIIS1 and the two innermost positively charged residues (R4E and R5E) in IIIS4 also increased the channel sensitivity to Lqh-dprIT(3). Besides enhancement of toxin sensitivity, the R4E substitution caused an additional 20-mV negative shift in the voltage dependence of activation of toxin-modified channels, inducing a unique toxin-modified state. Our findings provide the first direct evidence for the involvement of the domain III voltage-sensing module in the action of scorpion β-toxins. This hypersensitivity most likely reflects an increase in IIS4 trapping via allosteric mechanisms, suggesting coupling between the voltage sensors in neighboring domains during channel activation.
authors: Department of Entomology, Michigan State University, East Lansing, Michigan 48824, USA.
authors: Weizhong
authors: W
authors: Song
authors: Yuzhe
authors: Y
authors: Du
authors: Zhiqi
authors: Z
authors: Liu
authors: Ningguang
authors: N
authors: Luo
authors: Michael
authors: M
authors: Turkov
authors: Dalia
authors: D
authors: Gordon
authors: Michael
authors: M
authors: Gurevitz
authors: Alan L
authors: AL
authors: Goldin
authors: Ke
authors: K
authors: Dong
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects / Q000502:physiology; D017398:Alternative Splicing / Q000502:physiology; D019943:Amino Acid Substitution; D000818:Animals; D020048:Blattellidae / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects*; D020125:Mutation, Missense; D017434:Protein Structure, Tertiary; D012604:Scorpion Venoms / Q000737:chemistry / Q000494:pharmacology*; D012605:Scorpions / Q000737:chemistry; D015222:Sodium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus
chemical_list: D019476:Insect Proteins; D012604:Scorpion Venoms; D015222:Sodium Channels