Department of Pharmacology, School of Medicine, University of Washington, Seattle, WA 98195-7280, USA.
Proc Natl Acad Sci U S A. 2011 Sep 13;108(37):15426-31. doi: 10.1073/pnas.1112320108. Epub 2011 Aug 29.
The α-scorpions toxins bind to the resting state of Na(+) channels and inhibit fast inactivation by interaction with a receptor site formed by domains I and IV. Mutants T1560A, F1610A, and E1613A in domain IV had lower affinities for Leiurus quinquestriatus hebraeus toxin II (LqhII), and mutant E1613R had ~73-fold lower affinity. Toxin dissociation was accelerated by depolarization and increased by these mutations, whereas association rates at negative membrane potentials were not changed. These results indicate that Thr1560 in the S1-S2 loop, Phe1610 in the S3 segment, and Glu1613 in the S3-S4 loop in domain IV participate in toxin binding. T393A in the SS2-S6 loop in domain I also had lower affinity for LqhII, indicating that this extracellular loop may form a secondary component of the receptor site. Analysis with the Rosetta-Membrane algorithm resulted in a model of LqhII binding to the voltage sensor in a resting state, in which amino acid residues in an extracellular cleft formed by the S1-S2 and S3-S4 loops in domain IV interact with two faces of the wedge-shaped LqhII molecule. The conserved gating charges in the S4 segment are in an inward position and form ion pairs with negatively charged amino acid residues in the S2 and S3 segments of the voltage sensor. This model defines the structure of the resting state of a voltage sensor of Na(+) channels and reveals its mode of interaction with a gating modifier toxin.
α-蝎毒素与钠离子通道的静息状态结合，并通过与由 I 域和 IV 域形成的受体位点相互作用来抑制快速失活。IV 域中的突变体 T1560A、F1610A 和 E1613A 对 Leiurus quinquestriatus hebraeus 毒素 II (LqhII) 的亲和力较低，而突变体 E1613R 的亲和力降低了约 73 倍。去极化加速了毒素的解离，并增加了这些突变体的亲和力，而在负膜电位下的结合速率没有变化。这些结果表明，S1-S2 环中的 Thr1560、S3 段中的 Phe1610 和 S3-S4 环中的 Glu1613 在 IV 域中参与毒素结合。I 域中的 SS2-S6 环中的 T393A 对 LqhII 的亲和力也较低，表明该细胞外环可能形成受体位点的次要组成部分。使用 Rosetta-Membrane 算法进行分析，得到了 LqhII 与静息状态下电压传感器结合的模型，其中 IV 域中 S1-S2 和 S3-S4 环形成的细胞外环中的氨基酸残基与楔形 LqhII 分子的两个面相互作用。S4 段中的保守门控电荷处于内向位置，并与电压传感器的 S2 和 S3 段中的带负电荷的氨基酸残基形成离子对。该模型定义了钠离子通道电压传感器的静息状态结构，并揭示了其与门控修饰毒素相互作用的模式。
