It is commonly assumed that the voltage dependence for activation of voltage-gated channels is an intrinsic characteristic of the protein that remains unchanged during electrical activity. However, sporadic reports have suggested otherwise by showing that voltage dependence changes in a use-dependent manner resulting in a voltage dependence shift towards negative potentials (Bezanilla et al., 1982; Bruening-Wright and Larsson, 2007; Kuzmenkin et al., 2004; Labro et al., 2012; Larsson and Elinder, 2000; Olcese et al., 1997; Piper et al., 2003; Shirokov et al., 1992). Although the mechanism underlying the shift in voltage dependence remains unclear, this process seems to have two components. The first stage has been proposed to be related to the stabilization of the open conformation of the pore domain (Labro et al., 2012). The second stage seems to involve the stabilization of the activated state of the voltage sensing domain (VSD) (Labro et al., 2012; Lacroix et al., 2011) through a process known as VSD relaxation (Villalba-Galea, 2012; Villalba-Galea et al., 2008). This latter process has been proposed to be an intrinsic property of the VSD in which the domain is stabilized in an active-like state referred to as the relaxed state. Yet, the underlying mechanism remains unknown. This project expands upon the hypothesis that the movement of the fourth transmembrane (S4) segment of the VSD can induce conformational changes using the loop connecting the third and fourth transmembrane segments (S3-S4 loop) to couple VSD activation to VSD relaxation. Using the Drosophila potassium-selective, voltage-gated channel Shaker as a model, I show here that mutations in the S3-S4 loop of the VSD modulate the time constant of deactivation of the conductance and cause an apparent partial immobilization of the sensing charges of the VSD. These results hint, for the first time, at a mechanism for VSD relaxation. Particularly, these results indicate that the S3-S4 loop is intimately involved in the mechanism of coupling VSD activation to VSD relaxation.
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机译：通常认为激活电压门控通道的电压依赖性是蛋白质的固有特性，在电活动过程中保持不变。然而，零星的报告通过表明电压依赖性以使用依赖的方式变化而导致电压依赖性向负电位转变而提出其他建议（Bezanilla等人，1982； Bruening-Wright和Larsson，2007； Kuzmenkin等人，2004）。 ； Labro等人，2012； Larsson和Elinder，2000； Olcese等人，1997； Piper等人，2003； Shirokov等人，1992）。尽管电压依赖性变化的机理尚不清楚，但该过程似乎有两个组成部分。已经提出第一阶段与孔结构域的开放构象的稳定有关（Labro et al。，2012）。第二阶段似乎涉及通过称为VSD弛豫的过程（Villalba-Galea，2012; Villalba）稳定电压感测域（VSD）的激活状态（Labro等，2012; Lacroix等，2011）。 -Galea et al。，2008）。已提出后一种过程是VSD的固有属性，在该属性中，域稳定在称为松弛状态的类似主动的状态中。然而，其潜在机制仍然未知。该项目扩展了以下假设：使用连接第三和第四跨膜片段的环（S3-S4环）将VSD激活与VSD松弛耦合，VSD的第四跨膜（S4）片段的运动可以诱导构象变化。使用果蝇钾选择性，电压门控通道振荡器作为模型，我在这里显示VSD的S3-S4回路中的突变可调节电导失活的时间常数，并导致表观感应电荷的固定化。 VSD。这些结果首次暗示了VSD松弛的机制。特别地，这些结果表明，S3-S4环与VSD活化与VSD弛豫的偶联机制密切相关。
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