S4-based voltage sensors have three major conformations
S4-based voltage sensors have three major conformations
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DOI：
10.1073/pnas.0807387105
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发表时间：
2008-11-18
影响因子：
11.1
通讯作者：
Bezanilla, Francisco
中科院分区：
文献类型：
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作者：
Villalba-Galea, Carlos A.;Sandtner, Walter;Bezanilla, Francisco
含有带电S4膜片段的电压传感器显示取决于初始电压的门控电荷对电压（Q-V）曲线。不具有导电孔的电压依赖性磷酸酶（Ci-VSP）显示出相同的现象，并且用去极化的初始电压记录的Q-V至少稳定3RT。本文用电生理和定点荧光技术研究了Ci-VSP在长时间去极化作用下Q-V曲线的显著漂移。荧光显示了两个分量：一个是追踪静止状态和活动状态之间电荷运动的时间过程，另一个是追踪活动状态和更稳定状态之间的过渡的较慢分量，我们称之为松弛状态。温度依赖性示出了一个大的负熵变化时，从活跃的放松状态，几乎是由一个大的负熵变化补偿。对于在静息和活动状态之间移动传感器的脉冲测量的Q-V曲线中点，但不足以演变为松弛状态，显示120度的周期性，表明在组氨酸扫描下测定时S4片段的3（10）二级结构。我们假设S4片段在静息态和活性态之间以3（10）螺旋移动，并且当演变为松弛态时，它转化为α-螺旋，松弛态最有可能是晶体结构中捕获的状态。
Voltage sensors containing the charged S4 membrane segment display a gating charge vs. voltage (Q-V) curve that depends on the initial voltage. The voltage-dependent phosphatase (Ci-VSP), which does not have a conducting pore, shows the same phenomenon and the Q-V recorded with a depolarized initial voltage is more stable by at least 3RT. The leftward shift of the Q-V curve under prolonged depolarization was studied in the Ci-VSP by using electrophysiological and site-directed fluorescence measurements. The fluorescence shows two components: one that traces the time course of the charge movement between the resting and active states and a slower component that traces the transition between the active state and a more stable state we call the relaxed state. Temperature dependence shows a large negative enthalpic change when going from the active to the relaxed state that is almost compensated by a large negative entropic change. The Q-V curve midpoint measured for pulses that move the sensor between the resting and active states, but not long enough to evolve into the relaxed states, show a periodicity of 120 degrees, indicating a 3(10) secondary structure of the S4 segment when determined under histidine scanning. We hypothesize that the S4 segment moves as a 3(10) helix between the resting and active states and that it converts to an a-helix when evolving into the relaxed state, which is most likely to be the state captured in the crystal structures.