Estimating the voltage-dependent free energy change of ion channels using the median voltage for activation.
Estimating the voltage-dependent free energy change of ion channels using the median voltage for activation.
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DOI：
10.1085/jgp.201110722
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发表时间：
2012-01
期刊：
影响因子：
--
通讯作者：
Chanda B
中科院分区：
文献类型：
--
作者：
Chowdhury S;Chanda B
电压门控离子通道对于多种细胞类型的电活动和化学信号传导至关重要。涉及突变体电生理学表征的结构-活性研究被广泛使用，使我们能够通过测量宏观电流并将观察到的电导电压依赖性拟合到玻尔兹曼方程来快速实现突变的能量效应。然而，这种方法有一定的局限性，主要是因为通道激活是两种状态过程的固有假设。在此分析中，我们表明门控电荷位移曲线及其纵轴所描绘的面积与电压门控离子通道的激活自由能有关。我们推导出一个参数，电荷转移的中值电压（Vm），它与该面积成正比，并证明系统自由能变化的化学成分可以从Vm和最大转移电荷数的知识中获得。我们的方法不受中间状态的数量或连通性的限制，并且适用于观察到的响应显示多相行为的情况。我们考虑了具有电压依赖性步骤、潜电荷移动、失活等的离子通道门控的各种模型，并讨论了这种方法在每种情况下的适用性。值得注意的是，我们的方法估计与 Shaker 钾通道的全面激活相关的约 -14 kcal/mol 的净自由能变化，与从单个玻尔兹曼拟合估计的 -2 至 -3 kcal/mol 相比。我们对系统中净自由能变化的估计与从详细动力学模型得出的估计一致（Zagotta et al. 1994. J. Gen. Physiol. doi:10.1085/jgp.103.2.321）。中值电压方法可以通过宏观平衡测量可靠地量化与电压相关系统的激活相关的自由能变化的幅度。这在扫描诱变实验中特别有用。
Voltage-gated ion channels are crucial for electrical activity and chemical signaling in a variety of cell types. Structure-activity studies involving electrophysiological characterization of mutants are widely used and allow us to quickly realize the energetic effects of a mutation by measuring macroscopic currents and fitting the observed voltage dependence of conductance to a Boltzmann equation. However, such an approach is somewhat limiting, principally because of the inherent assumption that the channel activation is a two-state process. In this analysis, we show that the area delineated by the gating charge displacement curve and its ordinate axis is related to the free energy of activation of a voltage-gated ion channel. We derive a parameter, the median voltage of charge transfer (Vm), which is proportional to this area, and prove that the chemical component of free energy change of a system can be obtained from the knowledge of Vm and the maximum number of charges transferred. Our method is not constrained by the number or connectivity of intermediate states and is applicable to instances in which the observed responses show a multiphasic behavior. We consider various models of ion channel gating with voltage-dependent steps, latent charge movement, inactivation, etc. and discuss the applicability of this approach in each case. Notably, our method estimates a net free energy change of approximately −14 kcal/mol associated with the full-scale activation of the Shaker potassium channel, in contrast to −2 to −3 kcal/mol estimated from a single Boltzmann fit. Our estimate of the net free energy change in the system is consistent with those derived from detailed kinetic models (Zagotta et al. 1994. J. Gen. Physiol. doi:10.1085/jgp.103.2.321). The median voltage method can reliably quantify the magnitude of free energy change associated with activation of a voltage-dependent system from macroscopic equilibrium measurements. This will be particularly useful in scanning mutagenesis experiments.
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影响因子：
3.8
作者：
Ledwell, JL;Aldrich, RW
通讯作者：
Aldrich, RW
影响因子：
16.2
作者：
Aggarwal, SK;MacKinnon, R
通讯作者：
MacKinnon, R
DOI：
10.1073/pnas.0806486105
发表时间：
2008-09-30
影响因子：
11.1
作者：
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通讯作者：
Catterall, William A.
DOI：
10.1085/jgp.113.3.415
发表时间：
1999-03
期刊：
The Journal of general physiology
影响因子：
--
作者：
Monks SA;Needleman DJ;Miller C
通讯作者：
Miller C
DOI：
10.1073/pnas.1103397108
发表时间：
2011-04-19
影响因子：
11.1
作者：
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通讯作者：
Bezanilla, Francisco