A tyrosine substitution in the cavity wall of a K channel induces an inverted inactivation
A tyrosine substitution in the cavity wall of a K channel induces an inverted inactivation
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DOI：
10.1529/biophysj.107.119842
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发表时间：
2008-04-15
影响因子：
3.4
通讯作者：
Elinder, Fredrik
中科院分区：
文献类型：
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作者：
Klement, Gran;Nilsson, Johanna;Elinder, Fredrik
电压门控K通道的离子渗透和门控动力学主要取决于腔壁的氨基酸组成。Shaker K通道中的残基470是异亮氨酸，这使得闭合通道中的腔体积对于水合K+离子来说不够大。在人类心脏Ethera-a-Go-Go相关基因通道中，呈现出缓慢激活和快速失活的特征，相应的残基是酪氨酸。为了探索酪氨酸在Shaker通道中这个位置的作用，我们研究了1470Y。激活变慢，失活变得更快和更复杂。在+60 mV时，通道以两种不同的速率失活(tau(I)=20ms，tau(2)=400ms)。用四乙基铵和高K+浓度进行的实验表明，较慢的组分是P/C型。此外，还引入了一种具有反向电压依赖关系的失活元件。阶跃至-40 mV会停用时间常数为500 ms的通道。负电压阶跃不会导致通道从此停用状态恢复(tau；>>10分钟)，而正电压阶跃会迅速恢复(在+60 mV时，tau=2 ms)。实验结果可以用一个简单的支化动力学模型来解释，该模型从开态开始有两条失活途径。
Ion permeation and gating kinetics of voltage-gated K channels critically depend on the amino-acid composition of the cavity wall. Residue 470 in the Shaker K channel is an isoleucine, making the cavity volume in a closed channel insufficiently large for a hydrated K+ ion. In the cardiac human ether-a-go-go-related gene channel, which exhibits slow activation and fast inactivation, the corresponding residue is tyrosine. To explore the role of a tyrosine at this position in the Shaker channel, we studied 1470Y. The activation became slower, and the inactivation faster and more complex. At +60 mV the channel inactivated with two distinct rates (,tau(i) = 20 MS, tau(2) = 400 ms). Experiments with tetraethylammonium and high K+ concentrations suggest that the slower component was of the P/C-type. In addition, an inactivation component with inverted voltage dependence was introduced. A step to -40 mV inactivates the channel with a time constant of 500 ms. Negative voltage steps do not cause the channel to recover from this inactivated state (tau >> 10 min), whereas positive voltage steps quickly do (tau = 2 ms at +60 mV). The experimental findings can be explained by a simple branched kinetic model with two inactivation pathways from the open state.