Activation-coupled inactivation in the bacterial potassium channel KcsA
Activation-coupled inactivation in the bacterial potassium channel KcsA
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DOI：
10.1073/pnas.0505158102
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发表时间：
2005-12-06
影响因子：
11.1
通讯作者：
Fan, Z
中科院分区：
文献类型：
--
作者：
Gao, LZ;Mi, XQ;Fan, Z
细菌K+通道KcsA的X射线结构使我们对离子通道结构的理解取得了前所未有的进展。因此，KcsA通道是用于研究离子通道功能的结构基础（包括门控机制）的原型模型。以前发现该通道在近中性细胞内pH（pHi）下关闭，在酸性pHi下打开。在这里，我们报告了一个以前未知的通道失活过程中发生的KcsA通道被激活后的存在。在我们的实验中，用编码KcsA蛋白的密码子优化的合成基因转染的哺乳动物细胞表达K+选择性通道，其响应于pHi的降低而激活。利用膜片钳和快速溶液交换技术，我们观察到KcsA通道在通道激活后数百毫秒内失活。在所有测试的pH值下，失活总是伴随着活化，并且在活化急剧增加的相同pH值范围内大大加速。观察到从失活中恢复，其程度取决于pHi和通道失活的时间量。KcsA通道失活可以通过动力学模型来描述，其中pHi通过pH依赖性激活来控制失活。这种迄今为止没有记载的失活过程增加了KcsA通道功能的复杂性，但它也提供了一个潜在的模型，用于研究离子通道失活的结构对应。
X-ray structures of the bacterial K+ channel KcsA have led to unparalleled progress in our understanding of ion channel structures. The KcsA channel has therefore been a prototypic model used to study the structural basis of ion channel function, including the gating mechanism. This channel was previously found to close at near-neutral intracellular pH (pHi) and to open at acidic pHi. Here, we report the presence of a previously unknown channel inactivation process that occurs after the KcsA channel is activated. In our experiments, mammalian cells transfected with a codon-optimized synthetic gene encoding the KcsA protein expressed K+-selective channels that activated in response to a decrease in pHi. Using patch-clamp and rapid solution exchange techniques, we observed that the KcsA channels inactivated within hundreds of milliseconds after channel activation. At all tested pHs, inactivation always accompanied activation, and it was profoundly accelerated in the same pH range at which activation increased steeply. Recovery from inactivation was observed, and its extent depended on the pHi and the amount of time that the channel was inactive. KcsA channel inactivation can be described by a kinetic model in which pHi controls inactivation through pH-dependent activation. This heretofore-undocumented inactivation process increases the complexity of KcsA channel function, but it also offers a potential model for studying the structural correspondence of ion channel inactivation.