深度透视钾离子通道的离子选择、配体门控和阻断机制

Potassium channels are one of the most common cellular machines in biologic life. They control the flow of K+ into and out of the cell and are ubiquitously expressed in nearly all organisms ranging from the simplest bacterium to humans. In humans, they are found in nearly all tissues serving a variety of tasks. Because of their prevalence and importance in the human body, dysfunction of a K+ channel is often to blame for a wide range of human pathologies. Ion selectivity, gating and blockage are three characteristic properties defining an ion channel. Ion selectivity means the passage of specific ions is allowed through the channel pore while others are excluded. Gating is the opening and closing of the channel in response to external stimuli. Channel blockage means inactivation while channel is open. The broad goal of this research is to understand the structure and mechanics of the K+ channel. More specifically, we will focus on studying the three characteristic properties in what has already proven to be an excellent model system, a Ca2+-activated K+ channel called MthK. To study this channel, we will use crystallographic, thermodynamic and elecrophysiological tools to obtain and combine both structural and functional information.

钾离子通道控制钾离子的流入和流出细胞，存在于从细菌到人类的几乎所有的生命体，是生命体最常见的分子机器之一。它们存在于人体几乎所有的组织，并在一系列重要的生理过程中起着关键作用。钾离子通道的功能缺陷导致许多人类疾病。离子通道有三个最重要的基本性质，离子选择性是指它能够选择性地通透钾离子；门控是指它能随外界刺激开放或关闭；阻断是指当通道开放时，相当大的分子可以从细胞内侧进入中央空穴，阻断通道而引起通道失活。本研究以一个钙门控的钾离子通道MthK为模型通道，结合X-射线晶体学、电生理学和热力学分析，针对钾离子通道上述三个和生理过程密切相关的基本性质展开研究，目的是揭示其深度机制。本项研究不仅将帮助我们更好地理解离子通道的传导以及动力学特征，为进一步研究与人类疾病直接相关的离子通道打下基础，而且还能对以离子通道为靶向系统的药物设计提供直接的结构与功能信息，从而使以分子结构为基础的药物设计成为可能。

我们针对配体门控的钾离子通道的两个最重要的科学问题：离子选择性和通道的门控，以钙离子门控的MthK钾离子通道为研究对象，首先，我们结合X-射线晶体学和电生理学两种研究手段，探讨了钡离子和钾离子在MthK钾离子通道离子选择筛内的相互作用，对钾离子对于钡离子从钾通道逃逸存在三个效应：外部锁定效应、增强效应和内部锁定效应提出了一个合理的模型。其次，我们通过大规模的分析多种不同状态的门控环结构，精准的捕捉到了钙离子在八聚体门控 环的结合诱发下游一系列结构变化事件的分子机制，并且结合电生理和 ITC 等功能实验证实这个机制。这是离子通道的第一个原子水平上的协同性结构变化的模型，并且为深入阐释离子通道协同性门控机制提供了坚实基础。