Oiki Shigetoshi
Department of Molecular Physiology and Biophysics, Faculty of Medical Sciences, University of Fukui, Fukui, 910-1193, Japan.
J Physiol. 2015 Jun 15;593(12):2553-73. doi: 10.1113/JP270025. Epub 2015 May 14.
The most essential properties of ion channels for their physiologically relevant functions are ion-selective permeation and gating. Among the channel species, the potassium channel is primordial and the most ubiquitous in the biological world, and knowledge of this channel underlies the understanding of features of other ion channels. The strategy applied to studying channels changed dramatically after the crystal structure of the potassium channel was resolved. Given the abundant structural information available, we exploited the bacterial KcsA potassium channel as a simple model channel. In the postcrystal age, there are two effective frameworks with which to decipher the functional codes present in the channel structure, namely reconstitution and re-animation. Complex channel proteins are decomposed into essential functional components, and well-examined parts are rebuilt for integrating channel function in the membrane (reconstitution). Permeation and gating are dynamic operations, and one imagines the active channel by breathing life into the 'frozen' crystal (re-animation). Capturing the motion of channels at the single-molecule level is necessary to characterize the behaviour of functioning channels. Advanced techniques, including diffracted X-ray tracking, lipid bilayer methods and high-speed atomic force microscopy, have been used. Here, I present dynamic pictures of the KcsA potassium channel from the submolecular conformational changes to the supramolecular collective behaviour of channels in the membrane. These results form an integrated picture of the active channel and offer insights into the processes underlying the physiological function of the channel in the cell membrane.
离子通道对于其生理相关功能而言，最基本的特性是离子选择性通透和门控。在各类通道中，钾通道是最原始且在生物界分布最广泛的，对该通道的了解是理解其他离子通道特性的基础。在钾通道晶体结构解析之后，用于研究通道的策略发生了巨大变化。鉴于有丰富的结构信息可用，我们利用细菌KcsA钾通道作为一个简单的模型通道。在晶体结构解析时代之后，有两个有效的框架可用于解读通道结构中存在的功能密码，即重组和复活。复杂的通道蛋白被分解为基本的功能组件，经过充分研究的部分被重新构建以整合通道在膜中的功能（重组）。通透和门控是动态操作，人们通过赋予“冻结”的晶体以活力来想象活性通道（复活）。在单分子水平上捕捉通道的运动对于表征功能通道的行为是必要的。已经使用了包括衍射X射线追踪、脂质双层方法和高速原子力显微镜在内的先进技术。在这里，我展示了KcsA钾通道从亚分子构象变化到膜中通道超分子集体行为的动态图像。这些结果形成了活性通道的完整图像，并为细胞膜中通道生理功能背后的过程提供了见解。
