Conformational rearrangements underlying ASIC1a gating

描述（由申请人提供）：上皮钠通道/变性素（ENaC/Deg）离子通道家族由涉及机械感觉、疼痛感觉、细胞外液容量调节和气道表面液体体积的蛋白质组成。ENaC/Deg通道受到多种刺激的门控，包括神经肽、机械力、细胞外质子，其中一些是组成活性的，如ENaC。这些通道可能组织为同源或异源三聚体，由具有相似拓扑结构的亚基组成，两个跨膜结构域（TMs）由一个具有短细胞内N-和C-末端的大细胞外结构域连接。最近报道了ENaC/Deg通道的细胞外和跨膜结构域的第一个高分辨率结构，鸡酸感离子通道1 （cASIC1）。asic是一种质子门控通道，在哺乳动物中枢和周围神经系统的神经元中表达，处于静止、功能失活状态，但在细胞外酸化后会经历快速激活和脱敏。cASIC1具有杯状形状，从膜平面突出一个大的细胞外结构域。细胞外区域被组织为离散的子域，称为“手掌，指关节，2-球，手指和拇指”。TMs和细胞外结构域之间的过渡构成了手腕。虽然晶体结构提供了cASIC1在脱敏状态下的大量分子细节，但asic和其他ENaC/Deg通道的门控机制仍未明确。本提案的第一个具体目标将定义与激活和脱敏相关的小鼠ASIC1a手腕和毛孔中的构象重排。在第二个具体目标中，我们将解决有关拇指和手掌子域在激活，脱敏和脱敏恢复中的作用的问题。在细胞外酸化后通道受限区域发生的构象变化将通过电压箝位荧光法进行研究，该技术可提供与特定门控步骤相关的局部蛋白质运动信息。取代半胱氨酸可及性方法将用于表征封闭和脱敏状态下特定区域的结构。本应用中提出的研究解决了关于小鼠ASIC1a的门控和脱敏的潜在机制的基本问题。本研究结果对理解Deg/ENaC通道调控的分子机制具有重要意义。

DESCRIPTION (provided by applicant): The epithelial sodium channel/degenerin (ENaC/Deg) family of ion channels is constituted of proteins that are implicated in mechanosensation, pain sensation, regulation of extracellular fluid volume and airway surface liquid volume. ENaC/Deg channels are gated by diverse stimuli including neuropeptides, mechanical forces, extracellular protons, and some of them are constitutively active, such as ENaCs. These channels are likely organized as homo- or hetero- trimers and are composed of subunits that have a similar topology with two transmembrane domains (TMs) connected by a large extracellular domain with short intracellular N- and C- termini. The first high resolution structure of the extracellular and membrane-spanning domains of an ENaC/Deg channel, Gallus gallus (chicken) acid-sensing ion channel 1 (cASIC1), was recently reported. ASICs are proton-gated channels expressed throughout neurons of mammalian central and peripheral nervous systems that exist in a resting, functionally inactive state, but undergo a rapid activation and desensitization following extracellular acidification. cASIC1 has a chalice-like shape with a large extracellular domain protruding from the plane of the membrane. The extracellular region is organized in discrete subdomains named the "palm, knuckle, 2-ball, finger and thumb". The transition between the TMs and extracellular domain constitute the wrist. While the crystal structure provides great molecular details of cASIC1 in the desensitized state, the mechanism of gating of ASICs and other ENaC/Deg channels remains largely undefined. The first specific aim of this proposal will define conformational rearrangements in the wrist and pore of mouse ASIC1a associated with activation and desensitization. In the second specific aim we will address questions regarding the role of the thumb and palm subdomains in activation, desensitization and recovery from desensitization. Conformational changes that occur in restricted areas of the channel following extracellular acidification will be investigated by voltage clamp fluorometry, a technique that provides information regarding local protein motion associated with specific gating steps. The substituted- cysteine-accessibility method will be used to characterize the structure of specific regions in the closed and desensitized states. Studies proposed in this application address fundamental questions regarding the underlying mechanism of gating and desensitization of mouse ASIC1a. Information derived from this work will be valuable to comprehend the molecular mechanisms of regulation of Deg/ENaC channels.