PDF(Pubmed)
Abstract：
Agonist binding in ligand-gated ion channels is coupled to structural rearrangements around the binding site, followed by the opening of the channel pore. In this process, agonist efficacy describes the equilibrium between open and closed conformations in a fully ligand-bound state. Calcium-activated chloride channels in the TMEM16 family are important sensors of intracellular calcium signals and are targets for pharmacological modulators, yet a mechanistic understanding of agonist efficacy has remained elusive. Using a combination of cryo-electron microscopy, electrophysiology, and autocorrelation analysis, we now show that agonist efficacy in the ligand-gated channel TMEM16A is dictated by the conformation of the pore-lining helix α6 around the Ca2+ -binding site. The closure of the binding site, which involves the formation of a π-helix below a hinge region in α6, appears to be coupled to the opening of the inner pore gate, thereby governing the channel\'s open probability and conductance. Our results provide a mechanism for agonist binding and efficacy and a structural basis for the design of potentiators and partial agonists in the TMEM16 family.
摘要：
配体门控离子通道中的激动剂结合与结合位点周围的结构重排偶联，然后是通道孔的开口。在这个过程中,激动剂功效描述了处于完全配体结合状态的开放和封闭构象之间的平衡。TMEM16家族中钙激活的氯离子通道是细胞内钙信号的重要传感器，是药理学调节剂的靶标，然而，对激动剂疗效的机械理解仍然难以捉摸。使用低温电子显微镜的组合，电生理学,和自相关分析，我们现在表明，配体门控通道TMEM16A中的激动剂功效由Ca2结合位点周围的孔衬螺旋α6的构象决定。结合位点的闭合，涉及在α6铰链区下方形成π螺旋，似乎与内部孔门的开口耦合，从而控制通道的开放概率和电导。我们的结果为TMEM16家族中的增强剂和部分激动剂的设计提供了激动剂结合和功效的机制和结构基础。
