Contreras Gustavo F, Shen Rong, Latorre Ramon, Perozo Eduardo
Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA.
Centro Interdisciplinario de Neurociencia, Instituto de Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
Nat Commun. 2025 Jul 1;16(1):5846. doi: 10.1038/s41467-025-60639-y.
The allosteric communication between the pore domain, voltage sensors, and Ca binding sites in the calcium- and voltage-activated K channel (BK) underlies its physiological role as the preeminent signal integrator in excitable systems. BK displays shallow voltage sensitivity with very fast gating charge kinetics, yet little is known about the molecular underpinnings of this distinctive behavior. Here, we explore the mechanistic basis of coupling between voltage-sensing domains (VSDs) and calcium sensors in Aplysia BK by locking the VSDs in their activated (R196Q and R199Q) and resting (R202Q) states, with or without calcium. Cryo-EM structures of these mutants reveal unique tilts at the S4 C-terminal end, together with large side-chain rotameric excursions of the gating charges. Notably, the VSD resting structure (R202Q) also revealed BK in its elusive, fully closed state, highlighting the reciprocal relation between calcium and voltage sensors. These structures provide a plausible path where voltage and Ca binding couple energetically and define the conformation of the pore domain and, thus, BK's full functional range.
钙激活钾通道（BK）的孔道结构域、电压感受器和钙结合位点之间的变构通讯，构成了其作为可兴奋系统中卓越信号整合器的生理作用基础。BK表现出较弱的电压敏感性和非常快速的门控电荷动力学，但对于这种独特行为的分子基础知之甚少。在这里，我们通过将电压感受器结构域（VSDs）锁定在激活状态（R196Q和R199Q）和静息状态（R202Q），研究了海兔BK中电压感受器结构域与钙感受器之间耦合的机制基础，同时存在或不存在钙离子。这些突变体的冷冻电镜结构揭示了S4 C末端独特的倾斜，以及门控电荷的大侧链旋转异构体偏移。值得注意的是，VSD静息结构（R202Q）还揭示了BK处于难以捉摸的完全关闭状态，突出了钙感受器和电压感受器之间的相互关系。这些结构提供了一条合理的途径，其中电压和钙结合在能量上耦合，并定义了孔道结构域的构象，从而确定了BK的完整功能范围。
