Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, USA.
Nature. 2020 Jul;583(7814):145-149. doi: 10.1038/s41586-020-2335-4. Epub 2020 May 27.
Voltage-gated potassium (K) channels coordinate electrical signalling and control cell volume by gating in response to membrane depolarization or hyperpolarization. However, although voltage-sensing domains transduce transmembrane electric field changes by a common mechanism involving the outward or inward translocation of gating charges, the general determinants of channel gating polarity remain poorly understood. Here we suggest a molecular mechanism for electromechanical coupling and gating polarity in non-domain-swapped K channels on the basis of the cryo-electron microscopy structure of KAT1, the hyperpolarization-activated K channel from Arabidopsis thaliana. KAT1 displays a depolarized voltage sensor, which interacts with a closed pore domain directly via two interfaces and indirectly via an intercalated phospholipid. Functional evaluation of KAT1 structure-guided mutants at the sensor-pore interfaces suggests a mechanism in which direct interaction between the sensor and the C-linker hairpin in the adjacent pore subunit is the primary determinant of gating polarity. We suggest that an inward motion of the S4 sensor helix of approximately 5-7 Å can underlie a direct-coupling mechanism, driving a conformational reorientation of the C-linker and ultimately opening the activation gate formed by the S6 intracellular bundle. This direct-coupling mechanism contrasts with allosteric mechanisms proposed for hyperpolarization-activated cyclic nucleotide-gated channels, and may represent an unexpected link between depolarization- and hyperpolarization-activated channels.
电压门控钾 (K) 通道通过响应膜去极化或超极化来门控，从而协调电信号和控制细胞体积。然而，尽管电压传感域通过涉及门控电荷外向或内向移位的共同机制来转导跨膜电场变化，但通道门控极性的一般决定因素仍知之甚少。在这里，我们基于拟南芥超极化激活 K 通道 KAT1 的冷冻电子显微镜结构，提出了非域交换 K 通道机电耦合和门控极性的分子机制。KAT1 显示出去极化的电压传感器，该传感器通过两个界面直接与关闭的孔域相互作用，并通过插入的磷脂间接相互作用。在传感器 - 孔界面上对 KAT1 结构导向突变体的功能评估表明，一种机制是传感器与相邻孔亚基中的 C 链接发夹之间的直接相互作用是门控极性的主要决定因素。我们认为，S4 传感器螺旋向内移动约 5-7 Å 可以为直接耦合机制提供基础，驱动 C 链接的构象重排，并最终打开由 S6 细胞内束形成的激活门。这种直接耦合机制与超极化激活环核苷酸门控通道提出的变构机制形成对比，并且可能代表去极化和超极化激活通道之间的意外联系。
