Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, New York, NY 10065.
HHMI, The Rockefeller University, New York, NY 10065.
Proc Natl Acad Sci U S A. 2023 May 23;120(21):e2301985120. doi: 10.1073/pnas.2301985120. Epub 2023 May 16.
Voltage-dependent ion channels underlie the propagation of action potentials and other forms of electrical activity in cells. In these proteins, voltage sensor domains (VSDs) regulate opening and closing of the pore through the displacement of their positive-charged S4 helix in response to the membrane voltage. The movement of S4 at hyperpolarizing membrane voltages in some channels is thought to directly clamp the pore shut through the S4-S5 linker helix. The KCNQ1 channel (also known as K7.1), which is important for heart rhythm, is regulated not only by membrane voltage but also by the signaling lipid phosphatidylinositol 4,5-bisphosphate (PIP). KCNQ1 requires PIP to open and to couple the movement of S4 in the VSD to the pore. To understand the mechanism of this voltage regulation, we use cryogenic electron microscopy to visualize the movement of S4 in the human KCNQ1 channel in lipid membrane vesicles with a voltage difference across the membrane, i.e., an applied electric field in the membrane. Hyperpolarizing voltages displace S4 in such a manner as to sterically occlude the PIP-binding site. Thus, in KCNQ1, the voltage sensor acts primarily as a regulator of PIP binding. The voltage sensors' influence on the channel's gate is indirect through the reaction sequence: voltage sensor movement → alter PIP ligand affinity → alter pore opening.
电压门控离子通道是细胞动作电位和其他形式电活动传播的基础。在这些蛋白质中，电压传感器结构域（VSD）通过其带正电荷的 S4 螺旋在响应膜电压时的位移来调节孔的开启和关闭。在一些通道中，超极化膜电压下 S4 的运动被认为通过 S4-S5 连接螺旋直接将孔钳制关闭。KCNQ1 通道（也称为 K7.1）对心律很重要，它不仅受膜电压调节，还受信号脂质磷脂酰肌醇 4,5-二磷酸（PIP）调节。KCNQ1 需要 PIP 才能打开并将 VSD 中 S4 的运动与孔耦合。为了理解这种电压调节的机制，我们使用低温电子显微镜在具有跨膜电压差的脂质膜泡中可视化人 KCNQ1 通道中 S4 的运动，即在膜中施加电场。超极化电压以空间位阻方式使 S4 移位，从而阻碍 PIP 结合位点。因此，在 KCNQ1 中，电压传感器主要作为 PIP 结合的调节剂。电压传感器对通道门的影响是间接的，通过反应序列：电压传感器运动→改变 PIP 配体亲和力→改变孔开口。
