The HCN channel voltage sensor undergoes a large downward motion during hyperpolarization
The HCN channel voltage sensor undergoes a large downward motion during hyperpolarization
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DOI：
10.1038/s41594-019-0259-1
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发表时间：
2019-08-01
影响因子：
16.8
通讯作者：
Zagotta, William N.
中科院分区：
文献类型：
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作者：
Dai, Gucan;Aman, Teresa K.;Zagotta, William N.
电压门控离子通道 (VGIC) 在电压传感域 (VSD) 的 S4 螺旋内含有带正电的残基，这些残基会响应跨膜电压的变化而发生位移，从而促进打开孔的构象变化。起搏器超极化激活的环核苷酸门控 (HCN) 通道在 VGIC 中是独特的，因为膜超极化而不是去极化会增加其开放概率。在这里，我们使用过渡金属离子荧光共振能量转移 (tmFRET) 测量了海胆 HCN 通道 S4 螺旋的精确运动。我们表明，S4 响应膜超极化而经历大幅（类似于 10 埃）向下运动。此外，通过将 tmFRET 实验确定的距离约束应用于 Rosetta 建模，我们发现 S4 螺旋的羧基末端部分在超极化激活过程中表现出意想不到的倾斜运动。这些数据提供了人们长期以来对功能性 VSD 超极化状态的一瞥，同时也为理解 HCN 通道中反向门控的动态提供了框架。
Voltage-gated ion channels (VGICs) contain positively charged residues within the S4 helix of the voltage-sensing domain (VSD) that are displaced in response to changes in transmembrane voltage, promoting conformational changes that open the pore. Pacemaker hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are unique among VGICs because their open probability is increased by membrane hyperpolarization rather than depolarization. Here we measured the precise movement of the S4 helix of a sea urchin HCN channel using transition metal ion fluorescence resonance energy transfer (tmFRET). We show that the S4 undergoes a substantial (similar to 10 angstrom) downward movement in response to membrane hyperpolarization. Furthermore, by applying distance constraints determined from tmFRET experiments to Rosetta modeling, we reveal that the carboxy-terminal part of the S4 helix exhibits an unexpected tilting motion during hyperpolarization activation. These data provide a long-sought glimpse of the hyperpolarized state of a functioning VSD and also a framework for understanding the dynamics of reverse gating in HCN channels.