Slow conformational changes of the voltage sensor during the mode shift in hyperpolarization-activated cyclic-nucleotide-gated channels
Slow conformational changes of the voltage sensor during the mode shift in hyperpolarization-activated cyclic-nucleotide-gated channels
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DOI：
10.1523/jneurosci.3801-06.2007
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发表时间：
2007-01-10
影响因子：
5.3
通讯作者：
Larsson, H. Peter
中科院分区：
文献类型：
--
作者：
Bruening-Wright, Andrew;Larsson, H. Peter
超极化激活的环核苷酸门控（HCN）通道被超极化激活，导致第四跨膜结构域（S4）的正电荷向内移动，从而触发通道打开。如果HCN通道长时间保持开放（> 50 ms）， HCN通道会发生模式移位，在海胆（spHCN）通道中，激活中点会产生> 50 mV的移位。模式转换的机制尚不清楚。模式移位可能是由于孔隙域的构象变化稳定了通道的开放状态，从而间接改变了通道的电压依赖性，或者是由于电压感应域的构象变化稳定了S4的向内位置，从而直接改变了通道的电压依赖性。我们使用电压钳荧光法检测S4运动，并将S4运动与spHCN通道的不同激活步骤相关联。我们在这里表明，附在S4上的荧光团在模式转换过程中报告了荧光变化，这表明模式转换不仅仅是由于孔域的稳定，而是S4在模式转换过程中发生了构象变化。我们提出了一个模型，其中模式转换归因于S4的缓慢横向运动，该运动是由最初的S4门控电荷运动和通道打开触发的。这种模式转换在HCN通道中产生了一种短期的、活动依赖的记忆，这对于起搏神经元的稳定节律放电很重要，并可能显著影响突触整合。
Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels are activated by hyperpolarizations that cause inward movements of the positive charges in the fourth transmembrane domain (S4), which triggers channel opening. If HCN channels are held open for prolonged times (> 50 ms), HCN channels undergo a mode shift, which in sea urchin (spHCN) channels induces a > 50 mV shift in the midpoint of activation. The mechanism underlying the mode shift is unknown. The mode shift could be attributable to conformational changes in the pore domain that stabilize the open state of the channel, which would indirectly shift the voltage dependence of the channel, or attributable to conformational changes in the voltage-sensing domain that stabilize the inward position of S4, thereby directly shifting the voltage dependence of the channel. We used voltage-clamp fluorometry to detect S4 movements and to correlate S4 movements to the different activation steps in spHCN channels. We here show that fluorophores attached to S4 report on fluorescence changes during the mode shift, demonstrating that the mode shift is not simply attributable to a stabilization of the pore domain but that S4 undergoes conformational changes during the mode shift. We propose a model in which the mode shift is attributable to a slow, lateral movement in S4 that is triggered by the initial S4 gating-charge movement and channel opening. The mode shift gives rise to a short-term, activity-dependent memory in HCN channels, which has been shown previously to be important for the stable rhythmic firing of pacemaking neurons and could significantly affect synaptic integration.