Ion channels of the cyclic nucleotide-binding domain (CNBD) family play a crucial role in the regulation of key biological processes, such as photoreception and pacemaking activity in the heart. These channels exhibit high sequence and structural similarity but differ greatly in their functional responses to membrane potential. The CNBD family includes hyperpolarization-activated ion channels and depolarization-activated ether-à-go-go channels. Structural and functional studies show that the differences in the coupling interface between these two subfamilies' voltage-sensing domain and pore domain may underlie their differential response to membrane polarity. However, other structural components may also contribute to defining the polarity differences in activation. Here, we focus on the role of the C-terminal domain, which interacts with elements in both the pore and voltage-sensing domains. By generating a series of chimeras involving the C-terminal domain derived from distant members of the CNBD family, we find that the nature of the C-termini profoundly influences the gating polarity of these ion channels. Scanning mutagenesis of the C-linker region, a helix-turn-helix motif connecting the pore helix to the CNBD, reveals that residues at the intersubunit interface between the C-linkers are crucial for hyperpolarization-dependent activation. These findings highlight the unique and unexpected role of the intersubunit interface of the C-linker region in regulating the gating polarity of voltage-gated ion channels.

中文翻译：

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映射 C-linker 结构域对 CNBD 通道中门控极性的贡献

环核苷酸结合域 (CNBD) 家族的离子通道在关键生物过程的调节中发挥着至关重要的作用，例如心脏的光感受和起搏活动。这些通道表现出高度的序列和结构相似性，但它们对膜电位的功能反应差异很大。 CNBD 系列包括超极化激活的离子通道和去极化激活的 ether-à-go-go 通道。结构和功能研究表明，这两个亚家族的电压传感域和孔域之间耦合界面的差异可能是它们对膜极性的不同响应的基础。然而，其他结构成分也可能有助于定义激活的极性差异。在这里，我们重点关注 C 端结构域的作用，它与孔和电压传感结构域中的元​​素相互作用。通过生成一系列涉及源自 CNBD 家族远亲成员的 C 端结构域的嵌合体，我们发现 C 端的性质深刻影响这些离子通道的门控极性。 C 接头区域（连接孔螺旋与 CNBD 的螺旋-转角-螺旋基序）的扫描诱变揭示了 C 接头之间亚基间界面上的残基对于超极化依赖性激活至关重要。这些发现强调了 C 连接子区域的亚基间界面在调节电压门控离子通道的门控极性方面的独特且意想不到的作用。