Abstract：
HCN1-4 channels are the molecular determinants of the If/Ih current that crucially regulates cardiac and neuronal cell excitability. HCN dysfunctions lead to sinoatrial block (HCN4), epilepsy (HCN1), and chronic pain (HCN2), widespread medical conditions awaiting subtype-specific treatments. Here, we address the problem by solving the cryo-EM structure of HCN4 in complex with ivabradine, to date the only HCN-specific drug on the market. Our data show ivabradine bound inside the open pore at 3 Å resolution. The structure unambiguously proves that Y507 and I511 on S6 are the molecular determinants of ivabradine binding to the inner cavity, while F510, pointing outside the pore, indirectly contributes to the block by controlling Y507. Cysteine 479, unique to the HCN selectivity filter (SF), accelerates the kinetics of block. Molecular dynamics simulations further reveal that ivabradine blocks the permeating ion inside the SF by electrostatic repulsion, a mechanism previously proposed for quaternary ammonium ions.
摘要：
HCN1-4通道是If/Ih电流的分子决定簇，至关重要地调节心脏和神经元细胞的兴奋性。HCN功能障碍导致窦房传导阻滞（HCN4），癫痫（HCN1），和慢性疼痛（HCN2），正在等待亚型特异性治疗的广泛医疗条件。这里,我们通过解决与伊伐布雷定复合的HCN4的低温EM结构来解决这个问题，迄今为止市场上唯一的HCN特异性药物。我们的数据显示，伊伐布雷定在3µ分辨率的开放孔隙内结合。结构明确证明S6上的Y507和I511是伊伐布雷定与内腔结合的分子决定子，而F510指向毛孔外面，通过控制Y507间接有助于该嵌段。半胱氨酸479，独特的HCN选择性过滤器（SF），加速块的动力学。分子动力学模拟进一步表明，伊伐布雷定通过静电排斥阻断SF内部的渗透离子，先前提出的季铵离子的机理。
