DataSheet1_Two small-molecule activators share similar effector sites in the KCNQ1 channel pore but have distinct effects on voltage sensor movements.PDF

ML277 and R-L3 are two small-molecule activators of KCNQ1, the pore-forming subunit of the slowly activating potassium channel IKs. KCNQ1 loss-of-function mutations prolong cardiac action potential duration and are associated with long QT syndrome, which predispose patients to lethal ventricular arrhythmia. ML277 and R-L3 enhance KCNQ1 current amplitude and slow deactivation. However, the presence of KCNE1, an auxiliary subunit of IKs channels, renders the channel insensitive to both activators. We found that ML277 effects are dependent on several residues in the KCNQ1 pore domain. Some of these residues are also necessary for R-L3 effects. These residues form a putative hydrophobic pocket located between two adjacent KCNQ1 subunits, where KCNE1 subunits are thought to dwell, thus providing an explanation for how KCNE1 renders the IKs channel insensitive to these activators. Our experiments showed that the effect of R-L3 on voltage sensor movement during channel deactivation was much more prominent than that of ML277. Simulations using a KCNQ1 kinetic model showed that the effects of ML277 and R-L3 could be reproduced through two different effects on channel gating: ML277 enhances KCNQ1 channel function through a pore-dependent and voltage sensor–independent mechanism, while R-L3 affects both channel pore and voltage sensor.

ML277与R-L3是KCNQ1的两种小分子激活剂，而KCNQ1是缓慢激活型钾通道IKs的孔形成亚基（pore-forming subunit）。KCNQ1功能丧失型突变会延长心脏动作电位时程，并与长QT综合征（long QT syndrome）相关，后者会使患者罹患致死性室性心律失常（ventricular arrhythmia）的风险升高。ML277与R-L3可增强KCNQ1的电流幅值并减缓通道去激活过程。然而，当存在IKs通道的辅助亚基（auxiliary subunit）KCNE1时，通道对这两种激活剂均不敏感。本研究发现，ML277的激活效应依赖于KCNQ1孔结构域中的多个残基，其中部分残基也是R-L3发挥其激活效应所必需的。这些残基构成了一个位于两个相邻KCNQ1亚基之间的推定疏水口袋，而KCNE1亚基被认为会驻留于该口袋区域，这为KCNE1如何使IKs通道对上述两种激活剂不敏感提供了合理的解释。实验结果表明，R-L3对通道去激活过程中电压传感器（voltage sensor）运动的调控效应远强于ML277。基于KCNQ1动力学模型的模拟显示，ML277与R-L3的效应可通过两种不同的通道门控调控机制实现：ML277通过孔结构域依赖且不依赖电压传感器的途径增强KCNQ1通道功能，而R-L3则同时作用于通道孔结构域与电压传感器。