The role of S4 charges in voltage-dependent and voltage-independent KCNQ1 potassium channel complexes.
The role of S4 charges in voltage-dependent and voltage-independent KCNQ1 potassium channel complexes.
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DOI：
10.1085/jgp.200609612
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发表时间：
2007-02
影响因子：
3.8
通讯作者：
Abbott, Geoffrey W
中科院分区：
文献类型：
--
作者：
Panaghie, Gianina;Abbott, Geoffrey W
电压门控钾通道通过与MinK相关肽（MiRPs）共组装来扩展其功能库。MinK减缓了KCNQ 1 α亚基形成的通道的激活，从而在人心脏中产生电压依赖性IKs通道; MiRP 1和MiRP 2消除了KCNQ 1的电压依赖性，从而在胃肠道上皮中产生钾“漏”电流。其他Kv α亚基与MiRP 1和MiRP 2相互作用，但不丧失电压依赖性;这种差异的机制尚不清楚。在这里，序列比对显示，KCNQ 1的电压敏感S4结构域比任何其他真核细胞电压门控离子通道具有更低的净电荷（+3）。因此，我们研究的作用KCNQ 1 S4电荷在通道激活使用丙氨酸扫描诱变和双电极电压钳。丙氨酸取代的R231，在N-末端侧的S4，产生组成型激活同源KCNQ 1通道，没有观察到的现象与以前的单一氨基酸取代S4的其他通道。同源KCNQ 4通道也通过诱变模拟R231 A-KCNQ 1的S4电荷平衡而具有组成型活性。在位置R231或R237处的单个S4电荷的损失产生组成型活性MinK-KCNQ 1通道，并增加MiRP 2-KCNQ 1电流的组成型活性成分。向S4的CO2 H-末端的一半添加电荷消除了MiRP 2-KCNQ 1通道中的组成性激活，而从KCNQ 4 S4去除同源电荷产生组成性激活的MiRP 2-KCNQ 4通道。结果表明，KCNQ 1独特的S4电荷缺乏有利于其独特的转换为泄漏通道的辅助亚基，如MiRP 2。
Voltage-gated potassium (Kv) channels extend their functional repertoire by coassembling with MinK-related peptides (MiRPs). MinK slows the activation of channels formed with KCNQ1 α subunits to generate the voltage-dependent IKs channel in human heart; MiRP1 and MiRP2 remove the voltage dependence of KCNQ1 to generate potassium “leak” currents in gastrointestinal epithelia. Other Kv α subunits interact with MiRP1 and MiRP2 but without loss of voltage dependence; the mechanism for this disparity is unknown. Here, sequence alignments revealed that the voltage-sensing S4 domain of KCNQ1 bears lower net charge (+3) than that of any other eukaryotic voltage-gated ion channel. We therefore examined the role of KCNQ1 S4 charges in channel activation using alanine-scanning mutagenesis and two-electrode voltage clamp. Alanine replacement of R231, at the N-terminal side of S4, produced constitutive activation in homomeric KCNQ1 channels, a phenomenon not observed with previous single amino acid substitutions in S4 of other channels. Homomeric KCNQ4 channels were also made constitutively active by mutagenesis to mimic the S4 charge balance of R231A-KCNQ1. Loss of single S4 charges at positions R231 or R237 produced constitutively active MinK-KCNQ1 channels and increased the constitutively active component of MiRP2-KCNQ1 currents. Charge addition to the CO2H-terminal half of S4 eliminated constitutive activation in MiRP2-KCNQ1 channels, whereas removal of homologous charges from KCNQ4 S4 produced constitutively active MiRP2-KCNQ4 channels. The results demonstrate that the unique S4 charge paucity of KCNQ1 facilitates its unique conversion to a leak channel by ancillary subunits such as MiRP2.