Calmodulin mediates Ca2+ sensitivity of sodium channels
Calmodulin mediates Ca2+ sensitivity of sodium channels
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DOI：
10.1074/jbc.m407286200
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发表时间：
2004-10-22
影响因子：
4.8
通讯作者：
Pitt, GS
中科院分区：
文献类型：
--
作者：
Kim, J;Ghosh, S;Pitt, GS
钙离子被认为通过与IQ基序结合的钙调蛋白(CaM)的作用或通过直接与Na(V)1C末端的成对EF手状基序结合来调节Na+通道。这些位点的突变会导致心律失常或自闭症，但关于钙离子如何赋予敏感性的细节尚不清楚。对同源Ca(V)1.2通道的研究揭示了非典型的CaM相互作用，为探索Na+通道提供了一个框架。与以往的报道不同，我们发现钙离子不直接与钠离子通道C末端结合。相反，钙敏感性似乎是由结合到C末端的CaM介导的，其方式与CaM对Ca(V)1.2的调节有很大不同。在Na(V)1.2或Na(V)1.5中，CaM结合到包含IQ基序的定域区域，不支持在Ca(V)1.2中看到的依赖于钙的大的构象变化。凸轮复合体。此外，与单独的CaM相比，CaM与Na(V)1C末端的结合降低了CaM与Ca~(2+)的结合亲和力和CaM结合位点之间的协同性。尽管如此，我们还是发现了钙/钙调素依赖的Na(V)1通道效应的证据。R1902C自闭症突变导致Na(V)1.2C末端钙离子依赖性构象改变。野生型复合体中不存在的CaM复合体。在Na(V)1.5中，CaM调节C端与III-IV连接子的相互作用，这被认为是稳定失活门、减少去极化过程中持续的通道活动以及防止导致猝死的心律失常所必需的。综上所述，这些数据为钙/钙调素调控钠离子通道功能提供了新的生化证据。
Ca2+ has been proposed to regulate Na+ channels through the action of calmodulin (CaM) bound to an IQ motif or through direct binding to a paired EF hand motif in the Na(v)1 C terminus. Mutations within these sites cause cardiac arrhythmias or autism, but details about how Ca2+ confers sensitivity are poorly understood. Studies on the homologous Ca(v)1.2 channel revealed non-canonical CaM interactions, providing a framework for exploring Na+ channels. In contrast to previous reports, we found that Ca2+ does not bind directly to Na+ channel C termini. Rather, Ca2+ sensitivity appears to be mediated by CaM bound to the C termini in a manner that differs significantly from CaM regulation of Ca(v)1.2. In Na(v)1.2 or Na(v)1.5, CaM bound to a localized region containing the IQ motif and did not support the large Ca2+-dependent conformational change seen in the Ca(v)1.2 . CaM complex. Furthermore, CaM binding to Na(v)1 C termini lowered Ca2+ binding affinity and cooperativity among the CaM-binding sites compared with CaM alone. Nonetheless, we found suggestive evidence for Ca2+/CaM-dependent effects upon Na(v)1 channels. The R1902C autism mutation conferred a Ca2+-dependent conformational change in Na(v)1.2 C terminus . CaM complex that was absent in the wild-type complex. In Na(v)1.5, CaM modulates the C-terminal interaction with the III-IV linker, which has been suggested as necessary to stabilize the inactivation gate, to minimize sustained channel activity during depolarization, and to prevent cardiac arrhythmias that lead to sudden death. Together, these data offer new biochemical evidence for Ca2+/CaM modulation of Na+ channel function.