Activation of the SK potassium channel-calmodulin complex by nanomolar concentrations of terbium
Activation of the SK potassium channel-calmodulin complex by nanomolar concentrations of terbium
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DOI：
10.1073/pnas.0812008106
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发表时间：
2009-01-27
影响因子：
11.1
通讯作者：
Aldrich, Richard W.
中科院分区：
文献类型：
--
作者：
Li, Weiyan;Aldrich, Richard W.
小电导钙激活K+(SK)通道通过相关的钙结合蛋白钙调蛋白来感知细胞内的钙离子浓度。结构和功能研究揭示了钙调蛋白与SK通道相互作用的基本特性。然而，钙离子与钙调蛋白的结合是如何导致通道开放的，目前还不完全清楚。借鉴前人对以稀土离子作为钙离子替代物的游离钙调素的生化研究，我们以稀土离子Tb~(3+)作为替代配体，研究了SK通道的激活特性。我们发现，纳米分子浓度的Tb3+可以完全激活SK通道，显示出明显的亲和力>；是钙离子的100倍。竞争实验表明，Tb~(3+)与Ca~(2+)结合到相同的部位激活通道。此外，Tb3+激活的SK通道表现出非常缓慢的失活过程。我们的结果与以前的生化研究结果比较表明，在完整的SK通道复合体中，钙调蛋白的N-叶为通道门控提供了配体结合部位，其配体结合特性与分离的钙调蛋白中的N-叶相当。
Small conductance Ca2+-activated K+ (SK) channels sense intracellular Ca2+ concentrations via the associated Ca2+-binding protein calmodulin. Structural and functional studies have revealed essential properties of the interaction between calmodulin and SK channels. However, it is not fully understood how the binding of Ca2+ to calmodulin leads to channel opening. Drawing on previous biochemical studies of free calmodulin using lanthanide ions as Ca2+ substitutes, we have used the lanthanide ion, Tb3+, as an alternative ligand to study the activation properties of SK channels. We found that SK channels can be fully activated by nanomolar concentrations of Tb3+, indicating an apparent affinity > 100-fold higher than Ca2+. Competition experiments show that Tb3+ binds to the same sites as Ca2+ to activate the channels. Additionally, SK channels activated by Tb3+ demonstrate a remarkably slow deactivation process. Comparison of our results with previous biochemical studies suggests that in the intact SK channel complex, the N-lobe of calmodulin provides ligand-binding sites for channel gating, and that its ligand-binding properties are comparable to those of the N-lobe in isolated calmodulin.