Instituto Biofisika, Consejo Superior de Investigaciones Científicas, CSIC, UPV/EHU, Barrio Sarriena s/n, 48940, Leioa, Spain.
Sci Rep. 2017 Oct 18;7(1):13425. doi: 10.1038/s41598-017-13811-4.
Tetrameric coiled-coil structures are present in many ion channels, often adjacent to a calmodulin (CaM) binding site, although the relationship between the two is not completely understood. Here we examine the dynamic properties of the ABCD domain located in the intracellular C-terminus of tetrameric, voltage-dependent, potassium selective Kv7.2 channels. This domain encompasses the CaM binding site formed by helices A and B, followed by helix C, which is linked to the helix D coiled-coil. The data reveals that helix D stabilizes CaM binding, promoting trans-binding (CaM embracing neighboring subunits), and they suggest that the ABCD domain can be exchanged between subunits of the tetramer. Exchange is faster when mutations in AB weaken the CaM interaction. The exchange of ABCD domains is slower in the presence of Ca, indicating that CaM stabilization of the tetrameric assembly is enhanced when loaded with this cation. Our observations are consistent with a model that involves a dynamic mechanism of helix D assembly, which supports reciprocal allosteric coupling between the A-B module and the coiled-coil formed by the helix D. Thus, formation of the distal helix D tetramer influences CaM binding and CaM-dependent Kv7.2 properties, whereas reciprocally, CaM and Ca influence the dynamic behavior of the helix D coiled-coil.
四聚体卷曲螺旋结构存在于许多离子通道中，通常紧邻钙调蛋白（CaM）结合位点，尽管两者之间的关系尚未完全了解。在这里，我们研究了位于四聚体、电压依赖性、钾选择性 Kv7.2 通道细胞内 C 末端的 ABCD 结构域的动态特性。该结构域包含由螺旋 A 和 B 形成的 CaM 结合位点，其后是与螺旋 D 卷曲螺旋相连的螺旋 C。数据表明，螺旋 D 稳定了 CaM 的结合，促进了跨结合（CaM 环抱相邻亚基），并且它们表明 ABCD 结构域可以在四聚体的亚基之间交换。当 AB 中的突变削弱 CaM 相互作用时，交换更快。在 Ca 存在的情况下，ABCD 结构域的交换较慢，表明当加载这种阳离子时，CaM 对四聚体组装的稳定作用增强。我们的观察结果与一个涉及螺旋 D 组装的动态机制的模型一致，该模型支持 A-B 模块和由螺旋 D 形成的卷曲螺旋之间的反向变构偶联。因此，远端螺旋 D 四聚体的形成影响 CaM 结合和 CaM 依赖性 Kv7.2 特性，而反之，CaM 和 Ca 影响螺旋 D 卷曲螺旋的动态行为。
