a Instituto Biofisika , Consejo Superior de Investigaciones Científicas, CSIC, UPV/EHU , Leioa , Spain.
Channels (Austin). 2018;12(1):299-310. doi: 10.1080/19336950.2018.1511512.
Heteromers of Kv7.2/Kv7.3 subunits constitute the main substrate of the neuronal M-current that limits neuronal hyper-excitability and firing frequency. Calmodulin (CaM) binding is essential for surface expression of Kv7 channels, and disruption of this interaction leads to diseases ranging from mild epilepsy to early onset encephalopathy. In this study, we addressed the impact of a charge neutralizing mutation located at the periphery of helix B (K526N). We found that, CaM binding and surface expression was impaired, although current amplitude was not altered. Currents were reduced at a faster rate after activation of a voltage-dependent phosphatase, suggesting that phosphatidylinositol-4,5-bisphosphate (PIP) binding was weaker. In contrast, a charge neutralizing mutation located at the periphery of helix A (R333Q) did not affect CaM binding, but impaired trafficking and led to a reduction in current amplitude. Taken together, these results suggest that disruption of CaM-dependent or CaM-independent trafficking of Kv7.2/Kv7.3 channels can lead to pathology regardless of the consequences on the macroscopic ionic flow through the channel.
Kv7.2/Kv7.3 亚基的异源二聚体构成了神经元 M 电流的主要底物，神经元 M 电流限制神经元的过度兴奋和放电频率。钙调蛋白（CaM）与 Kv7 通道的结合对于其表面表达是必需的，而这种相互作用的破坏会导致从轻度癫痫到早发性脑病等各种疾病。在这项研究中，我们研究了位于螺旋 B （K526N）外围的一个带点中性突变对 Kv7.2/Kv7.3 通道的影响。我们发现，尽管电流幅度没有改变，但 CaM 结合和表面表达受到了损害。电压依赖性磷酸酶激活后电流衰减速度更快，表明磷脂酰肌醇-4,5-二磷酸（PIP）结合较弱。相比之下，位于螺旋 A （R333Q）外围的带点中性突变不会影响 CaM 结合，但会损害运输，导致电流幅度减小。总之，这些结果表明，无论对通道宏观离子流的影响如何，CaM 依赖性或 CaM 非依赖性 Kv7.2/Kv7.3 通道的运输中断都可能导致病理学。
