Chen Szu-Han, Fu Ssu-Ju, Huang Jing-Jia, Tang Chih-Yung
Department of Physiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan.
Sci Rep. 2016 Jan 18;6:19378. doi: 10.1038/srep19378.
Voltage-gated potassium (Kv) channels are essential for setting neuronal membrane excitability. Mutations in human Kv1.1 channels are linked to episodic ataxia type 1 (EA1). The EA1-associated mutation I262T was identified from a patient with atypical phenotypes. Although a previous report has characterized its suppression effect, several key questions regarding the impact of the I262T mutation on Kv1.1 as well as other members of the Kv1 subfamily remain unanswered. Herein we show that the dominant-negative effect of I262T on Kv1.1 current expression is not reversed by co-expression with Kvβ1.1 or Kvβ2 subunits. Biochemical examinations indicate that I262T displays enhanced protein degradation and impedes membrane trafficking of Kv1.1 wild-type subunits. I262T appears to be the first EA1 mutation directly associated with impaired protein stability. Further functional analyses demonstrate that I262T changes the voltage-dependent activation and Kvβ1.1-mediated inactivation, uncouples inactivation from activation gating, and decelerates the kinetics of cumulative inactivation of Kv1.1 channels. I262T also exerts similar dominant effects on the gating of Kv1.2 and Kv1.4 channels. Together our data suggest that I262T confers altered channel gating and reduced functional expression of Kv1 channels, which may account for some of the phenotypes of the EA1 patient.
电压门控钾（Kv）通道对于设定神经元膜兴奋性至关重要。人类Kv1.1通道的突变与1型发作性共济失调（EA1）相关。EA1相关突变I262T是从一名具有非典型表型的患者中鉴定出来的。尽管先前的一份报告已经描述了其抑制作用，但关于I262T突变对Kv1.1以及Kv1亚家族其他成员的影响的几个关键问题仍未得到解答。在此我们表明，I262T对Kv1.1电流表达的显性负效应不会因与Kvβ1.1或Kvβ2亚基共表达而逆转。生化检查表明，I262T表现出增强的蛋白质降解，并阻碍Kv1.1野生型亚基的膜转运。I262T似乎是第一个与蛋白质稳定性受损直接相关的EA1突变。进一步的功能分析表明，I262T改变了电压依赖性激活和Kvβ1.1介导的失活，使失活与激活门控解偶联，并减慢了Kv1.1通道累积失活的动力学。I262T对Kv1.2和Kv1.4通道的门控也有类似的显性作用。我们的数据共同表明，I262T导致Kv1通道门控改变和功能表达降低，这可能解释了EA1患者的一些表型。
