Phan Kevin, Ng Chai Ann, David Erikka, Shishmarev Dmitry, Kuchel Philip W, Vandenberg Jamie I, Perry Matthew D
From the Victor Chang Cardiac Research Institute, 405 Liverpool Street, Darlinghurst, New South Wales 2010.
the St. Vincent's Clinical School, University of New South Wales, New South Wales 2052, and.
J Biol Chem. 2017 May 5;292(18):7688-7705. doi: 10.1074/jbc.M117.779298. Epub 2017 Mar 9.
Congenital mutations in the cardiac Kv11.1 channel can cause long QT syndrome type 2 (LQTS2), a heart rhythm disorder associated with sudden cardiac death. Mutations act either by reducing protein expression at the membrane and/or by perturbing the intricate gating properties of Kv11.1 channels. A number of clinical LQTS2-associated mutations have been reported in the first transmembrane segment (S1) of Kv11.1 channels, but the role of this region of the channel is largely unexplored. In part, this is due to problems defining the extent of the S1 helix, as a consequence of its low sequence homology with other Kv family members. Here, we used NMR spectroscopy and electrophysiological characterization to show that the S1 of Kv11.1 channels extends seven helical turns, from Pro-405 to Phe-431, and is flanked by unstructured loops. Functional analysis suggests that pre-S1 loop residues His-402 and Tyr-403 play an important role in regulating the kinetics and voltage dependence of channel activation and deactivation. Multiple residues within the S1 helix also play an important role in fine-tuning the voltage dependence of activation, regulating slow deactivation, and modulating C-type inactivation of Kv11.1 channels. Analyses of LQTS2-associated mutations in the pre-S1 loop or S1 helix of Kv11.1 channels demonstrate perturbations to both protein expression and most gating transitions. Thus, S1 region mutations would reduce both the action potential repolarizing current passed by Kv11.1 channels in cardiac myocytes, as well as the current passed in response to premature depolarizations that normally helps protect against the formation of ectopic beats.
心脏Kv11.1通道的先天性突变可导致2型长QT综合征（LQTS2），这是一种与心源性猝死相关的心律失常。突变的作用方式要么是降低膜上的蛋白质表达，和/或扰乱Kv11.1通道复杂的门控特性。在Kv11.1通道的第一个跨膜片段（S1）中已经报道了许多与临床LQTS2相关的突变，但该通道这一区域的作用在很大程度上尚未得到探索。部分原因是由于S1螺旋的低序列同源性，难以确定其范围。在这里，我们使用核磁共振光谱和电生理特性分析表明，Kv11.1通道的S1从Pro-405延伸到Phe-431，有七个螺旋圈，两侧是无结构的环。功能分析表明，S1前环残基His-402和Tyr-403在调节通道激活和失活的动力学及电压依赖性方面起重要作用。S1螺旋内的多个残基在微调激活的电压依赖性、调节缓慢失活以及调节Kv11.1通道的C型失活方面也起重要作用。对Kv11.1通道S1前环或S1螺旋中与LQTS2相关的突变分析表明，这些突变对蛋白质表达和大多数门控转换都有干扰。因此，S1区域的突变会减少心肌细胞中Kv11.1通道通过的动作电位复极化电流，以及对过早去极化响应而通过的电流，而过早去极化通常有助于防止异位搏动的形成。
