Zhang M, Liu J, Jiang M, Wu D-M, Sonawane K, Guy H R, Tseng G-N
Department of Physiology, Virginia Commonwealth University, Richmond, VA 23298, USA.
J Membr Biol. 2005 Oct;207(3):169-81. doi: 10.1007/s00232-005-0812-1.
Studies on voltage-gated K channels such as Shaker have shown that positive charges in the voltage-sensor (S4) can form salt bridges with negative charges in the surrounding transmembrane segments in a state-dependent manner, and different charge pairings can stabilize the channels in closed or open states. The goal of this study is to identify such charge interactions in the hERG channel. This knowledge can provide constraints on the spatial relationship among transmembrane segments in the channel's voltage-sensing domain, which are necessary for modeling its structure. We first study the effects of reversing S4's positive charges on channel activation. Reversing positive charges at the outer (K525D) and inner (K538D) ends of S4 markedly accelerates hERG activation, whereas reversing the 4 positive charges in between either has no effect or slows activation. We then use the 'mutant cycle analysis' to test whether D456 (outer end of S2) and D411 (inner end of S1) can pair with K525 and K538, respectively. Other positive charges predicted to be able, or unable, to interact with D456 or D411 are also included in the analysis. The results are consistent with predictions based on the distribution of these charged residues, and confirm that there is functional coupling between D456 and K525 and between D411 and K538.
对诸如Shaker等电压门控钾通道的研究表明，电压感受器（S4）中的正电荷能够以状态依赖的方式与周围跨膜片段中的负电荷形成盐桥，不同的电荷配对可使通道稳定于关闭或开放状态。本研究的目的是确定hERG通道中的此类电荷相互作用。这一知识可为通道电压感受域中跨膜片段之间的空间关系提供限制条件，而这些条件对于构建其结构模型是必要的。我们首先研究S4正电荷反转对通道激活的影响。反转S4外端（K525D）和内端（K538D）的正电荷可显著加速hERG激活，而反转两者之间的4个正电荷则要么没有影响，要么减缓激活。然后我们使用“突变循环分析”来测试D456（S2外端）和D411（S1内端）是否能分别与K525和K538配对。分析中还包括预计能够或不能够与D456或D411相互作用的其他正电荷。结果与基于这些带电残基分布的预测一致，并证实D456与K525以及D411与K538之间存在功能偶联。
