Structural and functional consequences of an amide-to-ester substitution in the selectivity filter of a potassium channel
Structural and functional consequences of an amide-to-ester substitution in the selectivity filter of a potassium channel
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DOI：
10.1021/ja0631955
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发表时间：
2006-09-06
影响因子：
15
通讯作者：
Muir, Tom W.
中科院分区：
文献类型：
--
作者：
Valiyaveetil, Francis I.;Sekedat, Matthew;Muir, Tom W.
K+通道的选择性过滤器包括四个相邻的离子结合部位，S1至S4。结构和功能数据表明，在任何给定的时间，过滤器平均含有两个K+离子，这些离子主要以两种配置存在，即位置S1和S3或位置S2和S4。当这两种结合构型之间的能量差为零时，预计会出现通过通道的最大离子通量。在这项研究中，我们使用蛋白质半合成通过使用酰胺到酯的取代来选择性地扰乱KCSA通道过滤器内的第一位点。这种修饰改变了K+的导电性。尽管失去了通常位于过滤器后面的有序水分子，但选择性过滤器的结构在很大程度上没有受到修改的影响。酯基的引入改变了滤池中K+、Rb+和Cs+的分布，其中Rb+的变化最为显著。离子的重新分布与过滤器外部的部分水合离子的出现有关，在野生型通道中没有观察到离子的位置。这个新的离子结合点的出现在一定程度上改变了一对K+离子之间的距离，显然导致了离子传导速度的降低。重要的是，这一发现表明，钾通道的选择性过滤器在绝对离子占有率和导电离子之间的距离方面都是优化的。
The selectivity filter of K+ channels comprises four contiguous ion binding sites, S1 through S4. Structural and functional data indicate that the filter contains on average two K+ ions at any given time and that these ions reside primarily in two configurations, namely to sites S1 and S3 or to sites S2 and S4. Maximum ion flux through the channel is expected to occur when the energy difference between these two binding configurations is zero. In this study, we have used protein semisynthesis to selectively perturb site 1 within the filter of the KcsA channel through use of an amide-to-ester substitution. The modification alters K+ conduction properties. The structure of the selectivity filter is largely unperturbed by the modification, despite the loss of an ordered water molecule normally located just behind the filter. Introduction of the ester moiety was found to alter the distribution of K+, Rb+, and Cs+ within the filter, with the most dramatic change found for Rb+. The redistribution of ions is associated with the appearance of a partially hydrated ion just external to the filter, at a position where no ion is observed in the wild-type channel. The appearance of this new ion-binding site creates a change in the distance between a pair of K+ ions some fraction of the time, apparently leading to a reduction in the ion conduction rate. Importantly, this finding suggests that the selectivity filter of a potassium channel is optimized both in terms of absolute ion occupancy and in terms of the separation in distance between the conducting ions.