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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >A microscopic view of ion conduction through the K+ channel.
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A microscopic view of ion conduction through the K+ channel.

机译：通过K +通道的离子传导的微观视图。

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摘要

Recent results from x-ray crystallography and molecular dynamics free-energy simulations have revealed the existence of a number of specific cation-binding sites disposed along the narrow pore of the K+ channel from Streptomyces lividans (KcsA), suggesting that K+ ions might literally "hop" in single file from one binding site to the next as permeation proceeds. In support of this view, it was found that the ion configurations correspond to energy wells of similar depth and that ion translocation is opposed only by small energy barriers. Although such features of the multiion potential energy surface are certainly essential for achieving a high throughput rate, diffusional and dissipative dynamical factors must also be taken into consideration to understand how rapid conduction of K+ is possible. To elucidate the mechanism of ion conduction, we established a framework theory enabling the direct simulation of nonequilibrium fluxes by extending the results of molecular dynamics over macroscopically long times. In good accord with experimental measurements, the simulated maximum conductance of the channel at saturating concentration is on the order of 550 and 360 pS for outward and inward ions flux, respectively, with a unidirectional flux-ratio exponent of 3. Analysis of the ion-conduction process reveals a lack of equivalence between the cation-binding sites in the selectivity filter.
机译：X射线晶体学和分子动力学自由能模拟的最新结果表明，沿着淡紫色链霉菌（KcsA）的K +通道的狭窄孔存在着许多特定的阳离子结合位点，这表明K +离子可能从字面上“随着渗透的进行，将单个文件中的“跳跃”从一个绑定位置转移到另一个绑定位置。为了支持该观点，发现离子构型对应于相似深度的能量阱，并且离子易位仅由小的能垒来对抗。尽管多离子势能表面的这些特征对于实现高吞吐速率必不可少，但也必须考虑扩散和耗散动力学因素，以了解如何快速传导K +。为了阐明离子传导的机理，我们建立了一个框架理论，通过将分子动力学的结果扩展到宏观上较长的时间，从而可以直接模拟非平衡通量。与实验测量结果非常吻合，在饱和浓度下，通道的模拟最大电导率分别为向外和向内离子通量分别为550和360 pS，单向通量比为3。传导过程表明选择性过滤器中的阳离子结合位点之间缺乏等效性。

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