Ionic Coulomb blockade and anomalous mole fraction effect in the NaChBac bacterial ion channel and its charge-varied mutants
Ionic Coulomb blockade and anomalous mole fraction effect in the NaChBac bacterial ion channel and its charge-varied mutants
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DOI：
10.1051/epjnbp/2017003
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发表时间：
2017-09-11
期刊：
影响因子：
--
通讯作者：
Eisenberg, Robert S.
中科院分区：
文献类型：
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作者：
Kaufman, Igor Kh.;Fedorenko, Olena A.;Eisenberg, Robert S.
背景生物阳离子通道的选择性由具有负净固定电荷Q（f）的短而窄的选择性过滤器定义。电压门控细菌通道（NaChBac和其他一些）在生物物理学中经常被用作哺乳动物钙和钠通道的简化模型。我们报告了一个实验，分析和数值研究的影响Q（f）和体离子浓度的Ca 2+和Na+的传导和选择性的NaChBac通道，野生型和Q（f）-变化的突变体。采用定点突变和电压钳技术研究了不同NaChBac野生型/突变型通道的Na+/Ca 2+选择性、二价阻断和异常摩尔分数效应（AMFE）以及对Q（f）的依赖性。实验结果与布朗动力学模拟和离子库仑阻塞（ICB）模型的分析预测进行了比较，该模型扩展到包括体浓度效应。结果表明，Q（f）从-4e（对于LESWAS野生型）变为-8e（对于LEDWAS突变体）导致微摩尔量的Ca 2+离子对Na+电流的强烈二价阻断，类似于在哺乳动物钙通道中观察到的效果。BD模拟揭示了导带的浓度相关的对数移位。这些结果与ICB模型预测结果一致。扩展的ICB模型解释了实验（二价封锁和AMFE）和模拟（多离子带和它们的浓度相关的位移）的选择性现象的NaChBac通道及其电荷变化的突变体。这些结果扩展了对离子通道选择性的理解，也可能适用于具有带电壁的仿生纳米孔。
Background. The selectivity of biological cation channels is defined by a short, narrow selectivity filter, having a negative net fixed charge Q(f). Voltage gated bacterial channels (NaChBac and some others) are frequently used in biophysics as simplified models of mammalian calcium and sodium channels. We report an experimental, analytic and numerical study of the effects of Q(f) and bulk ionic concentrations of Ca2+ and Na+ on conduction and selectivity of NaChBac channels, wild type and Q(f)-varied mutants.Methods. Site-directed mutagenesis and voltage clamp recordings were used to investigate the Na+/Ca2+ selectivity, divalent blockade and anomalous mole fraction effect (AMFE) for different NaChBac wild type/mutants channels and the properties dependence on Q(f). Experimental results were compared with Brownian dynamics simulations and with analytic predictions of the ionic Coulomb blockade (ICB) model, which was extended to encompass bulk concentration effects.Results. It was shown that changing of Q(f) from -4e (for LESWAS wild type) to -8e (for LEDWAS mutant) leads to strong divalent blockade of the Na+ current by micromolar amounts of Ca2+ ions, similar to the effects seen in mammalian calcium channels. The BD simulations revealed a concentration-related logarithmic shift of the conduction bands. These results were shown to be consistent with ICB model predictions.Conclusions. The extended ICB model explains the experimental (divalent blockade and AMFE) and simulated (multi-ion bands and their concentration-related shifts) selectivity phenomena of NaChBac channel and its charge-varied mutants. These results extend the understanding of ion channel selectivity and may also be applicable to biomimetic nanopores with charged walls.