电压门控离子通道的选择性和渗透性研究
Study of Selectivity and Permeation In Voltage-Gated Ion Channels
摘要：
离子通道是一种膜蛋白，具有广泛的生物学功能。离子选择性和渗透是基于简单的物理和化学定律。因此，离子通道是物理研究的理想候选者。一个简化的模型产生的电压门控L-型钙通道的选择性在广泛的离子条件下，使用只有两个参数不变的值。这个简化模型的成功背后的原因进行了调查。进行蒙特卡罗模拟，研究在宽范围的离子条件下侧链的灵活性在钙通道的选择性中的作用。结果表明，氧离子的确切位置和迁移率对钙通道的选择性行为几乎没有影响。钙通道中选择性的一阶决定因素是选择性过滤器中的电荷密度。灵活性似乎是一个二级决定因素。进行单通道平面脂质双层实验以确定大肠杆菌的细菌外膜通道NanC的选择性、渗透性和唾液酸特异性。NanC表现出随施加电压极性、阴离子选择性和电压门控而变化的大的单位电导。在缓冲液HEPES的存在下，NanC的单位电导显著降低。检测替代缓冲液。结果表明，NanC的唾液酸特异性应在低浓度盐溶液中进行，而无需调节至中性pH 7.0的pH缓冲液。Neu 5Ac改变了门控并显著增加了NanC的离子电导。Neu 5Ac对通过NanC的单位电流的影响在较高Neu 5Ac浓度下饱和。有趣的是，Neu 5Ac降低了OmpF的离子电导：观察到频繁的长闭合。因此，在大肠杆菌中，唾液酸易位由NanC特异性促进，而不是由OmpF促进。
英文摘要：
Ion channels are membrane proteins responsible for an enormous range of biological functions. Ion selectivity and permeation are based on simple laws of physics and chemistry. Ion channels are therefore ideal candidates for physical investigation. A reduced model generates the selectivity of voltage-gated L-type calcium channel under a wide range of ionic conditions using only two parameters with unchanging values. The reasons behind the success of this reduced model are investigated. Monte Carlo simulations are performed investigating the role of flexibility of the side chains in the selectivity of calcium channels under a wide range of ionic conditions. Results suggest that the exact location and mobility of oxygen ions have little effect on the selectivity behavior of calcium channels. The first order determinant of selectivity in calcium channels is the density of charge in the selectivity filter. Flexibility seems a second order determinant. Single channel planar lipid bilayer experiments are performed to determine the selectivity, permeation, and sialic acid specificity of a bacterial outer-membrane channel NanC of Ecoli. NanC exhibits a large unit conductance varying with the applied voltage polarity, anion selectivity, and voltage gating. Unitary conductance of NanC decreases significantly in presence of the buffer HEPES. Alternate buffers are tested. Results suggest that the sialic acid specificity of NanC should be performed in low concentration salt solutions without pH buffers adjusted to neutral pH 7.0. Neu5Ac changes the gating and considerably increases the ionic conductance of NanC. The effect of Neu5Ac on the unitary current through NanC saturates at higher Neu5Ac concentrations. Interestingly, Neu5Ac reduces the ionic conductance of OmpF: frequent, long closures are seen. Thus, in E.coli sialic acid translocation is specifically facilitated by NanC, and not by OmpF.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
