离子通道的选择性是由承压水介导的吗？
Is ion channel selectivity mediated by confined water?
摘要：
离子通道在脂质双层上形成孔，选择性地允许无机离子沿着其电化学梯度穿过膜。虽然离子去溶剂化自由能的研究已经引起了人们的广泛关注，但水在孔隙中的作用还不清楚。在这里，分子动力学模拟的KcsA选择性过滤器的简化模型表明，Na+的平衡位置，但不是K+，是强烈的受承压水的影响。后者与Na+形成稳定的复合物，将离子的平衡位置移动到骨架羰基的平面。几乎在结合位点的中心，水分子被有利的静电相互作用和主链氢键捕获。在没有承压水的情况下，Na+和K+的平衡位置是相同的。我们的观察结果强烈表明，以前未被注意的活性作用的封闭水的离子通道的选择性机制。
英文摘要：
Ion channels form pores across the lipid bilayer, selectively allowing inorganic ions to cross the membrane down their electrochemical gradient. While the study of ion desolvation free-energies have attracted much attention, the role of water inside the pore is less clear. Here, molecular dynamics simulations of a reduced model of the KcsA selectivity filter indicate that the equilibrium position of Na+, but not of K+, is strongly influenced by confined water. The latter forms a stable complex with Na+, moving the equilibrium position of the ion to the plane of the backbone carbonyls. Almost at the centre of the binding site, the water molecule is trapped by favorable electrostatic interactions and backbone hydrogen-bonds. In the absence of confined water the equilibrium position of both Na+ and K+ is identical. Our observations strongly suggest a previously unnoticed active role of confined water in the selectivity mechanism of ion channels.
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