Sansom M S, Smith G R, Adcock C, Biggin P C
Laboratory of Molecular Biophysics, University of Oxford, England.
Biophys J. 1997 Nov;73(5):2404-15. doi: 10.1016/S0006-3495(97)78269-9.
Ion channels contain extended columns of water molecules within their transbilayer pores. The dynamic properties of such intrapore water have been shown to differ from those of water in its bulk state. In previous molecular dynamics simulations of two classes of model pore (parallel bundles of Ala20 alpha-helices and antiparallel barrels of Ala10 beta-strands), a substantially reduced translational and rotational mobility of waters was observed within the pore relative to bulk water. Molecular dynamics simulations in the presence of a transpore electrostatic field (i.e., a voltage drop along the pore axis) have been used to estimate the resultant polarization (due to reorientation) of the intrapore water, and hence to determine the local dielectric behavior within the pore. It is shown that the local dielectric constant of water within a pore is reduced for models formed by parallel alpha-helix bundles, but not by those formed by beta-barrels. This result is discussed in the context of electrostatics calculations of ion permeation through channels, and the effect of the local dielectric of water within a helix bundle pore is illustrated with a simple Poisson-Boltzmann calculation.
离子通道在其跨膜孔内包含延伸的水分子柱。已表明这种孔内水的动力学性质与 bulk 状态的水不同。在先前对两类模型孔（Ala20 α-螺旋的平行束和 Ala10 β-链的反平行桶）的分子动力学模拟中，相对于 bulk 水，观察到孔内水的平移和旋转流动性大幅降低。在存在跨孔静电场（即沿孔轴的电压降）的情况下进行的分子动力学模拟已用于估计孔内水的 resultant 极化（由于重新定向），从而确定孔内的局部介电行为。结果表明，对于由平行α-螺旋束形成的模型，孔内水的局部介电常数降低，但由β-桶形成的模型则不然。在通过通道进行离子渗透的静电计算的背景下讨论了这一结果，并用简单的泊松 - 玻尔兹曼计算说明了螺旋束孔内水的局部介电的影响。
