Department of Physical Chemistry, University of Pannonia, P.O. Box 158, H-8201 Veszprém, Hungary.
J Chem Phys. 2013 Aug 7;139(5):055103. doi: 10.1063/1.4817205.
We present grand canonical Monte Carlo simulation results for a reduced model of the L-type calcium channel. While charged residues of the protein amino acids in the selectivity filter are treated explicitly, most of the degrees of freedom (including the rest of the protein and the solvent) are represented by their dielectric response, i.e., dielectric continua. The new aspect of this paper is that the dielectric coefficient in the channel is different from that in the baths. The ions entering the channel, thus, cross a dielectric boundary at the entrance of the channel. Simulating this case has been made possible by our recent methodological development [D. Boda, D. Henderson, B. Eisenberg, and D. Gillespie, J. Chem. Phys. 135, 064105 (2011)]. Our main focus is on the effect of solvation energy (represented by the Born energy) on monovalent vs. divalent ion selectivity in the channel. We find no significant change in selectivity by changing the dielectric coefficient in the channel because the larger solvation penalty is counterbalanced by the enhanced Coulomb attraction inside the channel as soon as we use the Born radii (fitted to experimental hydration energies) to compute the solvation penalty from the Born equation.
我们呈现了 L 型钙通道简化模型的巨正则蒙特卡罗模拟结果。虽然蛋白质氨基酸的带电残基在选择性过滤器中被明确处理，但大多数自由度（包括蛋白质的其余部分和溶剂）都由它们的介电响应表示，即介电连续体。本文的新方面是通道中的介电系数与浴中的介电系数不同。进入通道的离子因此在通道入口处穿过介电边界。我们最近的方法学发展[D. Boda、D. Henderson、B. Eisenberg 和 D. Gillespie，J. Chem. Phys. 135, 064105 (2011)] 使得模拟这种情况成为可能。我们的主要关注点是溶剂化能（由 Born 能表示）对通道中单价离子与二价离子选择性的影响。我们发现通过改变通道中的介电系数对选择性没有显著影响，因为一旦我们使用 Born 半径（拟合实验水合能）从 Born 方程计算溶剂化能，更大的溶剂化惩罚就会被通道内增强的库仑吸引力所平衡。
