Simakov Nikolay A, Kurnikova Maria G
Chemistry Department, Carnegie Mellon University, 4400 Fifth Ave, Pittsburgh, PA, 15213, USA.
J Membr Biol. 2018 Jun;251(3):393-404. doi: 10.1007/s00232-018-0013-3. Epub 2018 Jan 16.
The dependency of current-voltage characteristics of the α-hemolysin channel on the channel position within the membrane was studied using Poisson-Nernst-Planck theory of ion conductivity with soft repulsion between mobile ions and protein atoms (SP-PNP). The presence of the membrane environment also influences the protonation state of the residues at the boundary of the water-lipid interface. In this work, we predict that Asp and Lys residues at the protein rim change their protonation state upon penetration to the lipid environment. Free energies of protein insertion in the membrane for different penetration depths were estimated using the Poisson-Boltzmann/solvent-accessible surface area (PB/SASA) model. The results show that rectification and reversal potentials are very sensitive to the relative position of channel in the membrane, which in turn contributes to alternative protonation states of lipid-penetrating ionizable groups. The prediction of channel position based on the matching of calculated rectification with experimentally determined rectification is in good agreement with recent neutron reflection experiments. Based on the results, we conclude that α-hemolysin membrane position is determined by a combination of factors and not only by the pattern of the surface hydrophobicity as is typically assumed.
利用离子电导率的泊松 - 能斯特 - 普朗克理论以及移动离子与蛋白质原子之间的软排斥作用（SP - PNP），研究了α - 溶血素通道的电流 - 电压特性对通道在膜内位置的依赖性。膜环境的存在也会影响水 - 脂界面边界处残基的质子化状态。在这项工作中，我们预测蛋白质边缘的天冬氨酸（Asp）和赖氨酸（Lys）残基在渗透到脂质环境时会改变其质子化状态。使用泊松 - 玻尔兹曼/溶剂可及表面积（PB/SASA）模型估算了不同穿透深度下蛋白质插入膜中的自由能。结果表明，整流和反转电位对通道在膜中的相对位置非常敏感，这反过来又导致了脂质穿透性可电离基团的不同质子化状态。基于计算得到的整流与实验测定的整流相匹配来预测通道位置，这与最近的中子反射实验结果高度吻合。基于这些结果，我们得出结论，α - 溶血素在膜中的位置是由多种因素共同决定的，而不仅仅取决于通常所认为的表面疏水性模式。
