Nieto-Frausto J, Kleutsch B
Department of Biology, University of Konstanz, Germany.
Biochim Biophys Acta. 1992 Oct 19;1111(1):81-92. doi: 10.1016/0005-2736(92)90277-s.
Following the theory 'Fluctuations of barrier structure in ionic channels' (Läuger, P., Stephan, W. and Frehland, E. (1980) Biochim. Biophys. Acta 602, 167-180), we constructed a model of a channels with several conformational states. The origin of these conformational states and the source for the transitions from one to the other are given explicitly for the presented model. In this work the effect of multiple conformational states on the ion transport process is analyzed. We considered a channel protein with two main barriers and one binding site. The site is surrounded by dipolar groups. The dipole moment of these groups can be reoriented by thermal activity and also by electrical interaction with the transported ions. Differently polarized states generate different activation energy barriers for the ions. The set of conformational states of the channel is constituted by all the possible polarized states of the binding site. Using the rate-theory analysis of ion transport (Glässtone, S., Laider, K.J. and Eyring, H. (1941) The theory of rate processes, McGraw-Hill, New York), the possible coupling between ion flux and the channel conformational transitions has been incorporated into the model by considering the dependence of the rate constants on the heights of the energy barriers. The resulting multistate kinetic equations have been solved numerically. It was shown that the simple saturation characteristic of the flux-concentration curve was obtained. For certain values of the model parameters, the channel shows a strongly different conductance for anions compared to cations. In fact, the model contains an interesting mechanism that exhibits selectivity with respect to the charge of the ions.
遵循“离子通道中屏障结构的波动”理论（Läuger, P., Stephan, W. 和 Frehland, E. (1980) Biochim. Biophys. Acta 602, 167 - 180），我们构建了一个具有多个构象状态的通道模型。对于所呈现的模型，明确给出了这些构象状态的起源以及从一种状态转变为另一种状态的来源。在这项工作中，分析了多个构象状态对离子传输过程的影响。我们考虑了一种具有两个主要屏障和一个结合位点的通道蛋白。该位点被偶极基团包围。这些基团的偶极矩可通过热活动以及与被运输离子的电相互作用而重新定向。不同的极化状态为离子产生不同的活化能屏障。通道的构象状态集由结合位点的所有可能极化状态组成。利用离子传输的速率理论分析（Glässtone, S., Laider, K.J. 和 Eyring, H. (1941) The theory of rate processes, McGraw - Hill, New York），通过考虑速率常数对能垒高度的依赖性，将离子通量与通道构象转变之间可能的耦合纳入模型。所得多态动力学方程已通过数值方法求解。结果表明，获得了通量 - 浓度曲线的简单饱和特征。对于模型参数的某些值，该通道对阴离子的电导与对阳离子的电导有很大不同。实际上，该模型包含一种有趣的机制，表现出对离子电荷的选择性。
