Electron transfer and protein dynamics in the photosynthetic reaction center.
Electron transfer and protein dynamics in the photosynthetic reaction center.
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光合作用反应中心的电子转移和蛋白质动力学。
DOI：
10.1016/s0006-3495(98)77964-0
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发表时间：
1998
影响因子：
3.4
通讯作者：
Nienhaus,GU
中科院分区：
文献类型：
--
作者：
McMahon,BH;Müller,JD;Wraight,CA;Nienhaus,GU
本文测定了球形红细菌（Rhodobacter sphaeroides）的伯醌（QA）到反应中心（RC）复合物的特殊电子对（P）的电子转移动力学，它是温度（5- 300 K）、光照条件（110、160、180和280 K）和升温速率（1.3和13 mK/s）的函数。用量子力学ET模型（费米黄金法则和自旋玻色子模型）解释非指数动力学，其中蛋白质系综、弛豫和波动的异质性被投射到一个单一的坐标中，该坐标单调地弛豫，并且对ET引起的所有类型的弛豫敏感。我们的分析表明，响应于ET发生的结构变化使施主态和受主态之间的自由能隙降低了120 meV，并使施主态和受主态之间的电子耦合从2.7×10−4cm− 1降低到1.8×10−4cm−1。在低温下，构象变化可以减慢或完全停止，使我们能够监测退火时间尺度（103- 104秒）以及ET时间尺度（100毫秒）上的弛豫。弛豫发生在四个广泛的构象亚态层中，平均表观阿耳忒弥斯活化能分别为17、50、78和110 kJ/mol，指前因子分别为1013、1015、1021和1025 s −1。参数化提供了一个预测的时间过程中的松弛在所有温度下。在300 K时，预计弛豫发生在1 ps到1 ms之间，而在较低的温度下，预计弛豫时间的分布甚至更广。ET速率对温度和蛋白质构象的弱依赖性，以及用单个构象坐标建模异质性和动态的可能性，使RC成为探测蛋白质构象变化动态的有用模型系统。
We have measured the kinetics of electron transfer (ET) from the primary quinone (QA) to the special pair (P) of the reaction center (RC) complex fromRhodobacter sphaeroidesas a function of temperature (5–300K), illumination protocol (cooled in the dark and under illumination from 110, 160, 180, and 280K), and warming rate (1.3 and 13mK/s). The nonexponential kinetics are interpreted with a quantum-mechanical ET model (Fermi's golden rule and the spin-boson model), in which heterogeneity of the protein ensemble, relaxations, and fluctuations are cast into a single coordinate that relaxes monotonically and is sensitive to all types of relaxations caused by ET. Our analysis shows that the structural changes that occur in response to ET decrease the free energy gap between donor and acceptor states by 120meV and decrease the electronic coupling between donor and acceptor states from 2.7×10−4cm−1to 1.8×10−4cm−1. At cryogenic temperatures, conformational changes can be slowed or completely arrested, allowing us to monitor relaxations on the annealing time scale (∼103–104s) as well as the time scale of ET (∼100ms). The relaxations occur within four broad tiers of conformational substates with average apparent Arrhenius activation enthalpies of 17, 50, 78, and 110kJ/mol and preexponential factors of 1013, 1015, 1021, and 1025s−1, respectively. The parameterization provides a prediction of the time course of relaxations at all temperatures. At 300K, relaxations are expected to occur from 1ps to 1ms, whereas at lower temperatures, even broader distributions of relaxation times are expected. The weak dependence of the ET rate on both temperature and protein conformation, together with the possibility of modeling heterogeneity and dynamics with a single conformational coordinate, make RC a useful model system for probing the dynamics of conformational changes in proteins.