Weak temperature dependence of P (+) H A (-) recombination in mutant Rhodobacter sphaeroides reaction centers.
Weak temperature dependence of P (+) H A (-) recombination in mutant Rhodobacter sphaeroides reaction centers.
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DOI：
10.1007/s11120-016-0239-9
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发表时间：
2016-06
影响因子：
3.7
通讯作者：
Brettel K
中科院分区：
文献类型：
--
作者：
Gibasiewicz K;Białek R;Pajzderska M;Karolczak J;Burdziński G;Jones MR;Brettel K
与野生型球形红细菌反应中心的研究结果相反，双指数P+HA− → PHA电荷重组在78和298 K之间的温度下，在三个变体中，在初级电子受体附近交换单个氨基酸，显示出弱依赖性。这些突变的反应中心具有不同的整体动力学电荷复合，跨越平均寿命从~2到~20 ns。尽管存在这些差异，以前应用于野生型反应中心的蛋白质弛豫模型被成功地用于将观察到的动力学与状态P+HA-相对于P+BA-的自由能水平的时间演化联系起来。我们的结论是，观察到的电荷重组的动力学变化，连同其弱的温度依赖性，是由一个特定的突变复合体中的点突变在不同程度上影响的因素的组合。这些措施如下：（1）状态P+BA-和P+HA-之间的初始自由能隙，（2）P+BA-→ PBA电荷重组的固有速率，以及（3）响应于电荷分离态出现的蛋白质弛豫速率。在突变体中，P+HA−快速重组（ELL），大多数重组发生在非松弛蛋白中，其中P+BA−和P+HA−几乎是等能的。相反，在P+HA−重组相对缓慢的突变体（GML）中，大部分重组发生在松弛蛋白中，其中P+HA−的能量比P+HA−低得多。ELL反应中心和YLH突变体中的弱温度依赖性以两种方式建模：（1）通过假设未松弛蛋白质中的初始P+BA-和P+HA-状态是等能的，而在蛋白质松弛之后这些状态之间的最终自由能隙是大的（~250 meV或更高），与温度无关;（2）假设P+BA−和P+HA−之间的初始和最终自由能隙是中等的，并且与温度有关。在GML突变体的情况下，可以得出结论，P+BA−和P+HA−之间的自由能隙在任何时候都很大。本文的在线版本（doi：10.1007/s11120-016-0239-9）包含补充材料，可供授权用户使用。
In contrast with findings on the wild-type Rhodobacter sphaeroides reaction center, biexponential P+HA− → PHA charge recombination is shown to be weakly dependent on temperature between 78 and 298 K in three variants with single amino acids exchanged in the vicinity of primary electron acceptors. These mutated reaction centers have diverse overall kinetics of charge recombination, spanning an average lifetime from ~2 to ~20 ns. Despite these differences a protein relaxation model applied previously to wild-type reaction centers was successfully used to relate the observed kinetics to the temporal evolution of the free energy level of the state P+HA− relative to P+BA−. We conclude that the observed variety in the kinetics of charge recombination, together with their weak temperature dependence, is caused by a combination of factors that are each affected to a different extent by the point mutations in a particular mutant complex. These are as follows: (1) the initial free energy gap between the states P+BA− and P+HA−, (2) the intrinsic rate of P+BA− → PBA charge recombination, and (3) the rate of protein relaxation in response to the appearance of the charge separated states. In the case of a mutant which displays rapid P+HA− recombination (ELL), most of this recombination occurs in an unrelaxed protein in which P+BA− and P+HA− are almost isoenergetic. In contrast, in a mutant in which P+HA− recombination is relatively slow (GML), most of the recombination occurs in a relaxed protein in which P+HA− is much lower in energy than P+HA−. The weak temperature dependence in the ELL reaction center and a YLH mutant was modeled in two ways: (1) by assuming that the initial P+BA− and P+HA− states in an unrelaxed protein are isoenergetic, whereas the final free energy gap between these states following the protein relaxation is large (~250 meV or more), independent of temperature and (2) by assuming that the initial and final free energy gaps between P+BA− and P+HA− are moderate and temperature dependent. In the case of the GML mutant, it was concluded that the free energy gap between P+BA− and P+HA− is large at all times. The online version of this article (doi:10.1007/s11120-016-0239-9) contains supplementary material, which is available to authorized users.