由氢键减轻的介电各向异性决定了光合反应中心醌对内电荷输运的驱动力。

IF 2.8 2区 化学 Q3 CHEMISTRY, PHYSICAL
Muhammet Erkan Köse, Roshan Khatri, Barry D Dunietz
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引用次数: 0

摘要

在细菌光合反应中心(bRC)和光系统II (PSII)中,电荷传递(CT)发生在仲醌(QB)和仲醌(QA)之间。双重还原形式的QB在质子化后转化为离开结合位点的不稳定的喹啉。尽管两个反应中心(rc)中的醌对具有化学和结构上的相似性,但由于其静电环境、分子构象以及与附近辅因子和蛋白质残基的非键相互作用的不对称性,影响醌对CT的自由能变化差异很大。本研究旨在量化这些因素对醌间CT驱动力的能量贡献,解决与附近单元的关键非键相互作用,并解释RCs之间能量学的差异。为了实现这一目标,我们使用了一个筛选距离分离的混合函数,它正确地解释了极化环境。特别是,介质各向异性是两种rc中CT自由能变化的最大贡献者。确定了醌周围的氢键相互作用,并通过考虑周围环境的有效介电常数来评估它们的稳定性。通过求解自由能贡献,我们确定了影响醌的特定氢键网络,并确定了还原中点电位差。在这两种RCs中,醌似乎与三个蛋白质残基单位形成氢键,其中组氨酸具有最强的键。在考虑正向传递过程时,我们发现对于这两种RCs,阴离子QA与所有附近的蛋白质残基形成氢键,而处于中性状态的不稳定QB似乎将附近的丝氨酸残基排除在这种相互作用之外。计算得到的CT自由能变化与实验结果非常吻合。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Dielectric Anisotropy Mitigated by Hydrogen Bonding Governs the Driving Force of Charge Transport within Quinone Pairs in Photosynthetic Reaction Centers.

In a bacterial photosynthetic reaction center (bRC) and photosystem II (PSII), the charge transport (CT) is between the primary semiquinone (QA) and the secondary quinone (QB). The doubly reduced form of QB is converted upon protonation to a labile quinol that leaves the binding site. Despite the chemical and structural similarities of the quinone pairs in the two reaction centers (RCs), the free energy change affecting the quinone CT differs significantly due to asymmetries in their electrostatic environment, molecular conformation, and nonbonding interactions with nearby cofactors and protein residues. This study aims to quantify the energetic contributions of these factors to the driving force for the CT between the quinones, resolve the key nonbonded interactions with nearby units, and explain differences in the energetics between the RCs. Toward this goal, we use a screened range-separated hybrid functional, which correctly accounts for polarizable environment. In particular, dielectric anisotropy is found to be the largest contributor to the free energy change of CT in both RCs. Hydrogen-bonding interactions around quinones are identified, and their stabilization is evaluated by accounting for the effective dielectric constant of the surrounding environment. By resolving the free energy contributions, we identify the particular hydrogen-bonding networks affecting the quinones and which determine the reduction midpoint potential differences. In both RCs, the quinones appear to form hydrogen bonds with three protein residue units, of which histidines bear the strongest bond. In considering the forward transport process, we find for both RCs that the anionic QA is hydrogen-bonded with all nearby protein residues, while the labile QB in the neutral states appears to exclude the nearby serine residues from such interactions. The calculated free energy change for CT agrees remarkably well with experimental findings.

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来源期刊
The Journal of Physical Chemistry A
The Journal of Physical Chemistry A 化学-物理:原子、分子和化学物理
CiteScore
5.20
自引率
10.30%
发文量
922
审稿时长
1.3 months
期刊介绍: The Journal of Physical Chemistry A is devoted to reporting new and original experimental and theoretical basic research of interest to physical chemists, biophysical chemists, and chemical physicists.
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