Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 7, 9747 AG, Groningen, The Netherlands.
Department of Physics and Astronomy, Faculteit der Exacte Wetenschappen, Vrije Universiteit , De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
J Phys Chem B. 2017 Apr 20;121(15):3237-3249. doi: 10.1021/acs.jpcb.6b06865. Epub 2016 Sep 28.
Photosystem II (PSII) is one of the key protein complexes in photosynthesis. We introduce a coarse grained model of PSII and present the analysis of 60 μs molecular dynamics simulations of PSII in both monomeric and dimeric form, embedded in a thylakoid membrane model that reflects its native lipid composition. We describe in detail the setup of the protein complex and the many natural cofactors and characterize their mobility. Overall we find that the protein subunits and cofactors are more flexible toward the periphery of the complex as well as near the PLQ exchange cavity and at the dimer interface. Of all cofactors, β-carotenes show the highest mobility. Some of the β-carotenes diffuse in and out of the protein complex via the thylakoid membrane. In contrast with the PSII dimer, the monomeric form adopts a tilted conformation in the membrane, with strong interactions between the soluble PsbO subunit and the glycolipid headgroups. Interestingly, the tilted conformation causes buckling of the membrane. Together, our results provide an unprecedented view of PSII dynamics on a microsecond time scale. Our data may be used as basis for the interpretation of experimental data as well as for theoretical models describing exciton energy transfer.
光系统 II（PSII）是光合作用中的关键蛋白复合物之一。我们介绍了 PSII 的粗粒模型，并对单体和二聚体形式的 PSII 进行了 60 μs 分子动力学模拟分析，这些模拟是在反映其天然脂质组成的类囊体膜模型中进行的。我们详细描述了蛋白质复合物的设置以及许多天然辅助因子，并对它们的流动性进行了表征。总的来说，我们发现蛋白质亚基和辅助因子在复合物的外围以及靠近 PLQ 交换腔和二聚体界面处更加灵活。在所有的辅助因子中，β-胡萝卜素的流动性最高。一些β-胡萝卜素通过类囊体膜在蛋白质复合物内外扩散。与 PSII 二聚体相比，单体形式在膜中采用倾斜构象，可溶性 PsbO 亚基与糖脂头基之间存在强烈相互作用。有趣的是，倾斜构象导致膜的弯曲。总之，我们的结果提供了 PSII 在微秒时间尺度上动态的前所未有的视图。我们的数据可以作为解释实验数据以及描述激子能量转移的理论模型的基础。
