Department of Chemistry and Chemical Biology, The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, New York, 12180, USA.
Department of Chemistry, Yale University, New Haven, Connecticut, 06520, USA.
Faraday Discuss. 2022 May 18;234(0):195-213. doi: 10.1039/d1fd00094b.
The solar water-splitting protein complex, photosystem II (PSII), catalyzes one of the most energetically demanding reactions in nature by using light energy to drive a catalyst capable of oxidizing water. The water oxidation reaction is catalyzed at the MnCa-oxo cluster in the oxygen-evolving complex (OEC), which cycles through five light-driven S-state intermediates (S-S). A detailed mechanism of the reaction remains elusive as it requires knowledge of the delivery and binding of substrate water in the higher S-state intermediates. In this study, we use two-dimensional (2D) hyperfine sublevel correlation spectroscopy, in conjunction with quantum mechanics/molecular mechanics (QM/MM) and density functional theory (DFT), to probe the binding of the substrate analog, methanol, in the S state of the D1-N87A variant of PSII from sp. PCC 6803. The results indicate that the size and specificity of the "narrow" channel is altered in D1-N87A PSII, allowing for the binding of deprotonated C-labeled methanol at the Mn4(IV) ion of the catalytic cluster in the S state. This has important implications on the mechanistic models for water oxidation in PSII.
太阳能水分解蛋白复合物，光系统 II（PSII），利用光能驱动能够氧化水的催化剂，催化自然界中能量需求最高的反应之一。水氧化反应在产氧复合物（OEC）中的 MnCa-氧合簇中催化，该复合物通过五个光驱动的 S 态中间体（S-S）循环。由于需要了解在更高 S 态中间体中底物水的传递和结合，因此该反应的详细机制仍然难以捉摸。在这项研究中，我们使用二维（2D）超精细亚层相关光谱学，结合量子力学/分子力学（QM/MM）和密度泛函理论（DFT），在 sp 中探测底物类似物甲醇在 PSII 的 D1-N87A 变体的 S 态中的结合。. PCC 6803。结果表明，D1-N87A PSII 中“窄”通道的大小和特异性发生了改变，允许在 S 态下在催化簇的 Mn4(IV)离子上结合去质子化的 C 标记甲醇。这对 PSII 中水氧化的机制模型具有重要意义。
