Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kyoto, 606-8502, Japan.
Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8502, Japan.
Photosynth Res. 2022 Sep;153(3):135-156. doi: 10.1007/s11120-022-00921-y. Epub 2022 Jun 13.
Light-driven water oxidation in photosynthesis occurs at the oxygen-evolving center (OEC) of photosystem II (PSII). Chloride ions (Cl) are essential for oxygen evolution by PSII, and two Cl ions have been found to specifically bind near the MnCaO cluster in the OEC. The retention of these Cl ions within the OEC is critically supported by some of the membrane-extrinsic subunits of PSII. The functions of these two Cl ions and the mechanisms of their retention both remain to be fully elucidated. However, intensive studies performed recently have advanced our understanding of the functions of these Cl ions, and PSII structures from various species have been reported, aiding the interpretation of previous findings regarding Cl retention by extrinsic subunits. In this review, we summarize the findings to date on the roles of the two Cl ions bound within the OEC. Additionally, together with a short summary of the functions of PSII membrane-extrinsic subunits, we discuss the mechanisms of Cl retention by these extrinsic subunits.
光合作用中的光驱动水氧化发生在光系统 II（PSII）的氧释放中心（OEC）。氯离子（Cl）对于 PSII 的氧气释放是必不可少的，并且已经发现两个 Cl 离子在 OEC 中的 MnCaO 簇附近特异性结合。OEC 内这些 Cl 离子的保留受到 PSII 的一些膜外亚基的严格支持。这两个 Cl 离子的功能及其保留机制仍有待充分阐明。然而，最近进行的大量研究加深了我们对这些 Cl 离子功能的理解，并且已经报道了来自不同物种的 PSII 结构，有助于解释以前关于外亚基保留 Cl 的发现。在这篇综述中，我们总结了迄今为止关于结合在 OEC 内的两个 Cl 离子的作用的发现。此外，我们简要总结了 PSII 膜外亚基的功能，并讨论了这些外亚基保留 Cl 的机制。
