Department of Plant Biochemistry, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany.
Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried, Germany.
Nat Plants. 2021 Apr;7(4):524-538. doi: 10.1038/s41477-021-00895-0. Epub 2021 Apr 12.
Biogenesis of photosystem II (PSII), nature's water-splitting catalyst, is assisted by auxiliary proteins that form transient complexes with PSII components to facilitate stepwise assembly events. Using cryo-electron microscopy, we solved the structure of such a PSII assembly intermediate from Thermosynechococcus elongatus at 2.94 Å resolution. It contains three assembly factors (Psb27, Psb28 and Psb34) and provides detailed insights into their molecular function. Binding of Psb28 induces large conformational changes at the PSII acceptor side, which distort the binding pocket of the mobile quinone (Q) and replace the bicarbonate ligand of non-haem iron with glutamate, a structural motif found in reaction centres of non-oxygenic photosynthetic bacteria. These results reveal mechanisms that protect PSII from damage during biogenesis until water splitting is activated. Our structure further demonstrates how the PSII active site is prepared for the incorporation of the MnCaO cluster, which performs the unique water-splitting reaction.
光合作用系统 II（PSII）的生物发生是由辅助蛋白协助的，这些辅助蛋白与 PSII 组件形成瞬时复合物，以促进逐步组装事件。我们使用低温电子显微镜以 2.94Å 的分辨率解决了来自 elongatus 的 PSII 组装中间体的结构。它包含三个组装因子（Psb27、Psb28 和 Psb34），并提供了它们分子功能的详细见解。Psb28 的结合会引起 PSII 受体侧的大构象变化，从而扭曲可移动醌（Q）的结合口袋，并将非血红素铁的碳酸氢盐配体替换为谷氨酸，这种结构基序存在于非氧气光合作用细菌的反应中心中。这些结果揭示了在水分解被激活之前保护 PSII 免受生物发生过程中损伤的机制。我们的结构进一步表明 PSII 活性位点如何为 MnCaO 簇的掺入做好准备，MnCaO 簇执行独特的水分解反应。
