Faculty of Biochemistry, Biophysics, and Biotechnology, Jagiellonian University, Kraków, Poland.
Małopolska Centre of Biotechnology (MCB), Jagiellonian University, Kraków, Poland.
Sci Adv. 2023 Jan 13;9(2):eadd9688. doi: 10.1126/sciadv.add9688.
Plants use solar energy to power cellular metabolism. The oxidation of plastoquinol and reduction of plastocyanin by cytochrome bf (Cyt bf) is known as one of the key steps of photosynthesis, but the catalytic mechanism in the plastoquinone oxidation site (Q) remains elusive. Here, we describe two high-resolution cryo-EM structures of the spinach Cyt bf homodimer with endogenous plastoquinones and in complex with plastocyanin. Three plastoquinones are visible and line up one after another head to tail near Q in both monomers, indicating the existence of a channel in each monomer. Therefore, quinones appear to flow through Cyt bf in one direction, transiently exposing the redox-active ring of quinone during catalysis. Our work proposes an unprecedented one-way traffic model that explains efficient quinol oxidation during photosynthesis and respiration.
植物利用太阳能为细胞代谢提供动力。质体醌醇的氧化和细胞色素 bf（Cyt bf）还原质体蓝素被认为是光合作用的关键步骤之一，但质醌氧化部位（Q）的催化机制仍不清楚。在这里，我们描述了菠菜 Cyt bf 同源二聚体与内源性质体醌以及与质体蓝素复合物的两个高分辨率冷冻电镜结构。在两个单体中，有三个质体醌可见且一个接一个地从头至尾排列在 Q 附近，表明每个单体中都存在一个通道。因此，在一个方向上看来，质体醌在 Cyt bf 中流动，在催化过程中短暂地暴露出醌的氧化还原活性环。我们的工作提出了一个前所未有的单向交通模型，该模型解释了光合作用和呼吸作用中高效的氢醌氧化。
