Physics Department, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
Department of Chemistry - Ångström Laboratory, Molecular Biomimetics, Uppsala University, Lägerhyddsvägen 1, 75120, Uppsala, Sweden.
Nat Commun. 2020 Nov 30;11(1):6110. doi: 10.1038/s41467-020-19852-0.
Water oxidation and concomitant dioxygen formation by the manganese-calcium cluster of oxygenic photosynthesis has shaped the biosphere, atmosphere, and geosphere. It has been hypothesized that at an early stage of evolution, before photosynthetic water oxidation became prominent, light-driven formation of manganese oxides from dissolved Mn(2+) ions may have played a key role in bioenergetics and possibly facilitated early geological manganese deposits. Here we report the biochemical evidence for the ability of photosystems to form extended manganese oxide particles. The photochemical redox processes in spinach photosystem-II particles devoid of the manganese-calcium cluster are tracked by visible-light and X-ray spectroscopy. Oxidation of dissolved manganese ions results in high-valent Mn(III,IV)-oxide nanoparticles of the birnessite type bound to photosystem II, with 50-100 manganese ions per photosystem. Having shown that even today's photosystem II can form birnessite-type oxide particles efficiently, we propose an evolutionary scenario, which involves manganese-oxide production by ancestral photosystems, later followed by down-sizing of protein-bound manganese-oxide nanoparticles to finally yield today's catalyst of photosynthetic water oxidation.
水的氧化和伴随的氧气形成通过放氧光合作用的锰-钙簇已经塑造了生物圈、大气圈和岩石圈。有人假设，在进化的早期阶段，在光合作用水氧化变得突出之前，溶解的 Mn(2+)离子在光驱动下形成锰氧化物可能在生物能量学中发挥了关键作用，并可能促进了早期的地质锰矿床的形成。在这里，我们报告了光合作用系统形成扩展的锰氧化物颗粒的生化证据。通过可见光谱和 X 射线光谱跟踪菠菜光系统 II 颗粒中锰-钙簇缺失时的光化学氧化还原过程。溶解的锰离子的氧化导致与光系统 II 结合的 birnessite 型高价 Mn(III,IV)-氧化物纳米颗粒的形成，每个光系统 II 结合 50-100 个锰离子。我们已经表明，即使是今天的光系统 II 也能有效地形成 birnessite 型氧化物颗粒，因此我们提出了一个进化方案，涉及到祖先光合作用系统产生的氧化锰，然后将蛋白结合的氧化锰纳米颗粒缩小尺寸，最终生成今天光合作用水氧化的催化剂。
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