期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 144, 期 16, 页码 7171-7180出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.1c13041
关键词
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资金
- Knut and Alice Wallenberg Foundation
- Royal Society Wolfson Research Merit Award
- Biotechnology and Biological Sciences Research Council (BBSRC) [BB/K002627/1, BB/R00921X, SNIC 2021/6-143]
- Swedish Research Council [2016-07213]
- TU Munich-Imperial College Collaboration Fund
- TUM Global Incentive Fund
- Excellence Strategy of the Federal Government
- Lander
- German Research Foundation (DFG) via the Collaborative Research Centre [SFB1078]
Photosystem II (PSII) catalyzes light-driven water oxidization and we found that it uses a redox-triggered proton transfer mechanism for water oxidation. This mechanism resembles functional motifs in other enzymes involved in biological energy conversion, modulating the catalytic barriers for water oxidation.
Photosystem II (PSII) catalyzes light-driven water oxidization, releasing O-2 into the atmosphere and transferring the electrons for the synthesis of biomass. However, despite decades of structural and functional studies, the water oxidation mechanism of PSII has remained puzzling and a major challenge for modern chemical research. Here, we show that PSII catalyzes redox-triggered proton transfer between its oxygen-evolving Mn4O5Ca cluster and a nearby cluster of conserved buried ion-pairs, which are connected to the bulk solvent via a proton pathway. By using multi-scale quantum and classical simulations, we find that oxidation of a redox-active Tyr(z) (Tyr161) lowers the reaction barrier for the water-mediated proton transfer from a Ca2+-bound water molecule (W3) to Asp61 via conformational changes in a nearby ion-pair (Asp61/Lys317). Deprotonation of this W3 substrate water triggers its migration toward Mn1 to a position identified in recent X-ray free-electron laser (XFEL) experiments [Ibrahim et al. Proc. Natl. Acad. Sci. USA 2020, 117, 12,624-12,635]. Further oxidation of the Mn4O5Ca cluster lowers the proton transfer barrier through the water ligand sphere of the Mn4O5Ca cluster to Asp61 via a similar ion-pair dissociation process, while the resulting Mn-bound oxo/oxyl species leads to O-2 formation by a radical coupling mechanism. The proposed redox-coupled protonation mechanism shows a striking resemblance to functional motifs in other enzymes involved in biological energy conversion, with an interplay between hydration changes, ion-pair dynamics, and electric fields that modulate the catalytic barriers.
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