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Assessment of the manganese cluster's oxidation state via photoactivation of photosystem II microcrystals
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.ORCID iD: 0000-0001-5732-1524
Humboldt Univ, Inst Biol, D-10115 Berlin, Germany.
Umea Univ, Chem Biol Ctr, Dept Chem, S-90187 Umea, Sweden.ORCID iD: 0000-0002-5174-083X
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.ORCID iD: 0000-0002-6218-3039
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2020 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 117, no 1, p. 141-145Article in journal (Refereed) Published
Abstract [en]

Knowledge of the manganese oxidation states of the oxygenevolving Mn4CaO5 cluster in photosystem II (PSII) is crucial toward understanding the mechanism of biological water oxidation. There is a 4 decade long debate on this topic that historically originates from the observation of a multiline electron paramagnetic resonance (EPR) signal with effective total spin of S = 1/2 in the singly oxidized S-2 state of this cluster. This signal implies an overall oxidation state of either Mn(III)(3)Mn(IV) or Mn(III)Mn(IV)(3) for the S-2 state. These 2 competing assignments are commonly known as "low oxidation (LO)" and "high oxidation (HO)" models of the Mn4CaO5 cluster. Recent advanced EPR and Mn K-edge X-ray spectroscopy studies converge upon the HO model. However, doubts about these assignments have been voiced, fueled especially by studies counting the number of flash-driven electron removals required for the assembly of an active Mn4CaO5 cluster starting from Mn(II) and Mnfree PSII. This process, known as photoactivation, appeared to support the LO model since the first oxygen is reported to evolve already after 7 flashes. In this study, we improved the quantum yield and sensitivity of the photoactivation experiment by employing PSII microcrystals that retained all protein subunits after complete manganese removal and by oxygen detection via a custom built thin-layer cell connected to a membrane inlet mass spectrometer. We demonstrate that 9 flashes by a nanosecond laser are required for the production of the first oxygen, which proves that the HO model provides the correct description of the Mn4CaO5 cluster's oxidation states.

Place, publisher, year, edition, pages
NATL ACAD SCIENCES , 2020. Vol. 117, no 1, p. 141-145
Keywords [en]
photosynthesis, oxygen evolving cluster, photoassembly, manganese oxidation state, mechanism of water oxidation
National Category
Biophysics
Identifiers
URN: urn:nbn:se:uu:diva-403248DOI: 10.1073/pnas.1915879117ISI: 000506001200027PubMedID: 31848244OAI: oai:DiVA.org:uu-403248DiVA, id: diva2:1388998
Funder
Swedish Research Council, 2016-05183German Research Foundation (DFG), EXC 2008/1 - 390540038Available from: 2020-01-28 Created: 2020-01-28 Last updated: 2020-01-28Bibliographically approved

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Cheah, Mun HonMamedov, FikretMessinger, Johannes

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