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Jeoung JH, Rünger S, Haumann M, Neumann B, Klemke F, Davis V, Fischer A, Dau H, Wollenberger U, Dobbek H. Bimetallic Mn, Fe, Co, and Ni Sites in a Four-Helix Bundle Protein: Metal Binding, Structure, and Peroxide Activation. Inorg Chem 2021; 60:17498-17508. [PMID: 34757735 DOI: 10.1021/acs.inorgchem.1c01919] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bimetallic active sites in enzymes catalyze small-molecule conversions that are among the top 10 challenges in chemistry. As different metal cofactors are typically incorporated in varying protein scaffolds, it is demanding to disentangle the individual contributions of the metal and the protein matrix to the activity. Here, we compared the structure, properties, and hydrogen peroxide reactivity of four homobimetallic cofactors (Mn(II)2, Fe(II)2, Co(II)2, Ni(II)2) that were reconstituted into a four-helix bundle protein. Reconstituted proteins were studied in solution and in crystals. All metals bind with high affinity and yield similar cofactor structures. Cofactor variants react with H2O2 but differ in their turnover rates, accumulated oxidation states, and trapped peroxide-bound intermediates. Varying the metal composition thus creates opportunities to tune the reactivity of the bimetallic cofactor and to study and functionalize reactive species.
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Affiliation(s)
- Jae-Hun Jeoung
- Department of Biology, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
| | - Stefan Rünger
- Department of Biology, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
| | - Michael Haumann
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Bettina Neumann
- Institute of Biochemistry and Biology, University of Potsdam, 14476 Potsdam, Germany
| | - Friederike Klemke
- Department of Biology, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
| | - Victoria Davis
- Institute for Inorganic and Analytical Chemistry (IAAC), Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.,Freiburg Material Research Center (FMF), University of Freiburg, 79104 Freiburg, Germany.,Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, 79104 Freiburg, Germany.,Cluster of Excellence livMatS@FIT─Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, 79104 Freiburg, Germany
| | - Anna Fischer
- Institute for Inorganic and Analytical Chemistry (IAAC), Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.,Freiburg Material Research Center (FMF), University of Freiburg, 79104 Freiburg, Germany.,Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, 79104 Freiburg, Germany.,Cluster of Excellence livMatS@FIT─Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, 79104 Freiburg, Germany
| | - Holger Dau
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Ulla Wollenberger
- Institute of Biochemistry and Biology, University of Potsdam, 14476 Potsdam, Germany
| | - Holger Dobbek
- Department of Biology, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
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Abstract
AbstractCyanobacteria and plants carry out oxygenic photosynthesis. They use water to generate the atmospheric oxygen we breathe and carbon dioxide to produce the biomass serving as food, feed, fibre and fuel. This paper scans the emergence of structural and mechanistic understanding of oxygen evolution over the past 50 years. It reviews speculative concepts and the stepped insight provided by novel experimental and theoretical techniques. Driven by sunlight photosystem II oxidizes the catalyst of water oxidation, a hetero-metallic Mn4CaO5(H2O)4 cluster. Mn3Ca are arranged in cubanoid and one Mn dangles out. By accumulation of four oxidizing equivalents before initiating dioxygen formation it matches the four-electron chemistry from water to dioxygen to the one-electron chemistry of the photo-sensitizer. Potentially harmful intermediates are thereby occluded in space and time. Kinetic signatures of the catalytic cluster and its partners in the photo-reaction centre have been resolved, in the frequency domain ranging from acoustic waves via infra-red to X-ray radiation, and in the time domain from nano- to milli-seconds. X-ray structures to a resolution of 1.9 Å are available. Even time resolved X-ray structures have been obtained by clocking the reaction cycle by flashes of light and diffraction with femtosecond X-ray pulses. The terminal reaction cascade from two molecules of water to dioxygen involves the transfer of four electrons, two protons, one dioxygen and one water. A rigorous mechanistic analysis is challenging because of the kinetic enslaving at millisecond duration of six partial reactions (4e−, 1H+, 1O2). For the time being a peroxide-intermediate in the reaction cascade to dioxygen has been in focus, both experimentally and by quantum chemistry. Homo sapiens has relied on burning the products of oxygenic photosynthesis, recent and fossil. Mankind's total energy consumption amounts to almost one-fourth of the global photosynthetic productivity. If the average power consumption equalled one of those nations with the highest consumption per capita it was four times greater and matched the total productivity. It is obvious that biomass should be harvested for food, feed, fibre and platform chemicals rather than for fuel.
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