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Five-coordinate Mn-IV intermediate in the activation of nature's water splitting cofactor
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- Chrysina, Maria (author)
- Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany
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- Heyno, Eiri (author)
- Ruhr Univ Bochum, Fac Biol & Biotechnol, Plant Biochem, D-44780 Bochum, Germany
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- Kutin, Yury (author)
- Max Planck Inst Chem Energiekonvers, D-45470 Mulheim, Germany;TU Dortmund Univ, Dept Chem & Chem Biol, D-44227 Dortmund, Germany
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- 2019-08-07
- 2019
- English.
- In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 116:34, s. 16841-16846
- Journal article (peer-reviewed)
Abstract
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- Nature's water splitting cofactor passes through a series of catalytic intermediates (S-0-S-4) before O-O bond formation and O-2 release. In the second last transition (S-2 to S-3) cofactor oxidation is coupled to water molecule binding to Mn1. It is this activated, water-enriched all Mn-IV form of the cofactor that goes on to form the O-O bond, after the next light-induced oxidation to S-4. How cofactor activation proceeds remains an open question. Here, we report a so far not described intermediate (S-3') in which cofactor oxidation has occurred without water insertion. This intermediate can be trapped in a significant fraction of centers (> 50%) in (i) chemical-modified cofactors in which Ca2+ is exchanged with Sr2+; the Mn4O5Sr cofactor remains active, but the S-2-S-3 and S-3-S-0 transitions are slower than for the Mn4O5Ca cofactor; and (ii) upon addition of 3% vol/vol methanol; methanol is thought to act as a substrate water analog. The S-3' electron paramagnetic resonance (EPR) signal is significantly broader than the untreated S-3 signal (2.5 T vs. 1.5 T), indicating the cofactor still contains a 5-coordinate Mn ion, as seen in the preceding S-2 state. Magnetic double resonance data extend these findings revealing the electronic connectivity of the S-3' cofactor is similar to the high spin form of the preceding S-2 state, which contains a cuboidal Mn3O4Ca unit tethered to an external, 5-coordinate Mn ion (Mn-4). These results demonstrate that cofactor oxidation regulates water molecule insertion via binding to Mn-4. The interaction of ammonia with the cofactor is also discussed.
Subject headings
- NATURVETENSKAP -- Kemi -- Organisk kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences -- Organic Chemistry (hsv//eng)
Keyword
- Photosystem II
- WOC/OEC
- EPR
- EDNMR
- methanol
Publication and Content Type
- ref (subject category)
- art (subject category)
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- Chrysina, Maria
- Heyno, Eiri
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