O<sub>2</sub> evolution and recovery of the water-oxidizing enzyme.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 29593210.
- Also identified by DOI 10.1038/s41467-018-03545-w and PMC identifier 5871790.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
In photosystem II, light-induced water oxidation occurs at the Mn<sub>4</sub>CaO<sub>5</sub> cluster. Here we demonstrate proton releases, dioxygen formation, and substrate water incorporation in response to Mn<sub>4</sub>CaO<sub>5</sub> oxidation in the protein environment, using a quantum mechanical/molecular mechanical approach and molecular dynamics simulations. In S<sub>2</sub>, H<sub>2</sub>O at the W1 site forms a low-barrier H-bond with D1-Asp61. In the S<sub>2</sub>-to-S<sub>3</sub> transition, oxidation of O<sub>W1</sub>H<sup>-</sup> to O<sub>W1</sub><sup>•-</sup>, concerted proton transfer from O<sub>W1</sub>H<sup>-</sup> to D1-Asp61, and binding of a water molecule W<sub>n-W1</sub> at O<sub>W1</sub><sup>•-</sup> are observed. In S<sub>4</sub>, W <sub>n</sub><sub>-W1</sub> facilitates oxo-oxyl radical coupling between O<sub>W1</sub><sup>•-</sup> and corner μ-oxo O4. Deprotonation via D1-Asp61 leads to formation of O<sub>W1</sub>=O4. As O<sub>W1</sub>=O4 moves away from Mn, H<sub>2</sub>O at W539 is incorporated into the vacant O4 site of the O<sub>2</sub>-evolved Mn<sub>4</sub>CaO<sub>4</sub> cluster, forming a μ-oxo bridge (Mn3-O<sub>W539</sub>-Mn4) in an exergonic process. Simultaneously, W<sub>n-W1</sub> is incorporated as W1, recovering the Mn<sub>4</sub>CaO<sub>5</sub> cluster.
Medical subject headings
- Cyanobacteria
- Oxygen
- Photosystem II Protein Complex
- Water