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          Institute: MPI für bioanorganische Chemie     Collection: MPI für bioanorganische Chemie     Display Documents

ID: 682099.0, MPI für bioanorganische Chemie / MPI für bioanorganische Chemie
Ammonia binding to the oxygen-evolving complex of photosystem II identifies the solvent-exchangeable oxygen bridge (mu-oxo) of the manganese tetramer
Authors:Perez-Navarro, Montserrat; Ames, William M.; Nilsson, Hakan; Lohmiller, Thomas; Pantazis, Dimitrios A.; Rapatskiy, Leonid; Nowaczyk, Marc M.; Neese, Frank; Boussac, Alain; Messinger, Johannes; Lubitz, Wolfgang; Cox, Nicholas
Date of Publication (YYYY-MM-DD):2013
Title of Journal:Proceedings of the National Academy of Sciences of the United States of America
Journal Abbrev.:Proc. Natl. Acad. Sci. U. S. A.
Start Page:15561
End Page:15566
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:The assignment of the two substrate water sites of the tetramanganese penta-oxygen calcium (Mn4O5Ca) cluster of photosystem II is essential for the elucidation of the mechanism of biological O-O bond formation and the subsequent design of bio-inspired water-splitting catalysts. We recently demonstrated using pulsed EPR spectroscopy that one of the five oxygen bridges (mu-oxo) exchanges unusually rapidly with bulk water and is thus a likely candidate for one of the substrates. Ammonia, a water analog, was previously shown to bind to the Mn4O5Ca cluster, potentially displacing a water/substrate ligand [Britt RD, et al. (1989) J Am Chem Soc 111(10):3522-3532]. Here we show by a combination of EPR and time-resolved membrane inlet mass spectrometry that the binding of ammonia perturbs the exchangeable mu-oxo bridge without drastically altering the binding/exchange kinetics of the two substrates. In combination with broken-symmetry density functional theory, our results show that (i) the exchangable mu-oxo bridge is O5 {using the labeling of the current crystal structure [Umena Y, et al. (2011) Nature 473(7345):55-60]}; (ii) ammonia displaces a water ligand to the outer manganese (Mn-A4-W1); and (iii) as W1 is trans to O5, ammonia binding elongates the Mn-A4-O5 bond, leading to the perturbation of the mu-oxo bridge resonance and to a small change in the water exchange rates. These experimental results support O-O bond formation between O5 and possibly an oxyl radical as proposed by Siegbahn and exclude W1 as the second substrate water.
Free Keywords:PSII; OEC; water oxidizing complex; water-oxidation; Mn cluster
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für bioanorganische Chemie
External Affiliations:Nilsson, H.; Messinger, J.; Umea Univ, Chem Biol Ctr, Dept Chem, S-90187 Umea, Sweden.
Nowaczyk, M.M.; Ruhr Univ Bochum, D-44780 Bochum, Germany.
Boussac, A.; CEA Saclay, CNRS, iBiTec S, UMR 8221, F-91191 Gif Sur Yvette, France.
Identifiers:ISI:000324765100024 [ID No:1]
ISSN:0027-8424 [ID No:2]
DOI:10.1073/pnas.1304334110 [ID No:3]
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