Ammonia Binding in the Second Coordination Sphere of the Oxygen-Evolving Complex of Photosystem II

David J. Vinyard, Mikhail Askerka, Richard J. Debus, Victor S. Batista, Gary W Brudvig

Research output: Contribution to journalArticle

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Abstract

Ammonia binds to two sites in the oxygen-evolving complex (OEC) of Photosystem II (PSII). The first is as a terminal ligand to Mn in the S2 state, and the second is at a site outside the OEC that is competitive with chloride. Binding of ammonia in this latter secondary site results in the S2 state S = 5/2 spin isomer being favored over the S = 1/2 spin isomer. Using electron paramagnetic resonance spectroscopy, we find that ammonia binds to the secondary site in wild-type Synechocystis sp. PCC 6803 PSII, but not in D2-K317A mutated PSII that does not bind chloride. By combining these results with quantum mechanics/molecular mechanics calculations, we propose that ammonia binds in the secondary site in competition with D1-D61 as a hydrogen bond acceptor to the OEC terminal water ligand, W1. Implications for the mechanism of ammonia binding via its primary site directly to Mn4 in the OEC are discussed.

Original languageEnglish
Pages (from-to)4432-4436
Number of pages5
JournalBiochemistry
Volume55
Issue number31
DOIs
Publication statusPublished - Aug 9 2016

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Photosystem II Protein Complex
Ammonia
Oxygen
Mechanics
Isomers
Chlorides
Ligands
Synechocystis
Molecular mechanics
Quantum theory
Electron Spin Resonance Spectroscopy
Paramagnetic resonance
Hydrogen
Spectrum Analysis
Hydrogen bonds
Spectroscopy
Water

ASJC Scopus subject areas

  • Biochemistry
  • Medicine(all)

Cite this

Ammonia Binding in the Second Coordination Sphere of the Oxygen-Evolving Complex of Photosystem II. / Vinyard, David J.; Askerka, Mikhail; Debus, Richard J.; Batista, Victor S.; Brudvig, Gary W.

In: Biochemistry, Vol. 55, No. 31, 09.08.2016, p. 4432-4436.

Research output: Contribution to journalArticle

Vinyard, David J. ; Askerka, Mikhail ; Debus, Richard J. ; Batista, Victor S. ; Brudvig, Gary W. / Ammonia Binding in the Second Coordination Sphere of the Oxygen-Evolving Complex of Photosystem II. In: Biochemistry. 2016 ; Vol. 55, No. 31. pp. 4432-4436.
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