title: Ammonia Binds to the Dangler Manganese of the Photosystem II Oxygen-Evolving Complex.
abstract: High-resolution X-ray structures of photosystem II reveal several potential substrate binding sites at the water-oxidizing/oxygen-evolving 4MnCa cluster. Aspartate-61 of the D1 protein hydrogen bonds with one such water (W1), which is bound to the dangler Mn4A of the oxygen-evolving complex. Comparison of pulse EPR spectra of (14)NH3 and (15)NH3 bound to wild-type Synechocystis PSII and a D1-D61A mutant lacking this hydrogen-bonding interaction demonstrates that ammonia binds as a terminal NH3 at this dangler Mn4A site and not as a partially deprotonated bridge between two metal centers. The implications of this finding on identifying the binding sites of the substrate and the subsequent mechanism of dioxygen formation are discussed.
authors.affiliation: †Department of Chemistry, University of California, Davis, Davis, California 95616, United States.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Oyala
authors.affiliation: †Department of Chemistry, University of California, Davis, Davis, California 95616, United States.
authors.forename: Troy A
authors.initials: TA
authors.lastname: Stich
authors.affiliation: ‡Department of Biochemistry, University of California, Riverside, Riverside, California 92521, United States.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Debus
authors.affiliation: †Department of Chemistry, University of California, Davis, Davis, California 95616, United States.
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D006860:Hydrogen Bonding; D008345:Manganese / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D046939:Synechocystis / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D008345:Manganese; D000641:Ammonia