Structural Effects of Ammonia Binding to the Mn4CaO5 Cluster of Photosystem II

David A Marchiori; Paul H Oyala; Richard J Debus; Troy A Stich; R David Britt

doi:10.1021/acs.jpcb.7b11101

Structural Effects of Ammonia Binding to the Mn₄CaO₅ Cluster of Photosystem II

J Phys Chem B. 2018 Feb 8;122(5):1588-1599. doi: 10.1021/acs.jpcb.7b11101. Epub 2018 Jan 24.

Authors

David A Marchiori¹, Paul H Oyala^{1

2}, Richard J Debus³, Troy A Stich¹, R David Britt¹

Affiliations

¹ Department of Chemistry, University of California, Davis , Davis, California 95616, United States.
² Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
³ Department of Biochemistry, University of California, Riverside , Riverside, California 92521, United States.

PMID: 29303579
DOI: 10.1021/acs.jpcb.7b11101

Abstract

The Mn₄CaO₅ oxygen-evolving complex (OEC) of photosystem II catalyzes the light-driven oxidation of two substrate waters to molecular oxygen. ELDOR-detected NMR along with computational studies indicated that ammonia, a substrate analogue, binds as a terminal ligand to the Mn4A ion trans to the O5 μ₄ oxido bridge. Results from electron spin echo envelope modulation (ESEEM) spectroscopy confirmed this and showed that ammonia hydrogen bonds to the carboxylate side chain of D1-Asp61. Here we further probe the environment of OEC with an emphasis on the proximity of exchangeable protons, comparing ammonia-bound and unbound forms. Our ESEEM and electron nuclear double resonance (ENDOR) results indicate that ammonia substitutes for the W1 terminal water ligand without significantly altering the electronic structure of the OEC.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.