The project's overall goal is to elucidate the molecular mechanism of photosynthetic oxygen evolution. This process takes place in Photosystem II and is the source of nearly all atmospheric oxygen. The catalytic site contains a (Mn)4-Ca cluster that interacts with a redox-active tyrosine residue known as YZ. The YZ( radical extracts electrons and protons from the (Mn)4-Ca cluster, leading to the oxidation of water and the release of oxygen. The project's primary goal is to characterize the structural changes that accompany the oxidation of the (Mn)4-Ca cluster during the individual steps of the catalytic cycle. This information is crucial to understanding the mechanism of oxygen evolution and will complement the information that is being obtained from X-ray crystallography. The primary investigative tool will be Fourier transform infrared (FTIR) difference spectroscopy. The project's specific aims are: (1) To identify the specific Mn ion(s) that undergo oxidation during the individual steps in the catalytic cycle; (2) To identify the amino acid residues that serve as the critical bases that facilitate the proton-coupled oxidations of the (Mn)4-Ca cluster during the catalytic cycle; (3) To characterize the final intermediate of the oxygen formation reaction, an intermediate that can be trapped by increasing the ambient oxygen pressure; (4) To employ modified bacterial reaction centers as model systems for characterizing changes that occur in the environment of a ligated metal ion in response to its oxidation; (5) To employ near-infrared excitation resonance Raman spectroscopy as an additional tool for characterizing the environment of the (Mn)4-Ca cluster. In addition to providing fundamental insight into the mechanism of photosynthetic oxygen evolution, the project will provide insight into the mechanisms of metalloradical enzymes and enzymes whose mechanisms involve proton-coupled electron transfer (PCET) reactions. Such enzymes catalyze biological energy transduction in mitochondria. Elucidating the catalytic mechanisms of these enzymes is essential for understanding the molecular basis of mitochondrial diseases and aging. Photosystem II is both an excellent example of a metalloradical enzyme and a unique laboratory for studying proton-coupled electron transfer reactions. Its advantages derive from its ability to be stepped through its catalytic cycle with single flashes of light, thereby facilitating kinetic studies of reaction cycle intermediates with high time resolution. ? ?

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Macromolecular Structure and Function A Study Section (MSFA)
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Fabian, Miles
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University of California Riverside
Schools of Earth Sciences/Natur
United States
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Service, Rachel J; Yano, Junko; McConnell, Iain et al. (2011) Participation of glutamate-354 of the CP43 polypeptide in the ligation of manganese and the binding of substrate water in photosystem II. Biochemistry 50:63-81
Yano, Junko; Walker, Lee M; Strickler, Melodie A et al. (2011) Altered structure of the Mn4Ca cluster in the oxygen-evolving complex of photosystem II by a histidine ligand mutation. J Biol Chem 286:9257-67
Stich, Troy A; Yeagle, Gregory J; Service, Rachel J et al. (2011) Ligation of D1-His332 and D1-Asp170 to the manganese cluster of photosystem II from Synechocystis assessed by multifrequency pulse EPR spectroscopy. Biochemistry 50:7390-404
Stull, Jamie A; Stich, Troy A; Service, Rachel J et al. (2010) 13C ENDOR reveals that the D1 polypeptide C-terminus is directly bound to Mn in the photosystem II oxygen evolving complex. J Am Chem Soc 132:446-7
Service, Rachel J; Hillier, Warwick; Debus, Richard J (2010) Evidence from FTIR difference spectroscopy of an extensive network of hydrogen bonds near the oxygen-evolving Mn(4)Ca cluster of photosystem II involving D1-Glu65, D2-Glu312, and D1-Glu329. Biochemistry 49:6655-69
Strickler, Melodie A; Hwang, Hong Jin; Burnap, Robert L et al. (2008) Glutamate-354 of the CP43 polypeptide interacts with the oxygen-evolving Mn4Ca cluster of photosystem II: a preliminary characterization of the Glu354Gln mutant. Philos Trans R Soc Lond B Biol Sci 363:1179-87;discussion 1187-8
Debus, Richard J (2008) Protein Ligation of the Photosynthetic Oxygen-Evolving Center. Coord Chem Rev 252:244-258
Strickler, Melodie A; Walker, Lee M; Hillier, Warwick et al. (2007) No evidence from FTIR difference spectroscopy that aspartate-342 of the D1 polypeptide ligates a Mn ion that undergoes oxidation during the S0 to S1, S1 to S2, or S2 to S3 transitions in photosystem II. Biochemistry 46:3151-60
Hwang, Hong Jin; McLain, Aaron; Debus, Richard J et al. (2007) Photoassembly of the manganese cluster in mutants perturbed in the high affinity Mn-binding site of the H2O-oxidation complex of photosystem II. Biochemistry 46:13648-57
Hwang, Hong Jin; Dilbeck, Preston; Debus, Richard J et al. (2007) Mutation of arginine 357 of the CP43 protein of photosystem II severely impairs the catalytic S-state cycle of the H2O oxidation complex. Biochemistry 46:11987-97