| 1. |
- Hoganson, C W, et al.
(författare)
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A hydrogen-atom abstraction model for the function of Y-Z in photosynthetic oxygen evolution
- 1995
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Ingår i: Photosynthesis Research. - 0166-8595. ; 46:1-2, s. 177-184
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Tidskriftsartikel (refereegranskat)abstract
- Recent magnetic-resonance work on Y-Z suggests that this species exhibits considerable motional flexibility in its functional site and that its phenol oxygen is not involved in a well-ordered hydrogen-bond interaction (Tang et al., submitted; Tommos et al., in press). Both of these observations are inconsistent with a simple electron-transfer function for this radical in photosynthetic water oxidation. By considering the roles of catalytically active amino acid radicals in other enzymes and recent data on the water-oxidation process in Photosystem II, we rationalize these observations by suggesting that Y-Z functions to abstract hydrogen atoms from aquo- and hydroxy-bound manganese ions in the (Mn)(4) cluster on each S-state transition. The hydrogen-atom abstraction process may occur either by sequential or concerted kinetic pathways. Within this model, the (Mn)(4)/Y-Z center forms a single catalytic center that comprises the Oxygen Evolving Complex in Photosystem II.
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| 2. |
- Berry, Bruce W., 1974-, et al.
(författare)
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Reversible voltammograms and a Pourbaix diagram for a protein tyrosine radical
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:25, s. 9739-9743
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Tidskriftsartikel (refereegranskat)abstract
- Reversible voltammograms and a voltammetry half-wave potential versus solution pH diagram are described for a protein tyrosine radical. This work required a de novo designed tyrosine-radical protein displaying a unique combination of structural and electrochemical properties. The alpha Y-3 protein is structurally stable across a broad pH range. The redox-active tyrosine Y32 resides in a desolvated and well-structured environment. Y32 gives rise to reversible square-wave and differential pulse voltammograms at alkaline pH. The formal potential of the Y32-O-center dot/Y32-OH redox couple is determined to 918 +/- 2 mV versus the normal hydrogen electrode at pH 8.40 +/- 0.01. The observation that Y32 gives rise to fully reversible voltammograms translates into an estimated lifetime of >= 30 ms for the Y32-O-center dot state. This illustrates the range of tyrosine-radical stabilization that a structured protein can offer. Y32 gives rise to quasireversible square-wave and differential pulse voltammograms at acidic pH. These voltammograms represent the Y32 species at the upper edge of the quasirevesible range. The square-wave net potential closely approximates the formal potential of the Y32-O center dot/Y32-OH redox couple to 1,070 +/- 1 mV versus the normal hydrogen electrode at pH 5.52 +/- 0.01. The differential pulse voltammetry half-wave potential of the Y32-O-center dot/Y32-OH redox pair is measured between pH 4.7 and 9.0. These results are described and analyzed.
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| 3. |
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| 4. |
- Martinez-Rivera, Melissa C., et al.
(författare)
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Electrochemical and Structural Properties of a Protein System Designed To Generate Tyrosine Pourbaix Diagrams
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:44, s. 17786-17795
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Tidskriftsartikel (refereegranskat)abstract
- This report describes a model protein specifically tailored to electrochemically study the reduction potential of protein tyrosine radicals as a function of pH. The model system is based on the 67-residue alpha(3)Y three-helix bundle, alpha(3)Y contains a single buried tyrosine at position 32 and displays structural properties inherent to a protein. The present report presents differential pulse voltammograms obtained from alpha(3)Y at both:acidic (pH 5.6) and alkaline (pH 8.3) Conditions. The. observed Faradaic. response is uniquely associated. with Y32, as shown by site-directed mutagenesis. This is the first time voltammetry is successfully applied to detect a redox-active tyrosine residing in a structured protein environment. Tyrosine is a proton coupled electron transfer cofactor making voltammetry-based pH titrations a central experimental approach. A second set of experiments was performed to demonstrate that pH-dependent studies can be conducted on the redox-active tyrosine without introducing large-scale structural changes in the protein scaffold alpha(3)Y was re-engineered-with the specific aim to place the imidazole group of a histidine close to the Y32 phenol ring alpha(3)Y-K29H and alpha(3)Y-K36H each contain a histidine residue whose protonation perturbs the fluorescence of Y32. We show that these variants are stable and well-folded proteins whose helical: content, tertiary structure, solution aggregation state, and solvent-sequestered position of Y32 remain pH insensitive across a range of at least 3-4 pH units. These results confirm that the local environment of Y32 can be altered and the resulting radical site studied by voltammetry over a broad pH range without interference from long-range structural effects.
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