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Reversible voltammograms and a Pourbaix diagram for a protein tyrosine radical
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. University of Pennsylvania, USA.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. University of Pennsylvania, USA.
2012 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 25, 9739-9743 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2012. Vol. 109, no 25, 9739-9743 p.
Keyword [en]
protein voltammetry, proton-coupled electron transfer
National Category
Biological Sciences
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-80014DOI: 10.1073/pnas.1112057109ISI: 000306061400024OAI: oai:DiVA.org:su-80014DiVA: diva2:552079
Note

AuthorCount:3;

Available from: 2012-09-12 Created: 2012-09-12 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Using de novo design proteins to explore tyrosine radicals and cation-π interactions
Open this publication in new window or tab >>Using de novo design proteins to explore tyrosine radicals and cation-π interactions
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Redox cofactors and amino-acid free radicals play important roles in biology. Although many of the same cofactors and amino acids that form these radicals are found across a broad range of biological systems, identical cofactors can have different reduction potentials. The local environment plays a role in defining these redox potentials. An understanding of this local-environment effect can shed more light on how redox chemistry works in nature. Our laboratory has developed a library of model proteins that are well suited to study amino-acid radicals. a3X is a de novo designed protein that is composed of 67 residues. It forms a three-helix bundle connected by two glycine loops. The radical site is located at position 32 on the central a-helix. The a3X protein is designed to be well-folded and thermodynamically stable across a broad pH range. Paper 1 describes the structural and electrochemical characterization of a3Y, a tyrosine variant of a3X. We were able to obtain a unique Faradaic response from Y32 at both low and high pH, using differential pulse voltammetry. In addition, we successfully redesigned α3Y by introducing a histidine in close proximity to Y32, creating a tyrosine/histidine pair. Our goal in creating this pair was to study proton-coupled electron transfer (PCET) in a well-structured and solvent-sequestered protein environment.  In paper 2 we illustrated the redox reversibility of Y32 and produced the first ever Pourbaix diagram for a tyrosine radical in a protein. The formal potential of the Y32-OŸ/Y32-OH redox couple was determined to be 918 ± 2 mV vs. the normal hydrogen electrode (NHE) at pH 8.40.  While at pH 5.52, the formal potential of the Y32-OŸ/Y32-OH redox couple was recorded at 1.07 V. Papers 3 and 4 utilize a3W to study cation-π interactions. In paper 3, we showed how solvation can affect the strength of these interactions by -0.9 kcal/mol. In Paper 4, we were able to monitor the disruption of the cation-π interaction with the use of high-pressure fluorescence and were able to calculate the interaction energy for a solvent exposed cation-π. The aim of the work described in this thesis was to use model proteins to study tyrosine radicals to gain a broader perspective and better understanding of the versatility of biological electron transfer and to measure cation-π interactions and how they behave in different environments.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2014. 69 p.
Keyword
tyrosine, radicals, cation-pi interactions, de novo designed proteins, biochemistry, biophysics
National Category
Biological Sciences
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-102008 (URN)978-91-7447-885-3 (ISBN)
Public defence
2014-05-09, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2014-04-14 Created: 2014-03-20 Last updated: 2014-04-14Bibliographically approved

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