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Environmental modulation of protein cation-pi interactions
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.
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. University of Pennsylvania, USA.
2007 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 129, no 17, 5308+- p.Article in journal (Refereed) Published
Abstract [en]

Protein cation-pi interactions are frequently found near the protein surface with their interacting residues partly solvent exposed. The structurally characterized alpha W-3 model protein contains the W32/K36 cation-pi interaction which has properties similar to those of naturally occurring protein cation-pi interactions. alpha W-3 was studied with the following results: Cation-pi interactions formed by a buried tryptophan and a partly solvated lysine, arginine, or histidine range from -0.8 to -0.5 kcal mol(-1) and rank as: W32/K36 approximate to W32/R36 > W32/H36. The W32/K36 pair in alpha W-3 represents the first W/K cation-pi interaction for which both the structure and the bond energy have been experimentally determined. Upon increasing the solvent exposure of the cation-pi pair, the W/K interaction energy drops from -0.73 to -0.06 and +0.15 kcal mol(-1). These results suggest that solvent exposure can tune the interaction energy between a tryptophan and a lysine by at least 0.9 kcal mol(-1).

Place, publisher, year, edition, pages
2007. Vol. 129, no 17, 5308+- p.
Keyword [en]
alpha-helical peptides, aromatic side-chains, radical enzymes, model, stability
National Category
Biological Sciences
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-56576DOI: 10.1021/ja068957aISI: 000245946400005OAI: oai:DiVA.org:su-56576DiVA: diva2:412919
Note

authorCount :3

Available from: 2011-04-26 Created: 2011-04-19 Last updated: 2017-12-11Bibliographically 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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