Rheostat Re-Wired: Alternative Hypotheses for the Control of Thioredoxin Reduction Potentials
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Bewley-2015-Rheostat Re-Wired_ A.pdf
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Author(s)
Bewley, Kathryn D.
Dey, Mishtu
Bjork, Rebekah E.
Mitra, Sangha
Chobot, Sarah E.
Elliott, Sean J.
Drennan, Catherine L
Date Issued
April 2015
Journal
PLOS ONE
Publisher
Public Library of Science
Citation
Bewley, Kathryn D., Mishtu Dey, Rebekah E. Bjork, Sangha Mitra, Sarah E. Chobot, Catherine L. Drennan, and Sean J. Elliott. “Rheostat Re-Wired: Alternative Hypotheses for the Control of Thioredoxin Reduction Potentials.” Edited by Luis Eduardo Soares Netto. PLOS ONE 10, no. 4 (April 13, 2015): e0122466.
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Final published version
Abstract
Thioredoxins are small soluble proteins that contain a redox-active disulfide (CXXC). These disulfides are tuned to oxidizing or reducing potentials depending on the function of the thioredoxin within the cell. The mechanism by which the potential is tuned has been controversial, with two main hypotheses: first, that redox potential (E[subscript m]) is specifically governed by a molecular ‘rheostat’—the XX amino acids, which influence the Cys pK[subscript a] values, and thereby, E[subscript m]; and second, the overall thermodynamics of protein folding stability regulates the potential. Here, we use protein film voltammetry (PFV) to measure the pH dependence of the redox potentials of a series of wild-type and mutant archaeal Trxs, PFV and glutathionine-equilibrium to corroborate the measured potentials, the fluorescence probe BADAN to measure pK[subscript a] values, guanidinium-based denaturation to measure protein unfolding, and X-ray crystallography to provide a structural basis for our functional analyses. We find that when these archaeal thioredoxins are probed directly using PFV, both the high and low potential thioredoxins display consistent 2H+:2e- coupling over a physiological pH range, in conflict with the conventional ‘rheostat’ model. Instead, folding measurements reveals an excellent correlation to reduction potentials, supporting the second hypothesis and revealing the molecular mechanism of reduction potential control in the ubiquitous Trx family.
MIT Department
Massachusetts Institute of Technology. Department of Biology
Massachusetts Institute of Technology. Department of Chemical Engineering
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
https://doi.org/10.1371/journal.pone.0122466
