Hector Hernandez - Direct Electrochemical Analyses of a Thermophilic Thioredoxin Reductase: Interplay between Conformational Change and Redox Chemistry

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  Publication Details (including relevant citation   information):

  Hamill, Michael J., Chobot, Sarah E., Hernandez, Hector H.,   Drennan, Catherine L., Elliott, Sean J. Biochemistry  2008 47 (37) 9738-9746

  Abstract: Thioredoxin reductases (TrxRs) are   flavin-containing dithioloxidoreductases that couple reduction   equivalents from the soluble NAD(P)H pool to the soluble protein   thioredoxin (Trx). Previous crystallographic studies of the   Escherichia coli enzyme (ecTrxR) have shown that low molecular   weight TrxRs can adopt two distinct conformations: the first (FO)   is required for the oxidation of the flavin cofactor and the   generation of reduced Trx; the second (FR) is adopted for the   reduction of the flavin by NAD(P)H. Here, protein   electrochemistry has been used to interrogate the equilibrium   between the oxidized and reduced conformations of the ecTrxR and   a novel, low molecular weight TrxR from the thermophilic archaeon   Thermoplasma acidophilum (taTrxR) that is characterized   structurally and biochemically in the accompanying paper   [Hernandez et al. (2008) Biochemistry 47, 9728?9737]. A   reversible electrochemical response is observed that reveals a   dynamic behavior dependent upon the temperature of the   experiment. At low temperatures (283 K) a broad, quasi-reversible   electrochemical envelope is observed centered at a value of ??300   mV and displaying a peak width of over 150 mV. The voltammetric   response sharpens dramatically as the temperature increases,   becoming much more reversible (as determined by peak separation   and peak width). The overall potential and shape of the   voltammetric data indicate that the flavin (FAD/FADH2) and   disulfide/dithiol couples are very close in thermodynamic   potentials, and the data are interpreted in terms of the model of   two-state conformational change between flavin reducing (FR) and   flavin oxidizing (FO) states, where the difference in potential   for the flavin and disulfide cofactors must be within 40 mV of   one another. In this model, the low temperature peak broadening   is interpreted as an indication of a heterogeneous population of   TrxR conformations that exist at low temperature; at higher   temperatures, FO and FR conformers can rapidly interconvert, and   voltammetry reports upon an average potential of the   conformations.

  Address (URL): http://dx.doi.org/10.1021/bi800676g