Thermodynamic basis for redox regulation of the Yap1 signal transduction pathway.
The Yap1 oxidative stress signal transduction pathway found in Saccharomyces cerevisiae is redox-regulated. We have examined the thermodynamic basis of the disulfide/dithiol couples that are involved in the regulation of this pathway. The oxidized form of the Yap1 redox domain (Yap1-RD) fragment, derived from the Yap1 transcription factor, contains two disulfide bonds, one between Cys303 and Cys598 and one between Cys310 and Cys629. Oxidation-reduction titrations reveal the presence of two separate two-electron redox couples in Yap1-RD, with redox midpoint potentials (E(m)) of -155 and -330 mV, respectively, at pH 7.0. We measured E(m) values of -275 and -265 mV for the two cytoplasmic S. cerevisiae thioredoxins, Trx1 and Trx2, respectively, both at pH 7.0. Last, we measured an E(m) value of -255 mV for the Cys36-Cys82 disulfide bond at pH 6.0 in the glutathione peroxidase-like enzyme, oxidant receptor protein (Orp1). We were unable to obtain satisfactory redox titration data for Orp1 at pH 7.0, but if the redox-active disulfide of Orp1 exhibits the -59 mV per pH unit dependence for E(m) typical of protein disulfides in this pH region, an E(m) value of -315 mV can be estimated for Orp1 at pH 7.0 by extrapolation. Together, these data suggest that, at physiological ratios of Trx(ox)/Trx(red), the reduction of both the E(m) = -315 mV disulfide of Orp1 and the E(m) = -330 mV disulfide of Yap1 by either Trx1 or Trx2 would be thermodynamically possible.
Mason
Jeremy T
JT
Department of Chemistry and Biochemistry, Center for Biotechnology and Genomics, Texas Tech University, Lubbock, Texas 79409-1061, USA.
Kim
Sung-Kun
SK
Knaff
David B
DB
Wood
Matthew J
MJ
D000595:Amino Acid Sequence; D004220:Disulfides / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005979:Glutathione Peroxidase / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*; D013816:Thermodynamics; D013879:Thioredoxins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
D004220:Disulfides; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C086677:YAP1 protein, S cerevisiae; D013879:Thioredoxins; D005979:Glutathione Peroxidase; C494438:HYR1 protein, S cerevisiae