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Antioxidant function of thioredoxin and glutaredoxin systems.

A Holmgren1

  • 1Medical Nobel Institute for Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden. arne.holmgren@mbb.ki.se

Antioxidants & Redox Signaling
|February 24, 2001
PubMed
Summary

Selenium is crucial for thioredoxin reductase activity, essential for cell proliferation and redox balance. This study demonstrates selenium

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cellular Redox Biology

Background:

  • Selenium is an essential trace element with vital antioxidant functions.
  • Cytosolic thioredoxin reductase (TrxR) is a key flavoenzyme in cellular redox regulation.
  • Mammalian TrxR contains a unique selenocysteine (Sec) residue essential for its activity.

Purpose of the Study:

  • To investigate the role of selenocysteine in the catalytic activity and structure of cytosolic thioredoxin reductase.
  • To elucidate the impact of selenium deficiency on thioredoxin reductase function.
  • To explore the interaction of ebselen, a selenium-containing drug, with human thioredoxin reductase.

Main Methods:

  • Site-directed mutagenesis to replace selenocysteine with cysteine in rat TrxR.
  • Expression of wild-type and mutant TrxR in Escherichia coli.
  • Enzyme kinetics assays to determine substrate affinity and catalytic efficiency.
  • Expression and characterization of truncated TrxR lacking the C-terminal selenocysteine-glycine motif.
  • Measurement of human TrxR activity in the presence of ebselen.

Main Results:

  • Mutant TrxR with cysteine instead of selenocysteine exhibited drastically reduced activity (1% of wild-type) and a shift in pH optimum.
  • Truncated TrxR, lacking the C-terminal selenocysteine-glycine, was inactive, confirming the critical role of selenocysteine in the active site.
  • Ebselen significantly stimulated the hydrogen peroxide reductase activity of human TrxR.
  • The study highlights selenium's essentiality for TrxR activity and, consequently, for cell proliferation and redox homeostasis.

Conclusions:

  • Selenium is indispensable for the catalytic activity of thioredoxin reductase.
  • The selenocysteine residue is critical for the enzyme's function and its role in maintaining intracellular redox state.
  • These findings provide a molecular basis for selenium's requirement in cellular processes, including DNA synthesis and transcription factor regulation.
  • Ebselen's interaction suggests potential therapeutic applications in modulating redox signaling pathways.

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