The role of thiols in antioxidant systems

• Published in: Free radical biology & medicine Vol. 140; pp. 14 - 27
• Main Authors: Ulrich, Kathrin, Jakob, Ursula
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 20.08.2019
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2019.05.035

The sulfur biochemistry of the thiol group endows cysteines with a number of highly specialized and unique features that enable them to serve a variety of different functions in the cell. Typically highly conserved in proteins, cysteines are predominantly found in functionally or structurally crucial regions, where they act as stabilizing, catalytic, metal-binding and/or redox-regulatory entities. As highly abundant low molecular weight thiols, cysteine thiols and their oxidized disulfide counterparts are carefully balanced to maintain redox homeostasis in various cellular compartments, protect organisms from oxidative and xenobiotic stressors and partake actively in redox-regulatory and signaling processes. In this review, we will discuss the role of protein thiols as scavengers of hydrogen peroxide in antioxidant enzymes, use thiol peroxidases to exemplify how protein thiols contribute to redox signaling, provide an overview over the diverse set of low molecular weight thiol-based redox systems found in biology, and illustrate how thiol-based redox systems have evolved not only to protect against but to take full advantage of a world full of molecular oxygen. Biological functions of thiol-based redox systems The glutathione (GSH)/glutathione reductase (GR) system delivers the electrons for essential enzymes involved in the detoxification of hydroperoxides (Prx, GPx), xenobiotics (GST) and electrophiles (Glo1, 2), the reduction of disulfide bonds (PDI, Grx), the biogenesis of iron-sulfur clusters (Grx), and in the biosynthesis of nucleotides (RnR). Prx, peroxiredoxin; GPx, glutathione peroxidase; GST, glutathione S-transferase; Grx, glutaredoxin; RnR, ribonucleotide reductase; Glo, glyoxalase; PDI, protein disulfide isomerase. [Display omitted] •Thiols serve a central role in protein-based and low-molecular-weight redox systems.•Thiol-based antioxidants protect organisms against oxidative stress.•Thiols in antioxidant enzymes can relay oxidative signals to other proteins.•Glutathione represents a tightly balanced compartment-specific reducing currency.•Diverse low-molecular-weight thiol-based redox systems evolved in various organisms.