Molecular views of redox regulation: three-dimensional structures of redox regulatory proteins and protein complexes

The role of thioredoxin and glutathione systems in arsenic-induced liver injury in rats under glutathione depletion

Antioxidant systems like thioredoxin (Trx) and glutaredoxin (Grx) maintain oxidative stress balance. These systems have cross-talk supported by some in vitro studies. We investigated the underlying mechanisms of arsenic-induced liver injury in glutathione-deficient rats and whether there was any cross-talk between the Trx and Grx systems. The rats in arsenic-treated groups were administered with sodium arsenite (10, 20 mg/kg b w/d) for four weeks. In buthionine sulfoximine (BSO, an inhibitor of GSH) and 20 mg/kg arsenic combined groups, rats were injected with 2 mmol/kg BSO intraperitoneally twice per week. BSO exacerbated arsenic-induced liver injury by increasing arsenic accumulation in urine, serum, and liver while decreasing glutathione activity and resulting in upregulated mRNA expression of the Trx system and downregulation of Grx mRNA expression. The impact of Trx lasted longer than that of the Grx. The Trx system remained highly expressed, while GSH, Grx1, and Grx2 levels were decreased. The inhibitory effect of only BSO treatment on Grx1 and Grx2 was not pronounced. However, the combined impact of arsenic and BSO upregulated Trx expression, primarily related to further reduction of GSH. As a result, the suppressed Grxs were protected by the upregulated Trxs, which serve as a backup antioxidant defense system in the liver.

Small Molecules Govern Thiol Redox Switches

Oxygenic photosynthesis gave rise to a regulatory mechanism based on reversible redox-modifications of enzymes. In chloroplasts, such on-off switches separate metabolic pathways to avoid futile cycles. During illumination, the redox interconversions allow for rapidly and finely adjusting activation states of redox-regulated enzymes. Noncovalent effects by metabolites binding to these enzymes, here addressed as 'small molecules', affect the rates of reduction and oxidation. The chloroplast enzymes provide an example for a versatile regulatory principle where small molecules govern thiol switches to integrate redox state and metabolism for an appropriate response to environmental challenges. In general, this principle can be transferred to reactive thiols involved in redox signaling, oxidative stress responses, and in disease of all organisms.

A redox-dependent mechanism for regulation of AMPK activation by Thioredoxin1 during energy starvation

5'-AMP-activated protein kinase (AMPK) is a key regulator of metabolism and survival during energy stress. Dysregulation of AMPK is strongly associated with oxidative-stress-related disease. However, whether and how AMPK is regulated by intracellular redox status remains unknown. Here we show that the activity of AMPK is negatively regulated by oxidation of Cys130 and Cys174 in its α subunit, which interferes with the interaction between AMPK and AMPK kinases (AMPKK). Reduction of Cys130/Cys174 is essential for activation of AMPK during energy starvation. Thioredoxin1 (Trx1), an important reducing enzyme that cleaves disulfides in proteins, prevents AMPK oxidation, serving as an essential cofactor for AMPK activation. High-fat diet consumption downregulates Trx1 and induces AMPK oxidation, which enhances cardiomyocyte death during myocardial ischemia. Thus, Trx1 modulates activation of the cardioprotective AMPK pathway during ischemia, functionally linking oxidative stress and metabolism in the heart.

An introduction to thiol redox proteins in the endoplasmic reticulum and a review of current electrochemical methods of detection of thiols

This aim of this paper is to expound the complexity of thiol redox systems in the endoplasmic reticulum of eukaryotic cells to the electroanalytical community. A summary of the state of the art in electrochemical methods for detection of thiols gives an insight into the challenges that need to be addressed to bridge the disparity between current analytical techniques and applications in a 'real' biological scenario.

Identification and Characterization of TRP14, a Thioredoxin-related Protein of 14 kDa

We have identified and characterized a 14-kDa human thioredoxin (Trx)-related protein designated TRP14. This cytosolic protein was expressed in all tissues and cell types examined, generally in smaller amounts than Trx1. Although TRP14 contains five cysteines, only the two Cys residues in its WCPDC motif were exposed and redox sensitive. Unlike Trx1, which was an equally good substrate for both Trx reductase 1 (TrxR1) and TrxR2, oxidized TRP14 was reduced by TrxR1 but not by TrxR2. Biochemical characterization of TRP14 suggested that, like Trx1, TRP14 is a disulfide reductase; its active site cysteine is sufficiently nucleophilic with the pK(a) value of 6.1; and its redox potential (-257 mV) is similar to those of other cellular thiol reductants. However, although TRP14 reduced small disulfide-containing peptides, it did not reduce the disulfides of known Trx1 substrates, ribonucleotide reductase, peroxiredoxin, and methionine sulfoxide reductase. These results suggest that TRP14 and Trx1 might act on distinct substrate proteins.

Roles of TRP14, a thioredoxin-related protein in tumor necrosis factor-alpha signaling pathways

The possible roles of a 14-kDa human thioredoxin (Trx)-related protein (TRP14) in TNF-alpha signaling were studied in comparison with those of Trx1 by RNA interference in HeLa cells. Depletion of TRP14 augmented the TNF-alpha-induced phosphorylation and degradation of I kappa B alpha as well as the consequent activation of NF-kappa B to a greater extent than did Trx1 depletion. Deficiency of TRP14 or Trx1 enhanced TNF-alpha-induced activation of caspases and subsequent apoptosis by a similar extent. The TNF-alpha-induced activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinases (MAPKs), however, was promoted by depletion of TRP14 but not by that of Trx1. Unlike Trx1, TRP14 neither associated with nor inhibited the kinase activity of apoptosis signal-regulating kinase-1 (ASK1), an upstream activator of JNK and p38. In combination with the results in the accompanying paper that TRP14 did not reduce the known substrates of Trx1, these results suggest that TRP14 modulates TNF-alpha signaling pathways, provably by interacting with proteins distinct from the targets of Trx1. In an effort to identify target proteins of TRP14, a mutant of TRP14, in which the active site cysteine (Cys(46)) was substituted with serine, was shown to form a disulfide-linked complex with LC8 cytoplasmic dynein light chain. The complex was detected in HeLa cells treated with H(2)O(2) or TNF-alpha but not in untreated cells, suggesting that LC8 cytoplasmic dynein light chain is a possible substrate of TRP14.

Characterization of the redox properties of poplar glutaredoxin

The presence of glutaredoxins in plants is now well recognized, but their functions and natural substrates remain largely unknown. Recently, a poplar glutaredoxin has been biochemically characterized and several mutants have been engineered in order to explore its reactivity. This work focuses on some physiological functions of the enzyme. According to our findings, the poplar glutaredoxin can serve as an electron donor to the bacterial 3'-phosphoadenylylsulfate reductase as it supports both the catalysis by the enzyme in vitro and complements a methionine auxotroph strain of Escherichia coli. In addition, poplar glutaredoxin is able to reduce the Escherichia coli ribonucleotide reductase 1a (in vitro reduction of cytidine diphosphate). Although this glutaredoxin is described as an electron donor to a phloem-located peroxiredoxin, whose function is to detoxify hydroperoxides, we found that it does not directly reduce hydrogen peroxide or other alkyl hydroperoxides as described for yeast and rice glutaredoxins. However, the poplar glutaredoxin may be involved in the response to oxidative stress as its overexpression in Escherichia coli resulted in a higher resistance toward hydrogen peroxide, menadione, and tert-butyl hydroperoxide.

Redox control by dithiol-disulfide exchange in plants: II. The cytosolic and mitochondrial systems

This paper describes the existence of two pathways efficient in the reduction of disulfide bridges on selected proteins and mitochondria of photosynthetic organisms. The first is constituted by NADPH, the flavoenzyme NADPH thioredoxin reductase, and thioredoxin; and the second by NADPH, glutathione reductase, glutathione, and glutaredoxin. Molecular details concerning the proteins participating in these redox regulatory cascades are provided, and their molecular targets and functions are described.

Glutaredoxin-dependent peroxiredoxin from poplar: protein-protein interaction and catalytic mechanism

Recently, a poplar phloem peroxiredoxin (Prx) was found to accept both glutaredoxin (Grx) and thioredoxin (Trx) as proton donors. To investigate the catalytic mechanism of the Grx-dependent reduction of hydroperoxides catalyzed by Prx, a series of cysteinic mutants was constructed. Mutation of the most N-terminal conserved cysteine of Prx (Cys-51) demonstrates that it is the catalytic one. The second cysteine (Cys-76) is not essential for peroxiredoxin activity because the C76A mutant retained approximately 25% of the wild type Prx activity. Only one cysteine of the Grx active site (Cys-27) is essential for peroxiredoxin catalysis, indicating that Grx can act in this reaction either via a dithiol or a monothiol pathway. The creation of covalent heterodimers between Prx and Grx mutants confirms that Prx Cys-51 and Grx Cys-27 are the two residues involved in the catalytic mechanism. The integration of a third cysteine in position 152 of the Prx, making it similar in sequence to the Trx-dependent human Prx V, resulted in a protein that had no detectable activity with Grx but kept activity with Trx. Based on these experimental results, a catalytic mechanism is proposed to explain the Grx- and Trx-dependent activities of poplar Prx.