Explore the vast range of titles available.

Susanne Sievers and Daniela Zühlke were not included as authors in the original publication [...]

Abstract Thioredoxin (Trx) is a disulfide-containing redox protein that functions as a disulfide oxidoreductase. Myxococcus xanthus contains five Trxs (Trx1–Trx5) and one Trx reductase (TrxR). Trxs typically have a CGPC active-site motif; however, M. xanthus Trxs have slightly different active-site sequences, with the exception of Trx4. The five Trxs of M. xanthus exhibited reduced activities against insulin, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), cystine, glutathione disulfide (GSSG), S-nitrosoglutathione (GSNO), and H2O2 in the presence of TrxR. Myxococcus xanthus adenylate kinase and serine/threonine phosphatase activities, which were increased by the addition of dithiothreitol, were activated by the addition of Trxs and TrxR. Among these, Trx1, which has a CAPC sequence in its active site, exhibited the highest reducing activity with the exception of GSNO. Myxococcus xanthus TrxR showed weak reducing activity towards DTNB, GSSG, GSNO, and H2O2, suggesting that it has broad substrate specificity, unlike previously reported low-molecular-weight TrxRs. TrxR reduced oxidized Trx1 as the best substrate, with a kcat/Km value of 0.253 min−1 µM−1, which was 10–28-fold higher than that of the other Trxs. These results suggest that all Trxs possess reducing activity and that Trx1 may be the most functional in M. xanthus because TrxR most efficiently reduces oxidized Trx1. The myxobacterium Myxococcus xanthus has five thioredoxins that can reduce disulfide bonds in low-molecular-weight compounds, peptides, and enzymes.

The thiol-based redox regulation system is believed to adjust chloroplast functions in response to changes in light environments. A redox cascade via the ferredoxin-thioredoxin reductase (FTR)/thioredoxin (Trx) pathway has been traditionally considered to serve as a transmitter of light signals to target enzymes. However, emerging data indicate that chloroplasts have a complex redox network composed of diverse redox-mediator proteins and target enzymes. Despite extensive research addressing this system, two fundamental questions are still unresolved: How are redox pathways orchestrated within chloroplasts, and why are chloroplasts endowed with a complicated redox network? In this report, we show that NADPH-Trx reductase C (NTRC) is a key redox-mediator protein responsible for regulatory functions distinct from those of the classically known FTR/Trx system. Target screening and subsequent biochemical assays indicated that NTRC and the Trx family differentially recognize their target proteins. In addition, we found that NTRC is an electron donor to Trx-z, which is a key regulator of gene expression in chloroplasts. We further demonstrate that cooperative control of chloroplast functions via the FTR/Trx and NTRC pathways is essential for plant viability. Arabidopsis double mutants impaired in FTR and NTRC expression displayed lethal phenotypes under autotrophic growth conditions. This severe growth phenotype was related to a drastic loss of photosynthetic performance. These combined results provide an expanded map of the chloroplast redox network and its biological functions.

Thioredoxin reductase-1 (TRXR-1) is the sole selenoprotein in C. elegans, and selenite is a substrate for thioredoxin reductase, so TRXR-1 may play a role in metabolism of selenium (Se) to toxic forms. To study the role of TRXR in Se toxicity, we cultured C. elegans with deletions of trxr-1, trxr-2, and both in axenic media with increasing concentrations of inorganic Se. Wild-type C. elegans cultured for 12 days in Se-deficient axenic media grow and reproduce equivalent to Se-supplemented media. Supplementation with 0-2 mM Se as selenite results in inverse, sigmoidal response curves with an LC50 of 0.20 mM Se, due to impaired growth rather than reproduction. Deletion of trxr-1, trxr-2 or both does not modulate growth or Se toxicity in C. elegans grown axenically, and (75)Se labeling showed that TRXR-1 arises from the trxr-1 gene and not from bacterial genes. Se response curves for selenide (LC50 0.23 mM Se) were identical to selenite, but selenate was 1/4(th) as toxic (LC50 0.95 mM Se) as selenite and not modulated by TRXR deletion. These nutritional and genetic studies in axenic media show that Se and TRXR are not essential for C. elegans, and that TRXR alone is not essential for metabolism of inorganic Se to toxic species.

Seeds preserve a far developed plant embryo in a quiescent state. Seed metabolism relies on stored resources and is reactivated to drive germination when the external conditions are favorable. Since the switchover from quiescence to reactivation provides a remarkable case of a cell physiological transition we investigated the earliest events in energy and redox metabolism of Arabidopsis seeds at imbibition. By developing fluorescent protein biosensing in intact seeds, we observed ATP accumulation and oxygen uptake within minutes, indicating rapid activation of mitochondrial respiration, which coincided with a sharp transition from an oxidizing to a more reducing thiol redox environment in the mitochondrial matrix. To identify individual operational protein thiol switches, we captured the fast release of metabolic quiescence in organello and devised quantitative iodoacetyl tandem mass tag (iodoTMT)-based thiol redox proteomics. The redox state across all Cys peptides was shifted toward reduction from 27.1% down to 13.0% oxidized thiol. A large number of Cys peptides (412) were redox switched, representing central pathways of mitochondrial energy metabolism, including the respiratory chain and each enzymatic step of the tricarboxylic acid (TCA) cycle. Active site Cys peptides of glutathione reductase 2, NADPH-thioredoxin reductase a/b, and thioredoxin-o1 showed the strongest responses. Germination of seeds lacking those redox proteins was associated with markedly enhanced respiration and deregulated TCA cycle dynamics suggesting decreased resource efficiency of energy metabolism. Germination in aged seeds was strongly impaired. We identify a global operation of thiol redox switches that is required for optimal usage of energy stores by the mitochondria to drive efficient germination.

The lumen of the endoplasmic reticulum (ER) is usually considered an oxidative environment; however, oxidized thiol-disulfides and reduced pyridine nucleotides occur there parallelly, indicating that the ER lumen lacks components which connect the two systems. Here, we investigated the luminal presence of the thioredoxin (Trx)/thioredoxin reductase (TrxR) proteins, capable of linking the protein thiol and pyridine nucleotide pools in different compartments. It was shown that specific activity of TrxR in the ER is undetectable, whereas higher activities were measured in the cytoplasm and mitochondria. None of the Trx/TrxR isoforms were expressed in the ER by Western blot analysis. Co-localization studies of various isoforms of Trx and TrxR with ER marker Grp94 by immunofluorescent analysis further confirmed their absence from the lumen. The probability of luminal localization of each isoform was also predicted to be very low by several in silico analysis tools. ER-targeted transient transfection of HeLa cells with Trx1 and TrxR1 significantly decreased cell viability and induced apoptotic cell death. In conclusion, the absence of this electron transfer chain may explain the uncoupling of the redox systems in the ER lumen, allowing parallel presence of a reduced pyridine nucleotide and a probably oxidized protein pool necessary for cellular viability.

Tight control of cellular redox homeostasis is essential for protection against oxidative damage and for maintenance of normal metabolism as well as redox signaling events. Under oxidative stress conditions, the tripeptide glutathione can switch from its reduced form (GSH) to oxidized glutathione disulfide (GSSG), and thus, forms an important cellular redox buffer. GSSG is normally reduced to GSH by 2 glutathione reductase (GR) isoforms encoded in the Arabidopsis genome, cytosolic GR1 and GR2 dual-targeted to chloroplasts and mitochondria. Measurements of total GR activity in leaf extracts of wild-type and 2 gr1 deletion mutants revealed that [almost equal to]65% of the total GR activity is attributed to GR1, whereas [almost equal to]35% is contributed by GR2. Despite the lack of a large share in total GR activity, gr1 mutants do not show any informative phenotype, even under stress conditions, and thus, the physiological impact of GR1 remains obscure. To elucidate its role in plants, glutathione-specific redox-sensitive GFP was used to dynamically measure the glutathione redox potential (EGSH) in the cytosol. Using this tool, it is shown that EGSH in gr1 mutants is significantly shifted toward more oxidizing conditions. Surprisingly, dynamic reduction of GSSG formed during induced oxidative stress in gr1 mutants is still possible, although significantly delayed compared with wild-type plants. We infer that there is functional redundancy in this critical pathway. Integrated biochemical and genetic assays identify the NADPH-dependent thioredoxin system as a backup system for GR1. Deletion of both, NADPH-dependent thioredoxin reductase A and GR1, prevents survival due to a pollen lethal phenotype.

Mammalian thioredoxin reductase (TrxR) is a selenoprotein with three existing isoenzymes (TrxR1, TrxR2, and TrxR3), which is found primarily intracellularly but also in extracellular fluids. The main substrate thioredoxin (Trx) is similarly found (as Trx1 and Trx2) in various intracellular compartments, in blood plasma, and is the cell’s major disulfide reductase. Thioredoxin reductase is necessary as a NADPH-dependent reducing agent in biochemical reactions involving Trx. Genetic and environmental factors like selenium status influence the activity of TrxR. Research shows that the Trx/TrxR system plays a significant role in the physiology of the adipose tissue, in carbohydrate metabolism, insulin production and sensitivity, blood pressure regulation, inflammation, chemotactic activity of macrophages, and atherogenesis. Based on recent research, it has been reported that the modulation of the Trx/TrxR system may be considered as a new target in the management of the metabolic syndrome, insulin resistance, and type 2 diabetes, as well as in the treatment of hypertension and atherosclerosis. In this review evidence about a possible role of this system as a marker of the metabolic syndrome is reported.

Pancreatic ductal adenocarcinoma (PDAC) shows substantial heterogeneity in cysteine dependence and ferroptosis sensitivity. We identify two PDAC subtypes distinguished by EMT status: mesenchymal-like cells are highly cysteine-dependent and rapidly undergo ferroptosis upon cystine deprivation or system xc− inhibition, whereas epithelial-type cells are ferroptosis-resistant. Selenium supplementation protects cells from erastin-induced ferroptosis, and this protection persists even when intracellular glutathione (GSH) is depleted, supporting an additional GPX4-independent protective mechanism. Sepp1 knockdown does not alter sensitivity, indicating that selenium’s protective effect is independent of Sepp1. Instead, epithelial-type cells rely on both cytosolic and mitochondrial thioredoxin reductases (TrxR1 and TrxR2) to maintain ferroptosis resistance. Chemical inhibition of thioredoxin reductases abolishes selenium-mediated protection and sensitizes epithelial cells to ferroptosis inducers, while dual genetic suppression of TrxR1 and TrxR2 similarly restores ferroptosis sensitivity. These findings uncover a selenium–thioredoxin redox axis that functions independently of GPX4 and contributes ferroptosis resistance in epithelial-type PDAC cells. Co-targeting cysteine metabolism and thioredoxin reductases may therefore represent a rational strategy to overcome ferroptosis resistance in some PDAC subtypes.