Ultraviolet-B acclimation is supported by functionally heterogeneous phenolic peroxidases.

Tobacco plants were grown in plant chambers for four weeks, then exposed to one of the following treatments for 4 days: (1) daily supplementary UV-B radiation corresponding to 6.9 kJ m-2 d-1 biologically effective dose (UV-B), (2) daily irrigation with 0.1 mM hydrogen peroxide, or (3) a parallel application of the two treatments (UV-B + H2O2). Neither the H2O2 nor the UV-B treatments were found to be damaging to leaf photosynthesis. Both single factor treatments increased leaf H2O2 contents but had distinct effects on various H2O2 neutralising mechanisms. Non-enzymatic H2O2 antioxidant capacities were increased by direct H2O2 treatment only, but not by UV-B. In contrast, enzymatic H2O2 neutralisation was mostly increased by UV-B, the responses showing an interesting diversity. When class-III peroxidase (POD) activity was assayed using an artificial substrate (ABTS, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid)), both treatments appeared to have a positive effect. However, only UV-B-treated leaves showed higher POD activities when phenolic compounds naturally occurring in tobacco leaves (chlorogenic acid or quercetin) were used as substrates. These results demonstrate a substrate-dependent, functional heterogeneity in POD and further suggest that the selective activation of specific isoforms in UV-B acclimated leaves is not triggered by excess H2O2 in these leaves.

Physiological and quantitative proteomic analysis of NtPRX63-overexpressing tobacco plants revealed that NtPRX63 functions in plant salt resistance.

High salinity is harmful to crop yield and productivity. Peroxidases (PRXs) play crucial roles in H2O2 scavenging. In our previous study, PRX63 significantly upregulated in tobacco plants under salt stress. Thus, in order to understand the function of PRX63 in tobacco salt response, we overexpressed this gene in tobacco (Nicotiana tabacum L.), investigated the morphological, physiological and proteomic profiles of NtPRX63-overexpressing tobacco transgenic lines and wild type. The results showed that, compared with the wild type, the transgenic tobacco plants presented enhanced salt tolerance and displayed lower ROS (reactive oxygen species), malondialdehyde (MDA) and Na+ contents; higher biomass, potassium content, soluble sugar content, and peroxidase activity; and higher expression levels of NtSOD, NtPOD and NtCAT. Protein abundance analysis revealed 123 differentially expressed proteins between the transgenic and wild-type plants. These proteins were functionally classified into 18 categories and are involved in 41 metabolic pathways. Furthermore, among the 123 proteins, eight proteins involved in the ROS-scavenging system, 12 involved in photosynthesis and energy metabolism processes, two stress response proteins, one signal transduction protein and one disulfide isomerase were significantly upregulated. Furthermore, three novel proteins that may be involved in the plant salt response were also identified. The results of our study indicate that an enhanced ROS-scavenging ability, together with the expression of proteins related to energy mobilization and the stress response, functions in the confirmed salt resistance of transgenic tobacco plants. Our data provide valuable information for research on the function of NtPRX63 in tobacco in response to abiotic stress.

Glutathione S-Transferase Regulates Mitochondrial Populations in Axons through Increased Glutathione Oxidation.

Mitochondria are essential in long axons to provide metabolic support and sustain neuron integrity. A healthy mitochondrial pool is maintained by biogenesis, transport, mitophagy, fission, and fusion, but how these events are regulated in axons is not well defined. Here, we show that the Drosophila glutathione S-transferase (GST) Gfzf prevents mitochondrial hyperfusion in axons. Gfzf loss altered redox balance between glutathione (GSH) and oxidized glutathione (GSSG) and initiated mitochondrial fusion through the coordinated action of Mfn and Opa1. Gfzf functioned epistatically with the thioredoxin peroxidase Jafrac1 and the thioredoxin reductase 1 TrxR-1 to regulate mitochondrial dynamics. Altering GSH:GSSG ratios in mouse primary neurons in vitro also induced hyperfusion. Mitochondrial changes caused deficits in trafficking, the metabolome, and neuronal physiology. Changes in GSH and oxidative state are associated with neurodegenerative diseases like Alzheimer's. Our demonstration that GSTs are key in vivo regulators of axonal mitochondrial length and number provides a potential mechanistic link.

Orchestration of Cu-Zn SOD and class III peroxidase with upstream interplay between NADPH oxidase and PM H+-ATPase mediates root growth in Vigna radiata (L.) Wilczek.

Post-germination plant growth depends on the regulation of reactive oxygen species (ROS) metabolism, spatiotemporal pH changes and Ca+2 homeostasis, whose potential integration has been studied during Vigna radiata (L.) Wilczek root growth. The dissipation of proton (H+) gradients across plasma membrane (PM) by CCCP (protonophore) and the inhibition of PM H+-ATPase by sodium orthovanadate repressed SOD (superoxide dismutase; EC 1.15.1.1) activity as revealed by spectrophotometric and native PAGE assay results. Similar results derived from treatment with DPI (NADPH oxidase inhibitor) and Tiron (O2- scavenger) denote a functional synchronization of SOD, PM H+-ATPase and NOX, as the latter two enzymes are substrate sources for SOD (H+ and O2-, respectively) and are involved in a feed-forward loop. After SOD inactivation, a decline in apoplastic H2O2 content was observed in each treatment group, emerging as a possible cause of the diminution of class III peroxidase (Prx; EC 1.11.1.7), which utilizes H2O2 as a substrate. In agreement with the pivotal role of Ca+2 in PM H+-ATPase and NOX activation, Ca+2 homeostasis antagonists, i.e., LaCl3 (Ca+2 channel inhibitor), EGTA (Ca+2 chelator) and LiCl (endosomal Ca+2 release blocker), inhibited both SOD and Prx. Finally, a drastic reduction in apoplastic OH (hydroxyl radical) concentrations (induced by each treatment, leading to Prx inhibition) was observed via fluorometric analysis. A consequential inhibition of root growth observed under each treatment denotes the importance of the orchestrated functioning of PM H+-ATPase, NOX, Cu-Zn SOD and Prx during root growth. A working model demonstrating postulated enzymatic synchronization with an intervening role of Ca+2 is proposed.

Glutathione peroxidase 7 has potential tumour suppressor functions that are silenced by location-specific methylation in oesophageal adenocarcinoma.

OBJECTIVE: To investigate the potential tumour suppressor functions of glutathione peroxidase 7 (GPX7) and examine the interplay between epigenetic and genetic events in regulating its expression in oesophageal adenocarcinomas (OAC). DESIGN: In vitro and in vivo cell models were developed to investigate the biological and molecular functions of GPX7 in OAC. RESULTS: Reconstitution of GPX7 in OAC cell lines, OE33 and FLO-1, significantly suppressed growth as shown by the growth curve, colony formation and EdU proliferation assays. Meanwhile, GPX7-expressing cells displayed significant impairment in G1/S progression and an increase in cell senescence. Concordant with the above functions, Western blot analysis displayed higher levels of p73, p27, p21 and p16 with a decrease in phosphorylated retinoblastoma protein (RB), indicating its increased tumour suppressor activities. On the contrary, knockdown of GPX7 in HET1A cells (an immortalised normal oesophageal cell line) rendered the cells growth advantage as indicated with a higher EdU rate, lower levels of p73, p27, p21 and p16 and an increase in phosphorylated RB. We confirmed the tumour suppressor function in vivo using GPX7-expressing OE33 cells in a mouse xenograft model. Pyrosequencing of the GPX7 promoter region (-162 to +138) demonstrated location-specific hypermethylation between +13 and +64 in OAC (69%, 54/78). This was significantly associated with the downregulation of GPX7 (p<0.01). Neither mutations in the coding exons of GPX7 nor DNA copy number losses were frequently present in the OAC examined (<5%). CONCLUSIONS: Our data suggest that GPX7 possesses tumour suppressor functions in OAC and is silenced by location-specific promoter DNA methylation.

Glutathione peroxidase 7 utilizes hydrogen peroxide generated by Ero1α to promote oxidative protein folding.

AIMS: Ero1 flavoproteins catalyze oxidative folding in the endoplasmic reticulum (ER), consuming oxygen and generating hydrogen peroxide (H2O2). The ER-localized glutathione peroxidase 7 (GPx7) shows protein disulfide isomerase (PDI)-dependent peroxidase activity in vitro. Our work aims at identifying the physiological role of GPx7 in the Ero1α/PDI oxidative folding pathway and at dissecting the reaction mechanisms of GPx7. RESULTS: Our data show that GPx7 can utilize Ero1α-produced H2O2 to accelerate oxidative folding of substrates both in vitro and in vivo. H2O2 oxidizes Cys57 of GPx7 to sulfenic acid, which can be resolved by Cys86 to form an intramolecular disulfide bond. Both the disulfide form and sulfenic acid form of GPx7 can oxidize PDI for catalyzing oxidative folding. GPx7 prefers to interact with the a domain of PDI, and intramolecular cooperation between the two redox-active sites of PDI increases the activity of the Ero1α/GPx7/PDI triad. INNOVATION: Our in vitro and in vivo evidence provides mechanistic insights into how cells consume potentially harmful H2O2 while optimizing oxidative protein folding via the Ero1α/GPx7/PDI triad. Cys57 can promote PDI oxidation in two ways, and Cys86 emerges as a novel noncanonical resolving cysteine. CONCLUSION: GPx7 promotes oxidative protein folding, directly utilizing Ero1α-generated H2O2 in the early secretory compartment. Thus, the Ero1α/GPx7/PDI triad generates two disulfide bonds and two H2O molecules at the expense of a single O2 molecule.

Deficiency of NPGPx, an oxidative stress sensor, leads to obesity in mice and human.

Elevated oxidative stress is closely associated with obesity. Emerging evidence shows that instead of being a consequence of obesity, oxidative stress may also contribute to fat formation. Nonselenocysteine-containing phospholipid hydroperoxide glutathione peroxidase (NPGPx) is a conserved oxidative stress sensor/transducer and deficiency of NPGPx causes accumulation of reactive oxygen species (ROS). In this communication, we show that NPGPx was highly expressed in preadipocytes of adipose tissue. Deficiency of NPGPx promoted preadipocytes to differentiate to adipocytes via ROS-dependent dimerization of protein kinase A regulatory subunits and activation of CCAAT/enhancer-binding protein beta (C/EBPß). This enhanced adipogenesis was alleviated by antioxidant N-acetylcysteine (NAC). Consistently, NPGPx-deficient mice exhibited markedly increased fat mass and adipocyte hypertrophy, while treatment with NAC ablated these phenotypes. Furthermore, single nucleotide polymorphisms (SNPs) in human NPGPx gene, which correlated with lower NPGPx expression level in adipose tissue, were associated with higher body mass index (BMI) in several independent human populations. These results indicate that NPGPx protects against fat accumulation in mice and human via modulating ROS, and highlight the importance of targeting redox homeostasis in obesity management.

Oxidation of the yeast mitochondrial thioredoxin promotes cell death.

AIMS: Yeast, like other eukaryotes, contains a complete mitochondrial thioredoxin system comprising a thioredoxin (Trx3) and a thioredoxin reductase (Trr2). Mitochondria are a main source of reactive oxygen species (ROS) in eukaryotic organisms, and this study investigates the role of Trx3 in regulating cell death during oxidative stress conditions. RESULTS: We have previously shown that the redox state of mitochondrial Trx3 is buffered by the glutathione redox couple such that oxidized mitochondrial Trx3 only accumulates in mutants simultaneously lacking Trr2 and a glutathione reductase (Glr1). We show here that the redox state of mitochondrial Trx3 is important for yeast growth and its oxidation in a glr1 trr2 mutant induces programmed cell death. Apoptosis is dependent on the Yca1 metacaspase, since loss of YCA1 abrogates cell death induced by oxidized Trx3. Our data also indicate a role for a mitochondrial 1-cysteine (Cys) peroxiredoxin (Prx1) in the oxidation of Trx3, since Trx3 does not become oxidized in glr1 trr2 mutants or in a wild-type strain exposed to hydrogen peroxide in the absence of PRX1. INNOVATION: This study provides evidence that the redox state of a mitochondrial thioredoxin regulates yeast apoptosis in response to oxidative stress conditions. Moreover, the results identify a signaling pathway, where the thioredoxin system functions in both antioxidant defense and in controlling cell death. CONCLUSIONS: Mitochondrial Prx1 functions as a redox signaling molecule that oxidizes Trx3 and promotes apoptosis. This would mean that under conditions where Prx1 cannot detoxify mitochondrial ROS, it induces cell death to remove the affected cells.

Functional analysis of potato genes involved in quantitative resistance to Phytophthora infestans.

The most significant threat to potato production worldwide is the late blight disease, which is caused by the oomycete pathogen Phytophthora infestans. Based on previous cDNA microarrays and cDNA-amplified fragment length polymorphism analysis, 63 candidate genes that are expected to contribute to developing a durable resistance to late blight were selected for further functional analysis. We performed virus-induced gene silencing (VIGS) to these candidate genes on both Nicotiana benthamiana and potato, subsequently inoculated detached leaves and assessed the resistance level. Ten genes decreased the resistance to P. infestans after VIGS treatment. Among those, a lipoxygenase (LOX; EC 1.13.11.12) and a suberization-associated anionic peroxidase affected the resistance in both N. benthamiana and potato. Our results identify genes that may play a role in quantitative resistance mechanisms to late blight.

Peroxides and peroxidases in the endoplasmic reticulum: integrating redox homeostasis and oxidative folding.

SIGNIFICANCE: The endoplasmic reticulum (ER), the port of entry into the secretory pathway, is a complex organelle that performs many fundamental functions, including protein synthesis and quality control, Ca(2+) storage and signaling. Redox homeostasis is of paramount importance for allowing the efficient folding of secretory proteins, most of which contain essential disulfide bonds. RECENT ADVANCES: revealed that an intricate protein network sustains the processes of disulfide bond formation and reshuffling in the ER. Remarkably, H(2)O(2), which is a known by-product of Ero1 flavoproteins in cells, is utilized by peroxiredoxin-4 and glutathione peroxidases-7 and -8, which reside in the mammalian secretory compartment and further fuel oxidative protein folding while limiting oxidative damage. CRITICAL ISSUES: that remain to be addressed are the sources, diffusibility and signaling role(s) of H(2)O(2) in and between organelles and cells, how the emerging redundancy in the systems is coupled to precise regulation, and how the distinct pathways operating in the early secretory compartment are integrated with one another. FUTURE DIRECTIONS: A further dissection of the pathways that integrate folding, redox homeostasis, and signaling in the early secretory pathway may allow to manipulate protein homeostasis and survival-death decisions in degenerative diseases or cancer.

Stage-specific expression of TNFα regulates bad/bid-mediated apoptosis and RIP1/ROS-mediated secondary necrosis in Birnavirus-infected fish cells.

Infectious pancreatic necrosis virus (IPNV) can induce Bad-mediated apoptosis followed by secondary necrosis in fish cells, but it is not known how these two types of cell death are regulated by IPNV. We found that IPNV infection can regulate Bad/Bid-mediated apoptotic and Rip1/ROS-mediated necrotic death pathways via the up-regulation of TNFα in zebrafish ZF4 cells. Using a DNA microarray and quantitative RT-PCR analyses, two major subsets of differentially expressed genes were characterized, including the innate immune response gene TNFα and the pro-apoptotic genes Bad and Bid. In the early replication stage (0-6 h post-infection, or p.i.), we observed that the pro-inflammatory cytokine TNFα underwent a rapid six-fold induction. Then, during the early-middle replication stages (6-12 h p.i.), TNFα level was eight-fold induction and the pro-apoptotic Bcl-2 family members Bad and Bid were up-regulated. Furthermore, specific inhibitors of TNFα expression (AG-126 or TNFα-specific siRNA) were used to block apoptotic and necrotic death signaling during the early or early-middle stages of IPNV infection. Inhibition of TNFα expression dramatically reduced the Bad/Bid-mediated apoptotic and Rip1/ROS-mediated necrotic cell death pathways and rescued host cell viability. Moreover, we used Rip1-specific inhibitors (Nec-1 and Rip1-specific siRNA) to block Rip1 expression. The Rip1/ROS-mediated secondary necrotic pathway appeared to be reduced in IPNV-infected fish cells during the middle-late stage of infection (12-18 h p.i.). Taken together, our results indicate that IPNV triggers two death pathways via up-stream induction of the pro-inflammatory cytokine TNFα, and these results may provide new insights into the pathogenesis of RNA viruses.

Airway peroxidases catalyze nitration of the {beta}2-agonist salbutamol and decrease its pharmacological activity.

ß(2)-agonists are the most effective bronchodilators for the rapid relief of asthma symptoms, but for unclear reasons, their effectiveness may be decreased during severe exacerbations. Because peroxidase activity and nitrogen oxides are increased in the asthmatic airway, we examined whether salbutamol, a clinically important ß(2)-agonist, is subject to potentially inactivating nitration. When salbutamol was exposed to myeloperoxidase, eosinophil peroxidase or lactoperoxidase in the presence of hydrogen peroxide (H(2)O(2)) and nitrite (NO(2)(-)), both absorption spectroscopy and mass spectrometry indicated formation of a new metabolite with features expected for the nitrated drug. The new metabolites showed an absorption maximum at 410 nm and pK(a) of 6.6 of the phenolic hydroxyl group. In addition to nitrosalbutamol (m/z 285.14), a salbutamol-derived nitrophenol, formed by elimination of the formaldehyde group, was detected (m/z 255.13) by mass spectrometry. It is noteworthy that the latter metabolite was detected in exhaled breath condensates of asthma patients receiving salbutamol but not in unexposed control subjects, indicating the potential for ß(2)-agonist nitration to occur in the inflamed airway in vivo. Salbutamol nitration was inhibited in vitro by ascorbate, thiocyanate, and the pharmacological agents methimazole and dapsone. The efficacy of inhibition depended on the nitrating system, with the lactoperoxidase/H(2)O(2)/NO(2)(-) being the most affected. Functionally, nitrated salbutamol showed decreased affinity for ß(2)-adrenergic receptors and impaired cAMP synthesis in airway smooth muscle cells compared with the native drug. These results suggest that under inflammatory conditions associated with asthma, phenolic ß(2)-agonists may be subject to peroxidase-catalyzed nitration that could potentially diminish their therapeutic efficacy.

Genetic and biochemical analysis of high iron toxicity in yeast: iron toxicity is due to the accumulation of cytosolic iron and occurs under both aerobic and anaerobic conditions.

Iron storage in yeast requires the activity of the vacuolar iron transporter Ccc1. Yeast with an intact CCC1 are resistant to iron toxicity, but deletion of CCC1 renders yeast susceptible to iron toxicity. We used genetic and biochemical analysis to identify suppressors of high iron toxicity in Δccc1 cells to probe the mechanism of high iron toxicity. All genes identified as suppressors of high iron toxicity in aerobically grown Δccc1 cells encode organelle iron transporters including mitochondrial iron transporters MRS3, MRS4, and RIM2. Overexpression of MRS3 suppressed high iron toxicity by decreasing cytosolic iron through mitochondrial iron accumulation. Under anaerobic conditions, Δccc1 cells were still sensitive to high iron toxicity, but overexpression of MRS3 did not suppress iron toxicity and did not result in mitochondrial iron accumulation. We conclude that Mrs3/Mrs4 can sequester iron within mitochondria under aerobic conditions but not anaerobic conditions. We show that iron toxicity in Δccc1 cells occurred under both aerobic and anaerobic conditions. Microarray analysis showed no evidence of oxidative damage under anaerobic conditions, suggesting that iron toxicity may not be solely due to oxidative damage. Deletion of TSA1, which encodes a peroxiredoxin, exacerbated iron toxicity in Δccc1 cells under both aerobic and anaerobic conditions, suggesting a unique role for Tsa1 in iron toxicity.

Role of cytochromes P450 and peroxidases in metabolism of the anticancer drug ellipticine: additional evidence of their contribution to ellipticine activation in rat liver, lung and kidney.

OBJECTIVE: Ellipticine is a potent antineoplastic agent exhibiting multiple mechanisms of action. This anticancer agent should be considered a pro-drug, whose pharmacological efficiency and/or genotoxic side effects are dependent on its cytochrome P450 (CYP)- and/or peroxidase-mediated activation to species forming covalent DNA adducts. The target of this study was to investigate a role of CYP and peroxidase enzymes in ellipticine oxidative activation in rats, a suitable model mimicking the fate of ellipticine in humans, in details. The contribution of pulmonary and renal CYP- and peroxidase enzymes to ellipticine metabolic activation is investigated and compared with that found in the liver. METHODS: Ellipticine oxidation and DNA adduct formation in vitro were investigated using microsomes isolated from liver, lung and kidney of rats, either control (untreated) or treated i.p. with a single dose of 40 mg of ellipticine per kg of body weight. HPLC with UV detection was employed for the separation and characterization of ellipticine metabolites. Inhibitors of CYPs and cyclooxygenase (prostaglandin H synthase, COX) were used to characterize the enzymes participating in ellipticine oxidative activation in rat liver, lung and kidney. Ellipticine-derived DNA adducts were detected by 32P-postlabeling. RESULTS: Using α-naphthoflavone, furafylline and ketoconazole, inhibitors of CYP1A, 1A2 and 3A, respectively, we found that the CYP1A and 3A enzymes play a major role in ellipticine activation to species forming DNA adducts in liver microsomes. Because of lower expression of these enzymes in lungs and kidneys, even after their induction by ellipticine, they play a minor role in ellipticine activation in these extrahepatic tissues. Arachidonic acid, a cofactor of COX, increased ellipticine activation in the microsomes of extrahepatic tissues. In addition, indomethacin, an inhibitor of COX, efficiently inhibited formation of ellipticine-derived DNA adduct in these microsomes. Based on these results, we attribute the higher activation of ellipticine in lung and kidney microsomes to COX than to CYP enzymes. CONCLUSION: The results demonstrate that whereas CYP enzymes of 1A and 3A subfamilies are the major enzymes activating ellipticine in rat livers, peroxidase COX plays a significant role in this process in lungs and kidneys.

Irreversible oxidation of the active-site cysteine of peroxiredoxin to cysteine sulfonic acid for enhanced molecular chaperone activity.

The thiol (-SH) of the active cysteine residue in peroxiredoxin (Prx) is known to be reversibly hyperoxidized to cysteine sulfinic acid (-SO(2)H), which can be reduced back to thiol by sulfiredoxin/sestrin. However, hyperoxidized Prx of an irreversible nature has not been reported yet. Using an antibody developed against the sulfonylated (-SO(3)H) yeast Prx (Tsa1p) active-site peptide (AFTFVCPTEI), we observed an increase in the immunoblot intensity in proportion to the H(2)O(2) concentrations administered to the yeast cells. We identified two species of hyperoxidized Tsa1p: one can be reduced back (reversible) with sulfiredoxin, and the other cannot (irreversible). Irreversibly hyperoxidized Tsa1p was identified as containing the active-site cysteine sulfonic acid (Tsa1p-SO(3)H) by mass spectrometry. Tsa1p-SO(3)H was not an autoxidation product of Tsa1p-SO(2)H and was maintained in yeast cells even after two doubling cycles. Tsa1p-SO(3)H self-assembled into a ring-shaped multimeric form was shown by electron microscopy. Although the Tsa1p-SO(3)H multimer lost its peroxidase activity, it gained approximately 4-fold higher chaperone activity compared with Tsa1p-SH. In this study, we identify an irreversibly hyperoxidized Prx, Tsa1p-SO(3)H, with enhanced molecular chaperone activity and suggest that Tsa1p-SO(3)H is a marker of cumulative oxidative stress in cells.

The yeast Tsa1 peroxiredoxin is a ribosome-associated antioxidant.

The yeast Tsa1 peroxiredoxin, like other 2-Cys peroxiredoxins, has dual activities as a peroxidase and as a molecular chaperone. Its peroxidase function predominates in lower-molecular-mass forms, whereas a super-chaperone form predominates in high-molecular-mass complexes. Loss of TSA1 results in aggregation of ribosomal proteins, indicating that Tsa1 functions to maintain the integrity of the translation apparatus. In the present study we report that Tsa1 functions as an antioxidant on actively translating ribosomes. Its peroxidase activity is required for ribosomal function, since mutation of the peroxidatic cysteine residue, which inactivates peroxidase but not chaperone activity, results in sensitivity to translation inhibitors. The peroxidatic cysteine residue is also required for a shift from ribosomes to its high-molecular-mass form in response to peroxide stress. Thus Tsa1 appears to function predominantly as an antioxidant in protecting both the cytosol and actively translating ribosomes against endogenous ROS (reactive oxygen species), but shifts towards its chaperone function in response to oxidative stress conditions. Analysis of the distribution of Tsa1 in thioredoxin system mutants revealed that the ribosome-associated form of Tsa1 is increased in mutants lacking thioredoxin reductase (trr1) and thioredoxins (trx1 trx2) in parallel with the general increase in total Tsa1 levels which is observed in these mutants. In the present study we show that deregulation of Tsa1 in the trr1 mutant specifically promotes translation defects including hypersensitivity to translation inhibitors, increased translational error-rates and ribosomal protein aggregation. These results have important implications for the role of peroxiredoxins in stress and growth control, since peroxiredoxins are likely to be deregulated in a similar manner during many different disease states.

Sulfiredoxin, the cysteine sulfinic acid reductase specific to 2-Cys peroxiredoxin: its discovery, mechanism of action, and biological significance.

Peroxiredoxin (Prx) is a family of bifunctional proteins that exhibit peroxidase and chaperone activities. Prx proteins contain a conserved Cys residue that undergoes a redox change between thiol and disulfide states. 2-Cys Prx enzymes, a subgroup of Prx family, are intrinsically susceptible to reversible hyperoxidation to cysteine sulfinic acid during catalysis. Cysteine hyperoxidation of Prx was shown to result in loss of peroxidase activity and a concomitant gain of chaperone activity. Reduction of sulfinic Prx enzymes, the first known biological example of such a reaction, is catalyzed by sulfiredoxin (Srx) in the presence of ATP. Srx appears to exist solely to support the reversible sulfinic modification of 2-Cys Prx enzymes. Srx specifically binds to 2-Cys Prx enzymes by recognizing several critical surface-exposed residues of the Prxs, and transfer the gamma-phosphate of ATP to their sulfinic moiety, using its conserved cysteine as the phosphate carrier. The resulting sulfinic phosphoryl ester is reduced to cysteine after oxidation of four thiol equivalents.

Are peroxiredoxins tumor suppressors?

It has been known for many years that free radicals, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS), promote diseases such as cancer. Peroxiredoxins (Prdxs) are small H(2)O(2) scavenging proteins that appear to have tumor preventive functions since loss of Prdx1 in mice leads to premature death from cancer. However, as Prdxs are antioxidants they also scavenge the H(2)O(2) in cancer cells that way supporting survival and tumor maintenance. This suggests that Prdxs function as tumor 'preventers' rather than as tumor suppressors since they do not induce cell death when re-expressed in cancer cells, as it occurs with the tumor suppressor p53. Therefore, the knowledge of Prdx function and regulation may help provide a fuller understanding of the role of ROS in tumorigenesis.

The significance of type II and PrxQ peroxiredoxins for antioxidative stress response in the purple bacterium Rhodobacter sphaeroides.

Two peroxiredoxins, classified as Type II and PrxQ, were characterized in the purple non-sulfur photosynthetic bacterium Rhodobacter sphaeroides. Both recombinant proteins showed remarkable thioredoxin-dependent peroxidase activity with broad substrate specificity in vitro. Nevertheless, PrxQ of R. sphaeroides, unlike typical PrxQs studied to date, does not contain one of the two conserved catalytic Cys residues. We found that R. sphaeroides PrxQ and other PrxQ-like proteins from several organisms conserve a different second Cys residue, indicating that these proteins should be categorized into a novel PrxQ subfamily. Disruption of either the Type II or PrxQ gene in R. sphaeroides had a dramatic effect on cell viability when the cells were grown under aerobic light or oxidative stress conditions created by exogenous addition of reactive oxygen species to the medium. Growth rates of the mutants were significantly decreased compared with that of wild type under aerobic but not anaerobic conditions. These results indicate that the peroxiredoxins are crucial for antioxidative stress response in this bacterium. The gene disruptants also demonstrated reduced levels of photopigment synthesis, suggesting that the peroxiredoxins are directly or indirectly involved in regulated synthesis of the photosynthetic apparatus.