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During land plant evolution, the number of genes encoding for components of the thiol redox regulatory network and the generator systems of reactive oxygen species (ROS) expanded, tentatively indicating that they have a role in tailored environmental acclimatization. This hypothesis has been validated both experimentally and theoretically during the last few decades. Recent developments of dynamic redox-sensitive GFP (roGFP)-based in vivo sensors for H2O2 and the redox potential of the glutathione pool have paved the way for dissecting the kinetics changes that occur in these crucial parameters in response to environmental stressors. The versatile cellular redox sensory and response regulatory system monitors alterations in redox metabolism and controls the activity of redox target proteins, and thereby affects most, if not all, cellular processes ranging from transcription to translation and metabolism. This review uses examples to describe the role of the redox- and ROS-dependent regulatory network in realising the appropriate responses to diverse environmental stresses. The selected case studies concern different environmental challenges, namely excess excitation energy, the heavy metal cadmium and the metalloid arsenic, nitrogen or phosphate shortages as examples for nutrient deficiency, wounding, and nematode infestation. Each challenge affects the redox-regulatory and ROS network, but our present state of knowledge also points toward pressing questions that remain open in relation to the translation of redox regulation to environmental acclimatization. [ABSTRACT FROM AUTHOR]

Summary: Peroxiredoxins (PRXs) are intracellular anti‐oxidative enzymes but work as inflammatory amplifiers under the extracellular condition. To date, the function of PRXs in the pathogenesis of multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) is not fully understood. The aim of this study was to investigate whether PRXs play a role in the pathogenesis of MS and NMOSD. We analyzed levels of PRXs (PRX1, PRX5 and PRX6) in the cerebrospinal fluid (CSF) and serum of 16 patients with MS, 16 patients with NMOSD and 15 patients with other neurological disorders (ONDs). We identified potential correlations between significantly elevated PRXs levels and the clinical variables in patients with MS and NMOSD. Additionally, pathological analyses of PRXs (PRX1‐6) in the central nervous system (CNS) were performed using the experimental autoimmune encephalomyelitis (EAE), animal model of MS. We found that serum levels of PRX5 and PRX6 in patients with MS and NMOSD were higher compared with those in patients with ONDs (P < 0·05). Furthermore, high levels of PRX5 and PRX6 were partly associated with blood–brain barrier dysfunction and disease duration in NMOSD patients. No significant elevation was found in CSF PRXs levels of MS and NMOSD. Spinal cords from EAE mice showed remarkable PRX5 staining, especially in CD45+ infiltrating cells. In conclusion, PRX5 and PRX6 may play a role in the pathogeneses of MS and NMOSD. [ABSTRACT FROM AUTHOR]

Redox regulation in heterotrophic organisms relies on NADPH, thioredoxins (TRXs), and an NADPH-dependent TRX reductase (NTR). In contrast, chloroplasts harbor two redox systems, one that uses photoreduced ferredoxin (Fd), an Fd-dependent TRX reductase (FTR), and TRXs, which links redox regulation to light, and NTRC, which allows the use of NADPH for redox regulation. It has been shown that NTRC-dependent regulation of 2-Cys peroxiredoxin (PRX) is critical for optimal function of the photosynthetic apparatus. Thus, the objective of the present study was the analysis of the interaction of NTRC and 2-Cys PRX in vivo and the identification of proteins interacting with them with the aim of identifying chloroplast processes regulated by this redox system. To assess this objective, we generated Arabidopsis thaliana plants expressing either an NTRC–tandem affinity purification (TAP)-Tag or a green fluorescent protein (GFP)–TAP-Tag, which served as a negative control. The presence of 2-Cys PRX and NTRC in complexes isolated from NTRC–TAP-Tag-expressing plants confirmed the interaction of these proteins in vivo. The identification of proteins co-purified in these complexes by MS revealed the relevance of the NTRC–2-Cys PRX system in the redox regulation of multiple chloroplast processes. The interaction of NTRC with selected targets was confirmed in vivo by bimolecular fluorescence complementation (BiFC) assays. [ABSTRACT FROM AUTHOR]

Plant 2-Cys peroxiredoxins (2-CysPRXs) are abundant plastidial thiol-peroxidases involved in key signaling processes such as photosynthesis deactivation at night. Their functions rely on the redox status of their two cysteines and on the enzyme quaternary structure, knowledge of which remains poor in plant cells. Using ex vivo and biochemical approaches, we thoroughly characterized the 2-CysPRX dimer/monomer distribution, hyperoxidation level, and thiol content in Arabidopsis, barley, and potato in relation to the light cycle. Our data reveal that the enzyme hyperoxidization level and its distribution as a dimer and monomer vary through the light cycle in a species-dependent manner. A differential susceptibility to hyperoxidation was observed for the two Arabidopsis 2-CysPRX isoforms and among the proteins of the three species, and was associated to sequence variation in hyperoxidation resistance motifs. Alkylation experiments indicate that only a minor fraction of the 2-CysPRX pool carries one free thiol in the three species, and that this content does not change during the light period. We conclude that most plastidial 2-CysPRX forms are oxidized and propose that there is a species-dependent variability in their functions since dimer and hyperoxidized forms fulfill distinct roles regarding direct oxidation of partners and signal transmission. [ABSTRACT FROM AUTHOR]

Peroxiredoxins from Pyrococcus horikoshii (PhPrx) and Thermococcus kodakaraensis (TkPrx) are highly homologous proteins sharing 196 of the 216 residues. We previously reported a pentagonal ring-type decameric structure of PhPrx. Here, we present the crystal structure of TkPrx. Despite their homology, unlike PhPrx, the quaternary structure of TkPrx was found to be a dodecamer comprised of six homodimers arranged in a hexagonal ring-type assembly. The possibility of the redox-dependent conversion of the molecular assembly, which had been observed in PhPrx, was excluded for TkPrx based on the crystal structure of a mutant in which all of the cysteine residues were substituted with serine. The monomer structures of the dodecameric TkPrx and decameric PhPrx coincided well, but there was a slight difference in the relative orientation of the two domains. Molecular assembly of PhPrx and TkPrx in solution evaluated by gel-filtration chromatography was consistent with the crystallographic results. For both PhPrx and TkPrx, the gel-filtration elution volume slightly increased with a decrease in the protein concentration, suggesting the existence of an equilibrium state between the decameric/dodecameric ring and lower-order assembly. This structural assembly difference between highly homologous Prxs suggests a significant influence of quaternary structure on function, worthy of further exploration. [ABSTRACT FROM AUTHOR]

The chloroplast redox network is composed of a complex set of thioredoxins (Trxs), reduced by ferredoxin (Fdx) via a Fdx-dependent Trx reductase (FTR), and an NADPH-dependent Trx reductase with a joint Trx domain, NTRC, which efficiently reduces 2-Cys peroxiredoxins (2-Cys Prxs). Recently, it was proposed that the redox balance of 2-Cys Prxs maintains the redox state of f -type Trxs, thus allowing the proper redox regulation of Calvin–Benson cycle enzymes such as fructose 1,6-bisphosphatase (FBPase). Here, we have addressed whether the action of 2-Cys Prxs is also exerted on Trx x. To that end, an Arabidopsis thaliana quadruple mutant, ntrc-trxx-Δ2cp, which is knocked out for NTRC and Trx x, and contains severely decreased levels of 2-Cys Prxs, was generated. In contrast to ntrc-trxx, which showed a severe growth inhibition phenotype and poor photosynthetic performance, the ntrc-trxx-Δ2cp mutant showed a significant recovery of growth rate and photosynthetic efficiency, indicating that the content of 2-Cys Prxs is critical for the performance of plants lacking both NTRC and Trx x. Light-dependent reduction of FBPase was severely impaired in mutant plants lacking NTRC or NTRC plus Trx x, despite the fact that neither NTRC nor Trx x is an effective reductant of this enzyme. However, FBPase reduction was recovered in the ntrc-trxx-Δ2cp mutant. Our results show that the redox balance of 2-Cys Prxs, which is mostly dependent on NTRC, modulates the activity of Trx x in a similar way as f -type Trxs, thus suggesting that the activity of these Trxs is highly interconnected. [ABSTRACT FROM AUTHOR]

Peroxiredoxin from Pyrococcus horikoshii (PhPrx) is a decameric protein formed by ring-type assembly of five dimers. To engineer the quaternary structure of PhPrx, we created a mutant PhPrx (PhPrx6m) by introducing six point mutations designed to dissociate PhPrx into dimers. Although PhPrx6m was a dimer in solution, the six dimers assembled into a dodecamer following crystallization. In the crystal structure, PhPrx6m was overoxidized, and the peroxidatic cysteine was in sulfonic acid form and two cysteines in the C-terminal region were linked by an intramolecular disulfide bond. Thus, we characterized the wild-type PhPrx overoxidized by hydrogen peroxide (PhPrxPer). Analytical ultracentrifugation showed that PhPrxPer had a higher molecular mass in solution than PhPrx. This was confirmed by analysis of the crystal structure of PhPrxPer, which was found to form a ring-type dodecamer composed of six dimers. The monomeric structures of PhPrx6m and PhPrxPer differed from that of PhPrx in the relative orientation of two domains, reflecting the number of dimers in the ring-type assembly. Unlike PhPrx, homologous peroxiredoxin from Aeropyrum pernix (ApPrx) did not undergo hexameric association. This property can be explained by the stronger connection between the two domains in ApPrx due to its C-terminal extension relative to PhPrx. [ABSTRACT FROM AUTHOR]

Fine-tuned and coordinated regulation of transport, metabolism and redox homeostasis allows plants to acclimate to osmotic and ionic stress caused by high salinity. Sugar beet is a highly salt tolerant crop plant and is therefore an interesting model to study sodium chloride (NaCl) acclimation in crops. Sugar beet plants were subjected to a final level of 300 mM NaCl for up to 14 d in hydroponics. Plants acclimated to NaCl stress by maintaining its growth rate and adjusting its cellular redox and reactive oxygen species (ROS) network. In order to understand the unusual suppression of ROS accumulation under severe salinity, the regulation of elements of the redox and ROS network was investigated at the transcript level. First, the gene families of superoxide dismutase (SOD), peroxiredoxins (Prx), alternative oxidase (AOX), plastid terminal oxidase (PTOX) and NADPH oxidase (RBOH) were identified in the sugar beet genome. Salinity induced the accumulation of Cu-Zn-SOD, Mn-SOD, Fe-SOD3, all AOX isoforms, 2-Cys-PrxB, PrxQ, and PrxIIF. In contrast, Fe-SOD1, 1-Cys-Prx, PrxIIB and PrxIIE levels decreased in response to salinity. Most importantly, RBOH transcripts of all isoforms decreased. This pattern offers a straightforward explanation for the low ROS levels under salinity. Promoters of stress responsive antioxidant genes were analyzed in silico for the enrichment of cis-elements, in order to gain insights into gene regulation. The results indicate that special cis-elements in the promoters of the antioxidant genes in sugar beet participate in adjusting the redox and ROS network and are fundamental to high salinity tolerance of sugar beet. [ABSTRACT FROM AUTHOR]

2-Cysteine peroxiredoxins (2-CysPrxs) switch between functions as a thiol peroxidase, chaperone, an interaction partner and possibly a proximity-based oxidase in a redox-dependent manner. In photosynthetic eukaryotes, 2-CysPrx localizes to the plastid, functions in the context of photosynthesis and enables an ascorbate peroxidase-independent water-water cycle for detoxifying H2O2. The high degree of evolutionary conservation of 2-CysPrx suggests that the switching is an essential characteristic and needed to transduce redox information to downstream pathways and regulation. The study aimed at exploring the dissociation behavior of 2-CysPrx and its interactions with cyclophilin depending on bulk phase conditions. Isothermal titration microcalorimetry (ITC), dynamic light scattering and size exclusion chromatography (SEC) proved the previously suggested model that reduced 2-CysPrx below a critical transition concentration (CTC) exists in its dimeric state, and above the CTC adopts the decameric state. The presence of cyclophilin 20-3 (Cyp20-3) affected the CTC of a 2-CysPrx decamer suggesting interaction which was further quantified by direct titration of 2-CysPrx with Cyp20-3, and in overlays. Finally catalytic inactivation assays showed the higher catalytic efficiency of 2-CysPrx at pH 8 compared with pH 7.2, but also revealed increased inactivation by hyperoxidation at pH 8. Interestingly, calculation of the average turnover number until inactivation gave rather similar values of 243 and 268 catalytic cycles at pH 8 and pH 7.2, respectively. These quantitative data support a model where 2-CysPrx and Cyp20-3, by interaction, form a redox-sensitive regulatory module in the chloroplast which is under control of the photosynthesis-linked stromal pH value, the redox state and additional stromal protein factor(s). [ABSTRACT FROM AUTHOR]

* Background and Aims Water is an increasingly scarce resource that limits crop productivity in many parts of the world, and the frequency and severity of drought are predicted to increase as a result of climate change. Improving tolerance to drought stress is therefore important for maximizing future crop yields. The aim of this study was to compare the effects of drought on soybean (Glycine max) leaves and nodules in order to define phenotypic markers and changes in cellular redox state that characterize the stress response in different organs, and to characterize the relationships between leaf and nodule senescence during drought. * Methods Leaf and crown nodule metabolite pools were measured together with leaf and soil water contents, and leaf chlorophyll, total protein contents and chlorophyll a fluorescence quenching parameters in nodulated soybeans that were grown under either well-watered conditions or deprived of water for up to 21 d. * Key Results Ureides, ascorbate, protein, chlorophyll and the ratios of variable chlorophyll a fluorescence (Fv') to maximal chlorophyll a fluorescence (Fm') fell to levels below detection in the oldest leaves after 21 d of drought. While these drought-induced responses were not observed in the youngest leaf ranks, the Fv'/Fm' ratios, pyridine nucleotide levels and the reduction state of the ascorbate pool were lower in all leaf ranks after 21 d of drought. In contrast to leaves, total nodule protein, pyridine nucleotides, ureides, ascorbate and glutathione contents increased as a result of the drought treatment. However, the nodule ascorbate pool was significantly less reduced as a result of drought. Higher levels of transcripts encoding two peroxiredoxins were detected in nodules exposed to drought stress but senescence-associated transcripts and other mRNAs encoding redox-related proteins were similar under both conditions. * Conclusions While the physiological impact of the drought was perceived throughout the shoot, stress-induced senescence occurred only in the oldest leaf ranks. At this stage, a number of drought-induced changes in nodule metabolites were observed but no metabolite or transcript markers of senescence could be detected. It is concluded that stress-induced senescence in the lowest leaf ranks precedes nodule senescence, suggesting that leaves of low photosynthetic capacity are sacrificed in favour of nodule nitrogen metabolism. [ABSTRACT FROM AUTHOR]

In plants, the presence of thioredoxin (Trx), peroxiredoxin (Prx), and sulfiredoxin (Srx) has been reported as a component of a redox system involved in the control of dithiol-disulfide exchanges of target proteins, which modulate redox signalling during development and stress adaptation. Plant thiols, and specifically redox state and regulation of thiol groups of cysteinyl residues in proteins and transcription factors, are emerging as key components in the plant response to almost all stress conditions. They function in both redox sensing and signal transduction pathways. Scarce information exists on the transcriptional regulation of genes encoding Trx/Prx and on the transcriptional and post-transcriptional control exercised by these proteins on their putative targets. As another point of control, posttranslational regulation of the proteins, such as S-nitrosylation and S-oxidation, is of increasing interest for its effect on protein structure and function. Special attention is given to the involvement of the Trx/Prx/Srx system and its redox state in plant signalling under stress, more specifically under abiotic stress conditions, as an important cue that influences plant yield and growth. This review focuses on the regulation of Trx and Prx through cysteine S-oxidation and/ or S-nitrosylation, which affects their functionality. Some examples of redox regulation of transcription factors and Trx- and Prx-related genes are also presented. [ABSTRACT FROM AUTHOR]

Background and Aims Eutrema parvulum (synonym, Thellungiella parvula) is an extreme halophyte that thrives in high salt concentrations (100–150 mm) and is closely related to Arabidopsis thaliana. The main aim of this study was to determine how E. parvulum uses reactive oxygen species (ROS) production, antioxidant systems and redox regulation of the electron transport system in chloroplasts to tolerate salinity. Methods Plants of E. parvulum were grown for 30 d and then treated with either 50, 200 or 300 mm NaCl. Physiological parameters including growth and water relationships were measured. Activities of antioxidant enzymes were determined in whole leaves and chloroplasts. In addition, expressions of chloroplastic redox components such as ferrodoxin thioredoxin reductases (FTR), NADPH thioredoxin reductases (NTRC), thioredoxins (TRXs) and peroxiredoxins (PRXs), as well as genes encoding enzymes of the water–water cycle and proline biosynthesis were measured. Key Results Salt treatment affected water relationships negatively and the accumulation of proline was increased by salinity. E. parvulum was able to tolerate 300 mm NaCl over long periods, as evidenced by H2O2 content and lipid peroxidation. While Ca2+ and K+ concentrations were decreased by salinity, Na+ and Cl– concentrations increased. Efficient induction of activities and expressions of water–water cycle enzymes might prevent accumulation of excess ROS in chloroplasts and therefore protect the photosynthetic machinery in E. parvulum. The redox homeostasis in chloroplasts might be achieved by efficient induction of expressions of redox regulatory enzymes such as FTR, NTRC, TRXs and PRXs under salinity. Conclusions E. parvulum was able to adapt to osmotic stress by an efficient osmotic adjustment mechanism involving proline and was able to regulate its ion homeostasis. In addition, efficient induction of water–water cycle enzymes and other redox regulatory components such as TRXs and PRXs in chloroplasts were able to protect the chloroplasts from salinity-induced oxidative stress. [ABSTRACT FROM AUTHOR]

The article studies the functional analysis of peroxiredoxin isoforms in Euglena gracilis. Topics discussed include study of metabolism of reactive oxygen species (ROS) in Euglena, isolation of four full length complementary deoxyribonucleic acids (cDNAs) of four Euglena peroxiredoxins (EgPrxs) and similarity observed between catalytic efficiencies of recombinant EgPrxs and plant thiol-peroxidases.

2-Cysteine peroxiredoxins (2-CysPrxs) are ubiquitous and highly abundant proteins that serve multiple functions as peroxidases, chaperones, and thiol oxidases and in redox-dependent cell signalling. The chloroplast protein plays a role in seedling development and protection of the photosynthetic apparatus. This study aimed to unequivocally link conformation and function. To this end, a set of non-tagged site-directed mutagenized At2-CysPrx variants was engineered, which mimicked the conformational states and their specific functions: hyperoxidized form (C54D), reduced form (C54S, C176S), oxidized form (C54DC176K), phosphorylated form (T92D), reduced ability for oligomerization by interfering with the dimer–dimer interface (F84R) and a C-terminally truncated form [ΔC (–20 aa)]. These variants were fully or partly fixed in their quaternary structure and function, respectively, and were analysed for their conformational state and peroxidase and chaperone activity, as well as for their sensitivity to hyperoxidation. The presence of a His6-tag strongly influenced the properties of the protein. The ΔC variant became insensitive to hyperoxidation, while T92D and F84R became more sensitive. The C54D variant revealed the highest chaperone activity. The highest peroxidase activity was observed for the F84R and ΔC variants. Efficient interaction with NADP-dependent thioredoxin reductase C depended on the presence of Cys residues and the C-terminal tail. The results suggest that the structural flexibility is important for the switch between peroxidase and chaperone function and that evolution has conserved the functional switch instead of maximizing a single function. These variants are ideal tools for future conformation-specific studies in vivo and in vitro. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) have been regarded as harmful molecules that damage various molecules inside cells by oxidation and are responsible for ageing and various human diseases. However, recent studies have revealed an opposite aspect of ROS that these are actively generated in cells and mediate physiological intracellular signalling as second messengers. Several proteins have been shown to function as effectors for ROS, which are sensitively and reversibly oxidized by ROS. Such ROS-effector proteins commonly possess a highly reactive cysteine (Cys) residue, of which oxidation changes the protein function, thus enabling signal transmission to downstream targets. Among the ROS effectors, protein tyrosine phosphatase (PTP), thioredoxin (TRX) and peroxiredoxin (PRX) family proteins possess special domains/motifs to maintain the reactivity of Cys and utilize them to respond to ROS. Progressively advancing identification of ROS-effector proteins reveals the pleiotropic functions of ROS in physiological and pathological cell biology. [ABSTRACT FROM PUBLISHER]

The magnetotactic bacterium Magnetospirillum magneticum AMB-1 can grow at variable oxygen concentrations, although the intracellular magnetic structures, magnetosomes, are only synthesized under microaerobic or anaerobic conditions. Three members of the peroxiredoxin family were identified in M. magneticum AMB-1. All purified recombinant proteins displayed thiol-dependent peroxidase activities. Allelic replacement mutagenesis revealed that, although the absence of the three peroxidase genes had no effect on either the growth or the formation of magnetosome under anaerobic conditions, the growth of mutants was compromised in an aerobic culture. Moreover, an accelerated loss in the genomic 'magnetosome island' (MAI) was observed in the null mutants cultured in the presence of oxygen. Taken together, these data suggest that the thiol-peroxidases identified act as key antioxidants in magnetotactic bacteria and, as a result, contribute to maintaining their capacity to synthesize magnetosome by shielding the genetic stability of the genomic MAI in adaptation to constant physiological change and stress. [ABSTRACT FROM AUTHOR]

Mitochondria play an essential role in reactive oxygen species (ROS) signal transduction in plants. Redox regulation is an essential feature of mitochondrial function, with thioredoxin (Trx), involved in disulphide/dithiol interchange, playing a prominent role. To explore the participation of mitochondrial PsTrxo1, Mn-superoxide dismutase (Mn-SOD), peroxiredoxin (PsPrxII F), and alternative oxidase (AOX) under salt stress, their transcriptional and protein levels were analysed in pea plants growing under 150 mM NaCl for a short and a long period. The activities of mitochondrial Mn-SOD and Trx together with the in vivo activities of the alternative pathway (AP) and the cytochrome pathway (CP) were also determined, combined with the characterization of the plant physiological status as well as the mitochondrial oxidative indicators. The analysis of protein and mRNA levels and activities revealed the importance of the post-transcriptional and post-translational regulation of these proteins in the response to salt stress. Increases in AOX protein amount correlated with increases in AP capacity, whereas in vivo AP activity was maintained under salt stress. Similarly, Mn-SOD activity was also maintained. Under all the stress treatments, photosynthesis, stomatal conductance, and CP activity were decreased although the oxidative stress in leaves was only moderate. However, an increase in lipid peroxidation and protein oxidation was found in mitochondria isolated from leaves under the short-term salinity conditions. In addition, an increase in mitochondrial Trx activity was produced in response to the long-term NaCl treatment. The results support a role for PsTrxo1 as a component of the defence system induced by NaCl in pea mitochondria, providing the cell with a mechanism by which it can respond to changing environment protecting mitochondria from oxidative stress together with Mn-SOD, AOX, and PrxII F. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) pathogenesis is characterized by senile plaques in the brain and evidence of oxidative damage. Oxidative stress may precede plaque formation in AD; however, the link between oxidative damage and plaque formation remains unknown. Presenilins are transmembrane proteins in which mutations lead to accelerated plaque formation and early-onset familial Alzheimer's disease. Presenilins physically interact with two antioxidant enzymes thiol-specific antioxidant (TSA) and proliferation-associated gene (PAG) of the peroxiredoxin family. The functional consequences of these interactions are unclear. In the current study we expressed a presenilin transgene in Drosophila wing and sensory organ precursors of the fly. This caused phenotypes typical of Notch signaling loss-of-function mutations. We found that while expression of TSA or PAG alone produced no phenotype, co-expression of TSA and PAG with presenilin led to an enhanced Notch loss-of-function phenotype. This phenotype was more severe and more penetrant than that caused by the expression of Psn alone. In order to determine whether these phenotypes were indeed affecting Notch signaling, this experiment was performed in a genetic background carrying an activated Notch (Abruptex) allele. The phenotypes were almost completely rescued by this activated Notch allele. These results link peroxiredoxins with the in vivo function of Presenilin, which ultimately connects two key pathogenetic mechanisms in AD, namely, antioxidant activity and plaque formation, and raises the possibility of a role for peroxiredoxin family members in Alzheimer's pathogenesis. [ABSTRACT FROM AUTHOR]

Epidemiological and in vivo studies have demonstrated that exposure to the pesticides paraquat (PQ) and maneb (MB) increase the risk of developing Parkinson’s disease (PD) and cause dopaminergic cell loss, respectively. PQ is a well-recognized cause of oxidative toxicity; therefore, the purpose of this study was to determine if MB potentiates oxidative stress caused by PQ, thus providing a mechanism for enhanced neurotoxicity by the combination. The results show that PQ alone at a moderately toxic dose (20–30% cell death in 24 h) caused increased reactive oxygen species (ROS) generation, oxidation of mitochondrial thioredoxin-2 and peroxiredoxin-3, lesser oxidation of cytoplasmic thioredoxin-1 and peroxiredoxin-1, and no oxidation of cellular GSH/GSSG. In contrast, MB alone at a similar toxic dose resulted in no ROS generation, no oxidation of thioredoxin and peroxiredoxin, and an increase in cellular GSH after 24 h. Together, MB increased GSH and inhibited ROS production and thioredoxin/peroxiredoxin oxidation observed with PQ alone, yet resulted in more extensive (> 50%) cell death. MB treatment resulted in increased abundance of nuclear Nrf2 and mRNA for phase II enzymes under the control of Nrf2, indicating activation of cell protective responses. The results show that MB potentiation of PQ neurotoxicity does not occur by enhancing oxidative stress and suggests that increased toxicity occurs by a combination of divergent mechanisms, perhaps involving alkylation by MB and oxidation by PQ. [ABSTRACT FROM AUTHOR]

Eukaryotic typical 2-Cys type peroxiredoxin (Prx) is inactivated by hyperoxidation of the peroxidatic cysteine to a sulphinic acid in a catalytic cycle-dependent manner. This inactivation process has been well documented for cytosolic isoforms of Prx. However, such a hyperoxidative inactivation has not fully been investigated in Prx-4, a secretable endoplasmic reticulum-resident isoform, in spite of being a typical 2-Cys type, and details of this process are reported herein. As has been observed in many peroxiredoxins, the peroxidase activity of Prx-4 was almost completely inhibited in the reaction with t-butyl hydroperoxide. On the other hand, when H2O2 was used as the substrate, the peroxidase activity significantly remained after oxidative damage. In spite of these different consequences, mass spectrometric analyses indicated that both reactions resulted in the same oxidative damage, i.e. sulphinic acid formation at the peroxidatic cysteine, suggesting that another cysteine in the active site confers the peroxidase activity. As suggested by the analyses using cysteine-substituted mutants sulphinic acid formation at the peroxidatic cysteine may play a role in the development of the possible alternative mechanism, thereby sustaining the peroxidase activity that prefers H2O2. [ABSTRACT FROM PUBLISHER]

Photosynthesis is a process that inevitably produces reactive oxygen species, such as hydrogen peroxide, which is reduced by chloroplast-localized detoxification mechanisms one of which involves 2-Cys peroxiredoxins (2-Cys Prxs). Arabidopsis chloroplasts contain two very similar 2-Cys Prxs (denoted A and B). These enzymes are reduced by two pathways: NADPH thioredoxin reductase C (NTRC), which uses NADPH as source of reducing power; and plastidial thioredoxins (Trxs) coupled to photosynthetically reduced ferredoxin of which Trx x is the most efficient reductant in vitro. With the aim of establishing the functional relationship between NTRC, Trx x, and 2-Cys Prxs in vivo, an Arabidopsis Trx x knock-out mutant has been identified and a double mutant (denoted Δ2cp) with <5% of 2-Cys Prx content has been generated. The phenotypes of the three mutants, ntrc, trxx, and Δ2cp, were compared under standard growth conditions and in response to continuous light or prolonged darkness and oxidative stress. Though all mutants showed altered redox homeostasis, no difference was observed in response to oxidative stress treatment. Moreover, the redox status of the 2-Cys Prx was imbalanced in the ntrc mutant but not in the trxx mutant. These results show that NTRC is the most relevant pathway for chloroplast 2-Cys Prx reduction in vivo, but the antioxidant function of this system is not essential. The deficiency of NTRC caused a more severe phenotype than the deficiency of Trx x or 2-Cys Prxs as determined by growth, pigment content, CO2 fixation, and Fv/Fm, indicating additional functions of NTRC. [ABSTRACT FROM PUBLISHER]

The budding yeast Saccharomyces cerevisiae has three homologues of glutathione peroxidase ( GPX1, GPX2, and GPX3). Two structural homologues of the mammalian glutathione peroxidase, Gpx2 and Gpx3, have been proven to be atypical 2-Cys peroxiredoxins, which prefer to use thioredoxin as an electron donor. Here, we show that Gpx1 is also an atypical 2-Cys peroxiredoxin, but uses glutathione and thioredoxin almost equally. We determined the redox state of Gpx1 in vivo. [ABSTRACT FROM AUTHOR]

Alkylhydroperoxide reductase (AhpC) is an abundant and important antioxidant protein present in Helicobacter pylori (HP), a spiral Gram-negative microaerophilic bacterium. By sequence alignment and structure comparison, HP-AhpC was found to be more homologous to human peroxiredoxins (hPrx) than to other eubacterial AhpC proteins. Similar to hPrxI, native HP-AhpC existed as a dimer of single subunit, comprising α-helix and β-sheet domains with low surface hydrophobicity. AhpC can form high-molecular-weight (HMW) aggregates ranging from 700 to higher than 2,000 kDa under oxidative stress, possessing chaperone activity in the presence of thioredoxin (Trx). Further analysis of peroxide-reductase activities showed that HP-AhpC was more resistant to H2O2 than hPrxI. However, the mechanism of enzyme inactivation to H2O2 appeared to be similar for both HP-AhpC and hPrxI as revealed by native gel electrophoresis followed by proteomic identification using two-dimensional gel electrophoresis (2-DE) and LC-MS/MS. In contrast to T90D-hPrxI mutant with chaperone activity, site-specific mutant T87D-HP-AhpC did not form HMW chaperone complexes. The comparison of these two evolutionarily distant and yet functionally related enzymes may shed some light on the mechanism(s) underlying the evolution and development of the dual functionality in HP-AhpC and hPrxI with similar protein structure. [ABSTRACT FROM PUBLISHER]

The antioxidant function of 2-Cys peroxiredoxin (Prx) involves the oxidation of its conserved peroxidatic cysteine to sulphenic acid that is recycled by a reductor agent. In conditions of oxidative stress, the peroxidatic cysteine can be overoxidized to sulphinic acid inactivating the Prx. An enzyme recently discovered, named sulfiredoxin (Srx), reduces the sulphinic 2-Cys Prx (Prx-SO2H). To explore the physiological functions of Srx in plants we have cloned, expressed and purified to homogeneity a Srx from Arabidopsis thaliana (AtSrx), as well as five variants by site-directed mutagenesis on amino acids involved in its activity. The activity of sulfiredoxin, determined by a new method, is dependent on the concentration of the sulphinic form of Prx and the conserved Srx is capable of regenerating the functionality of both pea and Arabidopsis Prx-SO2H. Molecular modelling of AtSrx and the facts that the R28Q variant shows a partial inactivation, that the activity of the E76A variant is equivalent to that of the native enzyme and that the double mutation R28Q/E76A abolishes the enzymatic activity suggests that the pair His100-Glu76 may be involved in the activation of C72 in the absence of R28. The knock-out mutant plants without Srx or 2-Cys Prx exhibited phenotypical differences under growth conditions of 16 h light, probably due to the signalling role of the sulphinic form of Prx. These mutants showed more susceptibility to oxidative stress than wild-type plants. This work presents the first systematic biochemical characterization of the Srx/Prx system from plants and contributes to a better understanding of its physiological function. [ABSTRACT FROM PUBLISHER]

Peroxiredoxin (Prx) reduces hydrogen peroxide and alkyl peroxides to water and corresponding alcohols, respectively. The reaction is dependent on a peroxidatic cysteine, whose sulphur atom nucleophilically attacks one of the oxygen atoms of the peroxide substrate. In spite of the many structural studies that have been carried out on this reaction, the tertiary structure of the hydrogen peroxide-bound form of Prx has not been elucidated. In this paper, we report the crystal structure of Prx from Aeropyrum pernix K1 in the peroxide-bound form. The conformation of the polypeptide chain is the same as that in the reduced apo-form. The hydrogen peroxide molecule is in close contact with the peroxidatic Cys50 and the neighbouring Thr47 and Arg126 side chain atoms, as well as with the main chain nitrogen atoms of Val49 and Cys50. Bound peroxide was also observed in the mutant C50S, in which the peroxidatic cysteine was replaced by serine. Therefore, the sulphur atom of the peroxidatic cysteine is not essential for peroxide binding, although it enhances the binding affinity. Hydrogen peroxide binds to the protein so that it fills the active site pocket. This study provides insight into the early stage of the Prx reaction. [ABSTRACT FROM PUBLISHER]

In plants, the highly abundant 2-cysteine peroxiredoxin (2-CysPrx) is associated with the chloroplast and involved in protecting photosynthesis. This work addresses the multiple interactions of the 2-CysPrx in the chloroplast, which depend on its redox state. Transcript co-regulation analysis showed a strong linkage to the peptidyl-prolyl-cis/trans isomerase Cyclophilin 20-3 (Cyp20-3) and other components of the photosynthetic apparatus. Co-expression in protoplasts and quantification of fluorescence resonance energy transfer (FRET) efficiency in vivo confirmed protein interactions of 2-CysPrx with Cyp20-3 as well as NADPH-dependent thioredoxin reductase C (NTRC), while thioredoxin x (Trx-x) did not form complexes that could enable FRET. Likewise, changes in FRET of fluorescently labeled 2-CysPrx in vitro and in vivo proved redox dependent dynamics of 2-CysPrx. Addition of Cyp20-3 to an in vitro peroxidase assay with 2-CysPrx had no significant effect on peroxide reduction. Also, in the presence of NTRC, addition of Cyp20-3 did not further enhance peroxide reduction. In addition, 2-CysPrx functioned as chaperone and inhibited aggregation of citrate synthase during heat treatment. This activity was partly inhibited by Cyp20-3. As a new interaction partner of decameric 2-CysPrx, photosystem II could be identified after chloroplast fractionation and in pull-down assays after reconstitution. In summary, the data indicate a dynamic function of plant 2-CysPrx as redox sensor, chaperone, and regulator in the chloroplast with diverse functions beyond its role as thiol peroxidase. [ABSTRACT FROM PUBLISHER]

Chloroplast 2-Cys peroxiredoxins (2-Cys Prxs) are efficiently reduced by NADPH Thioredoxin reductase C (NTRC). To investigate the effect of light/darkness on NTRC function, the content of abundant plastidial enzymes, Rubisco, glutamine synthetase (GS), and 2-Cys Prxs was analyzed during two consecutive days in Arabidopsis wild-type and ntrc mutant plants. No significant difference of the content of these proteins was observed during the day or the night in wild-type and mutant plants. NTRC deficiency caused a lower content of fully reduced 2-Cys Prxs, which was undetectable in darkness, suggesting that NTRC is the most important pathway for 2-Cys Prx reduction, probably the only one during the night. Arabidopsis contains two plastidial 2-Cys Prxs, A and B, for which T-DNA insertion lines were characterized showing the same phenotype as wild-type plants. Two-dimensional gel analysis of leaf extracts from these mutants allowed the identification of basic and acidic isoforms of 2-Cys Prx A and B. In-vitro assays and mass spectrometry analysis showed that the acidic isoform of both proteins is produced by overoxidation of the peroxidatic Cys residue to sulfinic acid. 2-Cys Prx overoxidation was lower in the NTRC mutant. These results show the important function of NTRC to maintain the redox equilibrium of chloroplast 2-Cys Prxs. [ABSTRACT FROM PUBLISHER]

Cyanobacteria have evolved ∼3×109 years ago from ancient phototrophic microorganisms that already lived on our planet Earth. By opening the era of an aerobic, oxygen-containing biosphere, they are the true pacemakers of geological and biological evolution. Cyanobacteria must have been among the first organisms to elaborate mechanisms for the detoxification of partially reduced oxygen species including (hydrogen) peroxide. Since there is still an suprising lack of knowledge on the type, role, and mechanism(s) of peroxide-degrading enzymes in these bacteria, all 44 fully or partially sequenced genomes for haem and non-haem catalases and peroxidases have been critically analysed based on well known structure–function relationships of the corresponding oxidoreductases. It is demonstrated that H2O2-dismutating enzymes are mainly represented by bifunctional (haem) catalase–peroxidases and (binuclear) manganese catalases, with the latter being almost exclusively found in diazotrophic species. Several strains even lack a gene that encodes an enzyme with catalase activity. Two groups of peroxidases are found. Genes encoding putative (primordial) haem peroxidases (with homology to corresponding mammalian enzymes) and vanadium-containing iodoperoxidases are found only in a few species, whereas genes encoding peroxiredoxins (1-Cys, 2-Cys, type II, and Q-type) are ubiquitous in cyanobacteria. In addition, ∼70% contain NADPH-dependent glutathione peroxidase-like proteins. The occurrence and phylogeny of these enzymes is discussed, as well as the present knowledge of their physiological role(s). [ABSTRACT FROM PUBLISHER]

Peroxiredoxins are a class of peroxide-scavenging enzymes having a conserved cysteine residue(s) in their active centers. Thiol peroxidase (Tpx) is one of the peroxiredoxins identified in Escherichia coli. Despite the absence of the N-terminal signal sequence for transport across the membrane, it has been characterized as a periplasmic protein. Reanalysis of Tpx localization, using active site cysteine mutants of thioredoxin 1 (Trx1), demonstrated that Tpx forms a mixed-disulfide complex with cytoplasmic Trx1, indicating that Tpx localizes in the cytoplasm. [ABSTRACT FROM AUTHOR]

Mitochondria from plants, yeast, and animals each contain at least one peroxiredoxin (Prx) that is involved in peroxide detoxification and redox signalling. The supramolecular dynamics of atypical type II Prx targeted to the mitochondrion was addressed in pea. Microcalorimetric (ITC) titrations identified an extremely high-affinity binding between the mitochondrial PsPrxIIF and Trx-o with a KD of 126±14 pM. Binding was driven by a favourable enthalpy change (ΔH= –60.6 kcal mol−1) which was counterbalanced by unfavourable entropy changes (TΔS= –47.1 kcal mol−1). This is consistent with the occurrence of large conformational changes during binding which was abolished upon site-directed mutaganesis of the catalytic C59S and C84S. The redox-dependent interaction was confirmed by gel filtration of mitochondrial extracts and co-immunoprecipitation from extracts. The heterocomplex of PsPrxIIF and Trx-o reduced peroxide substrates more efficiently than free PsPrxIIF suggesting that Trx-o serves as an efficient and specific electron donor to PsPrxIIF in vivo. Other Trx-s tested by ITC analysis failed to interact with PsPrxIIF indicating a specific recognition of PsPrxIIF by Trx-o. PsPrxIIF exists primarily as a dimer or a hexamer depending on the redox state. In addition to the well-characterized oligomerization of classical 2-Cys Prx the results also show that atypical Prx undergo large structural reorganization with implications for protein–protein interaction and function. [ABSTRACT FROM PUBLISHER]

Kawasaki disease causes systemic vasculitis. The development of skin lesions at the vaccination site with Bacillus Calmette-Guérin (BCG) is an important diagnostic symptom. We hypothesized that infection with ubiquitous microorganisms immunogenically related to BCG might induce an immunopathologic reaction leading to the development of Kawasaki disease. Mice were first inoculated with BCG, and then secondarily inoculated 4 weeks later with crude extract from Mycobacterium intracellulare (cMI), an abundant atypical mycobacterium. Animals inoculated with BCG followed by cMI developed coronary arteritis with infiltration of inflammatory cells, whereas control animals inoculated with only cMI or BCG did not, suggesting that the immune response to the mycobacteria induced autoimmunity to the vascular wall. Intravenous injection with antibodies to peroxiredoxin II, a modulator of vascular remodeling and a suggested target for autoimmune vasculitis, also resulted in coronary arteritis, but only after prior inoculation with BCG. Tumor necrosis factor-α, MCP1 and interferon-γ production were significantly higher in the animals inoculated with BCG than in the control groups ( P<0.05). BCG immunization was required for the development of coronary arteritis, suggesting that these cytokines might play important roles. The results indicate that BCG induces primary autoimmunity and stimulates cytokine induction, and that atypical mycobacterial infection boosts the autoimmunity resulting in coronary arteritis. [ABSTRACT FROM AUTHOR]

In 1996, cDNA sequences referred to as plant peroxiredoxins (Prx), i.e. a 1-Cys Prx and a 2-Cys Prx, were reported from barley. Ten years of research have advanced our understanding of plant Prx as thiol-based peroxide reductases with a broad substrate specificity, ranging from hydrogen peroxide to alkyl hydroperoxides and peroxinitrite. Prx have several features in common. (i) They are abundant proteins that are routinely detected in proteomics approaches. (ii) They interact with proteins such as glutaredoxins, thioredoxins, and cyclophilins as reductants, but also non-dithiol-disulphide exchange proteins. By work with transgenic plants, their activity was shown to (iii) affect metabolic integrity, (iv) protect DNA from damage in vitro and as shown here in vivo, and (v) modulate intracellular signalling related to reactive oxygen species and reactive nitrogen species. (vi) In all organisms Prx are encoded by small gene families that are of particular complexity in higher plants. A comparison of the Prx gene families in rice and Arabidopsis thaliana supports previous suggestions on Prx function in specific subcellular and metabolic context. (vii) Prx gene expression and activity are subjected to complex regulation realized by an integration of various signalling pathways. 2-Cys Prx expression depends on redox signals, abscisic acid, and protein kinase cascades. Besides these general properties, the chloroplast Prx have acquired specific roles in the context of photosynthesis. The thioredoxin-dependent peroxidase activity can be measured in crude plant extracts and contributes significantly to the overall H2O2 detoxification capacity. Thus organellar Prx proteins enable an alternative water–water cycle for detoxification of photochemically produced H2O2, which acts independently from the ascorbate-dependent Asada–Halliwell–Foyer cycle. 2-Cys Prx and Prx Q associate with thylakoid membrane components. The mitochondrial PrxII F is essential for root growth under stress. Following a more general introduction, the paper summarizes present knowledge on plant organellar Prx, addressing Prx in signalling, and also suggests some lines for future research. [ABSTRACT FROM PUBLISHER]

During the evolution of plants, chloroplasts have lost the exclusive genetic control over redox regulation and antioxidant gene expression. Together with many other genes, all genes encoding antioxidant enzymes and enzymes involved in the biosynthesis of low molecular weight antioxidants were transferred to the nucleus. On the other hand, photosynthesis bears a high risk for photo-oxidative damage. Concomitantly, an intricate network for mutual regulation by anthero- and retrograde signals has emerged to co-ordinate the activities of the different genetic and metabolic compartments. A major focus of recent research in chloroplast regulation addressed the mechanisms of redox sensing and signal transmission, the identification of regulatory targets, and the understanding of adaptation mechanisms. In addition to redox signals communicated through signalling cascades also used in pathogen and wounding responses, specific chloroplast signals control nuclear gene expression. Signalling pathways are triggered by the redox state of the plastoquinone pool, the thioredoxin system, and the acceptor availability at photosystem I, in addition to control by oxolipins, tetrapyrroles, carbohydrates, and abscisic acid. The signalling function is discussed in the context of regulatory circuitries that control the expression of antioxidant enzymes and redox modulators, demonstrating the principal role of chloroplasts as the source and target of redox regulation. [ABSTRACT FROM PUBLISHER]

Abstract: Evidence is mounting that nontypeable Haemophilus influenzae grows as a biofilm in the middle ear of children with otitis media and the airways of adults with chronic obstructive pulmonary disease. To begin to assess antigens expressed by H. influenzae in biofilms, cell envelopes of bacteria grown as a biofilm were compared to those grown planktonically. A ∼30kDa peroxiredoxin–glutaredoxin was present in greater abundance during growth in biofilms. Mutants deficient in expression of peroxiredoxin–glutaredoxin were constructed by homologous recombination in four clinical isolates. The mutants showed a 25–50% reduction in biofilm formation compared to the corresponding parent strains. To study in vivo expression of peroxiredoxin–glutaredoxin during human respiratory tract infection, paired pre- and post-exacerbation serum from adults with chronic obstructive pulmonary disease and H. influenzae in sputum were assayed using an enzyme-linked immunosorbent assay and purified recombinant peroxiredoxin–glutaredoxin. Eight from 18 (44.4%) paired serum samples showed a significant increase in antibody to peroxiredoxin–glutaredoxin from pre- to post-infection. These results indicate that (1) peroxiredoxin–glutaredoxin is present in greater abundance in H. influenzae biofilms compared to planktonically grown bacteria; (2) peroxiredoxin–glutaredoxin is involved in biofilm formation by H. influenzae and the degree of involvement varies among strains; and (3) peroxiredoxin–glutaredoxin is expressed by H. influenzae during infection of the human respiratory tract and is recognized by the human immune system. [Copyright &y& Elsevier]

Oxidative stress response in an anaerobic hyperthermophilic archaeon Pyrococcus horikoshii OT-3 was analyzed by two-dimensional gel electrophoresis. When P. horikoshii was grown on medium supplemented with air, a marked increase in the level of a 25-kDa protein was observed in comparison with cells grown under anaerobic conditions. The N-terminal amino acid sequence of the protein was determined to be VVIGEKFPEVEVKTTHGVIKLPDYF, which coincides with that of the putative alkyl hydroperoxide reductase that has been predicted in the genome database of P. horikoshii. The gene (PH1217) encoding the protein was cloned and expressed in Escherichia coli. The produced enzyme was a hyperthermostable peroxiredoxin whose activity was not lost after incubation at 90°C for 20 min. The enzyme catalyzes the reduction of cumene hydroperoxide and hydrogen peroxide using dithiothreitol as an electron donor. Northern blot analysis revealed that the transcription of the gene increased by the addition of exogenous oxygen and by the addition of an oxidative stress-inducing reagent, and reached maximum within 30 min. These results suggest that the peroxiredoxin plays an important role in the peroxide-scavenging system in an anaerobic archaeon P. horikoshii. [ABSTRACT FROM PUBLISHER]

A cDNA sequence coding for a pea (Pisum sativum L.) 2-Cys peroxiredoxin (2-Cys Prx) has been cloned. The deduced amino acid sequence showed a high sequence homology to the 2-Cys Prx enzymes of Phaseolus vulgaris (86%), Arabidopsis thaliana (75%), and Spinacia oleracea (75%), and contained a chloroplast target sequence at its N-terminus. The mature enzyme, without the transit peptide, has a molecular mass of 22 kDa as well as two cysteine residues (Cys-53 and Cys-175) which are well conserved among proteins of this group. The protein was expressed in a heterologous system using the expression vector pET3d, and was purified to homogeneity by three sequential chromatographic steps. The enzyme exhibits peroxidase activity on hydrogen peroxide (H2O2) and t-butyl hydroperoxide (TBHP) with DTT as reducing agent. Although both pea Trxs f and m reduce oxidized 2-Cys Prx, Trx m is more efficient. The precise conditions for oligomerization of 2-Cys Prx through extensive gel filtration studies are also reported. The transition dimer–decamer produced in vitro between pH 7.5 and 8.0 and the influence of DTT suggest that a great change in the enzyme quaternary structure of 2-Cys Prx may take place in the chloroplast during the dark–light transition. In addition, the cyclophilin-dependent reduction of chloroplast 2-Cys Prx is shown. [ABSTRACT FROM PUBLISHER]

Exposure to methyl viologen in the presence of light facilitates the production of superoxide that gives severe damage on photosynthetic apparatus as well as many cellular processes in cyanobacteria and plants. The effects of methyl viologen on global gene expression of a unicellular cyanobacterium Synechocystis sp. strain PCC 6803 were determined by DNA microarray. The ORFs sll1621, slr1738, slr0074, slr0075, and slr0589 were significantly induced by treatment of methyl viologen for 15 min commonly under conditions of normal and high light. One of these genes, slr1738, which encodes a ferric uptake repressor (Fur)-type transcriptional regulator, is located divergently next to another induced gene, sll1621, in the genome. We deleted slr1738, and compared the global gene expression patterns of this mutant to that of wild type under non-stressed conditions. It was found that sll1621 was derepressed to the greatest extent, while many other genes including slr0589 but not slr0074 or slr0075 were derepressed to lesser extent in the mutant. Genetic disruption of sll1621, which encodes a putative type 2 peroxiredoxin, indicates that it is essential for aerobic phototrophic growth in both liquid and solid media in high light and on solid medium even in low light. Slr1738 was prepared as a His-tagged recombinant protein and shown to specifically bind to the intergenic region between sll1621 and slr1738. The binding was enhanced by dithiothreitol and abolished by hydrogen peroxide. We concluded that the Fur homolog, Slr1738, plays a regulatory role in the induction of a potent antioxidant gene, sll1621, in response to oxidative stress. [ABSTRACT FROM AUTHOR]

Reports that peroxiredoxin (Prx)-linked hydroperoxide reductase activities have been detected in cell extracts of Saccharomyces, Synechocystis and Chlorella, and the enzyme activities of Saccharomyces and Chlorella were induced. Indication that the Prx-linked peroxidase system consists of two protein components; Thioredoxin and thioredoxin reductase.

Silica has been known to be a factor in acute cell injury and chronic pulmonary fibrosis. To date, many studies have emphasized the reactive oxygen species (ROS) as a primary cause of this pathogenesis. Previously, we demonstrated that silica induced acute radical generation and intracellular Ca2+ increase in Rat2 cells. Moreover, increases in intracellular Ca2+ directly affect the rapid degradation of peroxiredoxin (Prx), a newly discovererd antioxidant enzyme family. In the present study, we investigated the mechanism by which silica transfers its cellular signal downstream of the cell by using human lung epithelial cells, which are known to contribute to the inflammatory response after exposure to silica in the lung. In A549 cells, silica induced the generation of ROS immediately, although immediate responses were observed in C6 cells or in Rat2 cells. Nevertheless, the immediate production of ROS in response to silica in A549 cells was not clearly detected, but the initial step for NF-κB signaling, such as rapid degradation of IκB-α, was sensitive to the addition of silica. Additionally, silica triggered the rapid degradation of cytoplasmic antioxidant enzymes such as PrxI and PrxII, indicating that this may accelerate silica-induced cellular damage. Moreover, silica was observed to increase intracellular Ca2+ concentration. This report suggests that silica transduces diverse pathways, such as the rapid increase of intracellular Ca2+ concentration, NF-κB signaling or modulation of redox potential by destruction of antioxidant enzymes, without the immediate generation of ROS in A549 cells. [ABSTRACT FROM AUTHOR]