Peroxiredoxin Tsa1 is the key peroxidase suppressing genome instability and protecting against cell death in Saccharomyces cerevisiae

Tsa1 is the dominant peroxide scavenger and a source of H2O2-dependent GSSG production in yeast

Hydrogen peroxide (H2O2) is an important biological molecule, functioning both as a second messenger in cell signaling and, especially at higher concentrations, as a cause of cell damage. Cells harbor multiple enzymes that have peroxide reducing activity in vitro. However, the contribution of each of these enzymes towards peroxide scavenging in vivo is less clear. Therefore, to directly investigate in vivo peroxide scavenging, we used the genetically encoded peroxide probes, roGFP2-Tsa2ΔCR and HyPer7, to systematically screen the peroxide scavenging capacity of baker's yeast thiol and heme peroxidase mutants. We show that the 2-Cys peroxiredoxin Tsa1 alone is responsible for almost all exogenous H2O2 and tert-butyl hydroperoxide scavenging. Furthermore, Tsa1 can become an important source of H2O2-dependent cytosolic glutathione disulfide production. The two catalases and cytochrome c peroxidase only produce observable scavenging defects at higher H2O2 concentrations when these three heme peroxidases are removed in combination. We also analyzed the reduction of Tsa1 in vitro, revealing that the enzyme is efficiently reduced by thioredoxin-1 with a rate constant of 2.8 × 106 M-1s-1 but not by glutaredoxin-2. Tsa1 reduction by reduced glutathione occurs nonenzymatically with a rate constant of 2.9 M-1s-1. Hence, the observed Tsa1-dependent glutathione disulfide production in yeast probably requires the oxidation of thioredoxins. Our findings clarify the importance of the various thiol and heme peroxidases for peroxide removal and suggest that most thiol peroxidases have alternative or specialized functions in specific subcellular compartments.

AoPrdx2 Regulates Oxidative Stress, Reactive Oxygen Species, Trap Formation, and Secondary Metabolism in Arthrobotrys oligospora

Prdx2 is a peroxiredoxin (Prx) family protein that protects cells from attack via reactive oxygen species (ROS), and it has an important role in improving the resistance and scavenging capacity of ROS in fungi. Arthrobotrys oligospora is a widespread nematode-trapping fungus that can produce three-dimensional nets to capture and kill nematodes. In this study, AoPrdx2, a homologous protein of Prx5, was investigated in A. oligospora via gene disruption, phenotypic analysis, and metabolomics. The deletion of Aoprdx2 resulted in an increase in the number of mycelial septa and a reduction in the number of nuclei and spore yield. Meanwhile, the absence of Aoprdx2 increased sensitivity to oxidative stresses, whereas the ∆Aoprdx2 mutant strain resulted in higher ROS levels than that of the wild-type (WT) strain. In particular, the inactivation of Aoprdx2 severely influenced trap formation and pathogenicity; the number of traps produced by the ∆Aoprdx2 mutant strain was remarkably reduced and the number of mycelial rings of traps in the ∆Aoprdx2 mutant strain was less than that of the WT strain. In addition, the abundance of metabolites in the ∆Aoprdx2 mutant strain was significantly downregulated compared with the WT strain. These results indicate that AoPrdx2 plays an indispensable role in the scavenging of ROS, trap morphogenesis, and secondary metabolism.

Redox regulation of RAD51 Cys319 and homologous recombination by peroxiredoxin 1

RAD51 is a critical recombinase that functions in concert with auxiliary mediator proteins to direct the homologous recombination (HR) DNA repair pathway. We show that Cys319 RAD51 possesses nucleophilic characteristics and is important for irradiation-induced RAD51 foci formation and resistance to inhibitors of poly (ADP-ribose) polymerase (PARP). We have previously identified that cysteine (Cys) oxidation of proteins can be important for activity and modulated via binding to peroxiredoxin 1 (PRDX1). PRDX1 reduces peroxides and coordinates the signaling actions of protein binding partners. Loss of PRDX1 inhibits irradiation-induced RAD51 foci formation and represses HR DNA repair. PRDX1-deficient human breast cancer cells and mouse embryonic fibroblasts display disrupted RAD51 foci formation and decreased HR, resulting in increased DNA damage and sensitization of cells to irradiation. Following irradiation cells deficient in PRDX1 had increased incorporation of the sulfenylation probe DAz-2 in RAD51 Cys319, a functionally-significant, thiol that PRDX1 is critical for maintaining in a reduced state. Molecular dynamics (MD) simulations of dT-DNA bound to a non-oxidized RAD51 protein showed tight binding throughout the simulation, while dT-DNA dissociated from an oxidized Cys319 RAD51 filament. These novel data establish RAD51 Cys319 as a functionally-significant site for the redox regulation of HR and cellular responses to IR.

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A functionally-significant Cys319 was identified in RAD51 that possesses nucleophilic characteristics.

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RAD51 Cys319 plays a central role in RAD51-mediated repair of DNA double strand breaks (DSB).

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Loss of peroxiredoxin 1 (PRDX1) impairs DNA DSB repair by homologous recombination and results in DNA damage.

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PRDX1 is critical for maintaining RAD51 Cys319 in a reduced state.

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Molecular dynamic (MD) simulations suggest ssDNA to dissociate from sulfenylated and not reduced RAD51 Cys319.

Fe-S coordination defects in the replicative DNA polymerase delta cause deleterious DNA replication in vivo and subsequent DNA damage in the yeast Saccharomyces cerevisiae

B-type eukaryotic polymerases contain a [4Fe-4S] cluster in their C-terminus domain, whose role is not fully understood yet. Among them, DNA polymerase delta (Polδ) plays an essential role in chromosomal DNA replication, mostly during lagging strand synthesis. Previous in vitro work suggested that the Fe-S cluster in Polδ is required for efficient binding of the Pol31 subunit, ensuring stability of the Polδ complex. Here we analyzed the in vivo consequences resulting from an impaired coordination of the Fe-S cluster in Polδ. We show that a single substitution of the very last cysteine coordinating the cluster by a serine is responsible for the generation of massive DNA damage during S phase, leading to checkpoint activation, requirement of homologous recombination for repair, and ultimately to cell death when the repair capacities of the cells are overwhelmed. These data indicate that impaired Fe-S cluster coordination in Polδ is responsible for aberrant replication. More generally, Fe-S in Polδ may be compromised by various stress including anti-cancer drugs. Possible in vivo Polδ Fe-S cluster oxidation and collapse may thus occur, and we speculate this could contribute to induced genomic instability and cell death, comparable to that observed in pol3-13 cells.

Peroxiredoxins couple metabolism and cell division in an ultradian cycle

Redox cycles have been reported in ultradian, circadian and cell cycle-synchronized systems. Redox cycles persist in the absence of transcription and cyclin-CDK activity, indicating that cells harbor multiple coupled oscillators. Nonetheless, the causal relationships and molecular mechanisms by which redox cycles are embedded within ultradian, circadian or cell division cycles remain largely elusive. Yeast harbor an ultradian oscillator, the yeast metabolic cycle (YMC), which comprises metabolic/redox cycles, transcriptional cycles and synchronized cell division. Here, we reveal the existence of robust cycling of H₂O₂ and peroxiredoxin oxidation during the YMC and show that peroxiredoxin inactivation disrupts metabolic cycling and abolishes coupling with cell division. We find that thiol-disulfide oxidants and reductants predictably modulate the switching between different YMC metabolic states, which in turn predictably perturbs cell cycle entry and exit. We propose that oscillatory H₂O₂-dependent protein thiol oxidation is a key regulator of metabolic cycling and its coordination with cell division.

Genomic Instability and Cellular Senescence: Lessons From the Budding Yeast

Aging is a complex biological process that occurs in all living organisms. Aging is initiated by the gradual accumulation of biomolecular damage in cells leading to the loss of cellular function and ultimately death. Cellular senescence is one such pathway that leads to aging. The accumulation of nucleic acid damage and genetic alterations that activate permanent cell-cycle arrest triggers the process of senescence. Cellular senescence can result from telomere erosion and ribosomal DNA instability. In this review, we summarize the molecular mechanisms of telomere length homeostasis and ribosomal DNA stability, and describe how these mechanisms are linked to cellular senescence and longevity through lessons learned from budding yeast.

Kluyveromyces marxianus: Current State of Omics Studies, Strain Improvement Strategy and Potential Industrial Implementation

Bioethanol is considered an excellent alternative to fossil fuels, since it importantly contributes to the reduced consumption of crude oil, and to the alleviation of environmental pollution. Up to now, the baker yeast Saccharomyces cerevisiae is the most common eukaryotic microorganism used in ethanol production. The inability of S. cerevisiae to grow on pentoses, however, hinders its effective growth on plant biomass hydrolysates, which contain large amounts of C5 and C12 sugars. The industrial-scale bioprocessing requires high temperature bioreactors, diverse carbon sources, and the high titer production of volatile compounds. These criteria indicate that the search for alternative microbes possessing useful traits that meet the required standards of bioethanol production is necessary. Compared to other yeasts, Kluyveromyces marxianus has several advantages over others, e.g., it could grow on a broad spectrum of substrates (C5, C6 and C12 sugars); tolerate high temperature, toxins, and a wide range of pH values; and produce volatile short-chain ester. K. marxianus also shows a high ethanol production rate at high temperature and is a Crabtree-negative species. These attributes make K. marxianus promising as an industrial host for the biosynthesis of biofuels and other valuable chemicals.

Wine yeast peroxiredoxin TSA1 plays a role in growth, stress response and trehalose metabolism in biomass propagation

Peroxiredoxins are a family of peroxide-degrading enzymes for challenging oxidative stress. They receive their reducing power from redox-controlling proteins called thioredoxins, and these, in turn, from thioredoxin reductase. The main cytosolic peroxiredoxin is Tsa1, a moonlighting protein that also acts as protein chaperone a redox switch controlling some metabolic events. Gene deletion of peroxiredoxins in wine yeasts indicate that TSA1, thioredoxins and thioredoxin reductase TRR1 are required for normal growth in medium with glucose and sucrose as carbon sources. TSA1 gene deletion also diminishes growth in molasses, both in flasks and bioreactors. The TSA1 mutation brings about an expected change in redox parameters but, interestingly, it also triggers a variety of metabolic changes. It influences trehalose accumulation, lowering it in first molasses growth stages, but increasing it at the end of batch growth, when respiratory metabolism is set up. Glycogen accumulation at the entry of the stationary phase also increases in the tsa1Δ mutant. The mutation reduces fermentative capacity in grape juice, but the vinification profile does not significantly change. However, acetic acid and acetaldehyde production decrease when TSA1 is absent. Hence, TSA1 plays a role in the regulation of metabolic reactions leading to the production of such relevant enological molecules.

Trajectory and uniqueness of mutational signatures in yeast mutators

The acquisition of mutations plays critical roles in adaptation, evolution, senescence, and tumorigenesis. Massive genome sequencing has allowed extraction of specific features of many mutational landscapes but it remains difficult to retrospectively determine the mechanistic origin(s), selective forces, and trajectories of transient or persistent mutations and genome rearrangements. Here, we conducted a prospective reciprocal approach to inactivate 13 single or multiple evolutionary conserved genes involved in distinct genome maintenance processes and characterize de novo mutations in 274 diploid Saccharomyces cerevisiae mutation accumulation lines. This approach revealed the diversity, complexity, and ultimate uniqueness of mutational landscapes, differently composed of base substitutions, small insertions/deletions (InDels), structural variants, and/or ploidy variations. Several landscapes parallel the repertoire of mutational signatures in human cancers while others are either novel or composites of subsignatures resulting from distinct DNA damage lesions. Notably, the increase of base substitutions in the homologous recombination-deficient Rad51 mutant, specifically dependent on the Polζ translesion polymerase, yields COSMIC signature 3 observed in BRCA1/BRCA2-mutant breast cancer tumors. Furthermore, "mutome" analyses in highly polymorphic diploids and single-cell bottleneck lineages revealed a diverse spectrum of loss-of-heterozygosity (LOH) signatures characterized by interstitial and terminal chromosomal events resulting from interhomolog mitotic cross-overs. Following the appearance of heterozygous mutations, the strong stimulation of LOHs in the rad27/FEN1 and tsa1/PRDX1 backgrounds leads to fixation of homozygous mutations or their loss along the lineage. Overall, these mutomes and their trajectories provide a mechanistic framework to understand the origin and dynamics of genome variations that accumulate during clonal evolution.

Deciphering the in vivo redox behavior of human peroxiredoxins I and II by expressing in budding yeast

Peroxiredoxins (Prxs), scavenge cellular peroxides by forming recyclable disulfides but under high oxidative stress, hyperoxidation of their active-site Cys residue results in loss of their peroxidase activity. Saccharomyces cerevisiae deficient in human Prx (hPrx) orthologue TSA1 show growth defects under oxidative stress. They can be complemented with hPRXI but not by hPRXII, but it is not clear how the disulfide and hyperoxidation states of the hPrx vary in yeast under oxidative stress. To understand this, we used oxidative-stress sensitive tsa1tsa2Δ yeast strain to express hPRXI or hPRXII. We found that hPrxI in yeast exists as a mixture of disulfide-linked dimer and reduced monomer but becomes hyperoxidized upon elevated oxidative stress as analyzed under denaturing conditions (SDS-PAGE). In contrast, hPrxII was present predominantly as the disulfide in unstressed cells and readily converted to its hyperoxidized, peroxidase-inactive form even with mild oxidative stress. Interestingly, we found that plant extracts containing polyphenol antioxidants provided further protection against the growth defects of the tsa1tsa2Δ strain expressing hPrx and preserved the peroxidase-active forms of the Prxs. The extracts also helped to protect against hyperoxidation of hPrxs in HeLa cells. Based on these findings we can conclude that resistance to oxidative stress of yeast cells expressing individual hPrxs requires the hPrx to be maintained in a redox state that permits redox cycling and peroxidase activity. Peroxidase activity decreases as the hPrx becomes hyperoxidized and the limited protection by hPrxII compared with hPrxI can be explained by its greater sensitivity to hyperoxidation.

Hyperoxidation of mitochondrial peroxiredoxin limits H2 O2 -induced cell death in yeast

Hydrogen peroxide (H2 O2 ) plays important roles in cellular signaling, yet nonetheless is toxic at higher concentrations. Surprisingly, the mechanism(s) of cellular H2 O2 toxicity remain poorly understood. Here, we reveal an important role for mitochondrial 1-Cys peroxiredoxin from budding yeast, Prx1, in regulating H2 O2 -induced cell death. We show that Prx1 efficiently transfers oxidative equivalents from H2 O2 to the mitochondrial glutathione pool. Deletion of PRX1 abrogates glutathione oxidation and leads to a cytosolic adaptive response involving upregulation of the catalase, Ctt1. Both of these effects contribute to improved cell viability following an acute H2 O2 challenge. By replacing PRX1 with natural and engineered peroxiredoxin variants, we could predictably induce widely differing matrix glutathione responses to H2 O2 . Therefore, we demonstrated a key role for matrix glutathione oxidation in driving H2 O2 -induced cell death. Finally, we reveal that hyperoxidation of Prx1 serves as a switch-off mechanism to limit oxidation of matrix glutathione at high H2 O2 concentrations. This enables yeast cells to strike a fine balance between H2 O2 removal and limitation of matrix glutathione oxidation.

Piecing Together How Peroxiredoxins Maintain Genomic Stability

Peroxiredoxins, a highly conserved family of thiol oxidoreductases, play a key role in oxidant detoxification by partnering with the thioredoxin system to protect against oxidative stress. In addition to their peroxidase activity, certain types of peroxiredoxins possess other biochemical activities, including assistance in preventing protein aggregation upon exposure to high levels of oxidants (molecular chaperone activity), and the transduction of redox signals to downstream proteins (redox switch activity). Mice lacking the peroxiredoxin Prdx1 exhibit an increased incidence of tumor formation, whereas baker's yeast (Saccharomyces cerevisiae) lacking the orthologous peroxiredoxin Tsa1 exhibit a mutator phenotype. Collectively, these findings suggest a potential link between peroxiredoxins, control of genomic stability, and cancer etiology. Here, we examine the potential mechanisms through which Tsa1 lowers mutation rates, taking into account its diverse biochemical roles in oxidant defense, protein homeostasis, and redox signaling as well as its interplay with thioredoxin and thioredoxin substrates, including ribonucleotide reductase. More work is needed to clarify the nuanced mechanism(s) through which this highly conserved peroxidase influences genome stability, and to determine if this mechanism is similar across a range of species.

Expression of oxidized protein tyrosine phosphatase and γH2AX predicts poor survival of gastric carcinoma patients

Background

Oxidative stress induces various intracellular damage, which might be correlated with tumorigenesis. Accumulated oxidative stresses might inactivate protein tyrosine phosphatase (PTP) by oxidizing it, and inducing the phosphorylation of H2AX (γH2AX) in response to DNA damage.

Methods

We evaluated the clinical significance of the expression of oxidized-PTP and γH2AX in 169 gastric carcinomas.

Results

Immunohistochemical expression of nuclear oxidized-PTP, cytoplasmic oxidized-PTP, and γH2AX expression were significantly associated with each other, and their expressions predicted shorter survival of gastric carcinoma patients. In multivariate analysis, nuclear oxidized-PTP (overall survival; p <  0.001, relapse-free survival; P <  0.001) was an independent indicator of poor prognosis of gastric carcinoma patients. In addition, co-expression patterns of nuclear oxidized-PTP and γH2AX were independent indicators of poor prognosis of gastric carcinoma patients (overall survival; P <  0.001, relapse-free survival; P <  0.001).

Conclusions

This study suggests that oxidative stress-mediated oxidation of PTP might be involved in the progression of gastric carcinomas. In addition, this study suggests that individual and co-expression pattern of nuclear oxidized-PTP and γH2AX might be used as a prognostic marker of gastric carcinomas.

Thioredoxin and Glutaredoxin Systems Required for Oxidative Stress Resistance, Fungicide Sensitivity, and Virulence of Alternaria alternata

This study determined the function of thioredoxin and glutaredoxin systems in the phytopathogenic fungus Alternaria alternata via analyzing mutants obtained from the targeted deletion of genes encoding thioredoxin peroxidase (Tsa1), thioredoxin reductase (Trr1), and glutathione reductase (Glr1). Trr1 and Glr1, but not Tsa1, are required for growth and conidiation. The reduced growth and conidiation seen in the Trr1 or Glr1 deletion mutant can be restored by glutathione. Deletion mutants showing growth inhibition by oxidants are defective for H₂O₂ detoxification and induce smaller lesions on citrus leaves. Trr1 and Glr1, but not Tsa1, also contribute to NaCl resistance. Glr1 is required for sorbitol resistance and is responsible for resistance to mancozeb and boscalid but not chlorothalonil fungicides, a novel phenotype that has not been reported in fungi. Trr1 is required for resistance to boscalid and chlorothalonil fungicides but confers susceptibility to mancozeb. The Tsa1 deletion mutant displays wild-type sensitivity to the tested fungicides. The expression of Tsa1 and Trr1 is regulated by the oxidative stress responsive regulators Yap1, Hog1, and Skn7. The expression of Tsa1, but not Trr1, is also regulated indirectly by the NADPH oxidase. The results indicate that the capability to resist oxidative stress is required for virulence of A. alternataIMPORTANCE The thioredoxin and glutaredoxin systems are important thiol antioxidant systems in cells, and knowledge of these two systems in the plant-pathogenic fungus A. alternata is useful for finding new strategies to reduce the virulence of this pathogen. In this study, we demonstrated that thiol antioxidant system-related genes (Tsa1, Trr1, and Glr1) are required for H₂O₂ detoxification and virulence in A. alternata Moreover, deletion of Trr1 results in hypersensitivity to the fungicides chlorothalonil and boscalid, and Glr1 deletion mutants are highly sensitive to mancozeb, which is the fungicide mostly used in citrus fields. Therefore, our findings demonstrate that the ability to detoxify reactive oxygen species (ROS) plays a critical role in pathogenesis on citrus and provide novel insights into the physiological functions of thiol-containing systems in fungicide sensitivity for A. alternata.

Beyond ROS clearance: Peroxiredoxins in stress signaling and aging

Antioxidants were long predicted to have lifespan-promoting effects, but in general this prediction has not been well supported. While some antioxidants do seem to have a clear effect on longevity, this may not be primarily as a result of their role in the removal of reactive oxygen species, but rather mediated by other mechanisms such as the modulation of intracellular signaling. In this review we discuss peroxiredoxins, a class of proteinaceous antioxidants with redox signaling and chaperone functions, and their involvement in regulating longevity and stress resistance. Peroxiredoxins have a clear role in the regulation of lifespan and survival of many model organisms, including the mouse, Caenorhabditis elegans and Drosophila melanogaster. Recent research on peroxiredoxins - in these models and beyond - has revealed surprising new insights regarding the interplay between peroxiredoxins and longevity signaling, which will be discussed here in detail. As redox signaling is emerging as a potentially important player in the regulation of longevity and aging, increased knowledge of these fascinating antioxidants and their mode(s) of action is paramount.

Recombinant buckwheat glutaredoxin intake increases lifespan and stress resistance via hsf-1 upregulation in Caenorhabditis elegans

Glutaredoxin (Grx) is a polypeptide with low molecular weight, which has been extracted from buckwheat and has been suggested to have multiple functions revolving around oxidative stress responses and cell signaling. Here, we report the antioxidant activity of recombinant buckwheat Grx (rbGrx) to reduce aging effects in Caenorhabditis elegans (C. elegans) as well as the mechanism involved. Our results showed that rbGrx beneficially affected the health span of C. elegans, including pharyngeal-pumping rate, locomotion, and lipofuscin accumulation. Furthermore, stress assay showed that rbGrx could extend the lifespan under both oxidative and heat stress. Further studies indicated that the longevity-extending effects of rbGrx could be attributed to its in vitro and in vivo antioxidant activities. After treatment with rbGrx, SOD activity, CAT activity, GSH content, and GSH/GSSG ratio were increased, while MDA content was decreased, which led to low intracellular levels of reactive oxygen species in C. elegans. Moreover, rbGrx up-regulated hsf-1 mRNA level and could not expand the lifespan of the hsf-1 mutant C. elegans (sy441); however, this had no effect on the transcription of daf-16 and skn-1 and could expand the lifespan of both daf-16 and skn-1 mutants. These results suggested dependency of the rbGrx effect on the heat shock transcription factor (HSF-1) and independency on both DAF-16 and SKN-1. In summary, our results demonstrated the anti-aging activity of rbGrx, which increased resistance to cellular stress and improved the health span of C. elegans. These results are very important for the use of rbGrx in anti-aging research.

AID and Reactive Oxygen Species Can Induce DNA Breaks within Human Chromosomal Translocation Fragile Zones

DNA double-strand breaks (DSBs) occurring within fragile zones of less than 200 base pairs account for the formation of the most common human chromosomal translocations in lymphoid malignancies, yet the mechanism of how breaks occur remains unknown. Here, we have transferred human fragile zones into S. cerevisiae in the context of a genetic assay to understand the mechanism leading to DSBs at these sites. Our findings indicate that a combination of factors is required to sensitize these regions. Foremost, DNA strand separation by transcription or increased torsional stress can expose these DNA regions to damage from either the expression of human AID or increased oxidative stress. This damage causes DNA lesions that, if not repaired quickly, are prone to nuclease cleavage, resulting in DSBs. Our results provide mechanistic insight into why human neoplastic translocation fragile DNA sequences are more prone to enzymes or agents that cause longer-lived DNA lesions.

Enhanced fermentative performance under stresses of multiple lignocellulose-derived inhibitors by overexpression of a typical 2-Cys peroxiredoxin from Kluyveromyces marxianus

BACKGROUND

Bioethanol from lignocellulosic materials is of great significance to the production of renewable fuels due to its wide sources. However, multiple inhibitors generated from pretreatments represent great challenges for its industrial-scale fermentation. Despite the complex toxicity mechanisms, lignocellulose-derived inhibitors have been reported to be related to the levels of intracellular reactive oxygen species (ROS), which makes oxidoreductase a potential target for the enhancement of the tolerance of yeasts to these inhibitors.

RESULTS

A typical 2-Cys peroxiredoxin from Kluyveromyces marxianus Y179 (KmTPX1) was identified, and its overexpression was achieved in Saccharomyces cerevisiae 280. Strain TPX1 with overexpressed KmTPX1 gene showed an enhanced tolerance to oxidative stresses. Serial dilution assay indicated that KmTPX1 gene contributed to a better cellular growth behavior, when the cells were exposed to multiple lignocellulose-derived inhibitors, such as formic acid, acetic acid, furfural, ethanol, and salt. In particular, KmTPX1 expression also possessed enhanced tolerance to a mixture of formic acid, acetic acid, and furfural (FAF) with a shorter lag period. The maximum glucose consumption rate and ethanol generation rate in KmTPX1-expressing strain were significantly improved, compared with the control. The mechanism of improved tolerance to FAF depends on the lower level of intracellular ROS for cell survival under stress.

CONCLUSION

A new functional gene KmTPX1 from K. marxianus is firstly associated with the enhanced tolerance to multiple lignocellulose-derived inhibitors in S. cerevisiae. We provided a possible detoxification mechanism of the KmTPX1 for further theoretical research; meanwhile, we provided a powerful potential for application of the KmTPX1 overexpressing strain in ethanol production from lignocellulosic materials.

Effects of heterologous expression of human cyclic nucleotide phosphodiesterase 3A (hPDE3A) on redox regulation in yeast

Oxidative stress plays a pivotal role in pathogenesis of cardiovascular diseases and diabetes; however, the roles of protein kinase A (PKA) and human phosphodiesterase 3A (hPDE3A) remain unknown. Here, we show that yeast expressing wild-type (WT) hPDE3A or K13R hPDE3A (putative ubiquitinylation site mutant) exhibited resistance or sensitivity to exogenous hydrogen peroxide (H₂O₂), respectively. H₂O₂-stimulated ROS production was markedly increased in yeast expressing K13R hPDE3A (Oxidative stress Sensitive 1, OxiS1), compared with yeast expressing WT hPDE3A (Oxidative stress Resistant 1, OxiR1). In OxiR1, YAP1 and YAP1-dependent antioxidant genes were up-regulated, accompanied by a reduction in thioredoxin peroxidase. In OxiS1, expression of YAP1 and YAP1-dependent genes was impaired, and the thioredoxin system malfunctioned. H₂O₂ increased cyclic adenosine monophosphate (cAMP)-hydrolyzing activity of WT hPDE3A, but not K13R hPDE3A, through PKA-dependent phosphorylation of hPDE3A, which was correlated with its ubiquitinylation. The changes in antioxidant gene expression did not directly correlate with differences in cAMP-PKA signaling. Despite differences in their capacities to hydrolyze cAMP, total cAMP levels among OxiR1, OxiS1, and mock were similar; PKA activity, however, was lower in OxiS1 than in OxiR1 or mock. During exposure to H₂O₂, however, Sch9p activity, a target of Rapamycin complex 1-regulated Rps6 kinase and negative-regulator of PKA, was rapidly reduced in OxiR1, and Tpk1p, a PKA catalytic subunit, was diffusely spread throughout the cytosol, with PKA activation. In OxiS1, Sch9p activity was unchanged during exposure to H₂O₂, consistent with reduced activation of PKA. These results suggest that, during oxidative stress, TOR-Sch9 signaling might regulate PKA activity, and that post-translational modifications of hPDE3A are critical in its regulation of cellular recovery from oxidative stress.

An interdomain network: the endobacterium of a mycorrhizal fungus promotes antioxidative responses in both fungal and plant hosts

Arbuscular mycorrhizal fungi (AMF) are obligate plant biotrophs that may contain endobacteria in their cytoplasm. Genome sequencing of Candidatus Glomeribacter gigasporarum revealed a reduced genome and dependence on the fungal host. RNA-seq analysis of the AMF Gigaspora margarita in the presence and absence of the endobacterium indicated that endobacteria have an important role in the fungal pre-symbiotic phase by enhancing fungal bioenergetic capacity. To improve the understanding of fungal-endobacterial interactions, iTRAQ (isobaric tags for relative and absolute quantification) quantitative proteomics was used to identify differentially expressed proteins in G. margarita germinating spores with endobacteria (B+), without endobacteria in the cured line (B-) and after application of the synthetic strigolactone GR24. Proteomic, transcriptomic and biochemical data identified several fungal and bacterial proteins involved in interspecies interactions. Endobacteria influenced fungal growth, calcium signalling and metabolism. The greatest effects were on fungal primary metabolism and respiration, which was 50% higher in B+ than in B-. A shift towards pentose phosphate metabolism was detected in B-. Quantification of carbonylated proteins indicated that the B- line had higher oxidative stress levels, which were also observed in two host plants. This study shows that endobacteria generate a complex interdomain network that affects AMF and fungal-plant interactions.

Sup35 methionine oxidation is a trigger for de novo [PSI(+)] prion formation

The molecular basis by which fungal and mammalian prions arise spontaneously is poorly understood. A number of different environmental stress conditions are known to increase the frequency of yeast [PSI(+)] prion formation in agreement with the idea that conditions which cause protein misfolding may promote the conversion of normally soluble proteins to their amyloid forms. A recent study from our laboratory has shown that the de novo formation of the [PSI(+)] prion is significantly increased in yeast mutants lacking key antioxidants suggesting that endogenous reactive oxygen species are sufficient to promote prion formation. Our findings strongly implicate oxidative damage of Sup35 as an important trigger for the formation of the heritable [PSI(+)] prion in yeast. This review discusses the mechanisms by which the direct oxidation of Sup35 might lead to structural transitions favoring conversion to the transmissible amyloid-like form. This is analogous to various environmental factors which have been proposed to trigger misfolding of the mammalian prion protein (PrP(C)) into the aggregated scrapie form (PrP(Sc)).

Identification of proteins that are differentially expressed in brains with Alzheimer's disease using iTRAQ labeling and tandem mass spectrometry

Alzheimer's disease is one of the leading causes of dementia in the elderly. It is considered the result of complex events involving both genetic and environmental factors. To gain further insights into this complexity, we quantitatively analyzed the proteome of cortex region of brains from patients diagnosed with Alzheimer's disease, using a bottom-up proteomics approach. We identified 721 isobaric-tagged polypeptides. From this universe, 61 were found overexpressed and 69 subexpressed in three brains with Alzheimer's disease in comparison to a normal brain. We determined that the most affected processes involving the overexpressed polypeptides corresponded to ROS and stress responses. For the subexpressed polypeptides, the main processes affected were oxidative phosphorylation, organellar acidification and cytoskeleton. We used Drosophila to validate some of the hits, particularly those non-previously described as connected with the disease, such as Sideroflexin and Phosphoglucomutase-1. We manipulated their homolog genes in Drosophila models of Aβ- and Tau-induced pathology. We found proteins that can either modify Aβ toxicity, Tau toxicity or both, suggesting specific interactions with different pathways. This approach illustrates the potential of Drosophila to validate hits after MS studies and suggest that model organisms should be included in the pipeline to identify relevant targets for Alzheimer's disease.

BIOLOGICAL SIGNIFICANCE

We report a set of differentially expressed proteins in three Alzheimer's disease brains in comparison to a normal brain. Our analyses allowed us to identify that the main affected pathways were ROS and stress responses, oxidative phosphorylation, organellar acidification and cytoskeleton. We validated some identified proteins using genetic models of Amyloid-β and Tau-induced pathology in Drosophila melanogaster. With this approach, Sideroflexin and Phosphoglucomutase-1 were identified as novel proteins connected with Alzheimer's disease.

Mitochondrial proteomics of the acetic acid - induced programmed cell death response in a highly tolerant Zygosaccharomyces bailii - derived hybrid strain

Very high concentrations of acetic acid at low pH induce programmed cell death (PCD) in both the experimental model Saccharomyces cerevisiae and in Zygosaccharomyces bailii, the latter being considered the most problematic acidic food spoilage yeast due to its remarkable intrinsic resistance to this food preservative. However, while the mechanisms underlying S. cerevisiae PCD induced by acetic acid have been previously examined, the corresponding molecular players remain largely unknown in Z. bailii. Also, the reason why acetic acid concentrations known to be necrotic for S. cerevisiae induce PCD with an apoptotic phenotype in Z. bailii remains to be elucidated. In this study, a 2-DE-based expression mitochondrial proteomic analysis was explored to obtain new insights into the mechanisms involved in PCD in the Z. bailii derived hybrid strain ISA1307. This allowed the quantitative assessment of expression of protein species derived from each of the parental strains, with special emphasis on the processes taking place in the mitochondria known to play a key role in acetic acid - induced PCD. A marked decrease in the content of proteins involved in mitochondrial metabolism, in particular, in respiratory metabolism (Cor1, Rip1, Lpd1, Lat1 and Pdb1), with a concomitant increase in the abundance of proteins involved in fermentation (Pdc1, Ald4, Dld3) was registered. Other differentially expressed identified proteins also suggest the involvement of the oxidative stress response, protein translation, amino acid and nucleotide metabolism, among other processes, in the PCD response. Overall, the results strengthen the emerging concept of the importance of metabolic regulation of yeast PCD.

Adaptive aneuploidy protects against thiol peroxidase deficiency by increasing respiration via key mitochondrial proteins

Aerobic respiration is a fundamental energy-generating process; however, there is cost associated with living in an oxygen-rich environment, because partially reduced oxygen species can damage cellular components. Organisms evolved enzymes that alleviate this damage and protect the intracellular milieu, most notably thiol peroxidases, which are abundant and conserved enzymes that mediate hydrogen peroxide signaling and act as the first line of defense against oxidants in nearly all living organisms. Deletion of all eight thiol peroxidase genes in yeast (∆8 strain) is not lethal, but results in slow growth and a high mutation rate. Here we characterized mechanisms that allow yeast cells to survive under conditions of thiol peroxidase deficiency. Two independent ∆8 strains increased mitochondrial content, altered mitochondrial distribution, and became dependent on respiration for growth but they were not hypersensitive to H2O2. In addition, both strains independently acquired a second copy of chromosome XI and increased expression of genes encoded by it. Survival of ∆8 cells was dependent on mitochondrial cytochrome-c peroxidase (CCP1) and UTH1, present on chromosome XI. Coexpression of these genes in ∆8 cells led to the elimination of the extra copy of chromosome XI and improved cell growth, whereas deletion of either gene was lethal. Thus, thiol peroxidase deficiency requires dosage compensation of CCP1 and UTH1 via chromosome XI aneuploidy, wherein these proteins support hydroperoxide removal with the reducing equivalents generated by the electron transport chain. To our knowledge, this is the first evidence of adaptive aneuploidy counteracting oxidative stress.

A peroxiredoxin, PRDX-2, is required for insulin secretion and insulin/IIS-dependent regulation of stress resistance and longevity

Peroxiredoxins (Prx) are abundant thiol peroxidases with a conserved anti-ageing role. In contrast to most animals, the nematode worm, Caenorhabditis elegans, encodes a single cytosolic 2-Cys Prx, PRDX-2, rendering it an excellent model for examining how peroxiredoxins affect animal physiology and ageing. Our previous work revealed that, although PRDX-2 protects against the toxicity of peroxides, enigmatically, prdx-2-mutant animals are hyper-resistant to other forms of oxidative stress. Here, we have investigated the basis for this increased resistance. Mammalian FOXO and Nrf2 transcription factors directly promote the expression of a range of detoxification enzymes. We show that the FOXO orthologue, DAF-16, and the Nrf2 orthologue, SKN-1, are required for the increased stress resistance of prdx-2-mutant worms. Our data suggest that PRDX-2 is required for normal levels of insulin secretion and hence the inhibition of DAF-16 and SKN-1 by insulin/IGF-1-like signalling (IIS) under nutrient-rich conditions. Intriguingly, loss of PRDX-2 increases DAF-16 and SKN-1 activities sufficiently to increase arsenite resistance without initiating other IIS-inhibited processes. Together, these data suggest that loss of peroxiredoxin function may increase stress resistance by reducing insulin secretion, but that further changes in insulin signalling are required for the reprogramming of development and fat metabolism. In addition, we reveal that the temperature-dependent prolongevity function of PRDX-2 is required for the extended lifespan associated with several pathways, including further reductions in IIS.

Oxidative stress in fungi: its function in signal transduction, interaction with plant hosts, and lignocellulose degradation

In this review article, we want to present an overview of oxidative stress in fungal cells in relation to signal transduction, interaction of fungi with plant hosts, and lignocellulose degradation. We will discuss external oxidative stress which may occur through the interaction with other microorganisms or plant hosts as well as internally generated oxidative stress, which can for instance originate from NADPH oxidases or “leaky” mitochondria and may be modulated by the peroxiredoxin system or by protein disulfide isomerases thus contributing to redox signaling. Analyzing redox signaling in fungi with the tools of molecular genetics is presently only in its beginning. However, it is already clear that redox signaling in fungal cells often is linked to cell differentiation (like the formation of perithecia), virulence (in plant pathogens), hyphal growth and the successful passage through the stationary phase.

Oxidative stress conditions increase the frequency of de novo formation of the yeast [PSI+] prion

Prions are self‐perpetuating amyloid protein aggregates which underlie various neurodegenerative diseases in mammals and heritable traits in yeast. The molecular basis of how yeast and mammalian prions form spontaneously into infectious amyloid‐like structures is poorly understood. We have explored the hypothesis that oxidative stress is a general trigger for prion formation using the yeast [PSI⁺] prion, which is the altered conformation of the Sup35 translation termination factor. We show that the frequency of [PSI⁺] prion formation is elevated under conditions of oxidative stress and in mutants lacking key antioxidants. We detect increased oxidation of Sup35 methionine residues in antioxidant mutants and show that overexpression of methionine sulphoxide reductase abrogates both the oxidation of Sup35 and its conversion to the [PSI⁺] prion. [PSI⁺] prion formation is particularly elevated in a mutant lacking the Sod1 Cu,Zn‐superoxide dismutase. We have used fluorescence microscopy to show that the de novo appearance of [PSI⁺] is both rapid and increased in frequency in this mutant. Finally, electron microscopy analysis of native Sup35 reveals that similar fibrillar structures are formed in both the wild‐type and antioxidant mutants. Together, our data indicate that oxidative stress is a general trigger of [PSI⁺] formation, which can be alleviated by antioxidant defenses.

Proteomics investigation reveals cell death-associated proteins of basidiomycete fungus Trametes versicolor treated with Ferruginol

Ferruginol has antifungal activity against wood-rot fungi (basidiomycetes). However, specific research on the antifungal mechanisms of ferruginol is scarce. Two-dimensional gel electrophoresis and fluorescent image analysis were employed to evaluate the differential protein expression of wood-rot fungus Trametes versicolor treated with or without ferruginol. Results from protein identification of tryptic peptides via liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS) analyses revealed 17 protein assignments with differential expression. Downregulation of cytoskeleton β-tubulin 3 indicates that ferruginol has potential to be used as a microtubule-disrupting agent. Downregulation of major facilitator superfamily (MFS)–multiple drug resistance (MDR) transporter and peroxiredoxin TSA1 were observed, suggesting reduction in self-defensive capabilities of T. versicolor. In addition, the proteins involved in polypeptide sorting and DNA repair were also downregulated, while heat shock proteins and autophagy-related protein 7 were upregulated. These observations reveal that such cellular dysfunction and damage caused by ferruginol lead to growth inhibition and autophagic cell death of fungi.

Requirement of peroxiredoxin on the stationary phase of yeast cell growth

Toxic chemicals often induce reactive oxygen species (ROS). Although one of the most abundant ROS-sensitive proteins is in the peroxiredoxin (Prx) family, the function of Prx proteins is poorly understood because they are inactivated under high concentrations of hydrogen peroxide. Like mammalian cells, the model eukaryote Saccharomyces cerevisiae possesses multiple Prx proteins. Among the five Prx family proteins, Tsa1 and Ahp1 have the highest and second-highest expression levels, respectively. Here, we focused on a previously uncharacterized phenotype resulting from Tsa1 loss: impaired growth during the late exponential phase. We overexpressed catalase (CTT1) and Ahp1 in cells with disruptions in TSA1 and its homologue, TSA2 (tsa1/2Δ cells), and we found that neither Ctt1 nor Ahp1 overexpression suppressed the impaired cell growth at the stationary phase, although the ROS levels were successfully suppressed. Furthermore, the cell cycle profile was not altered by Tsa1/2 loss, at least in the late exponential phase; however, the glucose consumption rate slowed in the late exponential phase. Our results suggest that ROS levels are not responsible for the growth phenotype. Tsa1 might have a specific function that could not be replaced by Ahp1.

Thiol peroxidase deficiency leads to increased mutational load and decreased fitness in Saccharomyces cerevisiae

Thiol peroxidases are critical enzymes in the redox control of cellular processes that function by reducing low levels of hydroperoxides and regulating redox signaling. These proteins were also shown to regulate genome stability, but how their dysfunction affects the actual mutations in the genome is not known. Saccharomyces cerevisiae has eight thiol peroxidases of glutathione peroxidase and peroxiredoxin families, and the mutant lacking all these genes (∆8) is viable. In this study, we employed two independent ∆8 isolates to analyze the genome-wide mutation spectrum that results from deficiency in these enzymes. Deletion of these genes was accompanied by a dramatic increase in point mutations, many of which clustered in close proximity and scattered throughout the genome, suggesting strong mutational bias. We further subjected multiple lines of wild-type and ∆8 cells to long-term mutation accumulation, followed by genome sequencing and phenotypic characterization. ∆8 lines showed a significant increase in nonrecurrent point mutations and indels. The original ∆8 cells exhibited reduced growth rate and decreased life span, which were further reduced in all ∆8 mutation accumulation lines. Although the mutation spectrum of the two independent isolates was different, similar patterns of gene expression were observed, suggesting the direct contribution of thiol peroxidases to the observed phenotypes. Expression of a single thiol peroxidase could partially restore the growth phenotype of ∆8 cells. This study shows how deficiency in nonessential, yet critical and conserved oxidoreductase function, leads to increased mutational load and decreased fitness.

Metabolic and environmental conditions determine nuclear genomic instability in budding yeast lacking mitochondrial DNA

Mitochondrial dysfunctions are an internal cause of nuclear genome instability. Because mitochondria are key regulators of cellular metabolism, we have investigated a potential link between external growth conditions and nuclear chromosome instability in cells with mitochondrial defects. Using Saccharomyces cerevisiae, we found that cells lacking mitochondrial DNA (rho0 cells) have a unique feature, with nuclear chromosome instability that occurs in nondividing cells and strongly fluctuates depending on the cellular environment. Calorie restriction, lower growth temperatures, growth at alkaline pH, antioxidants (NAC, Tiron), or presence of nearby wild-type cells all efficiently stabilize nuclear genomes of rho0 cells, whereas high glucose and ethanol boost instability. In contrast, other respiratory mutants that still possess mitochondrial DNA (RHO(+)) keep fairly constant instability rates under the same growth conditions, like wild-type or other RHO(+) controls. Our data identify mitochondrial defects as an important driver of nuclear genome instability influenced by environmental factors.

Linking Peroxiredoxin and Vacuolar-ATPase Functions in Calorie Restriction-Mediated Life Span Extension

Calorie restriction (CR) is an intervention extending the life spans of many organisms. The mechanisms underlying CR-dependent retardation of aging are still poorly understood. Despite mechanisms involving conserved nutrient signaling pathways proposed, few target processes that can account for CR-mediated longevity have so far been identified. Recently, both peroxiredoxins and vacuolar-ATPases were reported to control CR-mediated retardation of aging downstream of conserved nutrient signaling pathways. In this review, we focus on peroxiredoxin-mediated stress-defence and vacuolar-ATPase regulated acidification and pinpoint common denominators between the two mechanisms proposed for how CR extends life span. Both the activities of peroxiredoxins and vacuolar-ATPases are stimulated upon CR through reduced activities in conserved nutrient signaling pathways and both seem to stimulate cellular resistance to peroxide-stress. However, whereas vacuolar-ATPases have recently been suggested to control both Ras-cAMP-PKA- and TORC1-mediated nutrient signaling, neither the physiological benefits of a proposed role for peroxiredoxins in H2O2-signaling nor downstream targets regulated are known. Both peroxiredoxins and vacuolar-ATPases do, however, impinge on mitochondrial iron-metabolism and further characterization of their impact on iron homeostasis and peroxide-resistance might therefore increase our understanding of the beneficial effects of CR on aging and age-related diseases.

The yeast peroxiredoxin Tsa1 protects against protein-aggregate-induced oxidative stress

Peroxiredoxins are ubiquitous thiol-specific proteins that have multiple functions in stress protection, including protection against oxidative stress. Tsa1 is the major yeast peroxiredoxin and we show that it functions as a specific antioxidant to protect the cell against the oxidative stress caused by nascent-protein misfolding and aggregation. Yeast mutants lacking TSA1 are sensitive to misfolding caused by exposure to the proline analogue azetidine-2-carboxylic acid (AZC). AZC promotes protein aggregation, and its toxicity to a tsa1 mutant is caused by the production of reactive oxygen species (ROS). The generation of [rho⁰] cells, which lack mitochondrial DNA, rescues the tsa1 mutant AZC sensitivity, indicating that mitochondria are the source of ROS. Inhibition of nascent-protein synthesis with cycloheximide prevents AZC-induced protein aggregation and abrogates ROS generation, confirming that the formation of aggregates causes ROS production. Protein aggregation is accompanied by mitochondrial fragmentation, and we show that Tsa1 localises to the sites of protein aggregation. Protein aggregates are formed adjacent to mitochondria, and our data indicate that active mitochondria generate ROS. These data indicate a new role for peroxiredoxins in protecting against ROS that are generated as a result of protein misfolding and aggregate formation.

Comparative proteomics analysis of engineered Saccharomyces cerevisiae with enhanced biofuel precursor production

The yeast Saccharomyces cerevisiae was metabolically modified for enhanced biofuel precursor production by knocking out genes encoding mitochondrial isocitrate dehydrogenase and over-expression of a heterologous ATP-citrate lyase. A comparative iTRAQ-coupled 2D LC-MS/MS analysis was performed to obtain a global overview of ubiquitous protein expression changes in S. cerevisiae engineered strains. More than 300 proteins were identified. Among these proteins, 37 were found differentially expressed in engineered strains and they were classified into specific categories based on their enzyme functions. Most of the proteins involved in glycolytic and pyruvate branch-point pathways were found to be up-regulated and the proteins involved in respiration and glyoxylate pathway were however found to be down-regulated in engineered strains. Moreover, the metabolic modification of S. cerevisiae cells resulted in a number of up-regulated proteins involved in stress response and differentially expressed proteins involved in amino acid metabolism and protein biosynthesis pathways. These LC-MS/MS based proteomics analysis results not only offered extensive information in identifying potential protein-protein interactions, signal pathways and ubiquitous cellular changes elicited by the engineered pathways, but also provided a meaningful biological information platform serving further modification of yeast cells for enhanced biofuel production.

Deletion of the major peroxiredoxin Tsa1 alters telomere length homeostasis

Reactive oxygen species (ROS) are proposed to play a major role in telomere length alterations during aging. The mechanisms by which ROS disrupt telomeres remain unclear. In Saccharomyces cerevisiae, telomere DNA consists of TG(1-3) repeats, which are maintained primarily by telomerase. Telomere length maintenance can be modulated by the expression level of telomerase subunits and telomerase activity. Additionally, telomerase-mediated telomere repeat addition is negatively modulated by the levels of telomere-bound Rap1-Rif1-Rif2 protein complex. Using a yeast strain defective in the major peroxiredoxin Tsa1 that is involved in ROS neutralization, we have investigated the effect of defective ROS detoxification on telomere DNA, telomerase, telomere-binding proteins, and telomere length. Surprisingly, the tsa1 mutant does not show significant increase in steady-state levels of oxidative DNA lesions at telomeres. The tsa1 mutant displays abnormal telomere lengthening, and reduction in oxidative exposure alleviates this phenotype. The telomere lengthening in the tsa1 cells was abolished by disruption of Est2, subtelomeric DNA, Rap1 C-terminus, or Rif2, but not by Rif1 deletion. Although telomerase expression and activity are not altered, telomere-bound Est2 is increased, while telomere-bound Rap1 is reduced in the tsa1 mutant. We propose that defective ROS scavenging can interfere with pathways that are critical in controlling telomere length homeostasis.

Glutathione levels in and total antioxidant capacity of Candida sp. cells exposed to oxidative stress caused by hydrogen peroxide

INTRODUCTION

The capacity to overcome the oxidative stress imposed by phagocytes seems to be critical for Candida species to cause invasive candidiasis.

METHODS

To better characterize the oxidative stress response (OSR) of 8 clinically relevant Candida sp., glutathione, a vital component of the intracellular redox balance, was measured using the 5,5'-dithiobis-(2-nitrobenzoic acid (DTNB)-glutathione disulfide (GSSG) reductase reconversion method; the total antioxidant capacity (TAC) was measured using a modified method based on the decolorization of the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic) acid radical cation (ABTS*+). Both methods were used with cellular Candida sp. extracts treated or not with hydrogen peroxide (0.5 mM).

RESULTS

Oxidative stress induced by hydrogen peroxide clearly reduced intracellular glutathione levels. This depletion was stronger in Candida albicans and the levels of glutathione in untreated cells were also higher in this species. The TAC demonstrated intra-specific variation.

CONCLUSIONS

Glutathione levels did not correlate with the measured TAC values, despite this being the most important non-enzymatic intracellular antioxidant molecule. The results indicate that the isolated measurement of TAC does not give a clear picture of the ability of a given Candida sp. to respond to oxidative stress.

Loss of vacuolar H+-ATPase (V-ATPase) activity in yeast generates an iron deprivation signal that is moderated by induction of the peroxiredoxin TSA2

Vacuolar H(+)-ATPases (V-ATPases) acidify intracellular organelles and help to regulate overall cellular pH. Yeast vma mutants lack V-ATPase activity and allow exploration of connections between cellular pH, iron, and redox homeostasis common to all eukaryotes. A previous microarray study in a vma mutant demonstrated up-regulation of multiple iron uptake genes under control of Aft1p (the iron regulon) and only one antioxidant gene, the peroxiredoxin TSA2 (Milgrom, E., Diab, H., Middleton, F., and Kane, P. M. (2007) Loss of vacuolar proton-translocating ATPase activity in yeast results in chronic oxidative stress. J. Biol. Chem. 282, 7125-7136). Fluorescent biosensors placing GFP under transcriptional control of either an Aft1-dependent promoter (P(FIT2)-GFP) or the TSA2 promoter (P(TSA2)-GFP) were constructed to monitor transcriptional signaling. Both biosensors were up-regulated in the vma2Δ mutant, and acute V-ATPase inhibition with concanamycin A induced coordinate up-regulation from both promoters. PTSA2-GFP induction was Yap1p-dependent, indicating an oxidative stress signal. Total cell iron measurements indicate that the vma2Δ mutant is iron-replete, despite up-regulation of the iron regulon. Acetic acid up-regulated P(FIT2)-GFP expression in wild-type cells, suggesting that loss of pH control contributes to an iron deficiency signal in the mutant. Iron supplementation significantly decreased P(FIT2)-GFP expression and, surprisingly, restored P(TSA2)-GFP to wild-type levels. A tsa2Δ mutation induced both nuclear localization of Aft1p and P(FIT2)-GFP expression. The data suggest a novel function for Tsa2p as a negative regulator of Aft1p-driven transcription, which is induced in V-ATPase mutants to limit transcription of the iron regulon. This represents a new mechanism bridging the antioxidant and iron-regulatory pathways that is intimately linked to pH homeostasis.

Peroxiredoxins, gerontogenes linking aging to genome instability and cancer

Age is the highest risk factor known for a large number of maladies, including cancers. However, it is unclear how aging mechanistically predisposes the organism to such diseases and which gene products are the primary targets of the aging process. Recent studies suggest that peroxiredoxins, antioxidant enzymes preventing tumor development, are targets of age-related deterioration and that bolstering their activity (e.g., by caloric restriction) extends cellular life span. This review focuses on how the peroxiredoxin functions (i.e., as peroxidases, signal transducers, and molecular chaperones) fit with contemporary theories of aging and whether peroxiredoxins could be targeted therapeutically in the treatment of age-associated cancers.

Disulfide biochemistry in 2-cys peroxiredoxin: requirement of Glu50 and Arg146 for the reduction of yeast Tsa1 by thioredoxin

2-Cys peroxiredoxin (Prx) enzymes are ubiquitously distributed peroxidases that make use of a peroxidatic cysteine (Cys(P)) to decompose hydroperoxides. A disulfide bond is generated as a consequence of the partial unfolding of the α-helix that contains Cys(P). Therefore, during its catalytic cycle, 2-Cys Prx alternates between two states, locally unfolded and fully folded. Tsa1 (thiol-specific antioxidant protein 1 from yeast) is by far the most abundant Cys-based peroxidase in Saccharomyces cerevisiae. In this work, we present the crystallographic structure at 2.8Å resolution of Tsa1(C47S) in the decameric form [(α(2))(5)] with a DTT molecule bound to the active site, representing one of the few available reports of a 2-Cys Prx (AhpC-Prx1 subfamily) (AhpC, alkyl hydroperoxide reductase subunit C) structure that incorporates a ligand. The analysis of the Tsa1(C47S) structure indicated that Glu50 and Arg146 participate in the stabilization of the Cys(P) α-helix. As a consequence, we raised the hypothesis that Glu50 and Arg146 might be relevant to the Cys(P) reactivity. Therefore, Tsa1(E50A) and Tsa1(R146Q) mutants were generated and were still able to decompose hydrogen peroxide, presenting a second-order rate constant in the range of 10(6)M(-1)s(-1). Remarkably, although Tsa1(E50A) and Tsa1(R146Q) were efficiently reduced by the low-molecular-weight reductant DTT, these mutants displayed only marginal thioredoxin (Trx)-dependent peroxidase activity, indicating that Glu50 and Arg146 are important for the Tsa1-Trx interaction. These results may impact the comprehension of downstream events of signaling pathways that are triggered by the oxidation of critical Cys residues, such as Trx.

Comparative proteome analysis of Saccharomyces cerevisiae: a global overview of in vivo targets of the yeast activator protein 1

Background

The activity of the yeast activator protein 1 (Yap1p) increases under stress conditions, which leads to enhanced transcription of a number of genes encoding protective enzymes or other proteins. To obtain a global overview of changes in expression of Yap1p-targeted proteins, we compared a Yap1p-overexpressing transformant with a control transformant by triplicate analysis of the proteome using two-dimensional gel electrophoresis (2-DE). Proteins of interest were identified using MALDI-MS or LC-MS/MS.

Results

The relative quantities of 55 proteins were elevated significantly upon overexpression of Yap1p, and most of these proteins were found to have a Yap1p-binding site upstream of their coding sequences. Interestingly, the main metabolic enzymes in the glycolysis and pyruvate-ethanol pathways showed a significant increase in the Yap1p-overexpressing transformant. Moreover, a comparison of our proteome data with transcriptome data from the literature suggested which proteins were regulated at the level of the proteome, and which proteins were regulated at the level of the transcriptome. Eight proteins involved in stress response, including seven heat-shock and chaperone proteins, were significantly more abundant in the Yap1p-overexpressing transformant.

Conclusions

We have investigated the general protein composition in Yap1p-overexpressing S. cerevisiae using proteomic techniques, and quantified the changes in the expression of the potential Yap1p-targeted proteins. Identification of the potential Yap1p targets and analysis of their role in cellular processes not only give a global overview of the ubiquitous cellular changes elicited by Yap1p, but also provide the framework for understanding the mechanisms behind Yap1p-regulated stress response in yeast.

Redox-sensitive YFP sensors monitor dynamic nuclear and cytosolic glutathione redox changes

Intracellular redox homeostasis is crucial for many cellular functions but accurate measurements of cellular compartment-specific redox states remain technically challenging. To better characterize redox control in the nucleus, we targeted a yellow fluorescent protein-based redox sensor (rxYFP) to the nucleus of the yeast Saccharomyces cerevisiae. Parallel analyses of the redox state of nucleus-rxYFP and cytosol-rxYFP allowed us to monitor distinctively dynamic glutathione (GSH) redox changes within these two compartments under a given condition. We observed that the nuclear GSH redox environment is highly reducing and similar to the cytosol under steady-state conditions. Furthermore, these sensors are able to detect redox variations specific for their respective compartments in glutathione reductase (Glr1) and thioredoxin pathway (Trr1, Trx1, Trx2) mutants that have altered subcellular redox environments. Our mutant redox data provide in vivo evidence that glutathione and the thioredoxin redox systems have distinct but overlapping functions in controlling subcellular redox environments. We also monitored the dynamic response of nucleus-rxYFP and cytosol-rxYFP to GSH depletion and to exogenous low and high doses of H₂O₂ bursts. These observations indicate a rapid and almost simultaneous oxidation of both nucleus-rxYFP and cytosol-rxYFP, highlighting the robustness of the rxYFP sensors in measuring real-time compartmental redox changes. Taken together, our data suggest that the highly reduced yeast nuclear and cytosolic redox states are maintained independently to some extent and under distinct but subtle redox regulation. Nucleus- and cytosol-rxYFP register compartment-specific localized redox fluctuations that may involve exchange of reduced and/or oxidized glutathione between these two compartments. Finally, we confirmed that GSH depletion has profound effects on mitochondrial genome stability but little effect on nuclear genome stability, thereby emphasizing that the critical requirement for GSH during growth is linked to a mitochondria-dependent process.

Increase in antioxidant gene transcripts, stress tolerance and biocontrol efficacy of Candida oleophila following sublethal oxidative stress exposure

A pretreatment of the yeast, Candida oleophila, with 5 mM H(2)O(2) for 30 min (sublethal) increased yeast tolerance to subsequent lethal levels of oxidative stress (50 mM H(2)O(2)), high temperature (40 °C), and low pH (pH 4). Compared with non-stress-adapted yeast cells, stress-adapted cells exhibited better control of apple fruit infections by Penicillium expansum and Botrytis cinerea and had initially higher growth rates in apple wounds. Suppression subtractive hybridization analysis was used to identify genes expressed in yeast in response to sublethal oxidative stress. Transcript levels were confirmed using semiquantitative reverse transcription-PCR. Seven antioxidant genes were upregulated. The elevated expression of these genes was associated with less accumulation of reactive oxygen species and a lower level of protein and lipid oxidation under subsequent stresses. These data support the premise that induction of abiotic stress tolerance in biocontrol yeast can improve biocontrol efficacy by upregulation of genes involved in the amelioration of oxidative stress.

Adaptation of organisms by resonance of RNA transcription with the cellular redox cycle

Sequence variation in organisms differs across the genome and the majority of mutations are caused by oxidation, yet its origin is not fully understood. It has also been shown that the reduction-oxidation reaction cycle is the fundamental biochemical cycle that coordinates the timing of all biochemical processes in the cell, including energy production, DNA replication, and RNA transcription. We show that the temporal resonance of transcriptome biosynthesis with the oscillating binary state of the reduction-oxidation reaction cycle serves as a basis for non-random sequence variation at specific genome-wide coordinates that change faster than by accumulation of chance mutations. This work demonstrates evidence for a universal, persistent and iterative feedback mechanism between the environment and heredity, whereby acquired variation between cell divisions can outweigh inherited variation.

Protein expression regulation under oxidative stress

Oxidative stress is known to affect both translation and protein turnover, but very few large scale studies describe protein expression under stress. We measure protein concentrations in Saccharomyces cerevisiae over the course of 2 h in response to a mild oxidative stress induced by diamide, providing detailed time-resolved information for 815 proteins, with additional data for another ~1,100 proteins. For the majority of proteins, we discover major differences between the global transcript and protein response. Although mRNA levels often return to baseline 1 h after treatment, protein concentrations continue to change. Integrating our data with features of translation and protein degradation, we are able to predict expression patterns for 41% of the proteins in the core data set. Predictive features include, among others, targeting by RNA-binding proteins (Lhp1 and Khd1), RNA secondary structures, RNA half-life, and translation efficiency under unperturbed conditions and in response to oxidative reagents, but not chaperone binding. We are able to both describe general dynamics of protein concentration changes and suggest possible regulatory mechanisms for individual proteins.

Aspasing out metacaspases and caspases: proteases of many trades

Execution of programmed cell death (PCD) in nonmetazoan organisms is morphologically different from apoptotic PCD in animals and lacks a number of key molecular components of apoptotic machinery, including caspases. Yet protozoan, fungal, and plant cells exhibit caspase-like proteolytic activities, which increase in a PCD-dependent manner. This poses a question whether nonmetazoan organisms contain structurally dissimilar proteases that functionally substitute for caspases. Putative ancestors of caspases, metacaspases, are candidates for this role; however, their distinct substrate specificity raises doubts. The identification of a common biological target of caspases and metacaspases and previously unknown functions unrelated to cell death of metacaspases provide new food for thought.

Ribosome-associated peroxiredoxins suppress oxidative stress-induced de novo formation of the [PSI+] prion in yeast

Peroxiredoxins (Prxs) are ubiquitous antioxidants that protect cells against oxidative stress. We show that the yeast Tsa1/Tsa2 Prxs colocalize to ribosomes and function to protect the Sup35 translation termination factor against oxidative stress-induced formation of its heritable [PSI(+)] prion conformation. In a tsa1 tsa2 [psi(-)] [PIN(+)] strain, the frequency of [PSI(+)] de novo formation is significantly elevated. The Tsa1/Tsa2 Prxs, like other 2-Cys Prxs, have dual activities as peroxidases and chaperones, and we show that the peroxidase activity is required to suppress spontaneous de novo [PSI(+)] prion formation. Molecular oxygen is required for [PSI(+)] prion formation as growth under anaerobic conditions prevents prion formation in the tsa1 tsa2 mutant. Conversely, oxidative stress conditions induced by exposure to hydrogen peroxide elevates the rate of de novo [PSI(+)] prion formation leading to increased suppression of all three termination codons in the tsa1 tsa2 mutant. Altered translational fidelity in [PSI(+)] strains may provide a mechanism that promotes genetic variation and phenotypic diversity (True HL, Lindquist SL (2000) Nature 407:477-483). In agreement, we find that prion formation provides yeast cells with an adaptive advantage under oxidative stress conditions, as elimination of the [PSI(+)] prion from tsa1 tsa2 mutants renders the resulting [psi(-)] [pin(-)] cells hypersensitive to hydrogen peroxide. These data support a model in which Prxs function to protect the ribosomal machinery against oxidative damage, but when these systems become overwhelmed, [PSI(+)] prion formation provides a mechanism for uncovering genetic traits that aid survival during oxidative stress conditions.