Cytosolic thioredoxin peroxidase I is essential for the antioxidant defense of yeast with dysfunctional mitochondria

Peroxiredoxins in erythrocytes: far beyond the antioxidant role

The red blood cells (RBCs) are essential to transport oxygen (O2) and nutrients throughout the human body. Changes in the structure or functioning of the erythrocytes can lead to several deficiencies, such as hemolytic anemias, in which an increase in reactive oxidative species generation is involved in the pathophysiological process, playing a significant role in the severity of several clinical manifestations. There are important lines of defense against the damage caused by oxidizing molecules. Among the antioxidant molecules, the enzyme peroxiredoxin (Prx) has the higher decomposition power of hydrogen peroxide, especially in RBCs, standing out because of its abundance. This review aimed to present the recent findings that broke some paradigms regarding the three isoforms of Prxs found in RBC (Prx1, Prx2, and Prx6), showing that in addition to their antioxidant activity, these enzymes may have supplementary roles in transducing peroxide signals, as molecular chaperones, protecting from membrane damage, and maintenance of iron homeostasis, thus contributing to the overall survival of human RBCs, roles that seen to be disrupted in hemolytic anemia conditions.

Analyses of the three 1-Cys Peroxiredoxins from Aspergillus fumigatus reveal that cytosolic Prx1 is central to H2O2 metabolism and virulence

Standing among the front defense strategies against pathogens, host phagocytic cells release various oxidants. Therefore, pathogens have to cope with stressful conditions at the site of infection. Peroxiredoxins (Prx) are highly reactive and abundant peroxidases that can support virulence and persistence of pathogens in distinct hosts. Here, we revealed that the opportunistic human pathogen A. fumigatus presents three 1-Cys Prx (Prx6 subfamily), which is unprecedented. We showed that PrxB and PrxC were in mitochondria, while Prx1 was in cytosol. As observed for other Prxs, recombinant Prx1 and PrxC decomposed H₂O₂ at elevated velocities (rate constants in the 10⁷ M⁻¹s⁻¹ range). Deletion mutants for each Prx displayed higher sensitivity to oxidative challenge in comparison with the wild-type strain. Additionally, cytosolic Prx1 was important for A. fumigatus survival upon electron transport dysfunction. Expression of Prxs was dependent on the SakA^HOG1 MAP kinase and the Yap1^YAP1 transcription factor, a global regulator of the oxidative stress response in fungi. Finally, cytosolic Prx1 played a major role in pathogenicity, since it is required for full virulence, using a neutropenic mouse infection model. Our data indicate that the three 1-Cys Prxs act together to maintain the redox balance of A. fumigatus.

Sphingolipids and mitochondrial function in budding yeast

BACKGROUND

Sphingolipids (SLs) are not only key components of cellular membranes, but also play an important role as signaling molecules in orchestrating both cell growth and apoptosis. In Saccharomyces cerevisiae, three complex SLs are present and hydrolysis of either of these species is catalyzed by the inositol phosphosphingolipid phospholipase C (Isc1p). Strikingly, mutants deficient in Isc1p display several hallmarks of mitochondrial dysfunction such as the inability to grow on a non-fermentative carbon course, increased oxidative stress and aberrant mitochondrial morphology.

SCOPE OF REVIEW

In this review, we focus on the pivotal role of Isc1p in regulating mitochondrial function via SL metabolism, and on Sch9p as a central signal transducer. Sch9p is one of the main effectors of the target of rapamycin complex 1 (TORC1), which is regarded as a crucial signaling axis for the regulation of Isc1p-mediated events. Finally, we describe the retrograde response, a signaling event originating from mitochondria to the nucleus, which results in the induction of nuclear target genes. Intriguingly, the retrograde response also interacts with SL homeostasis.

MAJOR CONCLUSIONS

All of the above suggests a pivotal signaling role for SLs in maintaining correct mitochondrial function in budding yeast.

GENERAL SIGNIFICANCE

Studies with budding yeast provide insight on SL signaling events that affect mitochondrial function.

Gene targets for fungal and mycotoxin control

It was initially shown that gallic acid, from hydrolysable tannins in the pelliele of walnut kernels, dramatically inhibits biosynthesis of aflatoxin byAspergillus flavus. The mechanism of this inhibition was found to take place upstream from the gene cluster, including the regulatory gene,aflR, involved in aflatoxin biosynthesis. Additional research using other antioxidant phenolics showed similar antiaflatoxigenic activity to gallic acid. Treatment ofA. flavus withtert-butyl hydroperoxide resulted in an almost doubling of aflatoxin biosynthesis compared to untreated samples. Thus, antioxidative response systems are potentially useful molecular targets for control ofA. flavus. A high throughput screening system was developed using yeast,Saccharomyces cerevisiae, as a model fungus. This screening provided an avenue to quickly identify fungal genes that were vulnerable to treatment by phenolic compounds. The assay also provided a means to quickly assess effects of combinations of phenolics and certain fungicides affecting mitochondrial respiration. For example, theS. cerevisiae sod2† mutant was highly sensitive to treatment by certain phenolics and strobilurins/antimycin A, fungicides which inhibit complex III of the mitochondrial respiratory chain. Verification of stress to this system in the target fungus,A. flavus, was shown through complementation analysis, wherein the mitochondrial superoxide dismutase (Mn-SOD) gene (sodA) ofA. flavus in the ortholog mutant,sod2†, ofS. cerevisiae, relieved phenolic-induced stress. Mitochondrial antioxidative stress systems play an important role in fungal response to antifungals. Combined treatment of fungi with phenolics and inhibitors of mitochondrial respiration can effectively suppress growth ofA. flavus in a synergistic fashion.

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.

Molecular cloning and characterization of a thioredoxin peroxidase gene from Apis cerana cerana

Thioredoxin peroxidases (Tpxs) play important roles in protecting organisms against the toxicity of reactive oxygen species (ROS) and regulating intracellular signal transduction. In the present study, we cloned the full cDNA of Tpx1 encoding a 195-amino acid protein from Apis cerana cerana (Acc). Based on the genomic DNA sequence, a 1442-bp 5'-flanking region was obtained, and the putative transcription factor binding sites were predicted. Quantitative PCR analysis showed that AccTpx1 was highly expressed in thorax and that the AccTpx1 transcript reached its highest level in two-week-old adult worker honeybees. Moreover, expression of the AccTpx1 transcript was increased by various abiotic stresses, such as ultraviolet light, HgCl(2) , and insecticide treatments. In addition, the recombinant AccTpx1 protein exhibited antioxidant activity; it removed hydrogen peroxide and protected DNA. These results suggest that AccTpx1 plays an important role in protecting honeybees from oxidative injury and may act in extending the lifespan of them.

Changes in the proteome of Candida albicans in response to azole, polyene, and echinocandin antifungal agents

The yeast Candida albicans is an opportunistic human fungal pathogen and the cause of superficial and systemic infections in immunocompromised patients. The classes of antifungal agents most commonly used to treat Candida infections are the azoles, polyenes, and echinocandins. In the present study, we identified changes in C. albicans protein abundance using two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption ionization-time of flight mass spectroscopy following exposure to representatives of the azole (ketoconazole), polyene (amphotericin B), and echinocandin (caspofungin) antifungals in an effort to elucidate the adaptive responses to these classes of antifungal agents. We identified 39 proteins whose abundance changed in response to ketoconazole exposure. Some of these proteins are involved in ergosterol biosynthesis and are associated with azole resistance. Exposure to amphotericin B altered the abundance of 43 proteins, including those associated with oxidative stress and osmotic tolerance. We identified 50 proteins whose abundance changed after exposure to caspofungin, including enzymes involved in cell wall biosynthesis and integrity, as well as the regulator of beta-1,3-glucan synthase activity, Rho1p. Exposure to caspofungin also increased the abundance of the proteins involved in oxidative and osmotic stress. The common adaptive responses shared by all three antifungal agents included proteins involved in carbohydrate metabolism. Some of these antifungal-responsive proteins may represent potential targets for the development of novel therapeutics that could enhance the antifungal activities of these drugs.

Glucose transporter protein 1 expression in mucoepidermoid carcinoma of salivary gland: correlation with grade of malignancy

Mucoepidermoid carcinoma (MEC), the most common primary salivary malignancy, shows great variability in clinical behaviour, thus demanding investigation to identify of prognostic markers. Since Warburg's studies, unrestricted cell growth during tumorigenesis has been linked to altered metabolism, implying hypoxic stimulation of glycolysis and diminished contribution of mitochondrial oxidative phosphorylation to cellular ATP supply. Hypothesizing that the study of MEC metabolic status could lead to the discovery of prognostic markers, we investigated by immunohistochemistry the expression of glucose transporter 1 (Glut-1), mitochondrial antigen and peroxiredoxin I (Prx I) in samples of MEC from different histological grades. Our results showed that mitochondrial antigen and Prx I were expressed in the majority of the MEC cases independent of the histological grade. In contrast Glut-1 expression increased significantly as the tumours became more aggressive. These results suggested that oxidative phosphorylation may contribute to ATP supply in all stages of MEC progression, and that the relative contribution of glycolysis over mitochondria for cellular ATP supply increases during MEC progression, favouring growth under low oxygen concentration. In addition, the observed high Prx I protein levels could provide protection to tumour cells against reactive oxygen species generated as a consequence of mitochondrial function and hypoxia-reoxygenation cycling. Altogether our findings suggest that upregulation of Glut-1 and Prx I constitute successful adaptive strategies of MEC cells conferring a growth advantage over normal salivary gland cells in the unstable oxygenation tumour environment.

Increased riboflavin production from activated bleaching earth by a mutant strain of Ashbya gossypii

The production of riboflavin from vegetable oil was increased using a mutant strain of Ashbya gossypii. This mutant was generated by treating the wild-type strain with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Riboflavin production was 10-fold higher in the mutant compared to the wild-type strain. The specific intracellular catalase activity after 3 d of culture was 6-fold higher in the mutant than in the wild-type strain. For the mutant, riboflavin production in the presence of 40 mM hydrogen peroxide was 16% less than that in the absence of hydrogen peroxide, whereas it was 56% less for the wild-type strain. The isocitrate lyase (ICL) activity of the mutant was 0.26 mU/mg of protein during the active riboflavin production phase, which was 2.6-fold higher than the wild-type strain. These data indicate that the mutant utilizes the carbon flux from the TCA cycle to the glyoxylate cycle more efficiently than the wild-type strain, resulting in enhanced riboflavin production. This novel mutant has the potential to be of use for industrial-scale riboflavin production from waste-activated bleaching earth (ABE), thereby transforming a useless material into a valuable bioproduct.

Cellular factors required for protection from hyperoxia toxicity in Saccharomyces cerevisiae

Prolonged exposure to hyperoxia represents a serious danger to cells, yet little is known about the specific cellular factors that affect hyperoxia stress. By screening the yeast deletion library, we have identified genes that protect against high-O2 damage. Out of approx. 4800 mutants, 84 were identified as hyperoxia-sensitive, representing genes with diverse cellular functions, including transcription and translation, vacuole function, NADPH production, and superoxide detoxification. Superoxide plays a significant role, since the majority of hyperoxia-sensitive mutants displayed cross-sensitivity to superoxide-generating agents, and mutants with compromised SOD (superoxide dismutase) activity were particularly vulnerable to hyperoxia. By comparison, factors known to guard against H2O2 toxicity were poorly represented amongst hyperoxia-sensitive mutants. Although many cellular components are potential targets, our studies indicate that mitochondrial glutathione is particularly vulnerable to hyperoxia damage. During hyperoxia stress, mitochondrial glutathione is more susceptible to oxidation than cytosolic glutathione. Furthermore, two factors that help maintain mitochondrial GSH in the reduced form, namely the NADH kinase Pos5p and the mitochondrial glutathione reductase (Glr1p), are critical for hyperoxia resistance, whereas their cytosolic counterparts are not. Our findings are consistent with a model in which hyperoxia toxicity is manifested by superoxide-related damage and changes in the mitochondrial redox state.

Comparative study of two thioredoxin peroxidases from disk abalone (Haliotis discus discus): cloning, recombinant protein purification, characterization of antioxidant activities and expression analysis

Thioredoxin peroxidase (TPx), also named peroxiredoxin (Prx), is an important peroxidase, which can protect organisms against various oxidative stresses. Two TPxs were isolated from a disk abalone (Haliotis discus discus) cDNA library, named as AbTPx1 and AbTPx2, respectively. AbTPx1 and AbTPx2 consist of 1315 and 1045 bp full-length cDNA with 753 and 597 bp open reading frames encoding 251 and 199 amino acids, respectively. The TPx signature motif 1 (FYPLDFTFVCPTEI) and motif 2 (GEVCPA) were conserved in both AbTPx1 and AbTPx2 amino acid sequences. Purified recombinant abalone TPx fusion proteins catalyzed the reduction of H2O2 and butyl hydroperoxide in peroxidase assays. Furthermore, both AbTPx fusion proteins were shown to protect super-coiled DNA from damage by metal-catalyzed oxidation (MCO) in vitro. Escherichia coli cells transformed with AbTPx1 and AbTPx2 coding sequences in pMAL-c2x showed resistance to H2O2 at 0.8 mM concentration by in vivo H2O2 tolerance assay. AbTPx1 and AbTPx2 mRNA were constitutively expressed in gill, mantle, abductor muscle and digestive tract in a tissue specific manner. Additionally, both TPxs mRNA were up-regulated in gill and digestive tract tissues against H2O2 at 3h post injection. The results indicate that AbTPx1 and AbTPx2 gene expressions are induced by oxidative stress and their respective proteins function in the detoxification of different ROS molecules to maintain efficient antioxidant defense in disk abalone.

Human peroxiredoxin PrxI is an orthologue of yeast Tsa1, capable of suppressing genome instability in Saccharomyces cerevisiae

The peroxiredoxins (Prx) are conserved antioxidant proteins that use cysteine as the primary site of oxidation during the reduction of peroxides. Many organisms have more than one isoform of Prx. Deletion of TSA1, one of five Prxs in yeast Saccharomyces cerevisiae, results in accumulation of a broad spectrum of mutations including gross chromosomal rearrangements. Deletion of TSA1 is synthetically lethal with mutations in RAD6 and several key genes involved in DNA double-strand break repair. Here, we have examined the function of human PrxI and PrxII, which share a high degree of sequence identity with Tsa1, by expressing them in S. cerevisiae cells under the control of the native TSA1 promoter. We found that expression of PrxI, but not PrxII, was capable of complementing a tsa1Delta mutant for a variety of defects including genome instability, the synthetic lethality observed in rad6 Delta tsa1Delta and rad51 Delta tsa1Delta double mutants, and mutagen sensitivity. Moreover, expression of either Tsa1 or PrxI prevented Bax-induced cell death. These data indicate that PrxI is an orthologue of Tsa1. PrxI and Tsa1 seem to act on the same substrates in vivo and share similar mechanisms of function. The observation that PrxI is involved in suppressing genome instability and protecting against cell death potentially provides a better understanding of the consequences of PrxI dysfunction in human cells. The S. cerevisiae system described here could provide a sensitive tool to uncover the mechanisms that underlie the function of human Prxs.

Isc1 regulates sphingolipid metabolism in yeast mitochondria

The Saccharomyces cerevisiae inositol sphingolipid phospholipase C (Isc1p), a homolog of mammalian neutral sphingomyelinases, hydrolyzes complex sphingolipids to produce ceramide in vitro. Epitope-tagged Isc1p associates with the mitochondria in the post-diauxic phase of yeast growth. In this report, the mitochondrial localization of Isc1p and its role in regulating sphingolipid metabolism were investigated. First, endogenous Isc1p activity was enriched in highly purified mitochondria, and western blots using highly purified mitochondrial membrane fractions demonstrated that epitope-tagged Isc1p localized to the outer mitochondrial membrane as an integral membrane protein. Next, LC/MS was employed to determine the sphingolipid composition of highly purified mitochondria which were found to be significantly enriched in alpha-hydroxylated phytoceramides (21.7 fold) relative to the whole cell. Mitochondria, on the other hand, were significantly depleted in sphingoid bases. Compared to the parental strain, mitochondria from isc1Delta in the post-diauxic phase showed drastic reduction in the levels of alpha-hydroxylated phytoceramide (93.1% loss compared to WT mitochondria with only 2.58 fold enrichment in mitochondria compared to whole cell). Functionally, isc1Delta showed a higher rate of respiratory-deficient cells after incubation at high temperature and was more sensitive to hydrogen peroxide and ethidium bromide, indicating that isc1Delta exhibits defects related to mitochondrial function. These results suggest that Isc1p generates ceramide in mitochondria, and the generated ceramide contributes to the normal function of mitochondria. This study provides a first insight into the specific composition of ceramides in mitochondria.

Enhanced activity of strobilurin and fludioxonil by using berberine and phenolic compounds to target fungal antioxidative stress response

AIMS

Identify natural products that effectively target antioxidative signal transduction/stress response systems [i.e., mitogen-activated protein kinase (MAPK) pathway, mitochondrial superoxide dismutase (Mn-SOD)] of fungi. Enhance activity of strobilurin or fludioxonil with discovered compounds.

METHODS AND RESULTS

Enhancement of antifungal activity of strobilurins, inhibitors of complex III of the mitochondrial respiratory chain, was tested using berberine hemisulfate and different phenolic compounds. The Saccharomyces cerevisiae sod2Delta, a deletion mutant lacking Mn-SOD gene, was highly sensitive to berberine and veratraldehyde. Functional complementation analysis verified these compounds target Mn-SOD. Activity of strobilurin (25-50 micromol l(-1)) was elevated on most aspergilli and Penicillium expansum by co-application with berberine or veratraldehyde (2-4 mmol l(-1)). These compounds also prevented Aspergillus fumigatus MAPK mutants (sakADelta and mpkCDelta) from escaping toxicity of fludioxonil (a phenylpyrrole fungicide potentiated by the MAPK pathway), a typical phenotype of fungal MAPK mutants.

CONCLUSIONS

Strobilurin activity or prevention of fungal escape from fludioxonil toxicity can be enhanced by co-application of certain alkaloids or phenolics.

SIGNIFICANCE AND IMPACT OF THE STUDY

Natural products can be used to target cellular stress response systems in fungal pathogens and serve as alternatives/additives to commercial antifungal agents.

An approach to the hypoxic and oxidative stress responses inKluyveromyces lactisby analysis of mRNA levels

Genome duplication, after the divergence of Saccharomyces cerevisiae from Kluyveromyces lactis along evolution, has been proposed as a mechanism of yeast evolution from strict aerobics, such as Candida albicans, to facultatives/fermentatives, such as S. cerevisiae. This feature, together with the preponderance of respiration and the use of the pentose phosphate pathway in glucose utilization, makes K. lactis a model yeast for studies related to carbon and oxygen metabolism. In this work, and based on the knowledge of the sequence of the genome of K. lactis, obtained by the Génolevures project, we have constructed DNA arrays from K. lactis including a limited amount of selected probes. They are related to the aerobiosis-hypoxia adaptation and to the oxidative stress response, and have been used to test changes in mRNA levels in response to hypoxia and oxidative stress generated by H(2)O(2). The study was carried out in both wild-type and rag2 mutant K. lactis strains in which glycolysis is blocked at the phosphoglucose isomerase step. This approach is the first analysis carried out in K. lactis for the majority of the genes selected.

Reactive cysteine in proteins: protein folding, antioxidant defense, redox signaling and more

Cysteine plays structural roles in proteins and can also participate in electron transfer reactions, when some structural folds provide appropriated environments for stabilization of its sulfhydryl group in the anionic form, called thiolate (RS(-)). In contrast, sulfhydryl group of free cysteine has a relatively high pK(a) (8,5) and as a consequence is relatively inert for redox reaction in physiological conditions. Thiolate is considerable more powerful as nucleophilic agent than its protonated form, therefore, reactive cysteine are present mainly in its anionic form in proteins. In this review, we describe several processes in which reactive cysteine in proteins take part, showing a high degree of redox chemistry versatility.

Molecular cloning, expression of a peroxiredoxin gene in Chinese shrimp Fenneropenaeus chinensis and the antioxidant activity of its recombinant protein

Peroxiredoxin (Prx) is known to be an antioxidant protein that protects the organisms against various oxidative stresses and functions in intracellular signal transduction. A Prx gene was firstly isolated in the crustacean, Chinese shrimp Fenneropenaeus chinensis. The full-length cDNA consists of 942bp with a 594bp open reading frame, encoding 198 amino acids. The molecular mass of the deduced amino acid is 22041.17Da with an estimated pI of 5.17. Sequence comparison showed that Prx of F. chinensis shares 76%, 73% and 72% identity with that of Aedes aegypti, Branchiostoma belcheri tsingtaunese and Drosophila melanogaster, respectively. Northern blot analysis revealed the presence of Prx transcripts of F. chinensis in all tissues examined. Real-time PCR analysis indicated that the Prx showed different expression profiles in shrimp hemocytes and hepatopancreas after artificial infection with Vibrio anguillarum. In addition, a fusion protein containing Prx was produced in vitro. LC-ESI-MS analysis showed that four peptide fragments of the recombinant protein were identical to the corresponding sequence of F. chinensis Prx. And the purified recombinant proteins were shown to reduce H(2)O(2) in the presence of dithiothreitol.

In vitro potential antioxidant activity of (1-->3),(1-->6)-beta-D-glucan and protein fractions from Saccharomyces cerevisiae cell walls

(1-->3),(1-->6)-Beta-D-Glucan, a cell wall polysaccharide in many microorganisms, fungi and algae, is a well-known biological response modifier. Recently, it was found that (1-->3)-beta-D-glucan from Saccharomyces cerevisiae also exhibits antioxidative capabilities. In this study the antioxidative activity of the cell wall fractions of brewer's yeast was investigated. Particular emphasis was put on the question to which extent glucan is responsible for the antioxidative activity of the cell walls and how the other cell wall components might contribute. For the experiments yeast cell walls from brewery fermentations were used. Glucan was isolated by a three-step extraction procedure including a combination of hot water and enzymatic treatment. The level of (1-->3),(1-->6)-beta-D-glucan in the cell walls was analyzed enzymatically. The antioxidant activity was determined by electron paramagnetic resonance spectrometry and Trolox equivalent antioxidant capacity assay. The results show that the antioxidative activity of yeast cell wall proteins exceeds that of beta-glucan greatly. Especially aromatic side chains and free thiols from denatured proteins seem to work as antioxidants.

Regulation of the yeast TSA1 peroxiredoxin by ZAP1 is an adaptive response to the oxidative stress of zinc deficiency

Zinc deficiency is a potential risk factor for disease in humans because it leads to increased oxidative stress and DNA damage. We show here that the yeast Saccharomyces cerevisiae also experiences oxidative stress when zinc-deficient, and we have identified one mechanism yeast cells use to defend themselves against this stress. The Zap1p transcription factor is a central player in the response of yeast to zinc deficiency. To identify genes important for growth in low zinc, DNA microarrays were used to identify genes directly regulated by Zap1p. We found that the TSA1 gene is one such Zap1p target whose expression is increased under zinc deficiency. TSA1 encodes a cytosolic thioredoxin-dependent peroxidase responsible for degrading hydrogen peroxide and organic hydroperoxides. Consistent with its regulation by Zap1p, we showed that tsa1delta mutants have a growth defect in low zinc that can be suppressed by zinc but not by other metals. Anaerobic conditions also suppressed the tsa1delta low zinc growth defect indicating that oxidative stress is the likely cause of the poor growth. Consistent with this hypothesis, we demonstrated that zinc deficiency causes increased reactive oxygen species in wild type cells and that this increase is further exacerbated in tsa1delta mutants. The role of this regulation by Zap1p in limiting oxidative stress in low zinc was confirmed when the Zap1p-binding site was specifically mutated in the chromosomal TSA1 promoter. Thus, we conclude that TSA1 induction by Zap1p is an adaptive response to deal with the increased oxidative stress caused by zinc deficiency.

The structural molecular biology network of the State of São Paulo, Brazil

This article describes the achievements of the Structural Molecular Biology Network (SMolBNet), a collaborative program of structural molecular biology, centered in the State of São Paulo, Brazil, and supported by São Paulo State Funding Agency (FAPESP). It gathers twenty scientific groups and is coordinated by the scientific staff of the Center of Structural Molecular Biology, at the National Laboratory of Synchrotron Light (LNLS), in Campinas. The SMolBNet program has been aimed at 1) solving the structure of proteins of interest related to the research projects of the groups. In some cases, the choice has been to select proteins of unknown function or of possible novel structure obtained from the sequenced genomes of the FAPESP genomic program; 2) providing the groups with training in all the steps of the protein structure determination: gene cloning, protein expression, protein purification, protein crystallization and structure determination. Having begun in 2001, the program has been successful in both aims. Here, four groups reveal their participation in the program and describe the structural aspects of the proteins they have selected to study.

Controlling food-contaminating fungi by targeting their antioxidative stress-response system with natural phenolic compounds

The antioxidative stress-response system is essential to fungi for tolerating exposure to phenolic compounds. We show how this system can be targeted to improve fungal control by using compounds that inhibit the fungal mitochondrial respiratory chain. Targeting mitochondrial superoxide dismutase with selected phenolic acid derivatives (e.g., vanillyl acetone) resulted in a 100- to 1,000-fold greater sensitivity to strobilurin or carboxin fungicides. This synergism is significantly greater with strobilurin than with carboxin, suggesting that complex III of the mitochondrial respiratory chain is a better target than complex II for fungal control, using phenolics. These results show certain natural compounds are effective synergists to commercial fungicides and can be used for improving control of food-contaminating pathogens. These results suggest that the use of such compounds for fungal control can reduce environmental and health risks associated with commercial fungicides, lower cost for control, and the probability for development of resistance.

Yeast oxidative stress response. Influences of cytosolic thioredoxin peroxidase I and of the mitochondrial functional state

We investigated the changes in the oxidative stress response of yeast cells suffering mitochondrial dysfunction that could impair their viability. First, we demonstrated that cells with this dysfunction rely exclusively on cytosolic thioredoxin peroxidase I (cTPxI) and its reductant sulfiredoxin, among other antioxidant enzymes tested, to protect them against H2O2-induced death. This cTPxI-dependent protection could be related to its dual functions, as peroxidase and as molecular chaperone, suggested by mixtures of low and high molecular weight oligomeric structures of cTPxI observed in cells challenged with H2O2. We found that cTPxI deficiency leads to increased basal sulfhydryl levels and transcriptional activation of most of the H2O2-responsive genes, interpreted as an attempt by the cells to improve their antioxidant defense. On the other hand, mitochondrial dysfunction, specifically the electron transport blockage, provoked a huge depletion of sulfhydryl groups after H2O2 treatment and reduced the H2O2-mediated activation of some genes otherwise observed, impairing cell defense and viability. The transcription factors Yap1 and Skn7 are crucial for the antioxidant response of cells under inhibited electron flow condition and probably act in the same pathway of cTPxI to protect cells affected by this disorder. Yap1 cellular distribution was not affected by cTpxI deficiency and by mitochondrial dysfunction, in spite of the observed expression alterations of several Yap1-target genes, indicating alternative mechanisms of Yap1 activation/deactivation. Therefore, we propose that cTPxI is specifically important in the protection of yeast with mitochondrial dysfunction due to its functional versatility as an antioxidant, chaperone and modulator of gene expression.

Molecular cloning and characterization of a peroxiredoxin gene from the mole cricket, Gryllotalpa orientalis

We report the cloning, expression and characterization of a cDNA encoding the antioxidant enzyme peroxiredoxin (Prx) from the mole cricket, Gryllotalpa orientalis. The G. orientalis Prx (GoPrx) cDNA contains an open reading frame of 660 bp encoding 220 amino acid residues and possesses one cysteine residue that is characteristic of the 1-Cys subgroup of the peroxiredoxin family. The deduced amino acid sequence of the GoPrx cDNA showed 69% identity to Drosophila melanogaster DPx-2540, 50% to D. melanogaster DPx-6005, and 47% to Glossina morsitans morsitans Prx. Phylogenetic analysis further confirmed a closer relationship of the deduced amino acid sequences of the GoPrx gene to the DPx-2540 within the 1-Cys Prx cluster. The cDNA encoding GoPrx was expressed as a 27-kDa polypeptide in baculovirus-infected insect Sf9 cells. The purified recombinant GoPrx was shown to reduce H(2)O(2) in the presence of electrons donated by dithiothreitol, but did not show the activity in the presence of thioredoxin as electron donor. Northern blot analysis revealed the presence of GoPrx transcripts in all tissues examined. When H(2)O(2) was injected into the body cavity of G. orientalis adult, GoPrx mRNA expression was up-regulated in the fat body tissues. Furthermore, the expression levels of GoPrx mRNA in the fat body were particularly high when G. orientalis adult was exposed at low (4 degrees C) and high (37 degrees C) temperatures, suggesting that the GoPrx seems to play a protective role against oxidative stress caused by temperature shock.

Redox mechanisms of cytoprotection by Bcl-2

Bcl-2 is a multifunctional protein that protects against cell death induced by a wide variety of stimuli. The best characterized antiapoptotic Bcl-2 mechanism of action involves direct binding to proapoptotic proteins, e.g., Bax, inhibiting their ability to oligomerize and form pores in the mitochondrial outer membrane, through which soluble mitochondrial proapoptotic proteins, e.g., cytochrome c, are released into the cytosol. Bcl-2 also exerts antiapoptotic and antinecrotic effects that are mediated by its influence on cellular redox state and apparently independent of its interaction with proapoptotic proteins. Bcl-2 expression increases cell resistance to oxidants, augments the expression of intracellular defenses against reactive oxygen species, and may affect mitochondrial generation of superoxide radicals and hydrogen peroxide. This review focuses on the protective effects of Bcl-2 related to changes in mitochondrial redox capacity.

Characterization of thiol-specific antioxidant 1 (TSA1) ofCandida albicans

We previously identified several proteins that are differentially expressed in pathogenic hyphae by comparing protein profiles of yeast and hyphae of Candida albicans. One of these, thiol-specific antioxidant 1 (TSA1), attracted our attention because it may play some roles in surviving an unfavourable oxidative environment created by host cells. Two alleles of the C. albicans TSA1 (CaTSA1) gene are located in opposite orientation on the same chromosome. Using PCR-directed disruption cassettes and URA-Blaster, a series of deletion mutants that lack one to four copies were constructed to examine the functions of CaTSA1. Northern and Western analyses showed that both the transcript and protein products of CaTSA1 decreased proportionally to the disrupted copy number and were completely absent in the null mutant, indicating that all four TSA1 copies are equally functional at the transcriptional level. Intracellular H2O2 increased by an order of magnitude in deletion mutants lacking three to four copies, suggesting that CaTsa1p is not a redundant H2O2 scavenger. CaTsa1p was indispensable for yeast-to-hyphal transition when C. albicans was cultured under oxidative stress. The level of its oxidized form increased approximately five-fold in hyphal cells, whereas that of the reduced form increased two-fold compared to yeast cells. The ratio of oxidized to reduced form was increased three-fold in hyphal cells. This overall increase was found to be controlled at the post-transcriptional level. Interestingly, CaTsa1p is translocated to the nucleus of hyphal cells. These findings may be of biological significance for differentiation and pathogenicity.

Bcl-2 family proteins regulate mitochondrial reactive oxygen production and protect against oxidative stress

Bcl-2 family proteins protect against a variety of forms of cell death, including acute oxidative stress. Previous studies have shown that overexpression of the antiapoptotic protein Bcl-2 increases cellular redox capacity. Here we report that cell lines transfected with Bcl-2 paradoxically exhibit increased rates of mitochondrial H(2)O(2) generation. Using isolated mitochondria, we determined that increased H(2)O(2) release results from the oxidation of reduced nicotinamide adenine dinucleotide-linked substrates. Antiapoptotic Bcl-2 family proteins Bcl-xL and Mcl-1 also increase mitochondrial H(2)O(2) release when overexpressed. Chronic exposure of cells to low levels of the mitochondrial uncoupler carbonyl cyanide 4-(triflouromethoxy)phenylhydrazone reduced the rate of H(2)O(2) production by Bcl-xL overexpressing cells, resulting in a decreased ability to remove exogenous H(2)O(2) and enhanced cell death under conditions of acute oxidative stress. Our results indicate that chronic and mild elevations in H(2)O(2) release from Bcl-2, Bcl-xL, and Mcl-1 overexpressing mitochondria lead to enhanced cellular antioxidant defense and protection against death caused by acute oxidative stress.

Cytosolic Thioredoxin Peroxidase I and II Are Important Defenses of Yeast against Organic Hydroperoxide Insult

The cytosolic thioredoxin peroxidase II (cTPxII/Tsa2p) from Saccharomyces cerevisiae shares 86% identity with the relatively well characterized cytosolic thioredoxin peroxidase I (cTPxI/Tsa1p). In contrast to cTPxI protein, cTPxII is not abundant and is highly inducible by peroxides. Here, we describe a unique phenotype for DeltacTPxII strain; these cells were highly sensitive to tert-butylhydroperoxide (TBHP) but presented resistance to H(2)O(2) in fermentative and respiratory conditions. In contrast, DeltacTPxI strain was very sensitive to both TBHP and H(2)O(2), whatever the carbon source present in the media. These differences in the response of mutant cells to the different kinds of peroxide insult could not be attributed to enzymatic properties of cTPxI and cTPxII since the recombinant proteins showed similar in vitro efficiencies (K(cat) /K(m)) in the removals of both kinds of peroxide. This specific sensitivity of DeltacTPxII cells to TBHP could not be related to the expression pattern of TSA2 (cytosolic thioredoxin peroxidase II gene) either, since this gene is highly inducible by both H(2)O(2) and TBHP when cells were grown in different conditions. Finally, peroxide-removing assays were performed and showed that catalase activity increased significantly only in DeltacTPxII cells, which appear to be related with the resistance of this strain to H(2)O(2). Taken together, present data indicate that cTPxII and cTPxI are key components of the yeast defense system against organic peroxide insult. In regard to the stress induced by H(2)O(2), catalases (peroxisomal and/or cytosolic) and cTPxII seemed to cooperate with cTPxI in the defense of yeast against this oxidant.

Distinct regulatory mechanism of yeastGPX2encoding phospholipid hydroperoxide glutathione peroxidase by oxidative stress and a calcineurin/Crz1-mediated Ca2+signaling pathway

The GPX2 gene encodes a homologue of mammalian phospholipid hydroperoxide glutathione peroxidase in Saccharomyces cerevisiae. Previously, we have reported that the oxidative stress-induced expression of GPX2 is strictly regulated by Yap1 and Skn7 transcription factors. Here, we found that the expression of GPX2 is induced by CaCl(2) in a calcineurin (CN)/Crz1-dependent manner, and the CN-dependent response element was specified in the GPX2 promoter. Neither Yap1 nor Skn7 was required for Ca(2+)-dependent induction of GPX2, therefore, distinct regulation for the oxidative stress response and Ca(2+) signal response for GPX2 exists in yeast cells.

Glutathione and thioredoxin peroxidases mediate susceptibility of yeast mitochondria to Ca(2+)-induced damage

The effect of thioredoxin peroxidases on the protection of Ca(2+)-induced inner mitochondrial membrane permeabilization was studied in the yeast Saccharomyces cerevisiae using null mutants for these genes. Since deletion of a gene can promote several other effects besides the absence of the respective protein, characterizations of the redox state of the mutant strains were performed. Whole cellular extracts from all the mutants presented lower capacity to decompose H(2)O(2) and lower GSH/GSSG ratios, as expected for strains deficient for peroxide-removing enzymes. Interestingly, when glutathione contents in mitochondrial pools were analyzed, all mutants presented lower GSH/GSSG ratios than wild-type cells, with the exception of DeltacTPxI strain (cells in which cytosolic thioredoxin peroxidase I gene was disrupted) that presented higher GSH/GSSG ratio. Low GSH/GSSG ratios in mitochondria increased the susceptibility of yeast to damage induced by Ca(2+) as determined by membrane potential and oxygen consumption experiments. However, H(2)O(2) removal activity appears also to be important for mitochondria protection against permeabilization because exogenously added catalase strongly inhibited loss of mitochondrial potential. Moreover, exogenously added recombinant peroxiredoxins prevented inner mitochondrial membrane permeabilization. GSH/GSSG ratios decreased after Ca(2+) addition, suggesting that reactive oxygen species (ROS) probably mediate this process. Taken together our results indicate that both mitochondrial glutathione pools and peroxide-removing enzymes are key components for the protection of yeast mitochondria against Ca(2+)-induced damage.

Peroxiredoxin-null Yeast Cells Are Hypersensitive to Oxidative Stress and Are Genomically Unstable

Peroxiredoxins are a family of abundant peroxidases found in all organisms. Although these antioxidant enzymes are thought to be critically involved in cellular defense and redox signaling, their exact physiological roles are largely unknown. In this study, we took a genetic approach to address the functions of peroxiredoxins in budding yeast. We generated and characterized a yeast mutant lacking all five peroxiredoxins. The quintuple peroxiredoxin-null mutant was still viable, though the growth rate was lower under normal aerobic conditions. Although peroxiredoxins are not essential for cell viability, peroxiredoxin-null yeast cells were more susceptible to oxidative and nitrosative stress. In the complete absence of peroxiredoxins, the expression of other antioxidant proteins including glutathione peroxidase and glutathione reductase was induced. In addition, the quintuple mutant was hypersensitive to glutathione depletion. Thus, the glutathione system might cooperate with other antioxidant enzymes to compensate for peroxiredoxin deficiency. Interestingly, the peroxiredoxinnull yeast cells displayed an increased rate of spontaneous mutations that conferred resistance to canavanine. This mutator phenotype was rescued by yeast peroxiredoxin Tsa1p, but not by its active-site mutant defective for peroxidase activity. Our findings suggest that the antioxidant function of peroxiredoxins is important for maintaining genome stability in eukaryotic cells.

Thioredoxin peroxidases can foster cytoprotection or cell death in response to different stressors: over- and under-expression of thioredoxin peroxidase in Drosophila cells

Recently, we identified a set of five genes constituting the peroxiredoxin gene family in Drosophila melanogaster [Radyuk, Klichko, Spinola, Sohal and Orr (2001) Free Radical Biol. Med. 31, 1090-1100]. This set includes two abundant thioredoxin peroxidase (TPx) species, namely Drosophila peroxiredoxin DPx-4783, a cytosolic TPx and DPx-5037, a mitochondrial TPx. Overexpression of either one of them in Drosophila S2 cells conferred increased resistance to toxicity induced by hydrogen peroxide, paraquat or cadmium. To understand further the functional roles of these enzymes in vivo, we report in the present study the effects of decreased expression, using RNA interference, on the response of S2 cells to different stressors. When either of the TPxs was blocked, cells became relatively more susceptible to oxidative stress caused by exposure to hydrogen peroxide or paraquat, but were unaffected when challenged with copper and heat stress. In contrast, TPx overexpressing cells were more susceptible to copper and heat stress when compared with control cells and exhibited DNA fragmentation. Furthermore, when cells were supplemented with N -acetyl-L-cysteine together with copper, there was a clear negative effect on cell survival, which was exacerbated by TPx overexpression. Manipulations in the levels of TPxs demonstrated that, under different stress conditions, these enzymes might have both beneficial and detrimental effects on Drosophila cell viability.