Multiple glutathione disulfide removal pathways mediate cytosolic redox homeostasis

Simultaneous Quantitative Detection of Cysteine and Homocysteine Labeled by 1-Pyrenecarboxaldehyde Using MALDI-TOF MS

Cysteine (Cys) and homocysteine (Hcy) are two important reducing agents in living organisms and play crucial roles in many physiological processes. The quantitative analysis of Cys and Hcy holds significance in exploring the functions of biothiols in biological. In this work, 1-pyrenecarboxaldehyde (1-py) with high derivatization efficiency and ionization efficiency was used for quantitative analysis of Cys and Hcy by matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS). After 1-py derivatization, the detection limit of Cys and Hcy can reach as low as 250 amol/L. Without internal standards, the simultaneous quantitative detection of Cys and Hcy was achieved by analyzing the proportion of peak intensities of derivative products to total compounds. The linear quantitative ranges for Cys and Hcy were over the concentrations from 5 to 2500 μM. Moreover, the specific hydrogen loss of the derivatized products was observed in MALDI-TOF detection, and the potential fragment pathway and nitrogen protonation mechanism were demonstrated through density functional theory (DFT) calculations. Finally, this method was successfully applied to the quantification of Cys and Hcy in HepG2 cell lysate, offering a rapid and highly sensitive approach for the quantitative analysis of Cys and Hcy using MALDI-TOF MS.

The glutathione system maintains the thiol redox balance in the mitochondria of fission yeast

The thioredoxin and glutathione (GSH)-glutaredoxin electron donor pathways provide a reducing environment to the cell and maintain homeostasis of numerous redox reactions. The abundant tripeptide GSH has multiple roles, including redox buffering, detoxification, peroxide scavenging and iron-sulfur cluster assembly. Glutathione reductase, Pgr1 in fission yeast, maintains glutathione reduced, and it is essential in most organisms. Cells lacking Pgr1 exhibit severe pleiotropic defects. We used multiple approaches to unravel the compartment-specific roles of Pgr1. Our findings confirmed that Pgr1 had dual cytosolic and mitochondrial localization. Mitochondrial homeostasis was severely impaired in Δpgr1 cells and most of these defects were restored by expression of an exclusively mitochondrial Pgr1 isoform. As expected, the cytosol of Δpgr1 cells showed low ratio of reduced-to-oxidized glutathione. However, this did not significantly affect peroxiredoxin-dependent hydrogen peroxide scavenging, suggesting a minimal role, if any, of GSH in cytosolic thiol reduction. The transcriptome of Δpgr1 cells revealed signatures of oxidative stress and iron deprivation, suggesting that the GSH-containing sensor of iron starvation, the glutaredoxin Grx4, is also a sensor of GSH oxidation. In the mitochondria, Pgr1 not only provided the GSH electron donor for the glutaredoxin-based pathway but also recycled mitochondrial Trx2, thereby contributing to thiol redox homeostasis in the matrix. In conclusion, glutathione reductase is essential for maintaining a balanced redox environment in the mitochondria by recycling Trx2, Grx2 and the GSH-containing Grx5, and therefore contributes to the processes of iron-sulfur cluster assembly and respiration, while controlling Grx4 dynamics in the cytosol.

Impact of Oxygen Availability on the Organelle-Specific Redox Potentials and Stress in Recombinant Protein Producing Komagataella phaffii

The yeast Komagataella phaffii (syn. Pichia pastoris) is a highly effective and well-established host for the production of recombinant proteins. The redox balance of its secretory pathway, which is multi-organelle dependent, is of high importance for producing secretory proteins. Redox imbalance and oxidative stress can significantly influence protein folding and secretion. Glutathione serves as the main redox buffer of the cell and cellular redox conditions can be assessed through the status of the glutathione redox couple (GSH-GSSG). Previous research often focused on the redox potential of the endoplasmic reticulum (ER), where oxidative protein folding and disulphide bond formation occur. In this study, in vivo measurements of the glutathione redox potential were extended to different subcellular compartments by targeting genetically encoded redox sensitive fluorescent proteins (roGFPs) to the cytosol, ER, mitochondria and peroxisomes. Using these biosensors, the impact of oxygen availability on the redox potentials of the different organelles was investigated in non-producing and producing K. phaffii strains in glucose-limited chemostat cultures. It was found that the transition from normoxic to hypoxic conditions affected the redox potential of all investigated organelles, while the exposure to hyperoxic conditions did not impact them. Also, as reported previously, hypoxic conditions led to increased recombinant protein secretion. Finally, transcriptome and proteome analyses provided novel insights into the short-term response of the cells from normoxic to hypoxic conditions.

The ABC transporter Opp imports reduced glutathione, while Gsi imports glutathione disulfide in Escherichia coli

Glutathione is the major thiol-based antioxidant in a wide variety of biological systems, ranging from bacteria to eukaryotes. As a redox couple, consisting of reduced glutathione (GSH) and its oxidized form, glutathione disulfide (GSSG), it is crucial for the maintenance of the cellular redox balance. Glutathione transport out of and into cellular compartments and the extracellular space is a determinant of the thiol-disulfide redox state of the organelles and bodily fluids in question, but is currently not well understood. Here we use the genetically-encoded, glutathione-measuring redox probe Grx1-roGFP2 to comprehensively elucidate the import of extracellular glutathione into the cytoplasm of the model organism Escherichia coli. The elimination of only two ATP-Binding Cassette (ABC) transporter systems, Gsi and Opp, completely abrogates glutathione import into E. coli's cytoplasm, both in its reduced and oxidized form. The lack of only one of them, Gsi, completely prevents import of GSSG, while the lack of the other, Opp, substantially retards the uptake of reduced glutathione (GSH).

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.

A family of NADPH/NADP+ biosensors reveals in vivo dynamics of central redox metabolism across eukaryotes

The NADPH/NADP+ redox couple is central to metabolism and redox signalling. NADP redox state is differentially regulated by distinct enzymatic machineries at the subcellular compartment level. Nonetheless, a detailed understanding of subcellular NADP redox dynamics is limited by the availability of appropriate tools. Here, we introduce NAPstars, a family of genetically encoded, fluorescent protein-based NADP redox state biosensors. NAPstars offer real-time, specific measurements, across a broad-range of NADP redox states, with subcellular resolution. NAPstar measurements in yeast, plants, and mammalian cell models, reveal a conserved robustness of cytosolic NADP redox homoeostasis. NAPstars uncover cell cycle-linked NADP redox oscillations in yeast and illumination- and hypoxia-dependent NADP redox changes in plant leaves. By applying NAPstars in combination with selective impairment of the glutathione and thioredoxin antioxidative pathways under acute oxidative challenge, we find an unexpected and conserved role for the glutathione system as the primary mediator of antioxidative electron flux.

Monitoring electrophilic intermediates in reactions of thiols in aqueous solution directly with 19F NMR

Mechanistic studies of thiol reactivity can be challenging because electrophilic reaction intermediates, such as sulfenic acids (RSOH) and sulfenyl chlorides (RSCl), are generally too reactive to be observed directly. Herein we report the design and synthesis of a sterically-encumbered fluorinated triptycene thiol which enables direct observation of reaction intermediates in aqueous buffer by 19F NMR, as demonstrated in reactions with hydrogen peroxide and hypochlorous acid. Reactions with H2O2 resulted in the formation of a persistent RSOH species, which was subsequently converted to a sulfinic acid (RSO2H) and then a sulfonic acid (RSO3H), while RSCl was found to be the intermediate in reactions with HOCl. Utilizing the same scaffold, reactions of thiol with thermally and photochemically generated singlet oxygen afforded RSO2H as the primary product. The stark difference in product profile from sterically-unencumbered thiols - which yield disulfides - implies that the reaction proceeds through a sulfenyl hydroperoxide (RSOOH) intermediate. Sulfenic acids, which were not observed in reactions of thiols with singlet oxygen, were also found to rapidly react with singlet oxygen to afford sulfinic acids, which is proposed to involve initial formation of an analogous sulfinyl hydroperoxide (RS(O)OOH). The formation and reactions of RSOOH are explored by computations. Use of the water-soluble fluorinated triptycene scaffold to probe reductive processes on RSOH (e.g., with ascorbate and/or iron) is also illustrated, wherein it was found that RSOH are surprisingly resistant to reductive heterolysis - in stark contrast with hydroperoxides - owing to their strong S-O bond.

Genomic and transcriptomic analyses reveal insights into cadmium resistance mechanisms of Cupriavidus nantongensis strain E324

The cadmium-resistant Cupriavidus sp. strain E324 has been previously shown to have a high potential for use in cadmium (Cd) remediation, due to its high capacity for cadmium bioaccumulation. According to the comparative genomic analysis, the strain E324 was most closely related to C. nantongensis X1T, indicating that the strain E324 should be re-identified as C. nantongensis. To unravel the Cd tolerance mechanisms of C. nantongensis strain E324, the transcriptional response of this strain to acute Cd exposure was assessed using RNA-seq-based transcriptome analysis, followed by validation through qRT-PCR. The results showed that the upregulated Differentially Expressed Genes (DEGs) were significantly enriched in categories related to metal binding and transport, phosphate transport, and oxidative stress response. Consistently, we observed significant increases in both the cell wall and intracellular contents of certain essential metals (Cu, Fe, Mn, and Zn) upon Cd exposure. Among these, only the Zn pretreatment resulting in high Zn accumulation in the cell walls could enhance bacterial growth under Cd stress conditions through its role in inhibiting Cd accumulation. Additionally, the promotion of catalase activity and glutathione metabolism upon Cd exposure to cope with Cd-induced oxidative stress was demonstrated. Meanwhile, the upregulation of phosphate transport-related genes upon Cd treatment seems to be the bacterial response to Cd-induced phosphate depletion. Altogether, our findings suggest that these adaptive responses are critical mechanisms contributing to increased Cd tolerance in C. nantongensis strain E324 via the enhancement of metal-chelating and antioxidant capacities of the cells.

Structure of a dimeric full-length ABC transporter

Activities of ATP binding cassette (ABC) proteins are regulated by multiple mechanisms, including protein interactions, phosphorylation, proteolytic processing, and/or oligomerization of the ABC protein itself. Here we present the structure of yeast cadmium factor 1 (Ycf1p) in its mature form following cleavage by Pep4p protease. Ycf1p, a C subfamily ABC protein (ABCC), is homologue of human multidrug resistance protein 1. Remarkably, a portion of cleaved Ycf1p forms a well-ordered dimer, alongside monomeric particles also present in solution. While numerous other ABC proteins have been proposed to dimerize, no high-resolution structures have been reported. Both phosphorylation of the regulatory (R) region and ATPase activity are lower in the Ycf1p dimer compared to the monomer, indicating that dimerization affects Ycf1p function. The interface between Ycf1p protomers features protein-protein interactions and contains bound lipids, suggesting that lipids stabilize the dimer. The Ycf1p dimer structure may inform the dimerization interfaces of other ABCC dimers.

Deciphering the Conformations of Glutathione Oxidized Peptide: A Comparative NMR Study in Solution and Solid-State Environments

Glutathione (GSH) and its oxidized dimer (GSSG) play an important role in living systems as an antioxidant, balancing the presence of reactive oxygen species (ROS). The central thiol (-S-S-) bond in GSSG can undergo free rotation, providing multiple conformations with respect to the S-S bridge. The six titratable sites of GSSG, which are influenced by pH variations, affect these conformations in solution, whereas in solids, additionally crystal packing effects come into play. In view of differing reports about the structure of GSSG in literature, we have here conducted an extensive reexamination of its conformations using NMR, and contrasting results have been obtained for solution and solid state. In solution, the existence of more than one antiparallel orientation of the monomer unit with different hydrogen bonding schemes has been indicated by NOE and amide temperature coefficient results. On the other hand, in the solid-state, a 1H-1H double-quantum (DQ) to 13C single-quantum (SQ) correlation study has confirmed a parallel orientation, consistent with the reported X-ray crystal structure. Experimentally assigned solid-state NMR resonances have been validated using GIPAW calculations incorporated in the Quantum ESPRESSO package.

Role of mitochondria in reno-cardiac diseases: A study of bioenergetics, biogenesis, and GSH signaling in disease transition

Acute kidney injury (AKI) and chronic kidney disease (CKD) are global health burdens with rising prevalence. Their bidirectional relationship with cardiovascular dysfunction, manifesting as cardio-renal syndromes (CRS) types 3 and 4, underscores the interconnectedness and interdependence of these vital organ systems. Both the kidney and the heart are critically reliant on mitochondrial function. This organelle is currently recognized as a hub in signaling pathways, with emphasis on the redox regulation mediated by glutathione (GSH). Mitochondrial dysfunction, including impaired bioenergetics, redox, and biogenesis pathways, are central to the progression of AKI to CKD and the development of CRS type 3 and 4. This review delves into the metabolic reprogramming and mitochondrial redox signaling and biogenesis alterations in AKI, CKD, and CRS. We examine the pathophysiological mechanisms involving GSH redox signaling and the AMP-activated protein kinase (AMPK)-sirtuin (SIRT)1/3-peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α) axis in these conditions. Additionally, we explore the therapeutic potential of GSH synthesis inducers in mitigating these mitochondrial dysfunctions, as well as their effects on inflammation and the progression of CKD and CRS types 3 and 4.

Strategies to Maintain Redox Homeostasis in Yeast Cells with Impaired Fermentation-Dependent NADPH Generation

Redox homeostasis is the balance between oxidation and reduction reactions. Its maintenance depends on glutathione, including its reduced and oxidized form, GSH/GSSG, which is the main intracellular redox buffer, but also on the nicotinamide adenine dinucleotide phosphate, including its reduced and oxidized form, NADPH/NADP+. Under conditions that enable yeast cells to undergo fermentative metabolism, the main source of NADPH is the pentose phosphate pathway. The lack of enzymes responsible for the production of NADPH has a significant impact on yeast cells. However, cells may compensate in different ways for impairments in NADPH synthesis, and the choice of compensation strategy has several consequences for cell functioning. The present study of this issue was based on isogenic mutants: Δzwf1, Δgnd1, Δald6, and the wild strain, as well as a comprehensive panel of molecular analyses such as the level of gene expression, protein content, and enzyme activity. The obtained results indicate that yeast cells compensate for the lack of enzymes responsible for the production of cytosolic NADPH by changing the content of selected proteins and/or their enzymatic activity. In turn, the cellular strategy used to compensate for them may affect cellular efficiency, and thus, the ability to grow or sensitivity to environmental acidification.

Reduction midpoint potential of a paradigm light-oxygen-voltage receptor and its modulation by methionine residues

Light-dependent adaptations of organismal physiology, development, and behavior abound in nature and depend on sensory photoreceptors. As one class, light-oxygen-voltage (LOV) photoreceptors harness flavin-nucleotide chromophores to sense blue light. Photon absorption drives the LOV receptor to its signaling state, characterized by a metastable thioadduct between the flavin and a conserved cysteine residue. With this cysteine absent, LOV receptors instead undergo photoreduction to the flavin semiquinone which however can still elicit downstream physiological responses. Irrespective of the cysteine presence, the LOV photochemical response thus entails a formal reduction of the flavin. Against this backdrop, we here investigate the reduction midpoint potential E 0 in the paradigmatic LOV2 domain from Avena sativa phototropin 1 (AsLOV2), and how it can be deliberately varied. Replacements of residues at different sites near the flavin by methionine consistently increase E 0 from its value of around -280 mV by up to 40 mV. Moreover, methionine introduction invariably impairs photoactivation efficiency and thus renders the resultant AsLOV2 variants less light-sensitive. Although individual methionine substitutions also affect the stability of the signaling state and downstream allosteric responses, no clear-cut correlation with the redox properties emerges. With a reduction midpoint potential near -280 mV, AsLOV2 and, by inference, other LOV receptors may be partially reduced inside cells which directly affects their light responsiveness. The targeted modification of the chromophore environment, as presently demonstrated, may mitigate this effect and enables the design of LOV receptors with stratified redox sensitivities.

Unresolved questions regarding cellular cysteine sources and their possible relationships to ferroptosis

Cysteine is required for synthesis of glutathione (GSH), coenzyme A, other sulfur-containing metabolites, and most proteins. In most cells, cysteine comes from extracellular disulfide sources including cystine, glutathione-disulfide, and peptides. The thioredoxin reductase-1 (TrxR1)- or glutathione-disulfide reductase (GSR)-driven enzymatic systems can fuel cystine reduction via thioredoxins, glutaredoxins, or other thioredoxin-fold proteins. Free cystine enters cells thorough the cystine-glutamate antiporter, xCT, but systemically, plasma glutathione-disulfide might predominate as a cystine source. Erastin, inhibiting both xCT and voltage-dependent anion channels, induces ferroptotic cell death, so named because this type of cell death is antagonized by iron-chelators. Many cancer cells seem to be predisposed to ferroptosis, which has been proposed as a targetable cancer liability. Ferroptosis is associated with lipid peroxidation and loss of either glutathione peroxidase-4 (GPX4) or ferroptosis suppressor protein-1 (FSP1), which each prevent accumulation of lipid peroxides. It has been suggested that an xCT inhibition-induced cellular cysteine-deficiency lowers GSH levels, starving GPX4 for reducing power and allowing membrane lipid peroxides to accumulate, thereby causing ferroptosis. Aspects of ferroptosis are however not fully understood and need to be further scrutinized, for example that neither disruption of GSH synthesis, loss of GSH, nor disruption of glutathione disulfide reductase (GSR), triggers ferroptosis in animal models. Here we reevaluate the relationships between Erastin, xCT, GPX4, cellular cysteine and GSH, RSL3 or ML162, and ferroptosis. We conclude that, whereas both Cys and ferroptosis are potential liabilities in cancer, their relationship to each other remains insufficiently understood.

Ageing-dependent thiol oxidation reveals early oxidation of proteins with core proteostasis functions

Oxidative post-translational modifications of protein thiols are well recognized as a readily occurring alteration of proteins, which can modify their function and thus control cellular processes. The development of techniques enabling the site-specific assessment of protein thiol oxidation on a proteome-wide scale significantly expanded the number of known oxidation-sensitive protein thiols. However, lacking behind are large-scale data on the redox state of proteins during ageing, a physiological process accompanied by increased levels of endogenous oxidants. Here, we present the landscape of protein thiol oxidation in chronologically aged wild-type Saccharomyces cerevisiae in a time-dependent manner. Our data determine early-oxidation targets in key biological processes governing the de novo production of proteins, protein folding, and degradation, and indicate a hierarchy of cellular responses affected by a reversible redox modification. Comparison with existing datasets in yeast, nematode, fruit fly, and mouse reveals the evolutionary conservation of these oxidation targets. To facilitate accessibility, we integrated the cross-species comparison into the newly developed OxiAge Database.

Contrasting cytosolic glutathione redox dynamics under abiotic and biotic stress in barley as revealed by the biosensor Grx1-roGFP2

Barley is a staple crop of major global importance and relatively resilient to a wide range of stress factors in the field. Transgenic reporter lines to investigate physiological parameters during stress treatments remain scarce. We generated and characterized transgenic homozygous barley lines (cv. Golden Promise Fast) expressing the genetically encoded biosensor Grx1-roGFP2, which indicates the redox potential of the major antioxidant glutathione in the cytosol. Our results demonstrated functionality of the sensor in living barley plants. We determined the glutathione redox potential (EGSH) of the cytosol to be in the range of -308 mV to -320 mV. EGSH was robust against a combined NaCl (150 mM) and water deficit treatment (-0.8 MPa) but responded with oxidation to infiltration with the phytotoxic secretome of the necrotrophic fungus Botrytis cinerea. The generated reporter lines are a novel resource to study biotic and abiotic stress resilience in barley, pinpointing that even severe abiotic stress leading to a growth delay does not automatically induce cytosolic EGSH oxidation, while necrotrophic pathogens can undermine this robustness.

Structural Basis for Oxidized Glutathione Recognition by the Yeast Cadmium Factor 1

Transporters from the ABCC family have an essential role in detoxifying electrophilic compounds including metals, drugs, and lipids, often through conjugation with glutathione complexes. The Yeast Cadmium Factor 1 (Ycf1) transports glutathione alone as well as glutathione conjugated to toxic heavy metals including Cd2+, Hg2+, and As3+. To understand the complicated selectivity and promiscuity of heavy metal substrate binding, we determined the cryo-EM structure of Ycf1 bound to the substrate, oxidized glutathione. We systematically tested binding determinants with cellular survival assays against cadmium to determine how the substrate site accommodates different-sized metal complexes. We identify a "flex-pocket" for substrate binding that binds glutathione complexes asymmetrically and flexes to accommodate different size complexes.

Systemic and strict regulation of the glutathione redox state in mitochondria and cytosol is needed for zebrafish ontogeny

BACKGROUND

Redox control seems to be indispensable for proper embryonic development. The ratio between glutathione (GSH) and its oxidized disulfide (GSSG) is the most abundant cellular redox circuit.

METHODS

We used zebrafish harboring the glutaredoxin 1-redox sensitive green fluorescent protein (Grx1-roGFP) probe either in mitochondria or cytosol to test the hypothesis that the GSH:GSSG ratio is strictly regulated through zebrafish embryogenesis to sustain the different developmental processes of the embryo.

RESULTS

Following the GSSG:GSH ratio as a proxy for the GSH-dependent reduction potential (EhGSH) revealed increasing mitochondrial and cytosolic EhGSH during cleavage and gastrulation. During organogenesis, cytosolic EhGSH decreased, while that of mitochondria remained high. The similarity between EhGSH in brain and muscle suggests a central regulation. Modulation of GSH metabolism had only modest effects on the GSSG:GSH ratios of newly hatched larvae. However, inhibition of GSH reductase directly after fertilization led to dead embryos already 10 h later. Exposure to the emerging environmental pollutant Perfluorooctane Sulfonate (PFOS) disturbed the apparent regulated EhGSH as well.

CONCLUSIONS

Mitochondrial and cytosolic GSSG:GSH ratios are almost identical in different organs during zebrafish development indicating that the EhGSH might follow H2O2 levels and rather indirectly affect specific enzymatic activities needed for proper embryogenesis.

GENERAL SIGNIFICANCE

Our data confirm that vertebrate embryogenesis depends on strictly regulated redox homeostasis. Disturbance of the GSSG:GSH circuit, e.g. induced by environmental pollution, leads to malformation and death.

Structural basis for autoinhibition by the dephosphorylated regulatory domain of Ycf1

Yeast Cadmium Factor 1 (Ycf1) sequesters glutathione and glutathione-heavy metal conjugates into yeast vacuoles as a cellular detoxification mechanism. Ycf1 belongs to the C subfamily of ATP Binding Cassette (ABC) transporters characterized by long flexible linkers, notably the regulatory domain (R-domain). R-domain phosphorylation is necessary for activity, whereas dephosphorylation induces autoinhibition through an undefined mechanism. Because of its transient and dynamic nature, no structure of the dephosphorylated Ycf1 exists, limiting understanding of this R-domain regulation. Here, we capture the dephosphorylated Ycf1 using cryo-EM and show that the unphosphorylated R-domain indeed forms an ordered structure with an unexpected hairpin topology bound within the Ycf1 substrate cavity. This architecture and binding mode resemble that of a viral peptide inhibitor of an ABC transporter and the secreted bacterial WXG peptide toxins. We further reveal the subset of phosphorylation sites within the hairpin turn that drive the reorganization of the R-domain conformation, suggesting a mechanism for Ycf1 activation by phosphorylation-dependent release of R-domain mediated autoinhibition.

In-situ synthesis of quantum dots in the nucleus of live cells

The cell nucleus is the main site for the storage and replication of genetic material, and the synthesis of substances in the nucleus is rhythmic, regular and strictly regulated by physiological processes. However, whether exogenous substances, such as nanoparticles, can be synthesized in situ in the nucleus of live cells has not been reported. Here, we have achieved in-situ synthesis of CdSxSe1-x quantum dots (QDs) in the nucleus by regulation of the glutathione (GSH) metabolic pathway. High enrichment of GSH in the nucleus can be accomplished by the addition of GSH with the help of the Bcl-2 protein. Then, high-valence Se is reduced to low-valence Se by glutathione-reductase-catalyzed GSH, and interacts with the Cd precursor formed through Cd and thiol-rich proteins, eventually generating QDs in the nucleus. Our work contributes to a new understanding of the syntheses of substances in the cell nucleus and will pave the way for the development of advanced 'supercells'.

Deciphering the mechanism of glutaredoxin-catalyzed roGFP2 redox sensing reveals a ternary complex with glutathione for protein disulfide reduction

Glutaredoxins catalyze the reduction of disulfides and are key players in redox metabolism and regulation. While important insights were gained regarding the reduction of glutathione disulfide substrates, the mechanism of non-glutathione disulfide reduction remains highly debated. Here we determined the rate constants for the individual redox reactions between PfGrx, a model glutaredoxin from Plasmodium falciparum, and redox-sensitive green fluorescent protein 2 (roGFP2), a model substrate and versatile tool for intracellular redox measurements. We show that the PfGrx-catalyzed oxidation of roGFP2 occurs via a monothiol mechanism and is up to three orders of magnitude faster when roGFP2 and PfGrx are fused. The oxidation kinetics of roGFP2-PfGrx fusion constructs reflect at physiological GSSG concentrations the glutathionylation kinetics of the glutaredoxin moiety, thus allowing intracellular structure-function analysis. Reduction of the roGFP2 disulfide occurs via a monothiol mechanism and involves a ternary complex with GSH and PfGrx. Our study provides the mechanistic basis for understanding roGFP2 redox sensing and challenges previous mechanisms for protein disulfide reduction.

Mitochondrial Glutathione in Cellular Redox Homeostasis and Disease Manifestation

Mitochondria are critical for providing energy to maintain cell viability. Oxidative phosphorylation involves the transfer of electrons from energy substrates to oxygen to produce adenosine triphosphate. Mitochondria also regulate cell proliferation, metastasis, and deterioration. The flow of electrons in the mitochondrial respiratory chain generates reactive oxygen species (ROS), which are harmful to cells at high levels. Oxidative stress caused by ROS accumulation has been associated with an increased risk of cancer, and cardiovascular and liver diseases. Glutathione (GSH) is an abundant cellular antioxidant that is primarily synthesized in the cytoplasm and delivered to the mitochondria. Mitochondrial glutathione (mGSH) metabolizes hydrogen peroxide within the mitochondria. A long-term imbalance in the ratio of mitochondrial ROS to mGSH can cause cell dysfunction, apoptosis, necroptosis, and ferroptosis, which may lead to disease. This study aimed to review the physiological functions, anabolism, variations in organ tissue accumulation, and delivery of GSH to the mitochondria and the relationships between mGSH levels, the GSH/GSH disulfide (GSSG) ratio, programmed cell death, and ferroptosis. We also discuss diseases caused by mGSH deficiency and related therapeutics.

The role of thioredoxin and glutathione systems in arsenic-induced liver injury in rats under glutathione depletion

Antioxidant systems like thioredoxin (Trx) and glutaredoxin (Grx) maintain oxidative stress balance. These systems have cross-talk supported by some in vitro studies. We investigated the underlying mechanisms of arsenic-induced liver injury in glutathione-deficient rats and whether there was any cross-talk between the Trx and Grx systems. The rats in arsenic-treated groups were administered with sodium arsenite (10, 20 mg/kg b w/d) for four weeks. In buthionine sulfoximine (BSO, an inhibitor of GSH) and 20 mg/kg arsenic combined groups, rats were injected with 2 mmol/kg BSO intraperitoneally twice per week. BSO exacerbated arsenic-induced liver injury by increasing arsenic accumulation in urine, serum, and liver while decreasing glutathione activity and resulting in upregulated mRNA expression of the Trx system and downregulation of Grx mRNA expression. The impact of Trx lasted longer than that of the Grx. The Trx system remained highly expressed, while GSH, Grx1, and Grx2 levels were decreased. The inhibitory effect of only BSO treatment on Grx1 and Grx2 was not pronounced. However, the combined impact of arsenic and BSO upregulated Trx expression, primarily related to further reduction of GSH. As a result, the suppressed Grxs were protected by the upregulated Trxs, which serve as a backup antioxidant defense system in the liver.

Preventing acute liver injury via hepatocyte-targeting nano-antioxidants

Acute liver injury (ALI) is a severe liver disease that is characterized by sudden and massive hepatocyte necrosis and deterioration of liver functions. Oxidative stress is increasingly recognized as a key factor in the induction and progression of ALI. Scavenging excessive reactive oxygen species (ROS) with antioxidants has become a promising therapeutic option, but intrinsically hepatocyte-targeting antioxidants with excellent bioavailability and biocompatibility are yet to be developed. Herein, self-assembling nanoparticles (NPs) composed of amphiphilic polymers are introduced to encapsulate organic Selenium compound L-Se-methylselenocysteine (SeMC) and form SeMC NPs, which protect the viabilities and functions of cultured hepatocytes in drug- or chemical-induced acute hepatotoxicity models via efficient ROS removal. After further functionalization with the hepatocyte-targeting ligand glycyrrhetinic acid (GA), the resultant GA-SeMC NPs exhibit enhanced hepatocyte uptake and liver accumulation. In mouse models of ALI induced by acetaminophen (APAP) or carbon tetrachloride (CCl4 ), treatment with GA-SeMC NPs significantly decrease the levels of hepatic lipid peroxidation, tissue vacuolization and serum liver transaminases, while prominently increase that of endogenous antioxidant enzymes. Our study therefore presents a liver-targeting drug delivery strategy for the prevention and treatment of hepatic diseases.

PM2.5 exposure increases dry eye disease risks through corneal epithelial inflammation and mitochondrial dysfunctions

Dry eye disease (DED) is the most common disease affecting vision and quality of life. PM2.5 was a potential risk of DED. Herein, we conducted animal exposure and cell-based studies to evaluate the pathogenic effect of PM2.5 exposure on the ocular surface and DED etiological mechanisms. C57 mice were exposed to filtered air and PM2.5 aerosol. We assessed health conditions and inflammation of the ocular surface by corneal fluorescein staining and immunohistochemistry. In parallel, cultured human corneal epithelial cells (HCETs) were treated with PM2.5, followed by characterization of cell viability, intracellular ATP level, mitochondrial activities, and expression level of DED relevant mRNA and proteins. In mice, PM2.5 exposure induced severe superficial punctate keratopathy and inflammation in their cornea. In HCETs, cell proliferation and ROS generation followed dose-response and time-dependent manner; meanwhile, mitochondrial ROS (mtROS) level increased and mitochondrial membrane potential (MMP) level decreased. Inflammation cascade was triggered even after short-term exposure. The reduction of ATP production was alleviated with Nrf2 overexpression, NF-κB P65 knockdown, or ROS clearance. Nrf2 overexpression and P65 knockdown reduced inflammatory reaction through decreasing expression of P65 and increasing of Nrf2, respectively. They partly alleviated changes of ROS/mtROS/MMP. This research proved that PM2.5 would cause DED-related inflammation reaction on corneal epithelial cells and further explored its mechanism: ROS from mitochondrial dysfunctions of corneal epithelial cells after PM2.5 exposure partly inhibited the expression of anti-inflammatory protein Nrf2 led the activation of inflammatory protein P65 and its downstream molecules, which finally caused inflammation reaction.

A Mitochondria-Targeted Ferroptosis Inducer Activated by Glutathione-Responsive Imaging and Depletion for Triple Negative Breast Cancer Theranostics

Ferroptosis is a new type of iron-dependent programmed cell death characterized by glutathione (GSH) depletion, selenoprotein glutathione peroxidase 4 (GPX4) inactivation, and lipid peroxides accumulation. Mitochondria, as the main source of intracellular energy supply and reactive oxygen species (ROS) generation, play a central role in oxidative phosphorylation and redox homeostasis. Therefore, targeting cancer-cell mitochondria and attacking redox homeostasis is expected to induce robust ferroptosis-mediated anticancer effects. In this work, a theranostic ferroptosis inducer (IR780-SPhF), which can simultaneously achieve the imaging and therapy of triple-negative breast cancer (TNBC) by targeting mitochondria is presented. It is developed from a mitochondria-targeting small molecule (IR780) with cancer-preferential accumulation, enabling it to react with GSH by nucleophilic substitution, resulting in mitochondrial GSH depletion and redox imbalance. More interestingly, IR780-SPhF exhibits GSH-responsive near-infrared fluorescence emission and photoacoustic imaging characteristics, further facilitating diagnosis and treatment with real-time monitoring of TNBC with a highly elevated GSH level. Both in vitro and in vivo results demonstrate that IR780-SPhF exhibits potent anticancer effect, which is significantly stronger than cyclophosphamide, a classic drug commonly recommended for TNBC patients in clinic. Hence, the reported mitochondria-targeted ferroptosis inducer may represent a promising candidate and a prospective strategy for efficient cancer treatment.

Thioredoxin/Glutaredoxin Systems and Gut Microbiota in NAFLD: Interplay, Mechanism, and Therapeutical Potential

Non-alcoholic fatty liver disease (NAFLD) is a common clinical disease, and its pathogenesis is closely linked to oxidative stress and gut microbiota dysbiosis. Recently accumulating evidence indicates that the thioredoxin and glutaredoxin systems, the two thiol-redox dependent antioxidant systems, are the key players in the NAFLD's development and progression. However, the effects of gut microbiota dysbiosis on the liver thiol-redox systems are not well clarified. This review explores the role and mechanisms of oxidative stress induced by bacteria in NAFLD while emphasizing the crucial interplay between gut microbiota dysbiosis and Trx mediated-redox regulation. The paper explores how dysbiosis affects the production of specific gut microbiota metabolites, such as trimethylamine N-oxide (TMAO), lipopolysaccharides (LPS), short-chain fatty acids (SCFAs), amino acids, bile acid, and alcohol. These metabolites, in turn, significantly impact liver inflammation, lipid metabolism, insulin resistance, and cellular damage through thiol-dependent redox signaling. It suggests that comprehensive approaches targeting both gut microbiota dysbiosis and the thiol-redox antioxidant system are essential for effectively preventing and treating NAFLD. Overall, comprehending the intricate relationship between gut microbiota dysbiosis and thiol-redox systems in NAFLD holds significant promise in enhancing patient outcomes and fostering the development of innovative therapeutic interventions.

Characterization of a novel cysteine-less Cu/Zn-superoxide dismutase in Paenibacillus lautus missing a conserved disulfide bond

Cu/Zn-superoxide dismutase (CuZnSOD) is an enzyme that binds a copper and zinc ion and also forms an intramolecular disulfide bond. Together with the copper ion as the active site, the disulfide bond is completely conserved among these proteins; indeed, the disulfide bond plays critical roles in maintaining the catalytically competent conformation of CuZnSOD. Here, we found that a CuZnSOD protein in Paenibacillus lautus (PaSOD) has no Cys residue but exhibits a significant level of enzyme activity. The crystal structure of PaSOD revealed hydrophobic and hydrogen-bonding interactions in substitution for the disulfide bond of the other CuZnSOD proteins. Also notably, we determined that PaSOD forms a homodimer through an additional domain with a novel fold at the N terminus. While the advantages of lacking Cys residues and adopting a novel dimer configuration remain obscure, PaSOD does not require a disulfide-introducing/correcting system for maturation and could also avoid misfolding caused by aberrant thiol oxidations under an oxidative environment.

Redox perturbations in yeast cells lacking glutathione reductase

Cellular redox homeostasis has a major effect on cell functions and its maintenance is supported by glutathione and protein thiols which serve as redox buffers in cells. The regulation of the glutathione biosynthetic pathway is a focus of a lot of scientific research. However, still little is known about how complex cellular networks influence glutathione homeostasis. In this work was used an experimental system based on an S. cerevisiae yeast mutant with a lack of the glutathione reductase enzyme and allyl alcohol as a precursor of acrolein inside the cell to determine the cellular processes influencing glutathione homeostasis. The absence of Glr1p slows down the growth rate of the cell population, especially in the presence of allyl alcohol, but does not lead to complete inhibition of the cell's reproductive capacity. It also amends the GSH/GSSG ratio and the share of NADPH and NADP+ in the total NADP(H) pool. The obtained results show that potential pathways involved in the maintenance of redox homeostasis are based from one side on de novo synthesis of GSH as indicated by increased activity of γ-GCS and increased expression of GSH1 gene in the Δglr1 mutant, from the other hand, on increased the level of NADPH. This is because the lower ratio of GSH/GSSG can be counterbalanced with the NADPH/NADP+ alternative system. The higher level of NADPH can be used by the thioredoxin system and other enzymes requiring NADPH to reduce cytosolic GSSG and maintain glutathione redox potential.

Large-scale metabolome analysis reveals dynamic changes of metabolites during foxtail millet grain filling

Compared with traditional staple crops, foxtail millet grain is rich in nutrition and beneficial to human health. Foxtail millet is also tolerance to various abiotic stresses, including drought, making it a good plant for growing in barren land. The study on the composition of metabolites and its dynamics changes during grain development is helpful to understand the process of foxtail millet grain formation. In our study, metabolic and transcriptional analysis were used to uncover the metabolic processes that could influence grain filling in foxtail millet. A total of 2104 known metabolites, belonging to 14 categories, were identified during grain filling. Functional analysis of DAMs and DEGs revealed a stage-specific metabolic properties in foxtail millet grain filling. Some important metabolic processes, such as flavonoid biosynthesis, glutathione metabolism, linoleic acid metabolism, starch and sucrose metabolism and valine, leucine and isoleucine biosynthesis were co-mapped for DEGs and DAMs. Thus, we constructed a gene-metabolite regulatory network of these metabolic pathways to explain their potential functions during grain filling. Our study showed the important metabolic processes during grain filling and focused on the dynamic changes of related metabolites and genes at different stages, which provided a reference for us to better understand and improve foxtail millet grain development and yield.

3-Mercaptopyruvate sulfur transferase is a protein persulfidase

Protein S-persulfidation (P-SSH) is recognized as a common posttranslational modification. It occurs under basal conditions and is often observed to be elevated under stress conditions. However, the mechanism(s) by which proteins are persulfidated inside cells have remained unclear. Here we report that 3-mercaptopyruvate sulfur transferase (MPST) engages in direct protein-to-protein transpersulfidation reactions beyond its previously known protein substrates thioredoxin and MOCS3/Uba4, associated with H₂S generation and transfer RNA thiolation, respectively. We observe that depletion of MPST in human cells lowers overall intracellular protein persulfidation levels and identify a subset of proteins whose persulfidation depends on MPST. The predicted involvement of these proteins in the adaptation to stress responses supports the notion that MPST-dependent protein persulfidation promotes cytoprotective functions. The observation of MPST-independent protein persulfidation suggests that other protein persulfidases remain to be identified.

Dithiolopyrrolones are Prochelators that are Activated by Glutathione

Dithiolopyrrolones (DTPs), such as holomycin, are natural products that hold promise as scaffolds for antibiotics as they exhibit inhibitory activity against antibiotic-resistant pathogens. They consist of a unique bicyclic core containing a disulfide that is crucial for their biological activity. Herein, we establish the DTPs as prochelators. We show that the disulfides are reduced at cellular gluathione levels. This activates the drugs and initiates interactions with targets, particularly metal coordination. In addition, we report an expedient synthesis for the DTPs thiolutin and aureothricin, providing facile access to important natural DTPs and derivatives thereof.

Maintenance of small molecule redox homeostasis in mitochondria

Compartmentalisation of eukaryotic cells enables fundamental otherwise often incompatible cellular processes. Establishment and maintenance of distinct compartments in the cell relies not only on proteins, lipids and metabolites but also on small redox molecules. In particular, small redox molecules such as glutathione, NAD(P)H and hydrogen peroxide (H₂ O₂ ) cooperate with protein partners in dedicated machineries to establish specific subcellular redox compartments with conditions that enable oxidative protein folding and redox signalling. Dysregulated redox homeostasis has been directly linked with a number of diseases including cancer, neurological disorders, cardiovascular diseases, obesity, metabolic diseases and ageing. In this review, we will summarise mechanisms regulating establishment and maintenance of redox homeostasis in the mitochondrial subcompartments of mammalian cells.

UHPLC-HRMS-Based Analysis of S-Hydroxymethyl-Glutathione, GSH, and GSSG in Human Cells

Glutathione (GSH) is one of the main antioxidant molecules present in cells. It harbors a thiol group responsible for sustaining cellular redox homeostasis. This moiety can react with cellular electrophiles such as formaldehyde yielding the compound S-hydroxymethyl-GSH (HSMGSH). HSMGSH is the substrate of the enzyme alcohol dehydrogenase 5 (ADH5) and thus a key intermediate in formaldehyde metabolism. In this work, we describe a method for the chemical synthesis of HSMGSH and a pipeline to identify this compound in complex cell extracts by means of ultra-high-performance liquid chromatography coupled to high-resolution spectrometry (UHPLC-HRMS). This method also allows determining GSH and oxidized disulfide (GSSG) in the same samples, thus providing broad information about formaldehyde-GSH metabolism.

The antioxidant and oxidant properties of hydropersulfides (RSSH) and polysulfide species

It has become apparent that hydrogen sulfide (H2S), hydropersulfides (RSSH) and other polysulfide species are all intimately linked biochemically. Indeed, at least some of the biological activity attributed to hydrogen sulfide (H2S) may actually be due to its conversion to RSSH and derived polysulfur species (and vice-versa). The unique chemistry associated with the hydropersulfide functional group (-SSH) predicts that it possesses possible protective properties that can help a cell contend with oxidative and/or electrophilic stress. However, since RSSH and polysulfides possess chemical properties akin to disulfides (RSSR), they can also be sources of oxidative/electrophilic stress/signaling as well. Herein are discussed the unique chemistry, possible biochemistry and the physiological implications of RSSH (and polysulfides), especially as it pertains to their putative cellular protection properties against a variety of stresses and/or as possible stressors/signaling agents themselves.

The Role of the NRF2 Pathway in Maintaining and Improving Cognitive Function

Nuclear factor (erythroid-derived 2)-like 2 (NRF2) is a redox-sensitive transcription factor that binds to the antioxidant response element consensus sequence, decreasing reactive oxygen species and regulating the transcription of a wide array of genes, including antioxidant and detoxifying enzymes, regulating genes involved in mitochondrial function and biogenesis. Moreover, NRF2 has been shown to directly regulate the expression of anti-inflammatory mediators reducing the expression of pro-inflammatory cytokines. In recent years, attention has turned to the role NRF2 plays in the brain in different diseases such Alzheimer’s disease, Parkinson’s disease, Huntington’s disease and others. This review focused on the evidence, derived in vitro, in vivo and from clinical trials, supporting a role for NRF2 activation in maintaining and improving cognitive function and how its activation can be used to elicit neuroprotection and lead to cognitive enhancement. The review also brings a critical discussion concerning the possible prophylactic and/or therapeutic use of NRF2 activators in treating cognitive impairment-related conditions.

Rosmarinic acid relieves LPS-induced sickness and depressive-like behaviors in mice by activating the BDNF/Nrf2 signaling and autophagy pathway

Neuroinflammation is one of the main causes of sickness and depressive-like behavior. Rosmarinic acid (RA) has been shown to have a significant anti-neuroinflammatory effect. However, the protective effects and the underlying mechanism of RA on sickness and depressive-like behavior under conditions of neuroinflammation are still unclear.　In the present study,　we investigated the effects and　the underlying mechanism of RA on lipopolysaccharide (LPS)-treated mice with sickness behavior. The behavioral effects of LPS treatment and RA administration were assessed using behavioral tests including a sucrose preference test and an open field test. The neuroprotective effects of RA in conditions of neuroinflammatory injury were determined by HE staining, Nissl staining, and immunofluorescent staining. Moreover, its underlying mechanism was analyzed by using real-time PCR analysis, western blot, and immunofluorescent analysis. The results indicated that RA dramatically mitigated sickness behaviors and histologic brain damage in mice exposed to LPS. In addition, RA administration markedly promoted the expression of brain-derived neurotrophic factor (BDNF)/erythroid 2-related factor 2 (Nrf2), the key regulatory proteins for Nrf2 activation (p21 and p62), the downstream antioxidant enzymes (HO-1, NQO1, GCLC), the autophagy-related proteins (LC3II and Beclin1), and mitochondrial respiratory enzyme genes (ME1, IDH1, 6-PGDH), while reducing the expression of pro-inflammatory genes (CD44, iNOS, TNFα, IL-1β). Moreover, the double-label immunofluorescent analysis revealed that RA increased the fluorescence intensity of LC3 mostly co-localized with neurons and co-expressed with Nrf2. Taken together, our research found that RA could effectively alleviate sickness behaviors and nerve injury caused by neuroinflammation, and its protective effects were mediated by the Nrf2 signaling pathway, which reduced cellular oxidative stress, inflammation, mitochondrial respiratory function damage, and autophagy imbalance. Therefore, RA has the potential to prevent or treat sickness and depressive-like behaviors under conditions of neuroinflammation.

Crowning Touches in Positive-Strand RNA Virus Genome Replication Complex Structure and Function

Positive-strand RNA viruses, the largest genetic class of eukaryotic viruses, include coronaviruses and many other established and emerging pathogens. A major target for understanding and controlling these viruses is their genome replication, which occurs in virus-induced membrane vesicles that organize replication steps and protect double-stranded RNA intermediates from innate immune recognition. The structure of these complexes has been greatly illuminated by recent cryo-electron microscope tomography studies with several viruses. One key finding in diverse systems is the organization of crucial viral RNA replication factors in multimeric rings or crowns that among other functions serve as exit channels gating release of progeny genomes to the cytosol for translation and encapsidation. Emerging results suggest that these crowns serve additional important purposes in replication complex assembly, function, and interaction with downstream processes such as encapsidation. The findings provide insights into viral function and evolution and new bases for understanding, controlling, and engineering positive-strand RNA viruses. Expected final online publication date for the Annual Review of Virology, Volume 9 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The structural basis for regulation of the glutathione transporter Ycf1 by regulatory domain phosphorylation

Yeast Cadmium Factor 1 (Ycf1) sequesters heavy metals and glutathione into the vacuole to counter cell stress. Ycf1 belongs to the ATP binding cassette C-subfamily (ABCC) of transporters, many of which are regulated by phosphorylation on intrinsically-disordered domains. The regulatory mechanism of phosphorylation is still poorly understood. Here, we report two cryo-EM structures of Ycf1 at 3.4 Å and 4.0 Å resolution in inward-facing open conformations that capture previously unobserved ordered states of the intrinsically disordered regulatory domain (R-domain). R-domain phosphorylation is clearly evident and induces a topology promoting electrostatic and hydrophobic interactions with Nucleotide Binding Domain 1 (NBD1) and the Lasso motif. These interactions stay constant between the structures and are related by rigid body movements of the NBD1/R-domain complex. Biochemical data further show R-domain phosphorylation reorganizes the Ycf1 architecture and is required for maximal ATPase activity. Together, we provide insights into how R-domains control ABCC transporter activity.

Endogenous formaldehyde scavenges cellular glutathione resulting in redox disruption and cytotoxicity

Formaldehyde (FA) is a ubiquitous endogenous and environmental metabolite that is thought to exert cytotoxicity through DNA and DNA-protein crosslinking, likely contributing to the onset of the human DNA repair condition Fanconi Anaemia. Mutations in the genes coding for FA detoxifying enzymes underlie a human inherited bone marrow failure syndrome (IBMFS), even in the presence of functional DNA repair, raising the question of whether FA causes relevant cellular damage beyond genotoxicity. Here, we report that FA triggers cellular redox imbalance in human cells and in Caenorhabditis elegans. Mechanistically, FA reacts with the redox-active thiol group of glutathione (GSH), altering the GSH:GSSG ratio and causing oxidative stress. FA cytotoxicity is prevented by the enzyme alcohol dehydrogenase 5 (ADH5/GSNOR), which metabolizes FA-GSH products, lastly yielding reduced GSH. Furthermore, we show that GSH synthesis protects human cells from FA, indicating an active role of GSH in preventing FA toxicity. These findings might be relevant for patients carrying mutations in FA-detoxification systems and could suggest therapeutic benefits from thiol-rich antioxidants like N-acetyl-L-cysteine.

Allicin, an Antioxidant and Neuroprotective Agent, Ameliorates Cognitive Impairment

Allicin (diallylthiosulfinate) is a defense molecule produced by cellular contents of garlic (Allium sativum L.). On tissue damage, the non-proteinogenic amino acid alliin (S-allylcysteine sulfoxide) is converted to allicin in an enzyme-mediated process catalysed by alliinase. Allicin is hydrophobic in nature, can efficiently cross the cellular membranes and behaves as a reactive sulfur species (RSS) inside the cells. It is physiologically active molecule with the ability to oxidise the thiol groups of glutathione and between cysteine residues in proteins. Allicin has shown anticancer, antimicrobial, antioxidant properties and also serves as an efficient therapeutic agent against cardiovascular diseases. In this context, the present review describes allicin as an antioxidant, and neuroprotective molecule that can ameliorate the cognitive abilities in case of neurodegenerative and neuropsychological disorders. As an antioxidant, allicin fights the reactive oxygen species (ROS) by downregulation of NOX (NADPH oxidizing) enzymes, it can directly interact to reduce the cellular levels of different types of ROS produced by a variety of peroxidases. Most of the neuroprotective actions of allicin are mediated via redox-dependent pathways. Allicin inhibits neuroinflammation by suppressing the ROS production, inhibition of TLR4/MyD88/NF-κB, P38 and JNK pathways. As an inhibitor of cholinesterase and (AChE) and butyrylcholinesterase (BuChE) it can be applied to manage the Alzheimer's disease, helps to maintain the balance of neurotransmitters in case of autism spectrum disorder (ASD) and attention deficit hyperactive syndrome (ADHD). In case of acute traumatic spinal cord injury (SCI) allicin protects neuron damage by regulating inflammation, apoptosis and promoting the expression levels of Nrf2 (nuclear factor erythroid 2-related factor 2). Metal induced neurodegeneration can also be attenuated and cognitive abilities of patients suffering from neurological diseases can be ameliorates by allicin administration.

Can thiol-based redox systems be utilized as parts for synthetic biology applications?

OBJECTIVES

Synthetic biology has emerged from molecular biology and engineering approaches and aims to develop novel, biologically-inspired systems for industrial and basic research applications ranging from biocomputing to drug production. Surprisingly, redoxin (thioredoxin, glutaredoxin, peroxiredoxin) and other thiol-based redox systems have not been widely utilized in many of these synthetic biology applications.

METHODS

We reviewed thiol-based redox systems and the development of synthetic biology applications that have used thiol-dependent parts.

RESULTS

The development of circuits to facilitate cytoplasmic disulfide bonding, biocomputing and the treatment of intestinal bowel disease are amongst the applications that have used thiol-based parts. We propose that genetically encoded redox sensors, thiol-based biomaterials and intracellular hydrogen peroxide generators may also be valuable components for synthetic biology applications.

DISCUSSION

Thiol-based systems play multiple roles in cellular redox metabolism, antioxidant defense and signaling and could therefore offer a vast and diverse portfolio of components, parts and devices for synthetic biology applications. However, factors limiting the adoption of redoxin systems for synthetic biology applications include the orthogonality of thiol-based components, limitations in the methods to characterize thiol-based systems and an incomplete understanding of the design principles of these systems.

Effect of heat stress on the antioxidant defense system and erythrocyte morphology of Antarctic fishes

This study analyzed the effect of thermal stress on erythrocytes of Notothenia rossii and Notothenia coriiceps, abundant notothenioids in Admiralty Bay, Antarctic Peninsula. In both species, the antioxidant defense system enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione-S transferase, glutathione reductase were punctually altered (8°C for 1, 3 and 6 days) in erythrocytes, indicating that these markers are not ideal for termal stress. However, under the influence of thermal stress, morphological changes in Notothenia coriiceps erythrocytes were observed at all exposure times (1, 3 and 6 days at 8°C), and in Notothenia rossii occurred in 6 days. These results suggest that Notothenia corriceps presents a lower tolerance to thermal stress at 8°C for up to 6 days, since the cellular and nuclear alterations recorded are pathological and may be deleterious to the cells. Among the morphological markers analyzed in this work, we believe that the shape change and nuclear bubble formation may be good stress biomarkers in erythrocytes of Notothenia rossii and Notothenia coriiceps.

Methods in sulfide and persulfide research

Sulfides and persulfides/polysulfides (R-Sn-R', n > 2; R-Sn-H, n > 1) are endogenously produced metabolites that are abundant in mammalian and human cells and tissues. The most typical persulfides that are widely distributed among different organisms include various reactive persulfides-low-molecular-weight thiol compounds such as cysteine hydropersulfide, glutathione hydropersulfide, and glutathione trisulfide as well as protein-bound thiols. These species are generally more redox-active than are other simple thiols and disulfides. Although hydrogen sulfide (H2S) has been suggested for years to be a small signaling molecule, it is intimately linked biochemically to persulfides and may actually be more relevant as a marker of functionally active persulfides. Reactive persulfides can act as powerful antioxidants and redox signaling species and are involved in energy metabolism. Recent evidence revealed that cysteinyl-tRNA synthetases (CARSs) act as the principal cysteine persulfide synthases in mammals and contribute significantly to endogenous persulfide/polysulfide production, in addition to being associated with a battery of enzymes including cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase, which have been described as H2S-producing enzymes. The reactive sulfur metabolites including persulfides/polysulfides derived from CARS2, a mitochondrial isoform of CARS, also mediate not only mitochondrial biogenesis and bioenergetics but also anti-inflammatory and immunomodulatory functions. The physiological roles of persulfides, their biosynthetic pathways, and their pathophysiology in various diseases are not fully understood, however. Developing basic and high precision techniques and methods for the detection, characterization, and quantitation of sulfides and persulfides is therefore of great importance so as to thoroughly understand and clarify the exact functions and roles of these species in cells and in vivo.

Real-time monitoring of subcellular H2O2 distribution in Chlamydomonas reinhardtii

Hydrogen peroxide (H2O2) is recognized as an important signaling molecule in plants. We sought to establish a genetically encoded, fluorescent H2O2 sensor that allows H2O2 monitoring in all major subcompartments of a Chlamydomonas cell. To this end, we used the Chlamydomonas Modular Cloning toolbox to target the hypersensitive H2O2 sensor reduction-oxidation sensitive green fluorescent protein2-Tsa2ΔCR to the cytosol, nucleus, mitochondrial matrix, chloroplast stroma, thylakoid lumen, and endoplasmic reticulum (ER). The sensor was functional in all compartments, except for the ER where it was fully oxidized. Employing our novel sensors, we show that H2O2 produced by photosynthetic linear electron transport (PET) in the stroma leaks into the cytosol but only reaches other subcellular compartments if produced under nonphysiological conditions. Furthermore, in heat-stressed cells, we show that cytosolic H2O2 levels closely mirror temperature up- and downshifts and are independent from PET. Heat stress led to similar up- and downshifts of H2O2 levels in the nucleus and, more mildly, in mitochondria but not in the chloroplast. Our results thus suggest the establishment of steep intracellular H2O2 gradients under normal physiological conditions with limited diffusion into other compartments. We anticipate that these sensors will greatly facilitate future investigations of H2O2 biology in plant cells.

A dual role of cysteine residues in the maturation of prokaryotic Cu/Zn-superoxide dismutase

Bacterial Cu/Zn-superoxide dismutase (SodC) is an enzyme catalyzing the disproportionation of superoxide radicals, to which the binding of copper and zinc ions and the formation of an intramolecular disulfide bond are essential. We previously showed that Escherichia coli SodC (SodC) was prone to spontaneous degradation in vivo in an immature form prior to the introduction of the disulfide bond. The post-translational maintenance involving the metal binding and the disulfide formation would thus control the stability as well as the enzymatic function of SodC; however, a mechanism of the SodC maturation remains obscure. Here, we show that the disulfide-reduced SodC can secure a copper ion as well as a zinc ion through the thiolate groups. Furthermore, the disulfide-reduced SodC was found to bind cuprous and cupric ions more tightly than SodC with the disulfide bond. The thiolate groups ligating the copper ion were then autooxidized to form the intramolecular disulfide bond, leading to the production of enzymatically active SodC. Based upon the experiments in vitro, therefore, we propose a mechanism for the activation of SodC, in which the conserved Cys residues play a dual role: the acquisition of a copper ion for the enzymatic activity and the formation of the disulfide bond for the structural stabilization.

An intracellular assay for activity screening and characterization of glutathione-dependent oxidoreductases

The thioredoxin fold superfamily is highly diverse and contains many enzymatically active glutathione-dependent thiol-disulfide oxidoreductases, for example glutaredoxins and protein disulfide isomerases. However, many thioredoxin fold proteins remain completely uncharacterized, their cellular function is unknown, and it is unclear if they have a redox-dependent enzymatic activity with glutathione or not. Investigation of enzymatic activity traditionally involved time-consuming in vitro characterization of recombinant proteins, limiting the capacity to study novel mechanisms and structure-function relationships. To accelerate our investigation of glutathione-dependent oxidoreductases, we have developed a high-throughput and semi-quantitative assay in yeast. We combined overexpression of the glutathione transporter OPT1 with genetic fusion constructs between glutathione-dependent oxidoreductases and redox-sensitive green fluorescent protein 2 (roGFP2) to allow the rapid characterization of enzymatic activity with physiological substrates. We show that the kinetics of roGFP2 oxidation by glutathione disulfide correlate well with the in vitro-determined activity of the genetically fused glutaredoxins or mutants thereof. Our assay thus allows direct screening of glutaredoxin activity and rapid investigation of structure-function relationships. We also demonstrate that our assay can be used to monitor roGFP2 oxidation by S-nitrosoglutathione (GSNO). We show that glutaredoxins efficiently catalyze oxidation of roGFP2 by GSNO in both live yeast cells and in vitro. In summary, we have established a novel assay for activity screening and characterization of glutathione-dependent oxidoreductases.