The cysteine proteome

Profiling protein expression in Klebsiella pneumoniae with a carbohydrate-based covalent probe

We report the application of a covalent probe based on a d-glucosamine scaffold for the profiling of the bacterial pathogen Klebsiella pneumoniae. Incubation of K. pneumoniae lysates with the probe followed by electrophoretic separation and in-gel fluorescence detection allowed the generation of strain-specific signatures and the differentiation of a carbapenem-resistant strain. The labelling profile of the probe was independent of its anomeric configuration and included several low-abundance proteins not readily detectable by conventional protein staining. Initial target identification experiments by mass spectrometry suggest that target proteins include several carbohydrate-recognising proteins, which indicates that the sugar scaffold may have a role for target recognition.

A Global Profile of Reversible and Irreversible Cysteine Redox Post-Translational Modifications During Myocardial Ischemia/Reperfusion Injury and Antioxidant Intervention

Aims: Cysteine (Cys) is a major target for redox post-translational modifications (PTMs) that occur in response to changes in the cellular redox environment. We describe multiplexed, peptide-based enrichment and quantitative mass spectrometry (MS) applied to globally profile reversible redox Cys PTM in rat hearts during ischemia/reperfusion (I/R) in the presence or absence of an aminothiol antioxidant, N-2-mercaptopropionylglycine (MPG). Parallel fractionation also allowed identification of irreversibly oxidized Cys peptides (Cys-SO₂H/SO₃H). Results: We identified 4505 reversibly oxidized Cys peptides of which 1372 were significantly regulated by ischemia and/or I/R. An additional 219 peptides (247 sites) contained Cys-SO₂H/Cys-SO₃H modifications, and these were predominantly identified from hearts subjected to I/R (n = 168 peptides). Parallel reaction monitoring MS (PRM-MS) enabled relative quantitation of 34 irreversibly oxidized Cys peptides. MPG attenuated a large cluster of I/R-associated reversibly oxidized Cys peptides and irreversible Cys oxidation to less than nonischemic controls (n = 24 and 34 peptides, respectively). PRM-MS showed that Cys sites oxidized during ischemia and/or I/R and "protected" by MPG were largely mitochondrial, and were associated with antioxidant functions (peroxiredoxins 5 and 6) and metabolic processes, including glycolysis. Metabolomics revealed I/R induced changes in glycolytic intermediates that were reversed in the presence of MPG, which were consistent with irreversible PTM of triose phosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), altered GAPDH enzyme activity, and reduced I/R glycolytic payoff as evidenced by adenosine triphosphate and NADH levels. Innovation: Novel enrichment and PRM-MS approaches developed here enabled large-scale relative quantitation of Cys redox sites modified by reversible and irreversible PTM during I/R and antioxidant remediation. Conclusions: Cys sites identified here are targets of reactive oxygen species that can contribute to protein dysfunction and the pathogenesis of I/R.

Nucleophilicity of cysteine and related biothiols and the development of fluorogenic probes and other applications

Biothiols such as l-cysteine, l-homocysteine, and glutathione play essential roles in many biological processes, and are directly associated with several health conditions. Therefore, the development of fast, selective, sensitive, and inexpensive methods for quantitatively analyzing biothiols in aqueous solution, but especially in biological samples, is a very attractive research field. In this feature review, we have approached the relevance of biothiols' nucleophilicity to develop selective fluorogenic probes. Since biothiols have considerable structural similarity, relevant strategies are in full development, including several fluorescent molecular platforms, specific receptor sites, reaction conditions, and optical responses. All of these features are properly presented and discussed. Biothiol sensing protocols are based on traditional organic chemistry reactions such as (hetero)aromatic nucleophilic substitution, addition, and substitution at carbonyl carbon, conjugate addition, and nucleophilic substitution at saturated carbon, amongst others including combined processes; furthermore, mechanistic aspects are detailed herein, including some interesting historical contexts. The feasibility of related fluorogenic probes is illustrated by analysis in complex matrices such as serum, cells, tissues, and animal models. Applications of these reactions in more complex systems such as sulfhydryl-based peptides and proteins are also presented, aiming at functionalizing and detecting these nucleophiles. Most literature cited in this review is recent; however, some other prominent works are also detailed. It is believed that this review may be accessible for many academic levels and may efficiently contribute not only to popularizing science but also to the rational development of fluorogenic probes for biothiol sensing.

Targeting spectrin redox switches to regulate the mechanoproperties of red blood cells

The mechanical properties of red blood cells (RBCs) are fundamental for their physiological role as gas transporters. RBC flexibility and elasticity allow them to survive the hemodynamic changes in the different regions of the vascular tree, to dynamically contribute to the flow thereby decreasing vascular resistance, and to deform during the passage through narrower vessels. RBC mechanoproperties are conferred mainly by the structural characteristics of their cytoskeleton, which consists predominantly of a spectrin scaffold connected to the membrane via nodes of actin, ankyrin and adducin. Changes in redox state and treatment with thiol-targeting molecules decrease the deformability of RBCs and affect the structure and stability of the spectrin cytoskeleton, indicating that the spectrin cytoskeleton may contain redox switches. In this perspective review, we revise current knowledge about the structural and functional characterization of spectrin cysteine redox switches and discuss the current lines of research aiming to understand the role of redox regulation on RBC mechanical properties. These studies may provide novel functional targets to modulate RBC function, blood viscosity and flow, and tissue perfusion in disease conditions.

Are Reactive Sulfur Species the New Reactive Oxygen Species?

Significance: Oxidative stress in moderation positively affects homeostasis through signaling, while in excess it is associated with adverse health outcomes. Both activities are generally attributed to reactive oxygen species (ROS); hydrogen peroxide as the signal, and cysteines on regulatory proteins as the target. However, using antioxidants to affect signaling or benefit health has not consistently translated into expected outcomes, or when it does, the mechanism is often unclear. Recent Advances: Reactive sulfur species (RSS) were integral in the origin of life and throughout much of evolution. Sophisticated metabolic pathways that evolved to regulate RSS were easily "tweaked" to deal with ROS due to the remarkable similarities between the two. However, unlike ROS, RSS are stored, recycled, and chemically more versatile. Despite these observations, the relevance and regulatory functions of RSS in extant organisms are generally underappreciated. Critical Issues: A number of factors bias observations in favor of ROS over RSS. Research conducted in room air is hyperoxic to cells, and promotes ROS production and RSS oxidation. Metabolic rates of rodent models greatly exceed those of humans; does this favor ROS? Analytical methods designed to detect ROS also respond to RSS. Do these disguise the contributions of RSS? Future Directions: Resolving the ROS/RSS issue is vital to understand biology in general and human health in particular. Improvements in experimental design and analytical methods are crucial. Perhaps the most important is an appreciation of all the attributes of RSS and keeping an open mind.

Monohaloacetic Acids and Monohaloacetamides Attack Distinct Cellular Proteome Thiols

Disinfection byproduct (DBP) exposure has been linked to multiple adverse health outcomes. However, the molecular initiating events by which DBPs induce their toxicities remain unclear. Herein, we combined reporter cell lines and activity-based protein profiling (ABPP) chemical proteomics to identify the protein targets of three monohaloacetic acids (mHAAs) and three monohaloacetamides (mHAMs), at the proteome-wide level. While mHAAs and mHAMs have similar potencies in reducing MTT activity, mHAMs induced greater Nrf2-mediated oxidative stress responses, demonstrating their distinct toxicity pathways. ABPP on crude cell lysates suggested that general proteome thiol reactivity correlates with cytotoxicity. Interestingly, live cell ABPP results revealed class-specific proteins attacked by mHAMs or mHAAs. Subsequent proteomic analysis identified >100 unique targets per DBP. mHAMs preferentially react with redox proteins including disulfide oxidoreductase enzymes, accounting for their stronger Nrf2 responses. To further probe alkylation mechanisms, we directly monitored protein adducts and identified 120 and 37 unique peptides with iodoacetamide and iodoacetic acid adducts, respectively. Of the latter, we confirmed glyceraldehyde-3-phosphate dehydrogenase as a key target of IAA, specifically attacking the catalytic Cys 152. This is the first study reporting the distinct cellular protein targets of mHAAs and mHAMs at the proteome-wide level, which highlights their different toxicity pathways despite their similar structures.

Proteomic Complexity in Parkinson's Disease: A Redox Signaling Perspective of the Pathophysiology and Progression

Parkinson's disease (PD) is a prevalent age-related neurodegenerative disorder that results in the progressive impairment of motor and cognitive functions. The majority of PD cases are sporadic, and only 5% of patients are associated with mutations in a few genes, which cause the early onset or familial PD. Environmental toxic substances and the individual genetic susceptibility play a role in sporadic cases, but despite significant efforts to treat and prevent the disease, the pathophysiological mechanisms leading to its onset and progress are not fully understood. In the last decade, genomic and proteomic studies have shown an increasing molecular complexity of sporadic PD, suggesting that a broad spectrum of biochemical pathways underlie its progression. Recent investigations and the literature review suggest the potential role of deregulation of the sensitive-cysteine proteome as a convergent pathogenic mechanism that may contribute to this complexity, opening new therapeutic opportunities.

Targeted Antioxidants in Exercise-Induced Mitochondrial Oxidative Stress: Emphasis on DNA Damage

Exercise simultaneously incites beneficial (e.g., signal) and harming (e.g., damage to macromolecules) effects, likely through the generation of reactive oxygen and nitrogen species (RONS) and downstream changes to redox homeostasis. Given the link between nuclear DNA damage and human longevity/pathology, research attempting to modulate DNA damage and restore redox homeostasis through non-selective pleiotropic antioxidants has yielded mixed results. Furthermore, until recently the role of oxidative modifications to mitochondrial DNA (mtDNA) in the context of exercising humans has largely been ignored. The development of antioxidant compounds which specifically target the mitochondria has unveiled a number of exciting avenues of exploration which allow for more precise discernment of the pathways involved with the generation of RONS and mitochondrial oxidative stress. Thus, the primary function of this review, and indeed its novel feature, is to highlight the potential roles of mitochondria-targeted antioxidants on perturbations to mitochondrial oxidative stress and the implications for exercise, with special focus on mtDNA damage. A brief synopsis of the current literature addressing the sources of mitochondrial superoxide and hydrogen peroxide, and available mitochondria-targeted antioxidants is also discussed.

Network medicine in Cardiovascular Research

The ability to generate multi-omics data coupled with deeply characterizing the clinical phenotype of individual patients promises to improve understanding of complex cardiovascular pathobiology. There remains an important disconnection between the magnitude and granularity of these data and our ability to improve phenotype-genotype correlations for complex cardiovascular diseases. This shortcoming may be due to limitations associated with traditional reductionist analytical methods, which tend to emphasize a single molecular event in the pathogenesis of diseases more aptly characterized by crosstalk between overlapping molecular pathways. Network medicine is a rapidly growing discipline that considers diseases as the consequences of perturbed interactions between multiple interconnected biological components. This powerful integrative approach has enabled a number of important discoveries in complex disease mechanisms. In this review, we introduce the basic concepts of network medicine and highlight specific examples by which this approach has accelerated cardiovascular research. We also review how network medicine is well-positioned to promote rational drug design for patients with cardiovascular diseases, with particular emphasis on advancing precision medicine.

Redox Regulation by Protein S-Glutathionylation: From Molecular Mechanisms to Implications in Health and Disease

S-glutathionylation, the post-translational modification forming mixed disulfides between protein reactive thiols and glutathione, regulates redox-based signaling events in the cell and serves as a protective mechanism against oxidative damage. S-glutathionylation alters protein function, interactions, and localization across physiological processes, and its aberrant function is implicated in various human diseases. In this review, we discuss the current understanding of the molecular mechanisms of S-glutathionylation and describe the changing levels of expression of S-glutathionylation in the context of aging, cancer, cardiovascular, and liver diseases.

Thiol switches in membrane proteins - Extracellular redox regulation in cell biology

Redox-mediated signal transduction depends on the enzymatic production of second messengers such as hydrogen peroxide, nitric oxide and hydrogen sulfite, as well as specific, reversible redox modifications of cysteine-residues in proteins. So-called thiol switches induce for instance conformational changes in specific proteins that regulate cellular pathways e.g., cell metabolism, proliferation, migration, gene expression and inflammation. Reduction, oxidation and disulfide isomerization are controlled by oxidoreductases of the thioredoxin family, including thioredoxins, glutaredoxins, peroxiredoxins and protein dsisulfide isomerases. These proteins are located in different cellular compartments, interact with substrates and catalyze specific reactions. Interestingly, some of these proteins are released by cells. Their extracellular functions and generally extracellular redox control have been widely underestimated. Here, we give an insight into extracellular redox signaling, extracellular thiol switches and their regulation by secreted oxidoreductases and thiol-isomerases, a topic whose importance has been scarcely studied so far, likely due to methodological limitations. We focus on the secreted redox proteins and characterized thiol switches in the ectodomains of membrane proteins, such as integrins and the metalloprotease ADAM17, which are among the best-characterized proteins and discuss their underlying mechanisms and biological implications.

Complex IV - The regulatory center of mitochondrial oxidative phosphorylation

ATP, the universal energy currency in all living cells, is mainly synthesized in mitochondria by oxidative phosphorylation (OXPHOS). The final and rate limiting step of the respiratory chain is cytochrome c oxidase (COX) which represents the regulatory center of OXPHOS. COX is regulated through binding of various effectors to its "supernumerary" subunits, by reversible phosphorylation, and by expression of subunit isoforms. Of particular interest is its feedback inhibition by ATP, the final product of OXPHOS. This "allosteric ATP-inhibition" of phosphorylated and dimeric COX maintains a low and healthy mitochondrial membrane potential (relaxed state), and prevents the formation of ROS (reactive oxygen species) which are known to cause numerous diseases. Excessive work and stress abolish this feedback inhibition of COX by Ca²⁺-activated dephosphorylation which leads to monomerization and movement of NDUFA4 from complex I to COX with higher rates of COX activity and ATP synthesis (active state) but increased ROS formation and decreased efficiency.

Oxidative stress mitigation by antioxidants - An overview on their chemistry and influences on health status

The present review paper focuses on the chemistry of oxidative stress mitigation by antioxidants. Oxidative stress is understood as a lack of balance between the pro-oxidant and the antioxidant species. Reactive oxygen species in limited amounts are necessary for cell homeostasis and redox signaling. Excessive reactive oxygenated/nitrogenated species production, which counteracts the organism's defense systems, is known as oxidative stress. Sustained attack of endogenous and exogenous ROS results in conformational and oxidative alterations in key biomolecules. Chronic oxidative stress is associated with oxidative modifications occurring in key biomolecules: lipid peroxidation, protein carbonylation, carbonyl (aldehyde/ketone) adduct formation, nitration, sulfoxidation, DNA impairment such strand breaks or nucleobase oxidation. Oxidative stress is tightly linked to the development of cancer, diabetes, neurodegeneration, cardiovascular diseases, rheumatoid arthritis, kidney disease, eye disease. The deleterious action of reactive oxygenated species and their role in the onset and progression of pathologies are discussed. The results of oxidative attack become themselves sources of oxidative stress, becoming part of a vicious cycle that amplifies oxidative impairment. The term antioxidant refers to a compound that is able to impede or retard oxidation, acting at a lower concentration compared to that of the protected substrate. Antioxidant intervention against the radicalic lipid peroxidation can involve different mechanisms. Chain breaking antioxidants are called primary antioxidants, acting by scavenging radical species, converting them into more stable radicals or non-radical species. Secondary antioxidants quench singlet oxygen, decompose peroxides, chelate prooxidative metal ions, inhibit oxidative enzymes. Moreover, four reactivity-based lines of defense have been identified: preventative antioxidants, radical scavengers, repair antioxidants, and those relying on adaptation mechanisms. The specific mechanism of a series of endogenous and exogenous antioxidants in particular aspects of oxidative stress, is detailed. The final section resumes critical conclusions regarding antioxidant supplementation.

Mechanisms of Mitochondrial ROS Production in Assisted Reproduction: The Known, the Unknown, and the Intriguing

The consensus that assisted reproduction technologies (ART), like in vitro fertilization, to induce oxidative stress (i.e., the known) belies how oocyte/zygote mitochondria-a major presumptive oxidative stressor-produce reactive oxygen species (ROS) with ART being unknown. Unravelling how oocyte/zygote mitochondria produce ROS is important for disambiguating the molecular basis of ART-induced oxidative stress and, therefore, to rationally target it (e.g., using site-specific mitochondria-targeted antioxidants). I review the known mechanisms of ROS production in somatic mitochondria to critique how oocyte/zygote mitochondria may produce ROS (i.e., the unknown). Several plausible site- and mode-defined mitochondrial ROS production mechanisms in ART are proposed. For example, complex I catalyzed reverse electron transfer-mediated ROS production is conceivable when oocytes are initially extracted due to at least a 10% increase in molecular dioxygen exposure (i.e., the intriguing). To address the term oxidative stress being used without recourse to the underlying chemistry, I use the species-specific spectrum of biologically feasible reactions to define plausible oxidative stress mechanisms in ART. Intriguingly, mitochondrial ROS-derived redox signals could regulate embryonic development (i.e., their production could be beneficial). Their potential beneficial role raises the clinical challenge of attenuating oxidative damage while simultaneously preserving redox signaling. This discourse sets the stage to unravel how mitochondria produce ROS in ART, and their biological roles from oxidative damage to redox signaling.

Chemistry and Biochemistry of Sulfur Natural Compounds: Key Intermediates of Metabolism and Redox Biology

Sulfur contributes significantly to nature chemical diversity and thanks to its particular features allows fundamental biological reactions that no other element allows. Sulfur natural compounds are utilized by all living beings and depending on the function are distributed in the different kingdoms. It is no coincidence that marine organisms are one of the most important sources of sulfur natural products since most of the inorganic sulfur is metabolized in ocean environments where this element is abundant. Terrestrial organisms such as plants and microorganisms are also able to incorporate sulfur in organic molecules to produce primary metabolites (e.g., methionine, cysteine) and more complex unique chemical structures with diverse biological roles. Animals are not able to fix inorganic sulfur into biomolecules and are completely dependent on preformed organic sulfurous compounds to satisfy their sulfur needs. However, some higher species such as humans are able to build new sulfur-containing chemical entities starting especially from plants' organosulfur precursors. Sulfur metabolism in humans is very complicated and plays a central role in redox biochemistry. The chemical properties, the large number of oxidation states, and the versatile reactivity of the oxygen family chalcogens make sulfur ideal for redox biological reactions and electron transfer processes. This review will explore sulfur metabolism related to redox biochemistry and will describe the various classes of sulfur-containing compounds spread all over the natural kingdoms. We will describe the chemistry and the biochemistry of well-known metabolites and also of the unknown and poorly studied sulfur natural products which are still in search for a biological role.

Regulation of cytochrome c oxidase contributes to health and optimal life

The generation of cellular energy in the form of ATP occurs mainly in mitochondria by oxidative phosphorylation. Cytochrome c oxidase (CytOx), the oxygen accepting and rate-limiting step of the respiratory chain, regulates the supply of variable ATP demands in cells by “allosteric ATP-inhibition of CytOx.” This mechanism is based on inhibition of oxygen uptake of CytOx at high ATP/ADP ratios and low ferrocytochrome c concentrations in the mitochondrial matrix via cooperative interaction of the two substrate binding sites in dimeric CytOx. The mechanism keeps mitochondrial membrane potential ΔΨ_m and reactive oxygen species (ROS) formation at low healthy values. Stress signals increase cytosolic calcium leading to Ca²⁺-dependent dephosphorylation of CytOx subunit I at the cytosolic side accompanied by switching off the allosteric ATP-inhibition and monomerization of CytOx. This is followed by increase of ΔΨ_m and formation of ROS. A hypothesis is presented suggesting a dynamic change of binding of NDUFA4, originally identified as a subunit of complex I, between monomeric CytOx (active state with high ΔΨ_m, high ROS and low efficiency) and complex I (resting state with low ΔΨ_m, low ROS and high efficiency).

Redox Post-translational Modifications of Protein Thiols in Brain Aging and Neurodegenerative Conditions-Focus on S-Nitrosation

Reactive oxygen species and reactive nitrogen species (RONS) are by-products of aerobic metabolism. RONS trigger a signaling cascade that can be transduced through oxidation-reduction (redox)-based post-translational modifications (redox PTMs) of protein thiols. This redox signaling is essential for normal cellular physiology and coordinately regulates the function of redox-sensitive proteins. It plays a particularly important role in the brain, which is a major producer of RONS. Aberrant redox PTMs of protein thiols can impair protein function and are associated with several diseases. This mini review article aims to evaluate the role of redox PTMs of protein thiols, in particular S-nitrosation, in brain aging, and in neurodegenerative diseases. It also discusses the potential of using redox-based therapeutic approaches for neurodegenerative conditions.

Beyond repression of Nrf2: An update on Keap1

Nrf2 (NFE2L2 - nuclear factor (erythroid-derived 2)-like 2) is a transcription factor, which is repressed by interaction with a redox-sensitive protein Keap1 (Kelch-like ECH-associated protein 1). Deregulation of Nrf2 transcriptional activity has been described in the pathogenesis of multiple diseases, and the Nrf2/Keap1 axis has emerged as a crucial modulator of cellular homeostasis. Whereas the significance of Nrf2 in the modulation of biological processes has been well established and broadly discussed in detail, the focus on Keap1 rarely goes beyond the regulation of Nrf2 activity and redox sensing. However, recent studies and scrutinized analysis of available data point to Keap1 as an intriguing and potent regulator of cellular function. This review aims to shed more light on Keap1 structure, interactome, regulation and non-canonical functions, thereby enhancing its significance in cell biology. We also intend to highlight the impact of balance between Keap1 and Nrf2 in the maintenance of cellular homeostasis.

Protein LY6E as a candidate for mediating transport of adeno-associated virus across the human blood-brain barrier

The blood-brain barrier (BBB) is a major obstacle for the treatment of central nervous system (CNS) disorders. Significant progress has been made in developing adeno-associated virus (AAV) variants with increased ability to cross the BBB in mice. However, these variants are not efficacious in non-human primates. Herein, we employed various bioinformatic techniques to identify lymphocyte antigen-6E (LY6E) as a candidate for mediating transport of AAV across the human BBB based on the previously determined mechanism of transport in mice. Our results provide insight into future discovery and optimization of AAV variants for CNS gene delivery in humans.

The mitochondria-targeted antioxidant MitoQ, attenuates exercise-induced mitochondrial DNA damage

High-intensity exercise damages mitochondrial DNA (mtDNA) in skeletal muscle. Whether MitoQ - a redox active mitochondrial targeted quinone - can reduce exercise-induced mtDNA damage is unknown. In a double-blind, randomized, placebo-controlled design, twenty-four healthy male participants consisting of two groups (placebo; n = 12, MitoQ; n = 12) performed an exercise trial of 4 x 4-min bouts at 90–95% of heart rate max. Participants completed an acute (20 mg MitoQ or placebo 1-h pre-exercise) and chronic (21 days of supplementation) phase. Blood and skeletal muscle were sampled immediately pre- and post-exercise and analysed for nuclear and mtDNA damage, lipid hydroperoxides, lipid soluble antioxidants, and the ascorbyl free radical. Exercise significantly increased nuclear and mtDNA damage across lymphocytes and muscle (P < 0.05), which was accompanied with changes in lipid hydroperoxides, ascorbyl free radical, and α-tocopherol (P < 0.05). Acute MitoQ treatment failed to impact any biomarker likely due to insufficient initial bioavailability. However, chronic MitoQ treatment attenuated nuclear (P < 0.05) and mtDNA damage in lymphocytes and muscle tissue (P < 0.05). Our work is the first to show a protective effect of chronic MitoQ supplementation on the mitochondrial and nuclear genomes in lymphocytes and human muscle tissue following exercise, which is important for genome stability.

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Exercise damages mitochondrial DNA in lymphocytes and muscle tissue.

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Acute MitoQ ingestion has no impact on biomarkers of oxidative stress.

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Chronic MitoQ supplementation protects mitochondrial and nuclear DNA.

Aurora A regulation by reversible cysteine oxidation reveals evolutionarily conserved redox control of Ser/Thr protein kinase activity

Reactive oxygen species (ROS) are physiological mediators of cellular signaling and play potentially damaging roles in human diseases. In this study, we found that the catalytic activity of the Ser/Thr kinase Aurora A was inhibited by the oxidation of a conserved cysteine residue (Cys290) that lies adjacent to Thr288, a critical phosphorylation site in the activation segment. Cys is present at the equivalent position in ~100 human Ser/Thr kinases, a residue that we found was important not only for the activity of human Aurora A but also for that of fission yeast MAPK-activated kinase (Srk1) and PKA (Pka1). Moreover, the presence of this conserved Cys predicted biochemical redox sensitivity among a cohort of human CAMK, AGC, and AGC-like kinases. Thus, we predict that redox modulation of the conserved Cys290 of Aurora A may be an underappreciated regulatory mechanism that is widespread in eukaryotic Ser/Thr kinases. Given the key biological roles of these enzymes, these findings have implications for understanding physiological and pathological responses to ROS and highlight the importance of protein kinase regulation through multivalent modification of the activation segment.

Redox States of Protein Cysteines in Pathways of Protein Turnover and Cytoskeleton Dynamics Are Changed with Aging and Reversed by Slc7a11 Restoration in Mouse Lung Fibroblasts

Slc7a11 is the key component of system X_c⁻, an antiporter that imports cystine (CySS) and exports glutamate. It plays an important role in cellular defense against oxidative stress because cysteine (Cys), reduced from CySS, is used for and limits the synthesis of glutathione (GSH). We have shown that downregulation of Slc7a11 is responsible for oxidation of extracellular Cys/CySS redox potential in lung fibroblasts from old mice. However, how age-related change of Slc7a11 expression affects the intracellular redox environment of mouse lung fibroblasts remains unexplored. The purpose of this study is to evaluate the effects of aging on the redox states of intracellular proteins and to examine whether Slc7a11 contributes to the age-dependent effects. Iodoacetyl Tandem Mass Tags were used to differentially label reduced and oxidized forms of Cys residues in primary lung fibroblasts from young and old mice, as well as old fibroblasts transfected with Slc7a11. The ratio of oxidized/reduced forms (i.e., redox state) of a Cys residue was determined via multiplexed tandem mass spectrometry. Redox states of 151 proteins were different in old fibroblasts compared to young fibroblasts. Slc7a11 overexpression restored redox states of 104 (69%) of these proteins. Ingenuity Pathway Analysis (IPA) showed that age-dependent Slc7a11-responsive proteins were involved in pathways of protein translation initiation, ubiquitin-proteasome-mediated degradation, and integrin-cytoskeleton-associated signaling. Gene ontology analysis showed cell adhesion, protein translation, and organization of actin cytoskeleton were among the top enriched terms for biological process. Protein-protein interaction network demonstrated the interactions between components of the three enriched pathways predicted by IPA. Follow-up experiments confirmed that proteasome activity was lower in old cells than in young cells and that upregulation of Slc7a11 expression by sulforaphane restored this activity. This study finds that aging results in changes of redox states of proteins involved in protein turnover and cytoskeleton dynamics, and that upregulating Slc7a11 can partially restore the redox states of these proteins.

Transcriptomic and Proteomic Tools in the Study of Hg Toxicity: What Is Missing?

Mercury is a hazardous substance that has unique neurodevelopmental toxic effects in humans. However, the precise sequence of molecular events that culminate in Hg-induced neuropathology is still unknown. Though the omics studies have been generating an enormous amount of new data about Hg toxicity, our ability to interpret such a large quantity of information is still limited. In this opinion article, we will reinforce the necessity of new high throughput and accurate analytical proteomic methodologies, especially, thiol and selenol-proteome. Overall, we posit that improvements in thiol- and selenol-proteomic analyses will be pivotal in identifying the primary cellular targets of Hg. However, a better understanding of the complex cascades and molecular pathways involved in its toxicity will require extensive complementary studies in more complex systems.

Stress-mediated generation of deleterious ROS in healthy individuals - role of cytochrome c oxidase

Psychosocial stress is known to cause an increased incidence of coronary heart disease. In addition, multiple other diseases like cancer and diabetes mellitus have been related to stress and are mainly based on excessive formation of reactive oxygen species (ROS) in mitochondria. The molecular interactions between stress and ROS, however, are still unknown. Here we describe the missing molecular link between stress and an increased cellular ROS, based on the regulation of cytochrome c oxidase (COX). In normal healthy cells, the "allosteric ATP inhibition of COX" decreases the oxygen uptake of mitochondria at high ATP/ADP ratios and keeps the mitochondrial membrane potential (ΔΨm) low. Above ΔΨm values of 140 mV, the production of ROS in mitochondria increases exponentially. Stress signals like hypoxia, stress hormones, and high glutamate or glucose in neurons increase the cytosolic Ca2+ concentration which activates a mitochondrial phosphatase that dephosphorylates COX. This dephosphorylated COX exhibits no allosteric ATP inhibition; consequently, an increase of ΔΨm and ROS formation takes place. The excess production of mitochondrial ROS causes apoptosis or multiple diseases.

ESI MS studies highlight the selective interaction of Auranofin with protein free thiols

The clinically established gold drug Auranofin was reacted individually with a group of representative proteins, namely ubiquitin, ribonuclease A, carbonic anhydrase, haemoglobin and superoxide dismutase, and adduct formation was monitored in the various cases by ESI-MS analysis. We found that the reaction is highly selective for solvent exposed free cysteines that are modified through coordination of the AuPEt₃⁺ fragment. Indeed, ESI-Q-TOF MS spectra carried out on protein samples incubated with a three fold molar excess of Auranofin allowed direct detection of the native proteins bearing bound AuPEt₃⁺ fragments in the cases of carbonic anhydrase and haemoglobin. At variance, the two proteins that do not possess any free cysteine residue, i.e. ubiquitin and ribonuclease A, were unable to bind the gold fragment. In the case of superoxide dismutase, adduct formation is hindered by the scarce solvent accessibility of the free cysteine residue. These findings were further confirmed by a series of competition binding experiments with ebselen, a potent and selective cysteine-modifying reagent; we observed that pre-treatment with ebselen prevents the binding of the AuPEt₃⁺ fragment to both carbonic anhydrase and haemoglobin.

Immunological Techniques to Assess Protein Thiol Redox State: Opportunities, Challenges and Solutions

To understand oxidative stress, antioxidant defense, and redox signaling in health and disease it is essential to assess protein thiol redox state. Protein thiol redox state is seldom assessed immunologically because of the inability to distinguish reduced and reversibly oxidized thiols by Western blotting. An underappreciated opportunity exists to use Click PEGylation to realize the transformative power of simple, time and cost-efficient immunological techniques. Click PEGylation harnesses selective, bio-orthogonal Click chemistry to separate reduced and reversibly oxidized thiols by selectively ligating a low molecular weight polyethylene glycol moiety to the redox state of interest. The resultant ability to disambiguate reduced and reversibly oxidized species by Western blotting enables Click PEGylation to assess protein thiol redox state. In the present review, to enable investigators to effectively harness immunological techniques to assess protein thiol redox state we critique the chemistry, promise and challenges of Click PEGylation.

Oxidants, Antioxidants and Thiol Redox Switches in the Control of Regulated Cell Death Pathways

It is well appreciated that biological reactive oxygen and nitrogen species such as hydrogen peroxide, superoxide and nitric oxide, as well as endogenous antioxidant systems, are important modulators of cell survival and death in diverse organisms and cell types. In addition, oxidative stress, nitrosative stress and dysregulated cell death are implicated in a wide variety of pathological conditions, including cancer, cardiovascular and neurological diseases. Therefore, much effort is devoted to elucidate the molecular mechanisms linking oxidant/antioxidant systems and cell death pathways. This review is focused on thiol redox modifications as a major mechanism by which oxidants and antioxidants influence specific regulated cell death pathways in mammalian cells. Growing evidence indicates that redox modifications of cysteine residues in proteins are involved in the regulation of multiple cell death modalities, including apoptosis, necroptosis and pyroptosis. In addition, recent research suggests that thiol redox switches play a role in the crosstalk between apoptotic and necrotic forms of regulated cell death. Thus, thiol-based redox circuits provide an additional layer of control that determines when and how cells die.

Metabolomics and adductomics of newborn bloodspots to retrospectively assess the early-life exposome

PURPOSE OF REVIEW

Exposomics studies can measure health-relevant chemical exposures during a lifetime and estimate the 'internal' environment. However, sampling limitations make these features difficult to capture directly during the critical neonatal time period.

RECENT FINDINGS

We review the use of newborn dried bloodspots (DBS) archived from newborn screening programs for exposomic analysis in epidemiological children's health studies. Emerging 'omics technologies such as adductomics and metabolomics have been adapted for DBS analysis, and these technologies can now provide valuable etiological information on the complex interplay between exposures, biological response, and population phenotypes.

SUMMARY

Adductomics and metabolomics of DBS can provide robust measurements for retrospective epidemiological investigations. With extensive bioarchiving programs in the United States and other countries, DBS are poised to substantially aid epidemiological studies, particularly for rare and low-frequency childhood diseases and disorders.

Reactive oxygen species (ROS) as pleiotropic physiological signalling agents

'Reactive oxygen species' (ROS) is an umbrella term for an array of derivatives of molecular oxygen that occur as a normal attribute of aerobic life. Elevated formation of the different ROS leads to molecular damage, denoted as 'oxidative distress'. Here we focus on ROS at physiological levels and their central role in redox signalling via different post-translational modifications, denoted as 'oxidative eustress'. Two species, hydrogen peroxide (H₂O₂) and the superoxide anion radical (O₂^·-), are key redox signalling agents generated under the control of growth factors and cytokines by more than 40 enzymes, prominently including NADPH oxidases and the mitochondrial electron transport chain. At the low physiological levels in the nanomolar range, H₂O₂ is the major agent signalling through specific protein targets, which engage in metabolic regulation and stress responses to support cellular adaptation to a changing environment and stress. In addition, several other reactive species are involved in redox signalling, for instance nitric oxide, hydrogen sulfide and oxidized lipids. Recent methodological advances permit the assessment of molecular interactions of specific ROS molecules with specific targets in redox signalling pathways. Accordingly, major advances have occurred in understanding the role of these oxidants in physiology and disease, including the nervous, cardiovascular and immune systems, skeletal muscle and metabolic regulation as well as ageing and cancer. In the past, unspecific elimination of ROS by use of low molecular mass antioxidant compounds was not successful in counteracting disease initiation and progression in clinical trials. However, controlling specific ROS-mediated signalling pathways by selective targeting offers a perspective for a future of more refined redox medicine. This includes enzymatic defence systems such as those controlled by the stress-response transcription factors NRF2 and nuclear factor-κB, the role of trace elements such as selenium, the use of redox drugs and the modulation of environmental factors collectively known as the exposome (for example, nutrition, lifestyle and irradiation).

Redox Modifications of Proteins of the Mitochondrial Fusion and Fission Machinery

Mitochondrial fusion and fission tailors the mitochondrial shape to changes in cellular homeostasis. Players of this process are the mitofusins, which regulate fusion of the outer mitochondrial membrane, and the fission protein DRP1. Upon specific stimuli, DRP1 translocates to the mitochondria, where it interacts with its receptors FIS1, MFF, and MID49/51. Another fission factor of clinical relevance is GDAP1. Here, we identify and discuss cysteine residues of these proteins that are conserved in phylogenetically distant organisms and which represent potential sites of posttranslational redox modifications. We reveal that worms and flies possess only a single mitofusin, which in vertebrates diverged into MFN1 and MFN2. All mitofusins contain four conserved cysteines in addition to cysteine 684 in MFN2, a site involved in mitochondrial hyperfusion. DRP1 and FIS1 are also evolutionarily conserved but only DRP1 contains four conserved cysteine residues besides cysteine 644, a specific site of nitrosylation. MFF and MID49/51 are only present in the vertebrate lineage. GDAP1 is missing in the nematode genome and contains no conserved cysteine residues. Our analysis suggests that the function of the evolutionarily oldest proteins of the mitochondrial fusion and fission machinery, the mitofusins and DRP1 but not FIS1, might be altered by redox modifications.

The Role of Selenium in Oxidative Stress and in Nonthyroidal Illness Syndrome (NTIS): An Overview

Selenium is a trace element, nutritionally classified as an essential micronutrient, involved in maintaining the correct function of several enzymes incorporating the selenocysteine residue, namely the selenoproteins. The human selenoproteome including 25 proteins is extensively described here. The most relevant selenoproteins, including glutathione peroxidases, thioredoxin reductases and iodothyronine deiodinases are required for the proper cellular redox homeostasis as well as for the correct thyroid function, thus preventing oxidative stress and related diseases. This review summarizes the main advances on oxidative stress with a focus on selenium metabolism and transport. Moreover, thyroid-related disorders are discussed, considering that the thyroid gland contains the highest selenium amount per gram of tissue, also for future possible therapeutic implication.

Reactive oxygen species or reactive sulfur species: why we should consider the latter

The biological effects of oxidants, especially reactive oxygen species (ROS), include signaling functions (oxidative eustress), initiation of measures to reduce elevated ROS (oxidative stress), and a cascade of pathophysiological events that accompany excessive ROS (oxidative distress). Although these effects have long been studied in animal models with perturbed ROS, their actions under physiological conditions are less clear. I propose that some of the apparent uncertainty may be due to confusion of ROS with endogenously generated reactive sulfur species (RSS). ROS and RSS are chemically similar, but RSS are more reactive and versatile, and can be stored and reused. Both ROS and RSS signal via oxidation reactions with protein cysteine sulfur and they produce identical effector responses, but RSS appear to be more effective. RSS in the form of persulfidated cysteines (Cys-S-S) are produced endogenously and co-translationally introduced into proteins, and there is increasing evidence that many cellular proteins are persulfidated. A number of practical factors have contributed to confusion between ROS and RSS, and these are discussed herein. Furthermore, essentially all endogenous antioxidant enzymes appeared shortly after life began, some 3.8 billion years ago, when RSS metabolism dominated evolution. This was long before the rise in ROS, 600 million years ago, and I propose that these same enzymes, with only minor modifications, still effectively metabolize RSS in extant organisms. I am not suggesting that all ROS are RSS; however, I believe that the relative importance of ROS and RSS in biological systems needs further consideration.

Potential implications of hydrogen peroxide in the pathogenesis and therapeutic strategies of gliomas

Glioma is the most common type of primary brain tumor, and it has a high mortality rate. Currently, there are only a few therapeutic approaches for gliomas, and their effects are unsatisfactory. Therefore, uncovering the pathogenesis and exploring more therapeutic strategies for the treatment of gliomas are urgently needed to overcome the ongoing challenges. Cellular redox imbalance has been shown to be associated with the initiation and progression of gliomas. Among reactive oxygen species (ROS), hydrogen peroxide (H₂O₂) is considered the most suitable for redox signaling and is a potential candidate as a key molecule that determines the fate of cancer cells. In this review, we discuss the potential cellular and molecular roles of H₂O₂ in gliomagenesis and explore the potential implications of H₂O₂ in radiotherapy and chemotherapy and in the ongoing challenges of current glioma treatment. Moreover, we evaluate H₂O₂ as a potential redox sensor and potential driver molecule of nanocatalytic therapeutic strategies for glioma treatment.

Preserving Single Cells in Space and Time for Analytical Assays

Analytical assays performed within clinical laboratories influence roughly 70% of all medical decisions by facilitating disease detection, diagnosis, and management. Both in clinical and academic research laboratories, single-cell assays permit measurement of cell diversity and identification of rare cells, both of which are important in the understanding of disease pathogenesis. For clinically utility, the single-cell assays must be compatible with the clinical workflow steps of sample collection, sample transportation, pre-analysis processing, and single-cell assay; therefore, it is paramount to preserve cells in a state that resembles that in vivo rather than measuring signaling behaviors initiated in response to stressors such as sample collection and processing. To address these challenges, novel cell fixation (and more broadly, cell preservation) techniques incorporate programmable fixation times, reversible bond formation and cleavage, chemoselective reactions, and improved analyte recovery. These technologies will further the development of individualized, precision therapies for patients to yield improved clinical outcomes.

Hydrogen sulfide signaling in mitochondria and disease

Hydrogen sulfide can signal through 3 distinct mechanisms: 1) reduction and/or direct binding of metalloprotein heme centers, 2) serving as a potent antioxidant through reactive oxygen species/reactive nitrogen species scavenging, or 3) post-translational modification of proteins by addition of a thiol (-SH) group onto reactive cysteine residues: a process known as persulfidation. Below toxic levels, hydrogen sulfide promotes mitochondrial biogenesis and function, thereby conferring protection against cellular stress. For these reasons, increases in hydrogen sulfide and hydrogen sulfide-producing enzymes have been implicated in several human disease states. This review will first summarize our current understanding of hydrogen sulfide production and metabolism, as well as its signaling mechanisms; second, this work will detail the known mechanisms of hydrogen sulfide in the mitochondria and the implications of its mitochondrial-specific impacts in several pathologic conditions.-Murphy, B., Bhattacharya, R., Mukherjee, P. Hydrogen sulfide signaling in mitochondria and disease.

Systemic Lupus Erythematosus: Pathogenesis at the Functional Limit of Redox Homeostasis

Systemic lupus erythematosus (SLE) is a disease characterized by the production of autoreactive antibodies and cytokines, which are thought to have a major role in disease activity and progression. Immune system exposure to excessive amounts of autoantigens that are not efficiently removed is reported to play a significant role in the generation of autoantibodies and the pathogenesis of SLE. While several mechanisms of cell death-based autoantigenic exposure and compromised autoantigen removal have been described in relation to disease onset, a significant association with the development of SLE can be attributed to increased apoptosis and impaired phagocytosis of apoptotic cells. Both apoptosis and impaired phagocytosis can be caused by hydrogen peroxide whose cellular production is enhanced by exposure to endogenous hormones or environmental chemicals, which have been implicated in the pathogenesis of SLE. Hydrogen peroxide can cause lymphocyte apoptosis and glutathione depletion, both of which are associated with the severity of SLE. The cellular accumulation of hydrogen peroxide is facilitated by the myriad of stimuli causing increased cellular bioenergetic activity that enhances metabolic production of this toxic oxidizing agent such as emotional stress and infection, which are recognized SLE exacerbating factors. When combined with impaired cellular hydrogen peroxide removal caused by xenobiotics and genetically compromised hydrogen peroxide elimination due to enzymatic polymorphic variation, a mechanism for cellular accumulation of hydrogen peroxide emerges, leading to hydrogen peroxide-induced apoptosis and impaired phagocytosis, enhanced autoantigen exposure, formation of autoantibodies, and development of SLE.

The biophysics of superoxide dismutase-1 and amyotrophic lateral sclerosis

Few proteins have come under such intense scrutiny as superoxide dismutase-1 (SOD1). For almost a century, scientists have dissected its form, function and then later its malfunction in the neurodegenerative disease amyotrophic lateral sclerosis (ALS). We now know SOD1 is a zinc and copper metalloenzyme that clears superoxide as part of our antioxidant defence and respiratory regulation systems. The possibility of reduced structural integrity was suggested by the first crystal structures of human SOD1 even before deleterious mutations in the sod1 gene were linked to the ALS. This concept evolved in the intervening years as an impressive array of biophysical studies examined the characteristics of mutant SOD1 in great detail. We now recognise how ALS-related mutations perturb the SOD1 maturation processes, reduce its ability to fold and reduce its thermal stability and half-life. Mutant SOD1 is therefore predisposed to monomerisation, non-canonical self-interactions, the formation of small misfolded oligomers and ultimately accumulation in the tell-tale insoluble inclusions found within the neurons of ALS patients. We have also seen that several post-translational modifications could push wild-type SOD1 down this toxic pathway. Recently we have come to view ALS as a prion-like disease where both the symptoms, and indeed SOD1 misfolding itself, are transmitted to neighbouring cells. This raises the possibility of intervention after the initial disease presentation. Several small-molecule and biologic-based strategies have been devised which directly target the SOD1 molecule to change the behaviour thought to be responsible for ALS. Here we provide a comprehensive review of the many biophysical advances that sculpted our view of SOD1 biology and the recent work that aims to apply this knowledge for therapeutic outcomes in ALS.

Redox Proteomes in Human Physiology and Disease Mechanisms

Redox proteomics is a field of proteomics that is concerned with the characterization of the oxidation state of proteins to gain information about their modulated structure, function, activity, and involvement in different physiological pathways. Oxidative modifications of proteins have been shown to be implicated in normal physiological processes of cells as well as in pathomechanisms leading to the development of cancer, diabetes, neurodegenerative diseases, and some rare hereditary metabolic diseases, like classic galactosemia. Reactive oxygen species generate a variety of reversible and irreversible modifications in amino acid residue side chains and within the protein backbone. These oxidative post-translational modifications (Ox-PTMs) can participate in the activation of signal transduction pathways and mediate the toxicity of harmful oxidants. Thus the application of advanced redox proteomics technologies is important for gaining insights into molecular mechanisms of diseases. Mass-spectrometry-based proteomics is one of the most powerful methods that can be used to give detailed qualitative and quantitative information on protein modifications and allows us to characterize redox proteomes associated with diseases. This Review illustrates the role and biological consequences of Ox-PTMs under basal and oxidative stress conditions by focusing on protein carbonylation and S-glutathionylation, two abundant modifications with an impact on cellular pathways that have been intensively studied during the past decade.

Crosstalk Between Mitochondrial Hyperacetylation and Oxidative Stress in Vascular Dysfunction and Hypertension

Significance: Vascular dysfunction plays a key role in the development of arteriosclerosis, heart disease, and hypertension, which causes one-third of deaths worldwide. Vascular oxidative stress and metabolic disorders contribute to vascular dysfunction, leading to impaired vasorelaxation, vascular hypertrophy, fibrosis, and aortic stiffening. Mitochondria are critical in the regulation of metabolic and antioxidant functions; therefore, mitochondria-targeted treatments could be beneficial. Recent Advances: Vascular dysfunction is crucial in hypertension pathophysiology and exhibits bidirectional relationship. Metabolic disorders and oxidative stress contribute to the pathogenesis of vascular dysfunction and hypertension, which are associated with mitochondrial impairment and hyperacetylation. Mitochondrial deacetylase Sirtuin 3 (Sirt3) is critical in the regulation of metabolic and antioxidant functions. Clinical studies show that cardiovascular disease risk factors reduce Sirt3 level and Sirt3 declines with age, paralleling the increased incidence of cardiovascular disease and hypertension. An imbalance between mitochondrial acetylation and reduced Sirt3 activity contributes to mitochondrial dysfunction and oxidative stress. We propose that mitochondrial hyperacetylation drives a vicious cycle between metabolic disorders and mitochondrial oxidative stress, promoting vascular dysfunction and hypertension. Critical Issues: The mechanisms of mitochondrial dysfunction are still obscure in human hypertension. Mitochondrial hyperacetylation and oxidative stress contribute to mitochondrial dysfunction; however, regulation of mitochondrial acetylation, the role of GCN5L1 (acetyl-CoA-binding protein promoting acetyltransferase protein acetylation) acetyltransferase, Sirt3 deacetylase, and acetylation of specific proteins require further investigations. Future Directions: There is an urgent need to define molecular mechanisms and the pathophysiological role of mitochondrial hyperacetylation, identify novel pharmacological targets, and develop therapeutic approaches to reduce this phenomenon.

Catalyst-free Click PEGylation reveals substantial mitochondrial ATP synthase sub-unit alpha oxidation before and after fertilisation

Using non-reducing Western blotting to assess protein thiol redox state is challenging because most reduced and oxidised forms migrate at the same molecular weight and are, therefore, indistinguishable. While copper catalysed Click chemistry can be used to ligate a polyethylene glycol (PEG) moiety termed Click PEGylation to mass shift the reduced or oxidised form as desired, the potential for copper catalysed auto-oxidation is problematic. Here we define a catalyst-free trans-cyclooctene-methyltetrazine (TCO-Tz) inverse electron demand Diels Alder chemistry approach that affords rapid (k ~2000 M-1 s-1), selective and bio-orthogonal Click PEGylation. We used TCO-Tz Click PEGylation to investigate how fertilisation impacts reversible mitochondrial ATP synthase F1-Fo sub-unit alpha (ATP-α-F1) oxidation-an established molecular correlate of impaired enzyme activity-in Xenopus laevis. TCO-Tz Click PEGylation studies reveal substantial (~65%) reversible ATP-α-F1 oxidation at evolutionary conserved cysteine residues (i.e., C244 and C294) before and after fertilisation. A single thiol is, however, preferentially oxidised likely due to greater solvent exposure during the catalytic cycle. Selective reduction experiments show that: S-glutathionylation accounts for ~50-60% of the reversible oxidation observed, making it the dominant oxidative modification type. Intermolecular disulphide bonds may also contribute due to their relative stability. Substantial reversible ATP-α-F1 oxidation before and after fertilisation is biologically meaningful because it implies low mitochondrial F1-Fo ATP synthase activity. Catalyst-free TCO-Tz Click PEGylation is a valuable new tool to interrogate protein thiol redox state in health and disease.

Redox modifications of cysteine-containing proteins, cell cycle arrest and translation inhibition: Involvement in vitamin C-induced breast cancer cell death

Vitamin C (VitC) possesses pro-oxidant properties at high pharmacologic concentrations which favor repurposing VitC as an anti-cancer therapeutic agent. However, redox-based anticancer properties of VitC are yet partially understood. We examined the difference between the reduced and oxidized forms of VitC, ascorbic acid (AA) and dehydroascorbic acid (DHA), in terms of cytotoxicity and redox mechanisms toward breast cancer cells. Our data showed that AA displayed higher cytotoxicity towards triple-negative breast cancer (TNBC) cell lines in vitro than DHA. AA exhibited a similar cytotoxicity on non-TNBC cells, while only a minor detrimental effect on noncancerous cells. Using MDA-MB-231, a representative TNBC cell line, we observed that AA- and DHA-induced cytotoxicity were linked to cellular redox-state alterations. Hydrogen peroxide (H2O2) accumulation in the extracellular medium and in different intracellular compartments, and to a lesser degree, intracellular glutathione oxidation, played a key role in AA-induced cytotoxicity. In contrast, DHA affected glutathione oxidation and had less cytotoxicity. A "redoxome" approach revealed that AA treatment altered the redox state of key antioxidants and a number of cysteine-containing proteins including many nucleic acid binding proteins and proteins involved in RNA and DNA metabolisms and in energetic processes. We showed that cell cycle arrest and translation inhibition were associated with AA-induced cytotoxicity. Finally, bioinformatics analysis and biological experiments identified that peroxiredoxin 1 (PRDX1) expression levels correlated with AA differential cytotoxicity in breast cancer cells, suggesting a potential predictive value of PRDX1. This study provides insight into the redox-based mechanisms of VitC anticancer activity, indicating that pharmacologic doses of VitC and VitC-based rational drug combinations could be novel therapeutic opportunities for triple-negative breast cancer.

Heme ligation and redox chemistry in two bacterial thiosulfate dehydrogenase (TsdA) enzymes

Thiosulfate dehydrogenases (TsdAs) are bidirectional bacterial di-heme enzymes that catalyze the interconversion of tetrathionate and thiosulfate at measurable rates in both directions. In contrast to our knowledge of TsdA activities, information on the redox properties in the absence of substrates is rather scant. To address this deficit, we combined magnetic CD (MCD) spectroscopy and protein film electrochemistry (PFE) in a study to resolve heme ligation and redox chemistry in two representative TsdAs. We examined the TsdAs from Campylobacter jejuni, a microaerobic human pathogen, and from the purple sulfur bacterium Allochromatium vinosum. In these organisms, the enzyme functions as a tetrathionate reductase and a thiosulfate oxidase, respectively. The active site Heme 1 in both enzymes has His/Cys ligation in the ferric and ferrous states and the midpoint potentials (E_m) of the corresponding redox transformations are similar, −185 mV versus standard hydrogen electrode (SHE). However, fundamental differences are observed in the properties of the second, electron transferring, Heme 2. In C. jejuni, TsdA Heme 2 has His/Met ligation and an E_m of +172 mV. In A. vinosum TsdA, Heme 2 reduction triggers a switch from His/Lys ligation (E_m, −129 mV) to His/Met (E_m, +266 mV), but the rates of interconversion are such that His/Lys ligation would be retained during turnover. In summary, our findings have unambiguously assigned E_m values to defined axial ligand sets in TsdAs, specified the rates of Heme 2 ligand exchange in the A. vinosum enzyme, and provided information relevant to describing their catalytic mechanism(s).

A Unique SUMO-Interacting Motif of Trx2 Is Critical for Its Mitochondrial Presequence Processing and Anti-oxidant Activity

OBJECTIVE

Mitochondrial thioredoxin 2 (Trx2) is a vital mitochondrial redox protein that mediates normal protein thiol reduction and provides electrons to peroxiredoxin 3 (Prx3) to scavenge H2O2 in mitochondria. It has been widely reported that Trx2 deletion in cells or mice generates massive reactive oxygen species (ROS) which have been implicated in many pathological processes. On the contrary, how ROS regulate Trx2 processing and activity remains to be elucidated.

APPROACH AND RESULTS

Here we show that excess ROS induce endothelial cell senescence concomitant with an attenuation of Trx2 processing in which Trx2 presequence [i.e., mitochondrial targeting signal peptide (MTS)] is cleaved to generate a mature form. Mutation analyses indicate that Trx2 processing is mediated by mitochondrial processing peptidase (MPP) and mitochondrial intermediate peptidase (MIP)-recognition sites within the MTS. Interestingly, a mutation at a SUMO- interacting motif (SIM), but not the catalytic sites within the mature Trx2 protein, completely blocks Trx2 processing with no effect on Trx2 mitochondrial targeting. Consistently, chemical inhibition of protein SUMOylation attenuates, while SUMOylation agonist promotes, Trx2 processing. Moreover, we identify the α-MPP subunit is a SUMOylated protein that potentially mediates Trx2-binding and cleavage. Furthermore, the unprocessed form of Trx2-SIM is unable to protect cells from both ROS generation and oxidative stress-induced cellular senescence.

CONCLUSION

Our study reveals that a unique SUMO-interacting motif of Trx2 is critical for its mitochondrial processing and subsequent anti-oxidant/antisenescence activities.

Role of Glutathionylation in Infection and Inflammation

Glutathionylation, that is, the formation of mixed disulfides between protein cysteines and glutathione (GSH) cysteines, is a reversible post-translational modification catalyzed by different cellular oxidoreductases, by which the redox state of the cell modulates protein function. So far, most studies on the identification of glutathionylated proteins have focused on cellular proteins, including proteins involved in host response to infection, but there is a growing number of reports showing that microbial proteins also undergo glutathionylation, with modification of their characteristics and functions. In the present review, we highlight the signaling role of GSH through glutathionylation, particularly focusing on microbial (viral and bacterial) glutathionylated proteins (GSSPs) and host GSSPs involved in the immune/inflammatory response to infection; moreover, we discuss the biological role of the process in microbial infections and related host responses.

Hydrogen sulfide, reactive sulfur species and coping with reactive oxygen species

Life began in a ferruginous (anoxic and Fe²⁺ dominated) world around 3.8 billion years ago (bya). Hydrogen sulfide (H₂S) and other sulfur molecules from hydrothermal vents and other fissures provided many key necessities for life's origin including catalytic platforms (primordial enzymes) that also served as primitive boundaries (cell walls), substrates for organic synthesis and a continuous source of energy in the form of reducing equivalents. Anoxigenic photosynthesis oxidizing H₂S followed within a few hundred million years and laid the metabolic groundwork for oxidative photosynthesis some half-billion years later that slightly and episodically increased atmospheric oxygen around 2.3 bya. This oxidized terrestrial sulfur to sulfate which was washed to the sea where it was reduced creating vast euxinic (anoxic and sulfidic) areas. It was in this environment that eukaryotic cells appeared around 1.5 bya and where they evolved for nearly 1 billion additional years. Oxidative photosynthesis finally oxidized the oceans and around 0.6 bya oxygen levels in the atmosphere and oceans began to rise toward present day levels. This is purported to have been a life-threatening event due to the prevalence of reactive oxygen species (ROS) and thus necessitated the elaboration of chemical and enzymatic antioxidant mechanisms. However, these antioxidants initially appeared around the time of anoxigenic photosynthesis suggesting a commitment to metabolism of reactive sulfur species (RSS). This review examines these events and suggests that many of the biological attributes assigned to ROS may, in fact, be due to RSS. This is underscored by observations that ROS and RSS are chemically similar, often indistinguishable by analytical methods and the fact that the bulk of biochemical and physiological experiments are performed in unphysiologically oxic environments where ROS are artifactually favored over RSS.

Redox responses in skeletal muscle following denervation

Previous studies have shown a significant increase in the mitochondrial generation of hydrogen peroxide (H₂O₂) and other peroxides in recently denervated muscle fibers. The mechanisms for generation of these peroxides and how the muscle responds to these peroxides are not fully established. The aim of this work was to determine the effect of denervation on the muscle content of proteins that may contribute to mitochondrial peroxide release and the muscle responses to this generation. Denervation of the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles in mice was achieved by surgical removal of a small section of the peroneal nerve prior to its entry into the muscle. An increase in mitochondrial peroxide generation has been observed from 7 days and sustained up to 21 days following denervation in the TA muscle fibers. This increased peroxide generation was reduced by incubation of skinned fibers with inhibitors of monoamine oxidases, NADPH oxidases or phospholipase A2 enzymes and the muscle content of these enzymes together with peroxiredoxin 6 were increased following denervation. Denervated muscle also showed significant adaptations in the content of several enzymes involved in the protection of cells against oxidative damage. Morphological analyses indicated a progressive significant loss of muscle mass in the TA muscle from 7 days up to 21 days following denervation due to fiber atrophy but without fiber loss. These results support the possibility that, at least initially, the increase in peroxide production may stimulate adaptations in an attempt to protect the muscle fibers, but that these processes are insufficient and the increased peroxide generation over the longer term may activate degenerative and atrophic processes in the denervated muscle fibers.

Redox Homeostasis in Photosynthetic Organisms: Novel and Established Thiol-Based Molecular Mechanisms

Significance: Redox homeostasis consists of an intricate network of reactions in which reactive molecular species, redox modifications, and redox proteins act in concert to allow both physiological responses and adaptation to stress conditions. Recent Advances: This review highlights established and novel thiol-based regulatory pathways underlying the functional facets and significance of redox biology in photosynthetic organisms. In the last decades, the field of redox regulation has largely expanded and this work is aimed at giving the right credit to the importance of thiol-based regulatory and signaling mechanisms in plants. Critical Issues: This cannot be all-encompassing, but is intended to provide a comprehensive overview on the structural/molecular mechanisms governing the most relevant thiol switching modifications with emphasis on the large genetic and functional diversity of redox controllers (i.e., redoxins). We also summarize the different proteomic-based approaches aimed at investigating the dynamics of redox modifications and the recent evidence that extends the possibility to monitor the cellular redox state in vivo. The physiological relevance of redox transitions is discussed based on reverse genetic studies confirming the importance of redox homeostasis in plant growth, development, and stress responses. Future Directions: In conclusion, we can firmly assume that redox biology has acquired an established significance that virtually infiltrates all aspects of plant physiology.

Redox Is a Global Biodevice Information Processing Modality

Biology is well-known for its ability to communicate through (i) molecularly-specific signaling modalities and (ii) a globally-acting electrical modality associated with ion flow across biological membranes. Emerging research suggests that biology uses a third type of communication modality associated with a flow of electrons through reduction/oxidation (redox) reactions. This redox signaling modality appears to act globally and has features of both molecular and electrical modalities: since free electrons do not exist in aqueous solution, the electrons must flow through molecular intermediates that can be switched between two states - with electrons (reduced) or without electrons (oxidized). Importantly, this global redox modality is easily accessible through its electrical features using convenient electrochemical instrumentation. In this review, we explain this redox modality, describe our electrochemical measurements, and provide four examples demonstrating that redox enables communication between biology and electronics. The first two examples illustrate how redox probing can acquire biologically relevant information. The last two examples illustrate how redox inputs can transduce biologically-relevant transitions for patterning and the induction of a synbio transceiver for two-hop molecular communication. In summary, we believe redox provides a unique ability to bridge bio-device communication because simple electrochemical methods enable global access to biologically meaningful information. Further, we envision that redox may facilitate the application of information theory to the biological sciences.