Redox regulation by reversible protein S-thiolation in Gram-positive bacteria

Adaptive laboratory evolution for improved tolerance of vitamin K in Bacillus subtilis

Menaquinone-7 (MK-7), a subtype of vitamin K2 (VK2), assumes crucial roles in coagulation function, calcium homeostasis, and respiratory chain transmission. The production of MK-7 via microbial fermentation boasts mild technological conditions and high biocompatibility. Nevertheless, the redox activity of MK-7 imposes constraints on its excessive accumulation in microorganisms. To address this predicament, an adaptive laboratory evolution (ALE) protocol was implemented in Bacillus subtilis BS011, utilizing vitamin K3 (VK3) as a structural analog of MK-7. The resulting strain, BS012, exhibited heightened tolerance to high VK3 concentrations and demonstrated substantial enhancements in biofilm formation and total antioxidant capacity (T-AOC) when compared to BS011. Furthermore, MK-7 production in BS012 exceeded that of BS011 by 76% and 22% under static and shaking cultivation conditions, respectively. The molecular basis underlying the superior performance of BS012 was elucidated through genome and transcriptome analyses, encompassing observations of alterations in cell morphology, variations in central carbon and nitrogen metabolism, spore formation, and antioxidant systems. In summation, ALE technology can notably enhance the tolerance of B. subtilis to VK and increase MK-7 production, thus offering a theoretical framework for the microbial fermentation production of other VK2 subtypes. Additionally, the evolved strain BS012 can be developed for integration into probiotic formulations within the food industry to maintain intestinal flora homeostasis, mitigate osteoporosis risk, and reduce the incidence of cardiovascular disease. KEY POINTS: • Bacillus subtilis was evolved for improved vitamin K tolerance and menaquinone-7 (MK-7) production • Evolved strains formed wrinkled biofilms and elongated almost twofold in length • Evolved strains induced sporulation to improve tolerance when carbon was limited.

Regulation of oxidative stress response and antioxidant modification in Corynebacterium glutamicum

As an efficient and safe industrial bacterium, Corynebacterium glutamicum has extensive application in amino acid production. However, it often faces oxidative stress induced by reactive oxygen species (ROS), leading to diminished production efficiency. To enhance the robustness of C. glutamicum, numerous studies have focused on elucidating its regulatory mechanisms under various stress conditions such as heat, acid, and sulfur stress. However, a comprehensive review of its defense mechanisms against oxidative stress is needed. This review offers an in-depth overview of the mechanisms C. glutamicum employs to manage oxidative stress. It covers both enzymatic and non-enzymatic systems, including antioxidant enzymes, regulatory protein families, sigma factors involved in transcription, and physiological redox reduction pathways. This review provides insights for advancing research on the antioxidant mechanisms of C. glutamicum and sheds light on its potential applications in industrial production.

Stealing survival: Iron acquisition strategies of Mycobacteriumtuberculosis

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), faces iron scarcity within the host due to immune defenses. This review explores the importance of iron for Mtb and its strategies to overcome iron restriction. We discuss how the host limits iron as an innate immune response and how Mtb utilizes various iron acquisition systems, particularly the siderophore-mediated pathway. The review illustrates the structure and biosynthesis of mycobactin, a key siderophore in Mtb, and the regulation of its production. We explore the potential of targeting siderophore biosynthesis and uptake as a novel therapeutic approach for TB. Finally, we summarize current knowledge on Mtb's iron acquisition and highlight promising directions for future research to exploit this pathway for developing new TB interventions.

Low-molecular-weight thiol transferases in redox regulation and antioxidant defence

Low-molecular-weight (LMW) thiols are produced in all living cells in different forms and concentrations. Glutathione (GSH), coenzyme A (CoA), bacillithiol (BSH), mycothiol (MSH), ergothioneine (ET) and trypanothione T(SH)2 are the main LMW thiols in eukaryotes and prokaryotes. LMW thiols serve as electron donors for thiol-dependent enzymes in redox-mediated metabolic and signaling processes, protect cellular macromolecules from oxidative and xenobiotic stress, and participate in the reduction of oxidative modifications. The level and function of LMW thiols, their oxidized disulfides and mixed disulfide conjugates in cells and tissues is tightly controlled by dedicated oxidoreductases, such as peroxiredoxins, glutaredoxins, disulfide reductases and LMW thiol transferases. This review provides the first summary of the current knowledge of structural and functional diversity of transferases for LMW thiols, including GSH, BSH, MSH and T(SH)2. Their role in maintaining redox homeostasis in single-cell and multicellular organisms is discussed, focusing in particular on the conjugation of specific thiols to exogenous and endogenous electrophiles, or oxidized protein substrates. Advances in the development of new research tools, analytical methodologies, and genetic models for the analysis of known LMW thiol transferases will expand our knowledge and understanding of their function in cell growth and survival under oxidative stress, nutrient deprivation, and during the detoxification of xenobiotics and harmful metabolites. The antioxidant function of CoA has been recently discovered and the breakthrough in defining the identity and functional characteristics of CoA S-transferase(s) is soon expected.

Efficacy of treating bacterial bioaerosols with weakly acidic hypochlorous water: A simulation chamber study

The COVID-19 pandemic highlighted the dangers of airborne transmission and the risks of pathogen-containing small airborne droplet inhalation as an infection route. As a pathogen control, Weakly Acidic Hypochlorous Water (WAHW) is used for surface disinfection. However, there are limited assessments of air disinfection by WAHW against airborne pathogens like bioaerosols. This was an empirical study evaluating the disinfection efficacy of WAHW in an atmospheric simulation chamber system against four selected model bacteria. The strains tested included Staphylococcus aureus (SA), Escherichia coli (EC), Pseudomonas aeruginosa (PA), and Pseudomonas aeruginosa (PAO1). Each bacterial solution was nebulized into the chamber system as the initial step, and bioaerosol was collected into the liquid medium by a bio-sampler for colony forming units (CFU) determination. Secondly, the nebulized bacterial bioaerosol was exposed to nebulized double distilled water (DDW) as the control and nebulized 150 ppm of WAHW as the experimental groups. After the 3 and 30-min reaction periods, the aerosol mixture inside the chamber was sampled in liquid media and then cultured on agar plates with different dilution factors to determine the CFU. Survival rates were calculated by a pre-exposed CFU value as a reference point. The use of WAHW decreased bacterial survival rates to 1.65-30.15% compared to the DDW control. PAO1 showed the highest survival rates and stability at 3 min was higher than 30 min in all experiments. Statistical analysis indicated that bacteria survival rates were significantly reduced compared to the controls. This work verifies the bactericidal effects against Gram-positive/negative bioaerosols of WAHW treatment. As WAHW contains chlorine in the acid solution, residual chlorine air concentration is a concern and the disinfection effect at different concentrations also requires investigation. Future studies should identify optimal times to minimize the treated time range and require measurements in a real environment.

The neutrophil oxidant hypothiocyanous acid causes a thiol-specific stress response and an oxidative shift of the bacillithiol redox potential in Staphylococcus aureus

IMPORTANCE

Staphylococcus aureus colonizes the skin and the airways but can also lead to life-threatening systemic and chronic infections. During colonization and phagocytosis by immune cells, S. aureus encounters the thiol-reactive oxidant HOSCN. The understanding of the adaptation mechanisms of S. aureus toward HOSCN stress is important to identify novel drug targets to combat multi-resistant S. aureus isolates. As a defense mechanism, S. aureus uses the flavin disulfide reductase MerA, which functions as HOSCN reductase and protects against HOSCN stress. Moreover, MerA homologs have conserved functions in HOSCN detoxification in other bacteria, including intestinal and respiratory pathogens. In this work, we studied the comprehensive thiol-reactive mode of action of HOSCN and its effect on the reversible shift of the E BSH to discover new defense mechanisms against the neutrophil oxidant. These findings provide new leads for future drug design to fight the pathogen at the sites of colonization and infections.

Harnessing redox proteomics to study metabolic regulation and stress response in lignin-fed Rhodococci

BACKGROUND

Rhodococci are studied for their bacterial ligninolytic capabilities and proclivity to accumulate lipids. Lignin utilization is a resource intensive process requiring a variety of redox active enzymes and cofactors for degradation as well as defense against the resulting toxic byproducts and oxidative conditions. Studying enzyme expression and regulation between carbon sources will help decode the metabolic rewiring that stymies lignin to lipid conversion in these bacteria. Herein, a redox proteomics approach was applied to investigate a fundamental driver of carbon catabolism and lipid anabolism: redox balance.

RESULTS

A consortium of Rhodococcus strains was employed in this study given its higher capacity for lignin degradation compared to monocultures. This consortium was grown on glucose vs. lignin under nitrogen limitation to study the importance of redox balance as it relates to nutrient availability. A modified bottom-up proteomics workflow was harnessed to acquire a general relationship between protein abundance and protein redox states. Global proteomics results affirm differential expression of enzymes involved in sugar metabolism vs. those involved in lignin degradation and aromatics metabolism. As reported previously, several enzymes in the lipid biosynthetic pathways were downregulated, whereas many involved in β-oxidation were upregulated. Interestingly, proteins involved in oxidative stress response were also upregulated perhaps in response to lignin degradation and aromatics catabolism, which require oxygen and reactive oxygen species and generate toxic byproducts. Enzymes displaying little-to-no change in abundance but differences in redox state were observed in various pathways for carbon utilization (e.g., β‑ketoadipate pathway), lipid metabolism, as well as nitrogen metabolism (e.g., purine scavenging/synthesis), suggesting potential mechanisms of redox-dependent regulation of metabolism.

CONCLUSIONS

Efficient lipid production requires a steady carbon and energy flux while balancing fundamental requirements for enzyme production and cell maintenance. For lignin, we theorize that this balance is difficult to establish due to resource expenditure for enzyme production and stress response. This is supported by significant changes to protein abundances and protein cysteine oxidation in various metabolic pathways and redox processes.

Staphylococcus aureus adapts to the immunometabolite itaconic acid by inducing acid and oxidative stress responses including S-bacillithiolations and S-itaconations

Staphylococcus aureus is a major pathogen, which has to defend against reactive oxygen and electrophilic species encountered during infections. Activated macrophages produce the immunometabolite itaconate as potent electrophile and antimicrobial upon pathogen infection. In this work, we used transcriptomics, metabolomics and shotgun redox proteomics to investigate the specific stress responses, metabolic changes and redox modifications caused by sublethal concentrations of itaconic acid in S. aureus. In the RNA-seq transcriptome, itaconic acid caused the induction of the GlnR, KdpDE, CidR, SigB, GraRS, PerR, CtsR and HrcA regulons and the urease-encoding operon, revealing an acid and oxidative stress response and impaired proteostasis. Neutralization using external urea as ammonium source improved the growth and decreased the expression of the glutamine synthetase-controlling GlnR regulon, indicating that S. aureus experienced ammonium starvation upon itaconic acid stress. In the extracellular metabolome, the amounts of acetate and formate were decreased, while secretion of pyruvate and the neutral product acetoin were strongly enhanced to avoid intracellular acidification. Exposure to itaconic acid affected the amino acid uptake and metabolism as revealed by the strong intracellular accumulation of lysine, threonine, histidine, aspartate, alanine, valine, leucine, isoleucine, cysteine and methionine. In the proteome, itaconic acid caused widespread S-bacillithiolation and S-itaconation of redox-sensitive antioxidant and metabolic enzymes, ribosomal proteins and translation factors in S. aureus, supporting its oxidative and electrophilic mode of action in S. aureus. In phenotype analyses, the catalase KatA, the low molecular weight thiol bacillithiol and the urease provided protection against itaconic acid-induced oxidative and acid stress in S. aureus. Altogether, our results revealed that under physiological infection conditions, such as in the acidic phagolysome, itaconic acid is a highly effective antimicrobial against multi-resistant S. aureus isolates, which acts as weak acid causing an acid, oxidative and electrophilic stress response, leading to S-bacillithiolation and itaconation.

Mycothiol maintains the homeostasis and signalling of nitric oxide in Streptomyces coelicolor A3(2) M145

BACKGROUND

Previous studies have revealed a nitric oxide (NO) metabolic cycle in which NO, nitrate (NO3-), and nitrite (NO2-) circulate. The NO produced in this cycle serves as a signalling molecule that regulates actinorhodin (ACT) production via the DevS/DevR NO-dependent two-component system (TCS) in Streptomyces coelicolor A3(2) M145. However, the mechanisms involved in the regulation of NO signalling in S. coelicolor have not yet been elucidated. Mycothiol (MSH), a thiol molecule produced by Actinomyces, is involved in the defence mechanisms against oxidative stress. Therefore, this study focused on the correlation between intracellular NO and MSH levels.

RESULTS

To investigate the interaction of MSH with endogenously produced NO, we generated an S. coelicolor A3(2) strain deficient in MSH biosynthesis. This mutant strain exhibited a decrease in low-molecular-weight S-nitrosothiols and intracellular NO levels during culture compared to those of the wild-type strain. Moreover, the mutant strain exhibited reduced activity of the DevS/DevR TCS, a regulator of NO homeostasis and ACT production, from the early stage of culture, along with a decrease in ACT production compared to those of the wild-type strain.

CONCLUSIONS

This study suggests that MSH maintains intracellular NO homeostasis by forming S-nitrosomycothiol, which induces NO signalling. Finally, we propose a metabolic model in which MSH from endogenously produced NO facilitates the maintenance of both NO homeostasis and signalling in S. coelicolor A3(2) M145.

Antimicrobial Coatings for Medical Textiles via Reactive Organo-Selenium Compounds

Bleached and cationized cotton fabrics were chemically modified with reactive organoselenium compounds through the nucleophilic aromatic substitution (SNAr) reaction, which allowed for organo-selenium attachment onto the surface of cotton fabrics via covalent bonds and, in the case of the cationized cotton fabric, additional ionic interactions. The resulting textiles exhibited potent bactericidal activity against S. aureus (99.99% reduction), although only moderate activity was observed against E. coli. Fabrics treated with reactive organo-selenium compounds also exhibited fungicidal activities against C. albicans, and much higher antifungal activity was observed when organo-selenium compounds were applied to the cationized cotton in comparison to the bleached cotton. The treatment was found to be durable against rigorous washing conditions (non-ionic detergent/100 °C). This paper is the first report on a novel approach integrating the reaction of cotton fabrics with an organo-selenium antimicrobial agent. This approach is attractive because it provides a method for imparting antimicrobial properties to cotton fabrics which does not disrupt the traditional production processes of a textile mill.

Elucidating the Mechanisms of Cell-to-Cell Crosstalk in Probiotics Co-culture: A Proteomics Study of Limosilactobacillus reuteri ZJ625 and Ligilactobacillus salivarius ZJ614

Limosilactobacillus reuteri ZJ625 and Ligilactobacillus salivarius ZJ614 are potential probiotic bacteria with improved benefits when administered to the host as a multi-strain preparation. To elucidate the mechanisms of cell-to-cell crosstalk between these two strains, we studied their intracellular and extracellular proteomes in co-culture by liquid-chromatography mass-spectrometry (LC-MS) using Dionex Nano-RSLC and fusion mass spectrometer. The experiment consisted of five biological replicates, and samples were collected during the mid-exponential growth phase. The quantitative proteomic profiles revealed several differentially expressed proteins (DEPs), which are down- or up-regulated between and within groups for both the intracellular and extracellular proteomes. These DEPs include proteins synthesising autoinducer-2, a sensor compound for cell-to-cell bacterial crosstalk during quorum sensing in mixed culture. Other important DEPs identified include enolase, phosphoglycerate kinase, and l-lactate dehydrogenase, which play roles in carbohydrate metabolism. Proteins associated with transcription, ATP production and transport across the membrane, DNA repair, and those with the potential to bind to the host epithelium were also identified. The post-translational modifications associated with the proteins include oxidation, deamidation, and ammonia loss. Importantly, this study revealed a significant expression of S-ribosylhomocysteine lyase (luxS) involved in synthesising autoinducer-2 that plays important roles in quorum sensing, aiding bacterial cell-to-cell crosstalk in co-cultures. The proteome of L. salivarius ZJ614 was most affected when co-cultured with L. reuteri ZJ625. In contrast, omitting some medium components from the defined medium exerted more effects on L. reuteri ZJ625 than L. salivarius ZJ614.

Antioxidant defense of Deinococcus radiodurans: how does it contribute to extreme radiation resistance?

PURPOSE

Deinococcus radiodurans is an extremely radioresistant bacterium characterized by D10 of 10 kGy, and able to grow luxuriantly under chronic ionizing radiation of 60 Gy/h. The aim of this article is to review the antioxidant system of D. radiodurans and its possible role in the unusual resistance of this bacterium to ionizing radiation.

CONCLUSIONS

The unusual radiation resistance of D. radiodurans has apparently evolved as a side effect of the adaptation of this extremophile to other damaging environmental factors, especially desiccation. The antioxidant proteins and low-molecular antioxidants (especially low-molecular weight Mn2+ complexes and carotenoids, in particular, deinoxanthin), as well as protein and non-protein regulators, are important for the antioxidant defense of this species. Antioxidant protection of proteins from radiation inactivation enables the repair of DNA damage caused by ionizing radiation.

Chemoselective bicyclobutane-based mass spectrometric detection of biological thiols uncovers human and bacterial metabolites

Sulfur is an essential element of life. Thiol-containing metabolites in all organisms are involved in the regulation of diverse biological processes. Especially, the microbiome produces bioactive metabolites or biological intermediates of this compound class. The analysis of thiol-containing metabolites is challenging due to the lack of specific tools, making these compounds difficult to investigate selectively. We have now developed a new methodology comprising bicyclobutane for chemoselective and irreversible capturing of this metabolite class. We utilized this new chemical biology tool immobilized onto magnetic beads for the investigation of human plasma, fecal samples, and bacterial cultures. Our mass spectrometric investigation detected a broad range of human, dietary and bacterial thiol-containing metabolites and we even captured the reactive sulfur species cysteine persulfide in both fecal and bacterial samples. The described comprehensive methodology represents a new mass spectrometric strategy for the discovery of bioactive thiol-containing metabolites in humans and the microbiome.

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.

CRISPRi-microfluidics screening enables genome-scale target identification for high-titer protein production and secretion

Genome-scale target identification promises to guide microbial cell factory engineering for higher-titer production of biomolecules such as recombinant proteins (r-protein), but challenges remain due to the need not only for comprehensive genotypic perturbation but also in conjunction with high-throughput phenotypic screening strategies. Here, we developed a CRISPRi-microfluidics screening platform to systematically identify crucial gene targets that can be engineered to enhance r-protein secretion in Corynebacterium glutamicum. We created a CRISPR interference (CRISPRi) library containing 46,549 single-guide RNAs, where we aimed to unbiasedly target all genes for repression. Meanwhile, we developed a highly efficient droplet-based microfluidics system integrating the FlAsH-tetracysteine assay that enables screening of millions of strains to identify potential knockdowns conducive to nanobody VHH secretion. Among our highest-ranking candidates are a slew of previously unknown targets involved in transmembrane transport, amino-acid metabolism and redox regulation. Guided by these findings, we eventually constructed a hyperproducer for multiple proteins via combinatorial engineering of redox-response transcription factors. As the near-universal applicability of CRISPRi technology and the FlAsH-based screening platform, this procedure might be expanded to include a varied variety of microbial species and recombinant proteins.

Experimental Approaches for Investigating Disulfide-Based Redox Relays in Cells

Reversible oxidation of cysteine residues within proteins occurs naturally during normal cellular homeostasis and can increase during oxidative stress. Cysteine oxidation often leads to the formation of disulfide bonds, which can impact protein folding, stability, and function. Work in both prokaryotic and eukaryotic models over the past five decades has revealed several multiprotein systems that use thiol-dependent oxidoreductases to mediate disulfide bond reduction, formation, and/or rearrangement. Here, I provide an overview of how these systems operate to carry out disulfide exchange reactions in different cellular compartments, with a focus on their roles in maintaining redox homeostasis, transducing redox signals, and facilitating protein folding. Additionally, I review thiol-independent and thiol-dependent approaches for interrogating what proteins partner together in such disulfide-based redox relays. While the thiol-independent approaches rely either on predictive measures or standard procedures for monitoring protein-protein interactions, the thiol-dependent approaches include direct disulfide trapping methods as well as thiol-dependent chemical cross-linking. These strategies may prove useful in the systematic characterization of known and newly discovered disulfide relay mechanisms and redox switches involved in oxidant defense, protein folding, and cell signaling.

Catechin Mediates Ferroptosis to Exert an Anti-Inflammatory Effect on RAW 264.7 Cells

Catechin possesses a potential anti-inflammatory activity, but its anti-inflammatory mechanism is still unclear. Herein, the analysis of network pharmacology showed that catechin might mediate ferroptosis on macrophages to exhibit a significant anti-inflammatory effect on RAW264.7. The metabolomics further indicated that catechin might influence ferroptosis by activating two pathways of cysteine and methionine metabolism and glutathione metabolism, and inhibiting the pathway of ferroptosis to promote the reduction of l-methionine-s-oxide and s-glutathionyl-l-cysteine, and the reduction and synthesis of γ-glutamylcysteine. Furthermore, related proteins (MSRA, CDR, GSR and GCL) in three metabolic pathways and ferroptosis-related proteins (GPX4 and SLC7A11) might be relevant to catechin through molecular docking. Thus, we speculate that catechin plays an anti-inflammatory effect through mediating ferroptosis on RAW264.7, which still needs further focus on the detailed molecular mechanism.

N-Acetyl-Cysteinylated Streptophenazines from Streptomyces

Here, we describe two N-acetyl-cysteinylated streptophenazines (1 and 2) produced by the soil-derived Streptomyces sp. ID63040 and identified through a metabolomic approach. These metabolites attracted our interest due to their low occurrence frequency in a large library of fermentation broth extracts and their consistent presence in biological replicates of the producer strain. The compounds were found to possess broad-spectrum antibacterial activity while exhibiting low cytotoxicity. The biosynthetic gene cluster from Streptomyces sp. ID63040 was found to be highly similar to the streptophenazine reference cluster in the MIBiG database, which originates from the marine Streptomyces sp. CNB-091. Compounds 1 and 2 were the main streptophenazine products from Streptomyces sp. ID63040 at all cultivation times but were not detected in Streptomyces sp. CNB-091. The lack of obvious candidates for cysteinylation in the Streptomyces sp. ID63040 biosynthetic gene cluster suggests that the N-acetyl-cysteine moiety derives from cellular functions, most likely from mycothiol. Overall, our data represent an interesting example of how to leverage metabolomics for the discovery of new natural products and point out the often-neglected contribution of house-keeping cellular functions to natural product diversification.

Ohr - OhrR, a neglected and highly efficient antioxidant system: Structure, catalysis, phylogeny, regulation, and physiological roles

Ohrs (organic hydroperoxide resistance proteins) are antioxidant enzymes that play central roles in the response of microorganisms to organic peroxides. Here, we describe recent advances in the structure, catalysis, phylogeny, regulation, and physiological roles of Ohr proteins and of its transcriptional regulator, OhrR, highlighting their unique features. Ohr is extremely efficient in reducing fatty acid peroxides and peroxynitrite, two oxidants relevant in host-pathogen interactions. The highly reactive Cys residue of Ohr, named peroxidatic Cys (C_p), composes together with an arginine and a glutamate the catalytic triad. The catalytic cycle of Ohrs involves a condensation between a sulfenic acid (C_p-SOH) and the thiol of the second conserved Cys, leading to the formation of an intra-subunit disulfide bond, which is then reduced by dihydrolipoamide or lipoylated proteins. A structural switch takes place during catalysis, with the opening and closure of the active site by the so-called Arg-loop. Ohr is part of the Ohr/OsmC super-family that also comprises OsmC and Ohr-like proteins. Members of the Ohr, OsmC and Ohr-like subgroups present low sequence similarities among themselves, but share a high structural conservation, presenting two Cys residues in their active site. The pattern of gene expression is also distinct among members of the Ohr/OsmC subfamilies. The expression of ohr genes increases upon organic hydroperoxides treatment, whereas the signals for the upregulation of osmC are entry into the stationary phase and/or osmotic stress. For many ohr genes, the upregulation by organic hydroperoxides is mediated by OhrR, a Cys-based transcriptional regulator that only binds to its target DNAs in its reduced state. Since Ohrs and OhrRs are involved in virulence of some microorganisms and are absent in vertebrate and vascular plants, they may represent targets for novel therapeutic approaches based on the disruption of this key bacterial organic peroxide defense system.

Thiol Reductases in Deinococcus Bacteria and Roles in Stress Tolerance

Deinococcus species possess remarkable tolerance to extreme environmental conditions that generate oxidative damage to macromolecules. Among enzymes fulfilling key functions in metabolism regulation and stress responses, thiol reductases (TRs) harbour catalytic cysteines modulating the redox status of Cys and Met in partner proteins. We present here a detailed description of Deinococcus TRs regarding gene occurrence, sequence features, and physiological functions that remain poorly characterised in this genus. Two NADPH-dependent thiol-based systems are present in Deinococcus. One involves thioredoxins, disulfide reductases providing electrons to protein partners involved notably in peroxide scavenging or in preserving protein redox status. The other is based on bacillithiol, a low-molecular-weight redox molecule, and bacilliredoxin, which together protect Cys residues against overoxidation. Deinococcus species possess various types of thiol peroxidases whose electron supply depends either on NADPH via thioredoxins or on NADH via lipoylated proteins. Recent data gained on deletion mutants confirmed the importance of TRs in Deinococcus tolerance to oxidative treatments, but additional investigations are needed to delineate the redox network in which they operate, and their precise physiological roles. The large palette of Deinococcus TR representatives very likely constitutes an asset for the maintenance of redox homeostasis in harsh stress conditions.

Functional characterization of monothiol and dithiol glutaredoxins from Leptospira interrogans

Thiol redox proteins and low molecular mass thiols have essential functions in maintaining cellular redox balance in almost all living organisms. In the pathogenic bacterium Leptospira interrogans, several redox components have been described, namely, typical 2-Cys peroxiredoxin, a functional thioredoxin system, glutathione synthesis pathway, and methionine sulfoxide reductases. However, until now, information about proteins linked to GSH metabolism has not been reported in this pathogen. Glutaredoxins (Grxs) are GSH-dependent oxidoreductases that regulate and maintain the cellular redox state together with thioredoxins. This work deals with recombinant production at a high purity level, biochemical characterization, and detailed kinetic and structural study of the two Grxs (Lin1CGrx and Lin2CGrx) identified in L. interrogans serovar Copenhageni strain Fiocruz L1-130. Both recombinant LinGrxs exhibited the classical in vitro GSH-dependent 2-hydroxyethyl disulfide and dehydroascorbate reductase activity. Strikingly, we found that Lin2CGrx could serve as a substrate of methionine sulfoxide reductases A1 and B from L. interrogans. Distinctively, only recombinant Lin1CGrx contained a [2Fe2S] cluster confirming a homodimeric structure. The functionality of both LinGrxs was assessed by yeast complementation in null grx mutants, and both isoforms were able to rescue the mutant phenotype. Finally, our data suggest that protein glutathionylation as a post-translational modification process is present in L. interrogans. As a whole, our results support the occurrence of two new redox actors linked to GSH metabolism and iron homeostasis in L. interrogans.

A Fluorescent Probe to Detect Quick Disulfide Reductase Activity in Bacteria

The Trx and Grx systems, two disulfide reductase systems, play critical roles in various cell activities. There are great differences between the thiol redox systems in prokaryotes and mammals. Though fluorescent probes have been widely used to detect these systems in mammalian cells. Very few methods are available to detect rapid changes in the redox systems of prokaryotes. Here we investigated whether Fast-TRFS, a disulfide-containing fluorescent probe utilized in analysis of mammalian thioredoxin reductase, could be used to detect cellular disulfide reducibility in bacteria. Fast-TRFS exhibited good substrate qualities for both bacterial thioredoxin and GSH-glutaredoxin systems in vitro, with Trx system having higher reaction rate. Moreover, the Fast-TRFS was used to detect the disulfide reductase activity in various bacteria and redox-related gene null E. coli. Some glutaredoxin-deficient bacteria had stronger fast disulfide reducibility. The Trx system was shown to be the predominant disulfide reductase for fast disulfide reduction rather than the Grx system. These results demonstrated that Fast-TRFS is a viable probe to detect thiol-dependent disulfide reductases in bacteria. It also indicated that cellular disulfide reduction could be classified into fast and slow reaction, which are predominantly catalyzed by E. coli Trx and Grx system, respectively.

Antibacterial Profile of a Microbicidal Agent Targeting Tyrosine Phosphatases and Redox Thiols, Novel Drug Targets

The activity profile of a protein tyrosine phosphatase (PTP) inhibitor and redox thiol oxidant, nitropropenyl benzodioxole (NPBD), was investigated across a broad range of bacterial species. In vitro assays assessed inhibitory and lethal activity patterns, the induction of drug variants on long term exposure, the inhibitory interactions of NPBD with antibiotics, and the effect of plasma proteins and redox thiols on activity. A literature review indicates the complexity of PTP and redox signaling and suggests likely metabolic targets. NPBD was broadly bactericidal to pathogens of the skin, respiratory, urogenital and intestinal tracts. It was effective against antibiotic resistant strains and slowly replicating and dormant cells. NPBD did not induce resistant or drug-tolerant phenotypes and showed low cross reactivity with antibiotics in synergy assays. Binding to plasma proteins indicated lowered in-vitro bioavailability and reduction of bactericidal activity in the presence of thiols confirmed the contribution of thiol oxidation and oxidative stress to lethality. This report presents a broad evaluation of the antibacterial effect of PTP inhibition and redox thiol oxidation, illustrates the functional diversity of bacterial PTPs and redox thiols, and supports their consideration as novel targets for antimicrobial drug development. NPBD is a dual mechanism agent with an activity profile which supports consideration of tyrosine phosphatases and bacterial antioxidant systems as promising targets for drug development.

Influence of Redox Imbalances on the Transposition of Insertion Sequences in Deinococcus geothermalis

The transposition of insertion sequence elements was evaluated among different Deinococcus geothermalis lineages, including the wild-type, a cystine importer-disrupted mutant, a complemented strain, and a cystine importer-overexpressed strain. Cellular growth reached early exponential growth at OD₆₀₀ 2.0 and late exponential growth at OD₆₀₀ 4.0. Exposing the cells to hydrogen peroxide (80–100 mM) resulted in the transposition of insertion sequences (ISs) in genes associated with the carotenoid biosynthesis pathway. Particularly, ISDge7 (an IS5 family member) and ISDge5 (an IS701 family member) from the cystine importer-disrupted mutant were transposed into phytoene desaturase (dgeo_0524) via replicative transposition. Further, the cystine importer-overexpressed strain Δdgeo_1985R showed transposition of both ISDge2 and ISDge5 elements. In contrast, IS transposition was not detected in the complementary strain. Interestingly, a cystine importer-overexpressing strain exhibited streptomycin resistance, indicating that point mutation occurred in the rpsL (dgeo_1873) gene encoding ribosomal protein S12. qRT-PCR analyses were then conducted to evaluate the expression of oxidative stress response genes, IS elements, and low-molecular-weight thiol compounds such as mycothiol and bacillithiol. Nevertheless, the mechanisms that trigger IS transposition in redox imbalance conditions remain unclear. Here, we report that the active transposition of different IS elements was affected by intracellular redox imbalances caused by cystine importer deficiencies or overexpression.

Redox proteomic study of Bacillus cereus thiol proteome during fermentative anaerobic growth

Background

Bacillus cereus is a notorious foodborne pathogen, which can grow under anoxic conditions. Anoxic growth is supported by endogenous redox metabolism, for which the thiol redox proteome serves as an interface. Here, we studied the cysteine (Cys) proteome dynamics of B. cereus ATCC 14579 cells grown under fermentative anoxic conditions. We used a quantitative thiol trapping method combined with proteomics profiling.

Results

In total, we identified 153 reactive Cys residues in 117 proteins participating in various cellular processes and metabolic pathways, including translation, carbohydrate metabolism, and stress response. Of these reactive Cys, 72 were detected as reduced Cys. The B. cereus Cys proteome evolved during growth both in terms of the number of reduced Cys and the Cys-containing proteins identified, reflecting its growth-phase-dependence. Interestingly, the reduced status of the B. cereus thiol proteome increased during growth, concomitantly to the decrease of extracellular oxidoreduction potential.

Conclusions

Taken together, our data show that the B. cereus Cys proteome during unstressed fermentative anaerobic growth is a dynamic entity and provide an important foundation for future redox proteomic studies in B. cereus and other organisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07962-y.

Emerging Roles of Posttranslational Modifications in Plant-Pathogenic Fungi and Bacteria

Posttranslational modifications (PTMs) play crucial roles in regulating protein function and thereby control many cellular processes and biological phenotypes in both eukaryotes and prokaryotes. Several recent studies illustrate how plant fungal and bacterial pathogens use these PTMs to facilitate development, stress response, and host infection. In this review, we discuss PTMs that have key roles in the biological and infection processes of plant-pathogenic fungi and bacteria. The emerging roles of PTMs during pathogen-plant interactions are highlighted. We also summarize traditional tools and emerging proteomics approaches for PTM research. These discoveries open new avenues for investigating the fundamental infection mechanisms of plant pathogens and the discovery of novel strategies for plant disease control.

Biogenic Selenium Nanoparticles: A Fine Characterization to Unveil Their Thermodynamic Stability

Among the plethora of available metal(loid) nanomaterials (NMs), those containing selenium are interesting from an applicative perspective, due to their high biocompatibility. Microorganisms capable of coping with toxic Se-oxyanions generate mostly Se nanoparticles (SeNPs), representing an ideal and green alternative over the chemogenic synthesis to obtain thermodynamically stable NMs. However, their structural characterization, in terms of biomolecules and interactions stabilizing the biogenic colloidal solution, is still a black hole that impairs the exploitation of biogenic SeNP full potential. Here, spherical and thermodynamically stable SeNPs were produced by a metal(loid) tolerant Micrococcus sp. Structural characterization obtained by Scanning Electron Microscopy (SEM) revealed that these SeNPs were surrounded by an organic material that contributed the most to their electrosteric stabilization, as indicated by Zeta (ζ) potential measurements. Proteins were strongly adsorbed on the SeNP surface, while lipids, polysaccharides, and nucleic acids more loosely interacted with SeNMs as highlighted by Fourier Transform Infrared Spectroscopy (FTIR) and overall supported by multivariate statistical analysis. Nevertheless, all these contributors were fundamental to maintain SeNPs stable, as, upon washing, the NM-containing extract showed the arising of aggregated SeNPs alongside Se nanorods (SeNRs). Besides, Density Functional Theory (DFT) calculation unveiled how thiol-containing molecules appeared to play a role in SeO₃²⁻ bioreduction, stress oxidative response, and SeNP stabilization.

Determination of glutathione-binding to proteins by fluorescence spectroscopy

Glutathione (GSH) is the most abundant non-protein thiol and its cellular concentration has been reported as 17 mM in Escherichia coli. This study introduces a label-free method to determine the binding affinity of GSH to proteins, utilizing the intrinsic fluorescence of proteins; the dissociation constants of GSH for d-arabinose 5-phosphate isomerase KdsD, fumarase C, malate dehydrogenase, and RNA polymerase subunit α have been determined as 96 ± 8, 246 ± 42, 292 ± 78, and 296 ± 97 μM, respectively. The dissociation constants, less than 2% of the cellular concentration of GSH, suggests that protein-GSH interactions are strong enough to make all of the GSH-binding sites occupied fully. The method described here may be applicable to other proteins.

The Bacillus subtilis monothiol bacilliredoxin BrxC (YtxJ) and the Bdr (YpdA) disulfide reductase reduce S-bacillithiolated proteins

The bacterial cytosol is generally a reducing environment with protein cysteine residues maintained in their thiol form. The low molecular weight thiol bacillithiol (BSH) serves as a general thiol reductant, analogous to glutathione, in a wide range of bacterial species. Proteins modified by disulfide bond formation with BSH (S-bacillithiolation) are reduced by the action of bacilliredoxins, BrxA and BrxB. Here, the YtxJ protein is identified as a monothiol bacilliredoxin, renamed BrxC, and is implicated in BSH removal from oxidized cytosolic proteins, including the glyceraldehyde 3-phosphate dehydrogenases GapA and GapB. BrxC can also debacillithiolate the mixed disulfide form of the bacilliredoxin BrxB. Bdr is a thioredoxin reductase-like flavoprotein with bacillithiol-disulfide (BSSB) reductase activity. Here, Bdr is shown to additionally function as a bacilliredoxin reductase. Bdr and BrxB function cooperatively to debacillithiolate OhrR, a transcription factor regulated by S-bacillithiolation on its sole cysteine residue. Collectively, these results expand our understanding of the BSH redox network comprised of three bacilliredoxins and a BSSB reductase that serve to counter the widespread protein S-bacillithiolation that results from conditions of disulfide stress.

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Bacillithiol is the major low molecular weight thiol in Bacillus subtilis.

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Oxidative stress leads to protein S-bacillithiolation.

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BrxC functions as a monothiol class bacilliredoxin.

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The Bdr bacillithiol disulfide reductase is also a bacilliredoxin.

Overview of structurally homologous flavoprotein oxidoreductases containing the low Mr thioredoxin reductase-like fold - A functionally diverse group

Structural studies show that enzymes have a limited number of unique folds, although structurally related enzymes have evolved to perform a large variety of functions. In this review, we have focused on enzymes containing the low molecular weight thioredoxin reductase (low M_r TrxR) fold. This fold consists of two domains, both containing a three-layer ββα sandwich Rossmann-like fold, serving as flavin adenine dinucleotide (FAD) and, in most cases, pyridine nucleotide (NAD(P)H) binding-domains. Based on a search of the Protein Data Bank for all published structures containing the low M_r TrxR-like fold, we here present a comprehensive overview of enzymes with this structural architecture. These range from TrxR-like ferredoxin/flavodoxin NAD(P)⁺ oxidoreductases, through glutathione reductase, to NADH peroxidase. Some enzymes are solely composed of the low M_r TrxR-like fold, while others contain one or two additional domains. In this review, we give a detailed description of selected enzymes containing only the low M_r TrxR-like fold, however, catalyzing a diversity of chemical reactions. Our overview of this structurally similar, yet functionally distinct group of flavoprotein oxidoreductases highlights the fascinating and increasing number of studies describing the diversity among these enzymes, especially during the last decade(s).

Microorganisms: A Potential Source of Bioactive Molecules for Antioxidant Applications

Oxidative stress originates from an elevated intracellular level of free oxygen radicals that cause lipid peroxidation, protein denaturation, DNA hydroxylation, and apoptosis, ultimately impairing cell viability. Antioxidants scavenge free radicals and reduce oxidative stress, which further helps to prevent cellular damage. Medicinal plants, fruits, and spices are the primary sources of antioxidants from time immemorial. In contrast to plants, microorganisms can be used as a source of antioxidants with the advantage of fast growth under controlled conditions. Further, microbe-based antioxidants are nontoxic, noncarcinogenic, and biodegradable as compared to synthetic antioxidants. The present review aims to summarize the current state of the research on the antioxidant activity of microorganisms including actinomycetes, bacteria, fungi, protozoa, microalgae, and yeast, which produce a variety of antioxidant compounds, i.e., carotenoids, polyphenols, vitamins, and sterol, etc. Special emphasis is given to the mechanisms and signaling pathways followed by antioxidants to scavenge Reactive Oxygen Species (ROS), especially for those antioxidant compounds that have been scarcely investigated so far.

Common Signal Transduction Molecules Activated by Bacterial Entry into a Host Cell and by Reactive Oxygen Species

Significance: An increasing number of pathogens are acquiring resistance to antibiotics. Efficient antimicrobial drug regimens are important even for the most advanced therapies, which range from cutting-edge invasive clinical protocols, such as robotic surgeries, to the treatment of harmless bacterial diseases and to minor scratches to the skin. Therefore, there is an urgent need to survey alternative antimicrobial drugs that can reinforce or replace existing antibiotics. Recent Advances: Bacterial proteins that are critical for energy metabolism, promising novel anticancer thiourea derivatives, and the use of synthetic molecules that increase the sensitivity of currently used antibiotics are among the recently discovered antimicrobial drugs. Critical Issues: In the development of new drugs, serious consideration should be given to the previous bacterial evolutionary selection caused by antibiotics, by the high proliferation rate of bacteria, and by the simple prokaryotic structure of bacteria. Future Directions: The survey of drug targets has mainly focused on bacterial proteins, although host signaling molecules involved in the treatment of various pathologies may have unknown antimicrobial characteristics. Recent data have suggested that small molecule inhibitors might enhance the effect of antibiotics, for example, by limiting bacterial entry into host cells. Phagocytosis, the mechanism by which host cells internalize pathogens through β-actin cytoskeletal rearrangement, induces calcium signaling, small GTPase activation, and phosphorylation of the phosphatidylinositol 3-kinase-serine/threonine-specific protein kinase B pathway. Antioxid. Redox Signal. 34, 486-503.

Analysis of disulphide bond linkage between CoA and protein cysteine thiols during sporulation and in spores of Bacillus species

Spores of Bacillus species have novel properties, which allow them to lie dormant for years and then germinate under favourable conditions. In the current work, the role of a key metabolic integrator, coenzyme A (CoA), in redox regulation of growing cells and during spore formation in Bacillus megaterium and Bacillus subtilis is studied. Exposing these growing cells to oxidising agents or carbon deprivation resulted in extensive covalent protein modification by CoA (termed protein CoAlation), through disulphide bond formation between the CoA thiol group and a protein cysteine. Significant protein CoAlation was observed during sporulation of B. megaterium, and increased largely in parallel with loss of metabolism in spores. Mass spectrometric analysis identified four CoAlated proteins in B. subtilis spores as well as one CoAlated protein in growing B. megaterium cells. All five of these proteins have been identified as moderately abundant in spores. Based on these findings and published studies, protein CoAlation might be involved in facilitating establishment of spores' metabolic dormancy, and/or protecting sensitive sulfhydryl groups of spore enzymes.

The Crystal Structures of Bacillithiol Disulfide Reductase Bdr (YpdA) Provide Structural and Functional Insight into a New Type of FAD-Containing NADPH-Dependent Oxidoreductase

Low G+C Gram-positive Firmicutes, such as the clinically important pathogens Staphylococcus aureus and Bacillus cereus, use the low-molecular weight thiol bacillithiol (BSH) as a defense mechanism to buffer the intracellular redox environment and counteract oxidative stress encountered by human neutrophils during infections. The protein YpdA has recently been shown to function as an essential NADPH-dependent reductase of oxidized bacillithiol disulfide (BSSB) resulting from stress responses and is crucial for maintaining the reduced pool of BSH and cellular redox balance. In this work, we present the first crystallographic structures of YpdAs, namely, those from S. aureus and B. cereus. Our analyses reveal a uniquely organized biological tetramer; however, the structure of the monomeric subunit is highly similar to those of other flavoprotein disulfide reductases. The absence of a redox active cysteine in the vicinity of the FAD isoalloxazine ring implies a new direct disulfide reduction mechanism, which is backed by the presence of a potentially gated channel, serving as a putative binding site for BSSB in the proximity of the FAD cofactor. We also report enzymatic activities for both YpdAs, which along with the structures presented in this work provide important structural and functional insight into a new class of FAD-containing NADPH-dependent oxidoreductases, related to the emerging fight against pathogenic bacteria.

Mechanisms and consequences of protein cysteine oxidation: the role of the initial short-lived intermediates

Thiol groups in protein cysteine (Cys) residues can undergo one- and two-electron oxidation reactions leading to the formation of thiyl radicals or sulfenic acids, respectively. In this mini-review we summarize the mechanisms and kinetics of the formation of these species by biologically relevant oxidants. Most of the latter react with the deprotonated form of the thiol. Since the pKa of the thiols in protein cysteines are usually close to physiological pH, the thermodynamics and the kinetics of their oxidation in vivo are affected by the acidity of the thiol. Moreover, the protein microenvironment has pronounced effects on cysteine residue reactivity, which in the case of the oxidation mediated by hydroperoxides, is known to confer specificity to particular protein cysteines. Despite their elusive nature, both thiyl radicals and sulfenic acids are involved in the catalytic mechanism of several enzymes and in the redox regulation of protein function and/or signaling pathways. They are usually short-lived species that undergo further reactions that converge in the formation of different stable products, resulting in several post-translational modifications of the protein. Some of these can be reversed through the action of specific cellular reduction systems. Others damage the proteins irreversibly, and can make them more prone to aggregation or degradation.

Polymer Electrochromism Driven by Metabolic Activity Facilitates Rapid and Facile Bacterial Detection and Susceptibility Evaluation

The electrochromism of a water-soluble naturally oxidized electrochromic polymer, ox-PPE, is harnessed for rapid and facile bacterial detection, discrimination, and susceptibility testing. The ox-PPE solution shows distinct colorimetric and spectroscopic changes within 30 min when mixed with live bacteria. For the underlying mechanism, it is found that ox-PPE responds to the reducing species (e.g. cysteine and glutathione) released by metabolically active bacteria. This reduction reaction is ubiquitous among various bacterial strains, with a noticeable difference that enables discrimination of Gram-negative and Gram-positive bacterial strains. Combining ox-PPE with antibiotics, methicillin-susceptible and -resistant S. aureus can be differentiated within 2.5 h. Proof-of-concept demonstration of ox-PPE for antimicrobial susceptibility testing is carried out by incubating E. coli with various antibiotics. The obtained minimum inhibition concentrations are consistent with the conventional culture-based methods, but with the procedure time significantly shortened to 3 h.

Total Glucosides of Peony Protect Cardiomyocytes against Oxidative Stress and Inflammation by Reversing Mitochondrial Dynamics and Bioenergetics

Total glucosides of peony (TGP) are used to treat rheumatoid arthritis and systemic lupus erythematosus. We explored the protective effects of TGP on cardiomyocyte oxidative stress and inflammation in the presence of hydrogen peroxide by focusing on mitochondrial dynamics and bioenergetics. Our study demonstrated that hydrogen peroxide significantly repressed cardiomyocyte viability and promoted cell apoptosis through induction of the mitochondrial death pathway. TGP treatment sustained cardiomyocyte viability, reduced cardiomyocyte apoptosis, and decreased inflammation and oxidative stress. Molecular investigation indicated that hydrogen peroxide caused mitochondrial dynamics disruption and bioenergetics reduction in cardiomyocytes, but this alteration could be normalized by TGP. We found that disruption of mitochondrial dynamics abolished the regulatory effects of TGP on mitochondrial bioenergetics; TGP modulated mitochondrial dynamics through the AMP-activated protein kinase (AMPK) pathway; and inhibition of AMPK alleviated the protective effects of TGP on mitochondria. Our results showed that TGP treatment reduces cardiomyocyte oxidative stress and inflammation in the presence of hydrogen peroxide by correcting mitochondrial dynamics and enhancing mitochondrial bioenergetics. Additionally, the regulatory effects of TGP on mitochondrial function seem to be mediated through the AMPK pathway. These findings are promising for myocardial injury in patients with rheumatoid arthritis and systemic lupus erythematosus.

Thiol-based redox switches in the major pathogen Staphylococcus aureus

Staphylococcus aureus is a major human pathogen, which encounters reactive oxygen, nitrogen, chlorine, electrophile and sulfur species (ROS, RNS, RCS, RES and RSS) by the host immune system, during cellular metabolism or antibiotics treatments. To defend against redox active species and antibiotics, S. aureus is equipped with redox sensing regulators that often use thiol switches to control the expression of specific detoxification pathways. In addition, the maintenance of the redox balance is crucial for survival of S. aureus under redox stress during infections, which is accomplished by the low molecular weight (LMW) thiol bacillithiol (BSH) and the associated bacilliredoxin (Brx)/BSH/bacillithiol disulfide reductase (YpdA)/NADPH pathway. Here, we present an overview of thiol-based redox sensors, its associated enzymatic detoxification systems and BSH-related regulatory mechanisms in S. aureus, which are important for the defense under redox stress conditions. Application of the novel Brx-roGFP2 biosensor provides new insights on the impact of these systems on the BSH redox potential. These thiol switches of S. aureus function in protection against redox active desinfectants and antimicrobials, including HOCl, the AGXX® antimicrobial surface coating, allicin from garlic and the naphthoquinone lapachol. Thus, thiol switches could be novel drug targets for the development of alternative redox-based therapies to combat multi-drug resistant S. aureus isolates.

Oxidized LDL Causes Endothelial Apoptosis by Inhibiting Mitochondrial Fusion and Mitochondria Autophagy

Oxidized low-density lipoprotein (ox-LDL)-induced endothelial dysfunction is an initial step toward atherosclerosis development. Mitochondria damage correlates with ox-LDL-induced endothelial injury through an undefined mechanism. We explored the role of optic atrophy 1 (Opa1)-related mitochondrial fusion and mitophagy in ox-LDL-treated endothelial cells, focusing on mitochondrial damage and cell apoptosis. Oxidized low-density lipoprotein treatment reduced endothelial cell viability by increasing apoptosis. Endothelial cell proliferation and migration were also impaired by ox-LDL. At the molecular level, mitochondrial dysfunction was induced by ox-LDL, as demonstrated by decreased mitochondrial membrane potential, increased mitochondrial reactive oxygen species production, augmented mitochondrial permeability transition pore openings, and elevated caspase-3/9 activity. Mitophagy and mitochondrial fusion were also impaired by ox-LDL. Opa1 overexpression reversed this effect by increasing endothelial cell viability and decreasing apoptosis. Interestingly, inhibition of mitophagy or mitochondrial fusion through transfection of siRNAs against Atg5 or Mfn2, respectively, abolished the protective effects of Opa1. Our results illustrate the role of Opa1-related mitochondrial fusion and mitophagy in sustaining endothelial cell viability and mitochondrial homeostasis under ox-LDL stress.

Phosphoglycerate mutase 5 exacerbates cardiac ischemia-reperfusion injury through disrupting mitochondrial quality control

The death of cardiomyocytes either through apoptosis or necroptosis is the pathological feature of cardiac ischemia-reperfusion (I/R) injury. Phosphoglycerate mutase 5 (PGAM5), a mitochondrially-localized serine/threonine-protein phosphatase, functions as a novel inducer of necroptosis. However, intense debate exists regarding the effect of PGAM5 on I/R-related cardiomyocyte death. Using cardiac-specific PGAM5 knockout (PGAM5^CKO) mice, we comprehensively investigated the precise contribution and molecular mechanism of PGAM5 in cardiomyocyte death. Our data showed that both PGAM5 transcription and expression were upregulated in reperfused myocardium. Genetic ablation of PGAM5 suppressed I/R-mediated necroptosis but failed to prevent apoptosis activation, a result that went along with improved heart function and decreased inflammation response. Regardless of PGAM5 status, mitophagy-related cell death was not apparent following I/R. Under physiological conditions, PGAM5 overexpression in primary cardiomyocytes was sufficient to induce cardiomyocyte necroptosis rather than apoptosis. At the sub-cellular levels, PGAM5 deficiency increased mitochondrial DNA copy number and transcript levels, normalized mitochondrial respiration, repressed mitochondrial ROS production, and prevented abnormal mPTP opening upon I/R. Molecular investigation demonstrated that PGAM5 deletion interrupted I/R-mediated Drp^S637 dephosphorylation but failed to abolish I/R-induce Drp1^S616 phosphorylation, resulting in partial inhibition of mitochondrial fission. In addition, declining Mfn2 and OPA1 levels were restored in PGAM5^CKO cardiomyocytes following I/R. Nevertheless, PGAM5 depletion did not rescue suppressed mitophagy upon I/R injury. In conclusion, our results provide an insight into the specific role and working mechanism of PGAM5 in driving cardiomyocyte necroptosis through imposing mitochondrial quality control in cardiac I/R injury.

Redox regulation in host-pathogen interactions: thiol switches and beyond

Our organism is exposed to pathogens on a daily basis. Owing to this age-old interaction, both pathogen and host evolved strategies to cope with these encounters. Here, we focus on the consequences of the direct encounter of cells of the innate immune system with bacteria. First, we will discuss the bacterial strategies to counteract powerful reactive species. Our emphasis lies on the effects of hypochlorous acid (HOCl), arguably the most powerful oxidant produced inside the phagolysosome of professional phagocytes. We will highlight individual examples of proteins in gram-negative bacteria activated by HOCl via thiol-disulfide switches, methionine sulfoxidation, and N-chlorination of basic amino acid side chains. Second, we will discuss the effects of HOCl on proteins of the host. Recent studies have shown that both host and bacteria address failing protein homeostasis by activation of chaperone-like holdases through N-chlorination. After discussing the role of individual proteins in the HOCl-defense, we will turn our attention to the examination of effects on host and pathogen on a systemic level. Recent studies using genetically encoded redox probes and redox proteomics highlight differences in redox homeostasis in host and pathogen and give first hints at potential cellular HOCl signaling beyond thiol-disulfide switch mechanisms.

The Industrial Organism Corynebacterium glutamicum Requires Mycothiol as Antioxidant to Resist Against Oxidative Stress in Bioreactor Cultivations

In aerobic environments, bacteria are exposed to reactive oxygen species (ROS). To avoid an excess of ROS, microorganisms are equipped with powerful enzymatic and non-enzymatic antioxidants. Corynebacterium glutamicum, a widely used industrial platform organism, uses mycothiol (MSH) as major low molecular weight (LMW) thiol and non-enzymatic antioxidant. In aerobic bioreactor cultivations, C. glutamicum becomes exposed to oxygen concentrations surpassing the air saturation, which are supposed to constitute a challenge for the intracellular MSH redox balance. In this study, the role of MSH was investigated at different oxygen levels (pO₂) in bioreactor cultivations in C. glutamicum. Despite the presence of other highly efficient antioxidant systems, such as catalase, the MSH deficient ΔmshC mutant was impaired in growth in bioreactor experiments performed at pO₂ values of 30%. At a pO₂ level of 20%, this growth defect was abolished, indicating a high susceptibility of the MSH-deficient mutant towards elevated oxygen concentrations. Bioreactor experiments with C. glutamicum expressing the Mrx1-roGFP2 redox biosensor revealed a strong oxidative shift in the MSH redox potential (E_MSH) at pO₂ values above 20%. This indicates that the LMW thiol MSH is an essential antioxidant to maintain the robustness and industrial performance of C. glutamicum during aerobic fermentation processes.

Matrine attenuates cardiomyocyte ischemia-reperfusion injury through activating AMPK/Sirt3 signaling pathway

Matrine has been found to affect cell viability and function. In the present study, we explored the cardioprotective role of matrine in cardiomyocyte damage under hypoxia/reoxygenation. In vitro, cardiomyocyte hypoxia/reoxygenation was used to mimic ischemia/reperfusion injury in the presence of matrine. After exposure to hypoxia/reoxygenation, cardiomyocyte viability was reduced and cell apoptosis was increased; this alteration was inhibited by matrine. At the molecular levels, Sirt3 and AMPK were significantly downregulated by hypoxia/reoxygenation injury whereas matrine administration was able to upregulate Sirt3 and AMPK expression and activity in the presence of hypoxia/reoxygenation. Interestingly, inhibition of Sirt3/AMPK pathway abolished the cardioprotective action of matrine on cardiomyocyte in the presence of hypoxia/reoxygenation injury, resulting into cardiomyocyte viability reduction and cell death augmentation. Altogether, our results demonstrated a novel role played by matrine in regulating cardiomyocyte viability and death in the presence of hypoxia/reoxygenation, with a potential application in the clinical practice for the treatment of patients with myocardial infarction.

The plant-derived naphthoquinone lapachol causes an oxidative stress response in Staphylococcus aureus

Staphylococcus aureus is a major human pathogen, which causes life-threatening systemic and chronic infections and rapidly acquires resistance to multiple antibiotics. Thus, new antimicrobial compounds are required to combat infections with drug resistant S. aureus isolates. The 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone lapachol was previously shown to exert antimicrobial effects. In this study, we investigated the antimicrobial mode of action of lapachol in S. aureus using RNAseq transcriptomics, redox biosensor measurements, S-bacillithiolation assays and phenotype analyses of mutants. In the RNA-seq transcriptome, lapachol caused an oxidative and quinone stress response as well as protein damage as revealed by induction of the PerR, HypR, QsrR, MhqR, CtsR and HrcA regulons. Lapachol treatment further resulted in up-regulation of the SigB and GraRS regulons, which is indicative for cell wall and general stress responses. The redox-cycling mode of action of lapachol was supported by an elevated bacillithiol (BSH) redox potential (E_BSH), higher endogenous ROS levels, a faster H₂O₂ detoxification capacity and increased thiol-oxidation of GapDH and the HypR repressor in vivo. The ROS scavenger N-acetyl cysteine and microaerophilic growth conditions improved the survival of lapachol-treated S. aureus cells. Phenotype analyses revealed an involvement of the catalase KatA and the Brx/BSH/YpdA pathway in protection against lapachol-induced ROS-formation in S. aureus. However, no evidence for irreversible protein alkylation and aggregation was found in lapachol-treated S. aureus cells. Thus, the antimicrobial mode of action of lapachol in S. aureus is mainly caused by ROS formation resulting in an oxidative stress response, an oxidative shift of the E_BSH and increased protein thiol-oxidation. As ROS-generating compound, lapachol is an attractive alternative antimicrobial to combat multi-resistant S. aureus isolates.

Roles of RcsA, an AhpD Family Protein, in Reactive Chlorine Stress Resistance and Virulence in Pseudomonas aeruginosa

Reactive chlorine species (RCS), particularly hypochlorous acid (HOCl), are powerful antimicrobial oxidants generated by biological pathways and chemical syntheses. Pseudomonas aeruginosa is an important opportunistic pathogen that has adapted mechanisms for protection and survival in harsh environments, including RCS exposure. Based on previous transcriptomic studies of HOCl exposure in P. aeruginosa, we found that the expression of PA0565, or rcsA, which encodes an alkyl hydroperoxidase D-like protein, exhibited the highest induction among the RCS-induced genes. In this study, rcsA expression was dominant under HOCl stress and greatly increased under HOCl-related stress conditions. Functional analysis of RcsA showed that the distinguishing core amino acid residues Cys60, Cys63, and His67 were required for the degradation of sodium hypochlorite (NaOCl), suggesting an extended motif in the AhpD family. After allelic exchange mutagenesis in the P. aeruginosa rcsA, the P. aeruginosa rcsA deletion mutant showed significantly decreased HOCl resistance. Ectopic expression of P. aeruginosa rcsA led to significantly increased NaOCl resistance in Escherichia coli Moreover, the pathogenicity of the rcsA mutant decreased dramatically in both Caenorhabditis elegans and Drosophila melanogaster host model systems compared to the wild type (WT). Finally, the Cys60, Cys63, and His67 variants of RcsA were unsuccessful at complementing phenotypes of the rcsA mutant. Overall, our data indicate the importance of P. aeruginosa RcsA in defense against HOCl stress under disinfections and during infections of hosts, which involves the catalytic Cys60, Cys63, and His67 residues.IMPORTANCE Pseudomonas aeruginosa is a common pathogen that is a major cause of serious infections in many hosts. Hypochlorous acid (HOCl) is a potent antimicrobial agent found in household bleach and is a widely used disinfectant. P. aeruginosa has evolved adaptive mechanisms for protection and survival during HOCl exposure. We identified P. aeruginosa rcsA as a HOCl-responsive gene encoding an antioxidant protein that may be involved in HOCl degradation. RcsA has a distinguishing core motif containing functional Cys60, Cys63, and His67 residues. P. aeruginosa rcsA plays an important role in bleach tolerance, with expression of P. aeruginosa rcsA in Escherichia coli also conferring HOCl resistance. Interestingly, RcsA is required for full virulence in worm and fruit fly infection models, indicating a correlation between mechanisms of bleach toxicity and host immunity during infection. This provides new insights into the mechanisms used by P. aeruginosa to persist in harsh environments such as hospitals.

SERCA Overexpression Improves Mitochondrial Quality Control and Attenuates Cardiac Microvascular Ischemia-Reperfusion Injury

Despite significant advances in the treatment of myocardial ischemia-reperfusion (I/R) injury, coronary circulation is a so far neglected target of cardioprotection. In this study, we investigated the molecular mechanisms underlying I/R injury to cardiac microcirculation. Using gene delivery, we analyzed microvascular protective effects of sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase (SERCA) on the reperfused heart and examined the role of SERCA in regulating mitochondrial quality control in cardiac microvascular endothelial cells (CMECs). Our data showed that SERCA overexpression attenuates lumen stenosis, inhibits microthrombus formation, reduces inflammation response, and improves endothelium-dependent vascular relaxation. In vitro experiments demonstrated that SERCA overexpression improves endothelial viability, barrier integrity, and cytoskeleton assembly in CMECs. Mitochondrial quality control, including mitochondrial fusion, mitophagy, bioenergetics, and biogenesis, were disrupted by I/R injury but were restored by SERCA overexpression. SERCA overexpression also restored mitochondrial quality control by inhibiting calcium overload, inactivating xanthine oxidase (XO), and reducing intracellular/mitochondrial reactive oxygen species (ROS). Administration of exogenous XO or a calcium channel agonist abolished the protective effects of SERCA overexpression on mitochondrial quality control and offset the beneficial effects of SERCA overexpression after cardiac microvascular I/R injury. These findings indicate that SERCA overexpression may be an effective approach to targeting cardiac microvascular I/R injury by regulating calcium/XO/ROS signaling and preserving mitochondrial quality control.

Biocatalytic Oxidation of Alcohols

Enzymatic methods for the oxidation of alcohols are critically reviewed. Dehydrogenases and oxidases are the most prominent biocatalysts, enabling the selective oxidation of primary alcohols into aldehydes or acids. In the case of secondary alcohols, region and/or enantioselective oxidation is possible. In this contribution, we outline the current state-of-the-art and discuss current limitations and promising solutions.

Irisin alleviates LPS-induced liver injury and inflammation through inhibition of NLRP3 inflammasome and NF-κB signaling

Lipopolysaccharide (LPS) provokes severe inflammation and cell death in sepsis, with liver being the major affected organ. Up-to-date, neither the mechanism of action nor target treatment is readily available for LPS-induced liver injury. This study examined the effect of irisin, an endogenous hormonal peptide, on LPS-induced liver injury using animal and cell models, and the mechanism involved with a special focus on pyroptosis. Irisin is known to regulate glucose metabolism, inflammation, and immune response, while our earlier work denoted the anti-inflammatory and anti-apoptotic properties for irisin. Inflammatory factors and AST/ALT were also detected. Pyroptosis, apoptosis, and reactive oxygen species (ROS) were evaluated using PI staining, TUNEL staining, DCFH-DA fluorescence, and western blot, respectively. Our results indicated that irisin attenuated LPS-induced liver injury and release of inflammatory cytokines. Increased activity of NLRP3 inflammasome was discovered in LPS-challenged Raw264.7 cells, along with elevated levels of inflammation and apoptosis, the effects of which were mediated by activation of ROS and nuclear factor κB (NF-κB) signaling. These changes were reversed following irisin treatment. Our study demonstrated that irisin countered LPS-mediated liver injury via inhibiting apoptosis, NLRP3 inflammasome activation and NF-κB signaling. These findings revealed the role of irisin as a promising new anti-pyroptosis/apoptosis agent to reconcile the onset and progression of septic liver injury.

S-glutathionylation proteome profiling reveals a crucial role of a thioredoxin-like protein in interspecies competition and cariogenecity of Streptococcus mutans

S-glutathionylation is an important post-translational modification (PTM) process that targets protein cysteine thiols by the addition of glutathione (GSH). This modification can prevent proteolysis caused by the excessive oxidation of protein cysteine residues under oxidative or nitrosative stress conditions. Recent studies have suggested that protein S-glutathionylation plays an essential role in the control of cell-signaling pathways by affecting the protein function in bacteria and even humans. In this study, we investigated the effects of S-glutathionylation on physiological regulation within Streptococcus mutans, the primary etiological agent of human dental caries. To determine the S-glutathionylated proteins in bacteria, the Cys reactive isobaric reagent iodoacetyl Tandem Mass Tag (iodoTMT) was used to label the S-glutathionylated Cys site, and an anti-TMT antibody-conjugated resin was used to enrich the modified peptides. Proteome profiling identified a total of 357 glutathionylated cysteine residues on 239 proteins. Functional enrichment analysis indicated that these S-glutathionylated proteins were involved in diverse important biological processes, such as pyruvate metabolism and glycolysis. Furthermore, we studied a thioredoxin-like protein (Tlp) to explore the effect of S-glutathionylation on interspecies competition between oral streptococcal biofilms. Through site mutagenesis, it was proved that glutathionylation on Cys41 residue of Tlp is crucial to protect S. mutans from oxidative stress and compete with S. sanguinis and S. gordonii. An addition rat caries model showed that the loss of S-glutathionylation attenuated the cariogenicity of S. mutans. Taken together, our study provides an insight into the S-glutathionylation of bacterial proteins and the regulation of oxidative stress resistance and interspecies competition.

Wnt/β-catenin signaling pathway promotes renal ischemia-reperfusion injury through inducing oxidative stress and inflammation response

Oxidative stress and inflammation response have been found to be associated with renal ischemia reperfusion (I/R) injury through an undefined mechanism. The aim of our study is to explore the influence of Wnt/β-catenin signaling pathway on oxidative stress and inflammation response during renal I/R injury. The results of our study demonstrated that oxidative stress was induced whereas antioxidative factors were suppressed by renal I/R injury. Besides, the transcriptions and activities of pro-inflammation factors were also upregulated by renal I/R injury. Interestingly, inhibition of Wnt/β-catenin signaling pathway significantly attenuated I/R-mediated oxidative stress and inflammation response. Therefore, our results report a novel pathway responsible for renal I/R injury. Inhibition of Wnt/β-catenin signaling pathway would be considered as an effective approach to regulate oxidative stress and inflammation response in reperfused kidney.