A thioredoxin-dependent peroxiredoxin Q from Corynebacterium glutamicum plays an important role in defense against oxidative stress

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.

Characterization of oxidative stress-induced cgahp, a gene coding for alkyl hydroperoxide reductase, from industrial importance Corynebacterium glutamicum

Alkyl hydroperoxide reductase (Ahp), comprised of four different subunits AhpC, AhpD, AhpE, and AhpF, is a thiol-based antioxidative enzyme with the ability to protect bacteria against oxidative stress. Functionally, AhpC and AhpE considered as peroxidases directly detoxify peroxides, while AhpD and AhpF as oxidoreductases restore oxidized peroxidases to their reduced form. Corynebacterium glutamicum ncgl0877 encodes a putative Ahp with a unique Cys-Pro-Phe-Cys (C-P-G-C) active-site motif, similar with those of the thiol-disulfide oxidoreductases such as thioredoxin (Trx), mycoredoxin-1 (Mrx1) and AhpD. However, its physiological and biochemical functions remain unknown in C. glutamicum. Here, we report that NCgl0877, designated CgAhp, is involved in the protection against organic peroxide (OP) stress. The cgahp-deleted strain is notably more sensitive to OP stress. The cgahp expression is controlled by a MarR-type transcriptional repressor OasR (organic peroxide- and antibiotic-sensing regulator). The physiological role of CgAhp in resistance to OP stresses is corroborated by its induced expression under stresses. Although CgAhp has a weak peroxidase activity toward OP, it mainly supports the OP-scavenging activity of the thiol-dependent peroxidase preferentially linked to the dihydrolipoamide dehydrogenase (Lpd)/dihydrolipoamide succinyltransferase (SucB)/NADH system. The C-P-G-C motif of CgAhp is essential to maintain the reductase activity. In conclusion, our study identifies CgAhp, behaving like AhpD, as a key disulfide oxidoreductase involved in the oxidative stress tolerance and the functional electron donor for peroxidase.

Revealing Corynebacterium glutamicum proteoforms through top-down proteomics

Corynebacterium glutamicum is a bacterium widely employed in the industrial production of amino acids as well as a broad range of other biotechnological products. The present study describes the characterization of C. glutamicum proteoforms, and their post-translational modifications (PTMs) employing top-down proteomics. Despite previous evidence of PTMs having roles in the regulation of C. glutamicum metabolism, this is the first top-down proteome analysis of this organism. We identified 1125 proteoforms from 273 proteins, with 60% of proteins presenting at least one mass shift, suggesting the presence of PTMs, including several acetylated, oxidized and formylated proteoforms. Furthermore, proteins relevant to amino acid production, protein secretion, and oxidative stress were identified with mass shifts suggesting the presence of uncharacterized PTMs and proteoforms that may affect biotechnologically relevant processes in this industrial workhorse. For instance, the membrane proteins mepB and SecG were identified as a cleaved and a formylated proteoform, respectively. While in the central metabolism, OdhI was identified as two proteoforms with potential biological relevance: a cleaved proteoform and a proteoform with PTMs corresponding to a 70 Da mass shift.

The thiol-reductase activity of YUCCA6 enhances nickel heavy metal stress tolerance in Arabidopsis

Anthropogenic activities cause the leaching of heavy metals into groundwater and their accumulation in soil. Excess levels of heavy metals cause toxicity in plants, inducing the production of reactive oxygen species (ROS) and possible death caused by the resulting oxidative stress. Heavy metal stresses repress auxin biosynthesis and transport, inhibiting plant growth. Here, we investigated whether nickel (Ni) heavy metal toxicity is reduced by exogenous auxin application and whether Ni stress tolerance in Arabidopsis thaliana is mediated by the bifunctional enzyme YUCCA6 (YUC6), which functions as an auxin biosynthetic enzyme and a thiol-reductase (TR). We found that an application of up to 1 µM exogenous indole-3-acetic acid (IAA) reduces Ni stress toxicity. yuc6-1D, a dominant mutant of YUC6 with high auxin levels, was more tolerant of Ni stress than wild-type (WT) plants, despite absorbing significantly more Ni. Treatments of WT plants with YUCASIN, a specific inhibitor of YUC-mediated auxin biosynthesis, increased Ni toxicity; however yuc6-1D was not affected by YUCASIN and remained tolerant of Ni stress. This suggests that rather than the elevated IAA levels in yuc6-1D, the TR activity of YUC6 might be critical for Ni stress tolerance. The loss of TR activity in YUC6 caused by the point-mutation of Cys85 abolished the YUC6-mediated Ni stress tolerance. We also found that the Ni stress-induced ROS accumulation was inhibited in yuc6-1D plants, which consequently also showed reduced oxidative damage. An enzymatic assay and transcriptional analysis revealed that the peroxidase activity and transcription of PEROXIREDOXIN Q were enhanced by Ni stress to a greater level in yuc6-1D than in the WT. These findings imply that despite the need to maintain endogenous IAA levels for basal Ni stress tolerance, the TR activity of YUC6, not the elevated IAA levels, plays the predominant role inNi stress tolerance by lowering Ni-induced oxidative stress.

The TetR-type regulator AtsR is involved in multidrug response in Corynebacterium glutamicum

Background

The TetR (tetracycline repressor) family is one of the major transcription factor families that regulate expression of genes involved in bacterial antimicrobial resistance systems. NCgl0886 protein, designated as AtsR, is a member of the TetR family identified in Corynebacterium glutamicum, which is conserved in several species of the genera Corynebacterium, also including the well-known pathogen C. diphtheriae. AtsR is located at no far upstream of the identically oriented ncgl0884 gene, encoding a putative multidrug efflux pump protein, and in the same operon with ncgl0887, encoding a resistance, nodulation and cell division (RND) superfamily drug exporter. However, the role of AtsR is not clearly understood.

Results

Here we showed that dimeric AtsR directly repressed the expression of the ncgl0887-atsR operon, as well as indirectly controlled the ncgl0884 transcription. Antibiotics and toxic compounds induced the expression of ncgl0887-atsR operon. A perfect palindromic motif (5΄-TGCAA-N₂-TTGCA-3΄; 12 bp) was identified in the upstream region of ncgl0887-atsR operon. Electrophoretic mobility shift assays (EMSAs) demonstrated specific binding of AtsR to this motif, and hydrogen peroxide (H₂O₂) blocked binding. H₂O₂ oxidized cysteine residues to form Cys123-Cys187 intermolecular disulfide bonds between two subunits in AtsR dimer, which altered its DNA-binding characteristics and caused its dissociation, thereby leading to derepression of the drug efflux protein. Deletion of ncgl0884 and ncgl0887 increased the susceptibilities of C. glutamicum for several toxic compounds, but overexpression of atsR decreased the drug tolerance of C. glutamicum.

Conclusions

Our study revealed that AtsR was a redox regulator that sensed oxidative stress via thiol modification. The results obtained here will contribute to our understanding of the drug response mechanism not only in C. glutamicum but also in the related bacteria C. diphtheriae.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01850-0.

Genome Characterization and Probiotic Potential of Corynebacterium amycolatum Human Vaginal Isolates

The vaginal microbiome of healthy women contains nondiphtheria corynebacteria. The role and functions of nondiphtheria corynebacteria in the vaginal biotope are still under study. We sequenced and analysed the genomes of three vaginal C. amycolatum strains isolated from healthy women. Previous studies have shown that these strains produced metabolites that significantly increased the antagonistic activity of peroxide-producing lactic acid bacteria against pathogenic and opportunistic microorganisms and had strong antimicrobial activity against opportunistic pathogens. Analysis of the C. amycolatum genomes revealed the genes responsible for adaptation and survival in the vaginal environment, including acid and oxidative stress resistance genes. The genes responsible for the production of H₂O₂ and the synthesis of secondary metabolites, essential amino acids and vitamins were identified. A cluster of genes encoding the synthesis of bacteriocin was revealed in one of the annotated genomes. The obtained results allow us to consider the studied strains as potential probiotics that are capable of preventing the growth of pathogenic microorganisms and supporting colonisation resistance in the vaginal biotope.

Role of Rhizospheric Bacillus megaterium HGS7 in Maintaining Mulberry Growth Under Extremely Abiotic Stress in Hydro-Fluctuation Belt of Three Gorges Reservoir

Plant growth-promoting rhizobacteria have been shown to play important roles in maintaining host fitness under periods of abiotic stress, and yet their effect on mulberry trees which regularly suffer drought after flooding in the hydro-fluctuation belt of the Three Gorges Reservoir Region in China remains largely uncharacterized. In the present study, 74 bacterial isolates were obtained from the rhizosphere soil of mulberry after drought stress, including 12 phosphate-solubilizing and 10 indole-3-acetic-acid-producing isolates. Bacillus megaterium HGS7 was selected for further study due to the abundance of traits that might benefit plants. Genomic analysis revealed that strain HGS7 possessed multiple genes that contributed to plant growth promotion, stress tolerance enhancement, and antimicrobial compound production. B. megaterium HGS7 consistently exhibited antagonistic activity against phytopathogens and strong tolerance to abiotic stress in vitro. Moreover, this strain stimulated mulberry seed germination and seedling growth. It may also induce the production of proline and antioxidant enzymes in mulberry trees to enhance drought tolerance and accelerate growth recovery after drought stress. The knowledge of the interactions between rhizobacteria HGS7 and its host plant might provide a potential strategy to enhance the drought tolerance of mulberry trees in a hydro-fluctuation belt.

Involvement of a mycothiol-dependent reductase NCgl0018 in oxidative stress response of Corynebacterium glutamicum

Corynebacterium glutamicum is an important industrial strain for amino acids and a key model organism for human pathogens. The study of C. glutamicum oxidoreductases, such as mycoredoxin 1 (Mrx1), dithiol-disulfide isomerase DsbA, and DsbA-like Mrx1, is helpful for understanding the survival, pathogenic infection, and stress resistance of its homologous species. However, the action mode and enzymatic function of C. glutamicum NCgl0018 preserving the Cys-Pro-Phe-Cys motif, annotated as a putative DsbA, have remained enigmatic. Here, we report that the NCgl0018-deleted strain increased sensitivity to various oxidative stresses. The ncgl0018 expression was induced in the stress-responsive extracytoplasmic function-sigma (ECF-σ) factor SigH- and organic peroxide- and antibiotic-sensing regulator (OasR)-dependent manner by stress. NCgl0018 reduced S-mycothiolated mixed disulfides and intramolecular disulfides via a monothiol-disulfide mechanism preferentially linking the mycothiol/mycothione reductase/NADPH electron pathway. Site-directed mutagenesis confirmed Cys107 was the resolving Cys residue, while Cys104 was the nucleophilic cysteine that was oxidized to a sulfenic acid and then could form an intramolecular disulfide bond with Cys107 or a mixed disulfide with mycothiol under stress. Biochemical analyses indicated that NCgl0018 lacked oxidase properties like the classical DsbA. Further, enzymatic rates and substrate preferences of NCgl0018 were highly similar to those of DsbA-like Mrx1. Collectively, our study presented the first evidence that NCgl0018 protected against stresses by functioning as a novel DsbA-like Mrx1 but not DsbA and Mrx1.

Corynebacterium glutamicum Mycoredoxin 3 protects against multiple oxidative stresses and displays thioredoxin-like activity

Glutaredoxins (Grxs) and thioredoxins (Trxs) play a critical role in resistance to oxidative conditions. However, physiological and biochemical roles of Mycoredoxin 3 (Mrx3) that shared a high amino acid sequence similarity to Grxs remain unknown in Corynebacterium glutamicum. Here we showed that mrx3 deletion strains of C. glutamicum was involved in the protection against oxidative stress. Recombinant Mrx3 not only catalytically reduced the disulfide bonds in ribonucleotide reductase (RNR), insulin and 5,5'-dithiobis-(2-nitro-benzoicacid) (DTNB), but also reduced the mixed disulphides between mycothiol (MSH) and substrate, which was exclusively linked to the thioredoxin reductase (TrxR) electron transfer pathway by a dithiol mechanism. Site-directed mutagenesis confirmed that the conserved Cys17 and Cys20 in Mrx3 were necessary to maintain its activity. The mrx3 deletion mutant showed decreased resistance to various stress, and these sensitive phenotypes were almost fully restored in the complementary strain. The physiological roles of Mrx3 in resistance to various stress were further supported by the induced expression of mrx3 under various stress conditions, directly under the control of the stress-responsive extracytoplasmic function-sigma (ECF-σ) factor SigH. Thus, we presented the first evidence that Mrx3 protected against various oxidative stresses by acting as a disulfide oxidoreductase behaving like Trx.

Metaproteomics Reveals Alteration of the Gut Microbiome in Weaned Piglets Due to the Ingestion of the Mycotoxins Deoxynivalenol and Zearalenone

The ingestion of mycotoxins can cause adverse health effects and represents a severe health risk to humans and livestock. Even though several acute and chronic effects have been described, the effect on the gut metaproteome is scarcely known. For that reason, we used metaproteomics to evaluate the effect of the mycotoxins deoxynivalenol (DON) and zearalenone (ZEN) on the gut microbiome of 15 weaned piglets. Animals were fed for 28 days with feed contaminated with different concentrations of DON (DONlow: 870 μg DON/kg feed, DONhigh: 2493 μg DON/kg feed) or ZEN (ZENlow: 679 μg ZEN/kg feed, ZENhigh: 1623 μg ZEN/kg feed). Animals in the control group received uncontaminated feed. The gut metaproteome composition in the high toxin groups shifted compared to the control and low mycotoxin groups, and it was also more similar among high toxin groups. These changes were accompanied by the increase in peptides belonging to Actinobacteria and a decrease in peptides belonging to Firmicutes. Additionally, DONhigh and ZENhigh increased the abundance of proteins associated with the ribosomes and pentose-phosphate pathways, while decreasing glycolysis and other carbohydrate metabolism pathways. Moreover, DONhigh and ZENhigh increased the abundance of the antioxidant enzyme thioredoxin-dependent peroxiredoxin. In summary, the ingestion of DON and ZEN altered the abundance of different proteins associated with microbial metabolism, genetic processing, and oxidative stress response, triggering a disruption in the gut microbiome structure.

A novel mycothiol-dependent thiol-disulfide reductase in Corynebacterium glutamicum involving oxidative stress resistance

ncgl2478 gene from Corynebacterium glutamicum encodes a thiol–disulfide oxidoreductase enzyme annotated as dithiol–disulfide isomerase DsbA. It preserves a Cys–Pro–Phe–Cys active-site motif, which is presumed to be an exclusive characteristic of the novel DsbA–mycoredoxin 1 (Mrx1) cluster. However, the real mode of action, the nature of the electron donor pathway and biological functions of NCgl2478 in C. glutamicum have remained enigmatic so far. Herein, we report that NCgl2478 plays an important role in stress resistance. Deletion of the ncgl2478 gene increases the size of growth inhibition zones. The ncgl2478 expression is induced in the stress-responsive extra-cytoplasmic function-sigma (ECF-σ) factor SigH-dependent manner by stress. It receives electrons preferentially from the mycothiol (MSH)/mycothione reductase (Mtr)/NADPH pathway. Further, NCgl2478 reduces S-mycothiolated mixed disulfides and intramolecular disulfides via a monothiol–disulfide and a dithiol–disulfide exchange mechanism, respectively. NCgl2478 lacks oxidase activity; kinetic properties of its demycothiolation are different from those of Mrx1. Site-directed mutagenesis confirms Cys24 is the resolving Cys residue, while Cys21 is the nucleophilic cysteine that is oxidized to a sulfenic acid and then forms an intramolecular disulfide bond with Cys24 or a mixed disulfide with MSH under oxidative stress. In conclusion, our study presents the first evidence that NCgl2478 protects against various stresses by acting as an MSH-dependent thiol–disulfide reductase, belonging to a novel DsbA–Mrx1 cluster.

The cssR gene of Corynebacterium glutamicum plays a negative regulatory role in stress responses

Background

CssR, the product of the Corynebacterium glutamicum ncgl1578 gene cotranscribed with ncgl1579, is a TetR (tetracycline regulator) family repressor. Although many TetR-type regulators in C. glutamicum have been extensively described, members of the TetR family involved in the stress response remain unidentified.

Results

In this study, we found that CssR regulated the transcription of its own gene and the ncgl1576-ncgl1577 operon. The ncgl1576-ncgl1577 operon, which is located upstream of cssR in the orientation opposite that of the cssR operon, encodes an ATP-binding cassette (ABC), some of which are involved in the export of a wide range of antimicrobial compounds. The cssR-deletion (ΔcssR) mutant displayed increased resistance to various stresses. An imperfect palindromic motif (5′-TAA(G)TGN₁₃CA(G)TTA-3′; 25 bp) located at the intergenic region between cssR and ncgl1577 was identified as the sole binding site for CssR. Expression of cssR and ncgl1577 was induced by antibiotics and heavy metals but not H₂O₂ or diamide, and the DNA-binding activity of CssR was impaired by antibiotics and heavy metals but not H₂O₂. Antibiotics and heavy metals caused CssR dissociation from target gene promoters, thus derepressing their transcription. Oxidant treatment neither altered the conformation of CssR nor modified its cysteine residues, indicating that the cysteine residues in CssR have no redox activity. In the ΔcssR mutant strain, genes involved in redox homeostasis also showed increased transcription levels, and the NADPH/NADP⁺ ratio was higher than that of the parental strain.

Conclusion

The stress response mechanism of CssR in C. glutamicum is realized via ligand-induced conformational changes of the protein, not via cysteine oxidation-based thiol modification. Moreover, the crucial role of CssR in the stress response was demonstrated by negatively controlling the expression of the ncgl1576-ncgl1577 operon, its structural gene, and/or redox homeostasis-related genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01600-8.

The thiol oxidation-based sensing and regulation mechanism for the OasR-mediated organic peroxide and antibiotic resistance in C. glutamicum

Corynebacterium glutamicum, an important industrial and model microorganism, inevitably encountered stress environment during fermentative process. Therefore, the ability of C. glutamicum to withstand stress and maintain the cellular redox balance was vital for cell survival and enhancing fermentation efficiency. To robustly survive, C. glutamicum has been equipped with many types of redox sensors. Although cysteine oxidation-based peroxide-sensing regulators have been well described in C. glutamicum, redox sensors involving in multiple environmental stress response remained elusive. Here, we reported an organic peroxide- and antibiotic-sensing MarR (multiple antibiotics resistance regulators)-type regulator, called OasR (organic peroxide- and antibiotic-sensing regulator). The OasR regulator used Cys95 oxidation to sense oxidative stress to form S-mycothiolated monomer or inter-molecular disulfide-containing dimer, resulting in its dissociation from the target DNA promoter. Transcriptomics uncovered the strong up-regulation of many multidrug efflux pump genes and organic peroxide stress-involving genes in oasR mutant, consistent with the phenomenon that oasR mutant showed a reduction in sensitivity to antibiotic and organic peroxide. Importantly, the addition of stress-associated ligands such as cumene hydroperoxide and streptomycin induced oasR and multidrug efflux pump protein NCgl1020 expression in vivo. We speculated that cell resistance to antibiotics and organic peroxide correlated with stress response-induced up-regulation of genes expression. Together, the results revealed that OasR was a key MarR-type redox stress-responsive transcriptional repressor, and sensed oxidative stress generated through hydroxyl radical formation to mediate antibiotic resistance in C. glutamicum.

Molecular mechanisms of Mycoredoxin-1 in resistance to oxidative stress in Corynebacterium glutamicum

Glutaredoxins (Grxs) with Cys-Pro-Phe (Tyr)-Cys motif and a thioredoxin fold structure play an important role in the anti-oxidant system of bacteria by catalyzing a variety of thiol-disulfide exchange reactions with a 2-Cys mechanism or a 1-Cys mechanism. However, the catalytic and physiological mechanism of Corynebacterium glutamicum Mycoredoxin 1 (Mrx1) that shares a high amino acid sequence similarity to Grxs has not been fully elucidated. Here, we report that Mrx1 has a protective function against various adverse conditions, and the decrease of cell viability to various stress conditions by deletion of the Mrx1 in C. glutamicum was confirmed in the mrx1 mutant. The physiological roles of Mrx1 in defence to oxidative stress were corroborated by its induced expression under various stresses, regulated directly by the stress-responsive extracytoplasmic function-sigma (ECF-σ) factor SigH. As well as reducing mycothiol (MSH) mixed disulfide bonds via a 1-Cys mechanism, C. glutamicum Mrx1 catalytically reduced the disulfides in the Ib RNR, insulin and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) by exclusively linking the MSH/Mtr (mycothiol disulfide reductase)/NADPH electron pathway via a 2-Cys mechanism. Thus, we present the first evidence that the Mrx1 is able to protect against the damaging effects of various exogenous stresses by acting as a disulfide oxidoreductase, thereby giving a new insight in how C. glutamicum survives oxidative stressful conditions.

MsrR is a thiol-based oxidation-sensing regulator of the XRE family that modulates C. glutamicum oxidative stress resistance

Background

Corynebacterium glutamicum thrives under oxidative stress caused by the inevitably extreme environment during fermentation as it harbors antioxidative stress genes. Antioxidant genes are controlled by pathway-specific sensors that act in response to growth conditions. Although many families of oxidation-sensing regulators in C. glutamicum have been well described, members of the xenobiotic-response element (XRE) family, involved in oxidative stress, remain elusive.

Results

In this study, we report a novel redox-sensitive member of the XER family, MsrR (multiple stress resistance regulator). MsrR is encoded as part of the msrR-3-mst (3-mercaptopyruvate sulfurtransferase) operon; msrR-3-mst is divergent from multidrug efflux protein MFS. MsrR was demonstrated to bind to the intergenic region between msrR-3-mst and mfs. This binding was prevented by an MsrR oxidation-mediated increase in MsrR dimerization. MsrR was shown to use Cys62 oxidation to sense oxidative stress, resulting in its dissociation from the promoter. Elevated expression of msrR-3-mst and mfs was observed under stress. Furthermore, a ΔmsrR mutant strain displayed significantly enhanced growth, while the growth of strains lacking either 3-mst or mfs was significantly inhibited under stress.

Conclusion

This report is the first to demonstrate the critical role of MsrR-3-MST-MFS in bacterial stress resistance.

CarR, a MarR-family regulator from Corynebacterium glutamicum, modulated antibiotic and aromatic compound resistance

MarR (multiple antibiotic resistance regulator) proteins are a family of transcriptional regulators that is prevalent in Corynebacterium glutamicum. Understanding the physiological and biochemical function of MarR homologs in C. glutamicum has focused on cysteine oxidation-based redox-sensing and substrate metabolism-involving regulators. In this study, we characterized the stress-related ligand-binding functions of the C. glutamicum MarR-type regulator CarR (C. glutamicum antibiotic-responding regulator). We demonstrate that CarR negatively regulates the expression of the carR (ncgl2886)-uspA (ncgl2887) operon and the adjacent, oppositely oriented gene ncgl2885, encoding the hypothetical deacylase DecE. We also show that CarR directly activates transcription of the ncgl2882-ncgl2884 operon, encoding the peptidoglycan synthesis operon (PSO) located upstream of carR in the opposite orientation. The addition of stress-associated ligands such as penicillin and streptomycin induced carR, uspA, decE, and PSO expression in vivo, as well as attenuated binding of CarR to operator DNA in vitro. Importantly, stress response-induced up-regulation of carR, uspA, and PSO gene expression correlated with cell resistance to β-lactam antibiotics and aromatic compounds. Six highly conserved residues in CarR were found to strongly influence its ligand binding and transcriptional regulatory properties. Collectively, the results indicate that the ligand binding of CarR induces its dissociation from the carR-uspA promoter to derepress carR and uspA transcription. Ligand-free CarR also activates PSO expression, which in turn contributes to C. glutamicum stress resistance. The outcomes indicate that the stress response mechanism of CarR in C. glutamicum occurs via ligand-induced conformational changes to the protein, not via cysteine oxidation-based thiol modifications.

A Novel Thioredoxin-Dependent Peroxiredoxin (TPx-Q) Plays an Important Role in Defense Against Oxidative Stress and Is a Possible Drug Target in Babesia microti

Thioredoxin peroxidases (TPxs) are ubiquitous cysteine-based peroxidases that reduce peroxides as part of antioxidant defenses and redox signaling and are essential for Babesia microti protection against adverse environment agents like reactive oxygen species (ROS) and reactive nitrogen species (RNS). To better systematically understand TPxs, we identified a novel 2-Cys peroxiredoxin-Q (BmTPx-Q) of B. microti. The full-length BmTPx-Q gene is 653 bp that consists of an intact open reading frame of 594 bp that encodes a 197-amino acid protein. The predicted protein has a molecular weight of 22.3 kDa and an isoelectric point of 9.18. Moreover, BmTPx-Q showed low identity at the amino acid level to other peroxiredoxins (Prxs) among the currently known subfamilies. The recombinant BmTPx-Q protein (rBmTPx-Q) was expressed in Escherichia coli and purified with beads. The native protein BmTPx-Q was detected using mouse anti-BmTPx-Q polyclonal serum with western blotting and indirect immunofluorescence assay (IFA). In addition, enzyme activity was observed using nicotinamide adenine dinucleotide phosphate (NADPH) as substrate and triggered the NADPH-dependent reduction of the Trx/TrxR system. It was also discovered that BmTPx-Q mainly exists as a monomer whether under its native or functional states. In addition, when incubated with Chloroquine diphosphate salt for 24 h in vitro, the expression of BmTPx-Q showed a marked downward trend with the increase of drug concentration. These results suggest that B. microti uses BmTPx-Q to reduce and detoxify hydrogen peroxides to survive and proliferate inside the host. Furthermore, BmTPx-Q showed the lowest identity with host enzymes and could be a potential drug target for the development of novel strategies to control B. microti infection.

Thioredoxin and protein-disulfide isomerase selectivity for redox regulation of proteins in Corynebacterium glutamicum

Thioredoxins (Trxs) and protein-disulfide isomerases (PDIs) are believed to play a pivotal role in ensuring the proper folding of proteins, facilitating appropriate functioning of proteins, and maintaining intracellular redox homeostasis in bacteria. Two thioredoxins (Trxs) and three thiol-disulfide isomerases (PDIs) have been annotated in Corynebacterium glutamicum. However, nothing is known about their functional diversity in the redox regulation of proteins. Thus, we here analyzed the Trx- and PDI-dependent redox shifts of ribonucleotide reductase (RNR), insulin, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), and several thiol-dependent peroxidases by measuring enzyme activity and thiol status in vitro. We found that the two Trxs and the three PDIs had activities in the cleavage of the disulfidebond, whereas the PDIs had a lower efficiency than the two Trxs. Trx2 could activate thiol-dependent peroxidases with an efficiency comparable with that of Trx1, but the PDIs were inefficient. The redox-active Cys-X-X-Cys motif harbored in both Trxs and PDIs was essential to supply efficiently the donor of reducing equivalents for protein disulfides. In addition, stress-responsive extracytoplasmic function (ECF)-sigma factor H (SigH)-dependent Trxs and PDIs expressions were observed. These results contributed importantly to our overall understanding of reducing functionality of the Trx and PDI systems, and also highlighted the complexity and plasticity of the intracellular redox network.

Unravelling GSNOR-Mediated S-Nitrosylation and Multiple Developmental Programs in Tomato Plants

Nitric oxide (NO) impacts multiple developmental events and stress responses in plants. S-nitrosylation, regulated by S-nitrosoglutathione reductase (GSNOR), is considered as an important route for NO bioactivity. However, genetic evidence for GSNOR-mediated plant development and S-nitrosylation remains elusive in crop species. Genetic and site-specific nitrosoproteomic approach was used to obtain GSNOR-mediated phenotype and S-nitrosylated network. Knockdown of GSNOR increased the endogenous NO level and S-nitrosylation, resulting in higher germination rate, inhibition of root and hypocotyl growth, decreased photosynthesis, reduced plant growth, altered plant architecture, dysplastic pollen grains, and low fructification rate and fruit yield. For nitrosoproteomic analysis, 395 endogenously S-nitrosylated proteins with 554 S-nitrosylation sites were identified within a wide range of biological processes, especially for energy metabolism. Physiological and exogenous energy-support testing were consistent with the omic result, suggesting that GSNOR-mediated S-nitrosylation of energy metabolism plays key roles in impacting plant growth and development. Taken together, GSNOR is actively involved in the regulation of multiple developmental processes related to agronomically important traits. In addition, our results provide valuable resources and new clues for the study of S-nitrosylation-regulated metabolism in plants.

Characterization of Xi-class mycothiol S-transferase from Corynebacterium glutamicum and its protective effects in oxidative stress

Background

Oxidative stress caused by inevitable hostile conditions during fermentative process was the most serious threat to the survival of the well-known industrial microorganism Corynebacterium glutamicum. To survive, C. glutamicum developed several antioxidant defenses including millimolar concentrations of mycothiol (MSH) and protective enzymes. Glutathione (GSH) S-transferases (GSTs) with essentially defensive role in oxidative stress have been well defined in numerous microorganisms, while their physiological and biochemical functions remained elusive in C. glutamicum thus far.

Results

In the present study, we described protein NCgl1216 belonging to a novel MSH S-transferase Xi class (MstX), considered as the equivalent of GST Xi class (GSTX). MstX had a characteristic conserved catalytic motif (Cys-Pro-Trp-Ala, C-P-W-A). MstX was active as thiol transferase, dehydroascorbate reductase, mycothiolyl-hydroquinone reductase and MSH peroxidase, while it showed null activity toward canonical GSTs substrate as 1-chloro-2,4-dinitrobenzene (CDNB) and GST Omega’s specific substance glutathionyl-acetophenones, indicating MstX had some biochemical characteristics related with mycoredoxin (Mrx). Site-directed mutagenesis showed that, among the two cysteine residues of the molecule, only the residue at position 67 was required for the activity. Moreover, the residues adjacent to the active Cys67 were also important for activity. These results indicated that the thiol transferase of MstX operated through a monothiol mechanism. In addition, we found MstX played important role in various stress resistance. The lack of C. glutamicum mstX gene resulted in significant growth inhibition and increased sensitivity under adverse stress condition. The mstX expression was induced by stress.

Conclusion

Corynebacterium glutamicum MstX might be critically involved in response to oxidative conditions, thereby giving new insight in how C. glutamicum survived oxidative stressful conditions.

Catalysis of Peroxide Reduction by Fast Reacting Protein Thiols

Life on Earth evolved in the presence of hydrogen peroxide, and other peroxides also emerged before and with the rise of aerobic metabolism. They were considered only as toxic byproducts for many years. Nowadays, peroxides are also regarded as metabolic products that play essential physiological cellular roles. Organisms have developed efficient mechanisms to metabolize peroxides, mostly based on two kinds of redox chemistry, catalases/peroxidases that depend on the heme prosthetic group to afford peroxide reduction and thiol-based peroxidases that support their redox activities on specialized fast reacting cysteine/selenocysteine (Cys/Sec) residues. Among the last group, glutathione peroxidases (GPxs) and peroxiredoxins (Prxs) are the most widespread and abundant families, and they are the leitmotif of this review. After presenting the properties and roles of different peroxides in biology, we discuss the chemical mechanisms of peroxide reduction by low molecular weight thiols, Prxs, GPxs, and other thiol-based peroxidases. Special attention is paid to the catalytic properties of Prxs and also to the importance and comparative outlook of the properties of Sec and its role in GPxs. To finish, we describe and discuss the current views on the activities of thiol-based peroxidases in peroxide-mediated redox signaling processes.

The osnR gene of Corynebacterium glutamicum plays a negative regulatory role in oxidative stress responses

Among the Corynebacterium glutamicum ORFs that have been implicated in stress responses, we chose ORF cg3230, designated osnR, and analyzed it further. Unlike the osnR-deleted strain (ΔosnR), the osnR-overexpressing strain (P180-osnR) developed growth defects and increased sensitivity to various oxidants including H2O2. Transcription in the P180-osnR strain of genes such as sodA (superoxide dismutase), ftn (ferritin biosynthesis), and ahpD (alkyl hydroperoxide reductase; cg2674), which are involved in the detoxification of reactive oxygen species, was only 40% that of the wild type. However, transcription of katA, encoding H2O2-detoxifying catalase, was unchanged in this strain. Genes such as trxB (thioredoxin reductase) and mtr (mycothiol disulfide reductase), which play roles in redox homeostasis, also showed decreased transcription in the strain. 2D-PAGE analysis indicated that genes involved in redox reactions were considerably affected by osnR overexpression. The NADPH/NADP+ ratio of the P180-osnR strain (1.35) was higher than that of the wild-type stain (0.78). Collectively, the phenotypes of the ΔosnR and P180-osnR strains suggest a global regulatory role as well as a negative role for the gene in stress responses, particularly in katA-independent oxidative stress responses.

OhsR acts as an organic peroxide-sensing transcriptional activator using an S-mycothiolation mechanism in Corynebacterium glutamicum

Background

Corynebacterium glutamicum is a well-known producer of various l-amino acids in industry. During the fermenting process, C. glutamicum unavoidably encounters oxidative stress due to a specific reactive oxygen species (ROS) produced by consistent adverse conditions. To combat the ROS, C. glutamicum has developed many common disulfide bond-based regulatory devices to control a specific set of antioxidant genes. However, nothing is known about the mixed disulfide between the protein thiol groups and the mycothiol (MSH) (S-mycothiolation)-based sensor. In addition, no OhrR (organic hydroperoxide resistance regulator) homologs and none of the organic hydroperoxide reductase (Ohr) sensors have been described in the alkyl hydroperoxide reductase CF-missing C. glutamicum, while organic hydroperoxides (OHPs)-specific Ohr was a core detoxification system.

Results

In this study, we showed that the C. glutamicum OhsR acted as an OHPs sensor that activated ohr expression. OhsR conferred resistance to cumene hydroperoxide (CHP) and t-butyl hydroperoxide but not H₂O₂, hypochlorous acid, and diamide; this outcome was substantiated by the fact that the ohsR-deficient mutant was sensitive to OHPs but not inorganic peroxides. The DNA binding activity of OhsR was specifically activated by CHP. Mutational analysis of the two cysteines (Cys125 and Cys261) showed that Cys125 was primarily responsible for the activation of DNA binding. The oxidation of Cys125 produced a sulfenic acid (C125-SOH) that subsequently reacted with MSH to generate S-mycothiolation that was required to activate the ohr expression. Therefore, OhsR regulated the ohr expression using an S-mycothiolation mechanism in vivo.

Conclusion

This is the first report demonstrating that the regulatory OhsR specifically sensed OHPs stress and responded to it by activating a specific ohr gene under its control using an S-mycothiolated mechanism.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-1048-y) contains supplementary material, which is available to authorized users.

CosR is an oxidative stress sensing a MarR-type transcriptional repressor in Corynebacterium glutamicum

The MarR family is unique to both bacteria and archaea. The members of this family, one of the most prevalent families of transcriptional regulators in bacteria, enable bacteria to adapt to changing environmental conditions, such as the presence of antibiotics, toxic chemicals, or reactive oxygen species (ROS), mainly by thiol-disulfide switches. Although the genome of Corynebacterium glutamicum encodes a large number of the putative MarR-type transcriptional regulators, their physiological and biochemical functions have so far been limited to only two proteins, regulator of oxidative stress response RosR and quinone oxidoreductase regulator QosR. Here, we report that the ncgl2617 gene (cosR) of C. glutamicum encoding an MarR-type transcriptional regulator plays an important role in oxidative stress resistance. The cosR null mutant is found to be more resistant to various oxidants and antibiotics, accompanied by a decrease in ROS production and protein carbonylation levels under various stresses. Protein biochemical function analysis shows that two Cys residues presenting at 49 and 62 sites in CosR are redox-active. They form intermolecular disulfide bonds in CosR under oxidative stress. This CosR oxidation leads to its dissociation from promoter DNA, depression of the target DNA, and increased oxidative stress resistance of C. glutamicum. Together, the results reveal that CosR is a redox-sensitive regulator that senses peroxide stress to mediate oxidative stress resistance in C. glutamicum.

Novel functions of peroxiredoxin Q from Deinococcus radiodurans R1 as a peroxidase and a molecular chaperone

Deinococcus radiodurans R1 is extremely resistant to ionizing radiation and oxidative stress. In this study, we characterized DR0846, a candidate peroxiredoxin in D. radiodurans. DR0846 is a peroxiredoxin Q containing two conserved cysteine residues. DR0846 exists mainly in monomeric form with an intramolecular disulfide bond between the two cysteine residues. We found that DR0846 functions as a molecular chaperone as well as a peroxidase. A mutational analysis indicates that the two cysteine residues are essential for enzymatic activity. A double‐deletion mutant lacking DR0846 and catalase DR1998 exhibits decreased oxidative and heat shock stress tolerance with respect to the single mutants or the wild‐type cells. These results suggest that DR0846 contributes to resistance against oxidative and heat stresses in D. radiodurans.