The thioredoxin superfamily in oxidative protein folding

Auranofin induces disulfide bond-mimicking S-Au adducts in protein thiol pairs

Auranofin is an inhibitor of human thioredoxin reductase, clinically used in the treatment of rheumatoid arthritis. More recently, it has been shown to possess strong antibacterial activity. Despite the structural dissimilarity and the independent evolutionary origins of human thioredoxin reductase and its bacterial counterpart (TrxB), inhibition of bacterial thioredoxin reductase is often suggested to be a major factor in auranofin's antibacterial mode of action. To test this hypothesis, we attempted to determine the mechanism of inhibition of auranofin for bacterial TrxB in the presence of thioredoxin, TrxB's natural substrate. However, the data obtained in these experiments was not consistent with a specific and exclusive interaction between TrxB and auranofin. Instead, it suggested that auranofin directly interacts with the cysteine thiols in thioredoxin, TrxB's substrate. Using the fluorescent redox protein roGFP2, we showed that auranofin does indeed directly interact with cysteine pairs in proteins, forming a thiol modification that is similar to, but clearly distinct from a disulfide bond. The Au:protein stoichiometries of auranofin-treated roGFP2 and thioredoxin strongly suggest the presence of an S-Au-S bridge between two cysteines in those proteins. These S-Au adducts form independent of thioredoxin reductase at a rate that indicates their pertinence in auranofin's antibacterial mode of action.

Trp31 Residue of Trx-1 Is Essential for Maintaining Antioxidant Activity and Cellular Redox Defense Against Oxidative Stress

Thioredoxin-1 (Trx-1) is an important redox protein found in almost all prokaryotic and eukaryotic cells, which has a highly conserved active site sequence: Trp-Cys-Gly-Pro-Cys. To investigate whether the Trp31 residue is essential for the antioxidant activity of human Trx-1 (hTrx-1), we mutated Trx-1 by replacing Trp31 with Ala31 (31Ala) or deleting Trp31 residue (31Del). We introduced 31Ala and 31Del mutations into prokaryotic cells for hTrx-1 protein expression, protein purification and evaluation of antioxidant activity. The results showed that neither the replacing mutation to Ala31 nor the deletion of Trp31 residue affected the efficient expression of hTrx-1 protein in prokaryotic cells, indicating that neither form of Trp31 mutation would disrupt the folded structure of the Trx-1 protein. Comparison of the antioxidant activity of purified hTrx-1 proteins of wild-type, 31Ala and 31Del forms revealed that both mutant forms significantly decreased the antioxidant capacity of hTrx-1. Further investigations on eukaryotic cells showed that H2O2 treatment caused massive cell death in EA.Hy926 human endothelial cells with 31Ala and 31Del mutations compared to wild-type cells, which was associated with increased ROS production and downregulation of antioxidant Nrf2 and HO-1 expression in the mutant cells. These results suggested that mutations in the Trp31 residue of hTrx-1 remarkably disrupted cellular redox defense against oxidative stress. The antioxidant activity of hTrx-1 relies on the thiol-disulfide exchange reaction, in which the content of thiol groups forming disulfide bonds in hTrx-1 is critical. We found that the content of free thiol groups specifically participating in disulfide bond formation was significantly lower in Trp31 mutant hTrx-1 than in wild-type hTrx-1; that was speculated to affect the formation of disulfide bonds between Cys32 and Cys35 by virtual analysis, thus abolishing the antioxidant activity of hTrx-1 in cleaving oxidized groups and defending against oxidative stress. The present study provided valuable insights towards understanding the importance of Trp31 residue of hTrx-1 in maintaining the correct conformation of the Trx fold structure, the antioxidant functionality of hTrx-1 and the cellular redox defense capability against oxidative stress.

Structure-aided function assignment to the transcriptomic conopeptide Am931

Implementation of the next-generation technologies for gene sequencing of venom duct transcriptome has provided a large number of peptide sequences of marine cone snails. Emerging technologies on computational platforms are now rapidly evolving for the accurate predictions of the 3D structure of the polypeptide using the primary sequence. The current report aims to integrate the information derived from these two technologies to develop the concept of structure-aided function assignment of Conus peptides. The proof of the concept was demonstrated using the transcriptomic peptide Am931 of C. amadis. The 3D structure of Am931 was computed using Density Functional Theory (DFT) and the quality of the predicted structure was confirmed using 2D NMR spectroscopy of the corresponding synthetic peptide. The computed structure of Am931 aligns with the active site motif of thioredoxins, possess catalytic disulfide conformation of (+, -)AntiRHHook and selectively modulate the N-terminal Cys3 thiol. These structural features indicate that Am931 may act as a disulfide isomerase and modulate the oxidative folding of conotoxins. Synthetic peptide Am931 provides proof-of-function by exhibiting catalytic activity on the oxidative folding of α-conotoxin ImI and improving the yield of native globular fold. The approach of integration of new technologies in the Conus peptide research may help to accelerate the discovery pipeline of new/improved conotoxin functional.

The evolutionarily conserved PhLP3 is essential for sperm development in Drosophila melanogaster

Phosducin-like proteins (PhLP) are thioredoxin domain-containing proteins that are highly conserved across unicellular and multicellular organisms. PhLP family proteins are hypothesized to function as co-chaperones in the folding of cytoskeletal proteins. Here, we present the initial molecular, biochemical, and functional characterization of CG4511 as Drosophila melanogaster PhLP3. We cloned the gene into a bacterial expression vector and produced enzymatically active recombinant PhLP3, which showed similar kinetics to previously characterized orthologues. A fly strain homozygous for a P-element insertion in the 5' UTR of the PhLP3 gene exhibited significant downregulation of PhLP3 expression. We found these male flies to be sterile. Microscopic analysis revealed altered testes morphology and impairment of spermiogenesis, leading to a lack of mature sperm. Among the most significant observations was the lack of actin cones during sperm maturation. Excision of the P-element insertion in PhLP3 restored male fertility, spermiogenesis, and seminal vesicle size. Given the high level of conservation of PhLP3, our data suggests PhLP3 may be an important regulator of sperm development across species.

Stepwise release of Activin-A from its inhibitory prodomain is modulated by cysteines and requires furin coexpression to promote melanoma growth

The Activin-A precursor dimer can be cleaved by furin, but how this proteolytic maturation is regulated in vivo and how it facilitates access to signaling receptors is unclear. Here, analysis in a syngeneic melanoma grafting model shows that without furin coexpression, Activin-A failed to accelerate tumor growth, correlating with failure of one or both subunits to undergo cleavage in signal-sending cells, even though compensatory processing by host cells nonetheless sustained elevated circulating Activin-A levels. In reporter assays, furin-independent cleavage of one subunit enabled juxtacrine Activin-A signaling, whereas completion of proteolytic maturation by coexpressed furin or by recipient cells stimulated contact-independent activity, crosstalk with BMP receptors, and signal inhibition by follistatin. Mechanistically, Activin-A processing was modulated by allosteric disulfide bonds flanking the furin site. Disruption of these disulfide linkages with the prodomain enabled Activin-A binding to cognate type II receptors independently of proteolytic maturation. Stepwise proteolytic maturation is a novel mechanism to control Activin-A protein interactions and signaling.

Recent Progress in Anti-Tumor Nanodrugs Based on Tumor Microenvironment Redox Regulation

The growth state of tumor cells is strictly affected by the specific abnormal redox status of the tumor microenvironment (TME). Moreover, redox reactions at the biological level are also central and fundamental to essential energy metabolism reactions in tumors. Accordingly, anti-tumor nanodrugs targeting the disruption of this abnormal redox homeostasis have become one of the hot spots in the field of nanodrugs research due to the effectiveness of TME modulation and anti-tumor efficiency mediated by redox interference. This review discusses the latest research results of nanodrugs in anti-tumor therapy, which regulate the levels of oxidants or reductants in TME through a variety of therapeutic strategies, ultimately breaking the original "stable" redox state of the TME and promoting tumor cell death. With the gradual deepening of study on the redox state of TME and the vigorous development of nanomaterials, it is expected that more anti-tumor nano drugs based on tumor redox microenvironment regulation will be designed and even applied clinically.

TMX family genes and their association with prognosis, immune infiltration, and chemotherapy in human pan-cancer

BACKGROUND

The thioredoxin (TMX) system, an important redox system, plays crucial roles in several immune-related diseases. However, there is limited research on the correlation of TMX family gene expression with human pan-cancer prognosis, tumor microenvironment (TME), and immunotherapy.

METHODS

Based on the integration of several bioinformatics analysis methods, we explored the expression levels and prognostic value of TMX family members in pan-cancer and analyzed their association between TME, immune infiltration, stemness scores, and drug sensitivity. Using KEGG enrichment analysis, we explored the potential signaling pathways of their regulation. Additionally, we conducted a transwell assay to verify the relationship between TMX family gene expression and epithelial-mesenchymal transition (EMT) in liver cancer.

RESULTS

Expression of the TMX family genes was shown to have an obvious intratumoral heterogeneity. In some cancers, TMX family members expression was also been found to correlate with poor prognosis of patients. Furthermore, TMX family genes may serve important roles in TME. The expression of TMX family genes was found to have a strong correlation with the stromal scores, immune scores, DNAss and RNAss in pan-cancer. Specifically, the expression levels of TMX family genes have been found to be associated with immune subtypes of renal clear cell carcinoma and liver hepatocellular carcinoma. High TMX2 expression promote EMT in liver cancer.

CONCLUSIONS

The findings of this study may elucidate the biological roles of TMX family genes as potential targets for pan-cancer and also offer valuable insights for further investigating how these genes function in the development and spreading of cancer.

Chemoselective Fluorogenic Bioconjugation of Vicinal Dithiol-Containing Proteins for Live Cellular Imaging via Small Molecular Conjugate Acceptors

To develop small molecular fluorogenic tools for the chemoselective labeling of vicinal dithiol-containing proteins (VDPs) in live cells is important for studying intracellular redox homeostasis. With this research, we developed small molecule-based fluorescent probes, achieving selective labeling of VDPs through thiol-thiol substitutions on bisvinylogous thioester conjugated acceptors (IDAs). Initially, IDAs demonstrated its ability to bridge vicinal cysteine-sulfhydryls on a peptide as a mimic. Then, the peptide complex could be decoupled to recover the original peptide-SH in the presence of dithiothreitol. Furthermore, fluorometric signal amplification of the fluorescent probes occurred with high sensitivity, low limit of detection, and selectivity toward vicinal dithiols on reduced bovine serum albumin, as an example of real world VDPs. More importantly, the probes were utilized successfully for labeling of endogenous VDPs at different redox states in live cells. Thus, the bisvinylogous thioester-based receptor as a functional probe represents a new platform for uncovering the function of VDPs in live cells.

A Genome-Wide Association Study Reveals Region Associated with Seed Protein Content in Cowpea

Cowpea (Vigna unguiculata L. Walp., 2n = 2x = 22) is a protein-rich crop that complements staple cereals for humans and serves as fodder for livestock. It is widely grown in Africa and other developing countries as the primary source of protein in the diet; therefore, it is necessary to identify the protein-related loci to improve cowpea breeding. In the current study, we conducted a genome-wide association study (GWAS) on 161 cowpea accessions (151 USDA germplasm plus 10 Arkansas breeding lines) with a wide range of seed protein contents (21.8~28.9%) with 110,155 high-quality whole-genome single-nucleotide polymorphisms (SNPs) to identify markers associated with protein content, then performed genomic prediction (GP) for future breeding. A total of seven significant SNP markers were identified using five GWAS models (single-marker regression (SMR), the general linear model (GLM), Mixed Linear Model (MLM), Fixed and Random Model Circulating Probability Unification (FarmCPU), and Bayesian-information and Linkage-disequilibrium Iteratively Nested Keyway (BLINK), which are located at the same locus on chromosome 8 for seed protein content. This locus was associated with the gene Vigun08g039200, which was annotated as the protein of the thioredoxin superfamily, playing a critical function for protein content increase and nutritional quality improvement. In this study, a genomic prediction (GP) approach was employed to assess the accuracy of predicting seed protein content in cowpea. The GP was conducted using cross-prediction with five models, namely ridge regression best linear unbiased prediction (rrBLUP), Bayesian ridge regression (BRR), Bayesian A (BA), Bayesian B (BB), and Bayesian least absolute shrinkage and selection operator (BL), applied to seven random whole genome marker sets with different densities (10 k, 5 k, 2 k, 1 k, 500, 200, and 7), as well as significant markers identified through GWAS. The accuracies of the GP varied between 42.9% and 52.1% across the seven SNPs considered, depending on the model used. These findings not only have the potential to expedite the breeding cycle through early prediction of individual performance prior to phenotyping, but also offer practical implications for cowpea breeding programs striving to enhance seed protein content and nutritional quality.

Emerging Chemical Biology of Protein Persulfidation

Significance: Protein persulfidation (the formation of RSSH), an evolutionarily conserved oxidative posttranslational modification in which thiol groups in cysteine residues are converted into persulfides, has emerged as one of the main mechanisms through which hydrogen sulfide (H2S) conveys its signaling. Recent Advances: New methodological advances in persulfide labeling started unraveling the chemical biology of this modification and its role in (patho)physiology. Some of the key metabolic enzymes are regulated by persulfidation. RSSH levels are important for the cellular defense against oxidative injury, and they decrease with aging, leaving proteins vulnerable to oxidative damage. Persulfidation is dysregulated in many diseases. Critical Issues: A relatively new field of signaling by protein persulfidation still has many unanswered questions: the mechanism(s) of persulfide formation and transpersulfidation and the identification of "protein persulfidases," the improvement of methods to monitor RSSH changes and identify protein targets, and understanding the mechanisms through which this modification controls important (patho)physiological functions. Future Directions: Deep mechanistic studies using more selective and sensitive RSSH labeling techniques will provide high-resolution structural, functional, quantitative, and spatiotemporal information on RSSH dynamics and help with better understanding how H2S-derived protein persulfidation affects protein structure and function in health and disease. This knowledge could pave the way for targeted drug design for a wide variety of pathologies. Antioxid. Redox Signal. 39, 19-39.

Disruption of Bacterial Thiol-Dependent Redox Homeostasis by Magnolol and Honokiol as an Antibacterial Strategy

Some traditional Chinese medicines (TCMs) possess various redox-regulation properties, but whether the redox regulation contributes to antibacterial mechanisms is not known. Here, ginger juice processed Magnoliae officinalis cortex (GMOC) was found to show strong antibacterial activities against some Gram-positive bacteria, but not Gram-negative bacteria including E. coli, while the redox-related transcription factor oxyR deficient E. coli mutant was sensitive to GMOC. In addition, GMOC and its main ingredients, magnolol and honokiol, exhibited inhibitory effects on the bacterial thioredoxin (Trx) system, a major thiol-dependent disulfide reductase system in bacteria. The effects of magnolol and honokiol on cellular redox homeostasis were further verified by elevation of the intracellular ROS levels. The therapeutic efficacies of GMOC, magnolol and honokiol were further verified in S. aureus-caused mild and acute peritonitis mouse models. Treatments with GMOC, magnolol and honokiol significantly reduced the bacterial load, and effectively protected the mice from S. aureus-caused peritonitis infections. Meanwhile, magnolol and honokiol produced synergistic effects when used in combination with several classic antibiotics. These results strongly suggest that some TCMs may exert their therapeutic effects via targeting the bacterial thiol-dependent redox system.

The Importance of Thioredoxin-1 in Health and Disease

Thioredoxin-1 (Trx-1) is a multifunctional protein ubiquitously found in the human body. Trx-1 plays an important role in various cellular functions such as maintenance of redox homeostasis, proliferation, and DNA synthesis, but also modulation of transcription factors and control of cell death. Thus, Trx-1 is one of the most important proteins for proper cell and organ function. Therefore, modulation of Trx gene expression or modulation of Trx activity by various mechanisms, including post-translational modifications or protein-protein interactions, could cause a transition from the physiological state of cells and organs to various pathologies such as cancer, and neurodegenerative and cardiovascular diseases. In this review, we not only discuss the current knowledge of Trx in health and disease, but also highlight its potential function as a biomarker.

Apolipoprotein D in Oxidative Stress and Inflammation

Apolipoprotein D (ApoD) is lipocalin able to bind hydrophobic ligands. The APOD gene is upregulated in a number of pathologies, including Alzheimer's disease, Parkinson's disease, cancer, and hypothyroidism. Upregulation of ApoD is linked to decreased oxidative stress and inflammation in several models, including humans, mice, Drosophila melanogaster and plants. Studies suggest that the mechanism through which ApoD modulates oxidative stress and regulate inflammation is via its capacity to bind arachidonic acid (ARA). This polyunsaturated omega-6 fatty acid can be metabolised to generate large variety of pro-inflammatory mediators. ApoD serves as a sequester, blocking and/or altering arachidonic metabolism. In recent studies of diet-induced obesity, ApoD has been shown to modulate lipid mediators derived from ARA, but also from eicosapentaenoic acid and docosahexaenoic acid in an anti-inflammatory way. High levels of ApoD have also been linked to better metabolic health and inflammatory state in the round ligament of morbidly obese women. Since ApoD expression is upregulated in numerous diseases, it might serve as a therapeutic agent against pathologies aggravated by OS and inflammation such as many obesity comorbidities. This review will present the most recent findings underlying the central role of ApoD in the modulation of both OS and inflammation.

AC81 Is a Putative Disulfide Isomerase Involved in Baculoviral Disulfide Bond Formation

The correct formation of native disulfide bonds is critical for the proper structure and function of many proteins. Cellular disulfide bond formation pathways commonly consist of two parts: sulfhydryl oxidase-mediated oxidation and disulfide isomerase-mediated isomerization. Some large DNA viruses, such as baculoviruses, encode sulfhydryl oxidases, but viral disulfide isomerases have not yet been identified, although G4L in poxvirus has been suggested to serve such a function. Here, we report that the baculovirus core gene ac81 encodes a putative disulfide isomerase. ac81 is conserved in baculoviruses, nudiviruses, and hytrosaviruses. We found that AC81 homologs contain a typical thioredoxin fold conserved in disulfide isomerases. To determine the role of AC81, a series of Autographa californica nucleopolyhedrovirus (AcMNPV) bacmids containing ac81 knockout or point mutations was generated, and the results showed that AC81 is essential for budded virus production, multinucleocapsid occlusion-derived virus (ODV) formation, and ODV embedding in occlusion bodies. Nonreducing Western blot analysis indicated that disulfide bond formation in per os infectivity factor 5 (PIF5), a substrate of the baculoviral sulfhydryl oxidase P33, was abnormal when ac81 was knocked out or mutated. Pulldown assays showed that AC81 interacted with PIF5 and P33 in infected cells. In addition, two critical regions that harbor key amino acids for function were identified in AC81. Taken together, our results suggest that AC81 is a key component involved in the baculovirus disulfide bond formation pathway and likely functions as a disulfide isomerase. IMPORTANCE Many large DNA viruses, such as poxvirus, asfarvirus, and baculovirus, encode their own sulfhydryl oxidase to facilitate the disulfide bond formation of viral proteins. Here, we show that AC81 functions as a putative disulfide isomerase and is involved in multiple functions of the baculovirus life cycle. Interestingly, AC81 and P33 (sulfhydryl oxidase) are conserved in baculoviruses, nudiviruses, and hytrosaviruses, which are all insect-specific large DNA viruses replicating in the nucleus, suggesting that viral disulfide bond formation is an ancient mechanism shared by these viruses.

Promiscuity of response regulators for thioredoxin steers bacterial virulence

The exquisite specificity between a sensor kinase and its cognate response regulator ensures faithful partner selectivity within two-component pairs concurrently firing in a single bacterium, minimizing crosstalk with other members of this conserved family of paralogous proteins. We show that conserved hydrophobic and charged residues on the surface of thioredoxin serve as a docking station for structurally diverse response regulators. Using the OmpR protein, we identify residues in the flexible linker and the C-terminal β-hairpin that enable associations of this archetypical response regulator with thioredoxin, but are dispensable for interactions of this transcription factor to its cognate sensor kinase EnvZ, DNA or RNA polymerase. Here we show that the promiscuous interactions of response regulators with thioredoxin foster the flow of information through otherwise highly dedicated two-component signaling systems, thereby enabling both the transcription of Salmonella pathogenicity island-2 genes as well as growth of this intracellular bacterium in macrophages and mice.

Identification and characterization of Eimeria tenella EtTrx1 protein

Thioredoxin (Trx) is a widespread protein regulator of redox reactions in all organisms. It operates together with NADPH and thioredoxin reductase as a general protein disulfide catalytic system. Recently, Trx has been found to be related to the process by which apicomplexan protozoa invade host cells. In this study, Eimeria tenella thioredoxin (EtTrx1) was identified and its gene structural features, expression levels at different developmental stages, localization in sporozoites, roles in adhesion and invasion, and immunogenicity were investigated. Sequence analysis indicated that EtTrx1 contains a Trx domain with a WCGPC motif in 29-33 aa and a typical Trx fold, and belongs to thioredoxin family. EtTrx1 was detected on the surface of sporozoites using anti-EtTrx1 polyclonal antibodies under non-permeabilized conditions by indirect immunofluorescence assay (IFA) and also in a secretion form. EtTrx1 protein was highly transcribed and expressed in merozoites and sporozoites by quantitative PCR and western blot. The attachment assay showed that the adherence rates of yeast cells expressing EtTrx1 on the surface to host cells were 3.1-fold higher than those of the blank control. Specific anti-EtTrx1 antibodies inhibited the invasion of sporozoites into DF-1 cells. The highest inhibition rate was up to 36.75% compared to the control group. Immunization with recombinant EtTrx1 peptides also showed significant protection against lethal infections in chickens. It could offer moderate protective efficacy (Anticoccidial Index [ACI]: 163.70), induce humoral responses, and be an effective candidate for the development of new vaccines.

DciA Helicase Operators Exhibit Diversity across Bacterial Phyla

A fundamental requirement for life is the replication of an organism's DNA. Studies in Escherichia coli and Bacillus subtilis have set the paradigm for DNA replication in bacteria. During replication initiation in E. coli and B. subtilis, the replicative helicase is loaded onto the DNA at the origin of replication by an ATPase helicase loader. However, most bacteria do not encode homologs to the helicase loaders in E. coli and B. subtilis. Recent work has identified the DciA protein as a predicted helicase operator that may perform a function analogous to the helicase loaders in E. coli and B. subtilis. DciA proteins, which are defined by the presence of a DUF721 domain (termed the DciA domain herein), are conserved in most bacteria but have only been studied in mycobacteria and gammaproteobacteria (Pseudomonas aeruginosa and Vibrio cholerae). Sequences outside the DciA domain in Mycobacterium tuberculosis DciA are essential for protein function but are not conserved in the P. aeruginosa and V. cholerae homologs, raising questions regarding the conservation and evolution of DciA proteins across bacterial phyla. To comprehensively define the DciA protein family, we took a computational evolutionary approach and analyzed the domain architectures and sequence properties of DciA domain-containing proteins across the tree of life. These analyses identified lineage-specific domain architectures among DciA homologs, as well as broadly conserved sequence-structural motifs. The diversity of DciA proteins represents the evolution of helicase operation in bacterial DNA replication and highlights the need for phylum-specific analyses of this fundamental biological process. IMPORTANCE Despite the fundamental importance of DNA replication for life, this process remains understudied in bacteria outside Escherichia coli and Bacillus subtilis. In particular, most bacteria do not encode the helicase-loading proteins that are essential in E. coli and B. subtilis for DNA replication. Instead, most bacteria encode a DciA homolog that likely constitutes the predominant mechanism of helicase operation in bacteria. However, it is still unknown how DciA structure and function compare across diverse phyla that encode DciA proteins. In this study, we performed computational evolutionary analyses to uncover tremendous diversity among DciA homologs. These studies provide a significant advance in our understanding of an essential component of the bacterial DNA replication machinery.

Recent trends in the application of nanoparticles in cancer therapy: The involvement of oxidative stress

In the biomedical area, the interdisciplinary field of nanotechnology has the potential to bring numerous unique applications, including better tactics for cancer detection, diagnosis, and therapy. Nanoparticles (NPs) have been the topic of many research and material applications throughout the last decade. Unlike small-molecule medications, NPs are defined by distinct physicochemical characteristics, such as a large surface-to-volume ratio, which allows them to permeate live cells with relative ease. The versatility of NPs as both therapeutics and diagnostics makes them ideal for a broad spectrum of illnesses, from infectious diseases to cancer. A significant amount of data has been participated in the current scientific publications, emphasizing the concept that NPs often produce reactive oxygen species (ROS) to a larger degree than micro-sized particles. It is important to note that oxidative stress governs a wide range of cell signaling cascades, many of which are responsible for cancer cell cytotoxicity. Here, we aimed to provide insight into the signaling pathways triggered by oxidative stress in cancer cells in response to several types of nanomaterials, such as metallic and polymeric NPs and quantum dots. We discuss recent advances in developing integrated anticancer medicines based on NPs targeted to destroy malignant cells by increasing their ROS setpoint.

In vitro colistin susceptibility of pandrug-resistant Acinetobacter baumannii is restored in the presence of selenium nanoparticles

AIMS

To investigate the synergistic activity of colistin and selenium nanoparticles (SeNPs) against pandrug-resistant (PDR) Acinetobacter baumannii.

METHODS AND RESULTS

Chequerboard and time-kill assays were employed to explore the potential synergistic interactions between colistin and SeNPs against A. baumannii isolates (8), previously determined as colistin-resistant (MIC range 16-256 μg ml^-1 ). Also, whole-genome sequencing (WGS) and gene expression analyses were used to elucidate the mechanisms of colistin resistance. Exceptionally strong synergistic activity (FICI range 0.004-0.035) of colistin and SeNPs against colistin-resistant isolates was revealed. Colistin (0.5 or 1 μg ml^-1 ) used in combination with SeNPs (0.5 μg ml^-1 ) was able to reduce initial inoculum during the first 4 h of incubation, in contrast to colistin (0.5, 1 or 2 μg ml^-1 ) alone.

CONCLUSIONS

These findings propose colistin/SeNPs combination as a new option to fight PDR A. baumannii, the therapeutic possibilities of which should be proved in future in vivo studies.

SIGNIFICANCE AND IMPACT OF STUDY

Here we present the first evidence of synergy between colistin and selenium compounds against bacteria in general. Also, WGS and gene expression analyses provide some new insights into A. baumannii colistin resistance mechanisms.

Thioredoxin-1: A Promising Target for the Treatment of Allergic Diseases

Thioredoxin-1 (Trx1) is an important regulator of cellular redox homeostasis that comprises a redox-active dithiol. Trx1 is induced in response to various stress conditions, such as oxidative damage, infection or inflammation, metabolic dysfunction, irradiation, and chemical exposure. It has shown excellent anti-inflammatory and immunomodulatory effects in the treatment of various human inflammatory disorders in animal models. This review focused on the protective roles and mechanisms of Trx1 in allergic diseases, such as allergic asthma, contact dermatitis, food allergies, allergic rhinitis, and drug allergies. Trx1 plays an important role in allergic diseases through processes, such as antioxidation, inhibiting macrophage migration inhibitory factor (MIF), regulating Th1/Th2 immune balance, modulating allergic inflammatory cells, and suppressing complement activation. The regulatory mechanism of Trx1 differs from that of glucocorticoids that regulates the inflammatory reactions associated with immune response suppression. Furthermore, Trx1 exerts a beneficial effect on glucocorticoid resistance of allergic inflammation by inhibiting the production and internalization of MIF. Our results suggest that Trx1 has the potential for future success in translational research.

Identifying Interaction Partners of Yeast Protein Disulfide Isomerases Using a Small Thiol-Reactive Cross-Linker: Implications for Secretory Pathway Proteostasis

Protein disulfide isomerases (PDIs) function in forming the correct disulfide bonds in client proteins, thereby aiding the folding of proteins that enter the secretory pathway. Recently, several PDIs have been identified as targets of organic electrophiles, yet the client proteins of specific PDIs remain largely undefined. Here, we report that PDIs expressed in Saccharomyces cerevisiae are targets of divinyl sulfone (DVSF) and other thiol-reactive protein cross-linkers. Using DVSF, we identified the interaction partners that were cross-linked to Pdi1 and Eug1, finding that both proteins form cross-linked complexes with other PDIs, as well as vacuolar hydrolases, proteins involved in cell wall biosynthesis and maintenance, and many ER proteostasis factors involved ER stress signaling and ER-associated protein degradation (ERAD). The latter discovery prompted us to examine the effects of DVSF on ER quality control, where we found that DVSF inhibits the degradation of the ERAD substrate CPY*, in addition to covalently modifying Ire1 and blocking the activation of the unfolded protein response. Our results reveal that DVSF targets many proteins within the ER proteostasis network and suggest that these proteins may be suitable targets for covalent therapeutic development in the future.

Activity-based Crosslinking to Identify Substrates of Thioredoxin-domain Proteinsin Malaria Parasites

Malaria remains a major public health issue, infecting nearly 220 million people every year. The spread of drug-resistant strains of Plasmodium falciparum around the world threatens the progress made against this disease. Therefore, identifying druggable and essential pathways in P. falciparum parasites remains a major area of research. One poorly understood area of parasite biology is the formation of disulfide bonds, which is an essential requirement for the folding of numerous proteins. Specialized chaperones with thioredoxin (Trx) domains catalyze the redox functions necessary for breaking incorrect and forming correct disulfide bonds in proteins. Defining the substrates of these redox chaperones is difficult and immunoprecipitation based assays cannot distinguish between substrates and interacting partners. Further, the substrate or client interactions with the redox chaperones are usually transient in nature. Activity based crosslinkers that rely on the nucleophilic cysteines on Trx domains and the disulfide bond forming cysteines on clients provide an easily scalable method to trap and identify the substrates of Trx-domain containing chaperones. The cell permeable crosslinker divinyl sulfone (DVSF) is active only in the presence of nucleophilic cysteines in proteins and, therefore, traps Trx domains with their substrates, as they form mixed disulfide bonds during the course of their catalytic activity. This allows the identification of substrates that rely on Trx activity for their folding, as well as discovering small molecules that interfere with Trx domain activity. Graphic abstract: Identification of thioredoxin domain substrates via divinylsulfone crosslinking and immunoprecipitation-mass spectrometry.

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.

A proximity-based in silico approach to identify redox-labile disulfide bonds: The example of FVIII

Allosteric disulfide bonds permit highly responsive, transient 'switch-like' properties that are ideal for processes like coagulation and inflammation that require rapid and localised responses to damage or injury. Haemophilia A (HA) is a rare bleeding disorder managed with exogenous coagulation factor(F) VIII products. FVIII has eight disulfide bonds and is known to be redox labile, but it is not known how reduction/oxidation affects the structure-function relationship, or its immunogenicity-a serious complication for 30% severe HA patients. Understanding how redox-mediated changes influence FVIII can inform molecular engineering strategies aimed at improving activity and stability, and reducing immunogenicity. FVIII is a challenging molecule to work with owing to its poor expression and instability so, in a proof-of-concept study, we used molecular dynamics (MD) to identify which disulfide bonds were most likely to be reduced and how this would affect structure/function; results were then experimentally verified. MD identified Cys1899-Cys1903 disulfide as the most likely to undergo reduction based on energy and proximity criteria. Further MD suggested this reduction led to a more open conformation. Here we present our findings and highlight the value of MD approaches.

YjbH mediates the oxidative stress response and infection by regulating SpxA1 and the phosphoenolpyruvate-carbohydrate phosphotransferase system (PTS) in Listeria monocytogenes

The foodborne pathogen Listeria monocytogenes relies on its ability to fine-tune the expression of virulence factors and stress regulators in response to rapidly changing environments. Here, we reveal that YjbH, a putative thioredoxin family oxidoreductase, plays a pivotal role in bacterial adaption to oxidative stress and host infection. YjbH directly interacts with SpxA1, an ArsC family oxidative stress response regulator, and the deletion of YjbH compromised the oxidative stress tolerance of L. monocytogenes. Also, YjbH is required for the bacterial spread in host cells and proliferation in mouse organs, thereby contributing to virulence. Transcriptomic analysis of strains treated with Cd²⁺ revealed that most virulence genes and phosphoenolpyruvate-carbohydrate phosphotransferase system (PTS) genes were significantly downregulated in the absence of YjbH. However, YjbH inhibits PrfA expression when bacteria were grown in the media, suggesting that YjbH participates in regulating the virulence genes via a complicated regulatory network involving PrfA and PTS. Collectively, these findings provide a valuable model for clarifying the roles of thioredoxins from foodborne pathogens regarding improving survival in the external environment and, more importantly, successfully establishing infection within the host.

A fluorescent probe for specifically measuring the overall thioredoxin and glutaredoxin reducing activity in bacterial cells

Both bacterial thioredoxin and glutaredoxin systems can reduce TRFS-green selectively, which confers TRFS-green to be a remarkable probe to detect the dominant disulfide reductase activity with a slow reaction rate in bacteria, e. g. E. coli Grx2&3.

A Novel Immunomodulator Delivery Platform Based on Bacterial Biomimetic Vesicles for Enhanced Antitumor Immunity

T cell activation-induced cell death (AICD) during tumor pathogenesis is a tumor immune escape process dependent on dendritic cells (DCs). Proper immune-modulatory therapies effectively inhibit tumor-specific CD8+ T cell exhaustion and enhance antitumor immune responses. Here, high-pressure homogenization is utilized to drive immunomodulator IL10-modified bacteria to extrude through the gap and self-assemble into bacterial biomimetic vesicles exposing IL10 (IL10-BBVs) on the surface with high efficiency. IL10-BBVs efficiently target DCs in tumor-draining lymph nodes and thus increase the interaction between IL10 on BBVs and IL10R on DCs to suppress AICD and mitigate CD8+ T cell exhaustion specific to tumor antigens. Two subcutaneous peripheral injections of IL10-BBVs 1 week apart in tumor-bearing mice effectively increase systemic and intratumoral proportions of CD8+ T cells to suppress tumor growth and metastasis. Tumor-specific antigen E7 is enclosed into the periplasm of IL10-BBVs (IL10-E7-BBVs) to realize concurrent actions of the immunomodulator IL10 and the tumor antigen human papillomavirus (HPV) 16E7 in lymph nodes, further enhancing the antitumor effects mediated by CD8+ T cells. The development of this modified BBV delivery platform will expand the application of bacterial membranes and provide novel immunotherapeutic strategies for tumor treatment.

Aim32 is a dual-localized 2Fe-2S mitochondrial protein that functions in redox quality control

Yeast is a facultative anaerobe and uses diverse electron acceptors to maintain redox-regulated import of cysteine-rich precursors via the mitochondrial intermembrane space assembly (MIA) pathway. With the growing diversity of substrates utilizing the MIA pathway, understanding the capacity of the intermembrane space (IMS) to handle different types of stress is crucial. We used MS to identify additional proteins that interacted with the sulfhydryl oxidase Erv1 of the MIA pathway. Altered inheritance of mitochondria 32 (Aim32), a thioredoxin-like [2Fe-2S] ferredoxin protein, was identified as an Erv1-binding protein. Detailed localization studies showed that Aim32 resided in both the mitochondrial matrix and IMS. Aim32 interacted with additional proteins including redox protein Osm1 and protein import components Tim17, Tim23, and Tim22. Deletion of Aim32 or mutation of conserved cysteine residues that coordinate the Fe-S center in Aim32 resulted in an increased accumulation of proteins with aberrant disulfide linkages. In addition, the steady-state level of assembled TIM22, TIM23, and Oxa1 protein import complexes was decreased. Aim32 also bound to several mitochondrial proteins under nonreducing conditions, suggesting a function in maintaining the redox status of proteins by potentially targeting cysteine residues that may be sensitive to oxidation. Finally, Aim32 was essential for growth in conditions of stress such as elevated temperature and hydroxyurea, and under anaerobic conditions. These studies suggest that the Fe-S protein Aim32 has a potential role in general redox homeostasis in the matrix and IMS. Thus, Aim32 may be poised as a sensor or regulator in quality control for a broad range of mitochondrial proteins.

Modulating skin colour: role of the thioredoxin and glutathione systems in regulating melanogenesis

Different skin colour among individuals is determined by the varying amount and types of melanin pigment. Melanin is produced in melanocytes, a type of dendritic cell located in the basal layer of the epidermis, through the process of melanogenesis. Melanogenesis consists of a series of biochemical and enzymatic reactions catalysed by tyrosinase and other tyrosinase-related proteins, leading to the formation of two types of melanin, eumelanin and pheomelanin. Melanogenesis can be regulated intrinsically by several signalling pathways, including the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), stem cell factor (SCF)/c-kit and wingless-related integration site (Wnt)/β-catenin signalling pathways. Ultraviolet radiation (UVR) is the major extrinsic factor in the regulation of melanogenesis, through the generation of reactive oxygen species (ROS). Antioxidants or antioxidant systems, with the ability to scavenge ROS, may decrease melanogenesis. This review focuses on the two main cellular antioxidant systems, the thioredoxin (Trx) and glutathione (GSH) systems, and discusses their roles in melanogenesis. In the Trx system, high levels/activities of thioredoxin reductase (TrxR) are correlated with melanin formation. The GSH system is linked with regulating pheomelanin formation. Exogenous addition of GSH has been shown to act as a depigmenting agent, suggesting that other antioxidants may also have the potential to act as depigmenting agents for the treatment of human hyperpigmentation disorders.

Solution structure of multi-domain protein ER-60 studied by aggregation-free SAXS and coarse-grained-MD simulation

Multi-domain proteins (MDPs) show a variety of domain conformations under physiological conditions, regulating their functions through such conformational changes. One of the typical MDPs, ER-60 which is a protein folding enzyme, has a U-shape with four domains and is thought to have different domain conformations in solution depending on the redox state at the active centres of the edge domains. In this work, an aggregation-free small-angle X-ray scattering revealed that the structures of oxidized and reduced ER-60 in solution are different from each other and are also different from those in the crystal. Furthermore, structural modelling with coarse-grained molecular dynamics simulation indicated that the distance between the two edge domains of oxidized ER-60 is longer than that of reduced ER-60. In addition, one of the edge domains has a more flexible conformation than the other.

Cu(II)-Binding N-Terminal Sequences of Human Proteins

Proteins anchor copper(II) ions mainly by imidazole from histidine residues located in different positions in the primary protein structures. However, the motifs with histidine in the first three N-terminal positions (His¹ , His² , and His³ ) show unique Cu(II)-binding properties, such as availability from the surface of the protein, high flexibility, and high Cu(II) exchangeability with other ligands. It makes such sequences beneficial for the fast exchange of Cu(II) between ligands. Furthermore, sequences with His¹ and His² , thus, non-saturating the Cu(II) coordination sphere, are redox-active and may play a role in Cu(II) reduction to Cu(I). All human protein sequences deposited in UniProt Knowledgebase were browsed for those containing His¹ , His² , or His³ . Proteolytically modified sequences (with the removal of a propeptide or Met residue) were taken for the analysis. Finally, the sequences were sorted out according to the subcellular localization of the proteins to match the respective sequences with the probability of interaction with divalent copper.

Development of a Multiplex Bead Assay for the Detection of IgG Antibody Responses to Guinea Worm

The success of the Guinea Worm (GW) Eradication Program over the past three decades has been tempered by the persistence of GW disease in a few African nations and the potential for a future resurgence in cases. Domestic dogs are now a major concern as a disease reservoir as large numbers of cases of canine GW disease are now reported each year, mainly along the Chari River in Chad. As a first step toward the development of a serologic assay for dogs, archived human plasma samples from dracunculiasis-positive donors from Togo were used to select adult female GW antigens for peptide sequencing and cloning. Eight protein sequences of interest were expressed as recombinant glutathione-S-transferase (GST) fusion proteins, and the most promising proteins were coupled to carboxylated microspheres for use in multiplex assays. A thioredoxin-like protein (TRXL1) and a domain of unknown function (DUF148) were assessed for total IgG and IgG4 reactivities using a panel of specimens from GW cases, uninfected donors, and individuals infected with various nematode worms, including Onchocerca volvulus. Both the DUF148-GST and the TRXL1-GST assays cross-reacted with O. volvulus sera, but the latter assay was always the more specific. The IgG4 and total IgG TRXL1-GST assays both had sensitivities > 87% and specificities > 90%. Maximum specificity (> 96%) was obtained with the total IgG assay when reactivity to both antigens was used to define a positive case. Given the good performance of the human assay, we are now working to modify the assay for dog assessments.

Isofunctional Clustering and Conformational Analysis of the Arsenate Reductase Superfamily Reveals Nine Distinct Clusters

Arsenate reductase (ArsC) is a superfamily of enzymes that reduce arsenate. Due to active site similarities, some ArsC can function as low-molecular weight protein tyrosine phosphatases (LMW-PTPs). Broad superfamily classifications align with redox partners (Trx- or Grx-linked). To understand this superfamily's mechanistic diversity, the ArsC superfamily is classified on the basis of active site features utilizing the tools TuLIP (two-level iterative clustering process) and autoMISST (automated multilevel iterative sequence searching technique). This approach identified nine functionally relevant (perhaps isofunctional) protein groups. Five groups exhibit distinct ArsC mechanisms. Three are Grx-linked: group 4AA (classical ArsC), group 3AAA (YffB-like), and group 5BAA. Two are Trx-linked: groups 6AAAAA and 7AAAAAAAA. One is an Spx-like transcriptional regulatory group, group 5AAA. Three are potential LMW-PTP groups: groups 7BAAAA, and 7AAAABAA, which have not been previously identified, and the well-studied LMW-PTP family group 8AAA. Molecular dynamics simulations were utilized to explore functional site details. In several families, we confirm and add detail to literature-based mechanistic information. Mechanistic roles are hypothesized for conserved active site residues in several families. In three families, simulations of the unliganded structure sample specific conformational ensembles, which are proposed to represent either a more ligand-binding-competent conformation or a pathway toward a more binding-competent state; these active sites may be designed to traverse high-energy barriers to the lower-energy conformations necessary to more readily bind ligands. This more detailed biochemical understanding of ArsC and ArsC-like PTP mechanisms opens possibilities for further understanding of arsenate bioremediation and the LMW-PTP mechanism.

Depletion of multidrug-resistant uropathogenic Escherichia coli BC1 by ebselen and silver ion

Ebselen, an organo‐selenium compound with well‐characterized toxicology and pharmacology, recently exhibited potent antibacterial activity against glutathione (GSH)‐negative bacteria by disrupting redox homeostasis. In this paper, we show that ebselen and silver ion in combination exert strong bactericidal activity against multidrug‐resistant (MDR) uropathogenic Escherichia coli (UPEC) BC1, a model MDR GSH‐positive bacterium. The mechanisms were found to involve consumption of total intracellular GSH and inhibition of thioredoxin reductase activity, which was highly related to reactive oxygen species up‐regulation. Furthermore, the therapeutic efficacy of ebselen and silver ion against UPEC‐induced cystitis was assessed in a mouse model. Treatment with ebselen and silver ion significantly reduced bacterial loads, down‐regulated the expression levels of tumour necrosis factor‐α (TNF‐α) and interferon‐γ (IFN‐γ) on‐site and decreased white/red blood cell counts in mild cystitis model mice, which demonstrated the anti‐inflammatory property of these agents. In addition, ebselen and silver ion also exhibited significantly high protective ability (100%) against acute cystitis infections. These results together may lay the foundation for further analysis and development of ebselen and silver ion as antibacterial agents for treatment of MDR UPEC infections.

Oxidative Stress in Cancer

Contingent upon concentration, reactive oxygen species (ROS) influence cancer evolution in apparently contradictory ways, either initiating/stimulating tumorigenesis and supporting transformation/proliferation of cancer cells or causing cell death. To accommodate high ROS levels, tumor cells modify sulfur-based metabolism, NADPH generation, and the activity of antioxidant transcription factors. During initiation, genetic changes enable cell survival under high ROS levels by activating antioxidant transcription factors or increasing NADPH via the pentose phosphate pathway (PPP). During progression and metastasis, tumor cells adapt to oxidative stress by increasing NADPH in various ways, including activation of AMPK, the PPP, and reductive glutamine and folate metabolism.

Deletion of glutaredoxin promotes oxidative tolerance and intracellular infection in Listeria monocytogenes

Thiol-disulfide glutaredoxin systems of bacterial cytoplasm favor reducing conditions for the correct disulfide bonding of functional proteins, and therefore were employed by bacteria to defend against oxidative stress. Listeria monocytogenes has been shown to encode a putative glutaredoxin, Grx (encoded by lmo2344), while the underlying roles remain unknown. Here we suggest an unexpected role of L. monocytogenes Grx in oxidative tolerance and intracellular infection. The recombinant Grx was able to efficiently catalyze the thiol-disulfide oxidoreduction of insulin in the presence of DTT as an election donor. Unexpectedly, the deletion of grx resulted in a remarkably increased tolerance and survival ability of this bacteria when exposed to various oxidizing agents, including diamide, and copper and cadmium ions. Furthermore, loss of grx significantly promoted bacterial invasion and proliferation in human epithelial Caco-2 cells and murine macrophages, as well as a notably increasing invasion but not cell-to-cell spread in the murine fibroblasts L929 cells. More importantly, L. monocytogenes lacking the glutaredoxin exhibited more efficient proliferation and recovery in the spleens and livers of the infected mice, and hence became more virulent by upregulating the virulence factors, InlA and InlB. In summary, we here for the first time demonstrated that L. monocytogenes glutaredoxin plays a counterintuitive role in bacterial oxidative resistance and intracellular infection, which is the first report to provide valuable evidence for the role of glutaredoxins in bacterial infection, and more importantly suggests a favorable model to illustrate the functional diversity of bacterial Grx systems during environmental adaption and host infection.

Synthesis of N-Aryl- and N-alkyl-Substituted Imidazolium Silver Complexes: Cytotoxic Screening by Using Human Cell Lines Modelling Acute Myeloid Leukaemia

A series of N-aryl- and N-alkyl substituted imidazoles has been synthesised and complexed with Ag⁺ to obtain silver-NHC complexes of the form [Ag(NHC)₂ ]X. These silver-NHC complexes were tested in vitro against the human cell lines HL-60 and MOLM-13, which both model acute myeloid leukaemia (AML). A substantial difference in cytotoxicity was revealed varying in the range 13-4 μM and 22-9 μM for HL-60 and MOLM-13, respectively. Furthermore, this study revealed that when an alkyl group is installed on the imidazole scaffold, its position substantially influences the cytotoxicity of the corresponding silver NHC complex.

Redox Regulation in the Base Excision Repair Pathway: Old and New Players as Cancer Therapeutic Targets

BACKGROUND

Reactive Oxygen Species (ROS) are by-products of normal cellular metabolic processes, such as mitochondrial oxidative phosphorylation. While low levels of ROS are important signalling molecules, high levels of ROS can damage proteins, lipids and DNA. Indeed, oxidative DNA damage is the most frequent type of damage in the mammalian genome and is linked to human pathologies such as cancer and neurodegenerative disorders. Although oxidative DNA damage is cleared predominantly through the Base Excision Repair (BER) pathway, recent evidence suggests that additional pathways such as Nucleotide Excision Repair (NER) and Mismatch Repair (MMR) can also participate in clearance of these lesions. One of the most common forms of oxidative DNA damage is the base damage 8-oxoguanine (8-oxoG), which if left unrepaired may result in G:C to A:T transversions during replication, a common mutagenic feature that can lead to cellular transformation.

OBJECTIVE

Repair of oxidative DNA damage, including 8-oxoG base damage, involves the functional interplay between a number of proteins in a series of enzymatic reactions. This review describes the role and the redox regulation of key proteins involved in the initial stages of BER of 8-oxoG damage, namely Apurinic/Apyrimidinic Endonuclease 1 (APE1), human 8-oxoguanine DNA glycosylase-1 (hOGG1) and human single-stranded DNA binding protein 1 (hSSB1). Moreover, the therapeutic potential and modalities of targeting these key proteins in cancer are discussed.

CONCLUSION

It is becoming increasingly apparent that some DNA repair proteins function in multiple repair pathways. Inhibiting these factors would provide attractive strategies for the development of more effective cancer therapies.

Targeting the Redox Landscape in Cancer Therapy

Reactive oxygen species (ROS) are produced predominantly by the mitochondrial electron transport chain and by NADPH oxidases in peroxisomes and in the endoplasmic reticulum. The antioxidative defense counters overproduction of ROS with detoxifying enzymes and molecular scavengers, for instance, superoxide dismutase and glutathione, in order to restore redox homeostasis. Mutations in the redox landscape can induce carcinogenesis, whereas increased ROS production can perpetuate cancer development. Moreover, cancer cells can increase production of antioxidants, leading to resistance against chemo- or radiotherapy. Research has been developing pharmaceuticals to target the redox landscape in cancer. For instance, inhibition of key players in the redox landscape aims to modulate ROS production in order to prevent tumor development or to sensitize cancer cells in radiotherapy. Besides the redox landscape of a single cell, alternative strategies take aim at the multi-cellular level. Extracellular vesicles, such as exosomes, are crucial for the development of the hypoxic tumor microenvironment, and hence are explored as target and as drug delivery systems in cancer therapy. This review summarizes the current pharmaceutical and experimental interventions of the cancer redox landscape.

Molecular and functional characterization of unique thermo-halophilic thioredoxin from the metagenome of an exotic environment

The lower convective layer (LCL) at Atlantis II brine pool of the Red sea represents one of the exceptional, unique ecosystems. Thioredoxin is a multi-functional antioxidant redox protein that has a crucial role in various vital cellular processes. In the current study, a functional metagenomics approach was used to isolate and characterize thioredoxin from the LCL of Atlantis II Deep brine pool (Trx-ATII). From the metagenomic DNA of the LCL, the thioredoxin gene was directly retrieved and sequenced. Sequence analysis showed that the gene belonged to thioredoxin-like superfamily with classical Trx motif (-CXXC-). Phylogenetic analysis revealed that Trx-ATII was closely related to Trx of Prochlorococcus marinus with a maximum identity of 86%. Successfully, Trx-ATII was cloned and expressed in E. coli, where the purified protein had M.wt of 16 kDa. Characterization studies revealed that Trx-ATII protein is halophilic; can tolerate up to 2.5 M NaCl and thermostable, where 90% of its activity was retained at 60 °C. Trx-ATII can reduce both DTNB and insulin disulfide- containing substrates. In conclusion, a unique thioredoxin protein was isolated from a harsh environment that can maintain its activity under extreme conditions of salinity and temperature as a promising redox protein for biotechnological applications.

Predicting Reactive Cysteines with Implicit-Solvent-Based Continuous Constant pH Molecular Dynamics in Amber

Cysteines existing in the deprotonated thiolate form or having a tendency to become deprotonated are important players in enzymatic and cellular redox functions and frequently exploited in covalent drug design; however, most computational studies assume cysteines as protonated. Thus, developing an efficient tool that can make accurate and reliable predictions of cysteine protonation states is timely needed. We recently implemented a generalized Born (GB) based continuous constant pH molecular dynamics (CpHMD) method in Amber for protein pKa calculations on CPUs and GPUs. Here we benchmark the performance of GB-CpHMD for predictions of cysteine pKa's and reactivities using a data set of 24 proteins with both down- and upshifted cysteine pKa's. We found that 10 ns single-pH or 4 ns replica-exchange CpHMD titrations gave root-mean-square errors of 1.2-1.3 and correlation coefficients of 0.8-0.9 with respect to experiment. The accuracy of predicting thiolates or reactive cysteines at physiological pH with single-pH titrations is 86 or 81% with a precision of 100 or 90%, respectively. This performance well surpasses the traditional structure-based methods, particularly a widely used empirical pKa tool that gives an accuracy less than 50%. We discuss simulation convergence, dependence on starting structures, common determinants of the pKa downshifts and upshifts, and the origin of the discrepancies from the structure-based calculations. Our work suggests that CpHMD titrations can be performed on a desktop computer equipped with a single GPU card to predict cysteine protonation states for a variety of applications, from understanding biological functions to covalent drug design.

Evolution of mitochondrial protein import – lessons from trypanosomes

The evolution of mitochondrial protein import and the systems that mediate it marks the boundary between the endosymbiotic ancestor of mitochondria and a true organelle that is under the control of the nucleus. Protein import has been studied in great detail inSaccharomyces cerevisiae. More recently, it has also been extensively investigated in the parasitic protozoanTrypanosoma brucei, making it arguably the second best studied system. A comparative analysis of the protein import complexes of yeast and trypanosomes is provided. Together with data from other systems, this allows to reconstruct the ancestral features of import complexes that were present in the last eukaryotic common ancestor (LECA) and to identify which subunits were added later in evolution. How these data can be translated into plausible scenarios is discussed, providing insights into the evolution of (i) outer membrane protein import receptors, (ii) proteins involved in biogenesis of α-helically anchored outer membrane proteins, and (iii) of the intermembrane space import and assembly system. Finally, it is shown that the unusual presequence-associated import motor of trypanosomes suggests a scenario of how the two ancestral inner membrane protein translocases present in LECA evolved into the single bifunctional one found in extant trypanosomes.

Deciphering the Role of Multiple Thioredoxin Fold Proteins of Leptospirillum sp. in Oxidative Stress Tolerance

Thioredoxin fold proteins (TFPs) form a family of diverse proteins involved in thiol/disulfide exchange in cells from all domains of life. Leptospirillum spp. are bioleaching bacteria naturally exposed to extreme conditions like acidic pH and high concentrations of metals that can contribute to the generation of reactive oxygen species (ROS) and consequently the induction of thiol oxidative damage. Bioinformatic studies have predicted 13 genes that encode for TFP proteins in Leptospirillum spp. We analyzed the participation of individual tfp genes from Leptospirillum sp. CF-1 in the response to oxidative conditions. Genomic context analysis predicted the involvement of these genes in the general thiol-reducing system, cofactor biosynthesis, carbon fixation, cytochrome c biogenesis, signal transduction, and pilus and fimbria assembly. All tfp genes identified were transcriptionally active, although they responded differentially to ferric sulfate and diamide stress. Some of these genes confer oxidative protection to a thioredoxin-deficient Escherichia coli strain by restoring the wild-type phenotype under oxidative stress conditions. These findings contribute to our understanding of the diversity and complexity of thiol/disulfide systems, and of adaptations that emerge in acidophilic microorganisms that allow them to thrive in highly oxidative environments. These findings also give new insights into the physiology of these microorganisms during industrial bioleaching operations.

Topical Therapeutic Efficacy of Ebselen Against Multidrug-Resistant Staphylococcus aureus LT-1 Targeting Thioredoxin Reductase

As a thiol-dependent enzyme, thioredoxin reductase (TrxR) is a promising antibacterial drug target. Ebselen, an organo-selenium with well-characterized toxicology and pharmacology, was recently reported to have potent antibacterial activity against Staphylococcus aureus. In this paper, we demonstrated that ebselen has strong bactericidal activity against multidrug-resistant (MDR) S. aureus based on taking TrxR as a major target and disruption of the redox microenvironment. Further, the topical therapeutic efficacy of ebselen for staphylococcal skin infections was assessed in a rat model. Treatment with ebselen significantly reduced the bacterial load and the expression of pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1 beta (IL-1β) in S. aureus skin lesions; further, wound healing and pathological changes were obvious improved in ebselen-treated rats compare to controls. Finally, ebselen was found to sensitize S. aureus to curcumin, which may be due to their synergistic effects in inhibiting bacterial TrxR. Altogether, ebselen is an effective topical antibacterial agent in animal model of MDR S. aureus LT-1 skin infection. This may lay the foundation for further analysis and development of ebselen as an antibacterial agent for topical treatment of MDR staphylococcal infections.

Synergistic therapeutic efficacy of ebselen and silver ions against multidrug-resistant Acinetobacter baumannii-induced urinary tract infections

Ebselen (EbSe), an organo-selenium compound with well-characterized toxicology and pharmacology, exhibited potent antibacterial activity against glutathione (GSH)-positive bacteria when combined with silver ions (Ag⁺).

Dysregulation of the glutaredoxin/S-glutathionylation redox axis in lung diseases

Glutathione is a major redox buffer, reaching millimolar concentrations within cells and high micromolar concentrations in airways. While glutathione has been traditionally known as an antioxidant defense mechanism that protects the lung tissue from oxidative stress, glutathione more recently has become recognized for its ability to become covalently conjugated to reactive cysteines within proteins, a modification known as S-glutathionylation (or S-glutathiolation or protein mixed disulfide). S-glutathionylation has the potential to change the structure and function of the target protein, owing to its size (the addition of three amino acids) and charge (glutamic acid). S-glutathionylation also protects proteins from irreversible oxidation, allowing them to be enzymatically regenerated. Numerous enzymes have been identified to catalyze the glutathionylation/deglutathionylation reactions, including glutathione S-transferases and glutaredoxins. Although protein S-glutathionylation has been implicated in numerous biological processes, S-glutathionylated proteomes have largely remained unknown. In this paper, we focus on the pathways that regulate GSH homeostasis, S-glutathionylated proteins, and glutaredoxins, and we review methods required toward identification of glutathionylated proteomes. Finally, we present the latest findings on the role of glutathionylation/glutaredoxins in various lung diseases: idiopathic pulmonary fibrosis, asthma, and chronic obstructive pulmonary disease.

Monitoring cytosolic H2O2 fluctuations arising from altered plasma membrane gradients or from mitochondrial activity

Genetically encoded probes monitoring H₂O₂ fluctuations in living organisms are key to decipher redox signaling events. Here we use a new probe, roGFP2-Tpx1.C169S, to monitor pre-toxic fluctuations of peroxides in fission yeast, where the concentrations linked to signaling or to toxicity have been established. This probe is able to detect nanomolar fluctuations of intracellular H₂O₂ caused by extracellular peroxides; expression of human aquaporin 8 channels H₂O₂ entry into fission yeast decreasing membrane gradients. The probe also detects H₂O₂ bursts from mitochondria after addition of electron transport chain inhibitors, the extent of probe oxidation being proportional to the mitochondrial activity. The oxidation of this probe is an indicator of steady-state levels of H₂O₂ in different genetic backgrounds. Metabolic reprogramming during growth in low-glucose media causes probe reduction due to the activation of antioxidant cascades. We demonstrate how peroxiredoxin-based probes can be used to monitor physiological H₂O₂ fluctuations.

Reliable methods of measuring intracellular H₂O₂ fluctuations are necessary to advance redox biology. Here the authors design a H₂O₂ sensor based on the fission yeast peroxiredoxin Tpx1 to sense nanomolar fluctuations of intracellular H₂O₂ in response to genetic and environmental perturbations.

Development of the Mitochondrial Intermembrane Space Disulfide Relay Represents a Critical Step in Eukaryotic Evolution

The mitochondrial intermembrane space evolved from the bacterial periplasm. Presumably as a consequence of their common origin, most proteins of these compartments are stabilized by structural disulfide bonds. The molecular machineries that mediate oxidative protein folding in bacteria and mitochondria, however, appear to share no common ancestry. Here we tested whether the enzymes Erv1 and Mia40 of the yeast mitochondrial disulfide relay could be functionally replaced by corresponding components of other compartments. We found that the sulfhydryl oxidase Erv1 could be replaced by the Ero1 oxidase or the protein disulfide isomerase from the endoplasmic reticulum, however at the cost of respiration deficiency. In contrast to Erv1, the mitochondrial oxidoreductase Mia40 proved to be indispensable and could not be replaced by thioredoxin-like enzymes, including the cytoplasmic reductase thioredoxin, the periplasmic dithiol oxidase DsbA, and Pdi1. From our studies we conclude that the profound inertness against glutathione, its slow oxidation kinetics and its high affinity to substrates renders Mia40 a unique and essential component of mitochondrial biogenesis. Evidently, the development of a specific mitochondrial disulfide relay system represented a crucial step in the evolution of the eukaryotic cell.