Glutathione transferases are structural and functional outliers in the thioredoxin fold

Glutathione-Dependent Pathways in Cancer Cells

The most abundant tripeptide-glutathione (GSH)-and the major GSH-related enzymes-glutathione peroxidases (GPxs) and glutathione S-transferases (GSTs)-are highly significant in the regulation of tumor cell viability, initiation of tumor development, its progression, and drug resistance. The high level of GSH synthesis in different cancer types depends not only on the increasing expression of the key enzymes of the γ-glutamyl cycle but also on the changes in transport velocity of its precursor amino acids. The ability of GPxs to reduce hydroperoxides is used for cellular viability, and each member of the GPx family has a different mechanism of action and site for maintaining redox balance. GSTs not only catalyze the conjugation of GSH to electrophilic substances and the reduction of organic hydroperoxides but also take part in the regulation of cellular signaling pathways. By catalyzing the S-glutathionylation of key target proteins, GSTs are involved in the regulation of major cellular processes, including metabolism (e.g., glycolysis and the PPP), signal transduction, transcription regulation, and the development of resistance to anticancer drugs. In this review, recent findings in GSH synthesis, the roles and functions of GPxs, and GST isoforms in cancer development are discussed, along with the search for GST and GPx inhibitors for cancer treatment.

Biochemical and Histological Effects of Moringa oleifera Extract against Valproate-Induced Kidney Damage

Valproic acid is an effective treatment for generalized seizure and related neurological defects. Despite its efficacy and acceptability, its use is associated with adverse drug effects. Moringa oleifera leaves are rich in phytochemical and nutritional components. It has excellent antioxidant and ethnobotanical benefits, thus popular among folk medicines and nutraceuticals. In the present study, 70% ethanol extract of moringa leaves was assessed for its in vivo biochemical and histological effects against valproate-induced kidney damage. Female Sprague-Dawley rats were randomly divided into four groups: Group I: control animals given physiological saline (n = 8); Group II: Moringa extract-administered group (0.3 g/kg b.w./day, n = 8); Group III: valproate-administered animals (0.5 g/kg b.w./day, n = 15); and Group IV: valproate + moringa extract (given similar doses of both valproate and moringa extract, n = 12) administered group. Treatments were administered orally for 15 days, the animals were fasted overnight, anesthetized, and then tissue samples harvested. In the valproate-administered experimental group, serum urea and uric acid were elevated. In the kidney tissue of the valproate rats, glutathione was depleted, antioxidant enzyme activities (superoxide dismutase, catalase, glutathione reductase, glutathione S-transferase, and glutathione peroxidase) disrupted, while oxidative stress biomarker, inflammatory proteins (Tumor necrosis factor-alpha and interleukin-6), histological damage scores, and the number of PCNA-positive cells were elevated. M. oleifera attenuated all these biochemical defects through its plethora of diverse antioxidant and therapeutic properties.

Sigma-Class Glutathione Transferases (GSTσ): A New Target with Potential for Helminth Control

Glutathione transferases (GSTs EC 2.5.1.18) are critical components of phase II metabolism, instrumental in xenobiotics' metabolism. Their primary function involves conjugating glutathione to both endogenous and exogenous toxic compounds, which increases their solubility and enables their ejection from cells. They also play a role in the transport of non-substrate compounds and immunomodulation, aiding in parasite establishment within its host. The cytosolic GST subfamily is the most abundant and diverse in helminths, and sigma-class GST (GSTσ) belongs to it. This review focuses on three key functions of GSTσ: serving as a detoxifying agent that provides drug resistance, functioning as an immune system modulator through its involvement in prostaglandins synthesis, and acting as a vaccine antigen.

Repurposing Glutathione Transferases: Directed Evolution Combined with Chemical Modification for the Creation of a Semisynthetic Enzyme with High Hydroperoxidase Activity

Glutathione peroxidases (GPXs) are antioxidant selenoenzymes, which catalyze the reduction of hydroperoxides via glutathione (GSH), providing protection to cells against oxidative stress metabolites. The present study aims to create an efficient semisynthetic GPX based on the scaffold of tau class glutathione transferase (GSTU). A library of GSTs was constructed via DNA shuffling, using three homologue GSTUs from Glycine max as parent sequences. The DNA library of the shuffled genes was expressed in E. coli and the catalytic activity of the shuffled enzymes was screened using cumene hydroperoxide (CuOOH) as substrate. A chimeric enzyme variant (named Sh14) with 4-fold enhanced GPX activity, compared to the wild-type enzyme, was identified and selected for further study. Selenocysteine (Sec) was substituted for the active-site Ser13 residue of the Sh14 variant via chemical modification. The GPX activity (kcat) and the specificity constant (kcat/Κm) of the evolved seleno-Sh14 enzyme (SeSh14) was increased 177- and 2746-fold, respectively, compared to that of the wild-type enzyme for CuOOH. Furthermore, SeSh14 effectively catalyzed the reduction of hydrogen peroxide, an activity that is completely undetectable in all GSTs. Such an engineered GPX-like biocatalyst based on the GSTU scaffold might serve as a catalytic bioscavenger for the detoxification of hazardous hydroperoxides. Furthermore, our results shed light on the evolution of GPXs and their structural and functional link with GSTs.

On the occurrence of a glutaredoxin-like small protein in the anaerobic protozoan parasite Entamoeba histolytica

BACKGROUND

Entamoeba histolytica, an intestinal parasitic protozoan that usually lives and multiplies within the human gut, is the causative agent of amoebiasis. To date, de novo glutathione biosynthesis and its associated enzymes have not been identified in the parasite. Cysteine has been proposed to be the main intracellular thiol.

METHODS

Using bioinformatics tools to search for glutaredoxin homologs in the E. histolytica genome database, we identified a coding sequence for a putative Grx-like small protein (EhGLSP) in the E. histolytica HM-1:IMSS genome. We produced the recombinant protein and performed its biochemical characterization.

RESULTS

Through in vitro experiments, we observed that recombinant EhGLSP could bind GSH and L-Cys as ligands. However, the protein exhibited very low GSH-dependent disulfide reductase activity. Interestingly, via UV-Vis spectroscopy and chemical analysis, we detected that recombinant EhGLSP (freshly purified from Escherichia coli cells by IMAC) was isolated together with a redox-labile [FeS] bio-inorganic complex, suggesting that this protein could have some function linked to the metabolism of this cofactor. Western blotting showed that EhGLSP protein levels were modulated in E. histolytica cells exposed to exogenous oxidative species and metronidazole, suggesting that this protein cooperates with the antioxidant mechanisms of this parasite.

CONCLUSIONS AND GENERAL SIGNIFICANCE

Our findings support the existence of a new metabolic actor in this pathogen. To the best of our knowledge, this is the first report on this protein class in E. histolytica.

Functional significance of serine 13 in the active site of glutathione S-transferase F3 from Oryza sativa

Plant glutathione S-transferase (GST, EC 2.5.1.18) is an enzyme that detoxifies various electrophilic compounds including herbicides and organic pollutants by catalyzing the formation of conjugates with reduced glutathione (GSH). Although the structure and function of the GST subunits in rice, an important food in Asia, are not well understood, they are crucial for herbicide development. To investigate the role of active site residues in rice Phi-class GSTF3 (OsGSTF3), evolutionarily conserved serine residues were replaced with alanine using site-directed mutagenesis to obtain the mutants S13A, S38A, S69A, and S169A. These four mutants were expressed in Escherichia coli and purified to electrophoretic homogeneity using immobilized GSH affinity chromatography. Mutation of Ser13 to Ala resulted in substantial reductions in specific activities and kcat/Km values for the GSH-[1-chloro-2,4-dinitrobenzene (CDNB)] conjugation reaction. In contrast, mutations of Ser38, Ser69, and Ser169 to Ala had little effect on the activities and kinetic parameters. Additionally, the mutation of Ser13 to Ala significantly affected the KmGSH and I50 values of S-hexylglutathione and S-(2,4-dinitrophenyl)glutathione, which compete with GSH and the product of GSH-CDNB conjugation, respectively. A pH-log (kcat/KmCDNB) plot was used to estimate the pKa value of GSH in the enzyme-GSH complex of the wild-type enzyme, which was approximately 6.9. However, the pKa value of GSH in the enzyme-GSH complex of the S13A mutant was approximately 8.7, which was about 1.8 pK units higher than that of the wild-type enzyme. OsGSTF3 was also crystallized for crystallographic study, and the structure analyses revealed that Ser13 is located in the active site and that its side chain is in close proximity to the thiol group of glutathione bound in the enzyme. Based on these substitution effects on kinetic parameters, the dependence of kinetic parameters on the pH and 3-dimensional structure, it was suggested that Ser13 in rice OsGSTF3 is the residue responsible for catalytic activity by lowering the pKa of GSH in the enzyme-GSH complex and enhancing the nucleophilicity of the GSH thiol in the active site.

Potent GST Ketosteroid Isomerase Activity Relevant to Ecdysteroidogenesis in the Malaria Vector Anopheles gambiae

Nobo is a glutathione transferase (GST) crucially contributing to ecdysteroid biosynthesis in insects of the orders Diptera and Lepidoptera. Ecdysone is a vital steroid hormone in insects, which governs larval molting and metamorphosis, and the suppression of its synthesis has potential as a novel approach to insect growth regulation and combatting vectors of disease. In general, GSTs catalyze detoxication, whereas the specific function of Nobo in ecdysteroidogenesis is unknown. We report that Nobo from the malaria-spreading mosquito Anopheles gambiae is a highly efficient ketosteroid isomerase catalyzing double-bond isomerization in the steroids 5-androsten-3,17-dione and 5-pregnen-3,20-dione. These mammalian ketosteroids are unknown in mosquitoes, but the discovered prominent catalytic activity of these compounds suggests that the unknown Nobo substrate in insects has a ketosteroid functionality. Aminoacid residue Asp111 in Nobo is essential for activity with the steroids, but not for conventional GST substrates. Further characterization of Nobo may guide the development of new insecticides to prevent malaria.

Tat-GSTpi Inhibits Dopaminergic Cells against MPP+-Induced Cellular Damage via the Reduction of Oxidative Stress and MAPK Activation

Glutathione S-transferase pi (GSTpi) is a member of the GST family and plays many critical roles in cellular processes, including anti-oxidative and signal transduction. However, the role of anti-oxidant enzyme GSTpi against dopaminergic neuronal cell death has not been fully investigated. In the present study, we investigated the roles of cell permeable Tat-GSTpi fusion protein in a SH-SY5Y cell and a Parkinson’s disease (PD) mouse model. In the 1-methyl-4-phenylpyridinium (MPP+)-exposed cells, Tat-GSTpi protein decreased DNA damage and reactive oxygen species (ROS) generation. Furthermore, this fusion protein increased cell viability by regulating MAPKs, Bcl-2, and Bax signaling. In addition, Tat-GSTpi protein delivered into the substantia nigra (SN) of mice brains protected dopaminergic neuronal cell death in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD animal model. Our results indicate that the Tat-GSTpi protein inhibited cell death from MPP+- and MPTP-induced damage, suggesting that it plays a protective role during the loss of dopaminergic neurons in PD and that it could help to identify the mechanism responsible for neurodegenerative diseases, including PD.

Glutathione-Related Enzymes and Proteins: A Review

The tripeptide glutathione is found in all eukaryotic cells, and due to the compartmentalization of biochemical processes, its synthesis takes place exclusively in the cytosol. At the same time, its functions depend on its transport to/from organelles and interorgan transport, in which the liver plays a central role. Glutathione is determined as a marker of the redox state in many diseases, aging processes, and cell death resulting from its properties and reactivity. It also uses other enzymes and proteins, which enables it to engage and regulate various cell functions. This paper approximates the role of these systems in redox and detoxification reactions such as conjugation reactions of glutathione-S-transferases, glyoxylases, reduction of peroxides through thiol peroxidases (glutathione peroxidases, peroxiredoxins) and thiol-disulfide exchange reactions catalyzed by glutaredoxins.

Immaturin-Nuclease as a Model System for a Gene-Programmed Sexual Development and Rejuvenescence in Paramecium Life History

Fertilization-initiated development and adult-onset aging are standard features in the life history of eukaryotes. In Paramecium, the number of cell divisions after the birth of a new generation is an essential parameter of sexual phase transition and aging. However, the gene driving this process and its evolutionary origin have not yet been elucidated. Here we report several critical outcomes obtained by molecular genetics, immunofluorescence microscopy, transformation by microinjection, and enzymological analysis. The cloned immaturin gene induces sexual rejuvenation in both mature and senescent cells by microinjection. The immaturin gene originated from proteobacteria's glutathione-S-transferase (GST) gene. However, immaturin has been shown to lose GST activity and instead acquire nuclease activity. In vitro substrates for immaturin-nuclease are single- and double-stranded DNA, linear and circular DNA, and single-stranded viral genome RNA such as coronavirus. Anti-immaturin antibodies have shown that the subcellular localizations of immaturin are the macronucleus, cytoplasm, cell surface area, and cilia. The phase transition of sexuality is related to a decrease in the intracellular abundance of immaturin. We propose that sexual maturation and rejuvenation is a process programmed by the immaturin gene, and the sexual function of each age is defined by both the abundance and the intracellular localization mode of the immaturin-nuclease.

Role of GSTM1 in Hypertension, CKD, and Related Diseases across the Life Span

Over 20 years after the introduction of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, CKD remains a major public health burden with limited therapeutic options to halt or slow kidney disease progression at all ages. The consensus is that oxidative stress contributes to CKD development and progression. Yet, to date, there is no clear evidence that broad use of antioxidant therapy provides a beneficial effect in CKD. Understanding the specific pathophysiologic mechanisms in those who are genetically most susceptible to oxidative stress is a crucial step to inform therapy in an individualized medicine approach, considering differing exposures and risks across the life span. Glutathione-S-transferase μ 1 (GSTM1) is a phase 2 enzyme involved in inactivation of reactive oxygen species and metabolism of xenobiotics. In particular, those with the highly prevalent GSTM1 null genotype (GSTM1[0/0]) may be more susceptible to kidney disease progression, due to impaired capacity to handle the increased oxidative stress burden in disease states, and might specifically benefit from therapy that targets the redox imbalance mediated by loss of the GSTM1 enzyme. In this review, we will discuss the studies implicating the role of GSTM1 deficiency in kidney and related diseases from experimental rodent models to humans, from the prenatal period through senescence, and the potential underlying mechanism.

Biochemical characterization and peptide mass fingerprinting of two glutathione transferases from Biomphalaria alexandrina snails (Gastropoda: Planorbidae)

Background

The freshwater snails Biomphalaria alexandrina (Gastropoda: Planorbidae) has public health importance of being an intermediate host of Schistosoma mansoni, the parasite species that causes intestinal schistosomiasis in humans. Glutathione transferases (GSTs) play an important role in detoxification of a broad range of compounds including secondary metabolites and exogenous compounds. Studying GSTs in snails may clarify their role in detoxification of molluscicides.

Results

Two glutathione transferases (BaGST2 and BaGST3) were purified and characterized from B. alexandrina snails. BaGST2 and BaGST3 were electrophoretically homogeneous preparations with subunit molecular weight of 23.6 kDa and molecular weight of 45 kDa. Isoelectric focusing of BaGST2 revealed the presence of two components at pI 4.47 and 4.67, while BaGST3 showed one band at pI 4.17. The specific activity of BaGST2 and BaGST3 toward 1-chloro-2,4-dinitrobenzene (CDNB) was 19.0 and 45.2 μmol/min/mg protein following 146- and 346-fold purification, respectively. The catalytic pH optima, km values, and the activation energies for BaGST2 and BaGST3 were determined. BaGST2 and BaGST3 were significantly inhibited by hematin and Cibacron Blue and to a less extent by bromosulfophthalein, S-butyl-GSH, S-hexyl-GSH, and S-P-bromobenzyl-GSH. BaGST2 and BaGST3 showed high activity against ethacrynic acid as substrate, and they also exhibited peroxidase activity on cumene hydroperoxide. The two enzymes showed identical patterns of lysine-C digestion after high-performance liquid chromatography. The amino acid sequences of three peptide fragments and peptide mass fingerprinting of fourteen peptides were used to predict the primary structure of BaGST2. A polypeptide of 206 amino acids (with 7 gaps, 3 of which could not identified) was predicted for BaGST2. The theoretical subunit molecular weight of BaGST2 is 22.6 kDa, with pI of 8.58. BaGST2 has 65% sequence identity and 78% positive with Biomphalaria glabrata GST7. The overall structure of BaGST2 at the N-terminal domain is identical to the canonical GST N-terminal domain, having the typical thioredoxin-like fold with a βαβ-α-ββα motif, whereas the C-terminal domain is made from 6 α-helices. A conservative GST-N-domain includes glutathione binding sites Y11, L17, Q53, M54, Q65, and S66, while a variable GST-C domain contains electrophilic substrate binding site H99, R102, A103, F106, K107, L161, and Y167. Phylogenetic tree showed that BaGST2 was clustered in the sigma group with GSTs sigma class from invertebrates and vertebrates.

Conclusions

We have purified and characterized two GSTs from B. alexandrina snails. Our study broadens the biochemical information on freshwater snail GSTs by demonstrating the role of BaGSTs in defense mechanisms against structurally different electrophilic compounds. BaGST2 and BaGST3 have Se-independent peroxidase activity, which indicates their role in cellular antioxidant defense by reducing organic hydroperoxides in B. alexandrina. A polypeptide chain of 206 amino acids was predicted. The primary structure of BaGST2 showed 65% sequence identity with Biomphalaria glabrata GST7. Sequence analysis indicates that BaGST2 is a GST-N-sigma-like with a thioredoxin-like superfamily. Phylogenetic tree confirms that BaGST2 belongs to the sigma class of GSTs superfamily.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00372-x.

Expanding the family of Mu-class glutathione transferases in the cestode parasite Echinococcus granulosus sensu lato

Glutathione transferases (GSTs) perform catalytic and non-catalytic activities, mostly involved in stress-response and cell detoxification. Helminth parasites express several GSTs of multiple classes that are involved in the neutralization of potentially harmful oxidants, and in the inactivation or removal of xenobiotics. Additionally, GSTs participate in immunomodulatory processes that facilitate the parasite establishment and survival within its host. In Echinococcus granulosus sensu lato (s.l.) -the cestode parasite responsible for cystic echinococcosis- only one Mu-class GST has been reported. In the present work, by using bioinformatic and proteomic approaches we searched for novel Mu-class GSTs potentially involved in the parasite oxidative-stress metabolism. In the genome of E. granulosus s.l., 6 GST-related sequences were found to constitute a strongly conserved phylogenetical clade with Mu-class members. Among them, 5 displayed conserved gene structure (exon/intron), as well as specific residues and motifs characteristic of Mu-class enzymes. By proteomic analysis, 3 Mu-GSTs were identified to be expressed in the protoscolex parasite stage, 2 of them being firstly described as Mu-class GSTs here. The existence of more than one productive Mu-GST gene expands the parasite xenobiotic phase II metabolism, which might have beneficial roles on E. granulosus s.l. ability to successfully infect its host.

Early loss of glutathione -s- transferase (GST) activity during diverse forms of acute renal tubular injury

Glutathione‐S‐transferases (GSTs) are a diverse group of phase II detoxification enzymes which primarily evoke tissue protection via glutathione conjugation to xenobiotics and reactive oxygen species. Given their cytoprotective properties, potential changes in GST expression during AKI has pathophysiologic relevance. Hence, we evaluated total GST activity, and the mRNA responses of nine cytosolic GST isotypes (GST alpha1, kappa1, mu1/5, omega1, pi1 sigma1, theta1, zeta1 mRNAs), in five diverse mouse models of AKI (glycerol, ischemia/reperfusion; maleate, cisplatin, endotoxemia). Excepting endotoxemia, each AKI model significantly reduced GST activity (~35%) during both the AKI “initiation” (0‐4 h) and “maintenance” phases (18 or 72 h). During the AKI maintenance phase, increases in multiple GST mRNAs were observed. However, no improvement in GST activity resulted. Increased urinary GST excretion followed AKI induction. However, this could not explain the reduced renal GST activity given that it also fell in response to ex vivo renal ischemia (i.e., absent urinary excretion). GST alpha, a dominant proximal tubule GST isotype, manifested 5–10‐fold protein increases following AKI, arguing against GST proteolysis as the reason for the GST activity declines. Free fatty acids (FFAs) and lysophospholipids, which markedly accumulate during AKI, are known to bind to, and suppress, GST activity. Supporting this concept, arachidonic acid addition to renal cortical protein extracts caused rapid GST activity reductions. Based on these results, we conclude that diverse forms of AKI significantly reduce GST activity. This occurs despite increased GST transcription/translation and independent of urinary GST excretion. Injury‐induced generation of endogenous GST inhibitors, such as FFAs, appears to be a dominant cause.

Molecular cloning and oxidative-stress responses of a novel Phi class glutathione S-transferase (GSTF) gene in the freshwater algae Closterium ehrenbergii

Glutathione S-transferases (GSTs) belong to a family of enzymes involved in diverse biological processes, including detoxification and protection against oxidative damage. Here, we determined the full-length sequence (915 bp) of a novel Phi class cytosolic glutathione S-transferase (GSTF) gene from the green algae Closterium ehrenbergii. We examined the gene structure and expression patterns in response to metals and endocrine disrupting chemicals (EDCs). It was significantly upregulated by metals, but responded differently to EDCs. The highest up-regulation of CeGSTF was registered under 0.1 mg/L CuCl₂ and 0.01 mg/L CuSO₄ treatments. In a 72-h course experiment with treatment of 0.1 mg/L CuCl₂ , CeGSTF was dramatically induced at 6 h, and then gradually decreased with increasing exposure time. This was consistent with the increase in both GST activity and ROS production in copper-treated cells. These results suggest that CeGSTF may be involved in detoxification mechanisms associated with oxidative stress in green algae.

Bioinformatic Analyses of Peroxiredoxins and RF-Prx: A Random Forest-Based Predictor and Classifier for Prxs

Peroxiredoxins (Prxs) are a protein superfamily, present in all organisms, that play a critical role in protecting cellular macromolecules from oxidative damage but also regulate intracellular and intercellular signaling processes involving redox-regulated proteins and pathways. Bioinformatic approaches using computational tools that focus on active site-proximal sequence fragments (known as active site signatures) and iterative clustering and searching methods (referred to as TuLIP and MISST) have recently enabled the recognition of over 38,000 peroxiredoxins, as well as their classification into six functionally relevant groups. With these data providing so many examples of Prxs in each class, machine learning approaches offer an opportunity to extract additional information about features characteristic of these protein groups.In this study, we developed a novel computational method named "RF-Prx" based on a random forest (RF) approach integrated with K-space amino acid pairs (KSAAP) to identify peroxiredoxins and classify them into one of six subgroups. Our process performed in a superior manner compared to other machine learning classifiers. Thus the RF approach integrated with K-space amino acid pairs enabled the detection of class-specific conserved sequences outside the known functional centers and with potential importance. For example, drugs designed to target Prx proteins would likely suffer from cross-reactivity among distinct Prxs if targeted to conserved active sites, but this may be avoidable if remote, class-specific regions could be targeted instead.

Proposed mechanism for monomethylarsonate reductase activity of human omega-class glutathione transferase GSTO1-1

Contamination of drinking water with toxic inorganic arsenic is a major public health issue. The mechanisms of enzymes and transporters in arsenic elimination are therefore of interest. The human omega-class glutathione transferases have been previously shown to possess monomethylarsonate (V) reductase activity. To further understanding of this activity, molecular dynamics of human GSTO1-1 bound to glutathione with a monomethylarsonate isostere were simulated to reveal putative monomethylarsonate binding sites on the enzyme. The major binding site is in the active site, adjacent to the glutathione binding site. Based on this and previously reported biochemical data, a reaction mechanism for this enzyme is proposed. Further insights were gained from comparison of the human omega-class GSTs to homologs from a range of animals.

Transcriptome analysis reveals antioxidant defense mechanisms in the red swamp crayfish Procambarus clarkia after exposure to chromium

Chromium (Cr) as a chromate anion has a strong redox capacity that seriously threatens the ecological environment and human health. Cr can contaminate water and impart toxicity to aquatic species. Procambarus clarkii is an important food source that once represented a large proportion of the aquaculture industry due to its rapid reproduction and high economic value. However, there have been reports on the death of P. clarkii due to heavy metal pollution. The underlying mechanism regarding heavy metal toxicity was studied in this paper. The transcriptome data of hemocytes extracted from P. clarkii injected with Cr were analyzed by high-throughput sequencing and compared to the control group. In total, 48,128,748 clean reads were obtained in the treatment group and 56,480,556 clean reads were obtained in the control group. The reads were assembled using Trinity and the identified unigenes were then annotated. Then, 421 differentially-expressed genes (DEGs) were found, 170 of which were upregulated and 251 downregulated. Many of these genes were found to be related to glutathione metabolism and transportation. The glutathione metabolic pathway of P. clarkii was thus activated by Cr exposure to detoxify and maintain body function. Validation of DEGs with quantitative real-time PCR confirms the changes in gene expression. Thus, this study provides data supporting a glutathione-focused response of P. clarkii to exposure to heavy metals.

Hydroperoxide-Reducing Enzymes in the Regulation of Free-Radical Processes

The review presents current concepts of the molecular mechanisms of oxidative stress development and describes main stages of the free-radical reactions in oxidative stress. Endogenous and exogenous factors of the oxidative stress development, including dysfunction of cell oxidoreductase systems, as well as the effects of various external physicochemical factors, are discussed. The review also describes the main components of the antioxidant defense system and stages of its evolution, with a special focus on peroxiredoxins, glutathione peroxidases, and glutathione S-transferases, which share some phylogenetic, structural, and catalytic properties. The substrate specificity, as well as the similarities and differences in the catalytic mechanisms of these enzymes, are discussed in detail. The role of peroxiredoxins, glutathione peroxidases, and glutathione S-transferases in the regulation of hydroperoxide-mediated intracellular and intercellular signaling and interactions of these enzymes with receptors and non-receptor proteins are described. An important contribution of hydroperoxide-reducing enzymes to the antioxidant protection and regulation of such cell processes as growth, differentiation, and apoptosis is demonstrated.

GSTM1 Gene, Diet, and Kidney Disease: Implication for Precision Medicine?: Recent Advances in Hypertension

In the United States, the prevalence of chronic kidney disease in adults is ≈14%. The mainstay of therapy for chronic kidney disease is angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, but many patients with chronic kidney disease still progress to end-stage kidney disease. Increased oxidative stress is a major molecular underpinning of chronic kidney disease progression. In humans, a common deletion variant of the glutathione-S-transferase μ-1 (GSTM1) gene, the GSTM1 null allele (GSTM1(0)), results in decreased GSTM1 enzymatic activity and is associated with higher levels of oxidative stress. GSTM1 belongs to the superfamily of GSTs that are phase II antioxidant enzymes and are regulated by Nrf2 (nuclear factor erythroid 2-related factor 2). Cruciferous vegetables in general, and broccoli in particular, are rich in glucoraphanin, a precursor of sulforaphane that has been shown to have protective effects against oxidative damage through the activation of Nrf2. This review will highlight recent human and animal studies implicating the role of GSTM1 deficiency in hypertension and kidney disease, and its impact on the effects of cruciferous vegetables on kidney injury and disease progression, illustrating the significance of gene and environment interaction and a potential for targeted precision medicine in the treatment of kidney disease.

Association of GSTP1 p.Ile105Val (rs1695, c.313A > G) Variant with the Risk of Breast Carcinoma among Egyptian Women

Several reports examined the association of the GSTP1 p.Ile105Val (rs1695, c.313A > G) variant with the elevated risk of multiple cancerous diseases involving breast carcinoma, but with inconclusive findings. The primary purpose of this study is to test the association of this essential variant with the risk of breast carcinoma among Egyptian females. This case-control study was conducted based on 200 participants involving 100 women diagnosed with breast carcinoma and 100 unrelated cancer-free controls from the same district. The genomic DNA for all participants was genotyped utilizing T-ARMS-PCR procedure. The frequencies of the GSTP1 p.Ile105Val (rs1695, c.313A > G) variant indicated a statistically significant with the elevated risk of breast carcinoma under various genetic models, including allelic (OR = 2.48, P-value < 0.001) and dominant (OR = 2.36, P-value = 0.003) models. In conclusion, the GSTP1 p.Ile105Val (rs1695, c.313A > G) variant was considered as an independent risk factor for breast carcinoma among Egyptian women.

Glutathione S-transferases and their implications in the lung diseases asthma and chronic obstructive pulmonary disease: Early life susceptibility?

Our lungs are exposed daily to airborne pollutants, particulate matter, pathogens as well as lung allergens and irritants. Exposure to these substances can lead to inflammatory responses and may induce endogenous oxidant production, which can cause chronic inflammation, tissue damage and remodeling. Notably, the development of asthma and Chronic Obstructive Pulmonary Disease (COPD) is linked to the aforementioned irritants. Some inhaled foreign chemical compounds are rapidly absorbed and processed by phase I and II enzyme systems critical in the detoxification of xenobiotics including the glutathione-conjugating enzymes Glutathione S-transferases (GSTs). GSTs, and in particular genetic variants of GSTs that alter their activities, have been found to be implicated in the susceptibility to and progression of these lung diseases. Beyond their roles in phase II metabolism, evidence suggests that GSTs are also important mediators of normal lung growth. Therefore, the contribution of GSTs to the development of lung diseases in adults may already start in utero, and continues through infancy, childhood, and adult life. GSTs are also known to scavenge oxidants and affect signaling pathways by protein-protein interaction. Moreover, GSTs regulate reversible oxidative post-translational modifications of proteins, known as protein S-glutathionylation. Therefore, GSTs display an array of functions that impact the pathogenesis of asthma and COPD.

In this review we will provide an overview of the specific functions of each class of mammalian cytosolic GSTs. This is followed by a comprehensive analysis of their expression profiles in the lung in healthy subjects, as well as alterations that have been described in (epithelial cells of) asthmatics and COPD patients. Particular emphasis is placed on the emerging evidence of the regulatory properties of GSTs beyond detoxification and their contribution to (un)healthy lungs throughout life. By providing a more thorough understanding, tailored therapeutic strategies can be designed to affect specific functions of particular GSTs.

Glutathione S-Transferases in Cancer

In humans, the glutathione S-transferases (GST) protein family is composed of seven members that present remarkable structural similarity and some degree of overlapping functionalities. GST proteins are crucial antioxidant enzymes that regulate stress-induced signaling pathways. Interestingly, overactive GST proteins are a frequent feature of many human cancers. Recent evidence has revealed that the biology of most GST proteins is complex and multifaceted and that these proteins actively participate in tumorigenic processes such as cell survival, cell proliferation, and drug resistance. Structural and pharmacological studies have identified various GST inhibitors, and these molecules have progressed to clinical trials for the treatment of cancer and other diseases. In this review, we discuss recent findings in GST protein biology and their roles in cancer development, their contribution in chemoresistance, and the development of GST inhibitors for cancer treatment.

Ibuprofen as an emerging pollutant on non-target aquatic invertebrates: Effects on Chironomus riparius

The concern about pharmaceuticals has been increased over the last decade due to their burgeoning consumption. Ibuprofen has an extensive presence in surface water with risks for the aquatic biota. This study focuses on the effects of ibuprofen at environmental concentrations on the survival, transcriptional level, and enzymatic activity for 24, 96 h on Chironomus riparius. Ibuprofen developed a substantial effect on survival by all the conditions. mRNA levels of EcR, Dronc, and Met (endocrine system), hsp70, hsp24, and hsp27 (stress response), and Proph and Def (immune system) were modified, joined to increased GST and PO activity. The results confirmed alterations on the development of C. riparius, as well as two essential mechanisms, involved in protection against external toxicological challenge. Ibuprofen poses an incipient risk to C. riparius and could at an organismal level by compromising their survival, development, and ability to respond to adverse conditions on the future populations.

Comparative analyses and structural insights of new class glutathione transferases in Cryptosporidium species

Cryptosporidiosis, caused by protozoan parasites of the genus Cryptosporidium, is estimated to rank as a leading cause in the global burden of neglected zoonotic parasitic diseases. This diarrheal disease is the second leading cause of death in children under 5 years of age. Based on the C. parvum transcriptome data, glutathione transferase (GST) has been suggested as a drug target against this pathogen. GSTs are diverse multifunctional proteins involved in cellular defense and detoxification in organisms and help pathogens to alleviate chemical and environmental stress. In this study, we performed genome-wide data mining, identification, classification and in silico structural analysis of GSTs in fifteen Cryptosporidium species. The study revealed the presence three GSTs in each of the Cryptosporidium species analyzed in the study. Based on the percentage identity and comprehensive comparative phylogenetic analysis, we assigned Cryptosporidium species GSTs to three new GST classes, named Vega (ϑ), Gamma (γ) and Psi (ψ). The study also revealed an atypical thioredoxin-like fold in the C. parvum GST1 of the Vega class, whereas C. parvum GST2 of the Gamma class and C. melagridis GST3 of the Psi class has a typical thioredoxin-like fold in the N-terminal region. This study reports the first comparative analysis of GSTs in Cryptosporidium species.

Investigation of the active site of an unclassified glutathione transferase in Bombyx mori by alanine scanning

Glutathione transferase (GST) is an important class of detoxification enzymes that are vital for defense against various xenobiotics and cellular oxidative stress. Previously, we had reported an unclassified glutathione transferase 2 in Bombyx mori (bmGSTu2) to be responsible for detoxifying diazinon. In this study, we aimed to identify the amino acid residues that constitute a hydrogen-bonding network important for GST activity. Site-directed mutagenesis of bmGSTu2 suggested that residues Asn102, Pro162, and Ser166 contribute to its catalytic activity.

Metabolomics analysis reveals the protective effect of quercetin-3-O-galactoside (Hyperoside) on liver injury in mice induced by acetaminophen

We investigated the protective effect of Hyperoside (HPS) on liver injury induced by acetaminophen (APAP) in C57 mice. HPS was administered orally for 7 days and APAP was administered orally on the 7th day. Serum and liver samples were then collected for biochemical analyses, histopathology assessments, and metabolomics studies. Metabolites were assessed using a UHPLC-MS system. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were used to process the data. Pathway analyses were performed using Metaboanalyst 4.0. Western blot and qRT-PCR were used to determine the protein and mRNA levels, respectively. HPS interacted with active sites in CYP2E1 and caused protein degradation. In conclusion, our results suggested that HPS prevented the oxidative stress-induced liver injury caused by APAP. PRACTICAL APPLICATIONS: Hyperoside was shown to have potential protective and therapeutic effects against liver diseases. Male C57 mice were used to perform pharmacodynamic, pharmacology, and metabolomics evaluations. At a dose of 60 mg/kg, HPS prevented oxidative stress-induced liver injury caused by APAP by regulating the glutathione-related metabolites and enzymes through the inhibition of CYP2E1.

Structural and biochemical characterization of a glutathione transferase from the citrus canker pathogen Xanthomonas

The genus Xanthomonas comprises several cosmopolitan plant-pathogenic bacteria that affect more than 400 plant species, most of which are of economic interest. Citrus canker is a bacterial disease that affects citrus species, reducing fruit yield and quality, and is caused by the bacterium Xanthomonas citri subsp. citri (Xac). The Xac3819 gene, which has previously been reported to be important for citrus canker infection, encodes an uncharacterized glutathione S-transferase (GST) of 207 amino-acid residues in length (XacGST). Bacterial GSTs are implicated in a variety of metabolic processes such as protection against chemical and oxidative stresses. XacGST shares high sequence identity (45%) with the GstB dehalogenase from Escherichia coli O6:H1 strain CFT073 (EcGstB). Here, XacGST is reported to be able to conjugate glutathione (GSH) with bromoacetate with a Km of 6.67 ± 0.77 mM, a kcat of 42.69 ± 0.32 s-1 and a kcat/Km of 6.40 ± 0.72 mM-1 s-1 under a saturated GSH concentration (3.6 mM). These values are comparable to those previously reported for EcGstB. In addition, crystal structures of XacGST were determined in the apo form (PDB entry 6nxv) and in a GSH-bound complex (PDB entry 6nv6). XacGST has a canonical GST-like fold with a conserved serine residue (Ser12) at the GSH-binding site near the N-terminus, indicating XacGST to be a serine-type GST that probably belongs to the theta-class GSTs. GSH binding stabilizes a loop of about 20 residues containing a helix that is disordered in the apo XacGST structure.

The pivotal function of dehydroascorbate reductase in glutathione homeostasis in plants

Under natural conditions, plants are exposed to various abiotic and biotic stresses that trigger rapid changes in the production and removal of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2). The ascorbate-glutathione pathway has been recognized to be a key player in H2O2 metabolism, in which reduced glutathione (GSH) regenerates ascorbate by reducing dehydroascorbate (DHA), either chemically or via DHA reductase (DHAR), an enzyme belonging to the glutathione S-transferase (GST) superfamily. Thus, DHAR has been considered to be important in maintaining the ascorbate pool and its redox state. Although some GSTs and peroxiredoxins may contribute to GSH oxidation, analysis of Arabidopsis dhar mutants has identified the key role of DHAR in coupling H2O2 to GSH oxidation. The reaction of DHAR has been proposed to proceed by a ping-pong mechanism, in which binding of DHA to the free reduced form of the enzyme is followed by binding of GSH. Information from crystal structures has shed light on the formation of sulfenic acid at the catalytic cysteine of DHAR that occurs with the reduction of DHA. In this review, we discuss the molecular properties of DHAR and its importance in coupling the ascorbate and glutathione pools with H2O2 metabolism, together with its functions in plant defense, growth, and development.

Calsequestrin. Structure, function, and evolution

Calsequestrin is the major Ca²⁺ binding protein in the sarcoplasmic reticulum (SR), serves as the main Ca²⁺ storage and buffering protein and is an important regulator of Ca²⁺ release channels in both skeletal and cardiac muscle. It is anchored at the junctional SR membrane through interactions with membrane proteins and undergoes reversible polymerization with increasing Ca²⁺ concentration. Calsequestrin provides high local Ca²⁺ at the junctional SR and communicates changes in luminal Ca²⁺ concentration to Ca²⁺ release channels, thus it is an essential component of excitation-contraction coupling. Recent studies reveal new insights on calsequestrin trafficking, Ca²⁺ binding, protein evolution, protein-protein interactions, stress responses and the molecular basis of related human muscle disease, including catecholaminergic polymorphic ventricular tachycardia (CPVT). Here we provide a comprehensive overview of calsequestrin, with recent advances in structure, diverse functions, phylogenetic analysis, and its role in muscle physiology, stress responses and human pathology.

Diversity of Glutathione S-Transferases (GSTs) in Cyanobacteria with Reference to Their Structures, Substrate Recognition and Catalytic Functions

Glutathione S-Transferases (GSTs) comprise a diverse group of protein superfamily involved in cellular detoxification of various harmful xenobiotics and endobiotics. Cyanobacteria, being the primordial photosynthetic prokaryotes, served as an origin for the evolution of GSTs with diversity in their structures, substrate recognition, and catalytic functions. This study analysed the diversity of GSTs in cyanobacteria for the first time. Based on the sequence alignment and phylogenetic tree analysis, 12 GST classes were identified, which are distributed variedly within cyanobacterial orders such as four in Pleurocapsales, eight in Chroococcales, seven in Oscillatoriales, five in Stigonematales, and nine in Nostocales. Detailed evolutionary analysis of cyanobacterial GSTs suggested that the order Pleurocapsales served as the ancestry for GST evolution. The analysis also identified a conserved motif S[GLNTARS][ADE]I[LAI] with signature residues, cysteine, serine, and tyrosine at the N-terminal end that serves as the initiating residue for detoxification. Alternatively, the grouping of cyanobacterial GSTs and their unique signature residues were located, which serve as a possible discriminating factor. The study also described the mode of glutathione binding between the identified cyanobacterial GST groups highlighting the differences among the GST classes. New GST sequence data may improve further our understanding on GST evolution and other possible divergences in cyanobacteria.

Metalloproteomic approach of mercury-binding proteins in liver and kidney tissues of Plagioscion squamosissimus (corvina) and Colossoma macropomum (tambaqui) from Amazon region: Possible identification of mercury contamination biomarkers

Fish is an important source of protein, vitamins, and minerals. However, this food is also a major source of human exposure to toxic contaminants such as mercury. Thus, this paper aimed to evaluate mercury-binding proteins for possible application as biomarkers of mercury contamination in hepatic and renal tissues of Plagioscion squamosissimus (carnivorous fish) and Colossoma macropomum (omnivorous fish) from the Amazon region using metalloproteomic approach. The proteome of hepatic and renal tissues of fish species was separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), and the mercury concentrations in protein spots were determined by graphite furnace atomic absorption spectrometry (GFAAS). Finally, the protein spots associated to mercury were characterized by electrospray ionization mass spectrometry (ESI-MS/MS). The activity of antioxidant enzymes (SOD, CAT, GPx, and GST) and lipid peroxidation (LPO) were also determined. The results showed that the highest concentrations of mercury were found in the carnivorous species (P. squamosissimus) and that the accumulation pattern of this metal was higher in hepatic tissues than in renal tissues for both species. A tendency was observed for greater enzymatic activity in the hepatic and renal tissues of P. squamosissimus, the species with the highest concentration of mercury. Only GPx activity in the kidney and GST in the liver were lower for the P. squamosissimus species, and this finding can be explained by the interaction of mercury with these enzymes. The data obtained by ESI-MS/MS allowed for the characterization of the protein spots associated to mercury, revealing proteins involved in energy metabolism, biomolecules transport, protein synthesis and degradation, cell differentiation, gene regulation, and the antioxidant system. The results obtained in the present study can contribute to understanding the physiological processes underlying mercury toxicity and have provided new perspectives on possible candidates for mercury contamination biomarkers in fish.

Individual and combined effects of GSTM1, GSTT1, and GSTP1 polymorphisms on breast cancer risk: A meta-analysis and re-analysis of systematic meta-analyses

Background

Fourteen previous meta-analyses have been published to analyze the polymorphisms of individual GSTM1 present/null, GSTT1 present/null, and GSTP1 IIe105Val on breast cancer (BC) risk. However, their meta-analyses did not explore the combined effects of the three genetic polymorphisms on BC risk. In addition, they did not evaluate the credibility of statistically significant associations. Furthermore, a multitude of new articles have been published on these themes, and therefore a meta-analysis and re-analysis of systematic previous meta-analyses were performed to further explore these issues.

Objectives

To determine the association between the individual and combined effects of GSTM1, GSTT1, and GSTP1 polymorphisms on breast cancer risk.

Methods

Crude odds ratios (ORs) and their 95% confidence intervals (CIs) were applied to estimate the association between individual and combined effects of GSTM1, GSTT1, and GSTP1 polymorphisms on BC risk. To evaluate the credibility of statistically significant associations in the current and previous meta-analyses, we applied the the false-positive report probabilities (FPRP) test and the Venice criteria.

Results

101 publications were selected to evaluate the individual and combined effects of GSTM1, GSTT1 and GSTP1 polymorphisms on BC risk. Overall, statistically significant elevated BC risk was found in any individual and combined effects of GSTM1 present/null, GSTT1 present/null, and GSTP1 IIe105Val polymorphisms. However, when we restricted studies only involving with high-quality, matching, HWE, and genotyping examination performed blindly or with quality control, significantly increased BC risk was only found in overall population for GSTM1 null genotype, among all populations, Caucasians, and postmenopausal women for the combined effects of GSTM1 and GSTT1 polymorphisms, and in overall analysis for the combined effects of GSTM1, GSTT1, and GSTP1 IIe105Val polymorphisms. Further, less-credible positive results were identified when we evaluated the credibility of positive results of the current and previous meta-analyses.

Conclusions

This meta-analysis indicates that the individual and combined effects of GSTM1, GSTT1 and GSTP1 polymorphisms may be not associated with increased BC risk.

New Perspectives Related to the Bioluminescent System in Dinoflagellates: Pyrocystis lunula, a Case Study

Pyrocystis lunula is considered a model organism due to its bioluminescence capacity linked to circadian rhythms. The mechanisms underlying the bioluminescent phenomenon have been well characterized in dinoflagellates; however, there are still some aspects that remain an enigma. Such is the case of the presence and diversity of the luciferin-binding protein (LBP), as well as the synthesis process of luciferin. Here we carry out a review of the literature in relation to the molecular players responsible for bioluminescence in dinoflagellates, with particular interest in P. lunula. We also carried out a phylogenetic analysis of the conservation of protein sequence, structure and evolutionary pattern of these key players. The basic structure of the luciferase (LCF) is quite conserved among the sequences reported to date for dinoflagellate species, but not in the case of the LBP, which has proven to be more variable in terms of sequence and structure. In the case of luciferin, its synthesis has been shown to be complex process with more than one metabolic pathway involved. The glutathione S-transferase (GST) and the P630 or blue compound, seem to be involved in this process. In the same way, various hypotheses regarding the role of bioluminescence in dinoflagellates are exposed.

Genomic and transcriptomic analyses of glutathione S-transferases in an endoparasitoid wasp, Pteromalus puparum

Pteromalus puparum is a gregarious pupal endoparasitoid with a wide host range. It deposits eggs into pierid and papilionid butterfly pupae. Glutathione S-transferases (GSTs) are a family of multifunctional detoxification enzymes that act in xenobiotic metabolism in insects. Insect genome projects have facilitated identification and characterization of GST family members. We identified 20 putative GSTs in the P. puparum genome, including 19 cytosolic and one microsomal. Phylogenetic analysis showed that P. puparum GSTs are clustered into Hymenoptera-specific branches. Transcriptomic data of embryos, larvae, female pupae, male pupae, female adults, male adults, venom glands, carcass, salivary glands, and ovaries revealed stage-, sex-, and tissue-specific expression patterns of GSTs in P. puparum. This is the most comprehensive study of genome-wide identification, characterization, and expression profiling of GST family in hymenopterans. Our results provide valuable information for understanding the metabolic adaptation of this wasp.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Yeast glutaredoxin, GRX4, functions as a glutathione S-transferase required for red ade pigment formation in Saccharomyces cerevisiae

The adenine biosynthetic mutants ade1 and ade2 of Saccharomyces cerevisiae accumulate a characteristic red pigment in their vacuoles under adenine limiting conditions. This red pigmentation phenotype, widely used in a variety of genetic screens and assays, is the end product of a glutathione-mediated detoxification pathway, where the glutathione conjugates are transported into the vacuole. The glutathione conjugation step, however, has still remained unsolved. We show here, following a detailed analysis of all the members of the thioredoxinfold superfamily, the involvement of the monothiol glutaredoxin GRX4 as essential for pigmentation. GRX4 plays multiple roles in the cell, and we show that the role in ade pigmentation does not derive from its regulatory role of the iron transcription factor, Aft1p, but a newly identified GST activity of the protein that we could demonstrate using purified Grx4p. Further, we demonstrate that the GRX domain of GRX4 and its active site cysteine C171 is critical for this activity. The findings thus solve a decades old enigma on a critical step in the formation of this red pigmentation.

5,7,3',4'-flavan-on-ol (taxifolin) protects against acetaminophen-induced liver injury by regulating the glutathione pathway

Taxifolin (TAX) reportedly exerts protective and therapeutic effects in liver. Herein, the effects of TAX against acetaminophen (APAP)-induced hepatotoxicity were investigated. Pharmacodynamics, pharmacology and metabolomics analyses of TAX were assessed on C57 mice and L-02 cells. TAX was administered for 7 days, and APAP was given on the last day to establish an acute liver injury model. ALT and AST levels were determined, and liver ROS, MDA, GST, GSH and GPX1 were analysed. The expression and protein abundance of GPX1, GPS-Pi, GCLC and GCLM were assessed by PCR and western blotting, and metabolic changes in cells and serum were investigated by UPLC-Q-Orbitrap-MS. Serum ALT and AST, and liver ROS, MDA, GST, GSH and GPX1 levels confirmed the protective effects of TAX. Besides, we found Only treating with TAX decreased the expression of CYP2E1 in mice liver tissue. TAX reversed the APAP-induced decrease in cell viability in L-02 cells, and reduced cellular ROS levels. Furthermore, TAX reversed the APAP-induced decrease in antioxidant enzymes at both mRNA and protein levels. Metabolomics analysis identified metabolites mainly related to glutathione metabolism (36 in vivo and 23 in vitro). The concentration of glutathione, oxidized glutathione, carnitine, succinic acid, pyroglutamic acid, citrulline, taurine, palmitoleic acid, phytoshingosine-1-P and sphingosine-1-P were close to normal levels after treating with TAX. These results indicate that TAX prevents APAP-induced liver injury by inhibiting APAP metabolic activation mediated by CYP450 enzymes, modulating glutathione metabolism, and expression of related antioxidative signals. These properties could be harnessed to prevent or treat hepatotoxicity.

S-Glutathionylation of mouse selenoprotein W prevents oxidative stress-induced cell death by blocking the formation of an intramolecular disulfide bond

Mouse selenoprotein W (SELENOW) is a small protein containing a selenocysteine (Sec, U) and four cysteine (Cys, C) residues. The Sec residue in SELENOW is located within the conserved CXXU motif corresponding to the CXXC redox motif of thioredoxin (Trx). It is known that glutathione (GSH) binds to SELENOW and that this binding is involved in protecting cells from oxidative stress. However, the regulatory mechanisms controlling the glutathionylation of SELENOW in oxidative stress are unclear. In this study, using purified recombinant SELENOW in which Sec13 was changed to Cys, we found that SELENOW was glutathionylated at Cys33 and that this S-glutathionylation was enhanced by oxidative stress. We also found that the S-glutathionylation of SELENOW at Cys33 in HEK293 cells was due to glutathione S-transferase Pi (GSTpi) and that this modification was reversed by glutaredoxin1 (Grx1). In addition to the disulfide bond between the Cys10 and Cys13 of SELENOW, a second disulfide bond was formed between Cys33 and Cys87 under oxidative stress conditions. The second disulfide bond was reduced by Trx1, but the disulfide bond between Cys10 and Cys13 was not. The second disulfide bond was also reduced by glutathione, but the disulfide bond in the CXXC motif was not. The second disulfide bond of the mutant SELENOW, in which Cys37 was replaced with Ser, was formed at a much lower concentration of hydrogen peroxide than the wild type. We also observed that Cys37 was required for S-glutathionylation, and that S-glutathionylated SELENOW containing Cys37 protected the cells from oxidative stress. Furthermore, the SELENOW (C33, 87S) mutant, which could not form the second disulfide bond, also showed antioxidant activity. Taken together, these results indicate that GSTpi-mediated S-glutathionylation of mouse SELENOW at Cys33 is required for the protection of cells in conditions of oxidative stress, through inhibition of the formation of the second disulfide bond.

Identification of key residues for activities of atypical glutathione S-transferase of Ceriporiopsis subvermispora, a selective degrader of lignin in woody biomass, by crystallography and functional mutagenesis

Ceriporiopsis subvermispora (C. subvermispora) is a selective degrader of lignin in the woody biomass. Glutathione S-transferases (GSTs) are multifunctional enzymes that play important roles in cellular detoxification and metabolism. The crystal structures of a GST of C. subvermispora, CsGST83044, in GSH-free and -bound forms were solved at 1.95 and 2.19 Å resolution, respectively. The structure of the GSH-bound form revealed that CsGST83044 can be categorized as an atypical-type of GST. In the GSH-bound form of CsGST83044, Asn22, Asn24, and Tyr46 are located closest to the sulfur atom and form hydrogen bonds with the thiol group. The functional mutagenesis indicated that they are critical for the enzymatic activities of CsGST83044. The critical residues of an atypical-type GST belonging to the GSTFuA class were revealed for the first time. A previous study indicated that CsGST83044 and another GST, CsGST63524, differ in substrate preference; CsGST83044 prefers smaller substrates than CsGST63524 for its esterase activity. The GSH-bound pocket of CsGST83044 turns out to be small, which may explain the preference for smaller substrates. Protein engineering of GSTs of C. subvermispora in the light of the obtained insight may pave a path in the future for utilization of the woody biomass.

Genome-wide identification and expression of the entire 52 glutathione S-transferase (GST) subfamily genes in the Cu2+-exposed marine copepods Tigriopus japonicus and Paracyclopina nana

In this study, the entire glutathione S-transferases (GSTs), the major phase II detoxification enzyme, were identified in two marine copepod species Tigriopus japonicus and Paracyclopina nana. The genome-wide identification of GSTs in T. japonicus and P. nana resulted in 32 and 20 GSTs in total, respectively. Among the identified GSTs, two specific classes of GSTs, specifically sigma and delta/epsilon GSTs were the dominant form of cytosolic GSTs in T. japonicus, while delta/epsilon and mu classes were dominant cytosolic GSTs in P. nana. In addition, Membrane-Associated Proteins in Eicosanoid and Glutathione metabolism (MAPEG) family were found in relatively higher proportion compared to other classes. Moreover, sigma, delta/epsilon, and microsomal GSTs have shown to expand through tandem duplication. To validate the detoxification function of the identified GSTs, both copepods were exposed to copper (Cu²⁺) and the reactive oxygen species (ROS) level and GST activity were measured. With integration of phylogenetic analysis and xenobiotic-mediated GST mRNA expression patterns along with previous enzymatic activities, the functional divergence among species-specific GST genes was clearly observed. This study covers full identification of GST classes in two marine copepod species and their important role in marine environmental ecotoxicology.

Structure of a serine-type glutathione S-transferase of Ceriporiopsis subvermispora and identification of the enzymatically important non-canonical residues by functional mutagenesis

Ceriporiopsis subvermispora (C. subvermispora), one of the white-rot fungi, is known as a selective lignin degrader of the woody biomass. Glutathione S-transferases (GSTs) are multifunctional enzymes that are capable of catalyzing the reactions involved in detoxification and metabolic pathways. In this study, a GST of C. subvermispora, named CsGST63524, was overexpressed in E. coli, and then purified by affinity, anion exchange, and size exclusion column chromatography. The crystal structures of the CsGST63524 in ligand-free and complex with GSH were refined at 2.45 and 2.50 Å resolutions, respectively. The sulfur atom of glutathione forms a hydrogen bond with Ser21 of CsGST63524, indicating it is a serine-type GST. Mutagenesis of Ser21 unexpectedly indicated that this serine residue is not essential for the enzymatic activity of CsGST63524. Comparative sequence and structural analyses, together with functional mutagenesis, newly identified the enzymatically important non-canonical amino acid residues, Asn23 and Tyr45, other than the serine residue.

Monomeric Camelus dromedarius GSTM1 at low pH is structurally more thermostable than its native dimeric form

Glutathione S‒transferases (GSTs) are multifunctional enzymes that play an important role in detoxification, cellular signalling, and the stress response. Camelus dromedarius is well-adapted to survive in extreme desert climate and it has GSTs, for which limited information is available. This study investigated the structure-function and thermodynamic properties of a mu-class camel GST (CdGSTM1) at different pH. Recombinant CdGSTM1 (25.7 kDa) was expressed in E. coli and purified to homogeneity. Dimeric CdGSTM1 dissociated into stable but inactive monomeric subunits at low pH. Conformational and thermodynamic changes during the thermal unfolding pathway of dimeric and monomeric CdGSTM1 were characterised via a thermal shift assay and dynamic multimode spectroscopy (DMS). The thermal shift assay based on intrinsic tryptophan fluorescence revealed that CdGSTM1 underwent a two-state unfolding pathway at pH 1.0-10.0. Its Tm value varied with varying pH. Another orthogonal technique based on far-UV CD also exhibited two-state unfolding in the dimeric and monomeric states. Generally, proteins tend to lose structural integrity and stability at low pH; however, monomeric CdGSTM1 at pH 2.0 was thermally more stable and unfolded with lower van't Hoff enthalpy. The present findings provide essential information regarding the structural, functional, and thermodynamic properties of CdGSTM1 at pH 1.0-10.0.

Meroterpenoid-Rich Fraction of the Ethanolic Extract from Sargassum serratifolium Suppressed Oxidative Stress Induced by Tert-Butyl Hydroperoxide in HepG2 Cells

Sargassum species have been reported to be a source of phytochemicals, with a wide range of biological activities. In this study, we evaluated the hepatoprotective effect of a meroterpenoid-rich fraction of the ethanolic extract from Sargassum serratifolium (MES) against tert-butyl hydroperoxide (t-BHP)-treated HepG2 cells. Treatment with MES recovered the cell viability from the t-BHP-induced oxidative damage in a dose-dependent manner. It suppressed the reactive oxygen species production, lipid peroxidation, and glutathione depletion in the t-BHP-treated HepG2 cells. The activity of the antioxidants induced by t-BHP, including superoxide dismutase (SOD) and catalase, was reduced by the MES treatment. Moreover, it increased the nuclear translocation of nuclear factor erythroid 2-related factor 2, leading to the enhanced activity of glutathione S transferase, and the increased production of heme oxygenase-1 and NAD(P)H:quinine oxidoreductase 1 in t-BHP-treated HepG2 cells. These results demonstrate that the antioxidant activity of MES substituted the activity of the SOD and catalase, and induced the production of detoxifying enzymes, indicating that MES might be used as a hepatoprotectant against t-BHP-induced oxidative stress.

Development of an Efficient Dual-Action GST-Inhibiting Anticancer Platinum(IV) Prodrug

The cytotoxicity of cisplatin (cDDP) is enhanced when co-administered with ethacrynic acid (EA), a glutathione S-transferase (GST) inhibitor. A Pt^IV -EA conjugate containing a cDDP core and two axial ethacrynate ligands (compound 1) was shown to be an excellent inhibitor of GST, but did not readily release a Pt^II species to exert a synergistic cytotoxic effect. In this study, a redesigned Pt^IV construct composed of a cDDP core with one axial ethacrynate ligand and one axial hydroxido ligand (compound 2) was prepared and shown to overcome the limitations of compound 1. The EA ligand in 2 is readily released in vitro together with a cytotoxic Pt^II species derived from cisplatin, working together to inhibit cell proliferation in cDDP-resistant human ovarian cancer cells. The in vitro activity translates well in vivo with 2, showing effective (∼80 %) inhibition of tumor growth in a human ovarian carcinoma A2780 tumor model, while showing considerably lower toxicity than cisplatin, thus validating the new design strategy.