Characterization and structural analysis of human selenium-dependent glutathione peroxidase 4 mutant expressed in Escherichia coli

Targeting ferroptosis by natural products in pathophysiological conditions

Ferroptosis is a form of cell death that is induced by iron-mediated accumulation of lipid peroxidation. The involvement of ferroptosis in different pathophysiological conditions has offered new perspectives on potential therapeutic interventions. Natural products, which are widely recognized for their significance in drug discovery and repurposing, have shown great promise in regulating ferroptosis by targeting various ferroptosis players. In this review, we discuss the regulatory mechanisms of ferroptosis and its implications in different pathological conditions. We dissect the interactions between natural products and ferroptosis in cancer, ischemia/reperfusion, neurodegenerative diseases, acute kidney injury, liver injury, and cardiomyopathy, with an emphasis on the relevance of ferroptosis players to disease targetability.

Prospects for Anti-Tumor Mechanism and Potential Clinical Application Based on Glutathione Peroxidase 4 Mediated Ferroptosis

Ferroptosis, characterized by excessive iron accumulation and lipid peroxidation, is a novel form of iron-dependent cell death, which is morphologically, genetically, and biochemically distinct from other known cell death types, such as apoptosis, necrosis, and autophagy. Emerging evidence shows that glutathione peroxidase 4 (GPX4), a critical core regulator of ferroptosis, plays an essential role in protecting cells from ferroptosis by removing the product of iron-dependent lipid peroxidation. The fast-growing studies on ferroptosis in cancer have boosted a perspective on its use in cancer therapeutics. In addition, significant progress has been made in researching and developing tumor therapeutic drugs targeting GPX4 based on ferroptosis, especially in acquired drug resistance. Selenium modulates GPX4-mediated ferroptosis, and its existing form, selenocysteine (Sec), is the active center of GPX4. This review explored the structure and function of GPX4, with the overarching goal of revealing its mechanism and potential application in tumor therapy through regulating ferroptosis. A deeper understanding of the mechanism and application of GPX4-mediated ferroptosis in cancer therapy will provide new strategies for the research and development of antitumor drugs.

Reactive Human Plasma Glutathione Peroxidase Mutant with Diselenide Bond Succeeds in Tetramer Formation

Plasma glutathione peroxidase (GPx3) belongs to the GPx superfamily, and it is the only known secreted selenocysteine (Sec)−containing GPx in humans. It exists as a glycosylated homotetramer and catalyzes the reduction of hydrogen peroxide and lipid peroxides, depending on the Sec in its active center. In this study, a previously reported chimeric tRNA^UTuT6 was used for the incorporation of Sec at the UAG amber codon, and the mature form of human GPx3 (hGPx3) without the signal peptide was expressed in amber−less E. coli C321.ΔA.exp. Reactive Sec−hGPx3, able to reduce H₂O₂ and tert−butyl hydroperoxide (t−BuOOH), was produced with high purity and yield. Study of the quaternary structure suggested that the recombinant Sec−hGPx3 contained an intra−molecular disulfide bridge but failed to form tetramer. Mutational and structural analysis of the mutants with three Cys residues, individually or jointly replaced with Ser, indicated that the formation of intra−molecular disulfide bridges involved structure conformational changes. The secondary structure containing Cys77 and Cys132 was flexible and could form a disulfide bond, or form a sulfhydryl–selenyl bond with Sec49 in relative mutants. Mutation of Cys8 and Cys132 to Sec8 and Sec132 could fix the oligomerization loop through the formation of diselenide bond, which, in turn, facilitated tetramer formation and noticeably improved the GPx activity. This research provides an important foundation for the further catalysis and functional study of hGPx3.

Characterization of a patient-derived variant of GPX4 for precision therapy

GPX4, as the only enzyme in mammals capable of reducing esterified phospholipid hydroperoxides within a cellular context, protects cells from ferroptosis. We identified a homozygous point mutation in the GPX4 gene, resulting in an R152H coding mutation, in three patients with Sedaghatian-type spondylometaphyseal dysplasia (SSMD). With structure-based analyses and cell models, including patient fibroblasts, of this variant, we found that the missense variant destabilized a critical loop, which disrupted the active site and caused a substantial loss of enzymatic function. We also found that the R152H variant of GPX4 is less susceptible to degradation, revealing the degradation mechanism of the GPX4 protein. Proof-of-concept therapeutic treatments, which overcome the impaired R152H GPX4 activity, including selenium supplementation, selective antioxidants, and a deuterated PUFA were identified. In addition to revealing a general approach to investigating rare genetic diseases, we demonstrate the biochemical foundations for therapeutic strategies targeting GPX4.

Improvement of stability and in vivo antioxidant effect of human glutathione peroxidase mutant by PEGylation

Human glutathione peroxidase (GPx), as an important kind of antioxidant enzyme, is often used for the removal of reactive oxygen species. Unfortunately, the application has been hindered by its limited source and poor stability. To solve these problems, human glutathione peroxidase mutant (GPxM) with high activity and yield was obtained using Escherichia coli BL21(DE3) cys auxotrophic strain and the single-protein production system in our previous work. However, the antioxidant effect of this novel recombinant protein drug in animals has not been demonstrated, and its immunogenicity and short biological half-life as a biological macromolecule may have seriously hindered its clinical application. Therefore, it is important to find an effective strategy to address the above issues. In this work, PEGylated GPxM was prepared by conjugating the corresponding mutant with monomethoxy polyethylene glycol succinimidyl succinate (SS-mPEG). We researched the structure, stability, pharmacokinetic properties, antioxidant effect in vivo and protective mechanism against adriamycin (ADR)-mediated cardiotoxicity of modified products, and compared with the above properties of GPxM. The results revealed that GPxM had an excellent antioxidant effect in vivo, and PEGylation can enhance the stability, half-life and antioxidant effect of GPxM while reducing immunogenicity. In addition, the above improvement of PEGylated GPx1M was stronger than that of monoPEGylated GPx4M. Hence, PEGylation might be an effective method to broaden the applications of GPxM as the important antioxidant drug, especially the PEGylated GPx1M with high antioxidant effect.

Protective Effects and Mechanisms of Recombinant Human Glutathione Peroxidase 4 on Isoproterenol-Induced Myocardial Ischemia Injury

Ischemic heart disease (IHD) is a cardiovascular disease with high fatality rate, and its pathogenesis is closely related to oxidative stress. Reactive oxygen species (ROS) in oxidative stress can lead to myocardial ischemia (MI) injury in many ways. Therefore, the application of antioxidants may be an effective way to prevent IHD. In recent years, glutathione peroxidase 4 (GPx4) has received increasing attention due to its antioxidant effect. In a previous study, we used the new chimeric tRNA^UTuT6 to express highly active recombinant human GPx4 (rhGPx4) in amber-less Escherichia coli. In this study, we established an isoproterenol- (ISO-) induced MI injury model in rats and an in vitro model to research the protective effect and mechanism of rhGPx4 on MI injury. The results showed that rhGPx4 could reduce the area of myocardial infarction and ameliorate the pathological injury of heart tissue, significantly reduce ISO-induced abnormalities on electrocardiogram (ECG) and cardiac serum biomarkers, protect mitochondrial function, and attenuate cardiac oxidative stress injury. In an in vitro model, the results also confirmed that rhGPx4 could inhibit ISO-induced oxidative stress injury and cardiomyocyte apoptosis. The mechanism of action of rhGPx4 involves not only the inhibition of lipid peroxidation by eliminating ROS but also keeping a normal level of endogenous antioxidant enzymes by eliminating ROS, thereby preventing oxidative stress injury in cardiomyocytes. Additionally, rhGPx4 could inhibit cardiomyocyte apoptosis through a mitochondria-dependent pathway. In short, rhGPx4, a recombinant antioxidant enzyme, can play an important role in the prevention of IHD and may have great potential for application.

Ferroptosis: mechanisms and links with diseases

Ferroptosis is an iron-dependent cell death, which is different from apoptosis, necrosis, autophagy, and other forms of cell death. The process of ferroptotic cell death is defined by the accumulation of lethal lipid species derived from the peroxidation of lipids, which can be prevented by iron chelators (e.g., deferiprone, deferoxamine) and small lipophilic antioxidants (e.g., ferrostatin, liproxstatin). This review summarizes current knowledge about the regulatory mechanism of ferroptosis and its association with several pathways, including iron, lipid, and cysteine metabolism. We have further discussed the contribution of ferroptosis to the pathogenesis of several diseases such as cancer, ischemia/reperfusion, and various neurodegenerative diseases (e.g., Alzheimer's disease and Parkinson's disease), and evaluated the therapeutic applications of ferroptosis inhibitors in clinics.

The pathological role of ferroptosis in ischemia/reperfusion-related injury

Ischemia/reperfusion (I/R) is a pathological process that occurs in numerous organs throughout the human body, and it is frequently associated with severe cellular damage and death. Recently it has emerged that ferroptosis, a new form of regulated cell death that is caused by iron-dependent lipid peroxidation, plays a significantly detrimental role in many I/R models. In this review, we aim to revise the pathological process of I/R and then explore the molecular pathogenesis of ferroptosis. Furthermore, we aim to evaluate the role that ferroptosis plays in I/R, providing evidence to support the targeting of ferroptosis in the I/R pathway may present as a therapeutic intervention to alleviate ischemia/reperfusion injury (IRI) associated cell damage and death.

Selenium-Rich Diet Induces Myocardial Structural and Functional Abnormalities by Activating Caspase-9 and Caspase-3 in Gpx-1P198L-Overexpression Transgenic Mice

Background

Selenium (Se) deficiency and supplementation result in multiple effects. GPx-1 (Pro198Leu) polymorphism is associated with Se deficiency. This study aimed to observe associations between Se-deficiency/supplement and GPx-1-198Leu overexpression in myocardial injuries.

Material/Methods

GPx-1P198L transgenic (Tg) mice and non-transgenic wild-type (WT) littermates were divided into Control (CON, 0.1–0.2 mg/kg), Se-deficiency (SD, <0.02 mg/kg), and Se-supplement (SS, 0.4 mg/kg) groups. Cardiac functions were observed with animal M-mode echocardiography. Se level was measured using 2,3-diamino Kenai fluorospectrophotometry. Total cardiac GPx activity was also measured. Myocardial histopathology was determined with HE and Masson’s trichrome staining. Caspase-9 and caspase-3 were measured with Western blot analysis.

Results

In WT Se-deficient mice, cardiac GPx activity was significantly decreased, and was not elevated by overexpression of GPx-1-198Leu gene. Increased GPx activity was observed in WT Se-supplemented mice and Tg Se-supplemented mice (much more). Se deficiency as well as supplementation resulted in cardiac systolic dysfunction, which was not affected by GPx-1-198Leu gene. Se deficiency led to myocardial fibrosis and pathological changes accompanied by increased activation of caspase-9 and caspase-3. Se supplementation significantly reduced pathological changes, as well as caspase-9 and caspase-3 levels in the presence of increased myocardial fibrosis. In Se-deficient mice, GPx-1-198Leu overexpression did not significantly decrease myocardial pathological injuries and fibrosis. In Se-supplemented Tg mice, myocardial fibrosis and caspase-9 level were increased, although pathological injuries and caspase-3 were similar to that in Se-supplemented WT mice.

Conclusions

Se deficiency as well as supplementation induced myocardial structural and functional abnormalities through activation of caspase-9 and caspase-3 in GPx-1P198L overexpression transgenic mice.

Molecular modification, expression and purification of new subtype antioxidant peptide from Pinctada fucata by recombinant Escherichia coli to improve antioxidant-activity

The aim of this study was to establish a system for the efficient expression and purification of new subtype of antioxidant peptide from Pinctada fucata meat (NPFMAP), which is designed by molecular modification technology based on the sequence of purified and identified antioxidant peptide from Pinctada fucata meat (PFMAP, Gly-Ala-Gly-Leu-Pro-Gly-Lys-Arg-Glu-Arg), and to better understand the relationship between structure and antioxidant activity. Meanwhile, gene codon usage was optimized and the glutathione S-transferase (GST) tag of pGEX-6P-1 was added to facilitate expression and purification NPFMAP in Escherichia coli. The results of antioxidant activity assay in vitro showed a higher antioxidant activity in NPFMAP than that in enzymatic hydrolysis digested or chemically synthesized PFMAP. In particular, the DPPH scavenging radical activity increased by about 4.7 times after molecular modification. Structural bioanalysis indicated that new subtype antioxidant peptide had spatial conformation and good hydrophilic after modification, which was confirmed by antioxidant activity assays. Thus, the proposed method could be used to obtain NPFMAP with high antioxidant activity.

Custom selenoprotein production enabled by laboratory evolution of recoded bacterial strains

Incorporation of the rare amino acid selenocysteine to form diselenide bonds can improve stability and function of synthetic peptide therapeutics. However, application of this approach to recombinant proteins has been hampered by heterogeneous incorporation, low selenoprotein yields, and poor fitness of bacterial producer strains. We report the evolution of recoded Escherichia coli strains with improved fitness that are superior hosts for recombinant selenoprotein production. We apply an engineered β-lactamase containing an essential diselenide bond to enforce selenocysteine dependence during continuous evolution of recoded E. coli strains. Evolved strains maintain an expanded genetic code indefinitely. We engineer a fluorescent reporter to quantify selenocysteine incorporation in vivo and show complete decoding of UAG codons as selenocysteine. Replacement of native, labile disulfide bonds in antibody fragments with diselenide bonds vastly improves resistance to reducing conditions. Highly seleno-competent bacterial strains enable industrial-scale selenoprotein expression and unique diselenide architecture, advancing our ability to customize the selenoproteome.

Why should neuroscientists worry about iron? The emerging role of ferroptosis in the pathophysiology of neuroprogressive diseases

Ferroptosis is a unique form of programmed death, characterised by cytosolic accumulation of iron, lipid hydroperoxides and their metabolites, and effected by the fatal peroxidation of polyunsaturated fatty acids in the plasma membrane. It is a major driver of cell death in neurodegenerative neurological diseases. Moreover, cascades underpinning ferroptosis could be active drivers of neuropathology in major psychiatric disorders. Oxidative and nitrosative stress can adversely affect mechanisms and proteins governing cellular iron homeostasis, such as the iron regulatory protein/iron response element system, and can ultimately be a source of abnormally high levels of iron and a source of lethal levels of lipid membrane peroxidation. Furthermore, neuroinflammation leads to the upregulation of divalent metal transporter1 on the surface of astrocytes, microglia and neurones, making them highly sensitive to iron overload in the presence of high levels of non-transferrin-bound iron, thereby affording such levels a dominant role in respect of the induction of iron-mediated neuropathology. Mechanisms governing systemic and cellular iron homeostasis, and the related roles of ferritin and mitochondria are detailed, as are mechanisms explaining the negative regulation of ferroptosis by glutathione, glutathione peroxidase 4, the cysteine/glutamate antiporter system, heat shock protein 27 and nuclear factor erythroid 2-related factor 2. The potential role of DJ-1 inactivation in the precipitation of ferroptosis and the assessment of lipid peroxidation are described. Finally, a rational approach to therapy is considered, with a discussion on the roles of coenzyme Q₁₀, iron chelation therapy, in the form of deferiprone, deferoxamine (desferrioxamine) and deferasirox, and N-acetylcysteine.

Expression and characterization of recombinant bifunctional enzymes with glutathione peroxidase and superoxide dismutase activities

To balance the production and decomposition of reactive oxygen species, living organisms have generated antioxidant enzymes and non-enzymatic antioxidant defense systems. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) are two important antioxidant enzymes. Apart from their catalytic functions, they protect each other, resulting in more efficient removal of reactive oxygen species, protection of cells against injury, and maintenance of the normal metabolism of reactive oxygen species. SOD catalyzes the dismutation of the superoxide anion (O₂^•-) to oxygen (O₂) and hydrogen peroxide (H₂O₂). H₂O₂ is then detoxified to water by GPx. In this study, human GPx1^Ser and the Alvinella pompejana SOD (ApSOD) gene were used to design and generate several recombinant proteins with both GPx and SOD activities by combining traditional fusion protein technology, a cysteine auxotrophic expression system, and a single protein production (SPP) system. Among the fusion proteins, Se-hGPx1^Ser-L-ApSOD exhibited the highest SOD and GPx activities. Additional research was conducted to better understand the properties of Se-hGPx1^Ser-L-ApSOD. The synergism of Se-hGPx1^Ser-L-ApSOD was evaluated by using an in vitro model. This research may facilitate future studies on the cooperation and catalytic mechanisms of GPx and SOD. We believe that the bifunctional enzyme has potential applications as a potent antioxidant.

Glutathione peroxidase 4: a new player in neurodegeneration?

Glutathione peroxidase 4 (GPx4) is an antioxidant enzyme reported as an inhibitor of ferroptosis, a recently discovered non-apoptotic form of cell death. This pathway was initially described in cancer cells and has since been identified in hippocampal and renal cells. In this Perspective, we propose that inhibition of ferroptosis by GPx4 provides protective mechanisms against neurodegeneration. In addition, we suggest that selenium deficiency enhances susceptibility to ferroptotic processes, as well as other programmed cell death pathways due to a reduction in GPx4 activity. We review recent studies of GPx4 with an emphasis on neuronal protection, and discuss the relevance of selenium levels on its enzymatic activity.

Unglycosylated recombinant human glutathione peroxidase 3 mutant from Escherichia coli is active as a monomer

Glutathione peroxidase 3 (GPx3) is a glycosylated member of GPx family and can catalyze the reaction of different types of peroxides with GSH to form their corresponding alcohols in vitro. The active center of GPx3 is selenocysteine (Sec), which is incorporated into proteins by a specific mechanism. In this study, we prepared a recombinant human GPx3 (rhGPx3) mutant with all Cys changed to Ser from a Cys auxotrophic strain of E. coli, BL21(DE3)cys. Although lacking post-translational modification, rhGPx3 mutant still retained the ability to reduce H2O2 and PLPC-OOH. Study on the quaternary structure suggested that rhGPx3 mutant existed as a monomer in solution, which is different from native tetrameric GPx3. Loss of the catalytic activity was considered to be attributed to both the absence of glycosylation and the failure of the tetramer. Further analysis was performed to compare the structures of rhGPx3 and GPx4 mutant, which were quite similar except for oligomerization loop. The differences of amino acid composition and electrostatic potentials on the oligomerization loop may affect the binding of large substrates to rhGPx3 mutant. This research provides an important foundation for biosynthesis of functionally selenium-containing GPx3 mutant in E.coli.