GO:0033743 peptide-methionine (R)-S-oxide reductase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0033743 describes the enzymatic reduction of the R stereoisomer of methionine sulfoxide back to methionine within proteins, using thioredoxin as the electron donor.
• This activity is essential for reversing oxidative damage to methionine residues, a reversible post-translational modification that regulates protein function.
• The primary enzymes carrying this activity are methionine sulfoxide reductase B (MsrB) proteins, including the selenoprotein MSRB1 in mammals.
• Methionine oxidation and its reversal by MsrB influence diverse processes such as cancer metastasis, ferroptosis, and mitochondrial stress responses.
• Dysregulation of MsrB enzymes is implicated in aging, neurodegeneration, and cancer, making them attractive therapeutic targets.
• CRISPR-based knockout, knock-in, and overexpression models are powerful tools to dissect the physiological roles of MsrB enzymes in health and disease.
Description
Peptide-methionine (R)-S-oxide reductase activity, encoded by the GO term GO:0033743, is a molecular function that catalyzes the thioredoxin-dependent reduction of the R stereoisomer of methionine sulfoxide back to methionine within proteins. This activity is critical for repairing oxidative damage to methionine residues, a modification that can alter protein structure and function. The reversible oxidation of methionine serves as a regulatory switch in many biological processes, and its reduction by MsrB enzymes is essential for maintaining cellular redox homeostasis. Researchers study this activity to understand how cells cope with oxidative stress, how methionine oxidation regulates signaling pathways, and how its dysregulation contributes to diseases such as cancer and neurodegeneration. The discovery of MsrB as a selenoprotein highlighted its importance in antioxidant defense and its potential as a therapeutic target. This article provides a comprehensive overview of GO:0033743, covering its mechanism, key genes, disease relevance, and research methodologies.
peptide-methionine (R)-S-oxide reductase activity At A Glance
| GO ID | GO:0033743 |
|---|---|
| GO term | peptide-methionine (R)-S-oxide reductase activity |
| Ontology | molecular_function |
| Synonym | MsrB, methionine sulfoxide reductase B activity, selenoprotein R, SelR, PilB, pMSR |
| Major function | Reduction of R-methionine sulfoxide in proteins to methionine, using thioredoxin |
| Reaction | L-methionyl-[protein] + [thioredoxin]-disulfide + H2O = L-methionyl-(R)-S-oxide-[protein] + [thioredoxin]-dithiol |
| Cofactor | Thioredoxin (electron donor) |
| Localization | Cytoplasm, mitochondria, nucleus (varies by isoform) |
| EC number | 1.8.4.12 |
What Is GO:0033743?
GO:0033743, peptide-methionine (R)-S-oxide reductase activity, is defined as the catalysis of the reaction: L-methionyl-[protein] + [thioredoxin]-disulfide + H2O = L-methionyl-(R)-S-oxide-[protein] + [thioredoxin]-dithiol. In simpler terms, it is an enzyme activity that reduces the R-form of methionine sulfoxide in proteins back to methionine, using thioredoxin as a reducing agent. This activity is specific for the R stereoisomer, distinguishing it from MsrA, which reduces the S stereoisomer.
Why Is peptide-methionine (R)-S-oxide reductase activity Important in Cell Biology?
Peptide-methionine (R)-S-oxide reductase activity is vital for cellular protection against oxidative stress and for regulating protein function through reversible methionine oxidation. This activity is conserved across all domains of life and is essential for maintaining the reduced state of critical methionine residues that can otherwise lead to protein inactivation or degradation. In mammals, the selenoprotein MSRB1 is a key enzyme with this activity, and its dysfunction has been linked to increased susceptibility to oxidative damage, inflammation, and age-related diseases. Understanding GO:0033743 provides insights into redox signaling, protein quality control, and potential therapeutic strategies for diseases where methionine oxidation plays a role.
• Reverses oxidative damage to methionine residues, preventing irreversible protein oxidation.
• Regulates protein function through reversible methionine oxidation, impacting signaling pathways.
• Protects against oxidative stress-induced cell death, including ferroptosis.
• Modulates cancer progression, as methionine oxidation of pyruvate kinase M2 promotes pancreatic cancer metastasis.
• Involved in bacterial pathogenesis and stress responses through reversible methionine oxidation.
• Selenoprotein MSRB1 is implicated in inflammation and immune regulation.
• Deficiency of MsrA (which reduces S-isomer) aggravates acute kidney injury, highlighting the importance of methionine sulfoxide reduction.
• Potential target for developing antioxidants and therapies for neurodegenerative diseases.
• Plays a role in mitochondrial unfolded protein response and aging.
• Provides a model for studying stereospecific redox reactions and enzyme mechanisms.
What Happens During peptide-methionine (R)-S-oxide reductase activity?
Substrate Recognition and Binding
In simple terms: The enzyme finds and grabs onto a protein that has a damaged methionine residue.
The enzyme specifically recognizes proteins containing methionine (R)-S-oxide, the oxidized form of methionine. This modification typically arises from reactive oxygen species attacking methionine residues. The active site of MsrB is structured to accommodate the R stereoisomer, ensuring stereospecific binding. Structural studies have revealed a conserved fold with a catalytic cysteine or selenocysteine residue that attacks the sulfoxide oxygen.
Catalytic Reduction Mechanism
In simple terms: The enzyme uses a chemical reaction to remove the oxygen from the damaged methionine, restoring it to normal.
The catalytic cycle involves a nucleophilic attack by the active-site cysteine (or selenocysteine) on the sulfoxide oxygen, forming a sulfenic acid intermediate and releasing methionine. This intermediate is then reduced by thioredoxin, which donates electrons and restores the enzyme's active site. The reaction consumes thioredoxin and produces oxidized thioredoxin, linking this activity to the cellular thioredoxin system.
Thioredoxin Regeneration
In simple terms: Another protein, thioredoxin, gets recharged so it can keep helping the enzyme.
Thioredoxin reductase and NADPH regenerate reduced thioredoxin, ensuring a continuous supply of reducing equivalents for MsrB activity. This coupling integrates peptide-methionine (R)-S-oxide reductase activity into the broader cellular antioxidant network, which includes glutathione and other redox systems. The thioredoxin system is essential for maintaining the reducing environment of the cytosol and mitochondria.
Stereospecificity and Isoforms
In simple terms: Different versions of the enzyme handle different shapes of the damaged methionine.
MsrB enzymes are specific for the R isomer, while MsrA enzymes reduce the S isomer. In mammals, there are three MsrB isoforms: MSRB1 (selenoprotein), MSRB2 (mitochondrial), and MSRB3 (cytosolic), each with distinct subcellular localizations and tissue distributions. This compartmentalization allows for targeted repair of oxidized methionine in different cellular environments.
Key Genes Involved in GO:0033743 peptide-methionine (R)-S-oxide reductase activity
The following genes encode proteins that exhibit peptide-methionine (R)-S-oxide reductase activity or are directly involved in its regulation and function.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MSRB1 | Selenoprotein MsrB; reduces R-methionine sulfoxide in cytosol and nucleus | Inflammation, immune response, cancer, oxidative stress |
| MSRB2 | Mitochondrial MsrB; protects mitochondria from oxidative damage | Mitochondrial dysfunction, aging, neurodegeneration |
| MSRB3 | Cytosolic MsrB; widely expressed, involved in protein repair | Deafness, cancer, cellular redox balance |
| MsrA (MSRA) | Reduces S-methionine sulfoxide; complementary to MsrB | Ferroptosis, acute kidney injury, oxidative stress |
| Trx (TXN) | Thioredoxin; electron donor for MsrB | Redox regulation, cancer, inflammation |
| TrxR (TXNRD1) | Thioredoxin reductase; regenerates reduced thioredoxin | Antioxidant defense, cancer therapy target |
| PilB | Bacterial MsrB homolog; involved in pilus assembly | Bacterial pathogenesis, protein folding |
| SelR | Drosophila MsrB; regulates methionine oxidation | Aging, oxidative stress response |
| PKM2 | Pyruvate kinase M2; methionine oxidation activates it | Cancer metabolism, metastasis |
| SAM | S-adenosyl methionine; methyl donor, affects methionine cycle | Mitochondrial unfolded protein response |
| CaMKII | Calcium/calmodulin-dependent kinase II; regulated by oxidation | Ferroptosis, kidney injury |
| NRF2 | Transcription factor; regulates antioxidant genes | Oxidative stress response, kidney injury |
| HIF-1α | Hypoxia-inducible factor; modulated by redox | Cancer, kidney injury |
| AMPK | Energy sensor; interacts with redox pathways | Ferroptosis, metabolic stress |
| 6-PPD quinone | Environmental pollutant; induces oxidative stress | Mitochondrial unfolded protein response |
| Thioredoxin system | Maintains reduced thioredoxin pool | Redox homeostasis, antioxidant defense |
How Is peptide-methionine (R)-S-oxide reductase activity Regulated?
The activity of peptide-methionine (R)-S-oxide reductase is regulated at multiple levels. Expression of MSRB1 is influenced by selenium availability, as it is a selenoprotein, and by oxidative stress through transcription factors such as NRF2. The thioredoxin system, which provides reducing equivalents, is itself regulated by thioredoxin reductase and NADPH levels. Additionally, methionine oxidation can be reversed by MsrB, but the overall flux through the methionine cycle and S-adenosyl methionine levels can impact the availability of methionine for oxidation. In bacteria, MsrB expression is induced under oxidative stress conditions as part of the stress response. Post-translational modifications of MsrB, such as phosphorylation, may also modulate its activity, though specific mechanisms require further study.
peptide-methionine (R)-S-oxide reductase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MSRB1 | Inflammation, cancer, oxidative stress | MSRB1 knockout mice, cancer cell lines |
| MSRA | Acute kidney injury, ferroptosis | MsrA knockout mice, LPS-induced AKI model |
| PKM2 | Pancreatic cancer metastasis | PKM2 mutant knock-in mice, cancer cell lines |
| MSRB2 | Neurodegeneration, mitochondrial dysfunction | MSRB2 knockout neurons, mitochondrial stress models |
| MSRB3 | Deafness, cancer | MSRB3 knockout mice, auditory cell lines |
Cancer
Methionine oxidation and its reversal by MsrB play significant roles in cancer. Oxidation of pyruvate kinase M2 (PKM2) at methionine residues activates it, promoting pancreatic cancer metastasis. MSRB1, as a selenoprotein, may influence cancer progression by modulating redox balance and inflammation. Targeting methionine sulfoxide reductases could therefore be a therapeutic strategy in cancers dependent on redox adaptation.
Acute Kidney Injury and Ferroptosis
Deficiency of methionine sulfoxide reductase A (MsrA) aggravates ferroptosis in LPS-induced acute kidney injury by inhibiting the AMPK/NRF2 axis and activating the CaMKII/HIF-1α pathway. This highlights the importance of methionine sulfoxide reduction in protecting against ferroptotic cell death and kidney damage. Although this study focused on MsrA, the complementary MsrB activity is also likely involved in maintaining redox homeostasis in kidney cells.
Neurodegeneration and Aging
Oxidative damage to methionine residues is implicated in aging and neurodegenerative diseases. MsrB enzymes, particularly MSRB2 in mitochondria and MSRB3 in cytosol, protect neurons from oxidative stress. Selenoprotein MSRB1 is also expressed in the brain and may contribute to antioxidant defense. Enhancing MsrB activity could be a therapeutic approach for age-related neurodegenerative conditions.
Mitochondrial Dysfunction
Environmental stressors such as 6-PPD quinone induce mitochondrial unfolded protein response, which is suppressed by increased S-adenosyl methionine in Caenorhabditis elegans. This suggests a link between methionine metabolism and mitochondrial stress responses, where MsrB activity may play a protective role by repairing oxidized mitochondrial proteins.
From peptide-methionine (R)-S-oxide reductase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of MSRB1 in oxidative stress response? | MSRB1 knockout cell lines and mice |
| How does methionine oxidation regulate PKM2 function? | PKM2 point mutant (M239A) knock-in mice |
| Does MsrB activity protect against ferroptosis? | MsrB overexpression in kidney cells, ferroptosis inducers |
| What is the impact of MSRB2 on mitochondrial function? | MSRB2 knockout mitochondria, Seahorse analysis |
| How does selenium affect MSRB1 expression? | Selenium-deficient diets, MSRB1 tagged knock-in |
| Can MsrB enzymes be targeted for cancer therapy? | Xenograft models with MSRB1 knockdown |
How to Study the peptide-methionine (R)-S-oxide reductase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Enzymatic assay with synthetic peptide | MsrB catalytic activity | Kinetic characterization, inhibitor screening |
| Mass spectrometry proteomics | Methionine oxidation sites | Identification of MsrB substrates |
| CRISPR-Cas9 knockout | Loss-of-function phenotype | Studying MsrB role in oxidative stress |
| Site-directed mutagenesis | Catalytic residue function | Mechanistic studies |
| Western blot with anti-methionine sulfoxide | Global methionine oxidation levels | Assessing oxidative damage |
| Thioredoxin reductase-coupled assay | Thioredoxin consumption | Measuring MsrB activity |
| Fluorescent redox sensors (roGFP) | Cellular redox state | Live-cell imaging of oxidative stress |
| RNA-seq | Transcriptional changes upon MsrB modulation | Pathway analysis |
Enzymatic Activity Assays
Peptide-methionine (R)-S-oxide reductase activity can be measured using synthetic peptide substrates containing methionine (R)-S-oxide, coupled with thioredoxin and thioredoxin reductase. The reaction is monitored by NADPH oxidation at 340 nm or by HPLC detection of methionine formation. These assays are essential for characterizing enzyme kinetics and inhibitor screening.
Proteomic Detection of Methionine Oxidation
Mass spectrometry-based proteomics can identify and quantify methionine oxidation sites in proteins, providing insights into the substrates and extent of MsrB activity. Label-free or isotopic labeling approaches allow comparison of oxidized methionine levels between wild-type and MsrB knockout cells. This method is powerful for discovering new targets of methionine oxidation.
CRISPR-Cas9 Genome Editing
CRISPR-Cas9 is used to generate knockout, knock-in, or point mutations in MSRB genes to study their function. For example, MSRB1 knockout cells can be created to assess its role in oxidative stress response. Point mutations in the catalytic cysteine/selenocysteine can abolish activity and reveal substrate specificity.
Redox Imaging and Reporter Systems
Genetically encoded redox sensors, such as roGFP, can monitor changes in cellular redox state in response to MsrB activity. These reporters allow real-time imaging of oxidative stress and the impact of MsrB manipulation. Combining with fluorescent tagging of MsrB enables localization studies.
How CRISPR Can Be Used to Study GO:0033743 peptide-methionine (R)-S-oxide reductase activity
Knockout
CRISPR-Cas9 knockout of MSRB1, MSRB2, or MSRB3 allows researchers to study the loss-of-function phenotypes, such as increased sensitivity to oxidative stress, accumulation of oxidized proteins, and altered signaling pathways. Knockout cell lines and mouse models are valuable for understanding the physiological roles of these enzymes in development and disease.
Point Mutation
Introducing point mutations in the catalytic cysteine or selenocysteine residues of MSRB genes can abolish enzymatic activity, enabling the dissection of catalytic mechanisms and the distinction between enzymatic and non-enzymatic functions. For example, mutating the selenocysteine in MSRB1 to cysteine reduces activity and alters substrate specificity.
Knock-in
Knock-in of tagged versions of MSRB genes (e.g., FLAG, HA, or GFP) allows for localization, interaction, and purification studies. Additionally, knock-in of disease-associated mutations can model human conditions and test therapeutic interventions.
Overexpression
Overexpression of MSRB genes using CRISPR activation or lentiviral vectors can protect cells from oxidative stress and reveal gain-of-function phenotypes. This approach is useful for testing the protective effects of MsrB in disease models such as ferroptosis and neurodegeneration.
How EDITGENE Supports peptide-methionine (R)-S-oxide reductase activity Research
Researchers studying peptide-methionine (R)-S-oxide reductase activity-related genes often need to determine whether a candidate gene is causally involved in oxidative stress responses, protein regulation, or disease progression. EDITGENE provides comprehensive CRISPR-based services to generate precise cellular and animal models, enabling functional validation and therapeutic target discovery.
Contact EDITGENE today to design your custom CRISPR model for peptide-methionine (R)-S-oxide reductase activity research.
Frequently Asked Questions About peptide-methionine (R)-S-oxide reductase activity
What is peptide-methionine (R)-S-oxide reductase activity?
It is an enzymatic activity that reduces the R stereoisomer of methionine sulfoxide in proteins back to methionine, using thioredoxin as an electron donor.
What genes are involved in peptide-methionine (R)-S-oxide reductase activity?
The main genes are MSRB1, MSRB2, and MSRB3 in mammals, which encode methionine sulfoxide reductase B enzymes.
What is the difference between MsrA and MsrB?
MsrA reduces the S stereoisomer of methionine sulfoxide, while MsrB reduces the R stereoisomer, making them stereospecific.
Why is methionine oxidation important?
Methionine oxidation is a reversible post-translational modification that can regulate protein function and is linked to oxidative stress and disease.
How is peptide-methionine (R)-S-oxide reductase activity measured?
It is typically measured using synthetic peptide substrates containing methionine (R)-S-oxide, coupled with thioredoxin and thioredoxin reductase, monitoring NADPH oxidation.
What diseases are associated with MsrB dysfunction?
Dysfunction of MsrB enzymes has been implicated in cancer, neurodegeneration, acute kidney injury, and aging.
Can CRISPR be used to study MsrB genes?
Yes, CRISPR-Cas9 can generate knockout, knock-in, and point mutations in MSRB genes to study their function in cells and animal models.
What is the role of selenocysteine in MSRB1?
MSRB1 contains selenocysteine in its active site, which is critical for its catalytic activity and antioxidant function.
How does thioredoxin relate to MsrB activity?
Thioredoxin serves as the electron donor for MsrB, and its reduced state is maintained by thioredoxin reductase and NADPH.
What model systems are used to study MsrB?
Common models include knockout mice, cell lines, Drosophila, and C. elegans, as well as bacterial systems.
Conclusion
Peptide-methionine (R)-S-oxide reductase activity (GO:0033743) is a fundamental enzymatic function that protects proteins from oxidative damage and regulates cellular signaling through reversible methionine oxidation. The MsrB enzymes, including the selenoprotein MSRB1, play critical roles in health and disease, with implications for cancer, neurodegeneration, and acute kidney injury. Advances in CRISPR-based genome editing and proteomics are accelerating our understanding of these enzymes and their therapeutic potential. Targeting MsrB activity may offer new strategies for treating oxidative stress-related diseases.
References
- 1. Lu J et al.. 2014. The thioredoxin antioxidant system.. Free Radic Biol Med 66:75-87 PMID: 23899494
- 2. He D et al.. 2022. Methionine oxidation activates pyruvate kinase M2 to promote pancreatic cancer metastasis.. Mol Cell 82(16):3045-3060.e11 PMID: 35752173
- 3. Tarrago L et al.. 2022. The selenoprotein methionine sulfoxide reductase B1 (MSRB1).. Free Radic Biol Med 191:228-240 PMID: 36084791
- 4. Manta B et al.. 2017. Regulated methionine oxidation by monooxygenases.. Free Radic Biol Med 109:141-155 PMID: 28229915
- 5. Vincent MS et al.. 2023. Methionine oxidation in bacteria: A reversible post-translational modification.. Mol Microbiol 119(2):143-150 PMID: 36350090
- 6. Wang Y et al.. 2025. Increased S-adenosyl methionine strengthens the suppression in mitochondrial unfolded protein response induced by 6-PPD quinone at environmentally relevant concentrations in Caenorhabditis elegans.. Environ Pollut 386:127231 PMID: 41072709
- 7. Tarafdar S et al.. 2019. Drosophila methionine sulfoxide reductase A (MSRA) lacks methionine oxidase activity.. Free Radic Biol Med 131:154-161 PMID: 30529269
- 8. Yang L et al.. 2025. Methionine sulfoxide reductase A deficiency aggravated ferroptosis in LPS-induced acute kidney injury by inhibiting the AMPK/NRF2 axis and activating the CaMKII/HIF-1α pathway.. Free Radic Biol Med 234:248-263 PMID: 40288699
