{"gene":"MSRB1","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2013,"finding":"MsrB1 (selenoprotein) specifically reduces methionine-R-sulfoxide residues on actin (Met44 and another conserved Met) that were oxidized by Mical1/Mical2 monooxygenases, thereby restoring normal actin polymerization and promoting actin assembly. This reversible, stereoselective methionine oxidation/reduction cycle controls mammalian actin dynamics.","method":"In vitro biochemical reduction assays, macrophage cell biology, MsrB1 expression/activity modulation, actin polymerization assays, identification of Mical proteins as actin oxidases and MsrB1 as antagonist","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (in vitro assays, cell-based functional readouts, genetic approaches), replicated across two independent labs in the same year","pmids":["23911929"],"is_preprint":false},{"year":2013,"finding":"Drosophila SelR (MsrB1 ortholog) directly reduces Mical-oxidized actin Met44-R-sulfoxide back to methionine, restoring normal actin polymerization properties, and genetically opposes Semaphorin-Plexin repulsive guidance signaling in vivo.","method":"Genetic epistasis screen in Drosophila, in vitro reduction of Mical-oxidized actin, actin polymerization assays, site-specific mutagenesis of Met44","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution of actin reduction combined with in vivo genetic epistasis, independent lab corroborating PMID:23911929","pmids":["24212093"],"is_preprint":false},{"year":2008,"finding":"MsrB1 is the main mammalian cytosolic/nuclear selenoprotein MsrB, responsible for the bulk of methionine-R-sulfoxide reductase (MsrB) activity in liver and kidney; its knockout increases protein methionine sulfoxide, protein carbonyls, lipid peroxidation, and oxidized glutathione while decreasing free and protein thiols. MsrB1 deficiency also secondarily decreases MsrA activity.","method":"MsrB1 knockout mouse model, biochemical assays for MsrB/MsrA activity, oxidative stress markers (malondialdehyde, protein carbonyls, glutathione), 75Se labeling, mass spectrometry, immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — clean knockout mouse with multiple orthogonal biochemical readouts in multiple tissues","pmids":["18990697"],"is_preprint":false},{"year":2008,"finding":"A 5-kDa C-terminal selenoprotein fragment of MsrB1 exists as a distinct protein form in mouse tissues and human HEK293 cells; it is dependent on the same gene, selenium supply, and selenocysteine tRNA as the 14-kDa MsrB1.","method":"75Se labeling, mass spectrometry, immunoprecipitation with MsrB1 antibodies, siRNA knockdown, knockout mouse","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — identified by MS + 75Se + KO, but novel form not yet functionally characterized beyond its identification","pmids":["18990697"],"is_preprint":false},{"year":2010,"finding":"MsrB1 interacts with the alpha-kinase domain of the Mg2+ channel TRPM6 (identified by Ras recruitment system) and co-localizes in renal distal convoluted tubules. Under oxidative stress (H2O2), MsrB1 co-expression attenuates H2O2-induced inhibition of TRPM6 channel activity by reducing oxidation of Met1755 in TRPM6.","method":"Ras recruitment system (yeast two-hybrid-like), co-expression patch-clamp electrophysiology, site-directed mutagenesis of TRPM6 Met1755, cell surface biotinylation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 — protein interaction identified by Ras recruitment, functional rescue by co-expression, supported by mutagenesis of target Met residue","pmids":["20584906"],"is_preprint":false},{"year":2022,"finding":"In pro-inflammatory macrophages, MsrB1 reduces Met44 on GAPDH; MsrB1 knockout leads to sustained oxidation of GAPDH Met44, causing GAPDH aggregation, inflammasome activation, and increased IL-1β secretion. MsrB1-knockout mice show increased susceptibility to LPS-induced sepsis.","method":"MsrB1 knockout mice, LPS-induced sepsis model, metabolic profiling, GAPDH aggregation assay, inflammasome activation assay, IL-1β measurement","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO model with specific molecular target (GAPDH Met44) and defined downstream pathway (inflammasome/IL-1β), but direct in vitro reduction of GAPDH not shown","pmids":["36351405"],"is_preprint":false},{"year":2007,"finding":"The human MsrB1 promoter contains three Sp1 binding sites (within 169 bp upstream of the transcription start site) that are required for maximal promoter activity, and the promoter is also regulated by DNA methylation (epigenetic control), as demonstrated by demethylating agent 5-Aza-2'-deoxycytidine inducing MsrB1 expression in MDA-MB231 cells.","method":"Promoter-reporter transient transfection assays with mutant constructs, chromatin immunoprecipitation (ChIP) for Sp1, 5-Aza-2'-deoxycytidine treatment","journal":"BMC molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and mutant promoter constructs orthogonally support Sp1-dependent and methylation-dependent transcriptional regulation","pmids":["17519015"],"is_preprint":false},{"year":2013,"finding":"MsrB1 silencing in human lens epithelial cells aggravates peroxynitrite-induced F-actin disassembly by increasing nitration of F-actin and inactivating ERK signaling, indicating MsrB1 protects actin integrity via suppression of RNS-mediated modifications and maintenance of ERK activity.","method":"siRNA knockdown of MsrB1, F-actin imaging, ERK activity assay, actin nitration measurement in human lens epithelial cells","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 — single lab, siRNA KD with indirect pathway placement (ERK inactivation not directly linked to MsrB1 catalytic activity)","pmids":["24342607"],"is_preprint":false},{"year":2019,"finding":"Loss of MsrB1 in knockout mice impairs spatial learning and disrupts LTP/LTD in hippocampal CA1, associated with downregulation of synaptic proteins (PSD95, SYP, GluN2A, GluN2B) and decreased CaMKII phosphorylation at Thr286/287, indicating MsrB1-dependent redox homeostasis is required for synaptic plasticity.","method":"MsrB1 knockout mice, Morris water maze, hippocampal slice electrophysiology (LTP/LTD), western blotting for synaptic proteins and CaMKII phosphorylation","journal":"Neurobiology of learning and memory","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO with behavioral and electrophysiological readouts plus molecular correlates, though direct MsrB1-CaMKII reduction not shown","pmids":["31672630"],"is_preprint":false},{"year":2020,"finding":"MsrB1 regulates STAT6 phosphorylation in dendritic cells and potentiates LPS-induced IL-12 production, promoting Th1 differentiation and follicular helper T-cell differentiation in vivo.","method":"MsrB1 knockout mice, in vitro DC activation assays, STAT6 phosphorylation (western blot), IL-12 ELISA, T-cell differentiation assays, immunization experiments","journal":"Antioxidants (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 — KO mice with multiple immune functional readouts and defined signaling pathway (STAT6), though mechanistic link between MsrB1 catalytic activity and STAT6 is inferential","pmids":["33092166"],"is_preprint":false},{"year":2021,"finding":"MsrB1 interacts with β-catenin (confirmed by Co-IP), and this interaction leads to activation of GPX4 transcription, thereby inhibiting ferroptosis in colorectal cancer cells. The transcription factor KLF5 binds to the MsrB1 promoter and activates MsrB1 expression (validated by dual-luciferase reporter and ChIP assays).","method":"Co-immunoprecipitation, dual-luciferase reporter assay, ChIP assay, WGCNA, siRNA knockdown","journal":"Free radical biology & medicine","confidence":"Low","confidence_rationale":"Tier 3 — single lab, Co-IP for MsrB1-β-catenin interaction with limited mechanistic follow-up on how MsrB1 activates GPX4 transcription","pmids":["40210135"],"is_preprint":false},{"year":2024,"finding":"A fluorescence biosensor (RIYsense) composed of MsrB1 fused to a circularly permuted fluorescent protein and thioredoxin1 was used to identify two heterocyclic compounds as MsrB1 active-site inhibitors; these inhibitors decrease expression of anti-inflammatory cytokines (IL-10, IL-1rn) and recapitulate MsrB1 knockout phenotypes in an ear edema model.","method":"Fluorescence biosensor high-throughput screen (6868 compounds), molecular docking, affinity assays, MsrB1 activity measurement, ear edema mouse model","journal":"Antioxidants (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 1-2 — in vitro enzymatic assay with active-site docking validation and in vivo pharmacological confirmation","pmids":["39594490"],"is_preprint":false}],"current_model":"MSRB1 is a selenocysteine-containing methionine-R-sulfoxide reductase located in the cytosol and nucleus that stereospecifically reduces protein-bound methionine-R-sulfoxide back to methionine; its best-characterized role is antagonizing Mical-family monooxygenases to reversibly regulate actin Met44 oxidation state and thereby control actin assembly/disassembly dynamics, macrophage innate immune function, and dendritic cell-driven adaptive immunity, while also protecting TRPM6 channel activity, GAPDH function, and synaptic plasticity through its antioxidant catalytic activity."},"narrative":{"teleology":[{"year":2007,"claim":"Establishing how MSRB1 transcription is controlled resolved a basic gene-regulation question: the promoter depends on three Sp1 sites and is silenced by DNA methylation, providing a mechanism for tissue- and context-specific expression.","evidence":"Promoter-reporter assays with mutant constructs, ChIP for Sp1, and 5-Aza-2'-deoxycytidine treatment in MDA-MB231 cells","pmids":["17519015"],"confidence":"Medium","gaps":["No in vivo chromatin state data across tissues","Contribution of other transcription factors beyond Sp1 not addressed"]},{"year":2008,"claim":"Generating the MsrB1 knockout mouse established that MsrB1 is the dominant cytosolic/nuclear MsrB enzyme in mammals and that its loss produces systemic oxidative stress, answering whether other MsrB family members compensate.","evidence":"MsrB1 KO mouse with biochemical assays for MsrB/MsrA activity, protein carbonyls, lipid peroxidation, glutathione status, and 75Se labeling across liver and kidney","pmids":["18990697"],"confidence":"High","gaps":["Specific protein substrates responsible for the oxidative phenotype were not identified","A 5-kDa C-terminal fragment was detected but its function remains unknown"]},{"year":2010,"claim":"Demonstrating that MsrB1 interacts with and functionally protects TRPM6 under oxidative stress identified the first specific protein substrate beyond general antioxidant defense, establishing a direct link between methionine sulfoxide reduction and ion channel regulation.","evidence":"Ras recruitment interaction screen, patch-clamp electrophysiology with co-expression, and site-directed mutagenesis of TRPM6 Met1755","pmids":["20584906"],"confidence":"Medium","gaps":["Direct in vitro reduction of TRPM6 Met1755 by purified MsrB1 was not demonstrated","Physiological relevance in renal Mg²⁺ handling not tested in vivo"]},{"year":2013,"claim":"Two independent studies showed that MsrB1/SelR stereospecifically reduces Mical-oxidized actin Met44-R-sulfoxide, establishing a conserved reversible oxidation/reduction switch that directly controls actin polymerization — a paradigm shift from viewing methionine oxidation solely as damage.","evidence":"In vitro actin reduction and polymerization assays (mammalian), genetic epistasis in Drosophila Semaphorin–Plexin signaling, and Met44 mutagenesis","pmids":["23911929","24212093"],"confidence":"High","gaps":["Identity and roles of all actin methionine residues targeted in vivo remain incomplete","Whether MsrB1 is recruited to specific subcellular actin pools is unknown"]},{"year":2019,"claim":"Linking MsrB1 loss to impaired hippocampal LTP/LTD and spatial memory revealed that its redox-repair activity is required for synaptic plasticity, extending its biological role to the nervous system.","evidence":"MsrB1 KO mice assessed by Morris water maze, hippocampal slice electrophysiology, and western blotting for synaptic proteins and CaMKII phosphorylation","pmids":["31672630"],"confidence":"Medium","gaps":["Direct MsrB1 substrate in synapse not identified","Whether actin Met44 oxidation mediates the synaptic phenotype is untested","CaMKII Thr286 phosphorylation change is correlative"]},{"year":2020,"claim":"Showing that MsrB1 regulates STAT6 phosphorylation in dendritic cells and IL-12-dependent Th1/Tfh differentiation established a role in adaptive immunity beyond its previously known innate immune functions.","evidence":"MsrB1 KO mice with DC activation assays, STAT6 western blot, IL-12 ELISA, T-cell differentiation, and immunization experiments","pmids":["33092166"],"confidence":"Medium","gaps":["Whether MsrB1 directly reduces a methionine sulfoxide on STAT6 or an upstream regulator is unknown","In vivo immune challenge models beyond immunization not tested"]},{"year":2022,"claim":"Identifying GAPDH Met44 as a specific MsrB1 substrate in macrophages linked methionine sulfoxide accumulation to GAPDH aggregation, inflammasome activation, and sepsis susceptibility, providing a molecular mechanism for MsrB1's anti-inflammatory role.","evidence":"MsrB1 KO mice, LPS-induced sepsis, GAPDH aggregation assay, inflammasome and IL-1β measurements","pmids":["36351405"],"confidence":"Medium","gaps":["Direct in vitro enzymatic reduction of GAPDH Met44 by MsrB1 was not reconstituted","Contribution of other Met residues on GAPDH not assessed"]},{"year":2024,"claim":"Development of active-site inhibitors validated by a biosensor screen and in vivo ear edema model provided the first pharmacological tools for MsrB1 and confirmed that catalytic activity underlies its anti-inflammatory cytokine regulation.","evidence":"Fluorescence biosensor (RIYsense) high-throughput screen, molecular docking, enzymatic inhibition assays, and mouse ear edema model","pmids":["39594490"],"confidence":"Medium","gaps":["Inhibitor selectivity over MsrB2/MsrB3 not reported","Pharmacokinetic and off-target profiles not characterized"]},{"year":null,"claim":"Major open questions include the full substrate repertoire of MsrB1 in different tissues, how MsrB1 is recruited to specific substrates (actin pools, GAPDH, STAT6 pathway components), the function of the 5-kDa C-terminal fragment, and whether MsrB1 catalytic activity can be therapeutically targeted in inflammatory or neurodegenerative disease.","evidence":"","pmids":[],"confidence":"Low","gaps":["Comprehensive substrate identification (e.g., by substrate trapping or proteomics) has not been performed","Structural basis for substrate recognition beyond actin is lacking","Function of the 5-kDa MsrB1 fragment is uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,1,2,5]},{"term_id":"GO:0016209","term_label":"antioxidant activity","supporting_discovery_ids":[2]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2]}],"pathway":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,1]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[5,9,11]}],"complexes":[],"partners":["MICAL1","MICAL2","ACTB","TRPM6","GAPDH"],"other_free_text":[]},"mechanistic_narrative":"MSRB1 is a selenocysteine-containing methionine-R-sulfoxide reductase that serves as the principal cytosolic and nuclear enzyme restoring oxidized methionine residues on proteins, thereby linking redox homeostasis to actin dynamics, innate and adaptive immunity, ion channel regulation, and synaptic plasticity. Its best-characterized function is the stereospecific reduction of Mical-oxidized Met44-R-sulfoxide on actin, which reverses actin disassembly and constitutes a conserved, reversible regulatory switch controlling actin polymerization in mammals and Drosophila [PMID:23911929, PMID:24212093]. MsrB1 knockout mice exhibit elevated protein methionine sulfoxide and oxidative stress markers, GAPDH aggregation-driven inflammasome activation and sepsis susceptibility, impaired hippocampal LTP/LTD and spatial learning, and altered dendritic cell IL-12/STAT6 signaling that skews T-cell differentiation [PMID:18990697, PMID:36351405, PMID:31672630, PMID:33092166]. MsrB1 also protects TRPM6 channel activity under oxidative stress by reducing Met1755 in the TRPM6 alpha-kinase domain [PMID:20584906]."},"prefetch_data":{"uniprot":{"accession":"Q9NZV6","full_name":"Methionine-R-sulfoxide reductase B1","aliases":["Selenoprotein X","SelX"],"length_aa":116,"mass_kda":12.8,"function":"Methionine-sulfoxide reductase that specifically reduces methionine (R)-sulfoxide back to methionine. While in many cases, methionine oxidation is the result of random oxidation following oxidative stress, methionine oxidation is also a post-translational modification that takes place on specific residue. Acts as a regulator of actin assembly by reducing methionine (R)-sulfoxide mediated by MICALs (MICAL1, MICAL2 or MICAL3) on actin, thereby promoting filament repolymerization. Plays a role in innate immunity by reducing oxidized actin, leading to actin repolymerization in macrophages","subcellular_location":"Cytoplasm; Nucleus; Cytoplasm, cytoskeleton","url":"https://www.uniprot.org/uniprotkb/Q9NZV6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MSRB1","classification":"Not Classified","n_dependent_lines":30,"n_total_lines":1208,"dependency_fraction":0.024834437086092714},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MSRB1","total_profiled":1310},"omim":[{"mim_id":"613719","title":"METHIONINE SULFOXIDE REDUCTASE B3; MSRB3","url":"https://www.omim.org/entry/613719"},{"mim_id":"606216","title":"METHIONINE SULFOXIDE REDUCTASE B1; MSRB1","url":"https://www.omim.org/entry/606216"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"liver","ntpm":255.1}],"url":"https://www.proteinatlas.org/search/MSRB1"},"hgnc":{"alias_symbol":["SelR","SepR","SelX","SELENOX","SELENOR"],"prev_symbol":["SEPX1"]},"alphafold":{"accession":"Q9NZV6","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NZV6","model_url":"","pae_url":"","plddt_mean":null},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MSRB1","jax_strain_url":"https://www.jax.org/strain/search?query=MSRB1"},"sequence":{"accession":"Q9NZV6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NZV6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NZV6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NZV6"}},"corpus_meta":[{"pmid":"23911929","id":"PMC_23911929","title":"MsrB1 and MICALs regulate actin assembly and macrophage function via reversible stereoselective methionine oxidation.","date":"2013","source":"Molecular 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Switzerland)","url":"https://pubmed.ncbi.nlm.nih.gov/39594490","citation_count":1,"is_preprint":false},{"pmid":"32392920","id":"PMC_32392920","title":"[Cloning and expression of recombinant truncated SElX protein and evaluation on the related emetic activities].","date":"2020","source":"Zhonghua liu xing bing xue za zhi = Zhonghua liuxingbingxue zazhi","url":"https://pubmed.ncbi.nlm.nih.gov/32392920","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16102,"output_tokens":3196,"usd":0.048123},"stage2":{"model":"claude-opus-4-6","input_tokens":6562,"output_tokens":2448,"usd":0.141015},"total_usd":0.189138,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2013,\n      \"finding\": \"MsrB1 (selenoprotein) specifically reduces methionine-R-sulfoxide residues on actin (Met44 and another conserved Met) that were oxidized by Mical1/Mical2 monooxygenases, thereby restoring normal actin polymerization and promoting actin assembly. This reversible, stereoselective methionine oxidation/reduction cycle controls mammalian actin dynamics.\",\n      \"method\": \"In vitro biochemical reduction assays, macrophage cell biology, MsrB1 expression/activity modulation, actin polymerization assays, identification of Mical proteins as actin oxidases and MsrB1 as antagonist\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (in vitro assays, cell-based functional readouts, genetic approaches), replicated across two independent labs in the same year\",\n      \"pmids\": [\"23911929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Drosophila SelR (MsrB1 ortholog) directly reduces Mical-oxidized actin Met44-R-sulfoxide back to methionine, restoring normal actin polymerization properties, and genetically opposes Semaphorin-Plexin repulsive guidance signaling in vivo.\",\n      \"method\": \"Genetic epistasis screen in Drosophila, in vitro reduction of Mical-oxidized actin, actin polymerization assays, site-specific mutagenesis of Met44\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution of actin reduction combined with in vivo genetic epistasis, independent lab corroborating PMID:23911929\",\n      \"pmids\": [\"24212093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MsrB1 is the main mammalian cytosolic/nuclear selenoprotein MsrB, responsible for the bulk of methionine-R-sulfoxide reductase (MsrB) activity in liver and kidney; its knockout increases protein methionine sulfoxide, protein carbonyls, lipid peroxidation, and oxidized glutathione while decreasing free and protein thiols. MsrB1 deficiency also secondarily decreases MsrA activity.\",\n      \"method\": \"MsrB1 knockout mouse model, biochemical assays for MsrB/MsrA activity, oxidative stress markers (malondialdehyde, protein carbonyls, glutathione), 75Se labeling, mass spectrometry, immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean knockout mouse with multiple orthogonal biochemical readouts in multiple tissues\",\n      \"pmids\": [\"18990697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"A 5-kDa C-terminal selenoprotein fragment of MsrB1 exists as a distinct protein form in mouse tissues and human HEK293 cells; it is dependent on the same gene, selenium supply, and selenocysteine tRNA as the 14-kDa MsrB1.\",\n      \"method\": \"75Se labeling, mass spectrometry, immunoprecipitation with MsrB1 antibodies, siRNA knockdown, knockout mouse\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — identified by MS + 75Se + KO, but novel form not yet functionally characterized beyond its identification\",\n      \"pmids\": [\"18990697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"MsrB1 interacts with the alpha-kinase domain of the Mg2+ channel TRPM6 (identified by Ras recruitment system) and co-localizes in renal distal convoluted tubules. Under oxidative stress (H2O2), MsrB1 co-expression attenuates H2O2-induced inhibition of TRPM6 channel activity by reducing oxidation of Met1755 in TRPM6.\",\n      \"method\": \"Ras recruitment system (yeast two-hybrid-like), co-expression patch-clamp electrophysiology, site-directed mutagenesis of TRPM6 Met1755, cell surface biotinylation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — protein interaction identified by Ras recruitment, functional rescue by co-expression, supported by mutagenesis of target Met residue\",\n      \"pmids\": [\"20584906\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In pro-inflammatory macrophages, MsrB1 reduces Met44 on GAPDH; MsrB1 knockout leads to sustained oxidation of GAPDH Met44, causing GAPDH aggregation, inflammasome activation, and increased IL-1β secretion. MsrB1-knockout mice show increased susceptibility to LPS-induced sepsis.\",\n      \"method\": \"MsrB1 knockout mice, LPS-induced sepsis model, metabolic profiling, GAPDH aggregation assay, inflammasome activation assay, IL-1β measurement\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO model with specific molecular target (GAPDH Met44) and defined downstream pathway (inflammasome/IL-1β), but direct in vitro reduction of GAPDH not shown\",\n      \"pmids\": [\"36351405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The human MsrB1 promoter contains three Sp1 binding sites (within 169 bp upstream of the transcription start site) that are required for maximal promoter activity, and the promoter is also regulated by DNA methylation (epigenetic control), as demonstrated by demethylating agent 5-Aza-2'-deoxycytidine inducing MsrB1 expression in MDA-MB231 cells.\",\n      \"method\": \"Promoter-reporter transient transfection assays with mutant constructs, chromatin immunoprecipitation (ChIP) for Sp1, 5-Aza-2'-deoxycytidine treatment\",\n      \"journal\": \"BMC molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and mutant promoter constructs orthogonally support Sp1-dependent and methylation-dependent transcriptional regulation\",\n      \"pmids\": [\"17519015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MsrB1 silencing in human lens epithelial cells aggravates peroxynitrite-induced F-actin disassembly by increasing nitration of F-actin and inactivating ERK signaling, indicating MsrB1 protects actin integrity via suppression of RNS-mediated modifications and maintenance of ERK activity.\",\n      \"method\": \"siRNA knockdown of MsrB1, F-actin imaging, ERK activity assay, actin nitration measurement in human lens epithelial cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, siRNA KD with indirect pathway placement (ERK inactivation not directly linked to MsrB1 catalytic activity)\",\n      \"pmids\": [\"24342607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of MsrB1 in knockout mice impairs spatial learning and disrupts LTP/LTD in hippocampal CA1, associated with downregulation of synaptic proteins (PSD95, SYP, GluN2A, GluN2B) and decreased CaMKII phosphorylation at Thr286/287, indicating MsrB1-dependent redox homeostasis is required for synaptic plasticity.\",\n      \"method\": \"MsrB1 knockout mice, Morris water maze, hippocampal slice electrophysiology (LTP/LTD), western blotting for synaptic proteins and CaMKII phosphorylation\",\n      \"journal\": \"Neurobiology of learning and memory\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with behavioral and electrophysiological readouts plus molecular correlates, though direct MsrB1-CaMKII reduction not shown\",\n      \"pmids\": [\"31672630\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MsrB1 regulates STAT6 phosphorylation in dendritic cells and potentiates LPS-induced IL-12 production, promoting Th1 differentiation and follicular helper T-cell differentiation in vivo.\",\n      \"method\": \"MsrB1 knockout mice, in vitro DC activation assays, STAT6 phosphorylation (western blot), IL-12 ELISA, T-cell differentiation assays, immunization experiments\",\n      \"journal\": \"Antioxidants (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KO mice with multiple immune functional readouts and defined signaling pathway (STAT6), though mechanistic link between MsrB1 catalytic activity and STAT6 is inferential\",\n      \"pmids\": [\"33092166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MsrB1 interacts with β-catenin (confirmed by Co-IP), and this interaction leads to activation of GPX4 transcription, thereby inhibiting ferroptosis in colorectal cancer cells. The transcription factor KLF5 binds to the MsrB1 promoter and activates MsrB1 expression (validated by dual-luciferase reporter and ChIP assays).\",\n      \"method\": \"Co-immunoprecipitation, dual-luciferase reporter assay, ChIP assay, WGCNA, siRNA knockdown\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, Co-IP for MsrB1-β-catenin interaction with limited mechanistic follow-up on how MsrB1 activates GPX4 transcription\",\n      \"pmids\": [\"40210135\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A fluorescence biosensor (RIYsense) composed of MsrB1 fused to a circularly permuted fluorescent protein and thioredoxin1 was used to identify two heterocyclic compounds as MsrB1 active-site inhibitors; these inhibitors decrease expression of anti-inflammatory cytokines (IL-10, IL-1rn) and recapitulate MsrB1 knockout phenotypes in an ear edema model.\",\n      \"method\": \"Fluorescence biosensor high-throughput screen (6868 compounds), molecular docking, affinity assays, MsrB1 activity measurement, ear edema mouse model\",\n      \"journal\": \"Antioxidants (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro enzymatic assay with active-site docking validation and in vivo pharmacological confirmation\",\n      \"pmids\": [\"39594490\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MSRB1 is a selenocysteine-containing methionine-R-sulfoxide reductase located in the cytosol and nucleus that stereospecifically reduces protein-bound methionine-R-sulfoxide back to methionine; its best-characterized role is antagonizing Mical-family monooxygenases to reversibly regulate actin Met44 oxidation state and thereby control actin assembly/disassembly dynamics, macrophage innate immune function, and dendritic cell-driven adaptive immunity, while also protecting TRPM6 channel activity, GAPDH function, and synaptic plasticity through its antioxidant catalytic activity.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MSRB1 is a selenocysteine-containing methionine-R-sulfoxide reductase that serves as the principal cytosolic and nuclear enzyme restoring oxidized methionine residues on proteins, thereby linking redox homeostasis to actin dynamics, innate and adaptive immunity, ion channel regulation, and synaptic plasticity. Its best-characterized function is the stereospecific reduction of Mical-oxidized Met44-R-sulfoxide on actin, which reverses actin disassembly and constitutes a conserved, reversible regulatory switch controlling actin polymerization in mammals and Drosophila [PMID:23911929, PMID:24212093]. MsrB1 knockout mice exhibit elevated protein methionine sulfoxide and oxidative stress markers, GAPDH aggregation-driven inflammasome activation and sepsis susceptibility, impaired hippocampal LTP/LTD and spatial learning, and altered dendritic cell IL-12/STAT6 signaling that skews T-cell differentiation [PMID:18990697, PMID:36351405, PMID:31672630, PMID:33092166]. MsrB1 also protects TRPM6 channel activity under oxidative stress by reducing Met1755 in the TRPM6 alpha-kinase domain [PMID:20584906].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Establishing how MSRB1 transcription is controlled resolved a basic gene-regulation question: the promoter depends on three Sp1 sites and is silenced by DNA methylation, providing a mechanism for tissue- and context-specific expression.\",\n      \"evidence\": \"Promoter-reporter assays with mutant constructs, ChIP for Sp1, and 5-Aza-2'-deoxycytidine treatment in MDA-MB231 cells\",\n      \"pmids\": [\"17519015\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No in vivo chromatin state data across tissues\",\n        \"Contribution of other transcription factors beyond Sp1 not addressed\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Generating the MsrB1 knockout mouse established that MsrB1 is the dominant cytosolic/nuclear MsrB enzyme in mammals and that its loss produces systemic oxidative stress, answering whether other MsrB family members compensate.\",\n      \"evidence\": \"MsrB1 KO mouse with biochemical assays for MsrB/MsrA activity, protein carbonyls, lipid peroxidation, glutathione status, and 75Se labeling across liver and kidney\",\n      \"pmids\": [\"18990697\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific protein substrates responsible for the oxidative phenotype were not identified\",\n        \"A 5-kDa C-terminal fragment was detected but its function remains unknown\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that MsrB1 interacts with and functionally protects TRPM6 under oxidative stress identified the first specific protein substrate beyond general antioxidant defense, establishing a direct link between methionine sulfoxide reduction and ion channel regulation.\",\n      \"evidence\": \"Ras recruitment interaction screen, patch-clamp electrophysiology with co-expression, and site-directed mutagenesis of TRPM6 Met1755\",\n      \"pmids\": [\"20584906\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct in vitro reduction of TRPM6 Met1755 by purified MsrB1 was not demonstrated\",\n        \"Physiological relevance in renal Mg²⁺ handling not tested in vivo\"\n      ]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Two independent studies showed that MsrB1/SelR stereospecifically reduces Mical-oxidized actin Met44-R-sulfoxide, establishing a conserved reversible oxidation/reduction switch that directly controls actin polymerization — a paradigm shift from viewing methionine oxidation solely as damage.\",\n      \"evidence\": \"In vitro actin reduction and polymerization assays (mammalian), genetic epistasis in Drosophila Semaphorin–Plexin signaling, and Met44 mutagenesis\",\n      \"pmids\": [\"23911929\", \"24212093\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity and roles of all actin methionine residues targeted in vivo remain incomplete\",\n        \"Whether MsrB1 is recruited to specific subcellular actin pools is unknown\"\n      ]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Linking MsrB1 loss to impaired hippocampal LTP/LTD and spatial memory revealed that its redox-repair activity is required for synaptic plasticity, extending its biological role to the nervous system.\",\n      \"evidence\": \"MsrB1 KO mice assessed by Morris water maze, hippocampal slice electrophysiology, and western blotting for synaptic proteins and CaMKII phosphorylation\",\n      \"pmids\": [\"31672630\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct MsrB1 substrate in synapse not identified\",\n        \"Whether actin Met44 oxidation mediates the synaptic phenotype is untested\",\n        \"CaMKII Thr286 phosphorylation change is correlative\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showing that MsrB1 regulates STAT6 phosphorylation in dendritic cells and IL-12-dependent Th1/Tfh differentiation established a role in adaptive immunity beyond its previously known innate immune functions.\",\n      \"evidence\": \"MsrB1 KO mice with DC activation assays, STAT6 western blot, IL-12 ELISA, T-cell differentiation, and immunization experiments\",\n      \"pmids\": [\"33092166\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether MsrB1 directly reduces a methionine sulfoxide on STAT6 or an upstream regulator is unknown\",\n        \"In vivo immune challenge models beyond immunization not tested\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identifying GAPDH Met44 as a specific MsrB1 substrate in macrophages linked methionine sulfoxide accumulation to GAPDH aggregation, inflammasome activation, and sepsis susceptibility, providing a molecular mechanism for MsrB1's anti-inflammatory role.\",\n      \"evidence\": \"MsrB1 KO mice, LPS-induced sepsis, GAPDH aggregation assay, inflammasome and IL-1β measurements\",\n      \"pmids\": [\"36351405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct in vitro enzymatic reduction of GAPDH Met44 by MsrB1 was not reconstituted\",\n        \"Contribution of other Met residues on GAPDH not assessed\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Development of active-site inhibitors validated by a biosensor screen and in vivo ear edema model provided the first pharmacological tools for MsrB1 and confirmed that catalytic activity underlies its anti-inflammatory cytokine regulation.\",\n      \"evidence\": \"Fluorescence biosensor (RIYsense) high-throughput screen, molecular docking, enzymatic inhibition assays, and mouse ear edema model\",\n      \"pmids\": [\"39594490\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Inhibitor selectivity over MsrB2/MsrB3 not reported\",\n        \"Pharmacokinetic and off-target profiles not characterized\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Major open questions include the full substrate repertoire of MsrB1 in different tissues, how MsrB1 is recruited to specific substrates (actin pools, GAPDH, STAT6 pathway components), the function of the 5-kDa C-terminal fragment, and whether MsrB1 catalytic activity can be therapeutically targeted in inflammatory or neurodegenerative disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Comprehensive substrate identification (e.g., by substrate trapping or proteomics) has not been performed\",\n        \"Structural basis for substrate recognition beyond actin is lacking\",\n        \"Function of the 5-kDa MsrB1 fragment is uncharacterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 1, 2, 5]},\n      {\"term_id\": \"GO:0016209\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [5, 9, 11]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"MICAL1\",\n      \"MICAL2\",\n      \"ACTB\",\n      \"TRPM6\",\n      \"GAPDH\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}