{"gene":"MSRA","run_date":"2026-06-10T02:59:51","timeline":{"discoveries":[{"year":2000,"finding":"The conserved GCFWG motif in MsrA is essential for catalytic activity; site-directed mutagenesis of the cysteine within this motif (or treatment with iodoacetamide) causes complete loss of enzyme activity. The yeast MsrA is stereoselective for L-methionine S-sulfoxide (S-epimer), establishing substrate stereospecificity.","method":"Site-directed mutagenesis of active-site residues; iodoacetamide inactivation; in vitro enzymatic activity assays; circular dichroism; stereospecificity assays with S- and R-methionine sulfoxide","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with mutagenesis and in vitro activity assays; multiple orthogonal methods (mutagenesis, chemical inhibition, stereospecificity) in a single rigorous study","pmids":["10799493"],"is_preprint":false},{"year":2001,"finding":"MsrA knockout mice exhibit enhanced sensitivity to oxidative stress, shorter lifespan, accumulation of oxidized proteins, and impaired upregulation of thioredoxin reductase under oxidative stress, establishing MsrA as a key antioxidant defense and lifespan regulator in mammals.","method":"MsrA knockout mouse model; exposure to 100% oxygen; protein carbonyl measurements; lifespan analysis; Western blotting for thioredoxin reductase","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular/organismal phenotype, multiple outcome measures, widely replicated by subsequent studies","pmids":["11606777"],"is_preprint":false},{"year":2002,"finding":"Human MSRA is targeted to the mitochondrial matrix via an N-terminal 23 amino acid mitochondrial targeting sequence. The N-terminal signal sequence is not required for catalytic enzyme activity.","method":"EGFP fusion protein imaging in mammalian cell lines; deletion constructs; immunohistochemistry of mouse and rat liver; pre-embedding immunostaining with electron microscopy; in vitro activity assays","journal":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct subcellular localization by live imaging and EM, deletion constructs defining the signal sequence, functional validation in vitro; replicated in the same study by multiple orthogonal methods","pmids":["12039877"],"is_preprint":false},{"year":2003,"finding":"Rat liver MsrA exists as both mitochondrial matrix and cytosolic isoforms encoded by a single gene; the mitochondrial form contains a cleavable N-terminal signal sequence. Both isoforms carry oxidative modifications of cysteine residues in native tissue.","method":"Subcellular fractionation; enzymatic activity assays; Western blotting; immunoelectron microscopy; mass spectrometry identification; 2D gel electrophoresis","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (fractionation, EM, MS, 2D gels) demonstrating both isoform existence and mitochondrial localization; independent replication of mitochondrial targeting finding","pmids":["12693988"],"is_preprint":false},{"year":2005,"finding":"The human MSRA gene produces three isoforms from two distinct promoters: msrA1 (mitochondrial targeting), and msrA2/3 (cytosolic and nuclear localization). siRNA-mediated silencing of MSRA increases oxidative damage susceptibility in RPE cells.","method":"5'RACE cloning of transcripts; promoter analysis; subcellular localization of isoform-GFP fusions; siRNA knockdown; oxidative stress cell viability assays","journal":"Experimental eye research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (transcript cloning, fusion protein localization, siRNA KD with functional readout); single lab but comprehensive","pmids":["16364291"],"is_preprint":false},{"year":2008,"finding":"Mammals reduce methionine-S-sulfoxide via an MsrA-dependent pathway; MsrA knockout mice accumulate methionine-R-sulfoxide in plasma (but not S-sulfoxide), demonstrating MsrA is specifically required for reduction of the S-epimer of free methionine sulfoxide in vivo.","method":"MsrA knockout mouse; SK-Hep1 cell culture on methionine sulfoxides; plasma sulfoxide measurement; yeast free methionine-R-sulfoxide reductase complementation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO model combined with complementation and biochemical plasma measurements; mechanistically precise substrate specificity established in vivo","pmids":["18697736"],"is_preprint":false},{"year":2006,"finding":"Invariant Glu-94, Tyr-82, and Tyr-134 in the MsrA active site (Neisseria meningitidis) are required for catalysis of the reductase step: they stabilize the sulfurane transition state and lower the pKa of the catalytic Cys-51, which forms a sulfenic acid intermediate upon substrate reduction.","method":"Site-directed mutagenesis; kinetic analysis; mechanistic characterization of reductase step","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro mutagenesis coupled with kinetic analysis defining catalytic mechanism; single lab but rigorous mechanistic dissection","pmids":["17062561"],"is_preprint":false},{"year":2008,"finding":"MsrA knockout mice display abnormal dopamine levels (elevated at younger ages, decreased at 16 months) and impaired locomotor behavior, suggesting MsrA regulates dopamine signaling pathways, correlated with age-dependent changes in tyrosine hydroxylase activating protein expression.","method":"MsrA knockout mouse; dopamine measurements in striatal brain regions; amphetamine response testing; locomotor activity assays; tyrosine hydroxylase expression analysis","journal":"Free radical biology & medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with defined biochemical and behavioral phenotypes, single lab, correlation between dopamine levels and MsrA status established but molecular mechanism not fully resolved","pmids":["18466776"],"is_preprint":false},{"year":2008,"finding":"In Drosophila, MsrA is induced by ecdysone via the EcR-USP complex; this hormonal induction is required for ecdysone-mediated protection against H2O2-induced oxidative stress. EcR-deficient cells lose both ecdysone induction of MsrA and H2O2 resistance.","method":"Ecdysone treatment of Kc cells; RT-PCR; H2O2 viability assay; EcR-knockout cell line comparison","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function (EcR KO) combined with hormonal induction and functional survival assay; single lab, Drosophila ortholog","pmids":["17239346"],"is_preprint":false},{"year":2008,"finding":"The human MSRA gene is regulated by two distinct promoters: promoter 1 (upstream, drives the mitochondrial msrA1 isoform) and promoter 2 (downstream, drives cytosolic/nuclear msrA2/3 isoforms). Both promoters are partially regulated by all-trans retinoic acid via RARA and other RARs.","method":"Promoter-reporter assays; deletion analysis; retinoic acid treatment; RAR siRNA knockdown; cell-line-specific expression analysis","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter assays with deletion constructs and receptor knockdown; single lab, two orthogonal approaches","pmids":["18845237"],"is_preprint":false},{"year":2009,"finding":"MsrA co-immunoprecipitates with cytochrome c and four of the five mitochondrial electron transport chain complexes. MsrA repairs oxidized methionines (Met65 and Met80) in cytochrome c, restoring cytochrome c oxidase activity and reducing cytochrome c peroxidase activity. MsrA deletion causes accumulation and degradation of oxidized cytochrome c in lens.","method":"Co-immunoprecipitation; cyanogen bromide cleavage for oxidized methionine identification; in vitro MsrA repair assay with activity measurements; mass spectrometry; MsrA knockout mouse lens analysis","journal":"Molecular vision","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of repair activity with mass spectrometry confirmation, co-IP of binding partners, and KO mouse validation; multiple orthogonal methods","pmids":["19461988"],"is_preprint":false},{"year":2009,"finding":"Methionine oxidation of alpha-crystallin (Met138 of alphaA, Met68 of alphaB) abolishes its chaperone activity. MsrA reduces these methionine sulfoxides and restores chaperone function. Deletion of MsrA in mice results in increased PMSO-alpha-crystallin accumulation in lens.","method":"In vitro oxidation and MsrA repair of alpha-crystallin; CNBr cleavage and mass spectrometry for methionine sulfoxide identification; chaperone activity assay (light scattering); MsrA knockout mouse lens analysis","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of repair with mass spectrometry validation of substrate sites, functional activity assay, and KO mouse confirmation; multiple orthogonal methods","pmids":["19733220"],"is_preprint":false},{"year":2015,"finding":"Mitochondria-targeted MsrA overexpression, but not cytosolic MsrA, preserves insulin sensitivity in diet-induced obese mice without altering obesity itself. The protective effect is associated with activation of AMPK signaling, suggesting a mechanism by which mitochondrial protein methionine repair modulates metabolic homeostasis.","method":"Transgenic mouse models with compartment-specific MsrA overexpression (TgMito vs TgCyto); high-fat diet feeding; glucose tolerance and insulin sensitivity tests; AMPK activity measurements","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two transgenic mouse lines with distinct subcellular targeting enabling compartment-specific comparison, single lab, functional metabolic readouts","pmids":["26448611"],"is_preprint":false},{"year":2017,"finding":"Archaeal MsrA catalyzes ubiquitin-like (Ubl) protein modification in the presence of the Ubl-activating E1 enzyme UbaA and mild oxidant (DMSO), using the same active site as methionine sulfoxide reduction. This Ubl modification activity is distinct from and antagonized by the methionine sulfoxide reductase activity; MsrA-dependent Ubl conjugates include Orc3 and Cdc48d proteins involved in DNA replication and protein remodeling.","method":"In vitro Ubl modification assay; LC-MS/MS identification of conjugates; active-site mutant analysis; DMSO-dependent activity assay; reductant inhibition studies","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mass spectrometry confirmation; archaeal system, functional relevance to mammalian enzyme requires inference","pmids":["28874471"],"is_preprint":false},{"year":2018,"finding":"Mammalian MsrA mediates ubiquitination of 14-3-3 zeta protein in brain and promotes binding of 14-3-3 proteins to alpha-synuclein; it also enhances ubiquitination and phosphorylation of Ser129 of alpha-synuclein. MsrA competes for ubiquitin capture using the same active site as methionine sulfoxide binding.","method":"Co-immunoprecipitation; ubiquitination assays in brain tissue; phosphorylation analysis; MsrA knockout mouse brain comparison; active-site competition assays","journal":"Free radical biology & medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and biochemical assays in brain tissue with KO comparison; single lab, multiple substrates tested","pmids":["30096435"],"is_preprint":false},{"year":2020,"finding":"MsrA interacts with Jab1/CSN5 and enhances its deneddylase activity (removal of Nedd8 from Cullin-1). This interaction increases Jab1 binding affinity to P27, promoting P27 ubiquitination and degradation. MsrA ablation causes dramatic increase in P27 expression.","method":"Co-immunoprecipitation; deneddylase activity assay; P27 level measurement in MsrA-knockout cells; Cullin-1 neddylation state analysis","journal":"Antioxidants (Basel, Switzerland)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP of protein interaction, enzymatic activity assay, KO phenotype; single lab with multiple orthogonal approaches","pmids":["32456285"],"is_preprint":false},{"year":2007,"finding":"A novel splice variant of MSRA (msrA2a) exists in rat vascular smooth muscle cells, encoding a mitochondrially targeted isoform with confirmed enzymatic activity on methionine sulfoxide substrate. Endogenous MSRA immunoreactivity in VSMCs is exclusively mitochondrial.","method":"RT-PCR and sequence analysis of splice variants; recombinant protein expression and in vitro activity assay; immunofluorescence localization","journal":"Free radical research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — new splice variant characterized with in vitro activity confirmation and subcellular localization; single lab","pmids":["17907003"],"is_preprint":false},{"year":2018,"finding":"Drosophila MSRA lacks methionine oxidase activity despite having an active site sequence identical to mammalian MSRA. The Drosophila enzyme cannot complete the third step of the oxidase mechanism (disulfide exchange at carboxy-terminal cysteine to regenerate the active site), though it performs the reductase reaction and first two steps normally.","method":"Recombinant Drosophila MSRA expression; in vitro methionine sulfoxide reductase and oxidase assays; mechanistic dissection of active-site sulfenic acid chemistry; carboxy-terminal domain analysis","journal":"Free radical biology & medicine","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with stepwise mechanistic dissection of oxidase vs. reductase activities; rigorous biochemical characterization; single lab","pmids":["30529269"],"is_preprint":false},{"year":2024,"finding":"S-Methyl-L-cysteine (SMLC) acts as a methionine analog substrate for MsrA, enabling scavenging of free radicals. SMLC activates MsrA which reduces oxidized CaMKII (ox-CaMKII) and inhibits p38 MAPK phosphorylation, protecting against Ang II-induced atrial remodeling. MsrA knockdown abolishes the protective effects of SMLC, placing MsrA upstream of the p38 MAPK pathway.","method":"In vivo Ang II mouse model; siRNA knockdown of MsrA in HL-1 cells; RNA sequencing; Western blotting for ox-CaMKII and p38 MAPK; SB203580 (p38 inhibitor) rescue experiment","journal":"Food & function","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KD with pharmacological rescue defining pathway order; single lab with multiple orthogonal approaches","pmids":["39157962"],"is_preprint":false},{"year":2016,"finding":"Cytosolic MsrA overexpression (TgCyto) reduces age-related death rate in female mice by Gompertz analysis but does not extend median lifespan; mitochondrial MsrA overexpression improves insulin sensitivity in aged females, demonstrating subcellular localization-dependent effects on aging and metabolic phenotypes.","method":"Transgenic mouse models with cytosol- and mitochondria-targeted MsrA; Gompertz and log-rank lifespan analysis; glucose tolerance and insulin sensitivity tests","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two transgenic models enabling direct compartment comparison; single lab, mechanistic inference on subcellular localization consequence","pmids":["27821326"],"is_preprint":false},{"year":2025,"finding":"Iron coordinates to conserved E203-xx-H206 motifs to multimerize, stabilize, and enzymatically activate MSRA. Activated MSRA maintains reduced methionines near the ATP-binding site of Protein Kinase A (PKA), thereby facilitating PKA-driven adipose browning. MsrA deletion in PDA mouse models impairs WAT browning and improves survival of tumor-bearing animals.","method":"Iron-binding mutagenesis; structural/biophysical characterization of MSRA multimers; PKA methionine oxidation state analysis; MsrA knockout mouse model of PDA; WAT browning and cachexia measurements","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — mechanistic in vitro characterization (iron binding, multimerization) combined with in vivo KO mouse phenotype; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2025.07.16.664180"],"is_preprint":true}],"current_model":"MSRA is a stereospecific methionine sulfoxide reductase that catalyzes reduction of methionine-S-sulfoxide (S-epimer) back to methionine via a conserved GCFWG active-site cysteine (forming a sulfenic acid intermediate stabilized by Glu-94, Tyr-82, and Tyr-134), is expressed as multiple isoforms from two promoters that target it to the mitochondrial matrix (via an N-terminal 23-aa signal) and the cytosol/nucleus, acts as a broad antioxidant defense by repairing oxidized proteins including cytochrome c (restoring ETC activity), alpha-crystallin (restoring chaperone activity), CaMKII, and PKA, and also participates in non-canonical ubiquitination-like protein modification and in regulating signaling cascades (p38 MAPK, AMPK, Jab1/CSN5-P27, dopamine pathways), with its subcellular localization determining distinct functional consequences for metabolism, aging, and neurological homeostasis."},"narrative":{"mechanistic_narrative":"MSRA is a stereospecific methionine sulfoxide reductase that constitutes a core antioxidant defense system by catalytically repairing oxidized proteins and restoring their function [PMID:11606777, PMID:19461988]. Catalysis depends on a conserved active-site cysteine within the GCFWG motif, which forms a sulfenic acid intermediate during reduction; invariant Glu, Tyr, and a second Tyr stabilize the sulfurane transition state and lower the catalytic cysteine pKa, and the enzyme is strictly stereoselective for the S-epimer of methionine sulfoxide [PMID:10799493, PMID:17062561, PMID:18697736]. A single gene generates multiple isoforms from two promoters: an upstream promoter drives a mitochondrial-matrix isoform via a cleavable N-terminal 23-residue targeting sequence, while a downstream promoter drives cytosolic and nuclear isoforms, and this compartmentalization dictates distinct physiological consequences [PMID:12039877, PMID:12693988, PMID:16364291, PMID:18845237]. Through methionine repair MSRA restores activity to oxidatively damaged substrates including cytochrome c (recovering electron-transport-chain function) and alpha-crystallin (recovering chaperone activity) [PMID:19461988, PMID:19733220], and its loss in knockout mice causes accumulation of oxidized proteins, heightened oxidative-stress sensitivity, and shortened lifespan [PMID:11606777]. Compartment-specific transgenic studies show mitochondrial MSRA preserves insulin sensitivity via AMPK signaling whereas cytosolic MSRA modulates age-related mortality, establishing localization-dependent roles in metabolism and aging [PMID:26448611, PMID:27821326]. Beyond canonical reductase chemistry, MSRA participates in protein modification and signaling: it engages a ubiquitin-like conjugation activity through its active site, mediates ubiquitination of 14-3-3 and alpha-synuclein, enhances Jab1/CSN5 deneddylase activity to drive p27 degradation, and acts upstream of the p38 MAPK pathway by reducing oxidized CaMKII [PMID:28874471, PMID:30096435, PMID:32456285, PMID:39157962].","teleology":[{"year":2000,"claim":"Establishing the catalytic basis and substrate selectivity of MsrA was needed to define it as a true methionine sulfoxide reductase rather than a generic redox protein.","evidence":"Site-directed mutagenesis of the GCFWG cysteine, iodoacetamide inactivation, and stereospecificity assays with S/R methionine sulfoxide in yeast MsrA","pmids":["10799493"],"confidence":"High","gaps":["Catalytic mechanism of intermediate resolution not yet defined","Did not address subcellular localization or substrates in vivo"]},{"year":2001,"claim":"Genetic loss-of-function tested whether MsrA matters at the organismal level, defining it as an antioxidant defense and lifespan regulator.","evidence":"MsrA knockout mouse exposed to hyperoxia, with protein carbonyl, lifespan, and thioredoxin reductase measurements","pmids":["11606777"],"confidence":"High","gaps":["Specific oxidized protein substrates driving phenotype not identified","Mechanistic link between methionine repair and lifespan unresolved"]},{"year":2002,"claim":"Defining the mitochondrial targeting sequence answered where MSRA acts and separated localization from catalysis.","evidence":"EGFP-fusion imaging, deletion constructs, immuno-EM in liver, and in vitro activity assays","pmids":["12039877"],"confidence":"High","gaps":["Did not resolve how non-mitochondrial isoforms are generated","Regulation of targeting not addressed"]},{"year":2003,"claim":"Showing a single gene yields both mitochondrial and cytosolic isoforms clarified the structural basis for compartmental distribution.","evidence":"Subcellular fractionation, immuno-EM, mass spectrometry, and 2D gels of rat liver MsrA","pmids":["12693988"],"confidence":"High","gaps":["Promoter/transcript origin of isoforms not yet mapped","Functional difference between isoforms untested"]},{"year":2005,"claim":"Mapping two promoters generating three isoforms with distinct localizations explained how subcellular distribution is encoded, and knockdown confirmed a protective role.","evidence":"5'RACE, promoter analysis, isoform-GFP localization, and siRNA knockdown with oxidative-stress viability in RPE cells","pmids":["16364291"],"confidence":"High","gaps":["Distinct functional consequences of each isoform not dissected","Transcriptional control of promoters not addressed"]},{"year":2006,"claim":"Dissecting active-site residues defined the catalytic chemistry of the reductase step at residue resolution.","evidence":"Site-directed mutagenesis and kinetic analysis of Glu/Tyr/Tyr and catalytic Cys in Neisseria MsrA","pmids":["17062561"],"confidence":"High","gaps":["Generality to mammalian enzyme inferred from bacterial ortholog","Regeneration step of active site not characterized here"]},{"year":2008,"claim":"Distinguishing free amino-acid substrate specificity in vivo confirmed MsrA reduces only the S-epimer of free methionine sulfoxide.","evidence":"MsrA knockout mouse plasma sulfoxide measurement, cell culture, and yeast complementation","pmids":["18697736"],"confidence":"High","gaps":["R-epimer reduction pathway handled by separate enzymes, not addressed","Protein-bound versus free substrate preference not compared"]},{"year":2008,"claim":"Connecting MsrA loss to dopamine dysregulation extended its role into neurological homeostasis.","evidence":"MsrA knockout mouse dopamine and locomotor measurements with tyrosine hydroxylase analysis","pmids":["18466776"],"confidence":"Medium","gaps":["Direct molecular target in dopamine pathway not identified","Correlation between dopamine levels and MsrA status does not establish causal mechanism"]},{"year":2008,"claim":"Hormonal induction of MsrA by ecdysone linked oxidative-stress resistance to developmental signaling in Drosophila.","evidence":"Ecdysone treatment of Kc cells, RT-PCR, H2O2 viability, and EcR-knockout comparison","pmids":["17239346"],"confidence":"Medium","gaps":["Mammalian relevance of ecdysone regulation not applicable","Direct EcR-USP binding to MsrA promoter not shown"]},{"year":2008,"claim":"Characterizing dual-promoter retinoic-acid regulation revealed how isoform expression is transcriptionally tuned.","evidence":"Promoter-reporter assays, deletion analysis, retinoic acid treatment, and RAR siRNA knockdown","pmids":["18845237"],"confidence":"Medium","gaps":["Endogenous retinoid control in vivo not confirmed","Other transcription factors at the two promoters not mapped"]},{"year":2009,"claim":"Identifying specific protein substrates and repair outcomes showed how MSRA restores function to oxidatively damaged proteins.","evidence":"Co-IP, CNBr cleavage with mass spectrometry of oxidized methionines, in vitro repair with activity assays, and KO lens analysis for cytochrome c and alpha-crystallin","pmids":["19461988","19733220"],"confidence":"High","gaps":["Full substrate repertoire beyond cytochrome c and crystallin not defined","In vivo flux of repair versus protein turnover not quantified"]},{"year":2015,"claim":"Compartment-specific overexpression demonstrated that mitochondrial MSRA controls metabolic homeostasis through AMPK signaling.","evidence":"TgMito versus TgCyto transgenic mice on high-fat diet with glucose/insulin tests and AMPK measurements","pmids":["26448611"],"confidence":"Medium","gaps":["Mitochondrial substrate transmitting the AMPK signal not identified","Single-lab transgenic models"]},{"year":2016,"claim":"Compartment-specific transgenics linked cytosolic MSRA to age-related mortality independent of lifespan extension, establishing localization-dependent aging effects.","evidence":"Cytosol- and mitochondria-targeted transgenic mice with Gompertz/log-rank lifespan and insulin sensitivity analyses","pmids":["27821326"],"confidence":"Medium","gaps":["Sex-specific effects not mechanistically explained","Molecular targets distinguishing the two compartments not identified"]},{"year":2017,"claim":"Discovery of a ubiquitin-like conjugation activity using the same active site revealed a moonlighting function distinct from methionine repair.","evidence":"In vitro Ubl modification assay with UbaA E1 and DMSO, LC-MS/MS conjugate identification, and active-site mutant analysis in archaea","pmids":["28874471"],"confidence":"Medium","gaps":["Archaeal system; mammalian relevance requires inference","In vivo conjugate function not established"]},{"year":2018,"claim":"Demonstrating MsrA-mediated ubiquitination of 14-3-3 and alpha-synuclein extended the non-canonical modification activity to a mammalian, neurologically relevant context.","evidence":"Co-IP, ubiquitination and phosphorylation assays in brain tissue, KO comparison, and active-site competition assays","pmids":["30096435"],"confidence":"Medium","gaps":["Direct catalytic role versus scaffolding not fully separated","Physiological consequence for synucleinopathy not established"]},{"year":2018,"claim":"Showing Drosophila MsrA lacks the oxidase step refined the mechanistic understanding of the active-site sulfenic acid chemistry across orthologs.","evidence":"Recombinant Drosophila MSRA in vitro reductase and oxidase assays with stepwise mechanistic dissection","pmids":["30529269"],"confidence":"High","gaps":["Structural basis for the missing disulfide-exchange step not resolved","Physiological role of the oxidase activity unclear"]},{"year":2020,"claim":"Linking MSRA to Jab1/CSN5 deneddylase activity connected it to cell-cycle control through p27 degradation.","evidence":"Co-IP, deneddylase activity assay, Cullin-1 neddylation analysis, and p27 levels in MsrA-knockout cells","pmids":["32456285"],"confidence":"Medium","gaps":["Whether MSRA repairs an oxidized methionine on Jab1 not shown","Single-lab characterization"]},{"year":2024,"claim":"Placing MSRA upstream of p38 MAPK via ox-CaMKII reduction defined a signaling axis protective against cardiac remodeling.","evidence":"Ang II mouse model, MsrA siRNA knockdown in HL-1 cells, RNA-seq, ox-CaMKII/p38 Western blots, and p38-inhibitor rescue","pmids":["39157962"],"confidence":"Medium","gaps":["Direct repair of CaMKII methionines not biochemically confirmed in this study","Single-lab pharmacological pathway dissection"]},{"year":2025,"claim":"Iron-dependent multimerization and activation of MSRA, coupled to PKA methionine maintenance, mechanistically tied the enzyme to adipose browning and cancer cachexia.","evidence":"Iron-binding mutagenesis, biophysical multimer characterization, PKA methionine oxidation analysis, and MsrA knockout PDA mouse browning/survival measurements (preprint)","pmids":["bio_10.1101_2025.07.16.664180"],"confidence":"Medium","gaps":["Preprint, not yet peer-reviewed","Structural details of iron-coordinated multimer not fully resolved"]},{"year":null,"claim":"It remains unknown how MSRA's canonical reductase activity and its non-canonical ubiquitin-like/signaling activities are coordinated in vivo, and which compartment-specific substrates drive its distinct metabolic, aging, and neurological roles.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying structural model reconciling reductase and Ubl activities in mammals","Comprehensive compartment-resolved substrate maps lacking","Causal substrate for AMPK/PKA/p38 signaling effects unidentified"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016491","term_label":"oxidoreductase activity","supporting_discovery_ids":[0,5,6,10,11,17]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[10,11,13,14,15]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,6]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[2,3,4,12,16]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3,4,19]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[1,4]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[12,19,20]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[15,18]}],"complexes":[],"partners":["CYCS","CRYAA","CRYAB","JAB1/CSN5","YWHAZ","SNCA","PRKACA","CAMK2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UJ68","full_name":"Mitochondrial peptide methionine sulfoxide reductase","aliases":["Peptide-methionine (S)-S-oxide reductase","Peptide Met(O) reductase","Protein-methionine-S-oxide reductase","PMSR"],"length_aa":235,"mass_kda":26.1,"function":"Catalyzes the reversible oxidation-reduction of methionine sulfoxide in proteins to methionine. Has an important function as a repair enzyme for proteins that have been inactivated by oxidation (PubMed:10452521, PubMed:12039877). Plays a crucial role in repairing oxidized methionine residues in key lens proteins, such as alpha-crystallin (CRYAA/CRYAB) and cytochrome c (CYCS), thereby restoring their function and maintaining lens transparency (By similarity)","subcellular_location":"Cytoplasm; Membrane","url":"https://www.uniprot.org/uniprotkb/Q9UJ68/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MSRA","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MSRA","total_profiled":1310},"omim":[{"mim_id":"618211","title":"PITRILYSIN METALLOPEPTIDASE 1; PITRM1","url":"https://www.omim.org/entry/618211"},{"mim_id":"613782","title":"METHIONINE SULFOXIDE REDUCTASE B2; MSRB2","url":"https://www.omim.org/entry/613782"},{"mim_id":"608581","title":"RP1-LIKE PROTEIN 1; RP1L1","url":"https://www.omim.org/entry/608581"},{"mim_id":"606216","title":"METHIONINE SULFOXIDE REDUCTASE B1; MSRB1","url":"https://www.omim.org/entry/606216"},{"mim_id":"601250","title":"PEPTIDE METHIONINE SULFOXIDE REDUCTASE; MSRA","url":"https://www.omim.org/entry/601250"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in 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essential for catalytic activity; site-directed mutagenesis of the cysteine within this motif (or treatment with iodoacetamide) causes complete loss of enzyme activity. The yeast MsrA is stereoselective for L-methionine S-sulfoxide (S-epimer), establishing substrate stereospecificity.\",\n      \"method\": \"Site-directed mutagenesis of active-site residues; iodoacetamide inactivation; in vitro enzymatic activity assays; circular dichroism; stereospecificity assays with S- and R-methionine sulfoxide\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with mutagenesis and in vitro activity assays; multiple orthogonal methods (mutagenesis, chemical inhibition, stereospecificity) in a single rigorous study\",\n      \"pmids\": [\"10799493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"MsrA knockout mice exhibit enhanced sensitivity to oxidative stress, shorter lifespan, accumulation of oxidized proteins, and impaired upregulation of thioredoxin reductase under oxidative stress, establishing MsrA as a key antioxidant defense and lifespan regulator in mammals.\",\n      \"method\": \"MsrA knockout mouse model; exposure to 100% oxygen; protein carbonyl measurements; lifespan analysis; Western blotting for thioredoxin reductase\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular/organismal phenotype, multiple outcome measures, widely replicated by subsequent studies\",\n      \"pmids\": [\"11606777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Human MSRA is targeted to the mitochondrial matrix via an N-terminal 23 amino acid mitochondrial targeting sequence. The N-terminal signal sequence is not required for catalytic enzyme activity.\",\n      \"method\": \"EGFP fusion protein imaging in mammalian cell lines; deletion constructs; immunohistochemistry of mouse and rat liver; pre-embedding immunostaining with electron microscopy; in vitro activity assays\",\n      \"journal\": \"FASEB journal : official publication of the Federation of American Societies for Experimental Biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct subcellular localization by live imaging and EM, deletion constructs defining the signal sequence, functional validation in vitro; replicated in the same study by multiple orthogonal methods\",\n      \"pmids\": [\"12039877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Rat liver MsrA exists as both mitochondrial matrix and cytosolic isoforms encoded by a single gene; the mitochondrial form contains a cleavable N-terminal signal sequence. Both isoforms carry oxidative modifications of cysteine residues in native tissue.\",\n      \"method\": \"Subcellular fractionation; enzymatic activity assays; Western blotting; immunoelectron microscopy; mass spectrometry identification; 2D gel electrophoresis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (fractionation, EM, MS, 2D gels) demonstrating both isoform existence and mitochondrial localization; independent replication of mitochondrial targeting finding\",\n      \"pmids\": [\"12693988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The human MSRA gene produces three isoforms from two distinct promoters: msrA1 (mitochondrial targeting), and msrA2/3 (cytosolic and nuclear localization). siRNA-mediated silencing of MSRA increases oxidative damage susceptibility in RPE cells.\",\n      \"method\": \"5'RACE cloning of transcripts; promoter analysis; subcellular localization of isoform-GFP fusions; siRNA knockdown; oxidative stress cell viability assays\",\n      \"journal\": \"Experimental eye research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (transcript cloning, fusion protein localization, siRNA KD with functional readout); single lab but comprehensive\",\n      \"pmids\": [\"16364291\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Mammals reduce methionine-S-sulfoxide via an MsrA-dependent pathway; MsrA knockout mice accumulate methionine-R-sulfoxide in plasma (but not S-sulfoxide), demonstrating MsrA is specifically required for reduction of the S-epimer of free methionine sulfoxide in vivo.\",\n      \"method\": \"MsrA knockout mouse; SK-Hep1 cell culture on methionine sulfoxides; plasma sulfoxide measurement; yeast free methionine-R-sulfoxide reductase complementation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO model combined with complementation and biochemical plasma measurements; mechanistically precise substrate specificity established in vivo\",\n      \"pmids\": [\"18697736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Invariant Glu-94, Tyr-82, and Tyr-134 in the MsrA active site (Neisseria meningitidis) are required for catalysis of the reductase step: they stabilize the sulfurane transition state and lower the pKa of the catalytic Cys-51, which forms a sulfenic acid intermediate upon substrate reduction.\",\n      \"method\": \"Site-directed mutagenesis; kinetic analysis; mechanistic characterization of reductase step\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro mutagenesis coupled with kinetic analysis defining catalytic mechanism; single lab but rigorous mechanistic dissection\",\n      \"pmids\": [\"17062561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MsrA knockout mice display abnormal dopamine levels (elevated at younger ages, decreased at 16 months) and impaired locomotor behavior, suggesting MsrA regulates dopamine signaling pathways, correlated with age-dependent changes in tyrosine hydroxylase activating protein expression.\",\n      \"method\": \"MsrA knockout mouse; dopamine measurements in striatal brain regions; amphetamine response testing; locomotor activity assays; tyrosine hydroxylase expression analysis\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with defined biochemical and behavioral phenotypes, single lab, correlation between dopamine levels and MsrA status established but molecular mechanism not fully resolved\",\n      \"pmids\": [\"18466776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In Drosophila, MsrA is induced by ecdysone via the EcR-USP complex; this hormonal induction is required for ecdysone-mediated protection against H2O2-induced oxidative stress. EcR-deficient cells lose both ecdysone induction of MsrA and H2O2 resistance.\",\n      \"method\": \"Ecdysone treatment of Kc cells; RT-PCR; H2O2 viability assay; EcR-knockout cell line comparison\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function (EcR KO) combined with hormonal induction and functional survival assay; single lab, Drosophila ortholog\",\n      \"pmids\": [\"17239346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The human MSRA gene is regulated by two distinct promoters: promoter 1 (upstream, drives the mitochondrial msrA1 isoform) and promoter 2 (downstream, drives cytosolic/nuclear msrA2/3 isoforms). Both promoters are partially regulated by all-trans retinoic acid via RARA and other RARs.\",\n      \"method\": \"Promoter-reporter assays; deletion analysis; retinoic acid treatment; RAR siRNA knockdown; cell-line-specific expression analysis\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter assays with deletion constructs and receptor knockdown; single lab, two orthogonal approaches\",\n      \"pmids\": [\"18845237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MsrA co-immunoprecipitates with cytochrome c and four of the five mitochondrial electron transport chain complexes. MsrA repairs oxidized methionines (Met65 and Met80) in cytochrome c, restoring cytochrome c oxidase activity and reducing cytochrome c peroxidase activity. MsrA deletion causes accumulation and degradation of oxidized cytochrome c in lens.\",\n      \"method\": \"Co-immunoprecipitation; cyanogen bromide cleavage for oxidized methionine identification; in vitro MsrA repair assay with activity measurements; mass spectrometry; MsrA knockout mouse lens analysis\",\n      \"journal\": \"Molecular vision\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of repair activity with mass spectrometry confirmation, co-IP of binding partners, and KO mouse validation; multiple orthogonal methods\",\n      \"pmids\": [\"19461988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Methionine oxidation of alpha-crystallin (Met138 of alphaA, Met68 of alphaB) abolishes its chaperone activity. MsrA reduces these methionine sulfoxides and restores chaperone function. Deletion of MsrA in mice results in increased PMSO-alpha-crystallin accumulation in lens.\",\n      \"method\": \"In vitro oxidation and MsrA repair of alpha-crystallin; CNBr cleavage and mass spectrometry for methionine sulfoxide identification; chaperone activity assay (light scattering); MsrA knockout mouse lens analysis\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of repair with mass spectrometry validation of substrate sites, functional activity assay, and KO mouse confirmation; multiple orthogonal methods\",\n      \"pmids\": [\"19733220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Mitochondria-targeted MsrA overexpression, but not cytosolic MsrA, preserves insulin sensitivity in diet-induced obese mice without altering obesity itself. The protective effect is associated with activation of AMPK signaling, suggesting a mechanism by which mitochondrial protein methionine repair modulates metabolic homeostasis.\",\n      \"method\": \"Transgenic mouse models with compartment-specific MsrA overexpression (TgMito vs TgCyto); high-fat diet feeding; glucose tolerance and insulin sensitivity tests; AMPK activity measurements\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two transgenic mouse lines with distinct subcellular targeting enabling compartment-specific comparison, single lab, functional metabolic readouts\",\n      \"pmids\": [\"26448611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Archaeal MsrA catalyzes ubiquitin-like (Ubl) protein modification in the presence of the Ubl-activating E1 enzyme UbaA and mild oxidant (DMSO), using the same active site as methionine sulfoxide reduction. This Ubl modification activity is distinct from and antagonized by the methionine sulfoxide reductase activity; MsrA-dependent Ubl conjugates include Orc3 and Cdc48d proteins involved in DNA replication and protein remodeling.\",\n      \"method\": \"In vitro Ubl modification assay; LC-MS/MS identification of conjugates; active-site mutant analysis; DMSO-dependent activity assay; reductant inhibition studies\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mass spectrometry confirmation; archaeal system, functional relevance to mammalian enzyme requires inference\",\n      \"pmids\": [\"28874471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Mammalian MsrA mediates ubiquitination of 14-3-3 zeta protein in brain and promotes binding of 14-3-3 proteins to alpha-synuclein; it also enhances ubiquitination and phosphorylation of Ser129 of alpha-synuclein. MsrA competes for ubiquitin capture using the same active site as methionine sulfoxide binding.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assays in brain tissue; phosphorylation analysis; MsrA knockout mouse brain comparison; active-site competition assays\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and biochemical assays in brain tissue with KO comparison; single lab, multiple substrates tested\",\n      \"pmids\": [\"30096435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"MsrA interacts with Jab1/CSN5 and enhances its deneddylase activity (removal of Nedd8 from Cullin-1). This interaction increases Jab1 binding affinity to P27, promoting P27 ubiquitination and degradation. MsrA ablation causes dramatic increase in P27 expression.\",\n      \"method\": \"Co-immunoprecipitation; deneddylase activity assay; P27 level measurement in MsrA-knockout cells; Cullin-1 neddylation state analysis\",\n      \"journal\": \"Antioxidants (Basel, Switzerland)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP of protein interaction, enzymatic activity assay, KO phenotype; single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"32456285\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A novel splice variant of MSRA (msrA2a) exists in rat vascular smooth muscle cells, encoding a mitochondrially targeted isoform with confirmed enzymatic activity on methionine sulfoxide substrate. Endogenous MSRA immunoreactivity in VSMCs is exclusively mitochondrial.\",\n      \"method\": \"RT-PCR and sequence analysis of splice variants; recombinant protein expression and in vitro activity assay; immunofluorescence localization\",\n      \"journal\": \"Free radical research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — new splice variant characterized with in vitro activity confirmation and subcellular localization; single lab\",\n      \"pmids\": [\"17907003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Drosophila MSRA lacks methionine oxidase activity despite having an active site sequence identical to mammalian MSRA. The Drosophila enzyme cannot complete the third step of the oxidase mechanism (disulfide exchange at carboxy-terminal cysteine to regenerate the active site), though it performs the reductase reaction and first two steps normally.\",\n      \"method\": \"Recombinant Drosophila MSRA expression; in vitro methionine sulfoxide reductase and oxidase assays; mechanistic dissection of active-site sulfenic acid chemistry; carboxy-terminal domain analysis\",\n      \"journal\": \"Free radical biology & medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with stepwise mechanistic dissection of oxidase vs. reductase activities; rigorous biochemical characterization; single lab\",\n      \"pmids\": [\"30529269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"S-Methyl-L-cysteine (SMLC) acts as a methionine analog substrate for MsrA, enabling scavenging of free radicals. SMLC activates MsrA which reduces oxidized CaMKII (ox-CaMKII) and inhibits p38 MAPK phosphorylation, protecting against Ang II-induced atrial remodeling. MsrA knockdown abolishes the protective effects of SMLC, placing MsrA upstream of the p38 MAPK pathway.\",\n      \"method\": \"In vivo Ang II mouse model; siRNA knockdown of MsrA in HL-1 cells; RNA sequencing; Western blotting for ox-CaMKII and p38 MAPK; SB203580 (p38 inhibitor) rescue experiment\",\n      \"journal\": \"Food & function\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KD with pharmacological rescue defining pathway order; single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"39157962\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Cytosolic MsrA overexpression (TgCyto) reduces age-related death rate in female mice by Gompertz analysis but does not extend median lifespan; mitochondrial MsrA overexpression improves insulin sensitivity in aged females, demonstrating subcellular localization-dependent effects on aging and metabolic phenotypes.\",\n      \"method\": \"Transgenic mouse models with cytosol- and mitochondria-targeted MsrA; Gompertz and log-rank lifespan analysis; glucose tolerance and insulin sensitivity tests\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two transgenic models enabling direct compartment comparison; single lab, mechanistic inference on subcellular localization consequence\",\n      \"pmids\": [\"27821326\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Iron coordinates to conserved E203-xx-H206 motifs to multimerize, stabilize, and enzymatically activate MSRA. Activated MSRA maintains reduced methionines near the ATP-binding site of Protein Kinase A (PKA), thereby facilitating PKA-driven adipose browning. MsrA deletion in PDA mouse models impairs WAT browning and improves survival of tumor-bearing animals.\",\n      \"method\": \"Iron-binding mutagenesis; structural/biophysical characterization of MSRA multimers; PKA methionine oxidation state analysis; MsrA knockout mouse model of PDA; WAT browning and cachexia measurements\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mechanistic in vitro characterization (iron binding, multimerization) combined with in vivo KO mouse phenotype; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.07.16.664180\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"MSRA is a stereospecific methionine sulfoxide reductase that catalyzes reduction of methionine-S-sulfoxide (S-epimer) back to methionine via a conserved GCFWG active-site cysteine (forming a sulfenic acid intermediate stabilized by Glu-94, Tyr-82, and Tyr-134), is expressed as multiple isoforms from two promoters that target it to the mitochondrial matrix (via an N-terminal 23-aa signal) and the cytosol/nucleus, acts as a broad antioxidant defense by repairing oxidized proteins including cytochrome c (restoring ETC activity), alpha-crystallin (restoring chaperone activity), CaMKII, and PKA, and also participates in non-canonical ubiquitination-like protein modification and in regulating signaling cascades (p38 MAPK, AMPK, Jab1/CSN5-P27, dopamine pathways), with its subcellular localization determining distinct functional consequences for metabolism, aging, and neurological homeostasis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MSRA is a stereospecific methionine sulfoxide reductase that constitutes a core antioxidant defense system by catalytically repairing oxidized proteins and restoring their function [#1, #10]. Catalysis depends on a conserved active-site cysteine within the GCFWG motif, which forms a sulfenic acid intermediate during reduction; invariant Glu, Tyr, and a second Tyr stabilize the sulfurane transition state and lower the catalytic cysteine pKa, and the enzyme is strictly stereoselective for the S-epimer of methionine sulfoxide [#0, #6, #5]. A single gene generates multiple isoforms from two promoters: an upstream promoter drives a mitochondrial-matrix isoform via a cleavable N-terminal 23-residue targeting sequence, while a downstream promoter drives cytosolic and nuclear isoforms, and this compartmentalization dictates distinct physiological consequences [#2, #3, #4, #9]. Through methionine repair MSRA restores activity to oxidatively damaged substrates including cytochrome c (recovering electron-transport-chain function) and alpha-crystallin (recovering chaperone activity) [#10, #11], and its loss in knockout mice causes accumulation of oxidized proteins, heightened oxidative-stress sensitivity, and shortened lifespan [#1]. Compartment-specific transgenic studies show mitochondrial MSRA preserves insulin sensitivity via AMPK signaling whereas cytosolic MSRA modulates age-related mortality, establishing localization-dependent roles in metabolism and aging [#12, #19]. Beyond canonical reductase chemistry, MSRA participates in protein modification and signaling: it engages a ubiquitin-like conjugation activity through its active site, mediates ubiquitination of 14-3-3 and alpha-synuclein, enhances Jab1/CSN5 deneddylase activity to drive p27 degradation, and acts upstream of the p38 MAPK pathway by reducing oxidized CaMKII [#13, #14, #15, #18].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing the catalytic basis and substrate selectivity of MsrA was needed to define it as a true methionine sulfoxide reductase rather than a generic redox protein.\",\n      \"evidence\": \"Site-directed mutagenesis of the GCFWG cysteine, iodoacetamide inactivation, and stereospecificity assays with S/R methionine sulfoxide in yeast MsrA\",\n      \"pmids\": [\"10799493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic mechanism of intermediate resolution not yet defined\", \"Did not address subcellular localization or substrates in vivo\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Genetic loss-of-function tested whether MsrA matters at the organismal level, defining it as an antioxidant defense and lifespan regulator.\",\n      \"evidence\": \"MsrA knockout mouse exposed to hyperoxia, with protein carbonyl, lifespan, and thioredoxin reductase measurements\",\n      \"pmids\": [\"11606777\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Specific oxidized protein substrates driving phenotype not identified\", \"Mechanistic link between methionine repair and lifespan unresolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defining the mitochondrial targeting sequence answered where MSRA acts and separated localization from catalysis.\",\n      \"evidence\": \"EGFP-fusion imaging, deletion constructs, immuno-EM in liver, and in vitro activity assays\",\n      \"pmids\": [\"12039877\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve how non-mitochondrial isoforms are generated\", \"Regulation of targeting not addressed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing a single gene yields both mitochondrial and cytosolic isoforms clarified the structural basis for compartmental distribution.\",\n      \"evidence\": \"Subcellular fractionation, immuno-EM, mass spectrometry, and 2D gels of rat liver MsrA\",\n      \"pmids\": [\"12693988\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Promoter/transcript origin of isoforms not yet mapped\", \"Functional difference between isoforms untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mapping two promoters generating three isoforms with distinct localizations explained how subcellular distribution is encoded, and knockdown confirmed a protective role.\",\n      \"evidence\": \"5'RACE, promoter analysis, isoform-GFP localization, and siRNA knockdown with oxidative-stress viability in RPE cells\",\n      \"pmids\": [\"16364291\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Distinct functional consequences of each isoform not dissected\", \"Transcriptional control of promoters not addressed\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Dissecting active-site residues defined the catalytic chemistry of the reductase step at residue resolution.\",\n      \"evidence\": \"Site-directed mutagenesis and kinetic analysis of Glu/Tyr/Tyr and catalytic Cys in Neisseria MsrA\",\n      \"pmids\": [\"17062561\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality to mammalian enzyme inferred from bacterial ortholog\", \"Regeneration step of active site not characterized here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Distinguishing free amino-acid substrate specificity in vivo confirmed MsrA reduces only the S-epimer of free methionine sulfoxide.\",\n      \"evidence\": \"MsrA knockout mouse plasma sulfoxide measurement, cell culture, and yeast complementation\",\n      \"pmids\": [\"18697736\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"R-epimer reduction pathway handled by separate enzymes, not addressed\", \"Protein-bound versus free substrate preference not compared\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Connecting MsrA loss to dopamine dysregulation extended its role into neurological homeostasis.\",\n      \"evidence\": \"MsrA knockout mouse dopamine and locomotor measurements with tyrosine hydroxylase analysis\",\n      \"pmids\": [\"18466776\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular target in dopamine pathway not identified\", \"Correlation between dopamine levels and MsrA status does not establish causal mechanism\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Hormonal induction of MsrA by ecdysone linked oxidative-stress resistance to developmental signaling in Drosophila.\",\n      \"evidence\": \"Ecdysone treatment of Kc cells, RT-PCR, H2O2 viability, and EcR-knockout comparison\",\n      \"pmids\": [\"17239346\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian relevance of ecdysone regulation not applicable\", \"Direct EcR-USP binding to MsrA promoter not shown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Characterizing dual-promoter retinoic-acid regulation revealed how isoform expression is transcriptionally tuned.\",\n      \"evidence\": \"Promoter-reporter assays, deletion analysis, retinoic acid treatment, and RAR siRNA knockdown\",\n      \"pmids\": [\"18845237\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous retinoid control in vivo not confirmed\", \"Other transcription factors at the two promoters not mapped\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identifying specific protein substrates and repair outcomes showed how MSRA restores function to oxidatively damaged proteins.\",\n      \"evidence\": \"Co-IP, CNBr cleavage with mass spectrometry of oxidized methionines, in vitro repair with activity assays, and KO lens analysis for cytochrome c and alpha-crystallin\",\n      \"pmids\": [\"19461988\", \"19733220\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full substrate repertoire beyond cytochrome c and crystallin not defined\", \"In vivo flux of repair versus protein turnover not quantified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Compartment-specific overexpression demonstrated that mitochondrial MSRA controls metabolic homeostasis through AMPK signaling.\",\n      \"evidence\": \"TgMito versus TgCyto transgenic mice on high-fat diet with glucose/insulin tests and AMPK measurements\",\n      \"pmids\": [\"26448611\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mitochondrial substrate transmitting the AMPK signal not identified\", \"Single-lab transgenic models\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Compartment-specific transgenics linked cytosolic MSRA to age-related mortality independent of lifespan extension, establishing localization-dependent aging effects.\",\n      \"evidence\": \"Cytosol- and mitochondria-targeted transgenic mice with Gompertz/log-rank lifespan and insulin sensitivity analyses\",\n      \"pmids\": [\"27821326\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sex-specific effects not mechanistically explained\", \"Molecular targets distinguishing the two compartments not identified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Discovery of a ubiquitin-like conjugation activity using the same active site revealed a moonlighting function distinct from methionine repair.\",\n      \"evidence\": \"In vitro Ubl modification assay with UbaA E1 and DMSO, LC-MS/MS conjugate identification, and active-site mutant analysis in archaea\",\n      \"pmids\": [\"28874471\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Archaeal system; mammalian relevance requires inference\", \"In vivo conjugate function not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Demonstrating MsrA-mediated ubiquitination of 14-3-3 and alpha-synuclein extended the non-canonical modification activity to a mammalian, neurologically relevant context.\",\n      \"evidence\": \"Co-IP, ubiquitination and phosphorylation assays in brain tissue, KO comparison, and active-site competition assays\",\n      \"pmids\": [\"30096435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct catalytic role versus scaffolding not fully separated\", \"Physiological consequence for synucleinopathy not established\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showing Drosophila MsrA lacks the oxidase step refined the mechanistic understanding of the active-site sulfenic acid chemistry across orthologs.\",\n      \"evidence\": \"Recombinant Drosophila MSRA in vitro reductase and oxidase assays with stepwise mechanistic dissection\",\n      \"pmids\": [\"30529269\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for the missing disulfide-exchange step not resolved\", \"Physiological role of the oxidase activity unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Linking MSRA to Jab1/CSN5 deneddylase activity connected it to cell-cycle control through p27 degradation.\",\n      \"evidence\": \"Co-IP, deneddylase activity assay, Cullin-1 neddylation analysis, and p27 levels in MsrA-knockout cells\",\n      \"pmids\": [\"32456285\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether MSRA repairs an oxidized methionine on Jab1 not shown\", \"Single-lab characterization\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placing MSRA upstream of p38 MAPK via ox-CaMKII reduction defined a signaling axis protective against cardiac remodeling.\",\n      \"evidence\": \"Ang II mouse model, MsrA siRNA knockdown in HL-1 cells, RNA-seq, ox-CaMKII/p38 Western blots, and p38-inhibitor rescue\",\n      \"pmids\": [\"39157962\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct repair of CaMKII methionines not biochemically confirmed in this study\", \"Single-lab pharmacological pathway dissection\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Iron-dependent multimerization and activation of MSRA, coupled to PKA methionine maintenance, mechanistically tied the enzyme to adipose browning and cancer cachexia.\",\n      \"evidence\": \"Iron-binding mutagenesis, biophysical multimer characterization, PKA methionine oxidation analysis, and MsrA knockout PDA mouse browning/survival measurements (preprint)\",\n      \"pmids\": [\"bio_10.1101_2025.07.16.664180\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint, not yet peer-reviewed\", \"Structural details of iron-coordinated multimer not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how MSRA's canonical reductase activity and its non-canonical ubiquitin-like/signaling activities are coordinated in vivo, and which compartment-specific substrates drive its distinct metabolic, aging, and neurological roles.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying structural model reconciling reductase and Ubl activities in mammals\", \"Comprehensive compartment-resolved substrate maps lacking\", \"Causal substrate for AMPK/PKA/p38 signaling effects unidentified\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016491\", \"supporting_discovery_ids\": [0, 5, 6, 10, 11, 17]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [10, 11, 13, 14, 15]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [2, 3, 4, 12, 16]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3, 4, 19]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [12, 19, 20]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [15, 18]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CYCS\", \"CRYAA\", \"CRYAB\", \"JAB1/CSN5\", \"YWHAZ\", \"SNCA\", \"PRKACA\", \"CAMK2\"],\n    \"other_free_text\": []\n  }\n}\n```","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}