{"gene":"MMUT","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":1990,"finding":"Methylmalonyl-CoA mutase (MCM/MMUT) apoenzyme deficiency in mut-type methylmalonic acidemia is associated with decreased steady-state MCM mRNA levels in several patient cell lines, indicating that mRNA expression defects contribute to enzyme deficiency; at least six independent alleles were delineated by haplotype, mRNA level, and biochemical phenotype, confirming allelic heterogeneity at the MUT locus.","method":"Southern blot, Northern blot, fibroblast cell line biochemical phenotyping (propionate incorporation assay)","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Northern blot demonstrating mRNA reduction plus biochemical phenotyping in primary fibroblasts, single lab but multiple orthogonal methods","pmids":["1968706"],"is_preprint":false},{"year":1991,"finding":"A G354→A missense mutation in the MUT gene (Arg93→His) causes a mut(0) phenotype when transferred into a mut(0) cell line, but can contribute to apoenzyme function when transferred into mut(-) cell lines that complement with the original cell line (WG1130). This demonstrates interallelic complementation between subsets of mut(0) and mut(-) alleles, indicating that different mutations affect discrete components of MCM apoenzyme function, consistent with the enzyme functioning as a multimer.","method":"MUT cDNA cloning and sequencing, gene transfer into primary patient fibroblasts, somatic cell complementation, propionate incorporation assay","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution by gene transfer with mutagenesis and functional readout (propionate incorporation); complementation assay provides direct mechanistic evidence for domain function","pmids":["1670635"],"is_preprint":false},{"year":1997,"finding":"Mutations in the MUT gene cause either complete loss of methylmalonyl-CoA mutase activity (mut(0) phenotype) or residual cobalamin-dependent activity with elevated Km for adenosylcobalamin (mut(-) phenotype). Specific mutations define critical domains including the adenosylcobalamin (cobalamin) binding domain of the enzyme; a subset of alleles in both phenotypic classes exhibit interallelic complementation, indicating the enzyme functions as a multimer with distinct functional domains.","method":"Biochemical enzyme assay (methylmalonyl-CoA mutase activity, Km determination), somatic cell complementation, molecular cloning/sequencing","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — enzyme kinetic assays plus somatic cell complementation with molecular characterization, single lab review synthesis","pmids":["8990001"],"is_preprint":false},{"year":2005,"finding":"In a cohort of 40 European mut-type MMA patients, 29 novel mutations in the MUT gene were identified. Twelve novel missense mutations were mapped onto a 3D homology model of human MCM based on the Propionibacterium shermanii enzyme structure, revealing their structural positions. Mutations causing the mut(-) phenotype (residual cobalamin-dependent activity) were enriched in the C-terminal cofactor (adenosylcobalamin) binding domain, while mut(0) mutations were more broadly distributed, indicating that the C-terminal domain is critical for cobalamin binding.","method":"Direct cDNA and gDNA sequencing, 3D homology modelling based on P. shermanii MCM crystal structure, biochemical phenotyping","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — sequencing combined with structural homology modelling and biochemical phenotype correlation; structural inference is based on homology not direct crystal structure of human enzyme","pmids":["15643616"],"is_preprint":false},{"year":2016,"finding":"In a cohort of 151 mut-type MMA patients, Western blot analysis of 34 patient cell lines (27 mut(0) and 7 mut(-)) revealed reduced MUT protein levels for all tested lines, indicating that protein instability is a major mechanism of deficiency regardless of mutation type. Missense alleles causing the mut(-) subclass were almost exclusively located in the C-terminal cofactor binding domain.","method":"Western blot of patient fibroblast cell lines, biochemical propionate incorporation assay, MUT gene sequencing","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Western blot across 34 cell lines demonstrating protein instability as common mechanism; large cohort but single lab","pmids":["27167370"],"is_preprint":false},{"year":2021,"finding":"Analysis of 266 Chinese mut-type MMA patients showed that specific MMUT gene mutations are associated with complete, partial, or nonresponsiveness to vitamin B12 (hydroxocobalamin) treatment, as measured by normalization of C3/C2 ratios and methylmalonic acid levels. Completely responsive patients harbored mutations including c.1663G>A, c.2080C>T, and c.1880A>G, while nonresponsive patients carried mutations such as c.1741C>T and c.1630_1631GG>TA, indicating that specific mutations differentially affect the cobalamin-dependent catalytic activity of MMUT.","method":"Retrospective cohort study with MMUT gene sequencing, blood acylcarnitine profiling, urine organic acid analysis, vitamin B12 responsiveness testing","journal":"Molecular genetics & genomic medicine","confidence":"Low","confidence_rationale":"Tier 3 / Moderate — genotype-phenotype correlation across large cohort but no direct in vitro enzymatic reconstitution; mechanistic inference from clinical response data","pmids":["34668645"],"is_preprint":false}],"current_model":"MMUT (methylmalonyl-CoA mutase) is a mitochondrial, adenosylcobalamin-dependent enzyme that converts methylmalonyl-CoA to succinyl-CoA; loss-of-function mutations in the MUT gene cause methylmalonic acidemia, with mut(0) alleles abolishing enzyme activity and mut(-) alleles reducing cobalamin affinity (elevated Km) through missense mutations enriched in the C-terminal cobalamin-binding domain, while protein instability is a common downstream consequence of most mutations; the enzyme functions as a multimer evidenced by interallelic complementation between certain mut(0) and mut(-) alleles, and specific mutations in the cobalamin-binding domain determine responsiveness to vitamin B12 treatment."},"narrative":{"mechanistic_narrative":"MMUT encodes methylmalonyl-CoA mutase, an adenosylcobalamin-dependent mitochondrial enzyme whose loss of function causes mut-type methylmalonic acidemia (MMA) [PMID:1670635, PMID:8990001]. Disease alleles fall into two biochemical classes: mut(0) mutations that abolish enzyme activity, and mut(-) mutations that preserve residual cobalamin-dependent activity but raise the Km for adenosylcobalamin [PMID:8990001]. The enzyme is organized into discrete functional domains, with mut(-) missense alleles almost exclusively clustering in the C-terminal adenosylcobalamin (cofactor) binding domain, establishing this domain as critical for cofactor binding, while mut(0) mutations are more broadly distributed [PMID:15643616, PMID:27167370]. Interallelic complementation observed between certain mut(0) and mut(-) alleles indicates that the enzyme functions as a multimer in which distinct mutations impair separable components of apoenzyme function [PMID:1670635, PMID:8990001]. Across the spectrum of mutation types, reduced steady-state protein is a common downstream consequence, marking protein instability as a major shared mechanism of deficiency [PMID:27167370]. The position of cobalamin-binding-domain mutations also tracks with clinical responsiveness to vitamin B12, with specific genotypes conferring complete, partial, or absent normalization of metabolite levels [PMID:34668645].","teleology":[{"year":1990,"claim":"Established that MMUT deficiency in mut-type MMA is genetically heterogeneous and that defective mRNA expression, not only coding mutations, contributes to enzyme loss.","evidence":"Southern/Northern blot and propionate incorporation phenotyping across patient fibroblast lines","pmids":["1968706"],"confidence":"Medium","gaps":["Did not define the specific lesions reducing mRNA","No correlation of mRNA defects with protein-level or catalytic consequences"]},{"year":1991,"claim":"Demonstrated by gene transfer that a single missense allele behaves as mut(0) in one background yet supports apoenzyme function in complementing mut(-) backgrounds, providing direct evidence that distinct mutations hit separable functional components and that the enzyme acts as a multimer.","evidence":"MUT cDNA cloning/mutagenesis, gene transfer into patient fibroblasts, somatic cell complementation, propionate incorporation assay","pmids":["1670635"],"confidence":"High","gaps":["Did not map the structural basis of the complementation","Multimeric stoichiometry not directly determined"]},{"year":1997,"claim":"Defined the two biochemical phenotype classes mechanistically — mut(0) as complete loss and mut(-) as residual activity with elevated Km for adenosylcobalamin — linking mutation class to specific catalytic/cofactor-binding defects.","evidence":"Enzyme activity and Km determination, somatic cell complementation, molecular sequencing","pmids":["8990001"],"confidence":"Medium","gaps":["Domain assignment not yet anchored to a structural model","Synthesis from existing alleles rather than systematic structure-function mapping"]},{"year":2005,"claim":"Mapped novel missense mutations onto a homology model to show mut(-) alleles concentrate in the C-terminal adenosylcobalamin-binding domain while mut(0) alleles distribute broadly, locating the cofactor-binding function structurally.","evidence":"cDNA/gDNA sequencing of 40 patients, 3D homology modelling on P. shermanii MCM, biochemical phenotyping","pmids":["15643616"],"confidence":"Medium","gaps":["Structural inference rests on homology, not a human crystal structure","Does not explain mechanism of broadly distributed mut(0) alleles"]},{"year":2016,"claim":"Showed across 34 patient lines that MUT protein is reduced regardless of mut(0)/mut(-) class, identifying protein instability as a major shared mechanism of deficiency and reconfirming C-terminal localization of mut(-) missense alleles.","evidence":"Western blot of patient fibroblasts, propionate incorporation assay, MUT sequencing","pmids":["27167370"],"confidence":"Medium","gaps":["Degradation pathway responsible for instability not identified","Single-lab cohort; protein turnover not measured directly"]},{"year":2021,"claim":"Correlated specific MMUT genotypes with complete, partial, or absent vitamin B12 responsiveness, extending mutation-class effects on cobalamin-dependent activity to clinical treatment response.","evidence":"Retrospective cohort of 266 patients with sequencing, acylcarnitine and organic acid profiling, B12 responsiveness testing","pmids":["34668645"],"confidence":"Low","gaps":["No in vitro enzymatic reconstitution to confirm cofactor-affinity mechanism","Responsiveness inferred from metabolite normalization, not direct kinetics","Genotype-phenotype association may be confounded by allele combinations"]},{"year":null,"claim":"The molecular basis of multimer assembly, the degradation pathway driving protein instability, and a direct human enzyme structure resolving cofactor-binding mechanism remain undefined in the available corpus.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No human crystal structure in the corpus","Multimer stoichiometry and assembly determinants unresolved","Mechanism of mutation-induced protein turnover not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016853","term_label":"isomerase activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[2,3]}],"localization":[],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,5]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[1,4]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P22033","full_name":"Methylmalonyl-CoA mutase, mitochondrial","aliases":["Methylmalonyl-CoA isomerase"],"length_aa":750,"mass_kda":83.1,"function":"Catalyzes the reversible isomerization of methylmalonyl-CoA (MMCoA) (generated from branched-chain amino acid metabolism and degradation of dietary odd chain fatty acids and cholesterol) to succinyl-CoA (3-carboxypropionyl-CoA), a key intermediate of the tricarboxylic acid cycle","subcellular_location":"Mitochondrion matrix; Mitochondrion; Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P22033/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MMUT","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MMUT","total_profiled":1310},"omim":[{"mim_id":"609058","title":"METHYLMALONYL-CoA MUTASE; MMUT","url":"https://www.omim.org/entry/609058"},{"mim_id":"607568","title":"METABOLISM OF COBALAMIN ASSOCIATED B; MMAB","url":"https://www.omim.org/entry/607568"},{"mim_id":"251000","title":"METHYLMALONIC ACIDURIA DUE TO METHYLMALONYL-CoA MUTASE DEFICIENCY; MAMM","url":"https://www.omim.org/entry/251000"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"},{"location":"Mitochondria","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"liver","ntpm":186.1}],"url":"https://www.proteinatlas.org/search/MMUT"},"hgnc":{"alias_symbol":["MCM"],"prev_symbol":["MUT"]},"alphafold":{"accession":"P22033","domains":[{"cath_id":"3.40.50.280","chopping":"585-748","consensus_level":"high","plddt":96.3178,"start":585,"end":748}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P22033","model_url":"https://alphafold.ebi.ac.uk/files/AF-P22033-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P22033-F1-predicted_aligned_error_v6.png","plddt_mean":92.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MMUT","jax_strain_url":"https://www.jax.org/strain/search?query=MMUT"},"sequence":{"accession":"P22033","fasta_url":"https://rest.uniprot.org/uniprotkb/P22033.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P22033/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P22033"}},"corpus_meta":[{"pmid":"15833913","id":"PMC_15833913","title":"Functional 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discriminating heterogeneity in mut0 and mut- methylmalonic aciduria by interallelic complementation.","date":"1991","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/1670635","citation_count":33,"is_preprint":false},{"pmid":"8838655","id":"PMC_8838655","title":"Fission yeast Nda1 and Nda4, MCM homologs required for DNA replication, are constitutive nuclear proteins.","date":"1996","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/8838655","citation_count":33,"is_preprint":false},{"pmid":"19917723","id":"PMC_19917723","title":"Alternative mechanisms for coordinating polymerase alpha and MCM helicase.","date":"2009","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19917723","citation_count":32,"is_preprint":false},{"pmid":"32754920","id":"PMC_32754920","title":"Delineating the clinical spectrum of isolated methylmalonic acidurias: cblA and mut.","date":"2020","source":"Journal of inherited 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role of MCM proteins in cell proliferation and tumorigenesis].","date":"2010","source":"Postepy higieny i medycyny doswiadczalnej (Online)","url":"https://pubmed.ncbi.nlm.nih.gov/21160097","citation_count":25,"is_preprint":false},{"pmid":"20156367","id":"PMC_20156367","title":"Functional cooperation between FACT and MCM is coordinated with cell cycle and differential complex formation.","date":"2010","source":"Journal of biomedical science","url":"https://pubmed.ncbi.nlm.nih.gov/20156367","citation_count":25,"is_preprint":false},{"pmid":"28628830","id":"PMC_28628830","title":"Breviscapine (BVP) inhibits prostate cancer progression through damaging DNA by minichromosome maintenance protein-7 (MCM-7) modulation.","date":"2017","source":"Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie","url":"https://pubmed.ncbi.nlm.nih.gov/28628830","citation_count":25,"is_preprint":false},{"pmid":"39604733","id":"PMC_39604733","title":"MCM double hexamer loading visualized with human 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establishes replication timing patterns.","date":"2021","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33764973","citation_count":24,"is_preprint":false},{"pmid":"21984415","id":"PMC_21984415","title":"Molecular architecture of a multifunctional MCM complex.","date":"2011","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/21984415","citation_count":23,"is_preprint":false},{"pmid":"23284662","id":"PMC_23284662","title":"Mutation scanning using MUT-MAP, a high-throughput, microfluidic chip-based, multi-analyte panel.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23284662","citation_count":23,"is_preprint":false},{"pmid":"26504025","id":"PMC_26504025","title":"Expression of MCM-3 and MCM-7 in Primary Cutaneous T-cell Lymphomas.","date":"2015","source":"Anticancer 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reports","url":"https://pubmed.ncbi.nlm.nih.gov/34320356","citation_count":20,"is_preprint":false},{"pmid":"30069701","id":"PMC_30069701","title":"O-GlcNAc transferase associates with the MCM2-7 complex and its silencing destabilizes MCM-MCM interactions.","date":"2018","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/30069701","citation_count":20,"is_preprint":false},{"pmid":"21813639","id":"PMC_21813639","title":"Schizosaccharomyces pombe minichromosome maintenance-binding protein (MCM-BP) antagonizes MCM helicase.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21813639","citation_count":19,"is_preprint":false},{"pmid":"30407533","id":"PMC_30407533","title":"Genome-wide function of MCM-BP in Trypanosoma brucei DNA replication and transcription.","date":"2019","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/30407533","citation_count":19,"is_preprint":false},{"pmid":"33741931","id":"PMC_33741931","title":"Stabilisation of half MCM ring by Cdt1 during DNA insertion.","date":"2021","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/33741931","citation_count":18,"is_preprint":false},{"pmid":"22250201","id":"PMC_22250201","title":"The MCM-associated protein MCM-BP is important for human nuclear morphology.","date":"2012","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/22250201","citation_count":17,"is_preprint":false},{"pmid":"32761464","id":"PMC_32761464","title":"The Mut+ strain of Komagataella phaffii (Pichia pastoris) expresses PAOX1 5 and 10 times faster than Muts and Mut- strains: evidence that formaldehyde or/and formate are true inducers of PAOX1.","date":"2020","source":"Applied microbiology and biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/32761464","citation_count":17,"is_preprint":false},{"pmid":"36241664","id":"PMC_36241664","title":"Solving the MCM paradox by visualizing the scaffold of CMG helicase at active replisomes.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/36241664","citation_count":17,"is_preprint":false},{"pmid":"27592030","id":"PMC_27592030","title":"GINS complex protein Sld5 recruits SIK1 to activate MCM helicase during DNA replication.","date":"2016","source":"Cellular signalling","url":"https://pubmed.ncbi.nlm.nih.gov/27592030","citation_count":17,"is_preprint":false},{"pmid":"25712908","id":"PMC_25712908","title":"Evaluation of Mut(S) and Mut⁺ Pichia pastoris strains for membrane-bound catechol-O-methyltransferase biosynthesis.","date":"2015","source":"Applied biochemistry and biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/25712908","citation_count":16,"is_preprint":false},{"pmid":"36968087","id":"PMC_36968087","title":"EtcPRS Mut as a molecular marker of halofuginone resistance in Eimeria tenella and Toxoplasma gondii.","date":"2023","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/36968087","citation_count":16,"is_preprint":false},{"pmid":"34668645","id":"PMC_34668645","title":"Different mutations in the MMUT gene are associated with the effect of vitamin B12 in a cohort of 266 Chinese patients with mut-type methylmalonic acidemia: A retrospective study.","date":"2021","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/34668645","citation_count":15,"is_preprint":false},{"pmid":"31028111","id":"PMC_31028111","title":"Meiotic MCM Proteins Promote and Inhibit Crossovers During Meiotic Recombination.","date":"2019","source":"Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/31028111","citation_count":15,"is_preprint":false},{"pmid":"19540846","id":"PMC_19540846","title":"ATP binding and hydrolysis by Mcm2 regulate DNA binding by Mcm complexes.","date":"2009","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19540846","citation_count":15,"is_preprint":false},{"pmid":"38457222","id":"PMC_38457222","title":"A single-centre, real-world study of BTK inhibitors for the initial treatment of MYD88mut /CD79Bmut diffuse large B-cell lymphoma.","date":"2024","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/38457222","citation_count":14,"is_preprint":false},{"pmid":"22540012","id":"PMC_22540012","title":"Interactions of the human MCM-BP protein with MCM complex components and Dbf4.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22540012","citation_count":14,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":42950,"output_tokens":2029,"usd":0.079643,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8784,"output_tokens":2359,"usd":0.051448,"stage2_stop_reason":"end_turn"},"total_usd":0.131091,"stage1_batch_id":"msgbatch_01BbTCMyrRPyhtEq6b1MdwCN","stage2_batch_id":"msgbatch_011dEed5bbxYvTAaQWKJevxu","note":"batch pricing = 50% of standard"},"stage1_raw":"Looking through the abstracts, I need to identify papers about MMUT (methylmalonyl-CoA mutase, also known as MCM/MUT in the context of methylmalonic acidemia). Most papers in this corpus are about the MCM helicase complex (MCM2-7), which shares the \"MCM\" alias but is a completely different protein. I need to carefully separate:\n\n1. **MMUT/MUT** = methylmalonyl-CoA mutase (mitochondrial enzyme, cobalamin-dependent, causes methylmalonic acidemia when deficient)\n2. **MCM2-7** = minichromosome maintenance helicase complex (DNA replication)\n\nPapers about MMUT (the actual query gene): #27, #51, #53, #54, #62, #65, #68, #77, #78, #96\n\nAll other papers are about the MCM helicase complex (a completely different protein family) that share the \"MCM\" alias but are NOT the canonical MMUT gene product.\n\nNow extracting mechanistic discoveries from the MMUT-relevant papers:\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1990,\n      \"finding\": \"Methylmalonyl-CoA mutase (MCM/MMUT) apoenzyme deficiency in mut-type methylmalonic acidemia is associated with decreased steady-state MCM mRNA levels in several patient cell lines, indicating that mRNA expression defects contribute to enzyme deficiency; at least six independent alleles were delineated by haplotype, mRNA level, and biochemical phenotype, confirming allelic heterogeneity at the MUT locus.\",\n      \"method\": \"Southern blot, Northern blot, fibroblast cell line biochemical phenotyping (propionate incorporation assay)\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Northern blot demonstrating mRNA reduction plus biochemical phenotyping in primary fibroblasts, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"1968706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"A G354→A missense mutation in the MUT gene (Arg93→His) causes a mut(0) phenotype when transferred into a mut(0) cell line, but can contribute to apoenzyme function when transferred into mut(-) cell lines that complement with the original cell line (WG1130). This demonstrates interallelic complementation between subsets of mut(0) and mut(-) alleles, indicating that different mutations affect discrete components of MCM apoenzyme function, consistent with the enzyme functioning as a multimer.\",\n      \"method\": \"MUT cDNA cloning and sequencing, gene transfer into primary patient fibroblasts, somatic cell complementation, propionate incorporation assay\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution by gene transfer with mutagenesis and functional readout (propionate incorporation); complementation assay provides direct mechanistic evidence for domain function\",\n      \"pmids\": [\"1670635\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Mutations in the MUT gene cause either complete loss of methylmalonyl-CoA mutase activity (mut(0) phenotype) or residual cobalamin-dependent activity with elevated Km for adenosylcobalamin (mut(-) phenotype). Specific mutations define critical domains including the adenosylcobalamin (cobalamin) binding domain of the enzyme; a subset of alleles in both phenotypic classes exhibit interallelic complementation, indicating the enzyme functions as a multimer with distinct functional domains.\",\n      \"method\": \"Biochemical enzyme assay (methylmalonyl-CoA mutase activity, Km determination), somatic cell complementation, molecular cloning/sequencing\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — enzyme kinetic assays plus somatic cell complementation with molecular characterization, single lab review synthesis\",\n      \"pmids\": [\"8990001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In a cohort of 40 European mut-type MMA patients, 29 novel mutations in the MUT gene were identified. Twelve novel missense mutations were mapped onto a 3D homology model of human MCM based on the Propionibacterium shermanii enzyme structure, revealing their structural positions. Mutations causing the mut(-) phenotype (residual cobalamin-dependent activity) were enriched in the C-terminal cofactor (adenosylcobalamin) binding domain, while mut(0) mutations were more broadly distributed, indicating that the C-terminal domain is critical for cobalamin binding.\",\n      \"method\": \"Direct cDNA and gDNA sequencing, 3D homology modelling based on P. shermanii MCM crystal structure, biochemical phenotyping\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — sequencing combined with structural homology modelling and biochemical phenotype correlation; structural inference is based on homology not direct crystal structure of human enzyme\",\n      \"pmids\": [\"15643616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In a cohort of 151 mut-type MMA patients, Western blot analysis of 34 patient cell lines (27 mut(0) and 7 mut(-)) revealed reduced MUT protein levels for all tested lines, indicating that protein instability is a major mechanism of deficiency regardless of mutation type. Missense alleles causing the mut(-) subclass were almost exclusively located in the C-terminal cofactor binding domain.\",\n      \"method\": \"Western blot of patient fibroblast cell lines, biochemical propionate incorporation assay, MUT gene sequencing\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Western blot across 34 cell lines demonstrating protein instability as common mechanism; large cohort but single lab\",\n      \"pmids\": [\"27167370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Analysis of 266 Chinese mut-type MMA patients showed that specific MMUT gene mutations are associated with complete, partial, or nonresponsiveness to vitamin B12 (hydroxocobalamin) treatment, as measured by normalization of C3/C2 ratios and methylmalonic acid levels. Completely responsive patients harbored mutations including c.1663G>A, c.2080C>T, and c.1880A>G, while nonresponsive patients carried mutations such as c.1741C>T and c.1630_1631GG>TA, indicating that specific mutations differentially affect the cobalamin-dependent catalytic activity of MMUT.\",\n      \"method\": \"Retrospective cohort study with MMUT gene sequencing, blood acylcarnitine profiling, urine organic acid analysis, vitamin B12 responsiveness testing\",\n      \"journal\": \"Molecular genetics & genomic medicine\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — genotype-phenotype correlation across large cohort but no direct in vitro enzymatic reconstitution; mechanistic inference from clinical response data\",\n      \"pmids\": [\"34668645\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MMUT (methylmalonyl-CoA mutase) is a mitochondrial, adenosylcobalamin-dependent enzyme that converts methylmalonyl-CoA to succinyl-CoA; loss-of-function mutations in the MUT gene cause methylmalonic acidemia, with mut(0) alleles abolishing enzyme activity and mut(-) alleles reducing cobalamin affinity (elevated Km) through missense mutations enriched in the C-terminal cobalamin-binding domain, while protein instability is a common downstream consequence of most mutations; the enzyme functions as a multimer evidenced by interallelic complementation between certain mut(0) and mut(-) alleles, and specific mutations in the cobalamin-binding domain determine responsiveness to vitamin B12 treatment.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MMUT encodes methylmalonyl-CoA mutase, an adenosylcobalamin-dependent mitochondrial enzyme whose loss of function causes mut-type methylmalonic acidemia (MMA) [#1, #2]. Disease alleles fall into two biochemical classes: mut(0) mutations that abolish enzyme activity, and mut(-) mutations that preserve residual cobalamin-dependent activity but raise the Km for adenosylcobalamin [#2]. The enzyme is organized into discrete functional domains, with mut(-) missense alleles almost exclusively clustering in the C-terminal adenosylcobalamin (cofactor) binding domain, establishing this domain as critical for cofactor binding, while mut(0) mutations are more broadly distributed [#3, #4]. Interallelic complementation observed between certain mut(0) and mut(-) alleles indicates that the enzyme functions as a multimer in which distinct mutations impair separable components of apoenzyme function [#1, #2]. Across the spectrum of mutation types, reduced steady-state protein is a common downstream consequence, marking protein instability as a major shared mechanism of deficiency [#4]. The position of cobalamin-binding-domain mutations also tracks with clinical responsiveness to vitamin B12, with specific genotypes conferring complete, partial, or absent normalization of metabolite levels [#5].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Established that MMUT deficiency in mut-type MMA is genetically heterogeneous and that defective mRNA expression, not only coding mutations, contributes to enzyme loss.\",\n      \"evidence\": \"Southern/Northern blot and propionate incorporation phenotyping across patient fibroblast lines\",\n      \"pmids\": [\"1968706\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Did not define the specific lesions reducing mRNA\",\n        \"No correlation of mRNA defects with protein-level or catalytic consequences\"\n      ]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Demonstrated by gene transfer that a single missense allele behaves as mut(0) in one background yet supports apoenzyme function in complementing mut(-) backgrounds, providing direct evidence that distinct mutations hit separable functional components and that the enzyme acts as a multimer.\",\n      \"evidence\": \"MUT cDNA cloning/mutagenesis, gene transfer into patient fibroblasts, somatic cell complementation, propionate incorporation assay\",\n      \"pmids\": [\"1670635\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not map the structural basis of the complementation\",\n        \"Multimeric stoichiometry not directly determined\"\n      ]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Defined the two biochemical phenotype classes mechanistically — mut(0) as complete loss and mut(-) as residual activity with elevated Km for adenosylcobalamin — linking mutation class to specific catalytic/cofactor-binding defects.\",\n      \"evidence\": \"Enzyme activity and Km determination, somatic cell complementation, molecular sequencing\",\n      \"pmids\": [\"8990001\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Domain assignment not yet anchored to a structural model\",\n        \"Synthesis from existing alleles rather than systematic structure-function mapping\"\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mapped novel missense mutations onto a homology model to show mut(-) alleles concentrate in the C-terminal adenosylcobalamin-binding domain while mut(0) alleles distribute broadly, locating the cofactor-binding function structurally.\",\n      \"evidence\": \"cDNA/gDNA sequencing of 40 patients, 3D homology modelling on P. shermanii MCM, biochemical phenotyping\",\n      \"pmids\": [\"15643616\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Structural inference rests on homology, not a human crystal structure\",\n        \"Does not explain mechanism of broadly distributed mut(0) alleles\"\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed across 34 patient lines that MUT protein is reduced regardless of mut(0)/mut(-) class, identifying protein instability as a major shared mechanism of deficiency and reconfirming C-terminal localization of mut(-) missense alleles.\",\n      \"evidence\": \"Western blot of patient fibroblasts, propionate incorporation assay, MUT sequencing\",\n      \"pmids\": [\"27167370\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Degradation pathway responsible for instability not identified\",\n        \"Single-lab cohort; protein turnover not measured directly\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Correlated specific MMUT genotypes with complete, partial, or absent vitamin B12 responsiveness, extending mutation-class effects on cobalamin-dependent activity to clinical treatment response.\",\n      \"evidence\": \"Retrospective cohort of 266 patients with sequencing, acylcarnitine and organic acid profiling, B12 responsiveness testing\",\n      \"pmids\": [\"34668645\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No in vitro enzymatic reconstitution to confirm cofactor-affinity mechanism\",\n        \"Responsiveness inferred from metabolite normalization, not direct kinetics\",\n        \"Genotype-phenotype association may be confounded by allele combinations\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The molecular basis of multimer assembly, the degradation pathway driving protein instability, and a direct human enzyme structure resolving cofactor-binding mechanism remain undefined in the available corpus.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No human crystal structure in the corpus\",\n        \"Multimer stoichiometry and assembly determinants unresolved\",\n        \"Mechanism of mutation-induced protein turnover not established\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016853\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}