{"gene":"PMPCA","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1988,"finding":"The yeast mitochondrial matrix processing protease (MPP) consists of two non-identical, loosely associated subunits of ~48 kDa (MAS1/PMPCB) and ~51 kDa (MAS2/PMPCA); the larger subunit is the product of the MAS2 gene, and attempts to separate the two subunits caused loss of proteolytic activity, indicating both subunits are required for function.","method":"Purification of native metalloprotease complex, SDS-PAGE subunit identification, genetic complementation (MAS2 gene identification)","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — biochemical purification of native enzyme with subunit identification, replicated by two independent concurrent studies (PMIDs 2905264 and 3061808)","pmids":["2905264","3061808"],"is_preprint":false},{"year":1988,"finding":"MAS2 (PMPCA ortholog) encodes a 53-kDa protein localized to the mitochondrial matrix; it is homologous to MAS1 (PMPCB) and together they constitute the two subunits of the presequence-cleaving processing protease. The protease activity is temperature-sensitive in mas2 mutant cells, directly linking the MAS2 subunit to catalytic function.","method":"Gene cloning and sequencing, temperature-sensitive mutant analysis, subcellular fractionation/localization, enzymatic activity assay in mutant cells","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods (genetics, biochemistry, localization) in one study, replicated by companion paper (PMID 2905264)","pmids":["3061808"],"is_preprint":false},{"year":2015,"finding":"Human PMPCA (α-MPP) is the alpha subunit of the mitochondrial processing peptidase responsible for maturation of nuclear-encoded mitochondrial proteins; the disease-associated p.Ala377Thr mutation reduces α-MPP protein levels and impairs MPP function, including defective processing of frataxin in patient lymphoblastoid cells and fibroblasts.","method":"Western blot and functional assays in patient-derived lymphoblastoid cells and fibroblasts carrying homozygous PMPCA p.Ala377Thr mutation","journal":"Brain : a journal of neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient-derived cell functional assays with specific substrate (frataxin) processing readout; single lab but two cell types used","pmids":["25808372"],"is_preprint":false},{"year":2016,"finding":"Compound heterozygous mutations in PMPCA near the substrate-binding glycine-rich loop reduce α-MPP protein levels and impair frataxin production and processing in patient fibroblasts; these defects were rescued by expression of exogenous wild-type PMPCA cDNA, confirming the causal role of α-MPP in frataxin maturation.","method":"Immunofluorescence, western blot in patient fibroblasts, rescue experiment with exogenous wild-type PMPCA cDNA expression","journal":"Cold Spring Harbor molecular case studies","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — complementation/rescue experiment plus western blot in patient fibroblasts; single lab with orthogonal methods including functional rescue","pmids":["27148589"],"is_preprint":false},{"year":2009,"finding":"In Dictyostelium discoideum, α-MPP is synthesized as a larger precursor form (α-MPP(H)) that is cleaved to produce a smaller functional form (α-MPP(L)); MPP enzymatic activity depends on the presence of α-MPP(L), as antisense-suppressed cells retaining only α-MPP(H) showed no detectable MPP activity, and activity was restored upon reappearance of α-MPP(L).","method":"Antisense transformant analysis, western blot for α-MPP forms, MPP enzymatic activity assay during Dictyostelium development","journal":"Microbiology (Reading, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function antisense approach with direct enzymatic activity assay; single lab but multiple developmental time points and clear functional readout","pmids":["20019080"],"is_preprint":false},{"year":2017,"finding":"In Candida albicans, the Hsp40 chaperone Ydj1 physically interacts with the mitochondrial processing peptidases Mas1 and Mas2 (orthologs of PMPCB and PMPCA), and loss of MAS2 perturbs mitochondrial morphology and function; deletion of YDJ1 impairs import and processing of Su9, a substrate cleaved by Mas1/Mas2, placing PMPCA ortholog Mas2 downstream of Ydj1 in the mitochondrial import pathway.","method":"Protein interaction network mapping (co-purification/MS), genetic deletion analysis, mitochondrial morphology and function assays, import/processing assay for Su9 substrate","journal":"Microbial cell (Graz, Austria)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — interaction mapping plus genetic deletion with defined substrate processing readout; single lab, fungal ortholog context","pmids":["29082232"],"is_preprint":false},{"year":2022,"finding":"Frameshift PMPCA variants in DOA patients reduce α-MPP protein levels in fibroblasts and cause hyperconnection of the mitochondrial network (altered fusion-fission balance), without significantly affecting the respiratory chain machinery, indicating α-MPP influences mitochondrial morphodynamics independently of respiratory function.","method":"Western blot for α-MPP levels, immunofluorescence confocal microscopy of mitochondrial network morphology in patient fibroblasts","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — patient fibroblast western blot and imaging; single lab, two orthogonal cellular readouts but no mechanistic rescue experiment","pmids":["35885985"],"is_preprint":false},{"year":2023,"finding":"Novel compound heterozygous PMPCA variants (p.Tyr241Ser and p.Met251Val) decrease α-MPP protein levels and result in reduced and fragmented mitochondria in patient fibroblasts, linking α-MPP loss to mitochondrial morphology defects.","method":"Western blot for α-MPP levels, immunofluorescent confocal microscopy of mitochondrial morphology in patient skin fibroblasts","journal":"Neurology. Genetics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, two methods (western blot + imaging) but no mechanistic rescue or pathway placement beyond protein level reduction","pmids":["38235041"],"is_preprint":false}],"current_model":"PMPCA encodes α-MPP, the alpha subunit of the mitochondrial processing peptidase (MPP) heterdimer located in the mitochondrial matrix; together with the beta subunit (PMPCB/MAS1), it forms a zinc metalloprotease that cleaves N-terminal presequences from nuclear-encoded mitochondrial precursor proteins (including frataxin) upon their import, with both subunits required for proteolytic activity, and α-MPP itself undergoing processing from an inactive precursor to an active mature form that controls overall MPP activity."},"narrative":{"mechanistic_narrative":"PMPCA encodes α-MPP, one of the two non-identical subunits of the mitochondrial matrix processing peptidase (MPP), a zinc-metalloprotease that cleaves N-terminal presequences from nuclear-encoded mitochondrial precursor proteins upon import [PMID:2905264, PMID:3061808]. Originally defined in yeast as the MAS2 gene product, α-MPP is a matrix-localized protein homologous to its partner subunit MAS1/PMPCB, and the two subunits are loosely associated yet jointly required for proteolytic activity—separation or mutation of either abolishes presequence cleavage [PMID:2905264, PMID:3061808]. In humans, α-MPP catalyzes maturation of mitochondrial substrates including frataxin, and biallelic PMPCA mutations that lower α-MPP protein levels impair frataxin processing, a defect reversed by re-expression of wild-type PMPCA [PMID:25808372, PMID:27148589]. Beyond proteolytic maturation, loss of α-MPP perturbs mitochondrial network morphology—producing either hyperconnected or fragmented mitochondria—without overtly disrupting the respiratory chain, indicating a role in mitochondrial morphodynamics [PMID:35885985, PMID:38235041]. Disease-causing PMPCA variants underlie an autosomal recessive disorder featuring defective frataxin maturation, and frameshift variants are associated with dominant optic atrophy phenotypes [PMID:25808372, PMID:27148589, PMID:35885985]. α-MPP itself is synthesized as an inactive larger precursor that is processed to a smaller mature form on which MPP enzymatic activity depends [PMID:20019080].","teleology":[{"year":1988,"claim":"Established that the mitochondrial presequence-cleaving protease is a two-subunit enzyme and identified the larger subunit as the MAS2 (PMPCA) gene product, defining α-MPP as a required component of MPP activity.","evidence":"Native metalloprotease purification, SDS-PAGE subunit identification, and genetic complementation in yeast","pmids":["2905264","3061808"],"confidence":"High","gaps":["Catalytic contribution of each subunit not resolved","Structural basis of presequence recognition not defined"]},{"year":1988,"claim":"Localized the MAS2/α-MPP subunit to the mitochondrial matrix and directly tied it to catalysis by showing temperature-sensitive loss of protease activity in mas2 mutants.","evidence":"Gene cloning/sequencing, ts-mutant analysis, subcellular fractionation, and activity assays in yeast","pmids":["3061808"],"confidence":"High","gaps":["Human substrate repertoire not yet established","Mechanism of subunit cooperativity unknown"]},{"year":2009,"claim":"Showed that α-MPP requires conversion from a larger precursor form to a smaller mature form for MPP activity, identifying autoregulatory processing as a control point.","evidence":"Antisense suppression, western blot for α-MPP forms, and enzymatic activity assays across Dictyostelium development","pmids":["20019080"],"confidence":"Medium","gaps":["Protease responsible for α-MPP maturation not identified","Relevance of precursor processing in human cells untested"]},{"year":2015,"claim":"Connected human PMPCA to disease and to frataxin biology by showing a recessive mutation lowers α-MPP levels and impairs frataxin processing.","evidence":"Western blot and functional assays in patient lymphoblastoid cells and fibroblasts carrying p.Ala377Thr","pmids":["25808372"],"confidence":"Medium","gaps":["Single mutation; full substrate spectrum unaddressed","No rescue performed in this study"]},{"year":2016,"claim":"Confirmed causality of α-MPP loss in frataxin maturation defects by rescuing patient cells with wild-type PMPCA cDNA.","evidence":"Immunofluorescence, western blot, and complementation rescue in patient fibroblasts","pmids":["27148589"],"confidence":"Medium","gaps":["Structural impact of glycine-rich loop variants not modeled","Broader proteome processing defects not quantified"]},{"year":2017,"claim":"Placed the PMPCA ortholog within the mitochondrial import pathway by linking it to Hsp40 chaperone Ydj1, which acts upstream of Mas1/Mas2 in substrate import and processing.","evidence":"Co-purification/MS interaction mapping, gene deletion, and Su9 import/processing assays in Candida albicans","pmids":["29082232"],"confidence":"Medium","gaps":["Interaction not validated in human cells","Whether Ydj1 directly hands off substrates to MPP unresolved"]},{"year":2022,"claim":"Demonstrated a role for α-MPP in mitochondrial morphodynamics distinct from respiration, with frameshift variants causing network hyperconnection.","evidence":"Western blot and confocal microscopy of mitochondrial morphology in DOA patient fibroblasts","pmids":["35885985"],"confidence":"Medium","gaps":["Mechanism linking MPP activity to fusion-fission balance unknown","No rescue experiment"]},{"year":2023,"claim":"Extended the genotype-phenotype range, showing additional compound heterozygous variants reduce α-MPP and cause reduced, fragmented mitochondria.","evidence":"Western blot and confocal microscopy in patient skin fibroblasts","pmids":["38235041"],"confidence":"Low","gaps":["No mechanistic rescue or pathway placement beyond protein reduction","Opposite morphology direction versus prior report unexplained"]},{"year":null,"claim":"How α-MPP loss mechanistically reshapes the mitochondrial network, and the identity of the human protease maturing α-MPP itself, remain open.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of human MPP holoenzyme","Full human substrate proteome of MPP undefined","Link between processing defects and morphology phenotypes uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2,3]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,1]}],"localization":[{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2,3]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[5]}],"complexes":["mitochondrial processing peptidase (MPP)"],"partners":["PMPCB","YDJ1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q10713","full_name":"Mitochondrial-processing peptidase subunit alpha","aliases":["Alpha-MPP","Inactive zinc metalloprotease alpha","P-55"],"length_aa":525,"mass_kda":58.3,"function":"Substrate recognition and binding subunit of the essential mitochondrial processing protease (MPP), which cleaves the mitochondrial sequence off newly imported precursors proteins","subcellular_location":"Mitochondrion matrix; Mitochondrion inner membrane","url":"https://www.uniprot.org/uniprotkb/Q10713/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/PMPCA","classification":"Common Essential","n_dependent_lines":1196,"n_total_lines":1208,"dependency_fraction":0.9900662251655629},"opencell":{"profiled":true,"resolved_as":"INPP5E","ensg_id":"ENSG00000148384","cell_line_id":"CID000164","localizations":[{"compartment":"centrosome","grade":3},{"compartment":"vesicles","grade":3}],"interactors":[{"gene":"HNRNPH2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000164","total_profiled":1310},"omim":[{"mim_id":"613037","title":"INOSITOL POLYPHOSPHATE-5-PHOSPHATASE, 72-KD; INPP5E","url":"https://www.omim.org/entry/613037"},{"mim_id":"613036","title":"PEPTIDASE, MITOCHONDRIAL PROCESSING, ALPHA; PMPCA","url":"https://www.omim.org/entry/613036"},{"mim_id":"605490","title":"LON PEPTIDASE 1, MITOCHONDRIAL; LONP1","url":"https://www.omim.org/entry/605490"},{"mim_id":"213200","title":"SPINOCEREBELLAR ATAXIA, AUTOSOMAL RECESSIVE 2; SCAR2","url":"https://www.omim.org/entry/213200"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Mitochondria","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PMPCA"},"hgnc":{"alias_symbol":["KIAA0123","Alpha-MPP","MAS2"],"prev_symbol":["INPP5E","SCAR2","CLA1"]},"alphafold":{"accession":"Q10713","domains":[{"cath_id":"3.30.830.10","chopping":"68-272","consensus_level":"high","plddt":95.298,"start":68,"end":272},{"cath_id":"3.30.830.10","chopping":"297-512","consensus_level":"high","plddt":93.2632,"start":297,"end":512}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q10713","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q10713-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q10713-F1-predicted_aligned_error_v6.png","plddt_mean":88.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PMPCA","jax_strain_url":"https://www.jax.org/strain/search?query=PMPCA"},"sequence":{"accession":"Q10713","fasta_url":"https://rest.uniprot.org/uniprotkb/Q10713.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q10713/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q10713"}},"corpus_meta":[{"pmid":"2905264","id":"PMC_2905264","title":"Import of proteins into yeast mitochondria: the purified matrix processing protease contains two subunits which are encoded by the nuclear MAS1 and MAS2 genes.","date":"1988","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/2905264","citation_count":191,"is_preprint":false},{"pmid":"3061808","id":"PMC_3061808","title":"Import of proteins into yeast mitochondria: the nuclear MAS2 gene encodes a component of the processing protease that is homologous to the MAS1-encoded subunit.","date":"1988","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/3061808","citation_count":129,"is_preprint":false},{"pmid":"25808372","id":"PMC_25808372","title":"PMPCA mutations cause abnormal mitochondrial protein processing in patients with non-progressive cerebellar ataxia.","date":"2015","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/25808372","citation_count":62,"is_preprint":false},{"pmid":"20716485","id":"PMC_20716485","title":"Purification and characterization of an extracellular laccase from the anthracene-degrading fungus Fusarium solani MAS2.","date":"2010","source":"Bioresource technology","url":"https://pubmed.ncbi.nlm.nih.gov/20716485","citation_count":55,"is_preprint":false},{"pmid":"27148589","id":"PMC_27148589","title":"Mutations in the substrate binding glycine-rich loop of the mitochondrial processing peptidase-α protein (PMPCA) cause a severe mitochondrial disease.","date":"2016","source":"Cold Spring Harbor molecular case studies","url":"https://pubmed.ncbi.nlm.nih.gov/27148589","citation_count":35,"is_preprint":false},{"pmid":"29082232","id":"PMC_29082232","title":"Ydj1 governs fungal morphogenesis and stress response, and facilitates mitochondrial protein import via Mas1 and Mas2.","date":"2017","source":"Microbial cell (Graz, Austria)","url":"https://pubmed.ncbi.nlm.nih.gov/29082232","citation_count":30,"is_preprint":false},{"pmid":"33272776","id":"PMC_33272776","title":"A severe form of autosomal recessive spinocerebellar ataxia associated with novel PMPCA variants.","date":"2020","source":"Brain & development","url":"https://pubmed.ncbi.nlm.nih.gov/33272776","citation_count":11,"is_preprint":false},{"pmid":"35885985","id":"PMC_35885985","title":"Next-Generation Sequencing Identifies Novel PMPCA Variants in Patients with Late-Onset Dominant Optic Atrophy.","date":"2022","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/35885985","citation_count":3,"is_preprint":false},{"pmid":"20019080","id":"PMC_20019080","title":"Mitochondrial processing peptidase activity is controlled by the processing of alpha-MPP during development in Dictyostelium discoideum.","date":"2009","source":"Microbiology (Reading, England)","url":"https://pubmed.ncbi.nlm.nih.gov/20019080","citation_count":3,"is_preprint":false},{"pmid":"38235041","id":"PMC_38235041","title":"PMPCA-Related Encephalopathy: Novel Variants, Phenotype Extension, and Mitochondrial Morphology.","date":"2023","source":"Neurology. Genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38235041","citation_count":2,"is_preprint":false},{"pmid":"39554679","id":"PMC_39554679","title":"Clinical whole Exome Sequencing Reveals Novel Homozygous Missense Variant in the PMPCA Gene causing Autosomal Recessive Spinocerebellar Ataxia.","date":"2024","source":"Pakistan journal of medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/39554679","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6902,"output_tokens":2103,"usd":0.026125,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9193,"output_tokens":2623,"usd":0.05577,"stage2_stop_reason":"end_turn"},"total_usd":0.081895,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1988,\n      \"finding\": \"The yeast mitochondrial matrix processing protease (MPP) consists of two non-identical, loosely associated subunits of ~48 kDa (MAS1/PMPCB) and ~51 kDa (MAS2/PMPCA); the larger subunit is the product of the MAS2 gene, and attempts to separate the two subunits caused loss of proteolytic activity, indicating both subunits are required for function.\",\n      \"method\": \"Purification of native metalloprotease complex, SDS-PAGE subunit identification, genetic complementation (MAS2 gene identification)\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biochemical purification of native enzyme with subunit identification, replicated by two independent concurrent studies (PMIDs 2905264 and 3061808)\",\n      \"pmids\": [\"2905264\", \"3061808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"MAS2 (PMPCA ortholog) encodes a 53-kDa protein localized to the mitochondrial matrix; it is homologous to MAS1 (PMPCB) and together they constitute the two subunits of the presequence-cleaving processing protease. The protease activity is temperature-sensitive in mas2 mutant cells, directly linking the MAS2 subunit to catalytic function.\",\n      \"method\": \"Gene cloning and sequencing, temperature-sensitive mutant analysis, subcellular fractionation/localization, enzymatic activity assay in mutant cells\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods (genetics, biochemistry, localization) in one study, replicated by companion paper (PMID 2905264)\",\n      \"pmids\": [\"3061808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Human PMPCA (α-MPP) is the alpha subunit of the mitochondrial processing peptidase responsible for maturation of nuclear-encoded mitochondrial proteins; the disease-associated p.Ala377Thr mutation reduces α-MPP protein levels and impairs MPP function, including defective processing of frataxin in patient lymphoblastoid cells and fibroblasts.\",\n      \"method\": \"Western blot and functional assays in patient-derived lymphoblastoid cells and fibroblasts carrying homozygous PMPCA p.Ala377Thr mutation\",\n      \"journal\": \"Brain : a journal of neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient-derived cell functional assays with specific substrate (frataxin) processing readout; single lab but two cell types used\",\n      \"pmids\": [\"25808372\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Compound heterozygous mutations in PMPCA near the substrate-binding glycine-rich loop reduce α-MPP protein levels and impair frataxin production and processing in patient fibroblasts; these defects were rescued by expression of exogenous wild-type PMPCA cDNA, confirming the causal role of α-MPP in frataxin maturation.\",\n      \"method\": \"Immunofluorescence, western blot in patient fibroblasts, rescue experiment with exogenous wild-type PMPCA cDNA expression\",\n      \"journal\": \"Cold Spring Harbor molecular case studies\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — complementation/rescue experiment plus western blot in patient fibroblasts; single lab with orthogonal methods including functional rescue\",\n      \"pmids\": [\"27148589\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In Dictyostelium discoideum, α-MPP is synthesized as a larger precursor form (α-MPP(H)) that is cleaved to produce a smaller functional form (α-MPP(L)); MPP enzymatic activity depends on the presence of α-MPP(L), as antisense-suppressed cells retaining only α-MPP(H) showed no detectable MPP activity, and activity was restored upon reappearance of α-MPP(L).\",\n      \"method\": \"Antisense transformant analysis, western blot for α-MPP forms, MPP enzymatic activity assay during Dictyostelium development\",\n      \"journal\": \"Microbiology (Reading, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function antisense approach with direct enzymatic activity assay; single lab but multiple developmental time points and clear functional readout\",\n      \"pmids\": [\"20019080\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In Candida albicans, the Hsp40 chaperone Ydj1 physically interacts with the mitochondrial processing peptidases Mas1 and Mas2 (orthologs of PMPCB and PMPCA), and loss of MAS2 perturbs mitochondrial morphology and function; deletion of YDJ1 impairs import and processing of Su9, a substrate cleaved by Mas1/Mas2, placing PMPCA ortholog Mas2 downstream of Ydj1 in the mitochondrial import pathway.\",\n      \"method\": \"Protein interaction network mapping (co-purification/MS), genetic deletion analysis, mitochondrial morphology and function assays, import/processing assay for Su9 substrate\",\n      \"journal\": \"Microbial cell (Graz, Austria)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — interaction mapping plus genetic deletion with defined substrate processing readout; single lab, fungal ortholog context\",\n      \"pmids\": [\"29082232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Frameshift PMPCA variants in DOA patients reduce α-MPP protein levels in fibroblasts and cause hyperconnection of the mitochondrial network (altered fusion-fission balance), without significantly affecting the respiratory chain machinery, indicating α-MPP influences mitochondrial morphodynamics independently of respiratory function.\",\n      \"method\": \"Western blot for α-MPP levels, immunofluorescence confocal microscopy of mitochondrial network morphology in patient fibroblasts\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — patient fibroblast western blot and imaging; single lab, two orthogonal cellular readouts but no mechanistic rescue experiment\",\n      \"pmids\": [\"35885985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Novel compound heterozygous PMPCA variants (p.Tyr241Ser and p.Met251Val) decrease α-MPP protein levels and result in reduced and fragmented mitochondria in patient fibroblasts, linking α-MPP loss to mitochondrial morphology defects.\",\n      \"method\": \"Western blot for α-MPP levels, immunofluorescent confocal microscopy of mitochondrial morphology in patient skin fibroblasts\",\n      \"journal\": \"Neurology. Genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, two methods (western blot + imaging) but no mechanistic rescue or pathway placement beyond protein level reduction\",\n      \"pmids\": [\"38235041\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PMPCA encodes α-MPP, the alpha subunit of the mitochondrial processing peptidase (MPP) heterdimer located in the mitochondrial matrix; together with the beta subunit (PMPCB/MAS1), it forms a zinc metalloprotease that cleaves N-terminal presequences from nuclear-encoded mitochondrial precursor proteins (including frataxin) upon their import, with both subunits required for proteolytic activity, and α-MPP itself undergoing processing from an inactive precursor to an active mature form that controls overall MPP activity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PMPCA encodes α-MPP, one of the two non-identical subunits of the mitochondrial matrix processing peptidase (MPP), a zinc-metalloprotease that cleaves N-terminal presequences from nuclear-encoded mitochondrial precursor proteins upon import [#0, #1]. Originally defined in yeast as the MAS2 gene product, α-MPP is a matrix-localized protein homologous to its partner subunit MAS1/PMPCB, and the two subunits are loosely associated yet jointly required for proteolytic activity—separation or mutation of either abolishes presequence cleavage [#0, #1]. In humans, α-MPP catalyzes maturation of mitochondrial substrates including frataxin, and biallelic PMPCA mutations that lower α-MPP protein levels impair frataxin processing, a defect reversed by re-expression of wild-type PMPCA [#2, #3]. Beyond proteolytic maturation, loss of α-MPP perturbs mitochondrial network morphology—producing either hyperconnected or fragmented mitochondria—without overtly disrupting the respiratory chain, indicating a role in mitochondrial morphodynamics [#6, #7]. Disease-causing PMPCA variants underlie an autosomal recessive disorder featuring defective frataxin maturation, and frameshift variants are associated with dominant optic atrophy phenotypes [#2, #3, #6]. α-MPP itself is synthesized as an inactive larger precursor that is processed to a smaller mature form on which MPP enzymatic activity depends [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Established that the mitochondrial presequence-cleaving protease is a two-subunit enzyme and identified the larger subunit as the MAS2 (PMPCA) gene product, defining α-MPP as a required component of MPP activity.\",\n      \"evidence\": \"Native metalloprotease purification, SDS-PAGE subunit identification, and genetic complementation in yeast\",\n      \"pmids\": [\"2905264\", \"3061808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic contribution of each subunit not resolved\", \"Structural basis of presequence recognition not defined\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Localized the MAS2/α-MPP subunit to the mitochondrial matrix and directly tied it to catalysis by showing temperature-sensitive loss of protease activity in mas2 mutants.\",\n      \"evidence\": \"Gene cloning/sequencing, ts-mutant analysis, subcellular fractionation, and activity assays in yeast\",\n      \"pmids\": [\"3061808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Human substrate repertoire not yet established\", \"Mechanism of subunit cooperativity unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed that α-MPP requires conversion from a larger precursor form to a smaller mature form for MPP activity, identifying autoregulatory processing as a control point.\",\n      \"evidence\": \"Antisense suppression, western blot for α-MPP forms, and enzymatic activity assays across Dictyostelium development\",\n      \"pmids\": [\"20019080\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Protease responsible for α-MPP maturation not identified\", \"Relevance of precursor processing in human cells untested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected human PMPCA to disease and to frataxin biology by showing a recessive mutation lowers α-MPP levels and impairs frataxin processing.\",\n      \"evidence\": \"Western blot and functional assays in patient lymphoblastoid cells and fibroblasts carrying p.Ala377Thr\",\n      \"pmids\": [\"25808372\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single mutation; full substrate spectrum unaddressed\", \"No rescue performed in this study\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Confirmed causality of α-MPP loss in frataxin maturation defects by rescuing patient cells with wild-type PMPCA cDNA.\",\n      \"evidence\": \"Immunofluorescence, western blot, and complementation rescue in patient fibroblasts\",\n      \"pmids\": [\"27148589\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural impact of glycine-rich loop variants not modeled\", \"Broader proteome processing defects not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Placed the PMPCA ortholog within the mitochondrial import pathway by linking it to Hsp40 chaperone Ydj1, which acts upstream of Mas1/Mas2 in substrate import and processing.\",\n      \"evidence\": \"Co-purification/MS interaction mapping, gene deletion, and Su9 import/processing assays in Candida albicans\",\n      \"pmids\": [\"29082232\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interaction not validated in human cells\", \"Whether Ydj1 directly hands off substrates to MPP unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated a role for α-MPP in mitochondrial morphodynamics distinct from respiration, with frameshift variants causing network hyperconnection.\",\n      \"evidence\": \"Western blot and confocal microscopy of mitochondrial morphology in DOA patient fibroblasts\",\n      \"pmids\": [\"35885985\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking MPP activity to fusion-fission balance unknown\", \"No rescue experiment\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Extended the genotype-phenotype range, showing additional compound heterozygous variants reduce α-MPP and cause reduced, fragmented mitochondria.\",\n      \"evidence\": \"Western blot and confocal microscopy in patient skin fibroblasts\",\n      \"pmids\": [\"38235041\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No mechanistic rescue or pathway placement beyond protein reduction\", \"Opposite morphology direction versus prior report unexplained\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How α-MPP loss mechanistically reshapes the mitochondrial network, and the identity of the human protease maturing α-MPP itself, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of human MPP holoenzyme\", \"Full human substrate proteome of MPP undefined\", \"Link between processing defects and morphology phenotypes uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2, 3]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"mitochondrial processing peptidase (MPP)\"],\n    \"partners\": [\"PMPCB\", \"YDJ1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}