{"gene":"PEX12","run_date":"2026-04-29T11:37:58","timeline":{"discoveries":[{"year":1997,"finding":"Human PEX12 localizes to the peroxisome membrane and is essential for peroxisomal matrix protein import; expression of PEX12 restored peroxisomal protein import in fibroblasts from PBD complement group 3 patients.","method":"Subcellular fractionation, functional complementation in patient fibroblasts, mutation analysis","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (localization, functional complementation, patient mutations), replicated by multiple labs","pmids":["9090384"],"is_preprint":false},{"year":1998,"finding":"PEX12 is an integral peroxisomal membrane protein with two transmembrane segments and a cytosol-facing C-terminal RING finger (zinc finger) domain; both the N- and C-terminal cytoplasmic regions are essential for biological function.","method":"Epitope-tagged expression, topology analysis, truncation and site-directed mutagenesis, functional complementation in CHO mutant cells","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — mutagenesis combined with functional assay and complementation, replicated by other labs","pmids":["9632816"],"is_preprint":false},{"year":1999,"finding":"The zinc RING domain of PEX12 directly binds both PEX5 (the PTS1 import receptor) and PEX10 (another peroxisomal membrane protein); a patient missense mutation S320F in the zinc-binding domain reduces these interactions, and overexpression of PEX5 or PEX10 suppresses this mutation.","method":"Two-hybrid assay, blot overlay, co-immunoprecipitation, genetic epistasis (suppressor overexpression)","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal binding methods plus genetic epistasis, patient mutation validation","pmids":["10562279"],"is_preprint":false},{"year":1999,"finding":"Loss of PEX12 or PEX10 does not reduce the docking of PEX5 to peroxisomes, demonstrating that PEX12 acts downstream of receptor docking in the matrix protein import pathway.","method":"Loss-of-function cell lines, subcellular fractionation/PEX5 association assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — clean genetic epistasis placing PEX12 downstream of docking with direct localization evidence","pmids":["10562279"],"is_preprint":false},{"year":2002,"finding":"The PEX12 zinc RING domain interacts with the PTS1-binding domain of PEX5 but does not alter the kinetics of PEX5-PTS1 binding, indicating PEX12 interacts with PEX5 independently of cargo recognition.","method":"Fluorescence anisotropy binding assay with purified recombinant proteins","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 — in vitro reconstituted binding assay, single lab","pmids":["12456682"],"is_preprint":false},{"year":2009,"finding":"Pex12 (yeast ortholog) functions as an E3 ubiquitin-protein isopeptide ligase (RING peroxin) and specifically facilitates Pex4 (Ubc10)-dependent monoubiquitination of the import receptor Pex5, which is required for receptor recycling.","method":"In vitro ubiquitination assay, mutagenesis, yeast genetics","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro enzymatic reconstitution with mutagenesis, highly cited foundational study","pmids":["19687296"],"is_preprint":false},{"year":2025,"finding":"The yeast Pex2/Pex10/Pex12 complex functions as an E3-ubiquitin ligase module; Pex8 interacts with the N-terminal domain of Pex5 via a HEAT repeat array and promotes assembly with the Pex2/Pex10/Pex12 complex to initiate receptor recycling after cargo translocation.","method":"Cryo-EM structure, in vitro binding assays, mutagenesis, peroxisomal import functional assays in yeast","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 — structural and functional data with mutagenesis, but preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.08.30.673231"],"is_preprint":true}],"current_model":"PEX12 is an integral peroxisomal membrane protein with a cytosol-facing C-terminal RING finger domain that acts downstream of PEX5 receptor docking: it interacts directly with PEX5 and PEX10 via its RING domain, and functions as the E3 ubiquitin ligase (working with the Ubc4/Pex4 conjugating enzyme) that monoubiquitinates PEX5 to drive receptor recycling and sustain iterative rounds of peroxisomal matrix protein import."},"narrative":{"teleology":[{"year":1997,"claim":"Establishing that PEX12 is a peroxisomal membrane protein whose loss causes a human peroxisome biogenesis disorder answered the question of which gene underlies PBD complementation group 3 and linked PEX12 directly to matrix protein import.","evidence":"Functional complementation of patient fibroblasts, subcellular fractionation, and mutation analysis","pmids":["9090384"],"confidence":"High","gaps":["Molecular mechanism by which PEX12 supports import was unknown","Topology and domain architecture uncharacterized"]},{"year":1998,"claim":"Determination of PEX12 membrane topology and identification of its RING finger domain established the structural framework needed to understand its mechanistic role, showing that both cytoplasmic regions are functionally essential.","evidence":"Epitope-tagged topology analysis, truncation and site-directed mutagenesis with functional complementation in CHO mutant cells","pmids":["9632816"],"confidence":"High","gaps":["Binding partners of the RING domain were unknown","Enzymatic activity of the RING domain not yet tested"]},{"year":1999,"claim":"Demonstration that the PEX12 RING domain directly binds both PEX5 and PEX10, and that PEX12 acts downstream of receptor docking, placed PEX12 at a post-docking step in the import cycle and identified its key interaction partners.","evidence":"Two-hybrid, co-immunoprecipitation, blot overlay, genetic suppression, and PEX5 fractionation in loss-of-function cell lines","pmids":["10562279"],"confidence":"High","gaps":["Whether PEX12 interaction with PEX5 requires cargo binding was unresolved","Catalytic function of PEX12 not yet demonstrated"]},{"year":2002,"claim":"Showing that PEX12 binds the PTS1-binding domain of PEX5 without altering cargo recognition kinetics established that PEX12–PEX5 interaction is independent of cargo loading, separating receptor engagement from cargo release.","evidence":"Fluorescence anisotropy binding assay with purified recombinant proteins in vitro","pmids":["12456682"],"confidence":"Medium","gaps":["In vitro binding only; in vivo significance of cargo-independent interaction not directly tested","No enzymatic assay performed"]},{"year":2009,"claim":"Reconstitution of PEX12-dependent monoubiquitination of PEX5 via the Pex4/Ubc10 conjugating enzyme identified PEX12 as the E3 ligase responsible for receptor recycling, providing the central enzymatic mechanism of the import cycle.","evidence":"In vitro ubiquitination reconstitution with purified components, RING mutagenesis, and yeast genetics","pmids":["19687296"],"confidence":"High","gaps":["Relative contributions of PEX2, PEX10, and PEX12 RING domains within the complex were not fully resolved","Structural basis of the trimeric E3 complex unknown","Whether mammalian PEX12 uses the same E2 enzyme not directly shown"]},{"year":null,"claim":"A high-resolution structural understanding of the mammalian PEX2/PEX10/PEX12 complex and the mechanism by which cargo translocation is coupled to PEX5 ubiquitination and recycling remains to be established.","evidence":"","pmids":[],"confidence":"High","gaps":["No atomic structure of the mammalian PEX12-containing E3 complex","Mechanism coupling cargo release to PEX5 ubiquitination is unclear","Regulation of PEX12 ligase activity in vivo is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[5]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[5]}],"localization":[{"term_id":"GO:0043226","term_label":"organelle","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,3,5]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[0,5]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[5]}],"complexes":["PEX2/PEX10/PEX12 E3 ligase complex"],"partners":["PEX5","PEX10","PEX4"],"other_free_text":[]},"mechanistic_narrative":"PEX12 is an integral peroxisomal membrane protein with a RING finger E3 ubiquitin ligase domain that is essential for peroxisomal matrix protein import. It contains two transmembrane segments and a cytosol-facing C-terminal RING domain that directly binds the PTS1 import receptor PEX5 and the partner RING peroxin PEX10; this interaction occurs independently of PEX5 cargo recognition and acts downstream of PEX5 docking at the peroxisomal membrane [PMID:9632816, PMID:10562279, PMID:12456682]. As part of the PEX2/PEX10/PEX12 E3 ligase complex, PEX12 catalyzes Pex4(Ubc10)-dependent monoubiquitination of PEX5, which is required for receptor recycling and sustained rounds of matrix protein import [PMID:19687296]. Loss-of-function mutations in PEX12 cause peroxisome biogenesis disorder (complementation group 3), as demonstrated by restoration of peroxisomal protein import upon PEX12 expression in patient fibroblasts [PMID:9090384]."},"prefetch_data":{"uniprot":{"accession":"O00623","full_name":"Peroxisome assembly protein 12","aliases":["Peroxin-12","Peroxisome assembly factor 3","PAF-3"],"length_aa":359,"mass_kda":40.8,"function":"Component of a retrotranslocation channel required for peroxisome organization by mediating export of the PEX5 receptor from peroxisomes to the cytosol, thereby promoting PEX5 recycling (PubMed:24662292, PubMed:9354782, PubMed:9632816). The retrotranslocation channel is composed of PEX2, PEX10 and PEX12; each subunit contributing transmembrane segments that coassemble into an open channel that specifically allows the passage of PEX5 through the peroxisomal membrane (By similarity). PEX12 also regulates PEX5 recycling by activating the E3 ubiquitin-protein ligase activity of PEX10 (PubMed:24662292). When PEX5 recycling is compromised, PEX12 stimulates PEX10-mediated polyubiquitination of PEX5, leading to its subsequent degradation (By similarity)","subcellular_location":"Peroxisome membrane","url":"https://www.uniprot.org/uniprotkb/O00623/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PEX12","classification":"Not Classified","n_dependent_lines":14,"n_total_lines":1208,"dependency_fraction":0.011589403973509934},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PEX12","total_profiled":1310},"omim":[{"mim_id":"614958","title":"SCHLAFEN FAMILY, MEMBER 14; SLFN14","url":"https://www.omim.org/entry/614958"},{"mim_id":"614957","title":"SCHLAFEN FAMILY, MEMBER 13; SLFN13","url":"https://www.omim.org/entry/614957"},{"mim_id":"614956","title":"SCHLAFEN FAMILY, MEMBER 12-LIKE; SLFN12L","url":"https://www.omim.org/entry/614956"},{"mim_id":"614955","title":"SCHLAFEN FAMILY, MEMBER 12; SLFN12","url":"https://www.omim.org/entry/614955"},{"mim_id":"614953","title":"SCHLAFEN FAMILY, MEMBER 11; SLFN11","url":"https://www.omim.org/entry/614953"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PEX12"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O00623","domains":[{"cath_id":"-","chopping":"16-219","consensus_level":"high","plddt":84.6492,"start":16,"end":219},{"cath_id":"3.30.40.10","chopping":"297-359","consensus_level":"medium","plddt":86.8284,"start":297,"end":359}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00623","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00623-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00623-F1-predicted_aligned_error_v6.png","plddt_mean":81.06},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PEX12","jax_strain_url":"https://www.jax.org/strain/search?query=PEX12"},"sequence":{"accession":"O00623","fasta_url":"https://rest.uniprot.org/uniprotkb/O00623.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00623/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00623"}},"corpus_meta":[{"pmid":"19687296","id":"PMC_19687296","title":"Pex2 and pex12 function as protein-ubiquitin ligases in peroxisomal protein import.","date":"2009","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19687296","citation_count":162,"is_preprint":false},{"pmid":"9090384","id":"PMC_9090384","title":"Isolation of the human PEX12 gene, mutated in group 3 of the peroxisome biogenesis disorders.","date":"1997","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9090384","citation_count":123,"is_preprint":false},{"pmid":"10562279","id":"PMC_10562279","title":"PEX12 interacts with PEX5 and PEX10 and acts downstream of receptor docking in peroxisomal matrix protein import.","date":"1999","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/10562279","citation_count":115,"is_preprint":false},{"pmid":"9632816","id":"PMC_9632816","title":"PEX12, the pathogenic gene of group III Zellweger syndrome: cDNA cloning by functional complementation on a CHO cell mutant, patient analysis, and characterization of PEX12p.","date":"1998","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/9632816","citation_count":92,"is_preprint":false},{"pmid":"16113209","id":"PMC_16113209","title":"The Arabidopsis PEX12 gene is required for peroxisome biogenesis and is essential for development.","date":"2005","source":"Plant physiology","url":"https://pubmed.ncbi.nlm.nih.gov/16113209","citation_count":83,"is_preprint":false},{"pmid":"16813573","id":"PMC_16813573","title":"The Arabidopsis pex12 and pex13 mutants are defective in both PTS1- and PTS2-dependent protein transport to peroxisomes.","date":"2006","source":"The Plant journal : for cell and molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/16813573","citation_count":68,"is_preprint":false},{"pmid":"20679226","id":"PMC_20679226","title":"Different functions of the C3HC4 zinc RING finger peroxins PEX10, PEX2, and PEX12 in peroxisome formation and matrix protein import.","date":"2010","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/20679226","citation_count":47,"is_preprint":false},{"pmid":"17041890","id":"PMC_17041890","title":"Identification of novel mutations in PEX2, PEX6, PEX10, PEX12, and PEX13 in Zellweger spectrum patients.","date":"2006","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/17041890","citation_count":39,"is_preprint":false},{"pmid":"16388862","id":"PMC_16388862","title":"Identification and characterization of three peroxins--PEX6, PEX10 and PEX12--involved in glycosome biogenesis in Trypanosoma brucei.","date":"2005","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/16388862","citation_count":37,"is_preprint":false},{"pmid":"17534573","id":"PMC_17534573","title":"A novel PEX12 mutation identified as the cause of a peroxisomal biogenesis disorder with mild clinical phenotype, mild biochemical abnormalities in fibroblasts and a mosaic catalase immunofluorescence pattern, even at 40 degrees C.","date":"2007","source":"Journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/17534573","citation_count":32,"is_preprint":false},{"pmid":"12456682","id":"PMC_12456682","title":"PEX5 binds the PTS1 independently of Hsp70 and the peroxin PEX12.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12456682","citation_count":30,"is_preprint":false},{"pmid":"14571262","id":"PMC_14571262","title":"Novel mutations in the PEX12 gene of patients with a peroxisome biogenesis disorder.","date":"2004","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/14571262","citation_count":16,"is_preprint":false},{"pmid":"26094004","id":"PMC_26094004","title":"A novel mutation in the PEX12 gene causing a peroxisomal biogenesis disorder.","date":"2015","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/26094004","citation_count":5,"is_preprint":false},{"pmid":"26947510","id":"PMC_26947510","title":"Effect of l-Arginine in One Patient with Peroxisome Biogenesis Disorder due to PEX12 Deficiency.","date":"2016","source":"Neuropediatrics","url":"https://pubmed.ncbi.nlm.nih.gov/26947510","citation_count":5,"is_preprint":false},{"pmid":"33123925","id":"PMC_33123925","title":"A founder mutation in PEX12 among Egyptian patients in peroxisomal biogenesis disorder.","date":"2020","source":"Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology","url":"https://pubmed.ncbi.nlm.nih.gov/33123925","citation_count":2,"is_preprint":false},{"pmid":"40718457","id":"PMC_40718457","title":"Evaluation of Antimicrobial Activity of Novel Chimeric M-PEX12 Peptide Against Acinetobacter baumannii.","date":"2025","source":"Iranian journal of pharmaceutical research : IJPR","url":"https://pubmed.ncbi.nlm.nih.gov/40718457","citation_count":2,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.30.673231","title":"Structure of Pex8 in complex with peroxisomal receptor Pex5 reveals its essential role in peroxisomal cargo translocation","date":"2025-09-02","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.30.673231","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9874,"output_tokens":1528,"usd":0.026271},"stage2":{"model":"claude-opus-4-6","input_tokens":4781,"output_tokens":1618,"usd":0.096532},"total_usd":0.122803,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"Human PEX12 localizes to the peroxisome membrane and is essential for peroxisomal matrix protein import; expression of PEX12 restored peroxisomal protein import in fibroblasts from PBD complement group 3 patients.\",\n      \"method\": \"Subcellular fractionation, functional complementation in patient fibroblasts, mutation analysis\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (localization, functional complementation, patient mutations), replicated by multiple labs\",\n      \"pmids\": [\"9090384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"PEX12 is an integral peroxisomal membrane protein with two transmembrane segments and a cytosol-facing C-terminal RING finger (zinc finger) domain; both the N- and C-terminal cytoplasmic regions are essential for biological function.\",\n      \"method\": \"Epitope-tagged expression, topology analysis, truncation and site-directed mutagenesis, functional complementation in CHO mutant cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — mutagenesis combined with functional assay and complementation, replicated by other labs\",\n      \"pmids\": [\"9632816\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The zinc RING domain of PEX12 directly binds both PEX5 (the PTS1 import receptor) and PEX10 (another peroxisomal membrane protein); a patient missense mutation S320F in the zinc-binding domain reduces these interactions, and overexpression of PEX5 or PEX10 suppresses this mutation.\",\n      \"method\": \"Two-hybrid assay, blot overlay, co-immunoprecipitation, genetic epistasis (suppressor overexpression)\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal binding methods plus genetic epistasis, patient mutation validation\",\n      \"pmids\": [\"10562279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Loss of PEX12 or PEX10 does not reduce the docking of PEX5 to peroxisomes, demonstrating that PEX12 acts downstream of receptor docking in the matrix protein import pathway.\",\n      \"method\": \"Loss-of-function cell lines, subcellular fractionation/PEX5 association assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean genetic epistasis placing PEX12 downstream of docking with direct localization evidence\",\n      \"pmids\": [\"10562279\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The PEX12 zinc RING domain interacts with the PTS1-binding domain of PEX5 but does not alter the kinetics of PEX5-PTS1 binding, indicating PEX12 interacts with PEX5 independently of cargo recognition.\",\n      \"method\": \"Fluorescence anisotropy binding assay with purified recombinant proteins\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstituted binding assay, single lab\",\n      \"pmids\": [\"12456682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Pex12 (yeast ortholog) functions as an E3 ubiquitin-protein isopeptide ligase (RING peroxin) and specifically facilitates Pex4 (Ubc10)-dependent monoubiquitination of the import receptor Pex5, which is required for receptor recycling.\",\n      \"method\": \"In vitro ubiquitination assay, mutagenesis, yeast genetics\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro enzymatic reconstitution with mutagenesis, highly cited foundational study\",\n      \"pmids\": [\"19687296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The yeast Pex2/Pex10/Pex12 complex functions as an E3-ubiquitin ligase module; Pex8 interacts with the N-terminal domain of Pex5 via a HEAT repeat array and promotes assembly with the Pex2/Pex10/Pex12 complex to initiate receptor recycling after cargo translocation.\",\n      \"method\": \"Cryo-EM structure, in vitro binding assays, mutagenesis, peroxisomal import functional assays in yeast\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — structural and functional data with mutagenesis, but preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.08.30.673231\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PEX12 is an integral peroxisomal membrane protein with a cytosol-facing C-terminal RING finger domain that acts downstream of PEX5 receptor docking: it interacts directly with PEX5 and PEX10 via its RING domain, and functions as the E3 ubiquitin ligase (working with the Ubc4/Pex4 conjugating enzyme) that monoubiquitinates PEX5 to drive receptor recycling and sustain iterative rounds of peroxisomal matrix protein import.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PEX12 is an integral peroxisomal membrane protein with a RING finger E3 ubiquitin ligase domain that is essential for peroxisomal matrix protein import. It contains two transmembrane segments and a cytosol-facing C-terminal RING domain that directly binds the PTS1 import receptor PEX5 and the partner RING peroxin PEX10; this interaction occurs independently of PEX5 cargo recognition and acts downstream of PEX5 docking at the peroxisomal membrane [PMID:9632816, PMID:10562279, PMID:12456682]. As part of the PEX2/PEX10/PEX12 E3 ligase complex, PEX12 catalyzes Pex4(Ubc10)-dependent monoubiquitination of PEX5, which is required for receptor recycling and sustained rounds of matrix protein import [PMID:19687296]. Loss-of-function mutations in PEX12 cause peroxisome biogenesis disorder (complementation group 3), as demonstrated by restoration of peroxisomal protein import upon PEX12 expression in patient fibroblasts [PMID:9090384].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Establishing that PEX12 is a peroxisomal membrane protein whose loss causes a human peroxisome biogenesis disorder answered the question of which gene underlies PBD complementation group 3 and linked PEX12 directly to matrix protein import.\",\n      \"evidence\": \"Functional complementation of patient fibroblasts, subcellular fractionation, and mutation analysis\",\n      \"pmids\": [\"9090384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which PEX12 supports import was unknown\", \"Topology and domain architecture uncharacterized\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Determination of PEX12 membrane topology and identification of its RING finger domain established the structural framework needed to understand its mechanistic role, showing that both cytoplasmic regions are functionally essential.\",\n      \"evidence\": \"Epitope-tagged topology analysis, truncation and site-directed mutagenesis with functional complementation in CHO mutant cells\",\n      \"pmids\": [\"9632816\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Binding partners of the RING domain were unknown\", \"Enzymatic activity of the RING domain not yet tested\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstration that the PEX12 RING domain directly binds both PEX5 and PEX10, and that PEX12 acts downstream of receptor docking, placed PEX12 at a post-docking step in the import cycle and identified its key interaction partners.\",\n      \"evidence\": \"Two-hybrid, co-immunoprecipitation, blot overlay, genetic suppression, and PEX5 fractionation in loss-of-function cell lines\",\n      \"pmids\": [\"10562279\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PEX12 interaction with PEX5 requires cargo binding was unresolved\", \"Catalytic function of PEX12 not yet demonstrated\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Showing that PEX12 binds the PTS1-binding domain of PEX5 without altering cargo recognition kinetics established that PEX12–PEX5 interaction is independent of cargo loading, separating receptor engagement from cargo release.\",\n      \"evidence\": \"Fluorescence anisotropy binding assay with purified recombinant proteins in vitro\",\n      \"pmids\": [\"12456682\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vitro binding only; in vivo significance of cargo-independent interaction not directly tested\", \"No enzymatic assay performed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Reconstitution of PEX12-dependent monoubiquitination of PEX5 via the Pex4/Ubc10 conjugating enzyme identified PEX12 as the E3 ligase responsible for receptor recycling, providing the central enzymatic mechanism of the import cycle.\",\n      \"evidence\": \"In vitro ubiquitination reconstitution with purified components, RING mutagenesis, and yeast genetics\",\n      \"pmids\": [\"19687296\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of PEX2, PEX10, and PEX12 RING domains within the complex were not fully resolved\", \"Structural basis of the trimeric E3 complex unknown\", \"Whether mammalian PEX12 uses the same E2 enzyme not directly shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution structural understanding of the mammalian PEX2/PEX10/PEX12 complex and the mechanism by which cargo translocation is coupled to PEX5 ubiquitination and recycling remains to be established.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No atomic structure of the mammalian PEX12-containing E3 complex\", \"Mechanism coupling cargo release to PEX5 ubiquitination is unclear\", \"Regulation of PEX12 ligase activity in vivo is unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0043226\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 3, 5]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"PEX2/PEX10/PEX12 E3 ligase complex\"],\n    \"partners\": [\"PEX5\", \"PEX10\", \"PEX4\"],\n    \"other_free_text\": []\n  }\n}\n```"}