{"gene":"PEX16","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":1997,"finding":"In Yarrowia lipolytica, Pex16p is a peripheral protein located at the matrix face of the peroxisomal membrane; its C-terminal tripeptide (Ser-Thr-Leu, similar to PTS1) is not required for peroxisomal targeting; overexpression causes formation of enlarged peroxisomes containing the normal complement of peroxisomal proteins.","method":"Subcellular fractionation, epitope tagging, mutagenesis of C-terminal targeting motif, fluorescence microscopy","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical fractionation and mutagenesis in single lab, multiple orthogonal methods","pmids":["9182661"],"is_preprint":false},{"year":1998,"finding":"Human PEX16 encodes a 336-amino acid peroxisomal membrane protein (Pex16p); expression of HsPEX16 restores peroxisome biogenesis in fibroblasts from complementation group D Zellweger syndrome patients; a homozygous nonsense mutation (R176ter) abolishes this activity, indicating the C-terminal half is required for function.","method":"cDNA cloning, complementation assay in patient fibroblasts, epitope-tag localization, sequencing of patient mutations","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — complementation rescue with defined mutation in patient cells, replicated across labs subsequently","pmids":["9837814"],"is_preprint":false},{"year":2006,"finding":"Human PEX16 is cotranslationally inserted into the ER and serves to recruit other peroxisomal membrane proteins (PMPs) to ER membranes, thereby initiating de novo peroxisome biogenesis from the ER in both normal and peroxisome-less mutant mammalian cells.","method":"Photoactivatable GFP pulse-chase live imaging, subcellular fractionation, expression of PEX16 in peroxisome-deficient cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct live-cell imaging with photoactivatable GFP plus biochemical fractionation, foundational study replicated by subsequent work","pmids":["16717127"],"is_preprint":false},{"year":2011,"finding":"Sec16B (but not Sec16A) is required for the export of PEX16 from the ER to peroxisomes; knockdown of Sec16B inhibits PEX16 ER-to-peroxisome transport and causes redistribution of PEX3 and PEX16 to ER membranes, while overexpression of Sec16B redirects PEX3 and PEX16 from peroxisomes to ER.","method":"RNAi knockdown, overexpression, fluorescence microscopy, immunofluorescence co-localization, RNAi-resistant rescue","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — RNAi knockdown with rescue by RNAi-resistant construct, multiple orthogonal imaging approaches, single lab","pmids":["21768384"],"is_preprint":false},{"year":2014,"finding":"PEX16 mediates the peroxisomal trafficking of two distinct PMPs, PEX3 and PMP34, via the ER to pre-existing peroxisomes, supporting a constitutive ER-to-peroxisome membrane trafficking pathway for peroxisome maintenance.","method":"Quantitative time-lapse live-cell fluorescence microscopy, PEX16 depletion and overexpression, ER-targeted PEX3 reporter (ssPEX3), biochemical fractionation","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (live imaging, biochemistry, gain/loss-of-function), mechanistically specific to PEX16","pmids":["25002403"],"is_preprint":false},{"year":2015,"finding":"Comprehensive mutational analysis of human PEX16 identified multiple distinct domains: separate domains mediate ER-to-peroxisome trafficking of PEX16 itself and the recruitment of other PMPs (PEX3, MMP34) to the ER; this PMP-recruitment function is conserved in plant PEX16.","method":"Systematic deletion and point mutagenesis of PEX16, fluorescence microscopy of domain mutants, cross-species complementation with plant PEX16","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — systematic mutagenesis with functional readout, single lab, multiple domain mutants tested with orthogonal methods","pmids":["25903784"],"is_preprint":false},{"year":2021,"finding":"PEX16 knockdown in human RPE-1 cells reduces peroxisome abundance and activates pexophagy (autophagic peroxisome degradation), as shown by abrogation of peroxisome loss in ATG5-knockout cells and by co-localization of the autophagy adaptor p62 with the peroxisome marker ABCD3.","method":"siRNA knockdown, ATG5-KO cell lines, autophagy flux assay, co-localization microscopy, chloroquine inhibition","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (ATG5 KO) plus co-localization, single lab, single study","pmids":["34360754"],"is_preprint":false},{"year":2022,"finding":"CRISPR/Cas9-generated PEX16-KO mammalian cell lines can still form peroxisomes de novo and maintain them (though fewer and enlarged), demonstrating that PEX16 accelerates but is not absolutely required for de novo peroxisomal membrane formation; a patient-derived PEX16 mutant dominantly inhibits de novo peroxisomal membrane formation.","method":"CRISPR/Cas9 knockout in three mammalian cell lines, fluorescence microscopy, rescue by PEX16 re-expression, dominant-negative patient mutant expression","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with multiple cell lines and rescue experiment, single lab","pmids":["35437598"],"is_preprint":false},{"year":2016,"finding":"PEX16 is a transcriptional target of the adipogenesis master regulator PPARγ; stable silencing of Pex16 in 3T3-L1 cells reduces peroxisome number, impairs peroxisomal fatty acid oxidation leading to accumulation of long- and very long-chain fatty acids, and impairs adipocyte differentiation; these defects are rescued by PPARγ agonist rosiglitazone.","method":"Stable shRNA silencing, lipid mass spectrometry, oxygen consumption assay, adipocyte differentiation assay, rosiglitazone rescue","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with multiple metabolic readouts and pharmacological rescue, single lab","pmids":["28017862"],"is_preprint":false},{"year":2011,"finding":"In Drosophila, pex16 disruption eliminates most peroxisomes but a small number of peroxisome-like granules remain (unlike pex3 null which eliminates all), indicating that the requirement for pex16 in peroxisome biogenesis has diverged between Drosophila and mammals; pex16 expression in somatic cyst cells (not germline) is required for male germline cell maturation, implicating peroxisome-dependent paracrine signaling.","method":"Drosophila genetic knockout, fluorescence microscopy of peroxisome markers, tissue-specific rescue transgenes","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with cell-type-specific rescue, single lab, Drosophila model","pmids":["21826223"],"is_preprint":false},{"year":2028,"finding":"PEX16 overexpression in melanin-producing cells increases peroxisome number and inhibits melanogenesis by suppressing the Wnt/β-catenin signalling pathway, reducing expression of MITF, TYR, TYRP1 and DCT.","method":"PEX16 overexpression in MNT1 cells, melanin content measurement, gene expression analysis, Wnt/β-catenin pathway reporters","journal":"Experimental dermatology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single overexpression study, single lab, no mechanistic dissection of how PEX16 connects to Wnt/β-catenin","pmids":["41518585"],"is_preprint":false}],"current_model":"Human PEX16 is an integral peroxisomal membrane protein that is cotranslationally inserted into the ER, where it recruits other peroxisomal membrane proteins (PMPs such as PEX3 and MMP34) and drives their ER-to-peroxisome trafficking via a Sec16B-dependent COPII-like route, thereby initiating de novo peroxisome biogenesis and continuously supplying membranes to maintain pre-existing peroxisomes; it also modulates peroxisome abundance by restraining pexophagy, and its distinct N- and C-terminal domains separately control its own ER-to-peroxisome trafficking and its PMP-recruitment function at the ER."},"narrative":{"mechanistic_narrative":"PEX16 is an integral peroxisomal membrane protein that initiates and maintains peroxisome biogenesis from the endoplasmic reticulum [PMID:16717127, PMID:25002403]. Cloned as the gene defective in complementation group D Zellweger syndrome, human PEX16 restores peroxisome biogenesis in patient fibroblasts, and a C-terminal nonsense mutation (R176ter) abolishes this activity, establishing both its disease relevance and the functional importance of its C-terminal half [PMID:9837814]. PEX16 is cotranslationally inserted into the ER, where it recruits other peroxisomal membrane proteins—including PEX3 and PMP34/MMP34—to ER membranes, thereby seeding de novo peroxisome formation and supplying a constitutive ER-to-peroxisome membrane trafficking route that maintains pre-existing peroxisomes [PMID:16717127, PMID:25002403]. Export of PEX16 (and the PEX3 it carries) from the ER to peroxisomes requires Sec16B, defining a COPII-related exit pathway [PMID:21768384]. Systematic mutagenesis resolves PEX16 into separable domains controlling its own ER-to-peroxisome trafficking versus its PMP-recruitment activity, the latter conserved in plant PEX16 [PMID:25903784]. PEX16 also restrains peroxisome turnover, as its depletion lowers peroxisome abundance by activating ATG5-dependent pexophagy [PMID:34360754], and CRISPR knockout cells reveal that PEX16 accelerates but is not strictly required for de novo membrane formation, while a patient-derived mutant acts dominant-negatively [PMID:35437598]. Through its control of peroxisome number, PEX16 supports peroxisomal fatty-acid oxidation and adipocyte differentiation downstream of PPARγ [PMID:28017862].","teleology":[{"year":1997,"claim":"Established that Pex16p is a membrane-associated peroxisomal protein whose loss/overexpression alters peroxisome morphology, raising the question of its role in organelle biogenesis.","evidence":"Subcellular fractionation, epitope tagging, and C-terminal motif mutagenesis in Yarrowia lipolytica","pmids":["9182661"],"confidence":"Medium","gaps":["Mechanism of membrane recruitment not defined","Ortholog behavior may differ from mammalian PEX16","No molecular partners identified"]},{"year":1998,"claim":"Identified human PEX16 as the gene mutated in complementation group D Zellweger syndrome and showed its C-terminal half is required for function, linking the protein causally to peroxisome biogenesis disease.","evidence":"cDNA cloning, complementation rescue in patient fibroblasts, and sequencing of the R176ter mutation","pmids":["9837814"],"confidence":"High","gaps":["Molecular function of PEX16 not yet defined","Which PMPs it acts on unknown","Subcellular trafficking route unresolved"]},{"year":2006,"claim":"Defined PEX16's molecular role: cotranslational ER insertion followed by recruitment of other PMPs to initiate de novo peroxisome formation from the ER.","evidence":"Photoactivatable-GFP pulse-chase live imaging plus fractionation in normal and peroxisome-deficient mammalian cells","pmids":["16717127"],"confidence":"High","gaps":["ER exit machinery not identified","Domains responsible for distinct functions not mapped","Direct PMP-binding partners not biochemically defined"]},{"year":2011,"claim":"Identified the ER-exit machinery for PEX16, showing Sec16B (not Sec16A) drives PEX16/PEX3 export from ER to peroxisomes via a COPII-like route.","evidence":"RNAi knockdown with RNAi-resistant rescue and overexpression imaging in mammalian cells","pmids":["21768384"],"confidence":"High","gaps":["Direct PEX16–Sec16B interaction not shown biochemically","COPII coat involvement inferred, not fully reconstituted"]},{"year":2011,"claim":"Revealed evolutionary divergence and a tissue-context role, showing pex16 is dispensable for residual peroxisome-like granules in Drosophila and required in somatic cyst cells for germline maturation.","evidence":"Drosophila genetic knockout with tissue-specific rescue transgenes","pmids":["21826223"],"confidence":"Medium","gaps":["Mammalian requirement may differ from fly","Paracrine signaling mechanism not defined","Molecular function unaddressed in this model"]},{"year":2014,"claim":"Extended PEX16 function beyond de novo biogenesis to constitutive maintenance, showing it traffics PEX3 and PMP34 from ER to pre-existing peroxisomes.","evidence":"Quantitative time-lapse imaging, ER-targeted PEX3 reporter, and gain/loss-of-function with fractionation","pmids":["25002403"],"confidence":"High","gaps":["Cargo selectivity rules unknown","Whether all PMPs use this route unresolved"]},{"year":2015,"claim":"Mapped PEX16 into separable functional domains, distinguishing self-trafficking from PMP-recruitment activity and demonstrating conservation of recruitment in plants.","evidence":"Systematic deletion/point mutagenesis with imaging readouts and cross-species complementation","pmids":["25903784"],"confidence":"High","gaps":["Structural basis of each domain unknown","Residue-level binding interfaces undefined"]},{"year":2016,"claim":"Placed PEX16 in adipocyte metabolism as a PPARγ target whose loss impairs peroxisomal fatty-acid oxidation and differentiation.","evidence":"Stable shRNA silencing in 3T3-L1 cells with lipid mass spectrometry, oxygen consumption assays, and rosiglitazone rescue","pmids":["28017862"],"confidence":"Medium","gaps":["Direct PPARγ binding to PEX16 promoter not shown here","Whether defects are secondary to reduced peroxisome number unresolved"]},{"year":2021,"claim":"Showed PEX16 restrains peroxisome turnover, as its depletion lowers peroxisome abundance through ATG5-dependent pexophagy.","evidence":"siRNA knockdown, ATG5-KO epistasis, autophagy flux assays, and p62/ABCD3 co-localization in RPE-1 cells","pmids":["34360754"],"confidence":"Medium","gaps":["Mechanism linking PEX16 loss to pexophagy signaling undefined","Single study, single cell type"]},{"year":2022,"claim":"Refined the necessity of PEX16, demonstrating it accelerates but is not absolutely required for de novo peroxisome formation, while a patient mutant acts dominant-negatively.","evidence":"CRISPR/Cas9 knockout across three mammalian cell lines with re-expression rescue and dominant-negative mutant assays","pmids":["35437598"],"confidence":"Medium","gaps":["Compensating factors enabling PEX16-independent biogenesis unidentified","Molecular basis of dominant-negative effect unresolved"]},{"year":null,"claim":"How PEX16 mechanistically couples to downstream signaling pathways and the structural basis of its cargo recruitment remain open.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of PEX16 or its cargo complexes","Direct biochemical PMP-binding interfaces undefined","Connection to signaling pathways (e.g. Wnt/β-catenin) uncharacterized mechanistically"]}],"mechanism_profile":{"molecular_activity":[],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,3,4]},{"term_id":"GO:0005777","term_label":"peroxisome","supporting_discovery_ids":[0,1,2,4]}],"pathway":[{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[2,4]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[3,4]}],"complexes":[],"partners":["PEX3","PMP34","SEC16B"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y5Y5","full_name":"Peroxisomal membrane protein PEX16","aliases":["Peroxin-16","Peroxisomal biogenesis factor 16"],"length_aa":336,"mass_kda":38.6,"function":"Required for peroxisome membrane biogenesis. May play a role in early stages of peroxisome assembly. Can recruit other peroxisomal proteins, such as PEX3 and PMP34, to de novo peroxisomes derived from the endoplasmic reticulum (ER). May function as receptor for PEX3","subcellular_location":"Peroxisome membrane","url":"https://www.uniprot.org/uniprotkb/Q9Y5Y5/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PEX16","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PEX16","total_profiled":1310},"omim":[{"mim_id":"614877","title":"PEROXISOME BIOGENESIS DISORDER 8B; PBD8B","url":"https://www.omim.org/entry/614877"},{"mim_id":"614876","title":"PEROXISOME BIOGENESIS DISORDER 8A (ZELLWEGER); PBD8A","url":"https://www.omim.org/entry/614876"},{"mim_id":"603360","title":"PEROXISOME BIOGENESIS FACTOR 16; PEX16","url":"https://www.omim.org/entry/603360"},{"mim_id":"603164","title":"PEROXISOME BIOGENESIS FACTOR 3; PEX3","url":"https://www.omim.org/entry/603164"},{"mim_id":"601791","title":"PEROXISOME BIOGENESIS FACTOR 14; PEX14","url":"https://www.omim.org/entry/601791"}],"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/PEX16"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q9Y5Y5","domains":[{"cath_id":"-","chopping":"74-142_210-333","consensus_level":"medium","plddt":88.2691,"start":74,"end":333}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5Y5","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5Y5-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5Y5-F1-predicted_aligned_error_v6.png","plddt_mean":82.94},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PEX16","jax_strain_url":"https://www.jax.org/strain/search?query=PEX16"},"sequence":{"accession":"Q9Y5Y5","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y5Y5.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y5Y5/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5Y5"}},"corpus_meta":[{"pmid":"16717127","id":"PMC_16717127","title":"The origin and maintenance of mammalian peroxisomes involves a de novo PEX16-dependent pathway from the ER.","date":"2006","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/16717127","citation_count":270,"is_preprint":false},{"pmid":"9837814","id":"PMC_9837814","title":"Mutation in PEX16 is causal in the peroxisome-deficient Zellweger syndrome of complementation group D.","date":"1998","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9837814","citation_count":147,"is_preprint":false},{"pmid":"9182661","id":"PMC_9182661","title":"Enlarged peroxisomes are present in oleic acid-grown Yarrowia lipolytica overexpressing the PEX16 gene encoding an intraperoxisomal peripheral membrane peroxin.","date":"1997","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/9182661","citation_count":110,"is_preprint":false},{"pmid":"20647552","id":"PMC_20647552","title":"Identification of an unusual variant peroxisome biogenesis disorder caused by mutations in the PEX16 gene.","date":"2010","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/20647552","citation_count":75,"is_preprint":false},{"pmid":"21768384","id":"PMC_21768384","title":"Sec16B is involved in the endoplasmic reticulum export of the peroxisomal membrane biogenesis factor peroxin 16 (Pex16) in mammalian cells.","date":"2011","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/21768384","citation_count":74,"is_preprint":false},{"pmid":"26066397","id":"PMC_26066397","title":"Molecular snapshots of the Pex1/6 AAA+ complex in action.","date":"2015","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/26066397","citation_count":68,"is_preprint":false},{"pmid":"25002403","id":"PMC_25002403","title":"PEX16 contributes to peroxisome maintenance by constantly trafficking PEX3 via the ER.","date":"2014","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/25002403","citation_count":55,"is_preprint":false},{"pmid":"21826223","id":"PMC_21826223","title":"Drosophila carrying pex3 or pex16 mutations are models of Zellweger syndrome that reflect its symptoms associated with the absence of peroxisomes.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21826223","citation_count":39,"is_preprint":false},{"pmid":"25903784","id":"PMC_25903784","title":"Multiple Domains in PEX16 Mediate Its Trafficking and Recruitment of Peroxisomal Proteins to the ER.","date":"2015","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/25903784","citation_count":35,"is_preprint":false},{"pmid":"24027535","id":"PMC_24027535","title":"PEX16: a multifaceted regulator of peroxisome biogenesis.","date":"2013","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/24027535","citation_count":30,"is_preprint":false},{"pmid":"28017862","id":"PMC_28017862","title":"Critical role of the peroxisomal protein PEX16 in white adipocyte development and lipid homeostasis.","date":"2016","source":"Biochimica et biophysica acta. 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novo formation and maintenance of mammalian peroxisomes in cultured PEX16-knockout cells generated by CRISPR/Cas9.","date":"2022","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/35437598","citation_count":7,"is_preprint":false},{"pmid":"35106698","id":"PMC_35106698","title":"Clinical, neuroradiological, and molecular characterization of patients with atypical Zellweger spectrum disorder caused by PEX16 mutations: a case series.","date":"2022","source":"Neurogenetics","url":"https://pubmed.ncbi.nlm.nih.gov/35106698","citation_count":5,"is_preprint":false},{"pmid":"30057159","id":"PMC_30057159","title":"Pex16 is involved in peroxisome and Woronin body formation in the white koji fungus, Aspergillus luchuensis mut. kawachii.","date":"2018","source":"Journal of bioscience and bioengineering","url":"https://pubmed.ncbi.nlm.nih.gov/30057159","citation_count":5,"is_preprint":false},{"pmid":"26870756","id":"PMC_26870756","title":"Dataset for a case report of a 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<i>Drosophila</i>","date":"2024-11-15","source":"bioRxiv","url":"https://doi.org/10.1101/2024.11.14.623590","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2024.09.23.614586","title":"Genetic analysis of the X-linked Adrenoleukodystrophy  <i>ABCD1 gene</i>  in  <i>Drosophila</i>  uncovers a role in Peroxisomal dynamics","date":"2024-09-25","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.23.614586","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":16574,"output_tokens":2769,"usd":0.045629,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10012,"output_tokens":3221,"usd":0.065293,"stage2_stop_reason":"end_turn"},"total_usd":0.110922,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"In Yarrowia lipolytica, Pex16p is a peripheral protein located at the matrix face of the peroxisomal membrane; its C-terminal tripeptide (Ser-Thr-Leu, similar to PTS1) is not required for peroxisomal targeting; overexpression causes formation of enlarged peroxisomes containing the normal complement of peroxisomal proteins.\",\n      \"method\": \"Subcellular fractionation, epitope tagging, mutagenesis of C-terminal targeting motif, fluorescence microscopy\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical fractionation and mutagenesis in single lab, multiple orthogonal methods\",\n      \"pmids\": [\"9182661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human PEX16 encodes a 336-amino acid peroxisomal membrane protein (Pex16p); expression of HsPEX16 restores peroxisome biogenesis in fibroblasts from complementation group D Zellweger syndrome patients; a homozygous nonsense mutation (R176ter) abolishes this activity, indicating the C-terminal half is required for function.\",\n      \"method\": \"cDNA cloning, complementation assay in patient fibroblasts, epitope-tag localization, sequencing of patient mutations\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — complementation rescue with defined mutation in patient cells, replicated across labs subsequently\",\n      \"pmids\": [\"9837814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human PEX16 is cotranslationally inserted into the ER and serves to recruit other peroxisomal membrane proteins (PMPs) to ER membranes, thereby initiating de novo peroxisome biogenesis from the ER in both normal and peroxisome-less mutant mammalian cells.\",\n      \"method\": \"Photoactivatable GFP pulse-chase live imaging, subcellular fractionation, expression of PEX16 in peroxisome-deficient cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct live-cell imaging with photoactivatable GFP plus biochemical fractionation, foundational study replicated by subsequent work\",\n      \"pmids\": [\"16717127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Sec16B (but not Sec16A) is required for the export of PEX16 from the ER to peroxisomes; knockdown of Sec16B inhibits PEX16 ER-to-peroxisome transport and causes redistribution of PEX3 and PEX16 to ER membranes, while overexpression of Sec16B redirects PEX3 and PEX16 from peroxisomes to ER.\",\n      \"method\": \"RNAi knockdown, overexpression, fluorescence microscopy, immunofluorescence co-localization, RNAi-resistant rescue\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — RNAi knockdown with rescue by RNAi-resistant construct, multiple orthogonal imaging approaches, single lab\",\n      \"pmids\": [\"21768384\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PEX16 mediates the peroxisomal trafficking of two distinct PMPs, PEX3 and PMP34, via the ER to pre-existing peroxisomes, supporting a constitutive ER-to-peroxisome membrane trafficking pathway for peroxisome maintenance.\",\n      \"method\": \"Quantitative time-lapse live-cell fluorescence microscopy, PEX16 depletion and overexpression, ER-targeted PEX3 reporter (ssPEX3), biochemical fractionation\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (live imaging, biochemistry, gain/loss-of-function), mechanistically specific to PEX16\",\n      \"pmids\": [\"25002403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Comprehensive mutational analysis of human PEX16 identified multiple distinct domains: separate domains mediate ER-to-peroxisome trafficking of PEX16 itself and the recruitment of other PMPs (PEX3, MMP34) to the ER; this PMP-recruitment function is conserved in plant PEX16.\",\n      \"method\": \"Systematic deletion and point mutagenesis of PEX16, fluorescence microscopy of domain mutants, cross-species complementation with plant PEX16\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — systematic mutagenesis with functional readout, single lab, multiple domain mutants tested with orthogonal methods\",\n      \"pmids\": [\"25903784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PEX16 knockdown in human RPE-1 cells reduces peroxisome abundance and activates pexophagy (autophagic peroxisome degradation), as shown by abrogation of peroxisome loss in ATG5-knockout cells and by co-localization of the autophagy adaptor p62 with the peroxisome marker ABCD3.\",\n      \"method\": \"siRNA knockdown, ATG5-KO cell lines, autophagy flux assay, co-localization microscopy, chloroquine inhibition\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (ATG5 KO) plus co-localization, single lab, single study\",\n      \"pmids\": [\"34360754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CRISPR/Cas9-generated PEX16-KO mammalian cell lines can still form peroxisomes de novo and maintain them (though fewer and enlarged), demonstrating that PEX16 accelerates but is not absolutely required for de novo peroxisomal membrane formation; a patient-derived PEX16 mutant dominantly inhibits de novo peroxisomal membrane formation.\",\n      \"method\": \"CRISPR/Cas9 knockout in three mammalian cell lines, fluorescence microscopy, rescue by PEX16 re-expression, dominant-negative patient mutant expression\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with multiple cell lines and rescue experiment, single lab\",\n      \"pmids\": [\"35437598\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PEX16 is a transcriptional target of the adipogenesis master regulator PPARγ; stable silencing of Pex16 in 3T3-L1 cells reduces peroxisome number, impairs peroxisomal fatty acid oxidation leading to accumulation of long- and very long-chain fatty acids, and impairs adipocyte differentiation; these defects are rescued by PPARγ agonist rosiglitazone.\",\n      \"method\": \"Stable shRNA silencing, lipid mass spectrometry, oxygen consumption assay, adipocyte differentiation assay, rosiglitazone rescue\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with multiple metabolic readouts and pharmacological rescue, single lab\",\n      \"pmids\": [\"28017862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In Drosophila, pex16 disruption eliminates most peroxisomes but a small number of peroxisome-like granules remain (unlike pex3 null which eliminates all), indicating that the requirement for pex16 in peroxisome biogenesis has diverged between Drosophila and mammals; pex16 expression in somatic cyst cells (not germline) is required for male germline cell maturation, implicating peroxisome-dependent paracrine signaling.\",\n      \"method\": \"Drosophila genetic knockout, fluorescence microscopy of peroxisome markers, tissue-specific rescue transgenes\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with cell-type-specific rescue, single lab, Drosophila model\",\n      \"pmids\": [\"21826223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2028,\n      \"finding\": \"PEX16 overexpression in melanin-producing cells increases peroxisome number and inhibits melanogenesis by suppressing the Wnt/β-catenin signalling pathway, reducing expression of MITF, TYR, TYRP1 and DCT.\",\n      \"method\": \"PEX16 overexpression in MNT1 cells, melanin content measurement, gene expression analysis, Wnt/β-catenin pathway reporters\",\n      \"journal\": \"Experimental dermatology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single overexpression study, single lab, no mechanistic dissection of how PEX16 connects to Wnt/β-catenin\",\n      \"pmids\": [\"41518585\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"Human PEX16 is an integral peroxisomal membrane protein that is cotranslationally inserted into the ER, where it recruits other peroxisomal membrane proteins (PMPs such as PEX3 and MMP34) and drives their ER-to-peroxisome trafficking via a Sec16B-dependent COPII-like route, thereby initiating de novo peroxisome biogenesis and continuously supplying membranes to maintain pre-existing peroxisomes; it also modulates peroxisome abundance by restraining pexophagy, and its distinct N- and C-terminal domains separately control its own ER-to-peroxisome trafficking and its PMP-recruitment function at the ER.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PEX16 is an integral peroxisomal membrane protein that initiates and maintains peroxisome biogenesis from the endoplasmic reticulum [#2, #4]. Cloned as the gene defective in complementation group D Zellweger syndrome, human PEX16 restores peroxisome biogenesis in patient fibroblasts, and a C-terminal nonsense mutation (R176ter) abolishes this activity, establishing both its disease relevance and the functional importance of its C-terminal half [#1]. PEX16 is cotranslationally inserted into the ER, where it recruits other peroxisomal membrane proteins—including PEX3 and PMP34/MMP34—to ER membranes, thereby seeding de novo peroxisome formation and supplying a constitutive ER-to-peroxisome membrane trafficking route that maintains pre-existing peroxisomes [#2, #4]. Export of PEX16 (and the PEX3 it carries) from the ER to peroxisomes requires Sec16B, defining a COPII-related exit pathway [#3]. Systematic mutagenesis resolves PEX16 into separable domains controlling its own ER-to-peroxisome trafficking versus its PMP-recruitment activity, the latter conserved in plant PEX16 [#5]. PEX16 also restrains peroxisome turnover, as its depletion lowers peroxisome abundance by activating ATG5-dependent pexophagy [#6], and CRISPR knockout cells reveal that PEX16 accelerates but is not strictly required for de novo membrane formation, while a patient-derived mutant acts dominant-negatively [#7]. Through its control of peroxisome number, PEX16 supports peroxisomal fatty-acid oxidation and adipocyte differentiation downstream of PPARγ [#8].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that Pex16p is a membrane-associated peroxisomal protein whose loss/overexpression alters peroxisome morphology, raising the question of its role in organelle biogenesis.\",\n      \"evidence\": \"Subcellular fractionation, epitope tagging, and C-terminal motif mutagenesis in Yarrowia lipolytica\",\n      \"pmids\": [\"9182661\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of membrane recruitment not defined\", \"Ortholog behavior may differ from mammalian PEX16\", \"No molecular partners identified\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified human PEX16 as the gene mutated in complementation group D Zellweger syndrome and showed its C-terminal half is required for function, linking the protein causally to peroxisome biogenesis disease.\",\n      \"evidence\": \"cDNA cloning, complementation rescue in patient fibroblasts, and sequencing of the R176ter mutation\",\n      \"pmids\": [\"9837814\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular function of PEX16 not yet defined\", \"Which PMPs it acts on unknown\", \"Subcellular trafficking route unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defined PEX16's molecular role: cotranslational ER insertion followed by recruitment of other PMPs to initiate de novo peroxisome formation from the ER.\",\n      \"evidence\": \"Photoactivatable-GFP pulse-chase live imaging plus fractionation in normal and peroxisome-deficient mammalian cells\",\n      \"pmids\": [\"16717127\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ER exit machinery not identified\", \"Domains responsible for distinct functions not mapped\", \"Direct PMP-binding partners not biochemically defined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified the ER-exit machinery for PEX16, showing Sec16B (not Sec16A) drives PEX16/PEX3 export from ER to peroxisomes via a COPII-like route.\",\n      \"evidence\": \"RNAi knockdown with RNAi-resistant rescue and overexpression imaging in mammalian cells\",\n      \"pmids\": [\"21768384\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PEX16–Sec16B interaction not shown biochemically\", \"COPII coat involvement inferred, not fully reconstituted\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Revealed evolutionary divergence and a tissue-context role, showing pex16 is dispensable for residual peroxisome-like granules in Drosophila and required in somatic cyst cells for germline maturation.\",\n      \"evidence\": \"Drosophila genetic knockout with tissue-specific rescue transgenes\",\n      \"pmids\": [\"21826223\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mammalian requirement may differ from fly\", \"Paracrine signaling mechanism not defined\", \"Molecular function unaddressed in this model\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Extended PEX16 function beyond de novo biogenesis to constitutive maintenance, showing it traffics PEX3 and PMP34 from ER to pre-existing peroxisomes.\",\n      \"evidence\": \"Quantitative time-lapse imaging, ER-targeted PEX3 reporter, and gain/loss-of-function with fractionation\",\n      \"pmids\": [\"25002403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cargo selectivity rules unknown\", \"Whether all PMPs use this route unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Mapped PEX16 into separable functional domains, distinguishing self-trafficking from PMP-recruitment activity and demonstrating conservation of recruitment in plants.\",\n      \"evidence\": \"Systematic deletion/point mutagenesis with imaging readouts and cross-species complementation\",\n      \"pmids\": [\"25903784\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of each domain unknown\", \"Residue-level binding interfaces undefined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Placed PEX16 in adipocyte metabolism as a PPARγ target whose loss impairs peroxisomal fatty-acid oxidation and differentiation.\",\n      \"evidence\": \"Stable shRNA silencing in 3T3-L1 cells with lipid mass spectrometry, oxygen consumption assays, and rosiglitazone rescue\",\n      \"pmids\": [\"28017862\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PPARγ binding to PEX16 promoter not shown here\", \"Whether defects are secondary to reduced peroxisome number unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed PEX16 restrains peroxisome turnover, as its depletion lowers peroxisome abundance through ATG5-dependent pexophagy.\",\n      \"evidence\": \"siRNA knockdown, ATG5-KO epistasis, autophagy flux assays, and p62/ABCD3 co-localization in RPE-1 cells\",\n      \"pmids\": [\"34360754\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking PEX16 loss to pexophagy signaling undefined\", \"Single study, single cell type\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Refined the necessity of PEX16, demonstrating it accelerates but is not absolutely required for de novo peroxisome formation, while a patient mutant acts dominant-negatively.\",\n      \"evidence\": \"CRISPR/Cas9 knockout across three mammalian cell lines with re-expression rescue and dominant-negative mutant assays\",\n      \"pmids\": [\"35437598\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Compensating factors enabling PEX16-independent biogenesis unidentified\", \"Molecular basis of dominant-negative effect unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PEX16 mechanistically couples to downstream signaling pathways and the structural basis of its cargo recruitment remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of PEX16 or its cargo complexes\", \"Direct biochemical PMP-binding interfaces undefined\", \"Connection to signaling pathways (e.g. Wnt/β-catenin) uncharacterized mechanistically\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": []}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 3, 4]},\n      {\"term_id\": \"GO:0005777\", \"supporting_discovery_ids\": [0, 1, 2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PEX3\", \"PMP34\", \"SEC16B\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}