{"gene":"PEX19","run_date":"2026-04-29T11:37:58","timeline":{"discoveries":[{"year":2000,"finding":"PEX19 binds a broad spectrum of peroxisomal membrane proteins (PMPs) in the cytoplasm, is predominantly cytosolic at steady state, and its mislocalization to the nucleus causes nuclear accumulation of newly synthesized PMPs; loss of PEX19 leads to degradation or mistargeting of PMPs to mitochondria, establishing PEX19 as required for peroxisome membrane synthesis.","method":"Co-immunoprecipitation, subcellular fractionation, mislocalization assay, loss-of-function in PEX19-deficient cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal binding assays, mislocalization experiment, and loss-of-function with defined phenotypic readout; foundational study with 257 citations","pmids":["10704444"],"is_preprint":false},{"year":1999,"finding":"Human PEX19 encodes a 299-aa hydrophilic protein with a C-terminal CAAX farnesylation motif; farnesylated PEX19 is partly anchored in the peroxisomal membrane with its N-terminal region exposed to the cytosol; PEX19 is required for peroxisome membrane assembly at an early stage, before matrix protein import.","method":"Functional complementation of CHO mutant ZP119, mutation analysis in Zellweger patient, immunolocalization","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — functional complementation plus patient mutation analysis; highly cited foundational paper","pmids":["10051604"],"is_preprint":false},{"year":2004,"finding":"PEX19 functions as both a cytosolic chaperone and an import receptor for newly synthesized class 1 PMPs: it binds and stabilizes PMPs in the cytosol, interacts with hydrophobic PMP targeting signals (mPTSs), and is essential for class 1 PMP targeting and import; class 2 mPTSs are PEX19-independent.","method":"In vitro binding assays, PMP stabilization assays, complementation in PEX19-deficient cells, RNAi knockdown","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal in vitro and in vivo assays; 205 citations; replicated concept from same group with added mechanistic detail","pmids":["14709540"],"is_preprint":false},{"year":2004,"finding":"PEX3 is the docking factor for PEX19 at the peroxisomal membrane: PEX3 is required for PEX19 docking at peroxisomes, interacts specifically with the N-terminal docking domain of PEX19 via a conserved motif, is sufficient to dock PEX19 at heterologous organelles, and its transient inhibition abrogates class 1 PMP import but not class 2 or matrix protein import.","method":"Co-immunoprecipitation, heterologous targeting assay, transient inhibition/dominant-negative, complementation in PEX3-deficient cells","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, reciprocal interaction data, epistasis; 191 citations","pmids":["15007061"],"is_preprint":false},{"year":2006,"finding":"The tail-anchored peroxisomal membrane protein PEX26 contains two PEX19-binding sites in its C-terminal targeting signal: one overlapping with the transmembrane domain and one in the luminal domain; the luminal PEX19-binding site is essential for correct peroxisomal targeting and prevents mislocalization to mitochondria; PEX19 is required for PEX26 import.","method":"Deletion/mutation analysis, heterologous targeting assay, co-immunoprecipitation, PEX19 knockdown","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — mutagenesis combined with functional targeting assays and knockdown; 104 citations","pmids":["16763195"],"is_preprint":false},{"year":2005,"finding":"PEX19-binding sites on peroxisomal membrane proteins (including ALDP/adrenoleukodystrophy protein) serve as targeting motifs; the identified PEX19-binding site of ALDP is bound by both human and yeast PEX19 and is required for peroxisomal targeting in human fibroblasts and in yeast, demonstrating evolutionary conservation of PMP targeting signals.","method":"Peptide array binding, in vivo targeting assays in human fibroblasts and yeast, deletion mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods across species; 63 citations","pmids":["15781447"],"is_preprint":false},{"year":2009,"finding":"The N-terminal domain of Pex14 (Pex14N) adopts a three-helical fold and binds both Pex5 and Pex19 competitively at the same surface but with opposite directionality; a conserved F/YFxxxF motif in PEX19 mediates this interaction; mutations of Pex14 residues in the binding region disrupt Pex5/Pex19 binding in vitro and impair Pex14 peroxisomal membrane localization in vivo.","method":"Crystal structure, NMR, mutagenesis, in vitro binding, in vivo localization assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis plus in vivo validation; 73 citations","pmids":["19197237"],"is_preprint":false},{"year":2010,"finding":"Crystal structure of the cytosolic domain of PEX3 in complex with a PEX19-derived peptide reveals that PEX3 adopts a novel large helical bundle fold with a hydrophobic groove at its membrane-distal end that engages the PEX19 peptide with nanomolar affinity; phenylalanine 29 of PEX19 is critical for the PEX3-PEX19 interaction.","method":"X-ray crystallography, mutagenesis, binding affinity measurements","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis validation; 48 citations","pmids":["20554521"],"is_preprint":false},{"year":2003,"finding":"The PEX3-PEX19 interaction occurs predominantly at the peroxisomal membrane in living cells; the PEX19-binding domain in the C-terminal half of PEX3 is required for peroxisomal localization; deletion of the PEX3 N-terminal targeting sequence or the PEX19-binding domain mislocalizes PEX3 and abolishes interaction with PEX19.","method":"FRET imaging (EYFP/ECFP fusion proteins), donor photobleaching, complementation in PEX3- and PEX19-deficient fibroblasts","journal":"European journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — quantitative FRET in living cells with domain deletion analysis; 38 citations","pmids":["12924628"],"is_preprint":false},{"year":2013,"finding":"PEX19 forms a cytosolic complex with the tail-anchored peroxisomal membrane protein PEX26 and translocates it directly to peroxisomes by interacting with PEX3; this pathway is TRC40-independent; basic amino acids in the luminal domain of PEX26 are essential for PEX19 binding and peroxisomal targeting.","method":"Co-immunoprecipitation, dominant-negative/siRNA knockdown, mutagenesis, in vivo targeting assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, epistasis with TRC40, mutagenesis; 80 citations","pmids":["23460677"],"is_preprint":false},{"year":2017,"finding":"Farnesylation of PEX19 at its C-terminal CaaX motif allosterically reshapes the PEX19 C-terminal domain to form two hydrophobic pockets that recognize conserved aromatic/aliphatic side chains in PMPs; the farnesyl moiety is buried in an internal hydrophobic cavity inducing conformational changes; mutations abolishing farnesyl contacts or PMP recognition prevent cargo binding and cannot complement a ΔPEX19 phenotype in Zellweger patient fibroblasts.","method":"NMR structure of farnesylated PEX19 CTD, mutagenesis, in vivo complementation in patient fibroblasts","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — NMR structure plus mutagenesis plus functional complementation in vivo; 42 citations","pmids":["28281558"],"is_preprint":false},{"year":2012,"finding":"Mutagenesis of the PEX19-binding region of PEX3 reduces PEX19 affinity and destabilizes PEX3; the PEX3-PEX19 complex is required for de novo formation of peroxisomes; a hydrophobic groove near the base of PEX3 is involved in PMP insertion into the membrane.","method":"Site-directed mutagenesis, in vitro binding assays, functional complementation in peroxisome-deficient cells","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — mutagenesis combined with biochemical and functional assays; 38 citations","pmids":["22624858"],"is_preprint":false},{"year":2002,"finding":"PEX19 is farnesylated in vitro and in vivo at its C-terminal CAAX motif; two splice variants differ in biological activity: PEX19ΔE8 (lacking domain D3/CAAX) restores peroxisomal biogenesis in PEX19-deficient fibroblasts and interacts with PEX3, demonstrating that farnesylation is not absolutely essential; PEX19ΔE2 (lacking N-terminal domain D1) fails to restore biogenesis and cannot interact with PEX3 lacking its peroxisomal targeting region.","method":"In vitro farnesylation assay, co-immunoprecipitation, functional complementation in PEX19-deficient fibroblasts","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — multiple assays but single lab; 22 citations","pmids":["11883941"],"is_preprint":false},{"year":2017,"finding":"Deletion mapping in Pichia pastoris defines the minimum N-terminal (aa 1-150) and C-terminal (aa 89-300) regions of Pex19 required for peroxisome biogenesis; N-terminal deletions disrupt Pex3 binding while preserving Pex10 interaction; C-terminal deletions disrupt PMP (Pex10) binding while preserving Pex3 interaction; Pex25 overexpression can partially rescue Pex19 C-terminal truncation by enhancing Pex3 interaction.","method":"Deletion mutagenesis, co-immunoprecipitation, growth assay, yeast genetics","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — systematic deletion analysis with orthogonal biochemical and functional assays; single lab","pmids":["28526747"],"is_preprint":false},{"year":2018,"finding":"In budding yeast, Pex19 acts as an import mediator for a subset of mitochondrial tail-anchored (TA) proteins (Fis1 and Gem1); deletion of PEX19 causes growth defects under respiratory conditions, altered mitochondrial morphology, reduced steady-state levels of Fis1 and Gem1, and hampered in organello import of these TA proteins; recombinant Pex19 directly binds Fis1 and Gem1.","method":"Yeast genetics (PEX19 deletion), in organello import assay, direct binding with recombinant proteins, steady-state level analysis","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (genetic, biochemical, in organello); direct binding demonstrated with recombinant proteins; 40 citations","pmids":["30033679"],"is_preprint":false},{"year":2014,"finding":"PEX19 is an intrinsically disordered protein; upon interaction with PEX3, three regions of PEX19 become protected from hydrogen exchange (N-terminus, a middle stretch F64-L74, and C-terminus), while PEX3 becomes more protected in its binding groove; the N-terminus of PEX19 initiates binding to PEX3, followed by subtle conformational changes in PEX3 that allow higher-affinity engagement via folding of a short helix in PEX19.","method":"Hydrogen exchange mass spectrometry","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — H/D exchange MS provides conformational detail of complex formation; single lab, single method","pmids":["25062251"],"is_preprint":false},{"year":2022,"finding":"Pex11 contains one Pex19-binding site (Pex19-BS) required for Pex19-mediated membrane insertion but non-essential for peroxisomal trafficking; Pex19 acts as a chaperone by binding Pex19-BS in Pex11 and preventing spontaneous Pex11 oligomerization and aggregation; Pex11 also has a second, Pex19-independent mPTS for peroxisomal trafficking.","method":"Mutagenesis, co-immunoprecipitation, in vivo targeting assay, aggregation assay in Pichia pastoris","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 — extensive mutagenesis with functional assays; single lab","pmids":["35011719"],"is_preprint":false},{"year":2022,"finding":"Non-farnesylated PEX19 is sufficient to restore peroxisomal metabolic activity, while farnesylated PEX19 specifically controls lipid droplet (LD) protein composition and neutral lipid metabolism through a peroxisome-independent mechanism; in the absence of PEX19-dependent LD proteome, cells accumulate excess triacylglycerols and fail to deplete neutral lipid stores.","method":"Farnesylation mutant analysis, systems-level proteomics, lipid quantification, rescue experiments in PEX19-deficient cells","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple orthogonal methods (proteomics, lipidomics, rescue); single lab","pmids":["35557938"],"is_preprint":false},{"year":2024,"finding":"A conserved PEX19 helix (αd) prevents improper exposure of the PEX26 transmembrane domain (TMD) to cytosolic chaperones, and the αd helix also interacts with the cytosolic domain of the PEX3 receptor to trigger PEX26 release at the correct destination membrane; the PEX3-G138E mutant abolishes this secondary interaction, preventing PEX3-induced PEX26 release from PEX19.","method":"Biochemical analysis, mass spectrometry, mutagenesis, in vivo targeting assay","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 — biochemical and MS-based evidence with mutagenesis; single lab","pmids":["38585659"],"is_preprint":false},{"year":2021,"finding":"Viperin (an interferon-stimulated gene product) binds PEX19 as a physical interaction partner; viperin colocalizes with peroxisomal proteins and its augmentation of RIG-I-like receptor (RLR) signaling requires PEX19 expression; knockdown of PEX19 abolishes viperin-mediated augmentation of innate antiviral signaling.","method":"Proteomics-based screening, co-immunoprecipitation, colocalization, RNAi knockdown with functional readout (IFN-β induction)","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 3 — single pulldown/coIP plus functional knockdown; single lab","pmids":["34108265"],"is_preprint":false},{"year":2025,"finding":"In yeast, newly synthesized Pex15 is targeted to peroxisomes primarily via the Pex19-Pex3-dependent pathway; mistargeted Pex15 on mitochondria is extracted by the AAA-ATPase Msp1 and transferred to the ER for degradation or re-routed to peroxisomes via the Pex19-Pex3 pathway; even correctly localized peroxisomal Pex15 is extracted by peroxisomal Msp1 but returned to peroxisomes via Pex19-Pex3, revealing a dynamic quality-control cycle.","method":"Yeast genetics (deletion mutants), in vivo localization, epistasis analysis","journal":"The FEBS journal","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis with multiple deletion combinations and in vivo localization; single lab","pmids":["40344504"],"is_preprint":false},{"year":2017,"finding":"In Drosophila Pex19 mutants, loss of peroxisomes leads to HNF4-induced lipotoxicity: hyperactive HNF4 signaling upregulates lipase 3 and mitochondrial β-oxidation enzymes, resulting in enhanced lipolysis, elevated free fatty acids, and mitochondrial damage; increased acid lipase expression and free fatty acid accumulation are also observed in PEX19-deficient human patient fibroblasts.","method":"Drosophila Pex19 mutant analysis, genetic epistasis (Hnf4), patient fibroblast biochemical analysis","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 — Drosophila genetics with pathway placement plus patient fibroblast validation; 45 citations","pmids":["29282281"],"is_preprint":false}],"current_model":"PEX19 is a predominantly cytosolic, farnesylated chaperone and import receptor that binds newly synthesized peroxisomal membrane proteins (PMPs) via their hydrophobic targeting signals, stabilizes them in the cytosol, and delivers them to the peroxisomal membrane by docking onto PEX3 (via a conserved hydrophobic groove engaging PEX19 Phe29); farnesylation of PEX19 allosterically reshapes its C-terminal domain to enhance PMP recognition, and a conserved PEX19 helix (αd) both shields PMP transmembrane domains from cytosolic chaperones and interacts with PEX3 to trigger cargo release at the correct membrane; PEX19 additionally facilitates targeting of a subset of tail-anchored proteins to mitochondria and lipid droplets, and supports innate antiviral signaling through the peroxisome-MAVS pathway."},"narrative":{"teleology":[{"year":1999,"claim":"Identification of PEX19 as a farnesylated protein required for an early step of peroxisome membrane assembly established the gene's foundational role upstream of matrix protein import.","evidence":"Functional complementation of CHO mutant ZP119, patient mutation analysis, and immunolocalization","pmids":["10051604"],"confidence":"High","gaps":["Mechanism of membrane association unclear","Substrates (PMPs) bound by PEX19 not yet defined","Role of farnesylation not functionally dissected"]},{"year":2000,"claim":"Demonstration that PEX19 binds a broad spectrum of PMPs in the cytosol and that its loss causes PMP degradation or mitochondrial mistargeting established PEX19 as a cytosolic chaperone/receptor rather than a simple membrane component.","evidence":"Co-immunoprecipitation, subcellular fractionation, nuclear mislocalization assay, and loss-of-function in PEX19-deficient cells","pmids":["10704444"],"confidence":"High","gaps":["Nature of PMP targeting signals recognized by PEX19 unknown","Docking factor at the peroxisomal membrane unidentified"]},{"year":2003,"claim":"Showing that the PEX3–PEX19 interaction occurs predominantly at the peroxisomal membrane resolved where in the cell cargo handoff takes place, and domain mapping linked the PEX19 N-terminus to PEX3 binding.","evidence":"Quantitative FRET imaging in living cells with domain deletion analysis","pmids":["12924628"],"confidence":"High","gaps":["Structural basis of PEX3–PEX19 interface not resolved","Cargo release mechanism unknown"]},{"year":2004,"claim":"Defining PEX19 as both chaperone and import receptor for class 1 PMPs, and establishing PEX3 as the membrane docking factor, completed the core PEX3–PEX19 import pathway model.","evidence":"In vitro binding/stabilization assays, heterologous targeting, dominant-negative/transient inhibition, complementation in PEX3- and PEX19-deficient cells","pmids":["14709540","15007061"],"confidence":"High","gaps":["Structural details of PEX3–PEX19 docking unknown","Cargo release mechanism at the membrane unresolved","How PEX19 distinguishes class 1 from class 2 PMPs unclear"]},{"year":2005,"claim":"Mapping PEX19-binding sites on PMPs such as ALDP/PEX26 showed that these sites function as conserved targeting motifs, and luminal basic residues are critical for preventing mitochondrial mistargeting.","evidence":"Peptide array binding, mutagenesis, cross-species targeting assays in human fibroblasts and yeast","pmids":["15781447","16763195"],"confidence":"High","gaps":["Structural basis of PMP signal recognition by PEX19 unresolved","How the same signals avoid mitochondrial targeting machinery not fully explained"]},{"year":2009,"claim":"The crystal structure of PEX14N in complex with a PEX19 motif revealed that PEX5 and PEX19 compete for the same site on PEX14, suggesting PEX19 plays a role in PEX14 membrane insertion and connecting the membrane and matrix import machineries.","evidence":"Crystal structure, NMR, mutagenesis, in vivo localization in yeast","pmids":["19197237"],"confidence":"High","gaps":["Physiological consequence of PEX5/PEX19 competition at PEX14 not fully explored in mammalian cells","Whether PEX14 is a true cargo of PEX19 in vivo still debated"]},{"year":2010,"claim":"Crystal structures of the PEX3 cytosolic domain bound to PEX19 peptide revealed a hydrophobic groove on PEX3 engaging PEX19-Phe29, providing the atomic-level mechanism of receptor–docking factor recognition.","evidence":"X-ray crystallography, mutagenesis, binding affinity measurements","pmids":["20554521","22624858"],"confidence":"High","gaps":["Full-length PEX19 structure in complex with PEX3 not available","How PEX3 binding triggers cargo release unresolved"]},{"year":2013,"claim":"Reconstitution of PEX19-dependent, TRC40-independent targeting of the tail-anchored protein PEX26 to peroxisomes demonstrated a complete alternative TA insertion pathway distinct from the ER GET pathway.","evidence":"Co-immunoprecipitation, siRNA knockdown, mutagenesis, in vivo targeting assays","pmids":["23460677"],"confidence":"High","gaps":["Membrane insertion step not reconstituted in a cell-free system","Generality to other TA PMPs not fully tested"]},{"year":2017,"claim":"NMR structure of farnesylated PEX19 C-terminal domain showed that the farnesyl group is buried internally, allosterically creating hydrophobic pockets for PMP recognition—explaining why farnesylation enhances but is not absolutely required for PMP binding.","evidence":"NMR structure, mutagenesis, functional complementation in Zellweger patient fibroblasts","pmids":["28281558"],"confidence":"High","gaps":["Structure of full-length farnesylated PEX19 bound to intact PMP cargo unavailable","Energetic contribution of farnesylation versus direct PMP contacts not quantitatively separated"]},{"year":2018,"claim":"Discovery that yeast Pex19 mediates targeting of mitochondrial tail-anchored proteins Fis1 and Gem1 expanded PEX19's role beyond peroxisomes to mitochondrial biogenesis.","evidence":"Yeast genetics (PEX19 deletion), in organello import assay, direct binding with recombinant proteins","pmids":["30033679"],"confidence":"High","gaps":["Whether this mitochondrial targeting role is conserved in mammals not demonstrated","Mechanism distinguishing peroxisomal from mitochondrial delivery unknown"]},{"year":2022,"claim":"Separation-of-function analysis showed that farnesylated PEX19 specifically controls lipid droplet protein composition and neutral lipid metabolism through a peroxisome-independent mechanism, revealing a third organelle target for PEX19.","evidence":"Farnesylation mutant analysis, proteomics, lipidomics, rescue experiments in PEX19-deficient cells","pmids":["35557938"],"confidence":"Medium","gaps":["Identity of lipid droplet targeting receptor (PEX3 equivalent) unknown","Structural basis of farnesylation-dependent LD specificity unresolved","Not independently replicated"]},{"year":2024,"claim":"Identification of PEX19 helix αd as a dual-function element that shields PMP TMDs from cytosolic chaperones and triggers PEX3-dependent cargo release resolved the long-standing question of how PEX19 couples cargo protection to destination-specific release.","evidence":"Biochemical analysis, mass spectrometry, mutagenesis, in vivo targeting assay","pmids":["38585659"],"confidence":"Medium","gaps":["Structural visualization of αd–PEX3 interaction in the full complex not available","Generality of αd-mediated release to diverse PMP cargoes not tested","Single-lab finding"]},{"year":2025,"claim":"Epistasis analysis in yeast revealed a dynamic quality-control cycle in which Msp1 extracts both mistargeted and correctly localized Pex15, with Pex19–Pex3 mediating re-insertion, redefining PEX19's role as not just an import factor but a continuous maintenance chaperone.","evidence":"Yeast genetics with multiple deletion combinations and in vivo localization","pmids":["40344504"],"confidence":"Medium","gaps":["Whether mammalian PEX19 participates in analogous quality-control cycles unknown","Msp1/ATAD1-PEX19 handoff mechanism not biochemically reconstituted","Single-lab study"]},{"year":null,"claim":"A full structural model of PEX19 bound simultaneously to a PMP cargo and PEX3, and the mechanism by which PMP transmembrane domains are inserted into the peroxisomal lipid bilayer, remain unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structure of full-length farnesylated PEX19 in ternary complex with PEX3 and PMP cargo","Membrane insertion mechanism not reconstituted in vitro","Rules distinguishing peroxisomal, mitochondrial, and lipid droplet targeting by PEX19 undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[0,2,16]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,3,9]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[10,17]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0005777","term_label":"peroxisome","supporting_discovery_ids":[1,8]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[17]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,2,3,9,14]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[1,3,11]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[17,21]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[19]}],"complexes":["PEX3-PEX19 import complex"],"partners":["PEX3","PEX14","PEX26","PEX11","FIS1","GEM1","RSAD2"],"other_free_text":[]},"mechanistic_narrative":"PEX19 is a predominantly cytosolic, farnesylated chaperone and import receptor essential for peroxisomal membrane biogenesis. It binds newly synthesized peroxisomal membrane proteins (PMPs) through their hydrophobic targeting signals via its C-terminal domain—where farnesylation allosterically creates hydrophobic pockets for cargo recognition—stabilizes them against aggregation in the cytosol, and delivers them to the peroxisomal membrane by docking onto PEX3 through its N-terminal domain, with PEX19 Phe29 engaging a hydrophobic groove on PEX3 [PMID:10704444, PMID:14709540, PMID:20554521, PMID:28281558]. A conserved PEX19 helix (αd) shields PMP transmembrane domains from cytosolic chaperones and interacts with PEX3 to trigger cargo release at the destination membrane [PMID:38585659]. Beyond peroxisomal PMPs, PEX19 mediates targeting of tail-anchored proteins to mitochondria, controls lipid droplet protein composition via a farnesylation-dependent mechanism, and participates in a dynamic Msp1-dependent quality-control cycle that re-routes mistargeted membrane proteins back to peroxisomes [PMID:30033679, PMID:35557938, PMID:40344504]."},"prefetch_data":{"uniprot":{"accession":"P40855","full_name":"Peroxisomal biogenesis factor 19","aliases":["33 kDa housekeeping protein","Peroxin-19","Peroxisomal farnesylated protein"],"length_aa":299,"mass_kda":32.8,"function":"Necessary for early peroxisomal biogenesis. Acts both as a cytosolic chaperone and as an import receptor for peroxisomal membrane proteins (PMPs). Binds and stabilizes newly synthesized PMPs in the cytoplasm by interacting with their hydrophobic membrane-spanning domains, and targets them to the peroxisome membrane by binding to the integral membrane protein PEX3. Excludes CDKN2A from the nucleus and prevents its interaction with MDM2, which results in active degradation of TP53","subcellular_location":"Cytoplasm; Peroxisome membrane","url":"https://www.uniprot.org/uniprotkb/P40855/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PEX19","classification":"Not Classified","n_dependent_lines":44,"n_total_lines":1208,"dependency_fraction":0.03642384105960265},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PEX3","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/search/PEX19","total_profiled":1310},"omim":[{"mim_id":"617399","title":"PEROXISOMAL MEMBRANE PROTEIN 2; PXMP2","url":"https://www.omim.org/entry/617399"},{"mim_id":"614886","title":"PEROXISOME BIOGENESIS DISORDER 12A (ZELLWEGER); PBD12A","url":"https://www.omim.org/entry/614886"},{"mim_id":"600279","title":"PEROXISOME BIOGENESIS FACTOR 19; 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loss of PEX19 leads to degradation or mistargeting of PMPs to mitochondria, establishing PEX19 as required for peroxisome membrane synthesis.\",\n      \"method\": \"Co-immunoprecipitation, subcellular fractionation, mislocalization assay, loss-of-function in PEX19-deficient cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal binding assays, mislocalization experiment, and loss-of-function with defined phenotypic readout; foundational study with 257 citations\",\n      \"pmids\": [\"10704444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Human PEX19 encodes a 299-aa hydrophilic protein with a C-terminal CAAX farnesylation motif; farnesylated PEX19 is partly anchored in the peroxisomal membrane with its N-terminal region exposed to the cytosol; PEX19 is required for peroxisome membrane assembly at an early stage, before matrix protein import.\",\n      \"method\": \"Functional complementation of CHO mutant ZP119, mutation analysis in Zellweger patient, immunolocalization\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — functional complementation plus patient mutation analysis; highly cited foundational paper\",\n      \"pmids\": [\"10051604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PEX19 functions as both a cytosolic chaperone and an import receptor for newly synthesized class 1 PMPs: it binds and stabilizes PMPs in the cytosol, interacts with hydrophobic PMP targeting signals (mPTSs), and is essential for class 1 PMP targeting and import; class 2 mPTSs are PEX19-independent.\",\n      \"method\": \"In vitro binding assays, PMP stabilization assays, complementation in PEX19-deficient cells, RNAi knockdown\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal in vitro and in vivo assays; 205 citations; replicated concept from same group with added mechanistic detail\",\n      \"pmids\": [\"14709540\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PEX3 is the docking factor for PEX19 at the peroxisomal membrane: PEX3 is required for PEX19 docking at peroxisomes, interacts specifically with the N-terminal docking domain of PEX19 via a conserved motif, is sufficient to dock PEX19 at heterologous organelles, and its transient inhibition abrogates class 1 PMP import but not class 2 or matrix protein import.\",\n      \"method\": \"Co-immunoprecipitation, heterologous targeting assay, transient inhibition/dominant-negative, complementation in PEX3-deficient cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, reciprocal interaction data, epistasis; 191 citations\",\n      \"pmids\": [\"15007061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The tail-anchored peroxisomal membrane protein PEX26 contains two PEX19-binding sites in its C-terminal targeting signal: one overlapping with the transmembrane domain and one in the luminal domain; the luminal PEX19-binding site is essential for correct peroxisomal targeting and prevents mislocalization to mitochondria; PEX19 is required for PEX26 import.\",\n      \"method\": \"Deletion/mutation analysis, heterologous targeting assay, co-immunoprecipitation, PEX19 knockdown\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis combined with functional targeting assays and knockdown; 104 citations\",\n      \"pmids\": [\"16763195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"PEX19-binding sites on peroxisomal membrane proteins (including ALDP/adrenoleukodystrophy protein) serve as targeting motifs; the identified PEX19-binding site of ALDP is bound by both human and yeast PEX19 and is required for peroxisomal targeting in human fibroblasts and in yeast, demonstrating evolutionary conservation of PMP targeting signals.\",\n      \"method\": \"Peptide array binding, in vivo targeting assays in human fibroblasts and yeast, deletion mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods across species; 63 citations\",\n      \"pmids\": [\"15781447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The N-terminal domain of Pex14 (Pex14N) adopts a three-helical fold and binds both Pex5 and Pex19 competitively at the same surface but with opposite directionality; a conserved F/YFxxxF motif in PEX19 mediates this interaction; mutations of Pex14 residues in the binding region disrupt Pex5/Pex19 binding in vitro and impair Pex14 peroxisomal membrane localization in vivo.\",\n      \"method\": \"Crystal structure, NMR, mutagenesis, in vitro binding, in vivo localization assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis plus in vivo validation; 73 citations\",\n      \"pmids\": [\"19197237\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structure of the cytosolic domain of PEX3 in complex with a PEX19-derived peptide reveals that PEX3 adopts a novel large helical bundle fold with a hydrophobic groove at its membrane-distal end that engages the PEX19 peptide with nanomolar affinity; phenylalanine 29 of PEX19 is critical for the PEX3-PEX19 interaction.\",\n      \"method\": \"X-ray crystallography, mutagenesis, binding affinity measurements\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis validation; 48 citations\",\n      \"pmids\": [\"20554521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"The PEX3-PEX19 interaction occurs predominantly at the peroxisomal membrane in living cells; the PEX19-binding domain in the C-terminal half of PEX3 is required for peroxisomal localization; deletion of the PEX3 N-terminal targeting sequence or the PEX19-binding domain mislocalizes PEX3 and abolishes interaction with PEX19.\",\n      \"method\": \"FRET imaging (EYFP/ECFP fusion proteins), donor photobleaching, complementation in PEX3- and PEX19-deficient fibroblasts\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — quantitative FRET in living cells with domain deletion analysis; 38 citations\",\n      \"pmids\": [\"12924628\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PEX19 forms a cytosolic complex with the tail-anchored peroxisomal membrane protein PEX26 and translocates it directly to peroxisomes by interacting with PEX3; this pathway is TRC40-independent; basic amino acids in the luminal domain of PEX26 are essential for PEX19 binding and peroxisomal targeting.\",\n      \"method\": \"Co-immunoprecipitation, dominant-negative/siRNA knockdown, mutagenesis, in vivo targeting assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, epistasis with TRC40, mutagenesis; 80 citations\",\n      \"pmids\": [\"23460677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Farnesylation of PEX19 at its C-terminal CaaX motif allosterically reshapes the PEX19 C-terminal domain to form two hydrophobic pockets that recognize conserved aromatic/aliphatic side chains in PMPs; the farnesyl moiety is buried in an internal hydrophobic cavity inducing conformational changes; mutations abolishing farnesyl contacts or PMP recognition prevent cargo binding and cannot complement a ΔPEX19 phenotype in Zellweger patient fibroblasts.\",\n      \"method\": \"NMR structure of farnesylated PEX19 CTD, mutagenesis, in vivo complementation in patient fibroblasts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure plus mutagenesis plus functional complementation in vivo; 42 citations\",\n      \"pmids\": [\"28281558\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Mutagenesis of the PEX19-binding region of PEX3 reduces PEX19 affinity and destabilizes PEX3; the PEX3-PEX19 complex is required for de novo formation of peroxisomes; a hydrophobic groove near the base of PEX3 is involved in PMP insertion into the membrane.\",\n      \"method\": \"Site-directed mutagenesis, in vitro binding assays, functional complementation in peroxisome-deficient cells\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis combined with biochemical and functional assays; 38 citations\",\n      \"pmids\": [\"22624858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PEX19 is farnesylated in vitro and in vivo at its C-terminal CAAX motif; two splice variants differ in biological activity: PEX19ΔE8 (lacking domain D3/CAAX) restores peroxisomal biogenesis in PEX19-deficient fibroblasts and interacts with PEX3, demonstrating that farnesylation is not absolutely essential; PEX19ΔE2 (lacking N-terminal domain D1) fails to restore biogenesis and cannot interact with PEX3 lacking its peroxisomal targeting region.\",\n      \"method\": \"In vitro farnesylation assay, co-immunoprecipitation, functional complementation in PEX19-deficient fibroblasts\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple assays but single lab; 22 citations\",\n      \"pmids\": [\"11883941\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Deletion mapping in Pichia pastoris defines the minimum N-terminal (aa 1-150) and C-terminal (aa 89-300) regions of Pex19 required for peroxisome biogenesis; N-terminal deletions disrupt Pex3 binding while preserving Pex10 interaction; C-terminal deletions disrupt PMP (Pex10) binding while preserving Pex3 interaction; Pex25 overexpression can partially rescue Pex19 C-terminal truncation by enhancing Pex3 interaction.\",\n      \"method\": \"Deletion mutagenesis, co-immunoprecipitation, growth assay, yeast genetics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — systematic deletion analysis with orthogonal biochemical and functional assays; single lab\",\n      \"pmids\": [\"28526747\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In budding yeast, Pex19 acts as an import mediator for a subset of mitochondrial tail-anchored (TA) proteins (Fis1 and Gem1); deletion of PEX19 causes growth defects under respiratory conditions, altered mitochondrial morphology, reduced steady-state levels of Fis1 and Gem1, and hampered in organello import of these TA proteins; recombinant Pex19 directly binds Fis1 and Gem1.\",\n      \"method\": \"Yeast genetics (PEX19 deletion), in organello import assay, direct binding with recombinant proteins, steady-state level analysis\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (genetic, biochemical, in organello); direct binding demonstrated with recombinant proteins; 40 citations\",\n      \"pmids\": [\"30033679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PEX19 is an intrinsically disordered protein; upon interaction with PEX3, three regions of PEX19 become protected from hydrogen exchange (N-terminus, a middle stretch F64-L74, and C-terminus), while PEX3 becomes more protected in its binding groove; the N-terminus of PEX19 initiates binding to PEX3, followed by subtle conformational changes in PEX3 that allow higher-affinity engagement via folding of a short helix in PEX19.\",\n      \"method\": \"Hydrogen exchange mass spectrometry\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — H/D exchange MS provides conformational detail of complex formation; single lab, single method\",\n      \"pmids\": [\"25062251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Pex11 contains one Pex19-binding site (Pex19-BS) required for Pex19-mediated membrane insertion but non-essential for peroxisomal trafficking; Pex19 acts as a chaperone by binding Pex19-BS in Pex11 and preventing spontaneous Pex11 oligomerization and aggregation; Pex11 also has a second, Pex19-independent mPTS for peroxisomal trafficking.\",\n      \"method\": \"Mutagenesis, co-immunoprecipitation, in vivo targeting assay, aggregation assay in Pichia pastoris\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — extensive mutagenesis with functional assays; single lab\",\n      \"pmids\": [\"35011719\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Non-farnesylated PEX19 is sufficient to restore peroxisomal metabolic activity, while farnesylated PEX19 specifically controls lipid droplet (LD) protein composition and neutral lipid metabolism through a peroxisome-independent mechanism; in the absence of PEX19-dependent LD proteome, cells accumulate excess triacylglycerols and fail to deplete neutral lipid stores.\",\n      \"method\": \"Farnesylation mutant analysis, systems-level proteomics, lipid quantification, rescue experiments in PEX19-deficient cells\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (proteomics, lipidomics, rescue); single lab\",\n      \"pmids\": [\"35557938\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A conserved PEX19 helix (αd) prevents improper exposure of the PEX26 transmembrane domain (TMD) to cytosolic chaperones, and the αd helix also interacts with the cytosolic domain of the PEX3 receptor to trigger PEX26 release at the correct destination membrane; the PEX3-G138E mutant abolishes this secondary interaction, preventing PEX3-induced PEX26 release from PEX19.\",\n      \"method\": \"Biochemical analysis, mass spectrometry, mutagenesis, in vivo targeting assay\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — biochemical and MS-based evidence with mutagenesis; single lab\",\n      \"pmids\": [\"38585659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Viperin (an interferon-stimulated gene product) binds PEX19 as a physical interaction partner; viperin colocalizes with peroxisomal proteins and its augmentation of RIG-I-like receptor (RLR) signaling requires PEX19 expression; knockdown of PEX19 abolishes viperin-mediated augmentation of innate antiviral signaling.\",\n      \"method\": \"Proteomics-based screening, co-immunoprecipitation, colocalization, RNAi knockdown with functional readout (IFN-β induction)\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single pulldown/coIP plus functional knockdown; single lab\",\n      \"pmids\": [\"34108265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In yeast, newly synthesized Pex15 is targeted to peroxisomes primarily via the Pex19-Pex3-dependent pathway; mistargeted Pex15 on mitochondria is extracted by the AAA-ATPase Msp1 and transferred to the ER for degradation or re-routed to peroxisomes via the Pex19-Pex3 pathway; even correctly localized peroxisomal Pex15 is extracted by peroxisomal Msp1 but returned to peroxisomes via Pex19-Pex3, revealing a dynamic quality-control cycle.\",\n      \"method\": \"Yeast genetics (deletion mutants), in vivo localization, epistasis analysis\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with multiple deletion combinations and in vivo localization; single lab\",\n      \"pmids\": [\"40344504\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In Drosophila Pex19 mutants, loss of peroxisomes leads to HNF4-induced lipotoxicity: hyperactive HNF4 signaling upregulates lipase 3 and mitochondrial β-oxidation enzymes, resulting in enhanced lipolysis, elevated free fatty acids, and mitochondrial damage; increased acid lipase expression and free fatty acid accumulation are also observed in PEX19-deficient human patient fibroblasts.\",\n      \"method\": \"Drosophila Pex19 mutant analysis, genetic epistasis (Hnf4), patient fibroblast biochemical analysis\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Drosophila genetics with pathway placement plus patient fibroblast validation; 45 citations\",\n      \"pmids\": [\"29282281\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PEX19 is a predominantly cytosolic, farnesylated chaperone and import receptor that binds newly synthesized peroxisomal membrane proteins (PMPs) via their hydrophobic targeting signals, stabilizes them in the cytosol, and delivers them to the peroxisomal membrane by docking onto PEX3 (via a conserved hydrophobic groove engaging PEX19 Phe29); farnesylation of PEX19 allosterically reshapes its C-terminal domain to enhance PMP recognition, and a conserved PEX19 helix (αd) both shields PMP transmembrane domains from cytosolic chaperones and interacts with PEX3 to trigger cargo release at the correct membrane; PEX19 additionally facilitates targeting of a subset of tail-anchored proteins to mitochondria and lipid droplets, and supports innate antiviral signaling through the peroxisome-MAVS pathway.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PEX19 is a predominantly cytosolic, farnesylated chaperone and import receptor essential for peroxisomal membrane biogenesis. It binds newly synthesized peroxisomal membrane proteins (PMPs) through their hydrophobic targeting signals via its C-terminal domain—where farnesylation allosterically creates hydrophobic pockets for cargo recognition—stabilizes them against aggregation in the cytosol, and delivers them to the peroxisomal membrane by docking onto PEX3 through its N-terminal domain, with PEX19 Phe29 engaging a hydrophobic groove on PEX3 [PMID:10704444, PMID:14709540, PMID:20554521, PMID:28281558]. A conserved PEX19 helix (αd) shields PMP transmembrane domains from cytosolic chaperones and interacts with PEX3 to trigger cargo release at the destination membrane [PMID:38585659]. Beyond peroxisomal PMPs, PEX19 mediates targeting of tail-anchored proteins to mitochondria, controls lipid droplet protein composition via a farnesylation-dependent mechanism, and participates in a dynamic Msp1-dependent quality-control cycle that re-routes mistargeted membrane proteins back to peroxisomes [PMID:30033679, PMID:35557938, PMID:40344504].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Identification of PEX19 as a farnesylated protein required for an early step of peroxisome membrane assembly established the gene's foundational role upstream of matrix protein import.\",\n      \"evidence\": \"Functional complementation of CHO mutant ZP119, patient mutation analysis, and immunolocalization\",\n      \"pmids\": [\"10051604\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of membrane association unclear\", \"Substrates (PMPs) bound by PEX19 not yet defined\", \"Role of farnesylation not functionally dissected\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstration that PEX19 binds a broad spectrum of PMPs in the cytosol and that its loss causes PMP degradation or mitochondrial mistargeting established PEX19 as a cytosolic chaperone/receptor rather than a simple membrane component.\",\n      \"evidence\": \"Co-immunoprecipitation, subcellular fractionation, nuclear mislocalization assay, and loss-of-function in PEX19-deficient cells\",\n      \"pmids\": [\"10704444\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nature of PMP targeting signals recognized by PEX19 unknown\", \"Docking factor at the peroxisomal membrane unidentified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showing that the PEX3–PEX19 interaction occurs predominantly at the peroxisomal membrane resolved where in the cell cargo handoff takes place, and domain mapping linked the PEX19 N-terminus to PEX3 binding.\",\n      \"evidence\": \"Quantitative FRET imaging in living cells with domain deletion analysis\",\n      \"pmids\": [\"12924628\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PEX3–PEX19 interface not resolved\", \"Cargo release mechanism unknown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defining PEX19 as both chaperone and import receptor for class 1 PMPs, and establishing PEX3 as the membrane docking factor, completed the core PEX3–PEX19 import pathway model.\",\n      \"evidence\": \"In vitro binding/stabilization assays, heterologous targeting, dominant-negative/transient inhibition, complementation in PEX3- and PEX19-deficient cells\",\n      \"pmids\": [\"14709540\", \"15007061\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural details of PEX3–PEX19 docking unknown\", \"Cargo release mechanism at the membrane unresolved\", \"How PEX19 distinguishes class 1 from class 2 PMPs unclear\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Mapping PEX19-binding sites on PMPs such as ALDP/PEX26 showed that these sites function as conserved targeting motifs, and luminal basic residues are critical for preventing mitochondrial mistargeting.\",\n      \"evidence\": \"Peptide array binding, mutagenesis, cross-species targeting assays in human fibroblasts and yeast\",\n      \"pmids\": [\"15781447\", \"16763195\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PMP signal recognition by PEX19 unresolved\", \"How the same signals avoid mitochondrial targeting machinery not fully explained\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"The crystal structure of PEX14N in complex with a PEX19 motif revealed that PEX5 and PEX19 compete for the same site on PEX14, suggesting PEX19 plays a role in PEX14 membrane insertion and connecting the membrane and matrix import machineries.\",\n      \"evidence\": \"Crystal structure, NMR, mutagenesis, in vivo localization in yeast\",\n      \"pmids\": [\"19197237\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological consequence of PEX5/PEX19 competition at PEX14 not fully explored in mammalian cells\", \"Whether PEX14 is a true cargo of PEX19 in vivo still debated\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Crystal structures of the PEX3 cytosolic domain bound to PEX19 peptide revealed a hydrophobic groove on PEX3 engaging PEX19-Phe29, providing the atomic-level mechanism of receptor–docking factor recognition.\",\n      \"evidence\": \"X-ray crystallography, mutagenesis, binding affinity measurements\",\n      \"pmids\": [\"20554521\", \"22624858\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length PEX19 structure in complex with PEX3 not available\", \"How PEX3 binding triggers cargo release unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Reconstitution of PEX19-dependent, TRC40-independent targeting of the tail-anchored protein PEX26 to peroxisomes demonstrated a complete alternative TA insertion pathway distinct from the ER GET pathway.\",\n      \"evidence\": \"Co-immunoprecipitation, siRNA knockdown, mutagenesis, in vivo targeting assays\",\n      \"pmids\": [\"23460677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Membrane insertion step not reconstituted in a cell-free system\", \"Generality to other TA PMPs not fully tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"NMR structure of farnesylated PEX19 C-terminal domain showed that the farnesyl group is buried internally, allosterically creating hydrophobic pockets for PMP recognition—explaining why farnesylation enhances but is not absolutely required for PMP binding.\",\n      \"evidence\": \"NMR structure, mutagenesis, functional complementation in Zellweger patient fibroblasts\",\n      \"pmids\": [\"28281558\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length farnesylated PEX19 bound to intact PMP cargo unavailable\", \"Energetic contribution of farnesylation versus direct PMP contacts not quantitatively separated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Discovery that yeast Pex19 mediates targeting of mitochondrial tail-anchored proteins Fis1 and Gem1 expanded PEX19's role beyond peroxisomes to mitochondrial biogenesis.\",\n      \"evidence\": \"Yeast genetics (PEX19 deletion), in organello import assay, direct binding with recombinant proteins\",\n      \"pmids\": [\"30033679\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this mitochondrial targeting role is conserved in mammals not demonstrated\", \"Mechanism distinguishing peroxisomal from mitochondrial delivery unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Separation-of-function analysis showed that farnesylated PEX19 specifically controls lipid droplet protein composition and neutral lipid metabolism through a peroxisome-independent mechanism, revealing a third organelle target for PEX19.\",\n      \"evidence\": \"Farnesylation mutant analysis, proteomics, lipidomics, rescue experiments in PEX19-deficient cells\",\n      \"pmids\": [\"35557938\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of lipid droplet targeting receptor (PEX3 equivalent) unknown\", \"Structural basis of farnesylation-dependent LD specificity unresolved\", \"Not independently replicated\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identification of PEX19 helix αd as a dual-function element that shields PMP TMDs from cytosolic chaperones and triggers PEX3-dependent cargo release resolved the long-standing question of how PEX19 couples cargo protection to destination-specific release.\",\n      \"evidence\": \"Biochemical analysis, mass spectrometry, mutagenesis, in vivo targeting assay\",\n      \"pmids\": [\"38585659\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural visualization of αd–PEX3 interaction in the full complex not available\", \"Generality of αd-mediated release to diverse PMP cargoes not tested\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Epistasis analysis in yeast revealed a dynamic quality-control cycle in which Msp1 extracts both mistargeted and correctly localized Pex15, with Pex19–Pex3 mediating re-insertion, redefining PEX19's role as not just an import factor but a continuous maintenance chaperone.\",\n      \"evidence\": \"Yeast genetics with multiple deletion combinations and in vivo localization\",\n      \"pmids\": [\"40344504\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether mammalian PEX19 participates in analogous quality-control cycles unknown\", \"Msp1/ATAD1-PEX19 handoff mechanism not biochemically reconstituted\", \"Single-lab study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full structural model of PEX19 bound simultaneously to a PMP cargo and PEX3, and the mechanism by which PMP transmembrane domains are inserted into the peroxisomal lipid bilayer, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of full-length farnesylated PEX19 in ternary complex with PEX3 and PMP cargo\", \"Membrane insertion mechanism not reconstituted in vitro\", \"Rules distinguishing peroxisomal, mitochondrial, and lipid droplet targeting by PEX19 undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [0, 2, 16]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 3, 9]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [10, 17]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0005777\", \"supporting_discovery_ids\": [1, 8]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [17]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 2, 3, 9, 14]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [1, 3, 11]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [17, 21]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [19]}\n    ],\n    \"complexes\": [\n      \"PEX3-PEX19 import complex\"\n    ],\n    \"partners\": [\n      \"PEX3\",\n      \"PEX14\",\n      \"PEX26\",\n      \"PEX11\",\n      \"FIS1\",\n      \"GEM1\",\n      \"RSAD2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}