{"gene":"PRAF2","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2005,"finding":"PRAF2 (JM4) is a four-transmembrane protein that physically interacts with (co-precipitates with) the CCR5 chemokine receptor. It co-localizes with calnexin in the endoplasmic reticulum and with the mannose 6-phosphate receptor in the Golgi. PRAF2 also heterodimerizes with the related proteins JWA and GTRAP3-18, and harbors a Rab-acceptor motif, suggesting a function in vesicle formation at the Golgi complex.","method":"Co-immunoprecipitation, co-localization by immunofluorescence microscopy, two-hybrid interaction screen","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP and co-localization demonstrated, single lab, multiple orthogonal methods (Co-IP + immunofluorescence)","pmids":["15757671"],"is_preprint":false},{"year":2007,"finding":"PRAF2 protein localizes in bright cytoplasmic punctae in neuroblastoma cells (consistent with vesicular/ER-Golgi compartments), and its protein levels increase during cerulenin-induced apoptosis.","method":"Immunofluorescence microscopy, Annexin V staining, PARP cleavage assay","journal":"Clinical cancer research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, localization without functional mechanistic link established","pmids":["17975142"],"is_preprint":false},{"year":2010,"finding":"PRAF2 interacts with Bcl-xL, and this interaction depends on the transmembrane domain of Bcl-xL. PRAF2 also interacts with Bcl-2. Overexpression of PRAF2 induces translocation of Bax to mitochondria and apoptotic cell death; this death is prevented by co-transfection of Bcl-xL but not by a transmembrane-domain-deleted mutant of Bcl-xL. Knockdown of PRAF2 increases clonogenicity of U2OS cells after etoposide treatment by reducing cell death.","method":"Tandem affinity purification (TAP), Co-IP, overexpression/knockdown with apoptosis readouts (Annexin V, caspase), Bax mitochondrial translocation assay, domain-deletion mutagenesis","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — TAP screen, Co-IP validation, domain mutagenesis, and functional KD/OE with multiple orthogonal readouts in single rigorous study","pmids":["21203533"],"is_preprint":false},{"year":2010,"finding":"PRAF2 protein is detected in small vesicle-like structures throughout the cytoplasm and in/around cell nuclei of malignant glioma cells. Monomeric and dimeric forms of PRAF2 associate with different subcellular compartments. RNAi-mediated knockdown of PRAF2 significantly reduces cell viability, migration, and invasiveness of U-87 glioma cells.","method":"Immunofluorescence microscopy, cell fractionation, RNA interference, migration/invasion assays","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — multiple orthogonal methods (fractionation, microscopy, functional KD), single lab","pmids":["20412121"],"is_preprint":false},{"year":2015,"finding":"Ultrastructural and immunocytochemical analysis confirmed PRAF2 localization primarily in the ER of neurons, but also revealed previously unrecognized localizations in mitochondria, primary cilia, and the sub-synaptic region of mouse CNS. PRAF2 acts as a gatekeeper for the GABAB receptor GB1 subunit, preventing its progression through the biosynthetic pathway in the absence of heterodimerization with GB2.","method":"Immunofluorescence microscopy, electron microscopy (ultrastructural immunocytochemistry)","journal":"Brain structure & function","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — electron microscopy and immunofluorescence with functional context referenced, single lab","pmids":["26645984"],"is_preprint":false},{"year":2019,"finding":"JAG2-rich exosomes are released from colorectal cancer cells in a PRAF2-dependent manner, and these exosomes regulate metastasis of colorectal cancer cells in a paracrine manner, indicating PRAF2 has a role in exosome-mediated cargo trafficking.","method":"siRNA knockdown, transcriptome microarray, exosome isolation and functional assays","journal":"Cancer cell international","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, indirect evidence for PRAF2-dependent exosome release without direct mechanistic dissection","pmids":["31198409"],"is_preprint":false},{"year":2022,"finding":"PRAF2, an ER-resident gatekeeper, interacts stoichiometrically with both wild-type CFTR and the CF mutant CFTR-F508del, preventing newly synthesized CFTR from accessing ER exit sites (COPII vesicle recruitment). Because of its lower abundance, CFTR-F508del recruitment into COPII vesicles is suppressed by PRAF2. Pharmacological chaperones that rescue CFTR-F508del function in CF patients act at least partly by targeting CFTR-F508del retention by PRAF2.","method":"Co-immunoprecipitation, COPII vesicle budding assay, pharmacological chaperone treatment, proximity/co-localization assays","journal":"Cellular and molecular life sciences : CMLS","confidence":"High","confidence_rationale":"Tier 2 / Strong — stoichiometric Co-IP, COPII vesicle budding assay, pharmacological rescue experiments, multiple orthogonal approaches in one study","pmids":["36167862"],"is_preprint":false},{"year":2023,"finding":"PRAF2 inhibits CCR5 plasma membrane export in a concentration-dependent manner. PRAF2/CCR5 interaction does not require the CCR5 C-terminal tail but instead involves the transmembrane domains of both proteins. The di-leucine/RXR motif in the third intracellular loop of CCR5 does not affect PRAF2-mediated retention; rather, it impairs CCR5 interaction with its private escort protein CD4. PRAF2 and CD4 exert opposing effects on CCR5 cell-surface export, likely by regulating CCR5 recruitment into COPII vesicles at ER exit sites.","method":"BRET-based subcellular localization assay, BRET proximity assay, Co-immunoprecipitation, domain mutation analysis","journal":"International journal of molecular sciences","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (BRET localization, BRET proximity, Co-IP, mutagenesis) in single study; mechanistically rigorous","pmids":["38139265"],"is_preprint":false}],"current_model":"PRAF2 is an ER-resident four-transmembrane-domain gatekeeper protein that retains polytopic plasma membrane proteins (including the GABAB receptor GB1 subunit, CFTR, and CCR5) in the ER by preventing their access to COPII vesicle exit sites, interacts with anti-apoptotic Bcl-xL and Bcl-2 via their transmembrane domains to suppress its pro-apoptotic activity (which involves Bax mitochondrial translocation), and participates in vesicle trafficking and exosome-mediated cargo release."},"narrative":{"mechanistic_narrative":"PRAF2 is an ER-resident four-transmembrane protein that functions as a gatekeeper controlling the biosynthetic export of polytopic plasma membrane proteins, retaining them in the ER until they are properly assembled [PMID:26645984, PMID:36167862, PMID:38139265]. It binds newly synthesized client receptors and transporters through transmembrane-domain contacts and prevents their recruitment into COPII vesicles at ER exit sites: it retains the GABAB receptor GB1 subunit in the absence of GB2 heterodimerization [PMID:26645984], stoichiometrically holds both wild-type and F508del CFTR away from ER exit sites such that pharmacological chaperones act in part by relieving this retention [PMID:36167862], and limits CCR5 plasma membrane export through transmembrane-domain interaction, an effect opposed by the CCR5 escort protein CD4 [PMID:38139265]. Beyond its trafficking role, PRAF2 has a pro-apoptotic activity: its overexpression drives Bax translocation to mitochondria and cell death, an activity suppressed by interaction with the transmembrane domains of the anti-apoptotic proteins Bcl-xL and Bcl-2 [PMID:21203533]. PRAF2 localizes principally to the ER, co-localizing with calnexin, and also distributes to Golgi, cytoplasmic vesicular puncta, and additional neuronal compartments, consistent with its trafficking and Rab-acceptor-associated functions [PMID:15757671, PMID:26645984].","teleology":[{"year":2005,"claim":"Established PRAF2 as a four-transmembrane protein physically associated with a GPCR (CCR5) and resident in the early secretory pathway, framing it as a candidate trafficking regulator.","evidence":"Co-IP, immunofluorescence co-localization with calnexin and M6P receptor, and two-hybrid screen in cell lines","pmids":["15757671"],"confidence":"Medium","gaps":["No functional consequence of the CCR5 interaction shown","Rab-acceptor motif function not tested directly","Heterodimerization with JWA/GTRAP3-18 not mechanistically dissected"]},{"year":2010,"claim":"Defined a pro-apoptotic activity for PRAF2 that is gated by anti-apoptotic Bcl-family proteins, linking the protein to mitochondrial death control.","evidence":"TAP/Co-IP, domain-deletion mutagenesis of Bcl-xL, Bax translocation assay, and overexpression/knockdown apoptosis readouts in U2OS cells","pmids":["21203533"],"confidence":"High","gaps":["Molecular mechanism by which PRAF2 promotes Bax translocation is unresolved","Whether the ER-trafficking role and apoptotic role are mechanistically connected is unknown"]},{"year":2010,"claim":"Tied PRAF2 expression to cancer-cell viability and motility, with monomeric versus dimeric forms partitioning to distinct compartments.","evidence":"Immunofluorescence, cell fractionation, RNAi, and migration/invasion assays in U-87 glioma cells","pmids":["20412121"],"confidence":"Medium","gaps":["Functional difference between monomer and dimer not defined","Mechanism linking PRAF2 to invasion not established"]},{"year":2015,"claim":"Identified the core gatekeeper function: PRAF2 retains the GABAB GB1 subunit in the biosynthetic pathway until heterodimerization with GB2.","evidence":"Immunofluorescence and ultrastructural immunocytochemistry (electron microscopy) in mouse CNS neurons","pmids":["26645984"],"confidence":"Medium","gaps":["Mechanism of release upon GB2 assembly not detailed","Functional roles of mitochondrial and primary cilia localizations unexplored"]},{"year":2019,"claim":"Extended PRAF2 function to exosome-mediated cargo release relevant to cancer metastasis.","evidence":"siRNA knockdown, transcriptome microarray, and exosome isolation/functional assays in colorectal cancer cells","pmids":["31198409"],"confidence":"Low","gaps":["Indirect evidence without direct mechanistic dissection of PRAF2 in exosome biogenesis","Whether effect is direct or secondary to trafficking changes is unclear"]},{"year":2022,"claim":"Demonstrated that PRAF2 acts at COPII exit sites by stoichiometrically retaining CFTR, including the F508del mutant, providing a disease-relevant mechanism for pharmacological chaperone action.","evidence":"Stoichiometric Co-IP, COPII vesicle budding assay, and pharmacological chaperone treatment","pmids":["36167862"],"confidence":"High","gaps":["Determinants of client selectivity not defined","How chaperones relieve PRAF2 retention mechanistically not resolved"]},{"year":2023,"claim":"Resolved the molecular logic of PRAF2 client retention versus escort: transmembrane-domain interaction drives retention, opposed by the client-specific escort CD4 at ER exit sites.","evidence":"BRET subcellular localization and proximity assays, Co-IP, and domain mutagenesis of CCR5","pmids":["38139265"],"confidence":"High","gaps":["General rules governing which escort proteins counteract PRAF2 are unknown","Structural basis of the transmembrane-domain contact not determined"]},{"year":null,"claim":"How PRAF2's ER-gatekeeper trafficking activity and its Bcl-family-gated pro-apoptotic activity are mechanistically integrated remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of PRAF2 or its transmembrane-domain client interactions","No unifying mechanism linking COPII retention to Bax-dependent apoptosis","Functional significance of mitochondrial and ciliary localizations uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[4,6,7]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,6,7]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,4,6]},{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[1,3]},{"term_id":"GO:0005739","term_label":"mitochondrion","supporting_discovery_ids":[4]},{"term_id":"GO:0005929","term_label":"cilium","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[4,6,7]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[6,7]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[2]}],"complexes":[],"partners":["CCR5","BCL2L1","BCL2","CFTR","GABBR1","CD4"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O60831","full_name":"PRA1 family protein 2","aliases":[],"length_aa":178,"mass_kda":19.3,"function":"May be involved in ER/Golgi transport and vesicular traffic. Plays a proapoptotic role in cerulenin-induced neuroblastoma apoptosis","subcellular_location":"Endosome membrane","url":"https://www.uniprot.org/uniprotkb/O60831/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PRAF2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"COPB2","stoichiometry":0.2},{"gene":"MCM10","stoichiometry":0.2},{"gene":"RAB1A","stoichiometry":0.2},{"gene":"RTN4","stoichiometry":0.2},{"gene":"YIPF5","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PRAF2","total_profiled":1310},"omim":[{"mim_id":"301038","title":"H2A.B VARIANT HISTONE 2; H2AB2","url":"https://www.omim.org/entry/301038"},{"mim_id":"300840","title":"PRA1 DOMAIN FAMILY, MEMBER 2; PRAF2","url":"https://www.omim.org/entry/300840"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Endoplasmic reticulum","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"epididymis","ntpm":154.3}],"url":"https://www.proteinatlas.org/search/PRAF2"},"hgnc":{"alias_symbol":["JM4","Yip6a"],"prev_symbol":[]},"alphafold":{"accession":"O60831","domains":[{"cath_id":"-","chopping":"30-171","consensus_level":"high","plddt":87.1497,"start":30,"end":171}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60831","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60831-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60831-F1-predicted_aligned_error_v6.png","plddt_mean":83.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PRAF2","jax_strain_url":"https://www.jax.org/strain/search?query=PRAF2"},"sequence":{"accession":"O60831","fasta_url":"https://rest.uniprot.org/uniprotkb/O60831.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60831/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60831"}},"corpus_meta":[{"pmid":"31649487","id":"PMC_31649487","title":"Long non-coding RNA HOTAIR functions as a competitive endogenous RNA to regulate PRAF2 expression by sponging miR-326 in cutaneous squamous cell carcinoma.","date":"2019","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/31649487","citation_count":45,"is_preprint":false},{"pmid":"15757671","id":"PMC_15757671","title":"JM4 is a four-transmembrane protein binding to the CCR5 receptor.","date":"2005","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/15757671","citation_count":44,"is_preprint":false},{"pmid":"21203533","id":"PMC_21203533","title":"Praf2 is a novel Bcl-xL/Bcl-2 interacting protein with the ability to modulate survival of cancer cells.","date":"2010","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21203533","citation_count":36,"is_preprint":false},{"pmid":"17975142","id":"PMC_17975142","title":"Expression of prenylated Rab acceptor 1 domain family, member 2 (PRAF2) in neuroblastoma: correlation with clinical features, cellular localization, and cerulenin-mediated apoptosis regulation.","date":"2007","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/17975142","citation_count":23,"is_preprint":false},{"pmid":"20412121","id":"PMC_20412121","title":"Subcellular distribution and expression of prenylated Rab acceptor 1 domain family, member 2 (PRAF2) in malignant glioma: Influence on cell survival and migration.","date":"2010","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/20412121","citation_count":22,"is_preprint":false},{"pmid":"31198409","id":"PMC_31198409","title":"Mutual regulation of JAG2 and PRAF2 promotes migration and invasion of colorectal cancer cells uncoupled from epithelial-mesenchymal transition.","date":"2019","source":"Cancer cell international","url":"https://pubmed.ncbi.nlm.nih.gov/31198409","citation_count":14,"is_preprint":false},{"pmid":"27654286","id":"PMC_27654286","title":"The Glycosylphosphatidylinositol-Anchored Variable Region of Llama Heavy Chain-Only Antibody JM4 Efficiently Blocks both Cell-Free and T Cell-T Cell Transmission of Human Immunodeficiency Virus Type 1.","date":"2016","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/27654286","citation_count":14,"is_preprint":false},{"pmid":"33245963","id":"PMC_33245963","title":"JHDM1D-AS1 aggravates the development of gastric cancer through miR-450a-2-3p-PRAF2 axis.","date":"2020","source":"Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/33245963","citation_count":13,"is_preprint":false},{"pmid":"16647040","id":"PMC_16647040","title":"Genetics of subpeptin JM4-A and subpeptin JM4-B production by Bacillus subtilis JM4.","date":"2006","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/16647040","citation_count":12,"is_preprint":false},{"pmid":"32959273","id":"PMC_32959273","title":"Prolonged Beneficial Effect of Brief Erythropoietin Peptide JM4 Therapy on Chronic Relapsing EAE.","date":"2020","source":"Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/32959273","citation_count":10,"is_preprint":false},{"pmid":"34103991","id":"PMC_34103991","title":"Grape Seed Proanthocyanidins (GSPs) Inhibit the Development of Cutaneous Squamous Cell Carcinoma by Regulating the hsa_circ_0070934/miR-136-5p/PRAF2 Axis.","date":"2021","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/34103991","citation_count":9,"is_preprint":false},{"pmid":"30100755","id":"PMC_30100755","title":"PRAF2 expression indicates unfavorable clinical outcome in hepatocellular carcinoma.","date":"2018","source":"Cancer management and research","url":"https://pubmed.ncbi.nlm.nih.gov/30100755","citation_count":7,"is_preprint":false},{"pmid":"36478884","id":"PMC_36478884","title":"PRAF2 is an oncogene acting to promote the proliferation and invasion of breast cancer cells.","date":"2022","source":"Experimental and therapeutic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/36478884","citation_count":7,"is_preprint":false},{"pmid":"26645984","id":"PMC_26645984","title":"Anatomical and ultrastructural study of PRAF2 expression in the mouse central nervous system.","date":"2015","source":"Brain structure & function","url":"https://pubmed.ncbi.nlm.nih.gov/26645984","citation_count":4,"is_preprint":false},{"pmid":"36167862","id":"PMC_36167862","title":"Pharmacological chaperone-rescued cystic fibrosis CFTR-F508del mutant overcomes PRAF2-gated access to endoplasmic reticulum exit sites.","date":"2022","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/36167862","citation_count":4,"is_preprint":false},{"pmid":"38139265","id":"PMC_38139265","title":"Control of CCR5 Cell-Surface Targeting by the PRAF2 Gatekeeper.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38139265","citation_count":1,"is_preprint":false},{"pmid":"39773456","id":"PMC_39773456","title":"PRAF2 as a novel biomarker for breast cancer with machine learning and experimentation validation.","date":"2025","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/39773456","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12067,"output_tokens":2169,"usd":0.034368,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9162,"output_tokens":2739,"usd":0.057142,"stage2_stop_reason":"end_turn"},"total_usd":0.09151,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"PRAF2 (JM4) is a four-transmembrane protein that physically interacts with (co-precipitates with) the CCR5 chemokine receptor. It co-localizes with calnexin in the endoplasmic reticulum and with the mannose 6-phosphate receptor in the Golgi. PRAF2 also heterodimerizes with the related proteins JWA and GTRAP3-18, and harbors a Rab-acceptor motif, suggesting a function in vesicle formation at the Golgi complex.\",\n      \"method\": \"Co-immunoprecipitation, co-localization by immunofluorescence microscopy, two-hybrid interaction screen\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP and co-localization demonstrated, single lab, multiple orthogonal methods (Co-IP + immunofluorescence)\",\n      \"pmids\": [\"15757671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PRAF2 protein localizes in bright cytoplasmic punctae in neuroblastoma cells (consistent with vesicular/ER-Golgi compartments), and its protein levels increase during cerulenin-induced apoptosis.\",\n      \"method\": \"Immunofluorescence microscopy, Annexin V staining, PARP cleavage assay\",\n      \"journal\": \"Clinical cancer research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, localization without functional mechanistic link established\",\n      \"pmids\": [\"17975142\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PRAF2 interacts with Bcl-xL, and this interaction depends on the transmembrane domain of Bcl-xL. PRAF2 also interacts with Bcl-2. Overexpression of PRAF2 induces translocation of Bax to mitochondria and apoptotic cell death; this death is prevented by co-transfection of Bcl-xL but not by a transmembrane-domain-deleted mutant of Bcl-xL. Knockdown of PRAF2 increases clonogenicity of U2OS cells after etoposide treatment by reducing cell death.\",\n      \"method\": \"Tandem affinity purification (TAP), Co-IP, overexpression/knockdown with apoptosis readouts (Annexin V, caspase), Bax mitochondrial translocation assay, domain-deletion mutagenesis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — TAP screen, Co-IP validation, domain mutagenesis, and functional KD/OE with multiple orthogonal readouts in single rigorous study\",\n      \"pmids\": [\"21203533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PRAF2 protein is detected in small vesicle-like structures throughout the cytoplasm and in/around cell nuclei of malignant glioma cells. Monomeric and dimeric forms of PRAF2 associate with different subcellular compartments. RNAi-mediated knockdown of PRAF2 significantly reduces cell viability, migration, and invasiveness of U-87 glioma cells.\",\n      \"method\": \"Immunofluorescence microscopy, cell fractionation, RNA interference, migration/invasion assays\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — multiple orthogonal methods (fractionation, microscopy, functional KD), single lab\",\n      \"pmids\": [\"20412121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ultrastructural and immunocytochemical analysis confirmed PRAF2 localization primarily in the ER of neurons, but also revealed previously unrecognized localizations in mitochondria, primary cilia, and the sub-synaptic region of mouse CNS. PRAF2 acts as a gatekeeper for the GABAB receptor GB1 subunit, preventing its progression through the biosynthetic pathway in the absence of heterodimerization with GB2.\",\n      \"method\": \"Immunofluorescence microscopy, electron microscopy (ultrastructural immunocytochemistry)\",\n      \"journal\": \"Brain structure & function\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — electron microscopy and immunofluorescence with functional context referenced, single lab\",\n      \"pmids\": [\"26645984\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"JAG2-rich exosomes are released from colorectal cancer cells in a PRAF2-dependent manner, and these exosomes regulate metastasis of colorectal cancer cells in a paracrine manner, indicating PRAF2 has a role in exosome-mediated cargo trafficking.\",\n      \"method\": \"siRNA knockdown, transcriptome microarray, exosome isolation and functional assays\",\n      \"journal\": \"Cancer cell international\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, indirect evidence for PRAF2-dependent exosome release without direct mechanistic dissection\",\n      \"pmids\": [\"31198409\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PRAF2, an ER-resident gatekeeper, interacts stoichiometrically with both wild-type CFTR and the CF mutant CFTR-F508del, preventing newly synthesized CFTR from accessing ER exit sites (COPII vesicle recruitment). Because of its lower abundance, CFTR-F508del recruitment into COPII vesicles is suppressed by PRAF2. Pharmacological chaperones that rescue CFTR-F508del function in CF patients act at least partly by targeting CFTR-F508del retention by PRAF2.\",\n      \"method\": \"Co-immunoprecipitation, COPII vesicle budding assay, pharmacological chaperone treatment, proximity/co-localization assays\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — stoichiometric Co-IP, COPII vesicle budding assay, pharmacological rescue experiments, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"36167862\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"PRAF2 inhibits CCR5 plasma membrane export in a concentration-dependent manner. PRAF2/CCR5 interaction does not require the CCR5 C-terminal tail but instead involves the transmembrane domains of both proteins. The di-leucine/RXR motif in the third intracellular loop of CCR5 does not affect PRAF2-mediated retention; rather, it impairs CCR5 interaction with its private escort protein CD4. PRAF2 and CD4 exert opposing effects on CCR5 cell-surface export, likely by regulating CCR5 recruitment into COPII vesicles at ER exit sites.\",\n      \"method\": \"BRET-based subcellular localization assay, BRET proximity assay, Co-immunoprecipitation, domain mutation analysis\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (BRET localization, BRET proximity, Co-IP, mutagenesis) in single study; mechanistically rigorous\",\n      \"pmids\": [\"38139265\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PRAF2 is an ER-resident four-transmembrane-domain gatekeeper protein that retains polytopic plasma membrane proteins (including the GABAB receptor GB1 subunit, CFTR, and CCR5) in the ER by preventing their access to COPII vesicle exit sites, interacts with anti-apoptotic Bcl-xL and Bcl-2 via their transmembrane domains to suppress its pro-apoptotic activity (which involves Bax mitochondrial translocation), and participates in vesicle trafficking and exosome-mediated cargo release.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PRAF2 is an ER-resident four-transmembrane protein that functions as a gatekeeper controlling the biosynthetic export of polytopic plasma membrane proteins, retaining them in the ER until they are properly assembled [#4, #6, #7]. It binds newly synthesized client receptors and transporters through transmembrane-domain contacts and prevents their recruitment into COPII vesicles at ER exit sites: it retains the GABAB receptor GB1 subunit in the absence of GB2 heterodimerization [#4], stoichiometrically holds both wild-type and F508del CFTR away from ER exit sites such that pharmacological chaperones act in part by relieving this retention [#6], and limits CCR5 plasma membrane export through transmembrane-domain interaction, an effect opposed by the CCR5 escort protein CD4 [#7]. Beyond its trafficking role, PRAF2 has a pro-apoptotic activity: its overexpression drives Bax translocation to mitochondria and cell death, an activity suppressed by interaction with the transmembrane domains of the anti-apoptotic proteins Bcl-xL and Bcl-2 [#2]. PRAF2 localizes principally to the ER, co-localizing with calnexin, and also distributes to Golgi, cytoplasmic vesicular puncta, and additional neuronal compartments, consistent with its trafficking and Rab-acceptor-associated functions [#0, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Established PRAF2 as a four-transmembrane protein physically associated with a GPCR (CCR5) and resident in the early secretory pathway, framing it as a candidate trafficking regulator.\",\n      \"evidence\": \"Co-IP, immunofluorescence co-localization with calnexin and M6P receptor, and two-hybrid screen in cell lines\",\n      \"pmids\": [\"15757671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence of the CCR5 interaction shown\", \"Rab-acceptor motif function not tested directly\", \"Heterodimerization with JWA/GTRAP3-18 not mechanistically dissected\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined a pro-apoptotic activity for PRAF2 that is gated by anti-apoptotic Bcl-family proteins, linking the protein to mitochondrial death control.\",\n      \"evidence\": \"TAP/Co-IP, domain-deletion mutagenesis of Bcl-xL, Bax translocation assay, and overexpression/knockdown apoptosis readouts in U2OS cells\",\n      \"pmids\": [\"21203533\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which PRAF2 promotes Bax translocation is unresolved\", \"Whether the ER-trafficking role and apoptotic role are mechanistically connected is unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Tied PRAF2 expression to cancer-cell viability and motility, with monomeric versus dimeric forms partitioning to distinct compartments.\",\n      \"evidence\": \"Immunofluorescence, cell fractionation, RNAi, and migration/invasion assays in U-87 glioma cells\",\n      \"pmids\": [\"20412121\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional difference between monomer and dimer not defined\", \"Mechanism linking PRAF2 to invasion not established\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified the core gatekeeper function: PRAF2 retains the GABAB GB1 subunit in the biosynthetic pathway until heterodimerization with GB2.\",\n      \"evidence\": \"Immunofluorescence and ultrastructural immunocytochemistry (electron microscopy) in mouse CNS neurons\",\n      \"pmids\": [\"26645984\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of release upon GB2 assembly not detailed\", \"Functional roles of mitochondrial and primary cilia localizations unexplored\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended PRAF2 function to exosome-mediated cargo release relevant to cancer metastasis.\",\n      \"evidence\": \"siRNA knockdown, transcriptome microarray, and exosome isolation/functional assays in colorectal cancer cells\",\n      \"pmids\": [\"31198409\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Indirect evidence without direct mechanistic dissection of PRAF2 in exosome biogenesis\", \"Whether effect is direct or secondary to trafficking changes is unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated that PRAF2 acts at COPII exit sites by stoichiometrically retaining CFTR, including the F508del mutant, providing a disease-relevant mechanism for pharmacological chaperone action.\",\n      \"evidence\": \"Stoichiometric Co-IP, COPII vesicle budding assay, and pharmacological chaperone treatment\",\n      \"pmids\": [\"36167862\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Determinants of client selectivity not defined\", \"How chaperones relieve PRAF2 retention mechanistically not resolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Resolved the molecular logic of PRAF2 client retention versus escort: transmembrane-domain interaction drives retention, opposed by the client-specific escort CD4 at ER exit sites.\",\n      \"evidence\": \"BRET subcellular localization and proximity assays, Co-IP, and domain mutagenesis of CCR5\",\n      \"pmids\": [\"38139265\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"General rules governing which escort proteins counteract PRAF2 are unknown\", \"Structural basis of the transmembrane-domain contact not determined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PRAF2's ER-gatekeeper trafficking activity and its Bcl-family-gated pro-apoptotic activity are mechanistically integrated remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of PRAF2 or its transmembrane-domain client interactions\", \"No unifying mechanism linking COPII retention to Bax-dependent apoptosis\", \"Functional significance of mitochondrial and ciliary localizations uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [4, 6, 7]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 6, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 4, 6]},\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [1, 3]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005929\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [4, 6, 7]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CCR5\", \"BCL2L1\", \"BCL2\", \"CFTR\", \"GABBR1\", \"CD4\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}