{"gene":"SDF2","run_date":"2026-06-10T07:46:30","timeline":{"discoveries":[{"year":1996,"finding":"Human SDF2 was identified as a novel secretory protein whose amino acid sequence shows similarity to yeast dolichyl phosphate-D-mannose:protein mannosyltransferases (Pmt1p and Pmt2p), and its gene was mapped to chromosomal locus 17q11.2.","method":"Signal sequence trap method, cDNA cloning, sequence analysis, chromosomal mapping","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct cloning and sequence characterization, but functional role inferred by homology only; no enzymatic assay performed","pmids":["8918255"],"is_preprint":false},{"year":2014,"finding":"Mouse Sdf2 protein is localized to the endoplasmic reticulum, and its predicted 3D structure is a β-trefoil containing three MIR motifs, consistent with the crystal structure of the Arabidopsis SDF2-like ortholog.","method":"Recombinant protein expression, anti-Sdf2 antibody generation, subcellular localization by immunofluorescence/fractionation, 3D structure prediction and multiple sequence alignment","journal":"The international journal of biochemistry & cell biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — direct localization experiment, but structural information is from predicted/homology model; functional mechanism not directly tested","pmids":["24878610"],"is_preprint":false},{"year":2017,"finding":"SDF2 is an ER-resident protein that forms a stable complex with ERdj3 (DNAJB11/HSP40) and acts as a component of the BiP chaperone cycle to prevent aggregation of misfolded ER cargo proteins.","method":"Co-immunoprecipitation, in vitro aggregation suppression assay, dominant-negative ERdj3 mutant blocking BiP-ERdj3 interaction, subcellular fractionation","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, in vitro functional assay, dominant-negative mutant validation, independently replicated in subsequent publications","pmids":["28597544"],"is_preprint":false},{"year":2019,"finding":"SDF2 retains ERdj3 in the ER by forming a complex with it; the ERdj3 dimer incorporates two SDF2L1 molecules (replacing an ERdj3 homotetramer), and the ERdj3-SDF2/SDF2L1 complex shows higher chaperone activity than ERdj3 alone, suppressing protein aggregation independently of substrate transfer to BiP.","method":"In vitro co-immunoprecipitation, in vitro aggregation assay with denatured GST substrate, size-exclusion chromatography/complex stoichiometry analysis, in cellulo localization and chaperone assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution with defined substrates, stoichiometry determination, complementary in cellulo validation, single lab with multiple orthogonal methods","pmids":["31624144"],"is_preprint":false},{"year":2025,"finding":"SDF2 and SDF2L1 are essential subunits of the DNAJB11 (ERdj3) chaperone complex required for normal processing of Polycystin-1 (PC1); concomitant loss of SDF2 and SDF2L1 impairs PC1 processing, mimicking the biochemical phenotype of DNAJB11 loss. There is also a reciprocal interdependence of DNAJB11 and SDF2/SDF2L1 protein abundance.","method":"Unbiased interaction proteomics screen for DNAJB11-interacting proteins, knockout cell lines (SDF2/SDF2L1 double KO), rescue by reexpression, PC1 processing assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — unbiased proteomics identification, knockout cell lines with defined biochemical phenotype, rescue experiments; single lab but multiple orthogonal methods","pmids":["41109348"],"is_preprint":false},{"year":2025,"finding":"SDF2 knockdown in glioma cells increases GRP78 expression and reduces ATP7A and ATP7B expression via GRP78-mediated ER-associated degradation (ERAD); proteasome inhibitor MG132 and GRP78 silencing both block the SDF2 knockdown-induced decrease in ATP7A/ATP7B expression, indicating SDF2 normally suppresses GRP78-mediated ERAD of copper transporters.","method":"shRNA knockdown, Western blotting, proteasome inhibitor (MG132) treatment, GRP78 siRNA silencing, in vivo subcutaneous tumor model with GRP78 overexpression rescue","journal":"International journal of molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — defined biochemical pathway with pharmacological and genetic perturbations, but single lab, no in vitro reconstitution of the SDF2-GRP78-ATP7A/B axis","pmids":["40709395"],"is_preprint":false},{"year":2025,"finding":"SDF2 is a direct target of miR-210-3p; overexpression of SDF2 promotes proliferation, migration, and epithelial differentiation of UCB-MSCs, and activates JAK2/STAT3 signaling, counteracting the inhibitory effects of miR-210-3p mimics.","method":"Dual-luciferase reporter assay (validating SDF2 as miR-210-3p target), SDF2 overexpression, CCK8/EdU/Transwell assays, Western blotting for JAK2/STAT3 phosphorylation","journal":"Stem cell research & therapy","confidence":"Low","confidence_rationale":"Tier 3 / Weak — luciferase reporter validates miRNA targeting, but downstream JAK2/STAT3 mechanism is indirect; single lab, single study","pmids":["41184975"],"is_preprint":false}],"current_model":"SDF2 is a constitutively expressed ER-resident protein that functions as an essential co-factor of the DNAJB11 (ERdj3)–BiP chaperone complex: it forms a stable complex with ERdj3 dimers (two SDF2 molecules per dimer), retains ERdj3 in the ER, enhances its chaperone activity to prevent misfolded protein aggregation independent of substrate transfer to BiP, and is required for normal processing of Polycystin-1; additionally, SDF2 suppresses GRP78-mediated ERAD of copper transporters ATP7A/B."},"narrative":{"mechanistic_narrative":"SDF2 is a constitutively ER-resident protein that functions as an essential co-factor of the DNAJB11 (ERdj3)–BiP chaperone system, where it suppresses aggregation of misfolded ER cargo [PMID:28597544]. SDF2 forms a stable complex with the ERdj3 (DNAJB11/HSP40) dimer, with two SDF2/SDF2L1 molecules replacing an ERdj3 homotetramer; this complex retains ERdj3 in the ER and possesses higher chaperone activity than ERdj3 alone, suppressing protein aggregation independently of substrate transfer to BiP [PMID:31624144]. SDF2 and SDF2L1 act as essential subunits of the DNAJB11 complex required for normal processing of Polycystin-1, and their abundance is reciprocally interdependent with that of DNAJB11 [PMID:41109348]. Beyond its chaperone role, SDF2 suppresses GRP78-mediated ER-associated degradation of the copper transporters ATP7A and ATP7B [PMID:40709395]. The protein adopts a β-trefoil fold containing three MIR motifs [PMID:24878610].","teleology":[{"year":1996,"claim":"Established SDF2 as a discrete secretory gene product, providing the molecular entry point before any function was known.","evidence":"Signal sequence trap cloning, sequence analysis, and chromosomal mapping of human SDF2","pmids":["8918255"],"confidence":"Medium","gaps":["Functional role inferred only by sequence similarity to yeast mannosyltransferases","No enzymatic activity tested","Localization not directly demonstrated"]},{"year":2014,"claim":"Defined SDF2's subcellular compartment and structural architecture, anchoring it as an ER protein with a defined fold rather than a secreted enzyme.","evidence":"Immunofluorescence/fractionation localization and homology-based 3D structure prediction of mouse Sdf2","pmids":["24878610"],"confidence":"Low","gaps":["Structure is predicted/homology-modeled, not experimentally solved","No functional mechanism tested","Binding partners unidentified"]},{"year":2017,"claim":"Resolved SDF2's molecular function by placing it in the BiP chaperone cycle as a stable ERdj3 partner that prevents misfolded cargo aggregation.","evidence":"Reciprocal Co-IP, in vitro aggregation suppression assay, and dominant-negative ERdj3 mutant in cells","pmids":["28597544"],"confidence":"High","gaps":["Complex stoichiometry not yet defined","Specific physiological substrates unknown","Relationship to SDF2L1 unresolved"]},{"year":2019,"claim":"Defined the architecture and biochemical logic of the complex, showing SDF2/SDF2L1 reorganize ERdj3 oligomerization and confer enhanced chaperone activity that does not require substrate handoff to BiP.","evidence":"In vitro Co-IP and aggregation assays with denatured substrate, size-exclusion stoichiometry, and in cellulo localization/chaperone assays","pmids":["31624144"],"confidence":"High","gaps":["Native substrate repertoire not catalogued","Structural basis of the 2:2 complex not crystallographically resolved","Functional distinction between SDF2 and SDF2L1 unclear"]},{"year":2025,"claim":"Connected the chaperone complex to a defined physiological client, establishing SDF2/SDF2L1 as required subunits for Polycystin-1 processing with reciprocal abundance control over DNAJB11.","evidence":"Unbiased DNAJB11 interaction proteomics, SDF2/SDF2L1 double-knockout cell lines, rescue, and PC1 processing assay","pmids":["41109348"],"confidence":"High","gaps":["Direct disease link to SDF2 mutation not established","Mechanism of reciprocal abundance regulation unknown","Other physiological clients not mapped"]},{"year":2025,"claim":"Identified a distinct ERAD-regulatory role, showing SDF2 normally restrains GRP78-mediated degradation of copper transporters ATP7A/ATP7B.","evidence":"shRNA knockdown, MG132 and GRP78 silencing, and in vivo tumor model with GRP78 overexpression rescue in glioma cells","pmids":["40709395"],"confidence":"Medium","gaps":["No in vitro reconstitution of the SDF2–GRP78–ATP7A/B axis","Single lab and cell context (glioma)","Mechanistic link between SDF2 loss and GRP78 induction undefined"]},{"year":2025,"claim":"Placed SDF2 downstream of a microRNA and implicated it in proliferation/differentiation signaling, extending its biology beyond ER chaperone function.","evidence":"Dual-luciferase reporter, SDF2 overexpression, proliferation/migration assays, and JAK2/STAT3 phosphorylation Western blots in UCB-MSCs","pmids":["41184975"],"confidence":"Low","gaps":["JAK2/STAT3 link is indirect and not mechanistically connected to ER function","Single study, single cell type","No demonstration that ER-resident SDF2 mediates the signaling effect"]},{"year":null,"claim":"How SDF2's ER chaperone role mechanistically relates to its reported regulation of ERAD and to broader cell signaling outputs remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No experimentally solved structure of the human ERdj3–SDF2 complex","Full client substrate spectrum uncharacterized","Unclear whether ERAD and signaling phenotypes derive from the chaperone activity"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0044183","term_label":"protein folding chaperone","supporting_discovery_ids":[2,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,3,5]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[1,2,3]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,3,4]}],"complexes":["ERdj3 (DNAJB11)–SDF2/SDF2L1 chaperone complex"],"partners":["DNAJB11","SDF2L1","HSPA5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q99470","full_name":"Stromal cell-derived factor 2","aliases":[],"length_aa":211,"mass_kda":23.0,"function":"","subcellular_location":"Secreted","url":"https://www.uniprot.org/uniprotkb/Q99470/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SDF2","classification":"Not Classified","n_dependent_lines":17,"n_total_lines":1208,"dependency_fraction":0.014072847682119206},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SDF2","total_profiled":1310},"omim":[{"mim_id":"607551","title":"STROMAL CELL-DERIVED FACTOR 2-LIKE 1; SDF2L1","url":"https://www.omim.org/entry/607551"},{"mim_id":"602934","title":"STROMAL CELL-DERIVED FACTOR 2; SDF2","url":"https://www.omim.org/entry/602934"},{"mim_id":"300007","title":"INTERLEUKIN 9 RECEPTOR; IL9R","url":"https://www.omim.org/entry/300007"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SDF2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"Q99470","domains":[{"cath_id":"2.80.10.50","chopping":"24-198","consensus_level":"high","plddt":96.7343,"start":24,"end":198}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99470","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q99470-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q99470-F1-predicted_aligned_error_v6.png","plddt_mean":90.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SDF2","jax_strain_url":"https://www.jax.org/strain/search?query=SDF2"},"sequence":{"accession":"Q99470","fasta_url":"https://rest.uniprot.org/uniprotkb/Q99470.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q99470/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q99470"}},"corpus_meta":[{"pmid":"10373524","id":"PMC_10373524","title":"SDF-2 induction of terminal differentiation in Dictyostelium discoideum is mediated by the membrane-spanning sensor kinase DhkA.","date":"1999","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10373524","citation_count":76,"is_preprint":false},{"pmid":"8918255","id":"PMC_8918255","title":"Isolation and characterization of a novel secretory protein, stromal cell-derived factor-2 (SDF-2) using the signal sequence trap method.","date":"1996","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/8918255","citation_count":49,"is_preprint":false},{"pmid":"28597544","id":"PMC_28597544","title":"Endoplasmic reticulum proteins SDF2 and SDF2L1 act as components of the BiP chaperone cycle to prevent protein aggregation.","date":"2017","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/28597544","citation_count":31,"is_preprint":false},{"pmid":"31624144","id":"PMC_31624144","title":"SDF2-like protein 1 (SDF2L1) regulates the endoplasmic reticulum localization and chaperone activity of ERdj3 protein.","date":"2019","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/31624144","citation_count":28,"is_preprint":false},{"pmid":"23849113","id":"PMC_23849113","title":"The endoplasmic reticulum-quality control component SDF2 is essential for XA21-mediated immunity in rice.","date":"2013","source":"Plant science : an international journal of experimental plant biology","url":"https://pubmed.ncbi.nlm.nih.gov/23849113","citation_count":26,"is_preprint":false},{"pmid":"30776414","id":"PMC_30776414","title":"The potential contribution of stromal cell-derived factor 2 (SDF2) in endoplasmic reticulum stress response in severe preeclampsia and labor-onset.","date":"2019","source":"Biochimica et biophysica acta. Molecular basis of disease","url":"https://pubmed.ncbi.nlm.nih.gov/30776414","citation_count":24,"is_preprint":false},{"pmid":"24878610","id":"PMC_24878610","title":"Stromal cell derived factor-2 (Sdf2): a novel protein expressed in mouse.","date":"2014","source":"The international journal of biochemistry & cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/24878610","citation_count":16,"is_preprint":false},{"pmid":"41184975","id":"PMC_41184975","title":"Effects of miR-210-3p/SDF2 and miR-31-5p/FGF7 from hypoxic endometrial exosomes on UCB-MSC proliferation, migration, and differentiation.","date":"2025","source":"Stem cell research & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/41184975","citation_count":2,"is_preprint":false},{"pmid":"40709395","id":"PMC_40709395","title":"SDF2 promotes glioma progression via GRP78‑mediated ERAD and copper homeostasis disruption.","date":"2025","source":"International journal of molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40709395","citation_count":0,"is_preprint":false},{"pmid":"41109348","id":"PMC_41109348","title":"SDF2 and SDF2L1 are essential co-factors of DNAJB11 for Polycystin-1 processing.","date":"2025","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/41109348","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7094,"output_tokens":1907,"usd":0.024944,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8804,"output_tokens":2490,"usd":0.053135,"stage2_stop_reason":"end_turn"},"total_usd":0.078079,"stage1_batch_id":"msgbatch_013LWZZT6MWaqB9qyTSeQBmU","stage2_batch_id":"msgbatch_0194ZzQaTGNpruoNJBbEMbt3","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1996,\n      \"finding\": \"Human SDF2 was identified as a novel secretory protein whose amino acid sequence shows similarity to yeast dolichyl phosphate-D-mannose:protein mannosyltransferases (Pmt1p and Pmt2p), and its gene was mapped to chromosomal locus 17q11.2.\",\n      \"method\": \"Signal sequence trap method, cDNA cloning, sequence analysis, chromosomal mapping\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct cloning and sequence characterization, but functional role inferred by homology only; no enzymatic assay performed\",\n      \"pmids\": [\"8918255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Mouse Sdf2 protein is localized to the endoplasmic reticulum, and its predicted 3D structure is a β-trefoil containing three MIR motifs, consistent with the crystal structure of the Arabidopsis SDF2-like ortholog.\",\n      \"method\": \"Recombinant protein expression, anti-Sdf2 antibody generation, subcellular localization by immunofluorescence/fractionation, 3D structure prediction and multiple sequence alignment\",\n      \"journal\": \"The international journal of biochemistry & cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — direct localization experiment, but structural information is from predicted/homology model; functional mechanism not directly tested\",\n      \"pmids\": [\"24878610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SDF2 is an ER-resident protein that forms a stable complex with ERdj3 (DNAJB11/HSP40) and acts as a component of the BiP chaperone cycle to prevent aggregation of misfolded ER cargo proteins.\",\n      \"method\": \"Co-immunoprecipitation, in vitro aggregation suppression assay, dominant-negative ERdj3 mutant blocking BiP-ERdj3 interaction, subcellular fractionation\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, in vitro functional assay, dominant-negative mutant validation, independently replicated in subsequent publications\",\n      \"pmids\": [\"28597544\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SDF2 retains ERdj3 in the ER by forming a complex with it; the ERdj3 dimer incorporates two SDF2L1 molecules (replacing an ERdj3 homotetramer), and the ERdj3-SDF2/SDF2L1 complex shows higher chaperone activity than ERdj3 alone, suppressing protein aggregation independently of substrate transfer to BiP.\",\n      \"method\": \"In vitro co-immunoprecipitation, in vitro aggregation assay with denatured GST substrate, size-exclusion chromatography/complex stoichiometry analysis, in cellulo localization and chaperone assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution with defined substrates, stoichiometry determination, complementary in cellulo validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"31624144\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SDF2 and SDF2L1 are essential subunits of the DNAJB11 (ERdj3) chaperone complex required for normal processing of Polycystin-1 (PC1); concomitant loss of SDF2 and SDF2L1 impairs PC1 processing, mimicking the biochemical phenotype of DNAJB11 loss. There is also a reciprocal interdependence of DNAJB11 and SDF2/SDF2L1 protein abundance.\",\n      \"method\": \"Unbiased interaction proteomics screen for DNAJB11-interacting proteins, knockout cell lines (SDF2/SDF2L1 double KO), rescue by reexpression, PC1 processing assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — unbiased proteomics identification, knockout cell lines with defined biochemical phenotype, rescue experiments; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"41109348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SDF2 knockdown in glioma cells increases GRP78 expression and reduces ATP7A and ATP7B expression via GRP78-mediated ER-associated degradation (ERAD); proteasome inhibitor MG132 and GRP78 silencing both block the SDF2 knockdown-induced decrease in ATP7A/ATP7B expression, indicating SDF2 normally suppresses GRP78-mediated ERAD of copper transporters.\",\n      \"method\": \"shRNA knockdown, Western blotting, proteasome inhibitor (MG132) treatment, GRP78 siRNA silencing, in vivo subcutaneous tumor model with GRP78 overexpression rescue\",\n      \"journal\": \"International journal of molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — defined biochemical pathway with pharmacological and genetic perturbations, but single lab, no in vitro reconstitution of the SDF2-GRP78-ATP7A/B axis\",\n      \"pmids\": [\"40709395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SDF2 is a direct target of miR-210-3p; overexpression of SDF2 promotes proliferation, migration, and epithelial differentiation of UCB-MSCs, and activates JAK2/STAT3 signaling, counteracting the inhibitory effects of miR-210-3p mimics.\",\n      \"method\": \"Dual-luciferase reporter assay (validating SDF2 as miR-210-3p target), SDF2 overexpression, CCK8/EdU/Transwell assays, Western blotting for JAK2/STAT3 phosphorylation\",\n      \"journal\": \"Stem cell research & therapy\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — luciferase reporter validates miRNA targeting, but downstream JAK2/STAT3 mechanism is indirect; single lab, single study\",\n      \"pmids\": [\"41184975\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SDF2 is a constitutively expressed ER-resident protein that functions as an essential co-factor of the DNAJB11 (ERdj3)–BiP chaperone complex: it forms a stable complex with ERdj3 dimers (two SDF2 molecules per dimer), retains ERdj3 in the ER, enhances its chaperone activity to prevent misfolded protein aggregation independent of substrate transfer to BiP, and is required for normal processing of Polycystin-1; additionally, SDF2 suppresses GRP78-mediated ERAD of copper transporters ATP7A/B.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SDF2 is a constitutively ER-resident protein that functions as an essential co-factor of the DNAJB11 (ERdj3)–BiP chaperone system, where it suppresses aggregation of misfolded ER cargo [#2]. SDF2 forms a stable complex with the ERdj3 (DNAJB11/HSP40) dimer, with two SDF2/SDF2L1 molecules replacing an ERdj3 homotetramer; this complex retains ERdj3 in the ER and possesses higher chaperone activity than ERdj3 alone, suppressing protein aggregation independently of substrate transfer to BiP [#3]. SDF2 and SDF2L1 act as essential subunits of the DNAJB11 complex required for normal processing of Polycystin-1, and their abundance is reciprocally interdependent with that of DNAJB11 [#4]. Beyond its chaperone role, SDF2 suppresses GRP78-mediated ER-associated degradation of the copper transporters ATP7A and ATP7B [#5]. The protein adopts a β-trefoil fold containing three MIR motifs [#1].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established SDF2 as a discrete secretory gene product, providing the molecular entry point before any function was known.\",\n      \"evidence\": \"Signal sequence trap cloning, sequence analysis, and chromosomal mapping of human SDF2\",\n      \"pmids\": [\"8918255\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional role inferred only by sequence similarity to yeast mannosyltransferases\", \"No enzymatic activity tested\", \"Localization not directly demonstrated\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined SDF2's subcellular compartment and structural architecture, anchoring it as an ER protein with a defined fold rather than a secreted enzyme.\",\n      \"evidence\": \"Immunofluorescence/fractionation localization and homology-based 3D structure prediction of mouse Sdf2\",\n      \"pmids\": [\"24878610\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Structure is predicted/homology-modeled, not experimentally solved\", \"No functional mechanism tested\", \"Binding partners unidentified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Resolved SDF2's molecular function by placing it in the BiP chaperone cycle as a stable ERdj3 partner that prevents misfolded cargo aggregation.\",\n      \"evidence\": \"Reciprocal Co-IP, in vitro aggregation suppression assay, and dominant-negative ERdj3 mutant in cells\",\n      \"pmids\": [\"28597544\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Complex stoichiometry not yet defined\", \"Specific physiological substrates unknown\", \"Relationship to SDF2L1 unresolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined the architecture and biochemical logic of the complex, showing SDF2/SDF2L1 reorganize ERdj3 oligomerization and confer enhanced chaperone activity that does not require substrate handoff to BiP.\",\n      \"evidence\": \"In vitro Co-IP and aggregation assays with denatured substrate, size-exclusion stoichiometry, and in cellulo localization/chaperone assays\",\n      \"pmids\": [\"31624144\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native substrate repertoire not catalogued\", \"Structural basis of the 2:2 complex not crystallographically resolved\", \"Functional distinction between SDF2 and SDF2L1 unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connected the chaperone complex to a defined physiological client, establishing SDF2/SDF2L1 as required subunits for Polycystin-1 processing with reciprocal abundance control over DNAJB11.\",\n      \"evidence\": \"Unbiased DNAJB11 interaction proteomics, SDF2/SDF2L1 double-knockout cell lines, rescue, and PC1 processing assay\",\n      \"pmids\": [\"41109348\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct disease link to SDF2 mutation not established\", \"Mechanism of reciprocal abundance regulation unknown\", \"Other physiological clients not mapped\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified a distinct ERAD-regulatory role, showing SDF2 normally restrains GRP78-mediated degradation of copper transporters ATP7A/ATP7B.\",\n      \"evidence\": \"shRNA knockdown, MG132 and GRP78 silencing, and in vivo tumor model with GRP78 overexpression rescue in glioma cells\",\n      \"pmids\": [\"40709395\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution of the SDF2–GRP78–ATP7A/B axis\", \"Single lab and cell context (glioma)\", \"Mechanistic link between SDF2 loss and GRP78 induction undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Placed SDF2 downstream of a microRNA and implicated it in proliferation/differentiation signaling, extending its biology beyond ER chaperone function.\",\n      \"evidence\": \"Dual-luciferase reporter, SDF2 overexpression, proliferation/migration assays, and JAK2/STAT3 phosphorylation Western blots in UCB-MSCs\",\n      \"pmids\": [\"41184975\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"JAK2/STAT3 link is indirect and not mechanistically connected to ER function\", \"Single study, single cell type\", \"No demonstration that ER-resident SDF2 mediates the signaling effect\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SDF2's ER chaperone role mechanistically relates to its reported regulation of ERAD and to broader cell signaling outputs remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No experimentally solved structure of the human ERdj3–SDF2 complex\", \"Full client substrate spectrum uncharacterized\", \"Unclear whether ERAD and signaling phenotypes derive from the chaperone activity\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0044183\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [1, 2, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 3, 4]}\n    ],\n    \"complexes\": [\"ERdj3 (DNAJB11)–SDF2/SDF2L1 chaperone complex\"],\n    \"partners\": [\"DNAJB11\", \"SDF2L1\", \"HSPA5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"faith_supported":5,"faith_total":5,"faith_pct":100.0}}