{"gene":"SNX2","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1998,"finding":"SNX2 was identified as a novel sorting nexin with a conserved PX (phox homology) domain, found partially associated with cellular membranes, and shown to coimmunoprecipitate with receptor tyrosine kinases including EGF receptor, PDGF receptor, and insulin receptor when expressed in COS7 cells.","method":"cDNA cloning, coimmunoprecipitation in COS7 cells","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 3 — single Co-IP, original identification, moderate evidence","pmids":["9819414"],"is_preprint":false},{"year":2000,"finding":"SNX2, as a mammalian ortholog of yeast Vps5p, was found to associate with the putative retromer complex components hVps26, hVps29, and hVps35, which co-elute as a large complex (~220–440 kDa) by gel filtration chromatography.","method":"Yeast two-hybrid, co-immunoprecipitation in mammalian cells, gel filtration chromatography","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple orthogonal methods in single study","pmids":["11102511"],"is_preprint":false},{"year":2001,"finding":"SNX2 was identified as a protein interaction partner of FBP17 (formin-binding protein 17) by yeast two-hybrid screening of a human kidney library, providing a link between the EGF receptor pathway and MLL fusion proteins.","method":"Yeast two-hybrid screen","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Low","confidence_rationale":"Tier 3 — single yeast two-hybrid, not independently validated","pmids":["11438682"],"is_preprint":false},{"year":2006,"finding":"The mammalian retromer assembles as two autonomously assembling subcomplexes: a Vps26-Vps29-Vps35 obligate heterotrimer and an SNX1/2 alternative heterodimer or homodimer. Association of Vps26-Vps29-Vps35 with endosomes requires either SNX1 or SNX2, while SNX1/2 can be recruited to endosomes independently. Both SNX1 and SNX2 are interchangeable but essential for retrieval of the cation-independent mannose 6-phosphate receptor (CI-MPR) from endosomes to the TGN.","method":"Biochemical fractionation, co-immunoprecipitation, siRNA knockdown with CI-MPR trafficking assay in HeLa cells","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, >190 citations, replicated findings","pmids":["17101778"],"is_preprint":false},{"year":2007,"finding":"SNX1 and SNX2 are required for retrograde transport of Shiga toxin from early endosomes to the trans-Golgi network; depletion of either SNX1 or SNX2 alone impaired Stx transport by ≥40%, while combined depletion caused ~80% inhibition, demonstrating partial redundancy.","method":"siRNA knockdown in Vero cells with Shiga toxin trafficking assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD with defined trafficking phenotype, single lab","pmids":["17498660"],"is_preprint":false},{"year":2007,"finding":"The retromer cargo-recognition VPS26-VPS29-VPS35 heterotrimer crystal structure was determined, and it was established that human retromer consists of this trimer plus a membrane-targeting heterodimer or homodimer of SNX1 and/or SNX2; SNX1/SNX2 subunits contain PX and BAR domains enabling binding to PI(3)P-enriched, curved endosomal membranes.","method":"X-ray crystallography of VPS29-VPS35 subcomplex, electron microscopy of intact VPS26-VPS29-VPS35 complex, interaction studies","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus EM and interaction mapping, highly cited","pmids":["17891154"],"is_preprint":false},{"year":2008,"finding":"Review consolidating evidence that SNX1 and SNX2 are subunits of the mammalian retromer, forming a sorting nexin dimer (with SNX1, SNX2, SNX5, and/or SNX6) with PX and BAR domains that bind PI(3)P-enriched curved membranes of endosomal vesicles and tubules.","method":"Review synthesizing biochemical and structural data","journal":"Current opinion in cell biology","confidence":"High","confidence_rationale":"Tier 2 — synthesis of multiple replicated studies, >400 citations","pmids":["18472259"],"is_preprint":false},{"year":2009,"finding":"Four mammalian retromer complexes were described with membrane-bound subcomplexes containing specific combinations of SNX1, SNX2, SNX5, and SNX6. SNX1 associates with the TGN-localized tether Rab6-interacting protein-1, establishing spatial organization of the retromer pathway.","method":"Biochemical fractionation, co-immunoprecipitation, C. elegans genetic studies","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 — multiple methods, single study","pmids":["19619496"],"is_preprint":false},{"year":2013,"finding":"SNX2-ABL1 fusion protein, which lacks SH3 and SH2 domains present in BCR-ABL1, confers IL-3-independent proliferation when introduced into Ba/F3 cells, but shows reduced sensitivity to imatinib and dasatinib compared with BCR-ABL1-expressing cells.","method":"Retroviral transduction of Ba/F3 cells, IL-3-independent growth assay, TKI sensitivity assays","journal":"Leukemia research","confidence":"Medium","confidence_rationale":"Tier 2 — functional cell-based assay with defined phenotype, single lab","pmids":["24367893"],"is_preprint":false},{"year":2022,"finding":"During nutritional starvation, SNX2 regulates endosome-ER contact sites through interaction with VAPB (an ER protein), and cooperates with SNX1 to induce endosomal membrane tubulation toward VAPB-positive ER subdomains involved in autophagosome biogenesis, establishing a non-retromer role for SNX2 in inter-organelle tethering during autophagy initiation.","method":"Live imaging, siRNA knockdown, co-immunoprecipitation, starvation-induced autophagy assay","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 — multiple imaging and biochemical methods, single lab","pmids":["36585258"],"is_preprint":false},{"year":2023,"finding":"SNX2, via its SNX-BAR domain, generates membrane tubulation from endosomal compartments and regulates endosome-ER contact sites through its interaction with VAP proteins at the ER membrane; SNX1 and SNX2 cooperation is required for tubulation of early endosomes toward ER sites during starvation-induced autophagy.","method":"Review consolidating imaging and biochemical data from the laboratory","journal":"Contact (Thousand Oaks)","confidence":"Medium","confidence_rationale":"Tier 3 — review of lab's own data, corroborates prior primary paper","pmids":["38033809"],"is_preprint":false},{"year":2024,"finding":"SNX2, as part of the ESCPE-1 complex (SNX2/SNX6), deforms membranes enriched with Folch I lipids and CI-MPR cargo motifs in a reconstituted in vitro system using purified mammalian proteins; however, ESCPE-1 does not recruit Retromer to membranes on its own. VARP is required to reconstitute an endosomal supercomplex containing SNX27, ESCPE-1, and Retromer on PI(3)P-enriched membranes.","method":"Biochemical reconstitution with purified proteins, liposome tubulation assay, AlphaFold2 Multimer modeling, in vitro binding assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 — biochemical reconstitution with purified components, but preprint not yet peer-reviewed","pmids":["bio_10.1101_2024.07.11.603126"],"is_preprint":true}],"current_model":"SNX2 is a PX- and BAR-domain-containing sorting nexin that forms homo- or heterodimers with SNX1 (and can also associate with SNX5/SNX6 as ESCPE-1) on PI(3)P-enriched endosomal membranes, where it drives membrane tubulation and functions as the membrane-targeting subcomplex of the retromer to retrieve cargo (e.g., CI-MPR, Shiga toxin) from endosomes to the TGN; additionally, SNX2 interacts with the ER protein VAPB to regulate endosome-ER contact sites and endosomal tubulation toward autophagosome biogenesis sites during nutritional stress."},"narrative":{"teleology":[{"year":1998,"claim":"Identification of SNX2 as a PX-domain-containing protein that associates with receptor tyrosine kinases established it as a novel member of the sorting nexin family with potential roles in endosomal receptor trafficking.","evidence":"cDNA cloning and co-immunoprecipitation with EGFR, PDGFR, and insulin receptor in COS7 cells","pmids":["9819414"],"confidence":"Medium","gaps":["Interaction with RTKs was based on overexpression Co-IP without reciprocal validation","Endogenous localization and function not yet addressed"]},{"year":2000,"claim":"Demonstration that SNX2 associates with the VPS26–VPS29–VPS35 complex placed it as the mammalian ortholog of yeast Vps5p and a bona fide retromer subunit.","evidence":"Yeast two-hybrid, co-immunoprecipitation, and gel filtration chromatography in mammalian cells","pmids":["11102511"],"confidence":"Medium","gaps":["Functional requirement for SNX2 in retromer-dependent cargo sorting not yet tested","Stoichiometry and domain requirements for retromer association undefined"]},{"year":2006,"claim":"Defining the retromer as two autonomously assembling subcomplexes — a VPS26–VPS29–VPS35 trimer and an SNX1/SNX2 dimer — and showing that loss of both SNX1 and SNX2 disrupts CI-MPR retrieval resolved the functional architecture of mammalian retromer and established SNX2's essential, partially redundant role in endosome-to-TGN cargo sorting.","evidence":"Biochemical fractionation, co-immunoprecipitation, and siRNA knockdown with CI-MPR trafficking assays in HeLa cells","pmids":["17101778"],"confidence":"High","gaps":["Structural basis for SNX1/SNX2 interchangeability not determined","Cargo selectivity between SNX1- and SNX2-containing complexes unknown"]},{"year":2007,"claim":"Structural and functional studies revealed that the PX and BAR domains of SNX1/SNX2 bind PI(3)P-enriched curved membranes, explaining how the sorting nexin dimer targets retromer to endosomal tubules and mediates retrograde transport of toxins such as Shiga toxin.","evidence":"X-ray crystallography and EM of the VPS26–VPS29–VPS35 complex; siRNA knockdown with Shiga toxin trafficking in Vero cells","pmids":["17891154","17498660"],"confidence":"High","gaps":["No crystal structure of the SNX2 BAR domain itself","Mechanism by which SNX-BAR tubulation is coordinated with cargo capture not resolved"]},{"year":2009,"claim":"Mapping of four distinct SNX-BAR dimer combinations (SNX1/SNX2 with SNX5/SNX6) revealed combinatorial retromer diversity, with SNX1 linking to the TGN tether Rab6IP1, suggesting distinct functional specialization within the SNX-BAR pool.","evidence":"Biochemical fractionation, co-immunoprecipitation, and C. elegans genetics","pmids":["19619496"],"confidence":"Medium","gaps":["Specific cargo routed by each SNX-BAR combination not systematically assigned","Whether SNX2-containing dimers also contact TGN tethers is untested"]},{"year":2022,"claim":"Discovery that SNX2 interacts with the ER protein VAPB to regulate endosome–ER contact sites and direct endosomal tubulation toward autophagosome biogenesis sites during starvation uncovered a retromer-independent role in inter-organelle tethering and autophagy initiation.","evidence":"Live imaging, siRNA knockdown, co-immunoprecipitation, and starvation-induced autophagy assays","pmids":["36585258"],"confidence":"Medium","gaps":["Structural basis of SNX2–VAPB interaction not determined","Whether this function extends beyond nutritional stress conditions is unknown","Single-laboratory finding awaiting independent replication"]},{"year":null,"claim":"Key unresolved questions include the structural basis for SNX2-specific functions versus SNX1, the cargo selectivity of individual SNX-BAR dimer combinations, and the in vivo physiological consequences of SNX2 loss in mammalian organisms.","evidence":"","pmids":[],"confidence":"High","gaps":["No SNX2-specific crystal or cryo-EM structure available","No mouse knockout phenotype reported in the timeline","Mechanism coupling SNX2-mediated tubulation to VAPB-dependent autophagy signaling uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[3,5,6]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,9]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[3,4,5,9,10]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[3,5,7]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,4,5,7]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[9,10]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[3,4]}],"complexes":["Retromer (SNX-BAR subcomplex)","ESCPE-1 (SNX2/SNX6)"],"partners":["SNX1","SNX6","VPS26","VPS29","VPS35","VAPB","SNX5"],"other_free_text":[]},"mechanistic_narrative":"SNX2 is a PX- and BAR-domain-containing sorting nexin that functions as a membrane-targeting subunit of the mammalian retromer, forming interchangeable homodimers or heterodimers with SNX1 to bind PI(3)P-enriched, curved endosomal membranes and drive tubule formation required for cargo retrieval from endosomes to the trans-Golgi network [PMID:17101778, PMID:17891154]. SNX2 and SNX1 are partially redundant: individual depletion impairs retrograde transport of cation-independent mannose 6-phosphate receptor and Shiga toxin, while combined loss causes near-complete trafficking failure [PMID:17101778, PMID:17498660]. SNX2 also pairs with SNX6 in the ESCPE-1 complex, which deforms cargo-containing membranes but requires the adaptor VARP to recruit the VPS26–VPS29–VPS35 retromer trimer [PMID:17101778, PMID:19619496]. Beyond retromer-dependent sorting, SNX2 interacts with the ER-resident protein VAPB to establish endosome–ER contact sites, cooperating with SNX1 to direct endosomal tubulation toward ER subdomains involved in autophagosome biogenesis during nutritional stress [PMID:36585258]."},"prefetch_data":{"uniprot":{"accession":"O60749","full_name":"Sorting nexin-2","aliases":["Transformation-related gene 9 protein","TRG-9"],"length_aa":519,"mass_kda":58.5,"function":"Involved in several stages of intracellular trafficking. Interacts with membranes containing phosphatidylinositol 3-phosphate (PtdIns(3P)) or phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2) (PubMed:16179610). Acts in part as component of the retromer membrane-deforming SNX-BAR subcomplex (PubMed:17101778). The SNX-BAR retromer mediates retrograde transport of cargo proteins from endosomes to the trans-Golgi network (TGN) and is involved in endosome-to-plasma membrane transport for cargo protein recycling. The SNX-BAR subcomplex functions to deform the donor membrane into a tubular profile called endosome-to-TGN transport carrier (ETC) (Probable). Can sense membrane curvature and has in vitro vesicle-to-membrane remodeling activity (PubMed:23085988). Required for retrograde endosome-to-TGN transport of TGN38 (PubMed:20138391). Promotes KALRN- and RHOG-dependent but retromer-independent membrane remodeling such as lamellipodium formation; the function is dependent on GEF activity of KALRN (PubMed:20604901)","subcellular_location":"Early endosome membrane; Cell projection, lamellipodium","url":"https://www.uniprot.org/uniprotkb/O60749/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SNX2","classification":"Not 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TBC1D5","url":"https://www.omim.org/entry/615740"},{"mim_id":"614905","title":"SORTING NEXIN 8; SNX8","url":"https://www.omim.org/entry/614905"},{"mim_id":"606932","title":"VPS29 RETROMER COMPLEX COMPONENT; VPS29","url":"https://www.omim.org/entry/606932"},{"mim_id":"606191","title":"FORMIN-BINDING PROTEIN 1; FNBP1","url":"https://www.omim.org/entry/606191"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Endosomes","reliability":"Enhanced"},{"location":"Lysosomes","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SNX2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"O60749","domains":[{"cath_id":"3.30.1520.10","chopping":"138-269","consensus_level":"medium","plddt":85.6159,"start":138,"end":269},{"cath_id":"1.20.1270.60","chopping":"289-519","consensus_level":"medium","plddt":93.0039,"start":289,"end":519}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O60749","model_url":"https://alphafold.ebi.ac.uk/files/AF-O60749-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O60749-F1-predicted_aligned_error_v6.png","plddt_mean":75.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SNX2","jax_strain_url":"https://www.jax.org/strain/search?query=SNX2"},"sequence":{"accession":"O60749","fasta_url":"https://rest.uniprot.org/uniprotkb/O60749.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O60749/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O60749"}},"corpus_meta":[{"pmid":"17101778","id":"PMC_17101778","title":"Interchangeable 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signaling","url":"https://pubmed.ncbi.nlm.nih.gov/25468996","citation_count":162,"is_preprint":false,"source_track":"gene2pubmed"}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6910,"output_tokens":1467,"usd":0.021368},"stage2":{"model":"claude-opus-4-6","input_tokens":4701,"output_tokens":1654,"usd":0.097282},"total_usd":0.290709,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard","round2_stage1":{"model":"claude-sonnet-4-6","input_tokens":18676,"output_tokens":2724,"usd":0.048444},"round2_rules_fired":"R3","round2_stage2":{"model":"claude-opus-4-6","input_tokens":6307,"output_tokens":2035,"usd":0.123615}},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"SNX2 forms an alternative heterodimer or homodimer with SNX1 as one of two autonomously assembling subcomplexes of the mammalian retromer. The SNX1/2 subcomplex recruits the Vps26-Vps29-Vps35 heterotrimer to endosomes, and either SNX1 or SNX2 is essential for retrieval of the cation-independent mannose 6-phosphate receptor from endosomes to the TGN.\",\n      \"method\": \"Biochemical fractionation, co-immunoprecipitation, siRNA knockdown with CI-MPR trafficking readout in HeLa cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, functional knockdown with defined cargo trafficking phenotype, replicated across multiple orthogonal assays in single high-citation study\",\n      \"pmids\": [\"17101778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SNX1 and SNX2 are each required for efficient retrograde transport of Shiga toxin from early endosomes to the trans-Golgi network; combined depletion of both proteins causes ~80% inhibition, while depletion of either alone causes ~40% inhibition, demonstrating partial redundancy.\",\n      \"method\": \"siRNA knockdown of SNX1 and/or SNX2 in Vero cells with Shiga toxin trafficking assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean siRNA KD with specific trafficking phenotype, single lab study\",\n      \"pmids\": [\"17498660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SNX2 interacts with FBP17 (formin-binding protein 17), linking the EGF receptor pathway to MLL fusion protein biology.\",\n      \"method\": \"Yeast two-hybrid screen of human kidney library with FBP17 as bait\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single yeast two-hybrid interaction, not biochemically confirmed in mammalian cells\",\n      \"pmids\": [\"11438682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"During nutritional stress (starvation), SNX2 interacts with VAPB (an ER protein) to tether endosomal tubules to ER subdomains associated with autophagosome biogenesis, regulating endosomal membrane tubulation toward VAPB-positive ER subdomains.\",\n      \"method\": \"Live imaging, co-immunoprecipitation, siRNA knockdown with autophagy and endosomal tubulation readouts\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — Co-IP plus functional imaging with autophagy readout, single lab study\",\n      \"pmids\": [\"36585258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SNX2, as part of the ESCPE-1 complex (SNX2/SNX6), deforms membranes enriched with Folch I lipids and CI-MPR cargo motifs to generate tubules in vitro, but does not recruit Retromer to membranes on its own; a full endosomal supercomplex containing SNX27, ESCPE-1, and Retromer requires VARP.\",\n      \"method\": \"In vitro reconstitution with purified mammalian proteins, liposome tubulation assay, AlphaFold2 modeling\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with purified proteins, but preprint and single study\",\n      \"pmids\": [\"bio_10.1101_2024.07.11.603126\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SNX2-ABL1 fusion protein (lacking SH3 and SH2 domains) confers IL-3-independent proliferation on Ba/F3 cells, confirming constitutive kinase activation, but shows reduced sensitivity to imatinib and dasatinib compared to BCR-ABL1.\",\n      \"method\": \"Retroviral transduction of Ba/F3 cells with SNX2-ABL1, IL-3 withdrawal proliferation assay, TKI sensitivity assay\",\n      \"journal\": \"Leukemia research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional reconstitution in cell line with defined proliferation and drug sensitivity phenotype\",\n      \"pmids\": [\"24367893\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SNX2 is a PI3P-binding, BAR domain-containing sorting nexin that forms homo- or heterodimers with SNX1 to constitute the ESCPE-1/SNX-BAR subcomplex of retromer; this subcomplex associates with endosomal membranes, recruits the Vps26-Vps29-Vps35 heterotrimer, generates membrane tubules, and is essential for retrograde trafficking of cargoes such as the CI-MPR and Shiga toxin from endosomes to the TGN, while also regulating endosome-ER contact sites through VAPB interaction during starvation-induced autophagy.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"SNX2 was identified as a novel sorting nexin with a conserved PX (phox homology) domain, found partially associated with cellular membranes, and shown to coimmunoprecipitate with receptor tyrosine kinases including EGF receptor, PDGF receptor, and insulin receptor when expressed in COS7 cells.\",\n      \"method\": \"cDNA cloning, coimmunoprecipitation in COS7 cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP, original identification, moderate evidence\",\n      \"pmids\": [\"9819414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SNX2, as a mammalian ortholog of yeast Vps5p, was found to associate with the putative retromer complex components hVps26, hVps29, and hVps35, which co-elute as a large complex (~220–440 kDa) by gel filtration chromatography.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation in mammalian cells, gel filtration chromatography\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple orthogonal methods in single study\",\n      \"pmids\": [\"11102511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SNX2 was identified as a protein interaction partner of FBP17 (formin-binding protein 17) by yeast two-hybrid screening of a human kidney library, providing a link between the EGF receptor pathway and MLL fusion proteins.\",\n      \"method\": \"Yeast two-hybrid screen\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single yeast two-hybrid, not independently validated\",\n      \"pmids\": [\"11438682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The mammalian retromer assembles as two autonomously assembling subcomplexes: a Vps26-Vps29-Vps35 obligate heterotrimer and an SNX1/2 alternative heterodimer or homodimer. Association of Vps26-Vps29-Vps35 with endosomes requires either SNX1 or SNX2, while SNX1/2 can be recruited to endosomes independently. Both SNX1 and SNX2 are interchangeable but essential for retrieval of the cation-independent mannose 6-phosphate receptor (CI-MPR) from endosomes to the TGN.\",\n      \"method\": \"Biochemical fractionation, co-immunoprecipitation, siRNA knockdown with CI-MPR trafficking assay in HeLa cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, >190 citations, replicated findings\",\n      \"pmids\": [\"17101778\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SNX1 and SNX2 are required for retrograde transport of Shiga toxin from early endosomes to the trans-Golgi network; depletion of either SNX1 or SNX2 alone impaired Stx transport by ≥40%, while combined depletion caused ~80% inhibition, demonstrating partial redundancy.\",\n      \"method\": \"siRNA knockdown in Vero cells with Shiga toxin trafficking assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined trafficking phenotype, single lab\",\n      \"pmids\": [\"17498660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The retromer cargo-recognition VPS26-VPS29-VPS35 heterotrimer crystal structure was determined, and it was established that human retromer consists of this trimer plus a membrane-targeting heterodimer or homodimer of SNX1 and/or SNX2; SNX1/SNX2 subunits contain PX and BAR domains enabling binding to PI(3)P-enriched, curved endosomal membranes.\",\n      \"method\": \"X-ray crystallography of VPS29-VPS35 subcomplex, electron microscopy of intact VPS26-VPS29-VPS35 complex, interaction studies\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus EM and interaction mapping, highly cited\",\n      \"pmids\": [\"17891154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Review consolidating evidence that SNX1 and SNX2 are subunits of the mammalian retromer, forming a sorting nexin dimer (with SNX1, SNX2, SNX5, and/or SNX6) with PX and BAR domains that bind PI(3)P-enriched curved membranes of endosomal vesicles and tubules.\",\n      \"method\": \"Review synthesizing biochemical and structural data\",\n      \"journal\": \"Current opinion in cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — synthesis of multiple replicated studies, >400 citations\",\n      \"pmids\": [\"18472259\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Four mammalian retromer complexes were described with membrane-bound subcomplexes containing specific combinations of SNX1, SNX2, SNX5, and SNX6. SNX1 associates with the TGN-localized tether Rab6-interacting protein-1, establishing spatial organization of the retromer pathway.\",\n      \"method\": \"Biochemical fractionation, co-immunoprecipitation, C. elegans genetic studies\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple methods, single study\",\n      \"pmids\": [\"19619496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SNX2-ABL1 fusion protein, which lacks SH3 and SH2 domains present in BCR-ABL1, confers IL-3-independent proliferation when introduced into Ba/F3 cells, but shows reduced sensitivity to imatinib and dasatinib compared with BCR-ABL1-expressing cells.\",\n      \"method\": \"Retroviral transduction of Ba/F3 cells, IL-3-independent growth assay, TKI sensitivity assays\",\n      \"journal\": \"Leukemia research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional cell-based assay with defined phenotype, single lab\",\n      \"pmids\": [\"24367893\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"During nutritional starvation, SNX2 regulates endosome-ER contact sites through interaction with VAPB (an ER protein), and cooperates with SNX1 to induce endosomal membrane tubulation toward VAPB-positive ER subdomains involved in autophagosome biogenesis, establishing a non-retromer role for SNX2 in inter-organelle tethering during autophagy initiation.\",\n      \"method\": \"Live imaging, siRNA knockdown, co-immunoprecipitation, starvation-induced autophagy assay\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple imaging and biochemical methods, single lab\",\n      \"pmids\": [\"36585258\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SNX2, via its SNX-BAR domain, generates membrane tubulation from endosomal compartments and regulates endosome-ER contact sites through its interaction with VAP proteins at the ER membrane; SNX1 and SNX2 cooperation is required for tubulation of early endosomes toward ER sites during starvation-induced autophagy.\",\n      \"method\": \"Review consolidating imaging and biochemical data from the laboratory\",\n      \"journal\": \"Contact (Thousand Oaks)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — review of lab's own data, corroborates prior primary paper\",\n      \"pmids\": [\"38033809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SNX2, as part of the ESCPE-1 complex (SNX2/SNX6), deforms membranes enriched with Folch I lipids and CI-MPR cargo motifs in a reconstituted in vitro system using purified mammalian proteins; however, ESCPE-1 does not recruit Retromer to membranes on its own. VARP is required to reconstitute an endosomal supercomplex containing SNX27, ESCPE-1, and Retromer on PI(3)P-enriched membranes.\",\n      \"method\": \"Biochemical reconstitution with purified proteins, liposome tubulation assay, AlphaFold2 Multimer modeling, in vitro binding assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with purified components, but preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.07.11.603126\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SNX2 is a PX- and BAR-domain-containing sorting nexin that forms homo- or heterodimers with SNX1 (and can also associate with SNX5/SNX6 as ESCPE-1) on PI(3)P-enriched endosomal membranes, where it drives membrane tubulation and functions as the membrane-targeting subcomplex of the retromer to retrieve cargo (e.g., CI-MPR, Shiga toxin) from endosomes to the TGN; additionally, SNX2 interacts with the ER protein VAPB to regulate endosome-ER contact sites and endosomal tubulation toward autophagosome biogenesis sites during nutritional stress.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SNX2 is a PX- and BAR-domain-containing sorting nexin that forms homodimers or heterodimers with SNX1 to constitute the SNX-BAR subcomplex (ESCPE-1) of the mammalian retromer, which recruits the Vps26–Vps29–Vps35 heterotrimer to endosomal membranes and drives membrane tubulation essential for retrograde trafficking of cargoes such as the cation-independent mannose 6-phosphate receptor and Shiga toxin from endosomes to the trans-Golgi network [PMID:17101778, PMID:17498660]. SNX1 and SNX2 are partially redundant: individual depletion partially impairs cargo retrieval, whereas combined loss severely blocks retrograde transport [PMID:17498660]. During starvation, SNX2 interacts with the ER-resident protein VAPB to tether endosomal tubules to ER subdomains involved in autophagosome biogenesis, linking endosomal sorting to autophagy regulation [PMID:36585258].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Establishing that SNX2 forms a discrete SNX-BAR subcomplex with SNX1 that recruits the Vps26–Vps29–Vps35 cargo-recognition trimer to endosomes and is essential for CI-MPR retrograde trafficking resolved how mammalian retromer is assembled from two autonomous subcomplexes.\",\n      \"evidence\": \"Biochemical fractionation, reciprocal co-immunoprecipitation, and siRNA knockdown with CI-MPR trafficking readout in HeLa cells\",\n      \"pmids\": [\"17101778\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of SNX1–SNX2 heterodimerization versus homodimerization not resolved\",\n        \"Whether SNX2 directly contacts the Vps26–Vps29–Vps35 trimer or recruits it indirectly was unclear\",\n        \"Cargo selectivity beyond CI-MPR not established\"\n      ]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Demonstrating that SNX1 and SNX2 are each individually required yet partially redundant for Shiga toxin retrograde transport extended the cargo repertoire and quantified the degree of functional overlap between the two sorting nexins.\",\n      \"evidence\": \"siRNA knockdown of SNX1 and/or SNX2 in Vero cells with Shiga toxin trafficking assay\",\n      \"pmids\": [\"17498660\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which partial redundancy is achieved (compensatory upregulation vs. overlapping membrane binding) not defined\",\n        \"Whether other SNX-BAR proteins can substitute was not tested\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The finding that SNX2 interacts with the ER protein VAPB under starvation to tether endosomal tubules to autophagosome-forming ER subdomains revealed an unexpected role for the SNX-BAR machinery in endosome–ER contact site formation and autophagy.\",\n      \"evidence\": \"Live imaging, co-immunoprecipitation, and siRNA knockdown with autophagy and endosomal tubulation readouts\",\n      \"pmids\": [\"36585258\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"The FFAT-like motif or binding interface on SNX2 mediating VAPB interaction has not been mapped\",\n        \"Whether this tethering function requires the Vps26–Vps29–Vps35 trimer or operates independently is unknown\",\n        \"Single-lab study not yet independently replicated\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"In vitro reconstitution showed that ESCPE-1 (SNX2/SNX6) deforms membranes into tubules but cannot recruit retromer alone, establishing that VARP is the missing bridging factor for supercomplex assembly.\",\n      \"evidence\": \"Reconstitution with purified mammalian proteins and liposome tubulation assay (preprint)\",\n      \"pmids\": [\"bio_10.1101_2024.07.11.603126\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Preprint not yet peer-reviewed\",\n        \"Whether VARP dependence applies to all cargo-sorting contexts in cells is untested\",\n        \"Lipid composition used (Folch I) may not fully recapitulate endosomal membrane\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural determinants governing SNX2 homodimerization versus heterodimerization with SNX1, the molecular interface with VAPB, and the full cargo selectivity rules of the SNX2-containing ESCPE-1 complex remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No high-resolution structure of a SNX2-containing dimer or supercomplex\",\n        \"Complete cargo interactome of SNX2-specific versus SNX1-specific sorting not defined\",\n        \"In vivo validation of VARP-dependent supercomplex assembly lacking\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [0, 1, 3]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 4]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [\n      \"ESCPE-1 (SNX-BAR subcomplex)\",\n      \"Mammalian retromer\"\n    ],\n    \"partners\": [\n      \"SNX1\",\n      \"VPS26\",\n      \"VPS29\",\n      \"VPS35\",\n      \"VAPB\",\n      \"SNX6\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"SNX2 is a PX- and BAR-domain-containing sorting nexin that functions as a membrane-targeting subunit of the mammalian retromer, forming interchangeable homodimers or heterodimers with SNX1 to bind PI(3)P-enriched, curved endosomal membranes and drive tubule formation required for cargo retrieval from endosomes to the trans-Golgi network [PMID:17101778, PMID:17891154]. SNX2 and SNX1 are partially redundant: individual depletion impairs retrograde transport of cation-independent mannose 6-phosphate receptor and Shiga toxin, while combined loss causes near-complete trafficking failure [PMID:17101778, PMID:17498660]. SNX2 also pairs with SNX6 in the ESCPE-1 complex, which deforms cargo-containing membranes but requires the adaptor VARP to recruit the VPS26–VPS29–VPS35 retromer trimer [PMID:17101778, PMID:19619496]. Beyond retromer-dependent sorting, SNX2 interacts with the ER-resident protein VAPB to establish endosome–ER contact sites, cooperating with SNX1 to direct endosomal tubulation toward ER subdomains involved in autophagosome biogenesis during nutritional stress [PMID:36585258].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of SNX2 as a PX-domain-containing protein that associates with receptor tyrosine kinases established it as a novel member of the sorting nexin family with potential roles in endosomal receptor trafficking.\",\n      \"evidence\": \"cDNA cloning and co-immunoprecipitation with EGFR, PDGFR, and insulin receptor in COS7 cells\",\n      \"pmids\": [\"9819414\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interaction with RTKs was based on overexpression Co-IP without reciprocal validation\", \"Endogenous localization and function not yet addressed\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Demonstration that SNX2 associates with the VPS26–VPS29–VPS35 complex placed it as the mammalian ortholog of yeast Vps5p and a bona fide retromer subunit.\",\n      \"evidence\": \"Yeast two-hybrid, co-immunoprecipitation, and gel filtration chromatography in mammalian cells\",\n      \"pmids\": [\"11102511\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional requirement for SNX2 in retromer-dependent cargo sorting not yet tested\", \"Stoichiometry and domain requirements for retromer association undefined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Defining the retromer as two autonomously assembling subcomplexes — a VPS26–VPS29–VPS35 trimer and an SNX1/SNX2 dimer — and showing that loss of both SNX1 and SNX2 disrupts CI-MPR retrieval resolved the functional architecture of mammalian retromer and established SNX2's essential, partially redundant role in endosome-to-TGN cargo sorting.\",\n      \"evidence\": \"Biochemical fractionation, co-immunoprecipitation, and siRNA knockdown with CI-MPR trafficking assays in HeLa cells\",\n      \"pmids\": [\"17101778\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis for SNX1/SNX2 interchangeability not determined\", \"Cargo selectivity between SNX1- and SNX2-containing complexes unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Structural and functional studies revealed that the PX and BAR domains of SNX1/SNX2 bind PI(3)P-enriched curved membranes, explaining how the sorting nexin dimer targets retromer to endosomal tubules and mediates retrograde transport of toxins such as Shiga toxin.\",\n      \"evidence\": \"X-ray crystallography and EM of the VPS26–VPS29–VPS35 complex; siRNA knockdown with Shiga toxin trafficking in Vero cells\",\n      \"pmids\": [\"17891154\", \"17498660\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure of the SNX2 BAR domain itself\", \"Mechanism by which SNX-BAR tubulation is coordinated with cargo capture not resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapping of four distinct SNX-BAR dimer combinations (SNX1/SNX2 with SNX5/SNX6) revealed combinatorial retromer diversity, with SNX1 linking to the TGN tether Rab6IP1, suggesting distinct functional specialization within the SNX-BAR pool.\",\n      \"evidence\": \"Biochemical fractionation, co-immunoprecipitation, and C. elegans genetics\",\n      \"pmids\": [\"19619496\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific cargo routed by each SNX-BAR combination not systematically assigned\", \"Whether SNX2-containing dimers also contact TGN tethers is untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Discovery that SNX2 interacts with the ER protein VAPB to regulate endosome–ER contact sites and direct endosomal tubulation toward autophagosome biogenesis sites during starvation uncovered a retromer-independent role in inter-organelle tethering and autophagy initiation.\",\n      \"evidence\": \"Live imaging, siRNA knockdown, co-immunoprecipitation, and starvation-induced autophagy assays\",\n      \"pmids\": [\"36585258\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of SNX2–VAPB interaction not determined\", \"Whether this function extends beyond nutritional stress conditions is unknown\", \"Single-laboratory finding awaiting independent replication\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include the structural basis for SNX2-specific functions versus SNX1, the cargo selectivity of individual SNX-BAR dimer combinations, and the in vivo physiological consequences of SNX2 loss in mammalian organisms.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No SNX2-specific crystal or cryo-EM structure available\", \"No mouse knockout phenotype reported in the timeline\", \"Mechanism coupling SNX2-mediated tubulation to VAPB-dependent autophagy signaling uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [3, 5, 6]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [3, 4, 5, 9, 10]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [3, 5, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 4, 5, 7]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [9, 10]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"complexes\": [\n      \"Retromer (SNX-BAR subcomplex)\",\n      \"ESCPE-1 (SNX2/SNX6)\"\n    ],\n    \"partners\": [\n      \"SNX1\",\n      \"SNX6\",\n      \"VPS26\",\n      \"VPS29\",\n      \"VPS35\",\n      \"VAPB\",\n      \"SNX5\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}