{"gene":"RGP1","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":2000,"finding":"Rgp1p and Ric1p form a tight complex that binds Ypt6p in a nucleotide-dependent manner and stimulates guanine nucleotide exchange on Ypt6p in vitro. Deletion of RGP1 or RIC1 blocks recycling of the exocytic SNARE Snc1p from early endosomes to the Golgi, and this defect is rescued by overexpression of YPT6, placing Ric1p-Rgp1p as the GEF that activates Ypt6p on Golgi membranes.","method":"Genetic screen, co-purification, in vitro nucleotide exchange assay, fluorescence microscopy of SNARE trafficking, epistasis with YPT6 overexpression","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — reconstituted GEF activity in vitro combined with epistasis and trafficking phenotype; foundational paper","pmids":["10990452"],"is_preprint":false},{"year":2012,"finding":"Human Ric1 and Rgp1 form a complex that acts as a GEF for Rab6A, preferentially binding its GDP-bound form; both subunits are required for nucleotide exchange activity. Loss of either Ric1 or Rgp1 destabilizes Rab6 protein and blocks Rab6-dependent retrograde transport of mannose-6-phosphate receptors to the Golgi. Additionally, the C-terminus of Ric1 binds Rab33B-GTP (a medial Golgi Rab), establishing a Rab cascade linking medial and trans Golgi.","method":"Co-immunoprecipitation, in vitro nucleotide exchange assay, siRNA knockdown with retrograde trafficking readout (M6PR localization), pull-down of Rab33B-GTP by Ric1","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro GEF assay plus loss-of-function trafficking phenotype and Rab cascade binding, multiple orthogonal methods","pmids":["23091056"],"is_preprint":false},{"year":2011,"finding":"In yeast, deletion of RGP1 (along with RIC1, YPT6, or GARP subunits) causes hypersensitivity to the PE-binding peptide Ro09-0198 and leads to aberrant intracellular localization of the aminophospholipid flippase Dnf2p, demonstrating that the Ric1/Rgp1 GEF complex and its target Ypt6 are required for recycling of plasma membrane flippases to maintain phospholipid asymmetry.","method":"Deletion mutant screen for Ro09-0198 hypersensitivity, fluorescence microscopy of EGFP-Dnf2p localization","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2-3 — clean genetic loss-of-function with defined localization phenotype in yeast, single lab","pmids":["22177957"],"is_preprint":false},{"year":2014,"finding":"Overexpression of Ypt1 suppresses both vesicle trafficking defects (restoration of Snc1 plasma membrane delivery) and autophagic defects (increased GFP-Atg8 vacuolar sorting) in yeast rgp1∆, ric1∆, and ypt6 mutants under nutrient-rich and starvation conditions respectively, revealing a functional connection between Ypt1 and Ypt6/Rgp1 pathways in both exocytic and autophagic trafficking. However, Ypt1 overexpression does not restore Ypt6 intracellular localization in rgp1∆ cells.","method":"Genetic suppression analysis, fluorescence microscopy of Snc1-GFP and GFP-Atg8, Western blot GFP-Atg8 cleavage assay","journal":"Cell biology international","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis with defined trafficking and autophagy readouts, but single lab","pmids":["24843892"],"is_preprint":false},{"year":2008,"finding":"MYR1, encoding a coiled-coil/GYF domain protein, was identified as a high-copy suppressor of ypt6∆ temperature sensitivity and also suppresses ric1∆ temperature sensitivity, genetically linking Myr1 to the Ric1/Rgp1-Ypt6 pathway. Myr1 associates with membranes and large Triton X-100-insoluble structures, and its overexpression affects nuclear envelope morphology.","method":"High-copy suppressor genetic screen, immunofluorescence microscopy, membrane fractionation","journal":"Current genetics","confidence":"Low","confidence_rationale":"Tier 3 — genetic suppressor screen linking Myr1 to the pathway, no direct biochemical interaction with Rgp1 shown","pmids":["18327588"],"is_preprint":false},{"year":2023,"finding":"CRISPR-induced loss of Rgp1 in zebrafish causes craniofacial cartilage defects. In live rgp1 mutant chondrocytes, Rab6a+ vesicular compartment movements are altered, consistent with a conserved GEF mechanism. TEM and immunofluorescence show impaired collagen II secretion. Overexpression experiments reveal Rab8a participates in post-Golgi collagen II trafficking. Loss of Rgp1 triggers an Arf4b-mediated stress response followed by nuclear DNA fragmentation and chondrocyte death, proposing an Rgp1-Rab6a-Rab8a pathway for ECM cargo secretion.","method":"CRISPR zebrafish loss-of-function, live imaging of Rab6a+ vesicles, transmission electron microscopy, immunofluorescence, overexpression epistasis","journal":"Frontiers in endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo genetic model with multiple orthogonal readouts (live imaging, TEM, IF), single lab","pmids":["36843607"],"is_preprint":false},{"year":2024,"finding":"CryoEM structure of the Ric1-Rgp1-Rab6 complex reveals the mechanistic basis for Rab6 activation. Ric1-Rgp1 contacts the nucleotide-binding domain of Rab6 via a previously uncharacterized helical domain (designated RabGEF domain), and mutagenesis of residues within this domain abolishes Rab6 nucleotide exchange. Unexpectedly, the complex employs an arrestin fold (contributed by Rgp1) to interact with the Rab6 hypervariable C-terminal domain, suggesting a common mechanism by which Rab GEFs engage the unstructured tails of their substrates.","method":"CryoEM structure determination, site-directed mutagenesis of GEF interface residues validated by nucleotide exchange assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryoEM structure with mutagenesis validation of catalytic residues, published peer-reviewed","pmids":["39632878"],"is_preprint":false},{"year":2024,"finding":"Genome-wide optical pooled screening for STING trafficking regulators identified that loss of the GARP/RIC1-RGP1 complex increases STING signaling by delaying STING exit from the Golgi, placing Rgp1 (as part of the Ric1-Rgp1 GEF complex) as a regulator of STING Golgi trafficking.","method":"Genome-wide optical pooled CRISPR screen, subcellular imaging of STING localization in millions of cells, sgRNA perturbation","journal":"Cell systems","confidence":"Medium","confidence_rationale":"Tier 2 — large-scale functional screen with imaging phenotype, but RGP1 role defined as part of complex without individual mechanistic dissection","pmids":["39657680"],"is_preprint":false}],"current_model":"RGP1 (human) and its yeast ortholog Rgp1p function as an obligate subunit of the Ric1-Rgp1 heterodimeric guanine nucleotide exchange factor (GEF) complex, which activates Rab6 (Ypt6p in yeast) on Golgi membranes by catalyzing GDP-to-GTP exchange; the cryoEM structure shows Rgp1 contributes an arrestin fold that engages the Rab6 hypervariable C-terminal domain while Ric1 provides the RabGEF catalytic helical domain, and this complex is required for retrograde endosome-to-Golgi trafficking, collagen II secretion in chondrocytes, phospholipid flippase recycling, and proper STING Golgi exit."},"narrative":{"teleology":[{"year":2000,"claim":"The fundamental question of which factor activates Ypt6 was resolved by showing that Rgp1p and Ric1p form a tight complex that directly catalyzes GDP-to-GTP exchange on Ypt6p, and that deletion of either gene blocks Snc1p recycling from endosomes to the Golgi—establishing the Ric1–Rgp1 heterodimer as the dedicated Ypt6 GEF controlling retrograde trafficking.","evidence":"Co-purification, in vitro nucleotide exchange assay, genetic epistasis with YPT6 overexpression, and SNARE localization in S. cerevisiae deletion mutants","pmids":["10990452"],"confidence":"High","gaps":["No structural information on how the two subunits contribute to catalysis","Mammalian ortholog activity not yet demonstrated","Mechanism of Golgi membrane recruitment unknown"]},{"year":2008,"claim":"A high-copy suppressor screen identified MYR1 as a genetic interactor that suppresses ypt6Δ and ric1Δ temperature sensitivity, expanding the genetic network around the Ric1/Rgp1 pathway but without revealing a direct physical link to Rgp1.","evidence":"High-copy suppressor screen, immunofluorescence, and membrane fractionation in yeast","pmids":["18327588"],"confidence":"Low","gaps":["No direct biochemical interaction between Myr1 and Rgp1 demonstrated","Functional relevance of Myr1 to the GEF complex mechanism remains unclear","Not independently confirmed"]},{"year":2011,"claim":"The scope of Rgp1-dependent trafficking was broadened beyond SNAREs to include phospholipid flippase recycling, demonstrating that loss of Rgp1 mislocalized the aminophospholipid flippase Dnf2p and sensitized cells to PE-targeting agents.","evidence":"Deletion mutant sensitivity screen and fluorescence microscopy of EGFP-Dnf2p in S. cerevisiae","pmids":["22177957"],"confidence":"Medium","gaps":["Direct mechanistic link between Rab6/Ypt6 activation and flippase sorting not dissected","Mammalian relevance of this lipid asymmetry phenotype not tested"]},{"year":2012,"claim":"The mammalian Ric1–Rgp1 complex was confirmed as a Rab6A GEF, and a Rab cascade mechanism was uncovered in which Rab33B-GTP on medial Golgi recruits Ric1, enabling sequential Rab activation from medial to trans-Golgi.","evidence":"Co-immunoprecipitation, in vitro nucleotide exchange assay, siRNA knockdown with M6PR retrograde trafficking readout, Rab33B-GTP pull-down in human cells","pmids":["23091056"],"confidence":"High","gaps":["Structural basis for Rab33B binding to Ric1 C-terminus unresolved","Whether Rgp1 contacts Rab33B or only Rab6 not determined","In vivo validation of the Rab cascade model in animal tissues lacking"]},{"year":2014,"claim":"Functional cross-talk between the Ypt1 and Ypt6/Rgp1 pathways was demonstrated: Ypt1 overexpression suppressed both vesicle trafficking and autophagy defects in rgp1Δ cells, revealing that Rgp1-dependent Rab activation intersects with autophagic flux.","evidence":"Genetic suppression analysis, fluorescence microscopy of Snc1-GFP and GFP-Atg8, Western blot cleavage assay in S. cerevisiae","pmids":["24843892"],"confidence":"Medium","gaps":["Mechanism by which Ypt1 bypasses Ypt6 loss remains unclear","Whether autophagy regulation is a direct or indirect consequence of Rgp1 loss not resolved"]},{"year":2023,"claim":"In vivo vertebrate function was established: CRISPR-mediated loss of Rgp1 in zebrafish impaired Rab6a+ vesicle dynamics in chondrocytes, blocked collagen II secretion, and caused craniofacial cartilage defects and cell death, linking the GEF complex to ECM cargo secretion through a proposed Rab6a–Rab8a relay.","evidence":"CRISPR zebrafish knockout, live imaging of Rab6a+ vesicles, TEM, immunofluorescence, overexpression epistasis","pmids":["36843607"],"confidence":"Medium","gaps":["Direct physical interaction between Rgp1 and Rab8a not demonstrated","Whether cell death is primary or secondary to secretion failure not distinguished","Mammalian in vivo cartilage/bone phenotype not yet reported"]},{"year":2024,"claim":"The structural mechanism of Rab6 activation was solved: cryoEM revealed that Rgp1 contributes an arrestin fold engaging the Rab6 hypervariable C-terminal domain, while Ric1 provides the catalytic RabGEF helical domain contacting the nucleotide-binding pocket, and mutagenesis confirmed that specific interface residues are essential for exchange activity.","evidence":"CryoEM structure determination and site-directed mutagenesis validated by in vitro nucleotide exchange assay","pmids":["39632878"],"confidence":"High","gaps":["Role of the arrestin fold beyond tail engagement (e.g., membrane curvature sensing) not explored","Whether Rgp1 arrestin fold contacts other Rab substrates or is Rab6-specific untested","No structure of the full complex on a membrane"]},{"year":2024,"claim":"Genome-wide screening extended the functional repertoire of the Ric1–Rgp1 complex to innate immune signaling, showing that loss of the complex delays STING exit from the Golgi and enhances STING-dependent signaling.","evidence":"Genome-wide optical pooled CRISPR screen with subcellular STING imaging in human cells","pmids":["39657680"],"confidence":"Medium","gaps":["Whether Rgp1 loss affects STING trafficking independently of Ric1 not tested","Downstream consequences for type I interferon signaling in vivo not assessed","Mechanism linking Rab6 activation to STING Golgi export not dissected"]},{"year":null,"claim":"It remains unknown how the Ric1–Rgp1 complex is recruited to specific Golgi subdomains in vivo, whether the Rgp1 arrestin fold has functions beyond Rab6 tail engagement (e.g., membrane sensing), and whether RGP1 mutations cause human disease.","evidence":"","pmids":[],"confidence":"Low","gaps":["Membrane recruitment mechanism of the GEF complex unresolved","No human genetic disease linked to RGP1 mutations reported","Potential non-GEF functions of the Rgp1 arrestin fold unexplored"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,6]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,1,5,7]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[0,1,2,5,7]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[3]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,6]}],"complexes":["Ric1–Rgp1 GEF complex"],"partners":["RIC1","RAB6A","RAB33B"],"other_free_text":[]},"mechanistic_narrative":"RGP1 is an obligate subunit of the Ric1–Rgp1 heterodimeric guanine nucleotide exchange factor (GEF) complex that activates Rab6 (Ypt6 in yeast) on Golgi membranes, thereby controlling retrograde endosome-to-Golgi vesicle trafficking [PMID:10990452, PMID:23091056]. CryoEM structural analysis shows that Rgp1 contributes an arrestin fold that engages the hypervariable C-terminal domain of Rab6, while Ric1 provides the catalytic RabGEF helical domain that drives GDP-to-GTP exchange; mutagenesis of the GEF interface abolishes nucleotide exchange activity [PMID:39632878]. Loss of Rgp1 destabilizes Rab6, blocks mannose-6-phosphate receptor retrograde transport, impairs phospholipid flippase recycling, delays STING Golgi exit, and in zebrafish disrupts collagen II secretion in chondrocytes leading to craniofacial cartilage defects [PMID:23091056, PMID:22177957, PMID:39657680, PMID:36843607]."},"prefetch_data":{"uniprot":{"accession":"Q92546","full_name":"RAB6A-GEF complex partner protein 2","aliases":["Retrograde Golgi transport protein RGP1 homolog"],"length_aa":391,"mass_kda":42.5,"function":"The RIC1-RGP1 complex acts as a guanine nucleotide exchange factor (GEF), which activates RAB6A by exchanging bound GDP for free GTP and may thereby required for efficient fusion of endosome-derived vesicles with the Golgi compartment. The RIC1-RGP1 complex participates in the recycling of mannose-6-phosphate receptors","subcellular_location":"Cytoplasm, cytosol; Membrane","url":"https://www.uniprot.org/uniprotkb/Q92546/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RGP1","classification":"Not Classified","n_dependent_lines":572,"n_total_lines":1208,"dependency_fraction":0.4735099337748344},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RGP1","total_profiled":1310},"omim":[{"mim_id":"615742","title":"RGP1 HOMOLOG, RAB6A GEF COMPLEX PARTNER 1; RGP1","url":"https://www.omim.org/entry/615742"},{"mim_id":"612704","title":"RANBP2-LIKE AND GRIP DOMAIN-CONTAINING PROTEIN 1; RGPD1","url":"https://www.omim.org/entry/612704"},{"mim_id":"610354","title":"RIC1 HOMOLOG, RAB6A GEF COMPLEX PARTNER 1; RIC1","url":"https://www.omim.org/entry/610354"},{"mim_id":"179513","title":"RAS-ASSOCIATED PROTEIN RAB6A; RAB6A","url":"https://www.omim.org/entry/179513"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Cytosol","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RGP1"},"hgnc":{"alias_symbol":[],"prev_symbol":["KIAA0258"]},"alphafold":{"accession":"Q92546","domains":[{"cath_id":"2.60.40.640","chopping":"2-63_75-161_374-389","consensus_level":"high","plddt":89.4233,"start":2,"end":389},{"cath_id":"2.60.40.640","chopping":"211-334_356-370","consensus_level":"high","plddt":91.6425,"start":211,"end":370}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92546","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q92546-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q92546-F1-predicted_aligned_error_v6.png","plddt_mean":85.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RGP1","jax_strain_url":"https://www.jax.org/strain/search?query=RGP1"},"sequence":{"accession":"Q92546","fasta_url":"https://rest.uniprot.org/uniprotkb/Q92546.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q92546/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92546"}},"corpus_meta":[{"pmid":"7836351","id":"PMC_7836351","title":"Molecular cloning and structural characterization of the Arg-gingipain proteinase of Porphyromonas gingivalis. 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assay plus epistasis genetics with defined phenotypic readout\",\n      \"pmids\": [\"10990452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human Ric1 and Rgp1 form a complex that functions as a GEF for Rab6A (late Golgi), with both subunits required for nucleotide exchange; loss of Ric1 or Rgp1 destabilizes Rab6 and blocks Rab6-dependent retrograde transport of mannose 6-phosphate receptors to the Golgi. Additionally, the C-terminus of Ric1 binds Rab33B-GTP, establishing a Rab cascade between medial and trans-Golgi.\",\n      \"method\": \"In vitro GEF assay, Co-IP/binding assays, siRNA knockdown with defined trafficking phenotype (MPR retrograde transport)\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro nucleotide exchange assay plus reciprocal binding studies and KD with defined trafficking phenotype\",\n      \"pmids\": [\"23091056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CryoEM structure of the Ric1-Rgp1-Rab6 complex reveals that Ric1-Rgp1 interacts with the nucleotide-binding domain of Rab6 via an uncharacterized helical domain (designated RabGEF domain), and uses an arrestin fold to interact with the Rab6 hypervariable domain; mutagenesis of the RabGEF domain residues abolishes Rab6 activation.\",\n      \"method\": \"CryoEM structure determination, site-directed mutagenesis of catalytic residues, in vitro GEF assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryoEM structure with functional mutagenesis and in vitro assay validation in a single rigorous study\",\n      \"pmids\": [\"39632878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CryoEM structure of Ric1-Rgp1-Rab6 complex (preprint version): same structural findings as published paper — RabGEF helical domain contacts nucleotide-binding region of Rab6, arrestin fold contacts Rab6 hypervariable domain, mutagenesis confirms residues required for nucleotide exchange.\",\n      \"method\": \"CryoEM, mutagenesis, in vitro GEF assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — same data as peer-reviewed publication; structural + functional mutagenesis\",\n      \"pmids\": [\"38766083\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In zebrafish, loss-of-function of Rgp1 (CRISPR mutants) impairs craniofacial cartilage development; within live rgp1-mutant chondrocytes, Rab6a+ vesicular compartment movements are altered. Rgp1 is required for collagen II secretion in chondrocytes; overexpression experiments place Rab8a downstream of Rab6a in the post-Golgi collagen II trafficking pathway. Loss of Rgp1 activates Arf4b-mediated stress response and leads to nuclear DNA fragmentation and cell death.\",\n      \"method\": \"CRISPR-induced zebrafish loss-of-function mutants, live imaging of Rab6a+ vesicles, TEM and immunofluorescence for collagen II, overexpression epistasis\",\n      \"journal\": \"Frontiers in endocrinology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple orthogonal readouts (live imaging, TEM, IF) establishing pathway position in vivo\",\n      \"pmids\": [\"36843607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In yeast, overexpression of Ypt1 suppresses vesicle trafficking and autophagic defects in rgp1Δ mutants (restoring Snc1 transport to plasma membrane via Golgi and increasing GFP-Atg8 sorting to vacuoles), but does not restore Ypt6 intracellular localization in rgp1Δ cells, indicating Rgp1 is required for proper Ypt6 localization.\",\n      \"method\": \"Yeast genetic suppression, fluorescence microscopy of Snc1 and GFP-Atg8 reporters\",\n      \"journal\": \"Cell biology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with fluorescent reporter readouts; single lab study\",\n      \"pmids\": [\"24843892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In yeast, deletion of RGP1 (encoding the GEF subunit for Ypt6) causes hypersensitivity to the PE-binding peptide Ro09-0198 and aberrant intracellular localization of the aminophospholipid flippase Dnf2p, demonstrating that the Ric1/Rgp1-Ypt6 pathway is required for plasma membrane recycling of Dnf flippases.\",\n      \"method\": \"Yeast deletion screen, fluorescence microscopy of EGFP-Dnf2p localization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — genetic deletion with defined localization phenotype; single lab\",\n      \"pmids\": [\"22177957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Genome-wide optical pooled screening showed that loss of RGP1 (within the RIC1-RGP1 complex) increases STING signaling by delaying STING exit from the Golgi, placing the Ric1-Rgp1 GEF complex as a regulator of STING Golgi trafficking.\",\n      \"method\": \"Genome-wide optical pooled CRISPR screen with subcellular imaging of STING localization and STING signaling readout\",\n      \"journal\": \"Cell systems\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide functional screen with high-content imaging; mechanistic follow-up limited to localization and signaling assays\",\n      \"pmids\": [\"39657680\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MYR1 was identified as a high-copy suppressor of both ypt6Δ and ric1Δ (but not rgp1Δ) temperature-sensitive growth defects in yeast, genetically linking Myr1 to the Ypt6/Ric1-Rgp1 pathway.\",\n      \"method\": \"Yeast genetic suppressor screen, overexpression analysis\",\n      \"journal\": \"Current genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single genetic suppressor screen with limited mechanistic follow-up specific to Rgp1\",\n      \"pmids\": [\"18327588\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RGP1 is an obligate subunit of the Ric1-Rgp1 guanine nucleotide exchange factor (GEF) complex, which activates the Golgi-localized Rab GTPase Rab6 (Ypt6p in yeast) by catalyzing GDP-to-GTP exchange; structural analysis by cryoEM revealed that Ric1 engages the Rab6 nucleotide-binding domain through a RabGEF helical domain while an arrestin fold contacts the Rab6 hypervariable domain, and the complex is required in vivo for retrograde endosome-to-Golgi trafficking, SNARE recycling, collagen II secretion in chondrocytes, and regulation of STING Golgi exit.\"\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\nI'll systematically classify each paper before extracting discoveries.\n\n**Classification:**\n\n- Papers about RGP1 as Ric1-Rgp1 GEF complex for Rab6/Ypt6 (yeast/human/zebrafish): KEEP [2, 14, 25, 31, 33, 38, 39, 40, 41, 44, 46]\n- Papers about RGP-1 as Porphyromonas gingivalis arginine-specific cysteine proteinase: EXCLUDE (alias collision - bacterial gene)\n- Papers about plant RGP1 (reversibly glycosylated polypeptide, cell wall): EXCLUDE (symbol collision - plant gene)\n- Papers about rice rgp1 (ras-related GTP-binding protein in plants): EXCLUDE (plant gene, different context)\n- Papers about tobacco RGP-1 (RNA-binding proteins): EXCLUDE (plant gene)\n- Papers about relaxin-like gonad-stimulating peptides RGP1/RGP2 in starfish: EXCLUDE (symbol collision)\n- Papers about polysaccharides named RGP1: EXCLUDE\n- Papers about Streptococcus thermophilus rgp locus: EXCLUDE\n- Large-scale proteomics/interactome papers (BioPlex, BioID, etc.): these mention RGP1 only incidentally in large datasets — EXCLUDE (no mechanistic findings specific to RGP1)\n- Papers [34, 36, 37, 45, 47]: expression/association studies — EXCLUDE\n\n**KEEP list:** [2, 14, 25, 31, 33, 38, 39, 40, 41, 44, 46]\n\nNote: Papers [41] and [46] are the published and preprint versions of the same STING paper. Paper [40] has no abstract but is a yeast study of RGP1 in mitotic growth.\n\n```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"Rgp1p and Ric1p form a tight complex that binds Ypt6p in a nucleotide-dependent manner and stimulates guanine nucleotide exchange on Ypt6p in vitro. Deletion of RGP1 or RIC1 blocks recycling of the exocytic SNARE Snc1p from early endosomes to the Golgi, and this defect is rescued by overexpression of YPT6, placing Ric1p-Rgp1p as the GEF that activates Ypt6p on Golgi membranes.\",\n      \"method\": \"Genetic screen, co-purification, in vitro nucleotide exchange assay, fluorescence microscopy of SNARE trafficking, epistasis with YPT6 overexpression\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted GEF activity in vitro combined with epistasis and trafficking phenotype; foundational paper\",\n      \"pmids\": [\"10990452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human Ric1 and Rgp1 form a complex that acts as a GEF for Rab6A, preferentially binding its GDP-bound form; both subunits are required for nucleotide exchange activity. Loss of either Ric1 or Rgp1 destabilizes Rab6 protein and blocks Rab6-dependent retrograde transport of mannose-6-phosphate receptors to the Golgi. Additionally, the C-terminus of Ric1 binds Rab33B-GTP (a medial Golgi Rab), establishing a Rab cascade linking medial and trans Golgi.\",\n      \"method\": \"Co-immunoprecipitation, in vitro nucleotide exchange assay, siRNA knockdown with retrograde trafficking readout (M6PR localization), pull-down of Rab33B-GTP by Ric1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro GEF assay plus loss-of-function trafficking phenotype and Rab cascade binding, multiple orthogonal methods\",\n      \"pmids\": [\"23091056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In yeast, deletion of RGP1 (along with RIC1, YPT6, or GARP subunits) causes hypersensitivity to the PE-binding peptide Ro09-0198 and leads to aberrant intracellular localization of the aminophospholipid flippase Dnf2p, demonstrating that the Ric1/Rgp1 GEF complex and its target Ypt6 are required for recycling of plasma membrane flippases to maintain phospholipid asymmetry.\",\n      \"method\": \"Deletion mutant screen for Ro09-0198 hypersensitivity, fluorescence microscopy of EGFP-Dnf2p localization\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — clean genetic loss-of-function with defined localization phenotype in yeast, single lab\",\n      \"pmids\": [\"22177957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Overexpression of Ypt1 suppresses both vesicle trafficking defects (restoration of Snc1 plasma membrane delivery) and autophagic defects (increased GFP-Atg8 vacuolar sorting) in yeast rgp1∆, ric1∆, and ypt6 mutants under nutrient-rich and starvation conditions respectively, revealing a functional connection between Ypt1 and Ypt6/Rgp1 pathways in both exocytic and autophagic trafficking. However, Ypt1 overexpression does not restore Ypt6 intracellular localization in rgp1∆ cells.\",\n      \"method\": \"Genetic suppression analysis, fluorescence microscopy of Snc1-GFP and GFP-Atg8, Western blot GFP-Atg8 cleavage assay\",\n      \"journal\": \"Cell biology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis with defined trafficking and autophagy readouts, but single lab\",\n      \"pmids\": [\"24843892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MYR1, encoding a coiled-coil/GYF domain protein, was identified as a high-copy suppressor of ypt6∆ temperature sensitivity and also suppresses ric1∆ temperature sensitivity, genetically linking Myr1 to the Ric1/Rgp1-Ypt6 pathway. Myr1 associates with membranes and large Triton X-100-insoluble structures, and its overexpression affects nuclear envelope morphology.\",\n      \"method\": \"High-copy suppressor genetic screen, immunofluorescence microscopy, membrane fractionation\",\n      \"journal\": \"Current genetics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — genetic suppressor screen linking Myr1 to the pathway, no direct biochemical interaction with Rgp1 shown\",\n      \"pmids\": [\"18327588\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CRISPR-induced loss of Rgp1 in zebrafish causes craniofacial cartilage defects. In live rgp1 mutant chondrocytes, Rab6a+ vesicular compartment movements are altered, consistent with a conserved GEF mechanism. TEM and immunofluorescence show impaired collagen II secretion. Overexpression experiments reveal Rab8a participates in post-Golgi collagen II trafficking. Loss of Rgp1 triggers an Arf4b-mediated stress response followed by nuclear DNA fragmentation and chondrocyte death, proposing an Rgp1-Rab6a-Rab8a pathway for ECM cargo secretion.\",\n      \"method\": \"CRISPR zebrafish loss-of-function, live imaging of Rab6a+ vesicles, transmission electron microscopy, immunofluorescence, overexpression epistasis\",\n      \"journal\": \"Frontiers in endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic model with multiple orthogonal readouts (live imaging, TEM, IF), single lab\",\n      \"pmids\": [\"36843607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"CryoEM structure of the Ric1-Rgp1-Rab6 complex reveals the mechanistic basis for Rab6 activation. Ric1-Rgp1 contacts the nucleotide-binding domain of Rab6 via a previously uncharacterized helical domain (designated RabGEF domain), and mutagenesis of residues within this domain abolishes Rab6 nucleotide exchange. Unexpectedly, the complex employs an arrestin fold (contributed by Rgp1) to interact with the Rab6 hypervariable C-terminal domain, suggesting a common mechanism by which Rab GEFs engage the unstructured tails of their substrates.\",\n      \"method\": \"CryoEM structure determination, site-directed mutagenesis of GEF interface residues validated by nucleotide exchange assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryoEM structure with mutagenesis validation of catalytic residues, published peer-reviewed\",\n      \"pmids\": [\"39632878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Genome-wide optical pooled screening for STING trafficking regulators identified that loss of the GARP/RIC1-RGP1 complex increases STING signaling by delaying STING exit from the Golgi, placing Rgp1 (as part of the Ric1-Rgp1 GEF complex) as a regulator of STING Golgi trafficking.\",\n      \"method\": \"Genome-wide optical pooled CRISPR screen, subcellular imaging of STING localization in millions of cells, sgRNA perturbation\",\n      \"journal\": \"Cell systems\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — large-scale functional screen with imaging phenotype, but RGP1 role defined as part of complex without individual mechanistic dissection\",\n      \"pmids\": [\"39657680\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RGP1 (human) and its yeast ortholog Rgp1p function as an obligate subunit of the Ric1-Rgp1 heterodimeric guanine nucleotide exchange factor (GEF) complex, which activates Rab6 (Ypt6p in yeast) on Golgi membranes by catalyzing GDP-to-GTP exchange; the cryoEM structure shows Rgp1 contributes an arrestin fold that engages the Rab6 hypervariable C-terminal domain while Ric1 provides the RabGEF catalytic helical domain, and this complex is required for retrograde endosome-to-Golgi trafficking, collagen II secretion in chondrocytes, phospholipid flippase recycling, and proper STING Golgi exit.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RGP1 is an obligate subunit of the Ric1–Rgp1 guanine-nucleotide exchange factor (GEF) complex that activates the Golgi-localized Rab GTPase Rab6 (Ypt6 in yeast), thereby controlling retrograde endosome-to-Golgi vesicle trafficking. The complex catalyzes GDP-to-GTP exchange on Rab6 through a RabGEF helical domain on Ric1 that contacts the Rab6 nucleotide-binding pocket, while an arrestin fold engages the Rab6 hypervariable domain; both subunits are required for exchange activity [PMID:10990452, PMID:23091056, PMID:39632878]. Loss of Rgp1 blocks recycling of exocytic SNAREs and aminophospholipid flippases in yeast, impairs mannose-6-phosphate receptor retrograde transport in mammalian cells, disrupts collagen II secretion in zebrafish chondrocytes, and delays STING exit from the Golgi [PMID:10990452, PMID:23091056, PMID:22177957, PMID:36843607, PMID:39657680]. In the Golgi, the complex is itself positioned by an upstream Rab cascade in which Rab33B-GTP binds the Ric1 C-terminus, linking medial- and trans-Golgi identity [PMID:23091056].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing the core biochemical activity: the Ric1p–Rgp1p complex was shown to be the dedicated GEF for the Golgi Rab GTPase Ypt6p, and its loss blocked SNARE recycling from endosomes to the Golgi, defining Rgp1 as essential for retrograde trafficking.\",\n      \"evidence\": \"In vitro GEF assay with purified yeast Ric1p–Rgp1p complex on Ypt6p, combined with rgp1Δ deletion phenotypes and YPT6 overexpression rescue\",\n      \"pmids\": [\"10990452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural information on how the two-subunit complex engages Ypt6/Rab6\",\n        \"Mammalian ortholog function not yet tested\",\n        \"Mechanism of GEF recruitment to Golgi membranes unknown\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The Ric1/Rgp1–Ypt6 pathway was linked to plasma membrane lipid asymmetry by showing that rgp1Δ causes mis-localization of the aminophospholipid flippase Dnf2p, extending the functional reach of the complex beyond SNARE recycling.\",\n      \"evidence\": \"Yeast deletion screen with Ro09-0198 sensitivity and EGFP-Dnf2p fluorescence imaging\",\n      \"pmids\": [\"22177957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether Dnf2p mis-localization is a direct or indirect consequence of Ypt6 inactivation is unresolved\",\n        \"No biochemical interaction between Rgp1 and Dnf2 shown\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Conservation of the GEF activity was demonstrated in human cells: human Ric1–Rgp1 catalyzes Rab6A nucleotide exchange, and an upstream Rab33B-GTP→Ric1 interaction established a Rab cascade that couples medial- and trans-Golgi compartments.\",\n      \"evidence\": \"In vitro GEF assay on human Rab6A, co-IP/binding assays for Rab33B–Ric1 interaction, siRNA knockdown with mannose-6-phosphate receptor retrograde transport assay\",\n      \"pmids\": [\"23091056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis of the Rab33B–Ric1 interaction unknown\",\n        \"Whether additional Rabs feed into the cascade is untested\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Genetic epistasis showed Rgp1 is required for proper Ypt6 membrane targeting in yeast—overexpression of Ypt1 could bypass trafficking and autophagy defects of rgp1Δ but could not restore Ypt6 localization.\",\n      \"evidence\": \"Yeast genetic suppression with fluorescence microscopy of Snc1 and GFP-Atg8 reporters\",\n      \"pmids\": [\"24843892\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which Ypt1 bypasses rgp1Δ defects is not defined\",\n        \"Autophagy role of Rgp1 not tested with direct autophagy flux assays\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"In vivo developmental function was established: Rgp1 loss in zebrafish impairs collagen II secretion in chondrocytes and alters Rab6a+ vesicle dynamics, causing craniofacial cartilage defects and cell death via Arf4b-mediated stress.\",\n      \"evidence\": \"CRISPR-generated rgp1 zebrafish mutants with live Rab6a+ vesicle imaging, TEM, and collagen II immunofluorescence\",\n      \"pmids\": [\"36843607\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether the cell-death phenotype is a direct consequence of collagen mis-sorting or a parallel Rab6 effector pathway is unclear\",\n        \"Mammalian skeletal phenotype not yet reported\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The structural mechanism of Rab6 activation was resolved: cryoEM showed that Ric1 contacts the Rab6 nucleotide-binding domain via a novel RabGEF helical domain, while an arrestin fold contacts the hypervariable domain, and mutagenesis of catalytic residues abolished GEF activity.\",\n      \"evidence\": \"CryoEM structure determination of the Ric1–Rgp1–Rab6 ternary complex with site-directed mutagenesis and in vitro GEF assay\",\n      \"pmids\": [\"39632878\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structure captured without Golgi membrane context; how membrane association modulates activity is unknown\",\n        \"Contribution of Rgp1 subunit to catalysis versus complex stability not fully dissected structurally\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A new functional axis was identified: genome-wide CRISPR screening revealed that RGP1 loss delays STING exit from the Golgi and enhances STING signaling, connecting the Ric1–Rgp1 complex to innate immune regulation.\",\n      \"evidence\": \"Optical pooled CRISPR screen with subcellular STING imaging and STING signaling readout\",\n      \"pmids\": [\"39657680\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether the STING effect is mediated specifically through Rab6 or through additional trafficking pathways is untested\",\n        \"No direct physical interaction between Rgp1 and STING demonstrated\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include how the Ric1–Rgp1 complex is recruited to and activated on Golgi membranes, whether Rgp1 itself contributes catalytic residues or solely stabilizes Ric1, and how the complex coordinates its multiple cargo-specific trafficking outputs (SNAREs, flippases, collagen, STING).\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No membrane-reconstituted GEF assay to assess lipid or membrane curvature effects\",\n        \"No disease-associated mutations in human RGP1 reported\",\n        \"Tissue-specific roles in mammals largely uncharacterized\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 4, 7]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"complexes\": [\n      \"Ric1-Rgp1 GEF complex\"\n    ],\n    \"partners\": [\n      \"RIC1\",\n      \"RAB6A\",\n      \"RAB33B\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```\n\n--- ROUND 2 (R2/R3, augmented corpus) ---\n\n```json\n{\n  \"mechanistic_narrative\": \"RGP1 is an obligate subunit of the Ric1–Rgp1 heterodimeric guanine nucleotide exchange factor (GEF) complex that activates Rab6 (Ypt6 in yeast) on Golgi membranes, thereby controlling retrograde endosome-to-Golgi vesicle trafficking [PMID:10990452, PMID:23091056]. CryoEM structural analysis shows that Rgp1 contributes an arrestin fold that engages the hypervariable C-terminal domain of Rab6, while Ric1 provides the catalytic RabGEF helical domain that drives GDP-to-GTP exchange; mutagenesis of the GEF interface abolishes nucleotide exchange activity [PMID:39632878]. Loss of Rgp1 destabilizes Rab6, blocks mannose-6-phosphate receptor retrograde transport, impairs phospholipid flippase recycling, delays STING Golgi exit, and in zebrafish disrupts collagen II secretion in chondrocytes leading to craniofacial cartilage defects [PMID:23091056, PMID:22177957, PMID:39657680, PMID:36843607].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"The fundamental question of which factor activates Ypt6 was resolved by showing that Rgp1p and Ric1p form a tight complex that directly catalyzes GDP-to-GTP exchange on Ypt6p, and that deletion of either gene blocks Snc1p recycling from endosomes to the Golgi—establishing the Ric1–Rgp1 heterodimer as the dedicated Ypt6 GEF controlling retrograde trafficking.\",\n      \"evidence\": \"Co-purification, in vitro nucleotide exchange assay, genetic epistasis with YPT6 overexpression, and SNARE localization in S. cerevisiae deletion mutants\",\n      \"pmids\": [\"10990452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structural information on how the two subunits contribute to catalysis\",\n        \"Mammalian ortholog activity not yet demonstrated\",\n        \"Mechanism of Golgi membrane recruitment unknown\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"A high-copy suppressor screen identified MYR1 as a genetic interactor that suppresses ypt6Δ and ric1Δ temperature sensitivity, expanding the genetic network around the Ric1/Rgp1 pathway but without revealing a direct physical link to Rgp1.\",\n      \"evidence\": \"High-copy suppressor screen, immunofluorescence, and membrane fractionation in yeast\",\n      \"pmids\": [\"18327588\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No direct biochemical interaction between Myr1 and Rgp1 demonstrated\",\n        \"Functional relevance of Myr1 to the GEF complex mechanism remains unclear\",\n        \"Not independently confirmed\"\n      ]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"The scope of Rgp1-dependent trafficking was broadened beyond SNAREs to include phospholipid flippase recycling, demonstrating that loss of Rgp1 mislocalized the aminophospholipid flippase Dnf2p and sensitized cells to PE-targeting agents.\",\n      \"evidence\": \"Deletion mutant sensitivity screen and fluorescence microscopy of EGFP-Dnf2p in S. cerevisiae\",\n      \"pmids\": [\"22177957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct mechanistic link between Rab6/Ypt6 activation and flippase sorting not dissected\",\n        \"Mammalian relevance of this lipid asymmetry phenotype not tested\"\n      ]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"The mammalian Ric1–Rgp1 complex was confirmed as a Rab6A GEF, and a Rab cascade mechanism was uncovered in which Rab33B-GTP on medial Golgi recruits Ric1, enabling sequential Rab activation from medial to trans-Golgi.\",\n      \"evidence\": \"Co-immunoprecipitation, in vitro nucleotide exchange assay, siRNA knockdown with M6PR retrograde trafficking readout, Rab33B-GTP pull-down in human cells\",\n      \"pmids\": [\"23091056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural basis for Rab33B binding to Ric1 C-terminus unresolved\",\n        \"Whether Rgp1 contacts Rab33B or only Rab6 not determined\",\n        \"In vivo validation of the Rab cascade model in animal tissues lacking\"\n      ]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Functional cross-talk between the Ypt1 and Ypt6/Rgp1 pathways was demonstrated: Ypt1 overexpression suppressed both vesicle trafficking and autophagy defects in rgp1Δ cells, revealing that Rgp1-dependent Rab activation intersects with autophagic flux.\",\n      \"evidence\": \"Genetic suppression analysis, fluorescence microscopy of Snc1-GFP and GFP-Atg8, Western blot cleavage assay in S. cerevisiae\",\n      \"pmids\": [\"24843892\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Mechanism by which Ypt1 bypasses Ypt6 loss remains unclear\",\n        \"Whether autophagy regulation is a direct or indirect consequence of Rgp1 loss not resolved\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"In vivo vertebrate function was established: CRISPR-mediated loss of Rgp1 in zebrafish impaired Rab6a+ vesicle dynamics in chondrocytes, blocked collagen II secretion, and caused craniofacial cartilage defects and cell death, linking the GEF complex to ECM cargo secretion through a proposed Rab6a–Rab8a relay.\",\n      \"evidence\": \"CRISPR zebrafish knockout, live imaging of Rab6a+ vesicles, TEM, immunofluorescence, overexpression epistasis\",\n      \"pmids\": [\"36843607\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct physical interaction between Rgp1 and Rab8a not demonstrated\",\n        \"Whether cell death is primary or secondary to secretion failure not distinguished\",\n        \"Mammalian in vivo cartilage/bone phenotype not yet reported\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"The structural mechanism of Rab6 activation was solved: cryoEM revealed that Rgp1 contributes an arrestin fold engaging the Rab6 hypervariable C-terminal domain, while Ric1 provides the catalytic RabGEF helical domain contacting the nucleotide-binding pocket, and mutagenesis confirmed that specific interface residues are essential for exchange activity.\",\n      \"evidence\": \"CryoEM structure determination and site-directed mutagenesis validated by in vitro nucleotide exchange assay\",\n      \"pmids\": [\"39632878\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Role of the arrestin fold beyond tail engagement (e.g., membrane curvature sensing) not explored\",\n        \"Whether Rgp1 arrestin fold contacts other Rab substrates or is Rab6-specific untested\",\n        \"No structure of the full complex on a membrane\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Genome-wide screening extended the functional repertoire of the Ric1–Rgp1 complex to innate immune signaling, showing that loss of the complex delays STING exit from the Golgi and enhances STING-dependent signaling.\",\n      \"evidence\": \"Genome-wide optical pooled CRISPR screen with subcellular STING imaging in human cells\",\n      \"pmids\": [\"39657680\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether Rgp1 loss affects STING trafficking independently of Ric1 not tested\",\n        \"Downstream consequences for type I interferon signaling in vivo not assessed\",\n        \"Mechanism linking Rab6 activation to STING Golgi export not dissected\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"It remains unknown how the Ric1–Rgp1 complex is recruited to specific Golgi subdomains in vivo, whether the Rgp1 arrestin fold has functions beyond Rab6 tail engagement (e.g., membrane sensing), and whether RGP1 mutations cause human disease.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"Membrane recruitment mechanism of the GEF complex unresolved\",\n        \"No human genetic disease linked to RGP1 mutations reported\",\n        \"Potential non-GEF functions of the Rgp1 arrestin fold unexplored\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1, 5, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [0, 1, 2, 5, 7]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 6]}\n    ],\n    \"complexes\": [\n      \"Ric1–Rgp1 GEF complex\"\n    ],\n    \"partners\": [\n      \"RIC1\",\n      \"RAB6A\",\n      \"RAB33B\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}