{"gene":"RAB33B","run_date":"2026-04-28T19:45:45","timeline":{"discoveries":[{"year":1998,"finding":"RAB33B is a novel Rab GTPase that localizes to the medial Golgi cisternae, as demonstrated by co-localization with alpha-mannosidase II by immunofluorescence and immunoelectron microscopy, suggesting a role in intra-Golgi transport.","method":"Immunofluorescence, immunoelectron microscopy, Western blotting with Rab33B-specific monoclonal antibody","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 — direct localization experiment with multiple orthogonal methods (immunofluorescence + immunoEM), foundational paper","pmids":["9512502"],"is_preprint":false},{"year":2001,"finding":"RAB33B in its GTP-bound state interacts with Golgi protein GM130 and endocytic Rab effectors rabaptin-5 and rabex-5; microinjection of GTP-locked Rab33B mutants inhibited anterograde transport within the Golgi and recycling of glycosyltransferases from Golgi to ER.","method":"GST pulldown with GTP-locked Rab33B fusion protein, Western blotting/mass spectrometry for interactor identification, microinjection of GTPase mutants","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro pulldown with GTP-restricted mutant plus functional microinjection assay, foundational study","pmids":["11718716"],"is_preprint":false},{"year":2008,"finding":"RAB33B (and RAB33A) specifically interacts with Atg16L in a GTP-dependent manner; expression of GTPase-deficient RAB33B-Q92L induced LC3 lipidation under nutrient-rich conditions and attenuated macroautophagy, demonstrating that RAB33B modulates autophagosome formation through Atg16L interaction.","method":"Co-immunoprecipitation, GTP-dependent binding assay, overexpression of GTPase-deficient mutant (Q92L), LC3 lipidation assay, p62/SQSTM1 degradation assay","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — reciprocal interaction and multiple functional readouts in the same study, highly cited foundational paper","pmids":["18448665"],"is_preprint":false},{"year":2010,"finding":"RAB33B acts downstream of trans-Golgi Rab6 in a Rab cascade regulating intra-Golgi retrograde trafficking; GTP-restricted Rab6-induced relocation of Golgi enzymes to the ER was RAB33B-dependent, overexpression of GTP-RAB33B displaced Rab6 from Golgi membranes, and RAB33B was required for Shiga-like toxin B fragment transport from trans to cis Golgi and ER.","method":"siRNA knockdown, overexpression of GTP-locked mutants, Golgi ribbon disruption assay, Shiga toxin transport assay, immunofluorescence","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — epistasis established by multiple orthogonal functional approaches in the same study","pmids":["20163571"],"is_preprint":false},{"year":2011,"finding":"OATL1, an autophagosome-resident Rab-GAP, is recruited to autophagosomes via direct interaction with Atg8 homologues, and RAB33B is a target substrate of OATL1; both OATL1 GAP activity and Atg8 homologue binding are required for autophagosome-lysosome fusion, placing RAB33B in the autophagosomal maturation pathway.","method":"Identification of Rab33B as OATL1 GAP substrate by in vitro GTP hydrolysis assay, co-immunoprecipitation, loss-of-function (GAP mutants, Atg8 interaction mutants) with autophagosome-lysosome fusion readout","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro GAP assay plus multiple mutant functional studies and epistasis","pmids":["21383079"],"is_preprint":false},{"year":2011,"finding":"RUTBC1 (a TBC-domain Rab9A effector) activates GTP hydrolysis by RAB33B in vitro, requiring Arg-803 of RUTBC1 consistent with a dual-finger catalytic mechanism; however, RUTBC1 did not influence RAB33B–Atg16L1 interaction in cells.","method":"In vitro GTP hydrolysis assay, Arg-803 mutagenesis, co-immunoprecipitation in cells and cell extracts","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — in vitro GAP assay with active-site mutagenesis and mechanistic follow-up","pmids":["21808068"],"is_preprint":false},{"year":2012,"finding":"The Ric1–Rgp1 complex acts as a GEF for Rab6A and as an effector of RAB33B-GTP; the C terminus of Ric1 contains a distinct binding site for RAB33B-GTP, supporting a Rab cascade between medial (RAB33B) and trans (Rab6) Golgi compartments.","method":"In vitro nucleotide exchange assay (GEF activity reconstitution), binding assays for Rab33B-GTP interaction with Ric1 C-terminus, loss-of-function showing Rab6 destabilization and retrograde transport block","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro GEF reconstitution plus defined binding site and functional KO phenotype","pmids":["23091056"],"is_preprint":false},{"year":2015,"finding":"RAB33B is required for hepatitis B virus naked capsid formation and release; RAB33B functions together with its effector Atg5-Atg12/Atg16L1 complex in this process, as silencing of either RAB33B or ATG5/ATG12/ATG16L1 impaired capsid egress and proper particle assembly/stability.","method":"RNA interference knockdown, overexpression studies, capsid assembly/release assays, co-localization by immunofluorescence","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 2–3 — RNAi with defined phenotype but primarily single-method evidence for each step","pmids":["25439980"],"is_preprint":false},{"year":2016,"finding":"Atg5 is required for augmented nucleotide-dependent interaction of RAB33B with the Atg5-Atg16L1 dimeric complex; Arg-24 of Atg16L1 is critical for its interaction with Atg5, which in turn influences RAB33B binding to the complex.","method":"GST pulldown, isothermal titration calorimetry (ITC), mutational analysis of Atg16L1 Arg-24","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1–2 — in vitro binding and calorimetric assays with mutagenesis, but single lab study","pmids":["26975471"],"is_preprint":false},{"year":2017,"finding":"ACBD3 recruits TBC1D22, a RAB33B GTPase-activating protein, to a multi-protein complex containing Golgin45 and GRASP55 at the medial Golgi, acting as a scaffold for Golgi stacking proteins and a Rab33B-GAP.","method":"Proteomics/co-immunoprecipitation, co-expression targeting assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 3 — Co-IP/proteomics identifying the complex, moderate evidence from single study","pmids":["28777890"],"is_preprint":false},{"year":2017,"finding":"RAB33B is required for HBV propagation; it regulates nucleocapsid (NC) formation/trafficking and core membrane association through a membrane targeting module in the core protein C-terminal domain; GDP-restricted RAB33B phenocopied knockdown, and Rab33B inactivation reduced core membrane association and impaired core/NC sorting to envelope-positive compartments.","method":"RNAi knockdown, GDP-restricted mutant overexpression, immunofluorescence, Western blotting, viral replication assays","journal":"Viruses","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple functional assays with defined phenotypic readouts in a single study","pmids":["28635671"],"is_preprint":false},{"year":2020,"finding":"Crystal structures of RAB33B bound to the coiled-coil domain (CCD) of ATG16L1 revealed the molecular recognition mechanism; ATG16L1 acts as a noncanonical RAB-binding protein (RBP) that induces RAB33B to adopt an active conformation without nucleotide exchange; upon starvation, RAB33B translocates from the Golgi to phagophores and recruits the ATG12-ATG5-ATG16L1 complex, which is required for LC3 lipidation and autophagosome formation.","method":"X-ray crystallography, microscale thermophoresis (MST), FLIM-FRET, live imaging, mutagenesis, LC3 lipidation assay, correlative light and electron microscopy (CLEM)","journal":"Autophagy","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus multiple orthogonal functional and binding assays with mutagenesis in single rigorous study","pmids":["32960676"],"is_preprint":false},{"year":2022,"finding":"RAB33B interacts with Exoc6, a subunit of the exocyst complex, and mediates post-Golgi secretion to the plasma membrane; RAB33B regulates focal adhesion dynamics by controlling integrin delivery to focal adhesions, thereby promoting cell migration.","method":"siRNA screen for cell migration, Co-immunoprecipitation (RAB33B-Exoc6), focal adhesion turnover assay, integrin trafficking assay, live imaging","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA screen plus Co-IP and defined functional readout, single lab study","pmids":["35521520"],"is_preprint":false},{"year":2025,"finding":"RAB33B contains an LIR motif that specifically interacts with GATE16 (but not LC3B or other ATG8 homologs); upon autophagy induction, RAB33B is recruited from the Golgi to the phagophore in an LIR-dependent manner, interacts with TRPML3, and promotes autophagosome formation.","method":"Co-immunoprecipitation, LIR motif mutagenesis, live imaging of RAB33B translocation, autophagy assays with LC3B-puncta readout","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 — mutagenesis of LIR motif with functional readout, single lab, single study","pmids":["40855209"],"is_preprint":false},{"year":2025,"finding":"Five disease-causing RAB33B mutants (two truncations, three missense) mislocalize from the Golgi, are unstable and prematurely degraded, and overexpression of the missense variants severely reduces autophagosome (LC3B-puncta) number upon autophagy induction, demonstrating that Golgi localization is required for RAB33B's autophagy function.","method":"Ectopic expression of RAB33B disease variants, immunofluorescence localization, Western blot stability assay, LC3B-puncta counting assay","journal":"European journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple mutants analyzed with localization and functional readouts, single lab study","pmids":["41506134"],"is_preprint":false},{"year":2025,"finding":"RAB33B promotes influenza A virus (IAV) replication by enhancing autophagy and facilitates IAV M2 protein trafficking to the plasma membrane through autophagic-like vesicles; ATG16L1 (RAB33B effector) and TBC1D25 (RAB33B GAP) also contribute to this M2-induced autophagy.","method":"Transcriptomics, RAB33B overexpression/knockdown, autophagy assays, co-immunoprecipitation of M2-RAB33B-LC3, viral replication assays","journal":"Veterinary research","confidence":"Medium","confidence_rationale":"Tier 2–3 — multiple functional assays and Co-IP in a single study, single lab","pmids":["40598642"],"is_preprint":false}],"current_model":"RAB33B is a medial Golgi-resident small GTPase that, in its GTP-bound active form, interacts with ATG16L1 (crystal structure resolved) to recruit the ATG12-ATG5-ATG16L1 complex to phagophores for LC3 lipidation and autophagosome formation, translocating from Golgi to phagophores upon starvation via an LIR motif that binds GATE16; it also participates in a Rab cascade with Rab6 regulating intra-Golgi retrograde trafficking (with Ric1-Rgp1 as a downstream Rab6 GEF and effector of RAB33B-GTP), interacts with Exoc6/exocyst for integrin delivery to focal adhesions and cell migration, is subject to inactivation by multiple GAPs (OATL1, RUTBC1, TBC1D22/ACBD3 complex), and loss-of-function mutations in RAB33B cause Smith-McCort dysplasia through protein instability, Golgi mislocalization, and impaired autophagy."},"narrative":{"teleology":[{"year":1998,"claim":"Establishing that RAB33B is a novel Rab GTPase resident on medial-Golgi cisternae answered the fundamental question of where this GTPase acts and implicated it in intra-Golgi transport.","evidence":"Co-localization with alpha-mannosidase II by immunofluorescence and immunoelectron microscopy in mammalian cells","pmids":["9512502"],"confidence":"High","gaps":["No effectors or transport cargo identified","No functional loss-of-function data"]},{"year":2001,"claim":"Identifying GM130, rabaptin-5, and rabex-5 as GTP-dependent interactors and showing that constitutively active RAB33B blocks anterograde Golgi transport and glycosyltransferase recycling established that RAB33B regulates vesicular trafficking within the Golgi.","evidence":"GST pulldown with GTP-locked RAB33B, mass spectrometry identification, microinjection of GTPase mutants in mammalian cells","pmids":["11718716"],"confidence":"High","gaps":["Endogenous loss-of-function phenotype not tested","Direct versus indirect binding to GM130 not resolved"]},{"year":2008,"claim":"Discovery of the GTP-dependent RAB33B–ATG16L1 interaction and its ability to induce LC3 lipidation revealed an unexpected autophagy function for a Golgi Rab, linking Golgi membranes to autophagosome biogenesis.","evidence":"Co-immunoprecipitation, GTPase-deficient Q92L mutant expression, LC3 lipidation and p62 degradation assays in cultured cells","pmids":["18448665"],"confidence":"High","gaps":["Structural basis of RAB33B–ATG16L1 recognition unknown","Mechanism of RAB33B translocation to phagophores unclear"]},{"year":2010,"claim":"Demonstrating that RAB33B operates downstream of Rab6 and is required for Shiga toxin retrograde transport established a Rab cascade governing intra-Golgi retrograde trafficking.","evidence":"siRNA knockdown, GTP-locked mutant overexpression, Shiga toxin transport assay, Golgi ribbon disruption in mammalian cells","pmids":["20163571"],"confidence":"High","gaps":["The GEF connecting Rab6 activity to RAB33B activation was not identified","No reconstitution of the cascade in vitro"]},{"year":2011,"claim":"Identification of OATL1 and RUTBC1 as GAPs for RAB33B defined the inactivation machinery and placed RAB33B cycling in the context of autophagosome maturation (OATL1) and Rab9A effector function (RUTBC1).","evidence":"In vitro GTP hydrolysis assays with catalytic residue mutagenesis, co-immunoprecipitation, autophagosome–lysosome fusion readout","pmids":["21383079","21808068"],"confidence":"High","gaps":["Whether OATL1 and RUTBC1 act on RAB33B at distinct subcellular sites in vivo not resolved","Relative contributions of different GAPs to RAB33B steady-state activity unknown"]},{"year":2012,"claim":"Demonstrating that the Ric1–Rgp1 complex is both an effector of RAB33B-GTP and a GEF for Rab6A provided the molecular mechanism linking the medial-Golgi RAB33B pool to trans-Golgi Rab6 activation.","evidence":"In vitro nucleotide exchange assay, RAB33B-GTP binding to Ric1 C-terminus, loss-of-function phenocopying Rab6 destabilization","pmids":["23091056"],"confidence":"High","gaps":["Structural basis of Ric1–RAB33B interaction not determined","Whether additional GEFs exist for RAB33B itself remains unknown"]},{"year":2017,"claim":"Identification of ACBD3 as a scaffold recruiting the RAB33B-GAP TBC1D22 together with Golgin45 and GRASP55 revealed a multiprotein complex that couples RAB33B inactivation to Golgi stacking.","evidence":"Proteomics, co-immunoprecipitation, co-expression targeting assay in mammalian cells","pmids":["28777890"],"confidence":"Medium","gaps":["Functional consequence of TBC1D22 loss on RAB33B-GTP levels not quantified","No reconstitution of the quaternary complex in vitro","Single-lab observation"]},{"year":2020,"claim":"Crystal structures of RAB33B bound to the ATG16L1 coiled-coil domain resolved the molecular recognition mechanism and showed that ATG16L1 acts as a noncanonical Rab-binding protein stabilizing active RAB33B without nucleotide exchange, directly explaining how RAB33B recruits autophagy machinery to phagophores.","evidence":"X-ray crystallography, microscale thermophoresis, FLIM-FRET, mutagenesis, LC3 lipidation assay, correlative light-electron microscopy","pmids":["32960676"],"confidence":"High","gaps":["How RAB33B is activated (GEF identity) before encountering ATG16L1 remains unknown","Stoichiometry of the complex on native phagophore membranes not determined"]},{"year":2022,"claim":"Discovery of the RAB33B–Exoc6 interaction and its role in integrin delivery to focal adhesions extended RAB33B function from Golgi/autophagy to post-Golgi secretory trafficking and cell migration.","evidence":"siRNA migration screen, co-immunoprecipitation, focal adhesion turnover and integrin trafficking assays, live imaging","pmids":["35521520"],"confidence":"Medium","gaps":["Whether Exoc6 binding competes with ATG16L1 binding unknown","Mechanism of cargo selectivity for integrin not addressed","Single-lab study"]},{"year":2025,"claim":"Identification of an LIR motif in RAB33B that specifically binds GATE16 (not LC3B) defined the molecular mechanism for starvation-induced Golgi-to-phagophore translocation, while disease-causing RAB33B mutations were shown to cause protein instability, Golgi mislocalization, and impaired autophagy, explaining Smith–McCort dysplasia pathogenesis.","evidence":"LIR motif mutagenesis with live imaging, LC3B-puncta assays, ectopic expression of five disease variants with localization and stability readouts","pmids":["40855209","41506134"],"confidence":"Medium","gaps":["GATE16 selectivity over other ATG8 paralogs not structurally explained","Disease variant effects tested only by overexpression, not in patient cells or knockin models","Single-lab studies for each finding"]},{"year":null,"claim":"The GEF that activates RAB33B at the Golgi remains unidentified, and how RAB33B partitions between its Golgi trafficking, autophagy, and exocyst-mediated secretory roles is mechanistically unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No RAB33B GEF identified","Regulatory logic for switching between Golgi-resident and phagophore-targeted pools unknown","No animal model with conditional Rab33b loss to separate trafficking versus autophagy phenotypes"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003924","term_label":"GTPase activity","supporting_discovery_ids":[0,1,2,3]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,1,3,9,14]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[2,11]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[2,4,11,13,14]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,3,6,12]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[14]}],"complexes":[],"partners":["ATG16L1","EXOC6","GOLGA3","RIC1","RGP1","TBC1D22A","OATL1","GATE16"],"other_free_text":[]},"mechanistic_narrative":"RAB33B is a medial-Golgi-resident small GTPase that functions as a regulatory hub linking intra-Golgi retrograde trafficking with autophagosome biogenesis. In its GTP-bound form, RAB33B recruits the Ric1–Rgp1 Rab6 GEF complex to medial-Golgi membranes, establishing a Rab cascade that drives retrograde transport from trans- to cis-Golgi and ER, and also interacts with GM130 and the exocyst subunit Exoc6 to regulate Golgi integrity and integrin delivery to focal adhesions [PMID:20163571, PMID:23091056, PMID:11718716, PMID:35521520]. Upon starvation, RAB33B translocates from the Golgi to phagophores via an LIR motif that binds GATE16, where it directly engages the ATG16L1 coiled-coil domain—acting as a noncanonical Rab-binding protein that stabilizes the active RAB33B conformation—to recruit the ATG12–ATG5–ATG16L1 complex for LC3 lipidation and autophagosome formation [PMID:32960676, PMID:18448665, PMID:40855209]. Loss-of-function mutations in RAB33B cause Smith–McCort dysplasia through protein instability, Golgi mislocalization, and impaired autophagy [PMID:41506134]."},"prefetch_data":{"uniprot":{"accession":"Q9H082","full_name":"Ras-related protein Rab-33B","aliases":[],"length_aa":229,"mass_kda":25.7,"function":"The small GTPases Rab are key regulators of intracellular membrane trafficking, from the formation of transport vesicles to their fusion with membranes (PubMed:20163571, PubMed:21808068). Rabs cycle between an inactive GDP-bound form and an active GTP-bound form that is able to recruit to membranes different sets of downstream effectors directly responsible for vesicle formation, movement, tethering and fusion (PubMed:18448665, PubMed:20163571, PubMed:21808068). RAB33B acts, in coordination with RAB6A, to regulate intra-Golgi retrograde trafficking (PubMed:20163571). Participates in autophagosome formation by recruiting the ATG12-ATG5-ATG16L1 complex to phagophores, probably in a nucleotide-independent manner (PubMed:18448665, PubMed:32960676)","subcellular_location":"Golgi apparatus membrane; Golgi apparatus, cis-Golgi network; Preautophagosomal structure membrane","url":"https://www.uniprot.org/uniprotkb/Q9H082/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RAB33B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RAB33B","total_profiled":1310},"omim":[{"mim_id":"618716","title":"AUTOPHAGY 16-LIKE 2; ATG16L2","url":"https://www.omim.org/entry/618716"},{"mim_id":"615742","title":"RGP1 HOMOLOG, RAB6A GEF COMPLEX PARTNER 1; RGP1","url":"https://www.omim.org/entry/615742"},{"mim_id":"615222","title":"SMITH-MCCORT DYSPLASIA 2; SMC2","url":"https://www.omim.org/entry/615222"},{"mim_id":"610354","title":"RIC1 HOMOLOG, RAB6A GEF COMPLEX PARTNER 1; RIC1","url":"https://www.omim.org/entry/610354"},{"mim_id":"607326","title":"SMITH-MCCORT DYSPLASIA 1; SMC1","url":"https://www.omim.org/entry/607326"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RAB33B"},"hgnc":{"alias_symbol":["DKFZP434G099"],"prev_symbol":[]},"alphafold":{"accession":"Q9H082","domains":[{"cath_id":"3.40.50.300","chopping":"32-201","consensus_level":"high","plddt":93.8371,"start":32,"end":201}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H082","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H082-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9H082-F1-predicted_aligned_error_v6.png","plddt_mean":80.62},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAB33B","jax_strain_url":"https://www.jax.org/strain/search?query=RAB33B"},"sequence":{"accession":"Q9H082","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9H082.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9H082/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9H082"}},"corpus_meta":[{"pmid":"18448665","id":"PMC_18448665","title":"Golgi-resident small GTPase Rab33B interacts with Atg16L and modulates autophagosome formation.","date":"2008","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/18448665","citation_count":228,"is_preprint":false},{"pmid":"21383079","id":"PMC_21383079","title":"OATL1, a novel autophagosome-resident Rab33B-GAP, regulates autophagosomal maturation.","date":"2011","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/21383079","citation_count":137,"is_preprint":false},{"pmid":"11718716","id":"PMC_11718716","title":"Identification of rabaptin-5, rabex-5, and GM130 as putative effectors of rab33b, a regulator of retrograde traffic between the Golgi apparatus and ER.","date":"2001","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/11718716","citation_count":102,"is_preprint":false},{"pmid":"20163571","id":"PMC_20163571","title":"Rab33b and Rab6 are functionally overlapping regulators of Golgi homeostasis and trafficking.","date":"2010","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/20163571","citation_count":71,"is_preprint":false},{"pmid":"9512502","id":"PMC_9512502","title":"A novel Rab GTPase, Rab33B, is ubiquitously expressed and localized to the medial Golgi cisternae.","date":"1998","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/9512502","citation_count":65,"is_preprint":false},{"pmid":"23091056","id":"PMC_23091056","title":"Ric1-Rgp1 complex is a guanine nucleotide exchange factor for the late Golgi Rab6A GTPase and an effector of the medial Golgi Rab33B GTPase.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23091056","citation_count":63,"is_preprint":false},{"pmid":"21808068","id":"PMC_21808068","title":"RUTBC1 protein, a Rab9A effector that activates GTP hydrolysis by Rab32 and Rab33B proteins.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/21808068","citation_count":52,"is_preprint":false},{"pmid":"25439980","id":"PMC_25439980","title":"Rab33B and its autophagic Atg5/12/16L1 effector assist in hepatitis B virus naked capsid formation and release.","date":"2015","source":"Cellular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/25439980","citation_count":38,"is_preprint":false},{"pmid":"31408960","id":"PMC_31408960","title":"Multitasking Rab Proteins in Autophagy and Membrane Trafficking: A Focus on Rab33b.","date":"2019","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/31408960","citation_count":37,"is_preprint":false},{"pmid":"22652534","id":"PMC_22652534","title":"Mutation in RAB33B, which encodes a regulator of retrograde Golgi transport, defines a second Dyggve--Melchior--Clausen locus.","date":"2012","source":"Journal of medical genetics","url":"https://pubmed.ncbi.nlm.nih.gov/22652534","citation_count":33,"is_preprint":false},{"pmid":"32960676","id":"PMC_32960676","title":"RAB33B recruits the ATG16L1 complex to the phagophore via a noncanonical RAB binding protein.","date":"2020","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/32960676","citation_count":32,"is_preprint":false},{"pmid":"23042644","id":"PMC_23042644","title":"A novel RAB33B mutation in Smith-McCort dysplasia.","date":"2012","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/23042644","citation_count":32,"is_preprint":false},{"pmid":"27374232","id":"PMC_27374232","title":"A systematic High-Content Screening microscopy approach reveals key roles for Rab33b, OATL1 and Myo6 in nanoparticle trafficking in HeLa cells.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27374232","citation_count":20,"is_preprint":false},{"pmid":"28777890","id":"PMC_28777890","title":"ACBD3 functions as a scaffold to organize the Golgi stacking proteins and a Rab33b-GAP.","date":"2017","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/28777890","citation_count":18,"is_preprint":false},{"pmid":"28635671","id":"PMC_28635671","title":"Rab33B Controls Hepatitis B Virus Assembly by Regulating Core Membrane Association and Nucleocapsid Processing.","date":"2017","source":"Viruses","url":"https://pubmed.ncbi.nlm.nih.gov/28635671","citation_count":16,"is_preprint":false},{"pmid":"28127940","id":"PMC_28127940","title":"Additional three patients with Smith-McCort dysplasia due to novel RAB33B mutations.","date":"2017","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/28127940","citation_count":15,"is_preprint":false},{"pmid":"35521520","id":"PMC_35521520","title":"Rab33b-exocyst interaction mediates localized secretion for focal adhesion turnover and cell migration.","date":"2022","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/35521520","citation_count":7,"is_preprint":false},{"pmid":"26975471","id":"PMC_26975471","title":"Deciphering the role of Atg5 in nucleotide dependent interaction of Rab33B with the dimeric complex, Atg5-Atg16L1.","date":"2016","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/26975471","citation_count":6,"is_preprint":false},{"pmid":"21092243","id":"PMC_21092243","title":"Proteomic approach with LCMS-IT-TOF identified an increase of Rab33B after transient focal cerebral ischemia in mice.","date":"2010","source":"Experimental & translational stroke medicine","url":"https://pubmed.ncbi.nlm.nih.gov/21092243","citation_count":6,"is_preprint":false},{"pmid":"34284742","id":"PMC_34284742","title":"RAB33B and PCNT variants in two Pakistani families with skeletal dysplasia and short stature.","date":"2021","source":"BMC musculoskeletal disorders","url":"https://pubmed.ncbi.nlm.nih.gov/34284742","citation_count":5,"is_preprint":false},{"pmid":"37359363","id":"PMC_37359363","title":"A Rab33b missense mouse model for Smith-McCort dysplasia shows bone resorption defects and altered protein glycosylation.","date":"2023","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37359363","citation_count":1,"is_preprint":false},{"pmid":"40598642","id":"PMC_40598642","title":"Host cellular protein RAB33B facilitates influenza viral replication and modulates M2 trafficking by enhancing autophagy.","date":"2025","source":"Veterinary research","url":"https://pubmed.ncbi.nlm.nih.gov/40598642","citation_count":0,"is_preprint":false},{"pmid":"40855209","id":"PMC_40855209","title":"Two specific interactions of GATE16 with TRPML3 and RAB33B regulate autophagy.","date":"2025","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/40855209","citation_count":0,"is_preprint":false},{"pmid":"41506134","id":"PMC_41506134","title":"Mutations in the Rab33b protein that lead to the skeletal disease Smith-McCort dysplasia result in unstable proteins and altered autophagy function.","date":"2025","source":"European journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/41506134","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12373,"output_tokens":4029,"usd":0.048777},"stage2":{"model":"claude-opus-4-6","input_tokens":7468,"output_tokens":2804,"usd":0.16116},"total_usd":0.209937,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"RAB33B is a novel Rab GTPase that localizes to the medial Golgi cisternae, as demonstrated by co-localization with alpha-mannosidase II by immunofluorescence and immunoelectron microscopy, suggesting a role in intra-Golgi transport.\",\n      \"method\": \"Immunofluorescence, immunoelectron microscopy, Western blotting with Rab33B-specific monoclonal antibody\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — direct localization experiment with multiple orthogonal methods (immunofluorescence + immunoEM), foundational paper\",\n      \"pmids\": [\"9512502\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"RAB33B in its GTP-bound state interacts with Golgi protein GM130 and endocytic Rab effectors rabaptin-5 and rabex-5; microinjection of GTP-locked Rab33B mutants inhibited anterograde transport within the Golgi and recycling of glycosyltransferases from Golgi to ER.\",\n      \"method\": \"GST pulldown with GTP-locked Rab33B fusion protein, Western blotting/mass spectrometry for interactor identification, microinjection of GTPase mutants\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro pulldown with GTP-restricted mutant plus functional microinjection assay, foundational study\",\n      \"pmids\": [\"11718716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RAB33B (and RAB33A) specifically interacts with Atg16L in a GTP-dependent manner; expression of GTPase-deficient RAB33B-Q92L induced LC3 lipidation under nutrient-rich conditions and attenuated macroautophagy, demonstrating that RAB33B modulates autophagosome formation through Atg16L interaction.\",\n      \"method\": \"Co-immunoprecipitation, GTP-dependent binding assay, overexpression of GTPase-deficient mutant (Q92L), LC3 lipidation assay, p62/SQSTM1 degradation assay\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal interaction and multiple functional readouts in the same study, highly cited foundational paper\",\n      \"pmids\": [\"18448665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"RAB33B acts downstream of trans-Golgi Rab6 in a Rab cascade regulating intra-Golgi retrograde trafficking; GTP-restricted Rab6-induced relocation of Golgi enzymes to the ER was RAB33B-dependent, overexpression of GTP-RAB33B displaced Rab6 from Golgi membranes, and RAB33B was required for Shiga-like toxin B fragment transport from trans to cis Golgi and ER.\",\n      \"method\": \"siRNA knockdown, overexpression of GTP-locked mutants, Golgi ribbon disruption assay, Shiga toxin transport assay, immunofluorescence\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established by multiple orthogonal functional approaches in the same study\",\n      \"pmids\": [\"20163571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"OATL1, an autophagosome-resident Rab-GAP, is recruited to autophagosomes via direct interaction with Atg8 homologues, and RAB33B is a target substrate of OATL1; both OATL1 GAP activity and Atg8 homologue binding are required for autophagosome-lysosome fusion, placing RAB33B in the autophagosomal maturation pathway.\",\n      \"method\": \"Identification of Rab33B as OATL1 GAP substrate by in vitro GTP hydrolysis assay, co-immunoprecipitation, loss-of-function (GAP mutants, Atg8 interaction mutants) with autophagosome-lysosome fusion readout\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro GAP assay plus multiple mutant functional studies and epistasis\",\n      \"pmids\": [\"21383079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"RUTBC1 (a TBC-domain Rab9A effector) activates GTP hydrolysis by RAB33B in vitro, requiring Arg-803 of RUTBC1 consistent with a dual-finger catalytic mechanism; however, RUTBC1 did not influence RAB33B–Atg16L1 interaction in cells.\",\n      \"method\": \"In vitro GTP hydrolysis assay, Arg-803 mutagenesis, co-immunoprecipitation in cells and cell extracts\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro GAP assay with active-site mutagenesis and mechanistic follow-up\",\n      \"pmids\": [\"21808068\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The Ric1–Rgp1 complex acts as a GEF for Rab6A and as an effector of RAB33B-GTP; the C terminus of Ric1 contains a distinct binding site for RAB33B-GTP, supporting a Rab cascade between medial (RAB33B) and trans (Rab6) Golgi compartments.\",\n      \"method\": \"In vitro nucleotide exchange assay (GEF activity reconstitution), binding assays for Rab33B-GTP interaction with Ric1 C-terminus, loss-of-function showing Rab6 destabilization and retrograde transport block\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro GEF reconstitution plus defined binding site and functional KO phenotype\",\n      \"pmids\": [\"23091056\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"RAB33B is required for hepatitis B virus naked capsid formation and release; RAB33B functions together with its effector Atg5-Atg12/Atg16L1 complex in this process, as silencing of either RAB33B or ATG5/ATG12/ATG16L1 impaired capsid egress and proper particle assembly/stability.\",\n      \"method\": \"RNA interference knockdown, overexpression studies, capsid assembly/release assays, co-localization by immunofluorescence\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — RNAi with defined phenotype but primarily single-method evidence for each step\",\n      \"pmids\": [\"25439980\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Atg5 is required for augmented nucleotide-dependent interaction of RAB33B with the Atg5-Atg16L1 dimeric complex; Arg-24 of Atg16L1 is critical for its interaction with Atg5, which in turn influences RAB33B binding to the complex.\",\n      \"method\": \"GST pulldown, isothermal titration calorimetry (ITC), mutational analysis of Atg16L1 Arg-24\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro binding and calorimetric assays with mutagenesis, but single lab study\",\n      \"pmids\": [\"26975471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ACBD3 recruits TBC1D22, a RAB33B GTPase-activating protein, to a multi-protein complex containing Golgin45 and GRASP55 at the medial Golgi, acting as a scaffold for Golgi stacking proteins and a Rab33B-GAP.\",\n      \"method\": \"Proteomics/co-immunoprecipitation, co-expression targeting assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — Co-IP/proteomics identifying the complex, moderate evidence from single study\",\n      \"pmids\": [\"28777890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RAB33B is required for HBV propagation; it regulates nucleocapsid (NC) formation/trafficking and core membrane association through a membrane targeting module in the core protein C-terminal domain; GDP-restricted RAB33B phenocopied knockdown, and Rab33B inactivation reduced core membrane association and impaired core/NC sorting to envelope-positive compartments.\",\n      \"method\": \"RNAi knockdown, GDP-restricted mutant overexpression, immunofluorescence, Western blotting, viral replication assays\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple functional assays with defined phenotypic readouts in a single study\",\n      \"pmids\": [\"28635671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structures of RAB33B bound to the coiled-coil domain (CCD) of ATG16L1 revealed the molecular recognition mechanism; ATG16L1 acts as a noncanonical RAB-binding protein (RBP) that induces RAB33B to adopt an active conformation without nucleotide exchange; upon starvation, RAB33B translocates from the Golgi to phagophores and recruits the ATG12-ATG5-ATG16L1 complex, which is required for LC3 lipidation and autophagosome formation.\",\n      \"method\": \"X-ray crystallography, microscale thermophoresis (MST), FLIM-FRET, live imaging, mutagenesis, LC3 lipidation assay, correlative light and electron microscopy (CLEM)\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus multiple orthogonal functional and binding assays with mutagenesis in single rigorous study\",\n      \"pmids\": [\"32960676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RAB33B interacts with Exoc6, a subunit of the exocyst complex, and mediates post-Golgi secretion to the plasma membrane; RAB33B regulates focal adhesion dynamics by controlling integrin delivery to focal adhesions, thereby promoting cell migration.\",\n      \"method\": \"siRNA screen for cell migration, Co-immunoprecipitation (RAB33B-Exoc6), focal adhesion turnover assay, integrin trafficking assay, live imaging\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA screen plus Co-IP and defined functional readout, single lab study\",\n      \"pmids\": [\"35521520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAB33B contains an LIR motif that specifically interacts with GATE16 (but not LC3B or other ATG8 homologs); upon autophagy induction, RAB33B is recruited from the Golgi to the phagophore in an LIR-dependent manner, interacts with TRPML3, and promotes autophagosome formation.\",\n      \"method\": \"Co-immunoprecipitation, LIR motif mutagenesis, live imaging of RAB33B translocation, autophagy assays with LC3B-puncta readout\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — mutagenesis of LIR motif with functional readout, single lab, single study\",\n      \"pmids\": [\"40855209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Five disease-causing RAB33B mutants (two truncations, three missense) mislocalize from the Golgi, are unstable and prematurely degraded, and overexpression of the missense variants severely reduces autophagosome (LC3B-puncta) number upon autophagy induction, demonstrating that Golgi localization is required for RAB33B's autophagy function.\",\n      \"method\": \"Ectopic expression of RAB33B disease variants, immunofluorescence localization, Western blot stability assay, LC3B-puncta counting assay\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple mutants analyzed with localization and functional readouts, single lab study\",\n      \"pmids\": [\"41506134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAB33B promotes influenza A virus (IAV) replication by enhancing autophagy and facilitates IAV M2 protein trafficking to the plasma membrane through autophagic-like vesicles; ATG16L1 (RAB33B effector) and TBC1D25 (RAB33B GAP) also contribute to this M2-induced autophagy.\",\n      \"method\": \"Transcriptomics, RAB33B overexpression/knockdown, autophagy assays, co-immunoprecipitation of M2-RAB33B-LC3, viral replication assays\",\n      \"journal\": \"Veterinary research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — multiple functional assays and Co-IP in a single study, single lab\",\n      \"pmids\": [\"40598642\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAB33B is a medial Golgi-resident small GTPase that, in its GTP-bound active form, interacts with ATG16L1 (crystal structure resolved) to recruit the ATG12-ATG5-ATG16L1 complex to phagophores for LC3 lipidation and autophagosome formation, translocating from Golgi to phagophores upon starvation via an LIR motif that binds GATE16; it also participates in a Rab cascade with Rab6 regulating intra-Golgi retrograde trafficking (with Ric1-Rgp1 as a downstream Rab6 GEF and effector of RAB33B-GTP), interacts with Exoc6/exocyst for integrin delivery to focal adhesions and cell migration, is subject to inactivation by multiple GAPs (OATL1, RUTBC1, TBC1D22/ACBD3 complex), and loss-of-function mutations in RAB33B cause Smith-McCort dysplasia through protein instability, Golgi mislocalization, and impaired autophagy.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"RAB33B is a medial-Golgi-resident small GTPase that functions as a regulatory hub linking intra-Golgi retrograde trafficking with autophagosome biogenesis. In its GTP-bound form, RAB33B recruits the Ric1–Rgp1 Rab6 GEF complex to medial-Golgi membranes, establishing a Rab cascade that drives retrograde transport from trans- to cis-Golgi and ER, and also interacts with GM130 and the exocyst subunit Exoc6 to regulate Golgi integrity and integrin delivery to focal adhesions [PMID:20163571, PMID:23091056, PMID:11718716, PMID:35521520]. Upon starvation, RAB33B translocates from the Golgi to phagophores via an LIR motif that binds GATE16, where it directly engages the ATG16L1 coiled-coil domain—acting as a noncanonical Rab-binding protein that stabilizes the active RAB33B conformation—to recruit the ATG12–ATG5–ATG16L1 complex for LC3 lipidation and autophagosome formation [PMID:32960676, PMID:18448665, PMID:40855209]. Loss-of-function mutations in RAB33B cause Smith–McCort dysplasia through protein instability, Golgi mislocalization, and impaired autophagy [PMID:41506134].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Establishing that RAB33B is a novel Rab GTPase resident on medial-Golgi cisternae answered the fundamental question of where this GTPase acts and implicated it in intra-Golgi transport.\",\n      \"evidence\": \"Co-localization with alpha-mannosidase II by immunofluorescence and immunoelectron microscopy in mammalian cells\",\n      \"pmids\": [\"9512502\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No effectors or transport cargo identified\", \"No functional loss-of-function data\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identifying GM130, rabaptin-5, and rabex-5 as GTP-dependent interactors and showing that constitutively active RAB33B blocks anterograde Golgi transport and glycosyltransferase recycling established that RAB33B regulates vesicular trafficking within the Golgi.\",\n      \"evidence\": \"GST pulldown with GTP-locked RAB33B, mass spectrometry identification, microinjection of GTPase mutants in mammalian cells\",\n      \"pmids\": [\"11718716\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous loss-of-function phenotype not tested\", \"Direct versus indirect binding to GM130 not resolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery of the GTP-dependent RAB33B–ATG16L1 interaction and its ability to induce LC3 lipidation revealed an unexpected autophagy function for a Golgi Rab, linking Golgi membranes to autophagosome biogenesis.\",\n      \"evidence\": \"Co-immunoprecipitation, GTPase-deficient Q92L mutant expression, LC3 lipidation and p62 degradation assays in cultured cells\",\n      \"pmids\": [\"18448665\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of RAB33B–ATG16L1 recognition unknown\", \"Mechanism of RAB33B translocation to phagophores unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrating that RAB33B operates downstream of Rab6 and is required for Shiga toxin retrograde transport established a Rab cascade governing intra-Golgi retrograde trafficking.\",\n      \"evidence\": \"siRNA knockdown, GTP-locked mutant overexpression, Shiga toxin transport assay, Golgi ribbon disruption in mammalian cells\",\n      \"pmids\": [\"20163571\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The GEF connecting Rab6 activity to RAB33B activation was not identified\", \"No reconstitution of the cascade in vitro\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identification of OATL1 and RUTBC1 as GAPs for RAB33B defined the inactivation machinery and placed RAB33B cycling in the context of autophagosome maturation (OATL1) and Rab9A effector function (RUTBC1).\",\n      \"evidence\": \"In vitro GTP hydrolysis assays with catalytic residue mutagenesis, co-immunoprecipitation, autophagosome–lysosome fusion readout\",\n      \"pmids\": [\"21383079\", \"21808068\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether OATL1 and RUTBC1 act on RAB33B at distinct subcellular sites in vivo not resolved\", \"Relative contributions of different GAPs to RAB33B steady-state activity unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrating that the Ric1–Rgp1 complex is both an effector of RAB33B-GTP and a GEF for Rab6A provided the molecular mechanism linking the medial-Golgi RAB33B pool to trans-Golgi Rab6 activation.\",\n      \"evidence\": \"In vitro nucleotide exchange assay, RAB33B-GTP binding to Ric1 C-terminus, loss-of-function phenocopying Rab6 destabilization\",\n      \"pmids\": [\"23091056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of Ric1–RAB33B interaction not determined\", \"Whether additional GEFs exist for RAB33B itself remains unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identification of ACBD3 as a scaffold recruiting the RAB33B-GAP TBC1D22 together with Golgin45 and GRASP55 revealed a multiprotein complex that couples RAB33B inactivation to Golgi stacking.\",\n      \"evidence\": \"Proteomics, co-immunoprecipitation, co-expression targeting assay in mammalian cells\",\n      \"pmids\": [\"28777890\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of TBC1D22 loss on RAB33B-GTP levels not quantified\", \"No reconstitution of the quaternary complex in vitro\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Crystal structures of RAB33B bound to the ATG16L1 coiled-coil domain resolved the molecular recognition mechanism and showed that ATG16L1 acts as a noncanonical Rab-binding protein stabilizing active RAB33B without nucleotide exchange, directly explaining how RAB33B recruits autophagy machinery to phagophores.\",\n      \"evidence\": \"X-ray crystallography, microscale thermophoresis, FLIM-FRET, mutagenesis, LC3 lipidation assay, correlative light-electron microscopy\",\n      \"pmids\": [\"32960676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How RAB33B is activated (GEF identity) before encountering ATG16L1 remains unknown\", \"Stoichiometry of the complex on native phagophore membranes not determined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Discovery of the RAB33B–Exoc6 interaction and its role in integrin delivery to focal adhesions extended RAB33B function from Golgi/autophagy to post-Golgi secretory trafficking and cell migration.\",\n      \"evidence\": \"siRNA migration screen, co-immunoprecipitation, focal adhesion turnover and integrin trafficking assays, live imaging\",\n      \"pmids\": [\"35521520\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether Exoc6 binding competes with ATG16L1 binding unknown\", \"Mechanism of cargo selectivity for integrin not addressed\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of an LIR motif in RAB33B that specifically binds GATE16 (not LC3B) defined the molecular mechanism for starvation-induced Golgi-to-phagophore translocation, while disease-causing RAB33B mutations were shown to cause protein instability, Golgi mislocalization, and impaired autophagy, explaining Smith–McCort dysplasia pathogenesis.\",\n      \"evidence\": \"LIR motif mutagenesis with live imaging, LC3B-puncta assays, ectopic expression of five disease variants with localization and stability readouts\",\n      \"pmids\": [\"40855209\", \"41506134\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"GATE16 selectivity over other ATG8 paralogs not structurally explained\", \"Disease variant effects tested only by overexpression, not in patient cells or knockin models\", \"Single-lab studies for each finding\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The GEF that activates RAB33B at the Golgi remains unidentified, and how RAB33B partitions between its Golgi trafficking, autophagy, and exocyst-mediated secretory roles is mechanistically unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No RAB33B GEF identified\", \"Regulatory logic for switching between Golgi-resident and phagophore-targeted pools unknown\", \"No animal model with conditional Rab33b loss to separate trafficking versus autophagy phenotypes\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003924\", \"supporting_discovery_ids\": [0, 1, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 1, 3, 9, 14]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [2, 4, 11, 13, 14]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 3, 6, 12]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"ATG16L1\",\n      \"EXOC6\",\n      \"GOLGA3\",\n      \"RIC1\",\n      \"RGP1\",\n      \"TBC1D22A\",\n      \"OATL1\",\n      \"GATE16\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}