{"gene":"TBC1D9B","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":2014,"finding":"TBC1D9B functions as a GTPase-activating protein (GAP) for Rab11a via its TBC domain. In the presence of 2.5 mM Mg2+, TBC1D9B interacts with Rab11a, Rab11b, and Rab4a in a nucleotide-dependent manner, but only Rab11a is a substrate for TBC1D9B-stimulated GTP hydrolysis. At limiting Mg2+ concentrations (<0.5 mM), Rab8a is an additional substrate.","method":"In vitro GTP hydrolysis assay, nucleotide-dependent binding assay, active-site mutagenesis (inactive mutant), shRNA-mediated depletion, colocalization in polarized MDCK cells","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstituted GTPase assay plus mutagenesis plus cellular functional readout in a single rigorous study","pmids":["25232007"],"is_preprint":false},{"year":2014,"finding":"TBC1D9B colocalizes with Rab11a-positive recycling endosomes in polarized MDCK cells but less so with EEA1-positive early endosomes, transferrin-positive recycling endosomes, or late endosomes, placing it at the recycling endosome compartment.","method":"Immunofluorescence colocalization in polarized MDCK cells","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization experiment replicated across multiple compartment markers in one study","pmids":["25232007"],"is_preprint":false},{"year":2014,"finding":"TBC1D9B overexpression decreases the rate of basolateral-to-apical IgA transcytosis (a Rab11a-dependent pathway) and shRNA depletion increases it; TBC1D9B had no effect on Rab11a-independent pathways (basolateral recycling of transferrin receptor or EGFR degradation). TBC1D9B expression also decreased active Rab11a levels and disrupted the Rab11a–Sec15A effector interaction.","method":"Transcytosis assays in polarized MDCK cells, overexpression and shRNA knockdown, active Rab11a pulldown, co-immunoprecipitation of Rab11a with Sec15A","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain/loss-of-function with specific pathway controls and downstream effector interaction measured in one rigorous study","pmids":["25232007"],"is_preprint":false},{"year":2018,"finding":"TBC1D9B interacts with LC3B and other mammalian ATG8 homologues through a unique interacting domain distinct from the canonical LC3-interacting region (LIR). TBC1D9B co-localizes with LC3B on autophagosome membranes, and inhibition of TBC1D9B suppresses turnover of membrane-bound LC3B and autophagic degradation of long-lived proteins, indicating TBC1D9B positively regulates autophagic flux.","method":"Yeast two-hybrid, in vitro binding with purified proteins, co-immunoprecipitation, immunofluorescence colocalization, LC3B turnover assay, long-lived protein degradation assay","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Y2H, in vitro pulldown, co-IP, functional flux assays) in a single study","pmids":["30202024"],"is_preprint":false},{"year":2019,"finding":"TBC1D9B is a binding partner of LMTK1A (a membrane-bound Ser/Thr kinase regulated by Cdk5-p35). LMTK1A controls the GAP activity of TBC1D9B toward Rab11A, placing TBC1D9B downstream of LMTK1 in the Cdk5-LMTK1-TBC1D9B-Rab11A signaling cascade. Knockdown of TBC1D9B in primary neurons increases dendritic spine formation and density.","method":"Co-immunoprecipitation (LMTK1-TBC1D9B interaction), shRNA knockdown in primary neurons and in vivo, spine morphology analysis, Rab11A activity assay","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP plus loss-of-function with specific cellular phenotype and pathway placement in vivo and in vitro, replicated across multiple labs","pmids":["31628178"],"is_preprint":false},{"year":2025,"finding":"TBC1D9B contains a conserved TMEM55B-binding motif (TBM) that mediates interaction with TMEM55B, a lysosomal membrane protein. TMEM55B forms complexes with TBC1D9B independently of phospho-Rabs, placing TBC1D9B within a TMEM55B-centered lysosomal adaptor platform.","method":"Crystal structure of TMEM55B cytosolic domain, co-immunoprecipitation, mass spectrometry, mutational analysis","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus co-IP plus mutagenesis in a single study identifying the TBC1D9B-TMEM55B interaction","pmids":["41314214"],"is_preprint":false},{"year":2025,"finding":"TBC1D9B contains a conserved TMEM55B-binding motif (TBM) mediating interaction with TMEM55B on lysosomes; this interaction is independent of phospho-Rabs (preprint version corroborating the peer-reviewed finding above).","method":"Crystal structure, co-immunoprecipitation, mutational analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — structural and biochemical data in preprint, superseded by peer-reviewed publication (PMID:41314214)","pmids":["40894729"],"is_preprint":true},{"year":2026,"finding":"TBC1D9B is a critical negative regulator of the kinesin-activating small GTPase ARL8B: it associates with the lysosomal membrane protein TMEM55B, directly binds ARL8B-GTP, and stimulates ARL8B GTPase activity. Knockout of TBC1D9B causes lysosome dispersion, defective autophagic flux, and impaired adaptive degradative response to nutrient limitation; these phenotypes are rescued by concomitant depletion of ARL8.","method":"Knockout cell lines, lysosome positioning assays, autophagic flux assays, direct binding to ARL8B-GTP, epistasis (TBC1D9B KO rescued by ARL8 co-depletion), co-localization with TMEM55B","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding assay, genetic epistasis, KO phenotype with multiple orthogonal readouts in a single rigorous study","pmids":["41832156"],"is_preprint":false},{"year":2026,"finding":"Arl8b recruits TBC1D9B to LAMP1-positive membranes, where TBC1D9B inactivates Rab11a to prevent Rab11a-dependent recycling of LAMP1 to the plasma membrane, thereby promoting LAMP1 delivery to lysosomes. TBC1D9B knockdown also impairs CI-M6PR retrieval from Rab11a/Rab14-positive endosomes to the trans-Golgi network, disrupting pro-cathepsin trafficking and cargo degradation.","method":"RUSH assay for LAMP1 trafficking, TBC1D9B knockdown, Arl8b depletion, immunofluorescence, CI-M6PR trafficking assay, cathepsin processing assay","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — RUSH trafficking assay with specific cargo readouts, loss-of-function for both Arl8b and TBC1D9B, multiple pathway endpoints in one study","pmids":["42166252"],"is_preprint":false},{"year":2025,"finding":"Phosphorylated LMTK1 activates TBC1D9B, which in turn deactivates Rab11a and suppresses Rab11a-positive endosome trafficking and neurite growth in Alzheimer's disease mouse models. This mechanism was investigated by co-immunoprecipitation, proteomics, and point mutation experiments.","method":"Co-immunoprecipitation, proteomics, point mutagenesis, AAV-mediated LMTK1 knockdown in AD mouse models, immunofluorescence, electrophysiology","journal":"Neurotherapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and mutagenesis supporting the LMTK1-TBC1D9B-Rab11a cascade in a disease model, single lab","pmids":["41198459"],"is_preprint":false}],"current_model":"TBC1D9B is a TBC-domain GTPase-activating protein (GAP) that acts on multiple substrates depending on context: it is a bona fide GAP for Rab11a (and at low Mg2+ also Rab8a) at recycling endosomes, regulating transcytosis and dendritic spine formation downstream of the Cdk5-LMTK1 kinase cascade; it interacts with LC3B/ATG8 homologues on autophagosomes to promote autophagic flux; it is recruited to lysosomal membranes via TMEM55B where it directly binds and inactivates the kinesin-activating GTPase ARL8B, thereby controlling lysosome positioning, cargo sorting (LAMP1, CI-M6PR), and adaptive catabolism; and it participates in a TMEM55B-based lysosomal adaptor hub."},"narrative":{"mechanistic_narrative":"TBC1D9B is a TBC-domain GTPase-activating protein (GAP) that regulates membrane trafficking by inactivating specific Rab and Arf-like GTPases at endosomal and lysosomal compartments [PMID:25232007, PMID:41832156]. Its TBC domain confers bona fide GAP activity toward Rab11a—binding multiple Rab GTPases in a nucleotide-dependent manner but selectively stimulating Rab11a GTP hydrolysis (and Rab8a only at limiting Mg2+)—and it localizes to Rab11a-positive recycling endosomes [PMID:25232007]. Through this Rab11a inactivation, TBC1D9B controls Rab11a-dependent traffic: it restrains basolateral-to-apical IgA transcytosis by disrupting the Rab11a–Sec15A effector interaction [PMID:25232007], and downstream of the Cdk5–LMTK1A kinase cascade it limits dendritic spine formation in neurons, where LMTK1A binds TBC1D9B and controls its GAP activity toward Rab11a [PMID:31628178]. At lysosomes, TBC1D9B is recruited via a conserved TMEM55B-binding motif into a TMEM55B adaptor platform and via Arl8b to LAMP1-positive membranes [PMID:41314214, PMID:42166252]; there it directly binds and inactivates the kinesin-activating GTPase ARL8B to control lysosome positioning, autophagic flux, and adaptive catabolism, with its knockout phenotypes rescued by ARL8 co-depletion [PMID:41832156]. TBC1D9B additionally directs LAMP1 and CI-M6PR cargo sorting by suppressing their Rab11a-dependent missorting, supporting pro-cathepsin trafficking and cargo degradation [PMID:42166252], and engages mammalian ATG8/LC3B homologues through a non-canonical interacting domain to promote autophagic flux [PMID:30202024].","teleology":[{"year":2014,"claim":"Established TBC1D9B's core biochemical identity and substrate specificity, answering whether and which Rab GTPases it inactivates.","evidence":"In vitro GTP hydrolysis and nucleotide-dependent binding assays with active-site mutagenesis, plus colocalization in polarized MDCK cells","pmids":["25232007"],"confidence":"High","gaps":["Physiological relevance of the low-Mg2+ Rab8a activity unresolved","Mechanism of TBC1D9B recruitment to recycling endosomes not defined"]},{"year":2014,"claim":"Connected the GAP biochemistry to a cellular trafficking output by showing TBC1D9B specifically tunes Rab11a-dependent transcytosis and disrupts effector engagement.","evidence":"Reciprocal overexpression/shRNA transcytosis assays with pathway-specific controls, active-Rab11a pulldown, and Rab11a–Sec15A co-IP in MDCK cells","pmids":["25232007"],"confidence":"High","gaps":["Upstream regulators of TBC1D9B activity not identified at this stage","Whether other Rab11a effectors besides Sec15A are affected unknown"]},{"year":2018,"claim":"Extended TBC1D9B's role into autophagy by identifying a non-canonical ATG8/LC3B interaction that promotes autophagic flux.","evidence":"Yeast two-hybrid, in vitro binding with purified proteins, co-IP, colocalization, LC3B turnover and long-lived protein degradation assays","pmids":["30202024"],"confidence":"High","gaps":["Molecular definition of the unique non-LIR interacting domain incomplete","Whether the LC3B interaction requires GAP activity not established"]},{"year":2019,"claim":"Placed TBC1D9B within a defined kinase cascade, showing LMTK1A binds and regulates its Rab11a GAP activity to control dendritic spine density.","evidence":"Reciprocal co-IP, shRNA knockdown in primary neurons and in vivo, spine morphology analysis, Rab11A activity assay","pmids":["31628178"],"confidence":"High","gaps":["Direct phosphorylation site(s) on TBC1D9B not mapped","How LMTK1A binding mechanistically modulates GAP activity unclear"]},{"year":2025,"claim":"Identified a structural basis for TBC1D9B's lysosomal recruitment via a conserved TMEM55B-binding motif independent of phospho-Rabs.","evidence":"Crystal structure of TMEM55B cytosolic domain, co-IP, mass spectrometry, and mutational analysis (peer-reviewed; corroborated by a preprint)","pmids":["41314214","40894729"],"confidence":"High","gaps":["Functional consequence of the TMEM55B interaction not yet addressed in this study","Stoichiometry and other components of the adaptor platform undefined"]},{"year":2025,"claim":"Linked the LMTK1–TBC1D9B–Rab11a cascade to disease-relevant neuronal phenotypes, showing phospho-LMTK1 activates TBC1D9B to suppress Rab11a trafficking and neurite growth.","evidence":"Co-IP, proteomics, point mutagenesis, AAV-mediated LMTK1 knockdown in Alzheimer's disease mouse models, immunofluorescence, electrophysiology","pmids":["41198459"],"confidence":"Medium","gaps":["Single-lab disease-model evidence","Causal contribution of TBC1D9B itself versus upstream LMTK1 not isolated"]},{"year":2026,"claim":"Revealed a second GAP substrate and the lysosome-positioning function, establishing TBC1D9B as a TMEM55B-anchored negative regulator of ARL8B.","evidence":"Knockout cell lines, lysosome positioning and autophagic flux assays, direct ARL8B-GTP binding, and genetic epistasis (KO rescued by ARL8 co-depletion)","pmids":["41832156"],"confidence":"High","gaps":["Coordination between ARL8B-GAP and Rab11a-GAP activities not integrated","Whether TMEM55B recruitment is required for ARL8B inactivation not fully dissected"]},{"year":2026,"claim":"Defined how Arl8b-recruited TBC1D9B directs lysosomal cargo sorting by suppressing Rab11a-dependent missorting of LAMP1 and CI-M6PR.","evidence":"RUSH trafficking assays, TBC1D9B and Arl8b loss-of-function, CI-M6PR trafficking and cathepsin processing assays","pmids":["42166252"],"confidence":"High","gaps":["How TBC1D9B is dynamically switched between recycling-endosome and lysosome pools unknown","Relationship between Arl8b-mediated recruitment and ARL8B inactivation by TBC1D9B not reconciled"]},{"year":null,"claim":"How TBC1D9B's distinct activities—Rab11a GAP at recycling endosomes, ARL8B GAP at lysosomes, and ATG8 engagement—are coordinated and spatially partitioned within a single cell remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No structure of full-length TBC1D9B or its substrate-engaged GAP domain","Regulatory logic balancing Rab11a versus ARL8B targeting undefined","Phosphorylation-based control of substrate choice not characterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,2,7,8]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,7]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5,8]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[1,8]},{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[5,7,8]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[2,8]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[3,7]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[8]}],"complexes":["TMEM55B lysosomal adaptor platform"],"partners":["RAB11A","ARL8B","TMEM55B","LMTK1A","MAP1LC3B","RAB8A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q66K14","full_name":"TBC1 domain family member 9B","aliases":[],"length_aa":1250,"mass_kda":140.5,"function":"May act as a GTPase-activating protein for Rab family protein(s)","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/Q66K14/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/TBC1D9B","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/TBC1D9B","total_profiled":1310},"omim":[{"mim_id":"618039","title":"TBC1 DOMAIN FAMILY, MEMBER 9B; TBC1D9B","url":"https://www.omim.org/entry/618039"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Nucleoli fibrillar center","reliability":"Additional"},{"location":"Actin filaments","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/TBC1D9B"},"hgnc":{"alias_symbol":["KIAA0676","GRAMD9B"],"prev_symbol":[]},"alphafold":{"accession":"Q66K14","domains":[{"cath_id":"-","chopping":"3-126","consensus_level":"high","plddt":75.4015,"start":3,"end":126},{"cath_id":"2.30.29.30","chopping":"141-260","consensus_level":"medium","plddt":82.615,"start":141,"end":260},{"cath_id":"2.30.29.30","chopping":"278-397","consensus_level":"medium","plddt":89.9357,"start":278,"end":397},{"cath_id":"1.10.8.270","chopping":"514-632","consensus_level":"medium","plddt":91.9355,"start":514,"end":632},{"cath_id":"1.10.472.80","chopping":"634-790","consensus_level":"high","plddt":88.7339,"start":634,"end":790}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q66K14","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q66K14-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q66K14-F1-predicted_aligned_error_v6.png","plddt_mean":74.25},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=TBC1D9B","jax_strain_url":"https://www.jax.org/strain/search?query=TBC1D9B"},"sequence":{"accession":"Q66K14","fasta_url":"https://rest.uniprot.org/uniprotkb/Q66K14.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q66K14/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q66K14"}},"corpus_meta":[{"pmid":"25232007","id":"PMC_25232007","title":"TBC1D9B functions as a GTPase-activating protein for Rab11a in polarized MDCK cells.","date":"2014","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/25232007","citation_count":40,"is_preprint":false},{"pmid":"31628178","id":"PMC_31628178","title":"The LMTK1-TBC1D9B-Rab11A Cascade Regulates Dendritic Spine Formation via Endosome Trafficking.","date":"2019","source":"The Journal of neuroscience : the official journal of the Society for Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/31628178","citation_count":29,"is_preprint":false},{"pmid":"28337427","id":"PMC_28337427","title":"Comparative Proteomics Analysis of Human Macrophages Infected with Virulent Mycobacterium bovis.","date":"2017","source":"Frontiers in cellular and infection microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/28337427","citation_count":27,"is_preprint":false},{"pmid":"30202024","id":"PMC_30202024","title":"Interaction of TBC1D9B with Mammalian ATG8 Homologues Regulates Autophagic Flux.","date":"2018","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/30202024","citation_count":11,"is_preprint":false},{"pmid":"32714146","id":"PMC_32714146","title":"LMTK1, a Novel Modulator of Endosomal Trafficking in Neurons.","date":"2020","source":"Frontiers in molecular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/32714146","citation_count":6,"is_preprint":false},{"pmid":"40722175","id":"PMC_40722175","title":"Angiogenesis-related genes and immune microenvironment in moyamoya disease: a transcriptomic and functional analysis.","date":"2025","source":"Orphanet journal of rare diseases","url":"https://pubmed.ncbi.nlm.nih.gov/40722175","citation_count":2,"is_preprint":false},{"pmid":"41314214","id":"PMC_41314214","title":"Structural basis for binding of RILPL1 to TMEM55B reveals a lysosomal platform for adaptor assembly through a conserved peptide motif.","date":"2025","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/41314214","citation_count":2,"is_preprint":false},{"pmid":"41832156","id":"PMC_41832156","title":"Control of lysosome function by the GTPase-activating protein TBC1D9B and its binding partner TMEM55B.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41832156","citation_count":0,"is_preprint":false},{"pmid":"40894729","id":"PMC_40894729","title":"Structural basis for binding of RILPL1 to TMEM55B reveals a lysosomal platform for adaptor assembly through a conserved TBM motif.","date":"2025","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/40894729","citation_count":0,"is_preprint":false},{"pmid":"42166252","id":"PMC_42166252","title":"Arl8b inactivates the Rab11a recycling pathway to promote LAMP1 sorting and lysosome biogenesis.","date":"2026","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/42166252","citation_count":0,"is_preprint":false},{"pmid":"41198459","id":"PMC_41198459","title":"Restoration neurite growth by removing the blockage of endosome trafficking in Alzheimer-like mice.","date":"2025","source":"Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/41198459","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8457,"output_tokens":2879,"usd":0.034278,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10046,"output_tokens":3263,"usd":0.065903,"stage2_stop_reason":"end_turn"},"total_usd":0.100181,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2014,\n      \"finding\": \"TBC1D9B functions as a GTPase-activating protein (GAP) for Rab11a via its TBC domain. In the presence of 2.5 mM Mg2+, TBC1D9B interacts with Rab11a, Rab11b, and Rab4a in a nucleotide-dependent manner, but only Rab11a is a substrate for TBC1D9B-stimulated GTP hydrolysis. At limiting Mg2+ concentrations (<0.5 mM), Rab8a is an additional substrate.\",\n      \"method\": \"In vitro GTP hydrolysis assay, nucleotide-dependent binding assay, active-site mutagenesis (inactive mutant), shRNA-mediated depletion, colocalization in polarized MDCK cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstituted GTPase assay plus mutagenesis plus cellular functional readout in a single rigorous study\",\n      \"pmids\": [\"25232007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TBC1D9B colocalizes with Rab11a-positive recycling endosomes in polarized MDCK cells but less so with EEA1-positive early endosomes, transferrin-positive recycling endosomes, or late endosomes, placing it at the recycling endosome compartment.\",\n      \"method\": \"Immunofluorescence colocalization in polarized MDCK cells\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization experiment replicated across multiple compartment markers in one study\",\n      \"pmids\": [\"25232007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"TBC1D9B overexpression decreases the rate of basolateral-to-apical IgA transcytosis (a Rab11a-dependent pathway) and shRNA depletion increases it; TBC1D9B had no effect on Rab11a-independent pathways (basolateral recycling of transferrin receptor or EGFR degradation). TBC1D9B expression also decreased active Rab11a levels and disrupted the Rab11a–Sec15A effector interaction.\",\n      \"method\": \"Transcytosis assays in polarized MDCK cells, overexpression and shRNA knockdown, active Rab11a pulldown, co-immunoprecipitation of Rab11a with Sec15A\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain/loss-of-function with specific pathway controls and downstream effector interaction measured in one rigorous study\",\n      \"pmids\": [\"25232007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"TBC1D9B interacts with LC3B and other mammalian ATG8 homologues through a unique interacting domain distinct from the canonical LC3-interacting region (LIR). TBC1D9B co-localizes with LC3B on autophagosome membranes, and inhibition of TBC1D9B suppresses turnover of membrane-bound LC3B and autophagic degradation of long-lived proteins, indicating TBC1D9B positively regulates autophagic flux.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding with purified proteins, co-immunoprecipitation, immunofluorescence colocalization, LC3B turnover assay, long-lived protein degradation assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Y2H, in vitro pulldown, co-IP, functional flux assays) in a single study\",\n      \"pmids\": [\"30202024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TBC1D9B is a binding partner of LMTK1A (a membrane-bound Ser/Thr kinase regulated by Cdk5-p35). LMTK1A controls the GAP activity of TBC1D9B toward Rab11A, placing TBC1D9B downstream of LMTK1 in the Cdk5-LMTK1-TBC1D9B-Rab11A signaling cascade. Knockdown of TBC1D9B in primary neurons increases dendritic spine formation and density.\",\n      \"method\": \"Co-immunoprecipitation (LMTK1-TBC1D9B interaction), shRNA knockdown in primary neurons and in vivo, spine morphology analysis, Rab11A activity assay\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP plus loss-of-function with specific cellular phenotype and pathway placement in vivo and in vitro, replicated across multiple labs\",\n      \"pmids\": [\"31628178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TBC1D9B contains a conserved TMEM55B-binding motif (TBM) that mediates interaction with TMEM55B, a lysosomal membrane protein. TMEM55B forms complexes with TBC1D9B independently of phospho-Rabs, placing TBC1D9B within a TMEM55B-centered lysosomal adaptor platform.\",\n      \"method\": \"Crystal structure of TMEM55B cytosolic domain, co-immunoprecipitation, mass spectrometry, mutational analysis\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus co-IP plus mutagenesis in a single study identifying the TBC1D9B-TMEM55B interaction\",\n      \"pmids\": [\"41314214\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TBC1D9B contains a conserved TMEM55B-binding motif (TBM) mediating interaction with TMEM55B on lysosomes; this interaction is independent of phospho-Rabs (preprint version corroborating the peer-reviewed finding above).\",\n      \"method\": \"Crystal structure, co-immunoprecipitation, mutational analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — structural and biochemical data in preprint, superseded by peer-reviewed publication (PMID:41314214)\",\n      \"pmids\": [\"40894729\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"TBC1D9B is a critical negative regulator of the kinesin-activating small GTPase ARL8B: it associates with the lysosomal membrane protein TMEM55B, directly binds ARL8B-GTP, and stimulates ARL8B GTPase activity. Knockout of TBC1D9B causes lysosome dispersion, defective autophagic flux, and impaired adaptive degradative response to nutrient limitation; these phenotypes are rescued by concomitant depletion of ARL8.\",\n      \"method\": \"Knockout cell lines, lysosome positioning assays, autophagic flux assays, direct binding to ARL8B-GTP, epistasis (TBC1D9B KO rescued by ARL8 co-depletion), co-localization with TMEM55B\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding assay, genetic epistasis, KO phenotype with multiple orthogonal readouts in a single rigorous study\",\n      \"pmids\": [\"41832156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Arl8b recruits TBC1D9B to LAMP1-positive membranes, where TBC1D9B inactivates Rab11a to prevent Rab11a-dependent recycling of LAMP1 to the plasma membrane, thereby promoting LAMP1 delivery to lysosomes. TBC1D9B knockdown also impairs CI-M6PR retrieval from Rab11a/Rab14-positive endosomes to the trans-Golgi network, disrupting pro-cathepsin trafficking and cargo degradation.\",\n      \"method\": \"RUSH assay for LAMP1 trafficking, TBC1D9B knockdown, Arl8b depletion, immunofluorescence, CI-M6PR trafficking assay, cathepsin processing assay\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RUSH trafficking assay with specific cargo readouts, loss-of-function for both Arl8b and TBC1D9B, multiple pathway endpoints in one study\",\n      \"pmids\": [\"42166252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Phosphorylated LMTK1 activates TBC1D9B, which in turn deactivates Rab11a and suppresses Rab11a-positive endosome trafficking and neurite growth in Alzheimer's disease mouse models. This mechanism was investigated by co-immunoprecipitation, proteomics, and point mutation experiments.\",\n      \"method\": \"Co-immunoprecipitation, proteomics, point mutagenesis, AAV-mediated LMTK1 knockdown in AD mouse models, immunofluorescence, electrophysiology\",\n      \"journal\": \"Neurotherapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and mutagenesis supporting the LMTK1-TBC1D9B-Rab11a cascade in a disease model, single lab\",\n      \"pmids\": [\"41198459\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"TBC1D9B is a TBC-domain GTPase-activating protein (GAP) that acts on multiple substrates depending on context: it is a bona fide GAP for Rab11a (and at low Mg2+ also Rab8a) at recycling endosomes, regulating transcytosis and dendritic spine formation downstream of the Cdk5-LMTK1 kinase cascade; it interacts with LC3B/ATG8 homologues on autophagosomes to promote autophagic flux; it is recruited to lysosomal membranes via TMEM55B where it directly binds and inactivates the kinesin-activating GTPase ARL8B, thereby controlling lysosome positioning, cargo sorting (LAMP1, CI-M6PR), and adaptive catabolism; and it participates in a TMEM55B-based lysosomal adaptor hub.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TBC1D9B is a TBC-domain GTPase-activating protein (GAP) that regulates membrane trafficking by inactivating specific Rab and Arf-like GTPases at endosomal and lysosomal compartments [#0, #7]. Its TBC domain confers bona fide GAP activity toward Rab11a—binding multiple Rab GTPases in a nucleotide-dependent manner but selectively stimulating Rab11a GTP hydrolysis (and Rab8a only at limiting Mg2+)—and it localizes to Rab11a-positive recycling endosomes [#0, #1]. Through this Rab11a inactivation, TBC1D9B controls Rab11a-dependent traffic: it restrains basolateral-to-apical IgA transcytosis by disrupting the Rab11a–Sec15A effector interaction [#2], and downstream of the Cdk5–LMTK1A kinase cascade it limits dendritic spine formation in neurons, where LMTK1A binds TBC1D9B and controls its GAP activity toward Rab11a [#4]. At lysosomes, TBC1D9B is recruited via a conserved TMEM55B-binding motif into a TMEM55B adaptor platform and via Arl8b to LAMP1-positive membranes [#5, #8]; there it directly binds and inactivates the kinesin-activating GTPase ARL8B to control lysosome positioning, autophagic flux, and adaptive catabolism, with its knockout phenotypes rescued by ARL8 co-depletion [#7]. TBC1D9B additionally directs LAMP1 and CI-M6PR cargo sorting by suppressing their Rab11a-dependent missorting, supporting pro-cathepsin trafficking and cargo degradation [#8], and engages mammalian ATG8/LC3B homologues through a non-canonical interacting domain to promote autophagic flux [#3].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2014,\n      \"claim\": \"Established TBC1D9B's core biochemical identity and substrate specificity, answering whether and which Rab GTPases it inactivates.\",\n      \"evidence\": \"In vitro GTP hydrolysis and nucleotide-dependent binding assays with active-site mutagenesis, plus colocalization in polarized MDCK cells\",\n      \"pmids\": [\"25232007\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological relevance of the low-Mg2+ Rab8a activity unresolved\", \"Mechanism of TBC1D9B recruitment to recycling endosomes not defined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected the GAP biochemistry to a cellular trafficking output by showing TBC1D9B specifically tunes Rab11a-dependent transcytosis and disrupts effector engagement.\",\n      \"evidence\": \"Reciprocal overexpression/shRNA transcytosis assays with pathway-specific controls, active-Rab11a pulldown, and Rab11a–Sec15A co-IP in MDCK cells\",\n      \"pmids\": [\"25232007\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream regulators of TBC1D9B activity not identified at this stage\", \"Whether other Rab11a effectors besides Sec15A are affected unknown\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extended TBC1D9B's role into autophagy by identifying a non-canonical ATG8/LC3B interaction that promotes autophagic flux.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro binding with purified proteins, co-IP, colocalization, LC3B turnover and long-lived protein degradation assays\",\n      \"pmids\": [\"30202024\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular definition of the unique non-LIR interacting domain incomplete\", \"Whether the LC3B interaction requires GAP activity not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placed TBC1D9B within a defined kinase cascade, showing LMTK1A binds and regulates its Rab11a GAP activity to control dendritic spine density.\",\n      \"evidence\": \"Reciprocal co-IP, shRNA knockdown in primary neurons and in vivo, spine morphology analysis, Rab11A activity assay\",\n      \"pmids\": [\"31628178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphorylation site(s) on TBC1D9B not mapped\", \"How LMTK1A binding mechanistically modulates GAP activity unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified a structural basis for TBC1D9B's lysosomal recruitment via a conserved TMEM55B-binding motif independent of phospho-Rabs.\",\n      \"evidence\": \"Crystal structure of TMEM55B cytosolic domain, co-IP, mass spectrometry, and mutational analysis (peer-reviewed; corroborated by a preprint)\",\n      \"pmids\": [\"41314214\", \"40894729\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the TMEM55B interaction not yet addressed in this study\", \"Stoichiometry and other components of the adaptor platform undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Linked the LMTK1–TBC1D9B–Rab11a cascade to disease-relevant neuronal phenotypes, showing phospho-LMTK1 activates TBC1D9B to suppress Rab11a trafficking and neurite growth.\",\n      \"evidence\": \"Co-IP, proteomics, point mutagenesis, AAV-mediated LMTK1 knockdown in Alzheimer's disease mouse models, immunofluorescence, electrophysiology\",\n      \"pmids\": [\"41198459\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab disease-model evidence\", \"Causal contribution of TBC1D9B itself versus upstream LMTK1 not isolated\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Revealed a second GAP substrate and the lysosome-positioning function, establishing TBC1D9B as a TMEM55B-anchored negative regulator of ARL8B.\",\n      \"evidence\": \"Knockout cell lines, lysosome positioning and autophagic flux assays, direct ARL8B-GTP binding, and genetic epistasis (KO rescued by ARL8 co-depletion)\",\n      \"pmids\": [\"41832156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Coordination between ARL8B-GAP and Rab11a-GAP activities not integrated\", \"Whether TMEM55B recruitment is required for ARL8B inactivation not fully dissected\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Defined how Arl8b-recruited TBC1D9B directs lysosomal cargo sorting by suppressing Rab11a-dependent missorting of LAMP1 and CI-M6PR.\",\n      \"evidence\": \"RUSH trafficking assays, TBC1D9B and Arl8b loss-of-function, CI-M6PR trafficking and cathepsin processing assays\",\n      \"pmids\": [\"42166252\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How TBC1D9B is dynamically switched between recycling-endosome and lysosome pools unknown\", \"Relationship between Arl8b-mediated recruitment and ARL8B inactivation by TBC1D9B not reconciled\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How TBC1D9B's distinct activities—Rab11a GAP at recycling endosomes, ARL8B GAP at lysosomes, and ATG8 engagement—are coordinated and spatially partitioned within a single cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure of full-length TBC1D9B or its substrate-engaged GAP domain\", \"Regulatory logic balancing Rab11a versus ARL8B targeting undefined\", \"Phosphorylation-based control of substrate choice not characterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 2, 7, 8]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 7]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1, 8]},\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [5, 7, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [2, 8]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [3, 7]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [8]}\n    ],\n    \"complexes\": [\"TMEM55B lysosomal adaptor platform\"],\n    \"partners\": [\"RAB11A\", \"ARL8B\", \"TMEM55B\", \"LMTK1A\", \"MAP1LC3B\", \"RAB8A\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}