Affinage

TBC1D20

TBC1 domain family member 20 · UniProt Q96BZ9

Length
403 aa
Mass
45.9 kDa
Annotated
2026-06-10
11 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TBC1D20 is a TBC-domain RAB GTPase-activating protein (GAP) that inactivates specific RAB GTPases to govern ER-to-Golgi vesicular trafficking, autophagosome maturation, and ciliogenesis (PMID:17901050, PMID:24239381, PMID:27487390, PMID:39868814). Acting through its catalytic TBC domain, it stimulates GTP hydrolysis on RAB1 and RAB2, and its overexpression blocks anterograde ER-to-Golgi transport while its loss enlarges the Golgi, increases RAB1 activity, and produces aberrant lipid droplets (PMID:17901050, PMID:24239381, PMID:28088541). Via its RAB1B GAP activity it is required for autophagosome maturation and autophagic flux, with loss disrupting cargo degradation in lens fiber cells and testes and impairing acrosome formation in spermatids (PMID:27487390); an intact TBC domain is essential for these functions in vivo, as TBC-domain disruption phenocopies and fails to complement the spontaneous bs mutation, causing cataracts and abnormal acrosomal development (PMID:25476608). TBC1D20 also acts as a GAP for RAB11, where it restrains ciliogenesis: its loss promotes RAB11 vesicle accumulation and an enhanced RAB11-MICAL1 interaction that activates the MICAL1 monooxygenase to depolymerize centrosomal F-actin, facilitating premature ciliogenesis (PMID:39868814). In the testis, TBC1D20 deficiency in Sertoli cells links its trafficking function to ER homeostasis, triggering ER stress, caspase-12-mediated apoptosis, and impaired blood-testis barrier integrity (PMID:31633178, PMID:31994000). The enzyme is exploited by hepatitis C virus, whose NS5A protein recruits TBC1D20 and RAB1 to lipid droplets in an interaction required for viral replication (PMID:17901050, PMID:22491470).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2007 High

    Established TBC1D20 as a catalytically active RAB1 GAP and tied its activity to anterograde secretory transport, defining its core molecular function.

    Evidence In vitro GAP assay with catalytic-residue mutagenesis plus VSV-G ER-to-Golgi trafficking assay; also identified the HCV NS5A interaction

    PMID:17901050

    Open questions at the time
    • Did not define the full RAB substrate spectrum beyond RAB1
    • Physiological cell/tissue context of GAP activity not addressed
  2. 2012 Medium

    Showed how a host trafficking enzyme is hijacked: HCV NS5A recruits TBC1D20 and RAB1 to lipid droplets to support viral replication sites.

    Evidence Live-cell imaging, FRAP, and dominant-negative RAB1 expression in HCV-infected cells

    PMID:22491470

    Open questions at the time
    • Whether GAP catalytic activity per se is required at LDs not resolved
    • Single-lab imaging-based study
  3. 2012 Medium

    Demonstrated that excess TBC1D20 GAP activity can perturb a different viral envelope pathway, indicating dosage-sensitive control of secretory trafficking.

    Evidence TBC1D20 overexpression with HIV-1 envelope processing, detergent-resistant membrane fractionation, and VLP infectivity assays

    PMID:22260459

    Open questions at the time
    • Effect from overexpression rather than physiological levels
    • Specific RAB target mediating the envelope defect not pinned down
  4. 2013 High

    Broadened substrate range to RAB2 and connected enzyme loss to organelle morphology, linking TBC1D20 to Golgi and lipid droplet homeostasis in mammalian cells.

    Evidence Positional cloning, GAP assays, and Golgi/lipid-droplet morphology analysis in mouse and human fibroblasts

    PMID:24239381

    Open questions at the time
    • Mechanism connecting RAB1/RAB2 inactivation to lipid droplet defects unresolved
    • Did not address autophagy or ciliogenesis roles
  5. 2014 Medium

    Confirmed in vivo that an intact TBC domain is necessary for TBC1D20 function, genetically validating the catalytic domain as the disease-relevant module.

    Evidence Zinc-finger nuclease deletion within the TBC domain and allelic complementation test with histology of lens and seminiferous tubules

    PMID:25476608

    Open questions at the time
    • Did not identify the downstream RAB whose dysregulation causes the cataract/acrosome phenotypes
    • Single-lab in vivo study
  6. 2016 High

    Defined a RAB1B-dependent role in autophagosome maturation, explaining how trafficking GAP activity controls autophagic flux in lens and testicular tissue.

    Evidence Null-mutant cells and TBC1D20-deficient mice with autophagic flux readouts and GAP-active vs -inactive rescue

    PMID:27487390

    Open questions at the time
    • Step of autophagosome maturation directly controlled by RAB1B inactivation not fully mapped
    • Tissue-specificity of phenotypes not mechanistically explained
  7. 2019 Medium

    Linked TBC1D20 trafficking function to ER homeostasis, showing its loss triggers ER stress and caspase-12-mediated apoptosis in Sertoli cells.

    Evidence Western blot of ER stress markers and caspase-12, cell cycle analysis, and histopathology in TBC1D20-deficient Sertoli cells

    PMID:31633178

    Open questions at the time
    • Causal chain from RAB dysregulation to ER stress not biochemically dissected
    • Single-lab study
  8. 2020 Medium

    Extended the Sertoli-cell phenotype to blood-testis barrier integrity, connecting trafficking loss to junctional protein downregulation and F-actin rearrangement.

    Evidence Biotin tracer assay, TEM, junctional protein Western blots, and F-actin staining in bs Sertoli cells

    PMID:31994000

    Open questions at the time
    • Direct trafficking link to specific junctional proteins not established
    • RAB substrate driving barrier defect unidentified
  9. 2025 High

    Identified RAB11 as a novel substrate and revealed that TBC1D20 suppresses premature ciliogenesis via the RAB11-MICAL1-actin axis at the centrosome.

    Evidence RAB11 GAP assay, RAB11-MICAL1 co-IP, MICAL1 monooxygenase activity assay, F-actin imaging, and ciliogenesis assays in cycling cells

    PMID:39868814

    Open questions at the time
    • How TBC1D20 activity toward RAB11 is regulated during the cell cycle unknown
    • Single-lab study

Open questions

Synthesis pass · forward-looking unresolved questions
  • How TBC1D20 selects among RAB1, RAB2, and RAB11 in different cellular and tissue contexts, and how its activity is spatially and temporally regulated, remains unresolved.
  • No structural basis for multi-RAB substrate selectivity in the corpus
  • Upstream regulators of TBC1D20 GAP activity not identified
  • Recruitment determinants to distinct membranes not defined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0140096 catalytic activity, acting on a protein 3
Localization
GO:0005783 endoplasmic reticulum 2 GO:0005794 Golgi apparatus 1 GO:0005811 lipid droplet 1 GO:0005815 microtubule organizing center 1
Pathway
R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-1852241 Organelle biogenesis and maintenance 1 R-HSA-9612973 Autophagy 1
Partners
MICAL1NS5ARAB1RAB11RAB1BRAB2

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2007 TBC1D20 is a GTPase-activating protein (GAP) for Rab1; mutation of catalytic residues in the TBC domain abrogated GAP activity. TBC1D20 overexpression blocked ER-to-Golgi transport of VSV-G protein, confirming its role in anterograde trafficking. HCV NS5A binds TBC1D20 and this interaction is required for efficient HCV replication. Biochemical GAP activity screen, site-directed mutagenesis of TBC domain catalytic residues, VSV-G trafficking assay, Rab1 depletion (RNAi) with HCV RNA quantification The Journal of biological chemistry High 17901050
2013 TBC1D20 functions as a GAP for RAB1 and RAB2. Loss-of-function in mouse embryonic fibroblasts causes enlarged Golgi morphology and aberrant lipid droplet formation. Human fibroblasts deficient in TBC1D20 similarly exhibit aberrant lipid droplet formation. Positional cloning, GAP activity assays, morphological analysis of Golgi and lipid droplets in bs mouse embryonic fibroblasts and human fibroblasts American journal of human genetics High 24239381
2012 NS5A of HCV recruits TBC1D20 and its cognate GTPase Rab1 to lipid droplets (LDs). NS5A binding to LDs is apparently irreversible. The NS5A-TBC1D20 interaction is essential for the HCV viral life cycle. Expression of dominant-negative Rab1 abolished steady-state LDs and eliminated NS5A from viral replication sites. Live-cell fluorescence imaging, FRAP, co-localization in HCV-infected cells, dominant-negative Rab1 expression Journal of virology Medium 22491470
2012 Excessive TBC1D20 GAP activity perturbs early trafficking of the HIV-1 envelope protein through the secretory pathway, impairing envelope processing and its association with detergent-resistant membranes, thereby reducing HIV-1 virion infectivity. TBC1D20 overexpression, HIV-1 envelope processing assays, detergent-resistant membrane fractionation, infectivity assay of VLPs Retrovirology Medium 22260459
2016 TBC1D20, via its RAB1B GAP function, is a key regulator of autophagosome maturation required for autophagic flux. Loss of TBC1D20 impairs maturation of autophagosomes, disrupts degradation of autophagic cargo in lens fiber cells and testes, and disrupts acrosome formation in spermatids. Null mutant allele cell lines, TBC1D20-deficient mouse analysis, autophagic flux assays (autophagosome markers), rescue with GAP-active vs. -inactive TBC1D20 Autophagy High 27487390
2017 Knockdown of TBC1D20 in CHO cells increases Rab1 GTPase activity, enhancing ER-to-Golgi vesicular trafficking and improving antibody secretion. Combined siRNA-mediated knockdown of TBC1D20 and CerS2 recapitulates increased specific productivity observed with mitosRNA-1978 overexpression. siRNA knockdown, Rab1 activity assay, IgG productivity measurement in fed-batch CHO cell culture Metabolic engineering Medium 28088541
2019 TBC1D20 deficiency in Sertoli cells causes endoplasmic reticulum stress, G1/S cell cycle arrest, and caspase-12-mediated apoptosis. TBC1D20-deficient Sertoli cells display abnormal Golgi-ER structure, linking TBC1D20's membrane trafficking function to ER homeostasis in these cells. Western blotting for ER stress markers and caspase-12 activation, histopathology, cell cycle analysis of TBC1D20-deficient Sertoli cells Molecular human reproduction Medium 31633178
2020 TBC1D20 loss of function in Sertoli cells impairs blood-testis barrier integrity by downregulating junctional proteins (E-cadherin, ZO-1, β-catenin, Claudin 11), causing F-actin rearrangement and disrupting the epithelial-mesenchymal balance; also attenuates Sertoli cell differentiation (reduced SOX9, WT1; increased vimentin). Biotin tracer assay, transmission electron microscopy, Western blot of BTB components, F-actin staining in bs Sertoli cells in vitro Reproductive sciences Medium 31994000
2025 TBC1D20 is a GAP for Rab11 (novel substrate). Depletion of TBC1D20 promotes Rab11 vesicle accumulation and actin deconstruction around the centrosome, facilitating ciliogenesis initiation. Upon TBC1D20 loss, enhanced Rab11-MICAL1 interaction activates the MICAL1 monooxygenase domain, inducing F-actin depolymerization around the centrosome, which facilitates vesicle trafficking/docking to promote ciliogenesis. TBC1D20 depletion in cycling cells, Rab11 activity assays, co-immunoprecipitation of Rab11-MICAL1, MICAL1 monooxygenase activity assay, F-actin imaging, ciliogenesis assays The Journal of cell biology High 39868814
2014 Zinc-finger nuclease disruption of Tbc1d20 (deleting residues H140-Y143 in the conserved TBC domain) phenocopies the spontaneous bs mutation, causing cataracts and aberrant acrosomal development. Compound heterozygote Tbc1d20(ZFN/bs) mice fail to complement, confirming TBC1D20 function requires an intact TBC domain. Zinc-finger nuclease genome editing, allelic complementation test, histological analysis of lens and seminiferous tubules BMC genetics Medium 25476608

Source papers

Stage 0 corpus · 11 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2013 Loss-of-function mutations in TBC1D20 cause cataracts and male infertility in blind sterile mice and Warburg micro syndrome in humans. American journal of human genetics 107 24239381
2007 TBC1D20 is a Rab1 GTPase-activating protein that mediates hepatitis C virus replication. The Journal of biological chemistry 101 17901050
2016 TBC1D20 mediates autophagy as a key regulator of autophagosome maturation. Autophagy 63 27487390
2012 Role for TBC1D20 and Rab1 in hepatitis C virus replication via interaction with lipid droplet-bound nonstructural protein 5A. Journal of virology 45 22491470
2014 Targeted disruption of Tbc1d20 with zinc-finger nucleases causes cataracts and testicular abnormalities in mice. BMC genetics 19 25476608
2017 Secretory pathway optimization of CHO producer cells by co-engineering of the mitosRNA-1978 target genes CerS2 and Tbc1D20. Metabolic engineering 16 28088541
2012 Human immunodeficiency virus type 1 envelope proteins traffic toward virion assembly sites via a TBC1D20/Rab1-regulated pathway. Retrovirology 16 22260459
2020 TBC1D20 Is Essential for Mouse Blood-Testis Barrier Integrity Through Maintaining the Epithelial Phenotype and Modulating the Maturation of Sertoli Cells. Reproductive sciences (Thousand Oaks, Calif.) 9 31994000
2019 TBC1D20 deficiency induces Sertoli cell apoptosis by triggering irreversible endoplasmic reticulum stress in mice. Molecular human reproduction 9 31633178
2025 TBC1D20 coordinates vesicle transport and actin remodeling to regulate ciliogenesis. The Journal of cell biology 4 39868814
2020 Martsolf syndrome with novel mutation in the TBC1D20 gene in a family from Iran. American journal of medical genetics. Part A 4 32162791

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