Affinage

TBCD

Tubulin-specific chaperone D · UniProt Q9BTW9

Length
1192 aa
Mass
132.6 kDa
Annotated
2026-06-10
19 papers in source corpus 11 papers cited in narrative 11 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TBCD is a tubulin-specific cofactor that operates downstream of the CCT chaperonin in the de novo assembly of αβ-tubulin heterodimers, where it functions in CCT-driven folding reactions and, together with TBCC, acts as a GTPase-activating protein stimulating GTP hydrolysis by β-tubulin within the heterodimer (PMID:20740604). In cells its functional form is a stable ~200 kDa trimer of TBCD, ARL2, and β-tubulin, and disruption of the ARL2–TBCD interaction impairs maintenance of normal microtubule densities (PMID:28126905); within this trimer it is ARL2, not β-tubulin, that exchanges guanine nucleotide, and ARL2 nucleotide cycling drives conformational changes in β-tubulin, making the complex a regulated intermediate in the β-tubulin folding pathway (PMID:28970104). TBCD additionally drives tubulin heterodimer disassembly, an activity that ARL2 negatively regulates, since suppression of ARL2 allows TBCD to disrupt microtubule integrity in vivo (PMID:20740604). TBCD localizes to the centrosome and midbody in a cell-cycle-dependent manner and contributes to centriologenesis, spindle organization, and cytokinesis, with overexpression causing microtubule release and G1 arrest and depletion causing mitotic and cytokinetic defects (PMID:20107510). Pathogenic missense mutations in TBCD reduce protein stability and impair binding to β-tubulin, ARL2, and TBCE, lowering soluble tubulin levels, accelerating microtubule polymerization, and producing disorganized mitotic spindles (PMID:27666370, PMID:27666374); loss of TBCD function impairs cortical neuron proliferation and radial migration and causes a neurodevelopmental disorder, with CRISPR correction of a patient mutation rescuing spindle organization and cell death (PMID:28158450, PMID:37175696).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2010 High

    Established the dual biochemical activities of TBCD in the tubulin pathway, showing it both participates in folding and acts as a β-tubulin GAP with TBCC, while identifying ARL2 as a negative regulator of its destabilizing activity.

    Evidence In vitro CCT folding, tubulin disruption, and GAP assays plus recombinant expression and ARL2 siRNA in HeLa cells

    PMID:20740604

    Open questions at the time
    • Did not resolve the structural basis of ARL2 regulation
    • Difference between bovine and human TBCD co-complex behavior unexplained
  2. 2010 High

    Defined TBCD's spatial and cell-cycle-dependent role at centrosomes and midbody, linking its biochemical activity to centriologenesis, spindle organization, and cytokinesis.

    Evidence Immunofluorescence localization with overexpression and siRNA phenotyping in cultured and differentiating ciliated cells

    PMID:20107510

    Open questions at the time
    • Mechanism connecting tubulin chaperone activity to centriole assembly not defined
    • Direct centriolar binding partners not identified
  3. 2016 High

    Connected TBCD to human disease by showing pathogenic mutations destabilize the protein, impair tubulin/cofactor binding, perturb microtubule dynamics, and cause neurodevelopmental phenotypes in patient cells and model organisms.

    Evidence Patient fibroblast biochemistry, microtubule polymerization assays, spindle imaging, in utero mouse shRNA, zebrafish morpholino, and Drosophila genetics

    PMID:27666370 PMID:27666374 PMID:27807845 PMID:28158450

    Open questions at the time
    • Genotype-phenotype correlation across mutations incompletely resolved
    • Brain-specific dependency mechanism not fully defined
  4. 2017 High

    Resolved the functional form of TBCD in cells as a stable trimer with ARL2 and β-tubulin and showed the ARL2-TBCD interface is required for microtubule network maintenance.

    Evidence Native gels, affinity purification from HEK cells, and ARL2 point mutant analysis with microtubule density quantification across tissues and cell lines

    PMID:28126905

    Open questions at the time
    • Atomic-resolution structure of the trimer not determined
    • Stoichiometry of higher-order assemblies unknown
  5. 2017 High

    Established the nucleotide logic of the trimer, demonstrating that ARL2 (not β-tubulin) cycles GTP and that ARL2 nucleotide binding allosterically reshapes β-tubulin, defining the complex as a regulated folding intermediate.

    Evidence HDX-MS, nucleotide-binding assays, and comparison of ARL2 monomer versus trimer dynamics

    PMID:28970104

    Open questions at the time
    • Downstream fate of the conformationally altered β-tubulin not tracked
    • Timing of nucleotide cycling relative to heterodimer release unresolved
  6. 2017 Low

    Documented TBCD and TBCE expression and localization in human gametes, raising a possible role in reproductive cells.

    Evidence RT-PCR, western blot, and immunofluorescence on human sperm and oocytes

    PMID:28583220

    Open questions at the time
    • No functional consequence tested in gametes
    • Single descriptive study without loss-of-function validation
  7. 2023 Medium

    Confirmed causality of a pathogenic TBCD allele by isogenic correction, directly linking restored TBCD levels to rescued spindle organization and reduced cell death.

    Evidence CRISPR/Cas9 isogenic correction in patient iPSCs with protein, spindle, and cell-death readouts

    PMID:37175696

    Open questions at the time
    • Single mutation corrected; generality across alleles not tested
    • Single lab
  8. 2025 Medium

    Defined a mechanism by which excess TBCD competes with α-tubulin for β-tubulin, driving α-tubulin degradation, microtubule depolymerization, and cell death via NF-κB/TNF-α and ROS signaling.

    Evidence Binding competition and depolymerization assays, RNA-seq, ROS measurement, and tumor xenografts using bovine TBCD

    PMID:41232862

    Open questions at the time
    • Demonstrated for bovine, not human, TBCD
    • In vivo relevance of the NF-κB/TNF-α axis to physiological TBCD function unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • The atomic structure of the TBCD·ARL2·β-tubulin trimer and the precise sequence of conformational and nucleotide events linking it to heterodimer release remain undefined.
  • No high-resolution structure of the functional trimer
  • Coupling between centrosomal localization and tubulin folding mechanistically unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008092 cytoskeletal protein binding 3 GO:0044183 protein folding chaperone 2 GO:0098772 molecular function regulator activity 2
Localization
GO:0005856 cytoskeleton 2 GO:0005815 microtubule organizing center 1 GO:0005829 cytosol 1
Pathway
R-HSA-392499 Metabolism of proteins 3 R-HSA-1640170 Cell Cycle 2 R-HSA-1266738 Developmental Biology 1
Partners
ARL2TBCCTBCETUBB
Complex memberships
TBCD·ARL2·β-tubulin trimer

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2010 TBCD functions in vitro in CCT-driven tubulin folding reactions and in tubulin disruption reactions; it also acts as a GTPase-activating protein (GAP) together with TBCC to stimulate GTP hydrolysis by β-tubulin in the heterodimer at concentrations below those required for polymerization. Bovine TBCD forms a stoichiometric co-complex with β-tubulin when expressed in HeLa cells, whereas human TBCD does not. siRNA-mediated suppression of ARL2 enables human TBCD to disrupt microtubule integrity in vivo, demonstrating that ARL2 negatively regulates TBCD's microtubule-destabilizing activity. In vitro CCT folding assays, tubulin disruption assays, GTPase-activating protein (GAP) assays, recombinant protein expression in HeLa cells with Co-IP/co-complex analysis, siRNA knockdown of ARL2 Cytoskeleton (Hoboken, N.J.) High 20740604
2010 TBCD localizes to the centrosome and midbody in a cell-cycle-dependent manner: at the daughter centriole in G1, on procentrioles in S phase, and at the midbody during cytokinesis. Overexpression of TBCD causes microtubule release from the centrosome and G1 arrest; depletion causes mitotic aberrations and incomplete microtubule retraction at the midbody during cytokinesis. In differentiating ciliated cells, TBCD organizes into centriolar rosettes, supporting a role in both canonical and de novo centriolar assembly. Immunofluorescence localization, cell-cycle staging, TBCD overexpression and siRNA depletion with phenotypic readouts (mitotic aberrations, G1 arrest, cytokinesis defects), analysis in differentiating ciliated cells PloS one High 20107510
2017 TBCD, ARL2, and β-tubulin form a stable ~200 kDa trimeric complex (TBCD·ARL2·β-tubulin) in mouse tissues and multiple cell lines. The trimer was purified from human embryonic kidney cells. ARL2 point mutants that disrupt binding to TBCD impair proper maintenance of microtubule densities in cells, establishing that the ARL2–TBCD interaction within the trimer is required for normal microtubule network maintenance. Non-denaturing gel electrophoresis with immunoblotting, affinity purification from HEK cells, ARL2 point mutant analysis, microtubule density quantification The Journal of biological chemistry High 28126905
2017 Within the TBCD·ARL2·β-tubulin trimer, it is ARL2 (not β-tubulin) that exchanges GTP; ARL2 nucleotide-binding affinity for GTP is increased within the trimer compared to ARL2 monomer. Guanine nucleotide binding to ARL2 drives conformational changes in β-tubulin as detected by altered solvent accessibility. β-tubulin in the trimer also co-purifies with guanine nucleotide. The complex represents a functional intermediate in the β-tubulin folding pathway regulated by ARL2 nucleotide cycling. Hydrogen/deuterium exchange mass spectrometry (HDX-MS), nucleotide-binding assays, comparison of ARL2 monomer vs. trimer dynamics Journal of molecular biology High 28970104
2016 Pathogenic missense mutations in TBCD reduce protein stability (variably reduced TBCD levels in patient fibroblasts) and impair β-tubulin binding. Loss of TBCD function decreases soluble α/β-tubulin levels and accelerates microtubule polymerization, resulting in a more rapidly growing, stable microtubule population. Patient fibroblasts display aberrant mitotic spindles with disorganized tangle-shaped microtubules and reduced aster formation. Biochemical analysis of patient-derived fibroblasts (protein level quantification, β-tubulin binding assays), microtubule polymerization assays, immunofluorescence of mitotic spindles, molecular dynamics simulations American journal of human genetics High 27666370
2016 Most pathogenic TBCD missense mutations impair binding of TBCD to ARL2, TBCE, and β-tubulin in cell-based interaction experiments. In vivo experiments using Drosophila melanogaster olfactory projection neurons showed TBCD mutations cause loss-of-function phenotypes. In vitro cell-based binding experiments (co-immunoprecipitation/pulldown of mutant TBCD with ARL2, TBCE, β-tubulin), Drosophila in vivo genetics American journal of human genetics Medium 27666374
2016 In utero shRNA-mediated suppression of tbcd in the developing mouse brain impairs cortical cell proliferation and radial migration, establishing TBCD as required for normal cerebral cortex development. Mutant TBCD proteins (A475T and A586V) show partially compromised ability to participate in the heterodimer assembly pathway, with reduced intracellular TBCD abundance (~10% and ~40% of control, respectively). In utero shRNA knockdown in mouse brain with histological analysis of cell proliferation and radial migration; functional assembly assays with mutant proteins; protein quantification in patient fibroblasts Human molecular genetics High 28158450
2016 Reduced TBCD expression in patient fibroblasts is associated with accelerated microtubule re-polymerization. Morpholino-mediated TBCD knockdown in zebrafish recapitulates key disease pathological features, and TBCD overexpression in zebrafish confirms an obligate dependency on proper TBCD dosage for normal development. Microtubule re-polymerization assays in patient-derived fibroblasts, morpholino knockdown and overexpression in zebrafish with phenotypic analysis Clinical genetics Medium 27807845
2023 CRISPR/Cas9 correction of a pathogenic TBCD missense substitution in patient-derived iPSCs restored proper TBCD protein levels, rescued mitotic spindle organization, and reduced cellular death, confirming that loss of TBCD function directly causes mitotic spindle disorganization and increased cell death. CRISPR/Cas9 isogenic iPSC correction, protein level quantification, mitotic spindle immunofluorescence, cell death assays International journal of molecular sciences Medium 37175696
2025 Bovine TBCD (bTBCD) specifically competes with α-tubulin to bind β-tubulin; when bTBCD binds β-tubulin, it fails to form a functional TBCD/β-tubulin/ARL2 complex, resulting in α-tubulin degradation and microtubule depolymerization. This depolymerization combined with an unbalanced β/α-tubulin ratio leads to cell cycle arrest and cell death via activation of non-canonical NF-κB and TNF-α signaling pathways with increased ROS production. Protein binding competition assays, microtubule depolymerization assays, RNA-seq pathway analysis, ROS measurement, in vivo tumor xenograft experiments International journal of biological macromolecules Medium 41232862
2017 TBCD and TBCE proteins are expressed in human sperm (localized mainly to the middle piece and tail) and in human oocytes (cytosolic localization), as determined by RT-PCR, western blot, and immunofluorescence. TBCD mRNA is present in oocytes but not sperm. RT-PCR, western blot, immunofluorescence on human sperm and oocytes Zygote (Cambridge, England) Low 28583220

Source papers

Stage 0 corpus · 19 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2016 Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy. American journal of human genetics 67 27666370
2016 Biallelic TBCD Mutations Cause Early-Onset Neurodegenerative Encephalopathy. American journal of human genetics 54 27666374
2010 Effect of TBCD and its regulatory interactor Arl2 on tubulin and microtubule integrity. Cytoskeleton (Hoboken, N.J.) 41 20740604
2017 A Trimer Consisting of the Tubulin-specific Chaperone D (TBCD), Regulatory GTPase ARL2, and β-Tubulin Is Required for Maintaining the Microtubule Network. The Journal of biological chemistry 40 28126905
2016 Infantile neurodegenerative disorder associated with mutations in TBCD, an essential gene in the tubulin heterodimer assembly pathway. Human molecular genetics 30 28158450
2010 TBCD links centriologenesis, spindle microtubule dynamics, and midbody abscission in human cells. PloS one 27 20107510
2016 Microcephaly, intractable seizures and developmental delay caused by biallelic variants in TBCD: further delineation of a new chaperone-mediated tubulinopathy. Clinical genetics 25 27807845
2017 Nucleotide Binding to ARL2 in the TBCD∙ARL2∙β-Tubulin Complex Drives Conformational Changes in β-Tubulin. Journal of molecular biology 17 28970104
2016 TBCD may be a causal gene in progressive neurodegenerative encephalopathy with atypical infantile spinal muscular atrophy. Journal of human genetics 15 27928163
2019 Developmental Regression and Epilepsy of Infancy with Migrating Focal Seizures Caused by TBCD Mutation: A Case Report and Review of the Literature. Neuropediatrics 9 31569255
2019 Biallelic pathogenic variants in TBCD-related neurodevelopment disease with mild clinical features. Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology 8 31240573
2018 Cortical atrophy and hypofibrinogenemia due to FGG and TBCD mutations in a single family: a case report. BMC medical genetics 7 29769041
2021 Novel Compound Heterozygous Variants in TBCD Gene Associated with Infantile Neurodegenerative Encephalopathy. Children (Basel, Switzerland) 5 34943336
2023 CRISPR/Cas9 and piggyBac Transposon-Based Conversion of a Pathogenic Biallelic TBCD Variant in a Patient-Derived iPSC Line Allows Correction of PEBAT-Related Endophenotypes. International journal of molecular sciences 3 37175696
2022 PEBAT, an Intriguing Neurodegenerative Tubulinopathy Caused by a Novel Homozygous Variant in TBCD: A Case Series and Literature Review. Pediatric neurology 3 36527993
2023 [MOH SCREENING FOR TBCD IN COCHIN JEWS: COLLABORATION BETWEEN MEDICAL, RESEARCH AND COMMUNITY MEMBERS IN ACHIEVING PUBLIC HEALTH GOALS]. Harefuah 1 37394437
2017 Expression and localization of tubulin cofactors TBCD and TBCE in human gametes. Zygote (Cambridge, England) 1 28583220
2025 Bovine tubulin cofactor D (TBCD) disrupts tubulin dimers and inhibits tumor growth via the TNF-α signaling pathways-mediated ROS production. International journal of biological macromolecules 0 41232862
2023 A Variant in TBCD Associated with Motoneuronopathy and Corpus Callosum Hypoplasia: A Case Report. International journal of molecular sciences 0 37569761

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