Microcephaly, intractable seizures and developmental delay caused by biallelic variants in <i><scp>TBCD</scp></i>: further delineation of a new chaperone‐mediated tubulinopathy

Pode‐Shakked, Ben; Barash, Hila; Ziv, Limor; Gripp, Karen W.; Flex, Elisabetta; Barel, Ortal; Carvalho, Karen S.; Scavina, Mena; Chillemi, Giovanni; Niceta, Marcello; Eyal, Eran; Kol, Nitzan; Ben‐Zeev, Bruria; Bar‐Yosef, Omer; Marek‐Yagel, Dina; Bertini, Enrico; Duker, Angela L.; Anikster, Yair; Tartaglia, Marco; Raas‐Rothschild, Annick

doi:10.1111/cge.12914

Cited by 26 publications

(34 citation statements)

References 31 publications

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“…The TBCD mutants that had reduced binding to ␤-tubulin showed an increase in the rate of tubulin polymerization compared with control cells. Similar studies have recently added to our appreciation of the importance of TBCD and its binding to ARL2 and ␤-tubulin in related neurological syndromes (18,19,20,39). Together, these findings argue that the TBCD⅐ARL2⅐␤-tubulin complex is vital for the proper homeostasis that is required in microtubule dynamics and human health.…”

Section: Discussionsupporting

confidence: 53%

“…As a consequence, we propose the TBCD⅐ARL2⅐␤-tubulin complex to be a key player in the folding process and potentially separately in regulating the lifetime or stability of the microtubule array. Finally, the studies by Flex et al (17) and others (18,19,20,39) highlight the clinical significance of the TBCD⅐ARL2⅐␤-tubulin trimer and suggest that continued study of this complex will prove to be beneficial to both the scientific and clinical communities.…”

Section: Discussionmentioning

confidence: 97%

“…More recently, however, TBCD has been implicated in additional cellular roles, including actions at centrosomes (12)(13)(14) and at the cell surface (15,16). Several recent studies have identified a number of point mutations in TBCD found in patients with links to early-onset encephalopathy (17)(18)(19) and intractable seizures (20). Throughout the time when roles for TBCD in microtubule biology were being identified, there have also been strong functional links to the ARL2 GTPase, a member of the ADP-ribosylation factor (ARF) family of regulatory GTPases.…”

mentioning

confidence: 99%

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A Trimer Consisting of the Tubulin-specific Chaperone D (TBCD), Regulatory GTPase ARL2, and β-Tubulin Is Required for Maintaining the Microtubule Network

Francis

Newman

Cunningham

et al. 2017

Journal of Biological Chemistry

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Edited by Velia M. FowlerMicrotubule dynamics involves the polymerization and depolymerization of tubulin dimers and is an essential and highly regulated process required for cell viability, architecture, and division. The regulation of the microtubule network also depends on the maintenance of a pool of ␣␤-tubulin heterodimers. These dimers are the end result of complex folding and assembly events, requiring the TCP1 Ring Complex (TriC or CCT) chaperonin and five tubulin-specific chaperones, tubulin binding cofactors A-E (TBCA-TBCE). However, models of the actions of these chaperones are incomplete or inconsistent. We previously purified TBCD from bovine tissues and showed that it tightly binds the small GTPase ARL2 but appears to be inactive. Here, in an effort to identify the functional form of TBCD and using non-denaturing gels and immunoblotting, we analyzed lysates from a number of mouse tissues and cell lines to identify the quaternary state(s) of TBCD and ARL2. We found that both proteins co-migrated in native gels in a complex of ϳ200 kDa that also contained ␤-tubulin. Using human embryonic kidney cells enabled the purification of the TBCD⅐ARL2⅐␤-tubulin trimer found in cell and tissue lysates as well as two other novel TBCD complexes. Characterization of ARL2 point mutants that disrupt binding to TBCD suggested that the ARL2-TBCD interaction is critical for proper maintenance of microtubule densities in cells. We conclude that the TBCD⅐ARL2⅐␤-tubulin trimer represents a functional complex whose activity is fundamental to microtubule dynamics.Microtubules are highly dynamic polymers that are best known for their roles as the central cytoskeletal structure in cells and in mitotic spindles during cell division. They are also the tracks on which organelles traffic, particularly important in polarized cells that generate great distances between parts of the cell. Additionally, they are the core of sensory and motile cilia or flagella. The formation and destruction of microtubules and microtubule bundles are orchestrated by a large number of proteins that include the microtubule-associated proteins. Microtubules are polymers of the ␣␤-tubulin dimer, with several genes encoding each ␣-or ␤-tubulin subunit (e.g. see Lewis et al. (1)), resulting in some diversity in composition. Tubulins can also be modified by posttranslational modifications, including acetylation, tyrosination, and phosphorylation, which can alter the dynamics of the polymerization and depolymerization reactions. Because of the essential role of microtubules in cell division, they have also been the target of many antitumor therapies, e.g. the taxanes and Vinca alkaloids (2). However, despite their importance to cells and in the clinic and decades of research, we still lack a complete molecular-level understanding of the biosynthesis and regulation of the formation of ␣␤-tubulin.Tubulins are typically the most abundant proteins in mammalian cells, but the generation of the ␣␤-tubulin dimer requires a complex series of biosynthetic steps to ...

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Section: Discussionsupporting

confidence: 53%

Section: Discussionmentioning

confidence: 97%

mentioning

confidence: 99%

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A Trimer Consisting of the Tubulin-specific Chaperone D (TBCD), Regulatory GTPase ARL2, and β-Tubulin Is Required for Maintaining the Microtubule Network

Francis

Newman

Cunningham

et al. 2017

Journal of Biological Chemistry

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“…Notably, reduced soluble α/β-tubulin levels and accelerated microtubule polymerization has been reported in fibroblasts derived from patients with biallelic TBCD mutations, while cellular proliferation was not markedly reduced. While more work is required to investigate this, the reduced rate of microtubule polymerization and cellular proliferation associated with the PRUNE mutations described here may in part provide an explanation for the more marked neurodevelopmental impairment seen in Prune syndrome patients (Edvardson et al , 2016; Flex et al , 2016; Miyake et al , 2016; Pode-Shakked et al , 2016). …”

Section: Discussionmentioning

confidence: 90%

PRUNE is crucial for normal brain development and mutated in microcephaly with neurodevelopmental impairment

Zollo

Ahmed

Ferrucci

et al. 2017

Brain

104

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“…Also, a spate of recent reports describe point mutations in TBCD found in patients with links to early-onset encephalopathy [28–31] and intractable seizures [32]. A subset of these mutations were specifically shown to disrupt formation and stability of the TBCD•ARL2•β-tubulin complex [29], which we have recently purified and characterized [11].…”

Section: Introductionmentioning

confidence: 99%

Nucleotide Binding to ARL2 in the TBCD ∙ ARL2 ∙ β-Tubulin Complex Drives Conformational Changes in β-Tubulin

Francis

Goswami

Novick

et al. 2017

Journal of Molecular Biology

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Microtubules are highly dynamic tubulin polymers that are required for a variety of cellular functions. Despite the importance of a cellular population of tubulin dimers, we have incomplete information about the mechanisms involved in the biogenesis of αβ-tubulin heterodimers. In addition to prefoldin and the TCP-1 Ring Complex, five tubulin-specific chaperones, termed cofactors A-E (TBCA-E), and GTP are required for the folding of α- and β-tubulin subunits and assembly into heterodimers. We recently described the purification of a novel trimer, TBCD•ARL2•β-tubulin. Here, we employed hydrogen/deuterium exchange coupled with mass spectrometry to explore the dynamics of each of the proteins in the trimer. Addition of guanine nucleotides resulted in changes in the solvent accessibility of regions of each protein that led to predictions about each’s role in tubulin folding. Initial testing of that model confirmed that it is ARL2, and not β-tubulin, that exchanges GTP in the trimer. Comparisons of the dynamics of ARL2 monomer to ARL2 in the trimer suggested that its protein interactions were comparable to those of a canonical GTPase with an effector. This was supported by the use of nucleotide binding assays that revealed an increase in the affinity for GTP by ARL2 in the trimer. We conclude that the TBCD•ARL2•β-tubulin complex represents a functional intermediate in the β-tubulin folding pathway whose activity is regulated by the cycling of nucleotides on ARL2. The co-purification of guanine nucleotide on the β-tubulin in the trimer is also shown, with implications to modeling the pathway.

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Microcephaly, intractable seizures and developmental delay caused by biallelic variants in TBCD: further delineation of a new chaperone‐mediated tubulinopathy

Cited by 26 publications

References 31 publications

A Trimer Consisting of the Tubulin-specific Chaperone D (TBCD), Regulatory GTPase ARL2, and β-Tubulin Is Required for Maintaining the Microtubule Network

A Trimer Consisting of the Tubulin-specific Chaperone D (TBCD), Regulatory GTPase ARL2, and β-Tubulin Is Required for Maintaining the Microtubule Network

PRUNE is crucial for normal brain development and mutated in microcephaly with neurodevelopmental impairment

Nucleotide Binding to ARL2 in the TBCD ∙ ARL2 ∙ β-Tubulin Complex Drives Conformational Changes in β-Tubulin

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