title: The structure of the complex between α-tubulin, TBCE and TBCB reveals a tubulin dimer dissociation mechanism.
abstract: Tubulin proteostasis is regulated by a group of molecular chaperones termed tubulin cofactors (TBC). Whereas tubulin heterodimer formation is well-characterized biochemically, its dissociation pathway is not clearly understood. Here, we carried out biochemical assays to dissect the role of the human TBCE and TBCB chaperones in α-tubulin-β-tubulin dissociation. We used electron microscopy and image processing to determine the three-dimensional structure of the human TBCE, TBCB and α-tubulin (αEB) complex, which is formed upon α-tubulin-β-tubulin heterodimer dissociation by the two chaperones. Docking the atomic structures of domains of these proteins, including the TBCE UBL domain, as we determined by X-ray crystallography, allowed description of the molecular architecture of the αEB complex. We found that heterodimer dissociation is an energy-independent process that takes place through a disruption of the α-tubulin-β-tubulin interface that is caused by a steric interaction between β-tubulin and the TBCE cytoskeleton-associated protein glycine-rich (CAP-Gly) and leucine-rich repeat (LRR) domains. The protruding arrangement of chaperone ubiquitin-like (UBL) domains in the αEB complex suggests that there is a direct interaction of this complex with the proteasome, thus mediating α-tubulin degradation.
authors.affiliation: Departamento de Estructura de Macromoléculas, Centro Nacional de Biotecnología (CNB-CSIC), Madrid 28049, Spain.
authors.forename: Marina
authors.initials: M
authors.lastname: Serna
authors.affiliation: Departamento de Biología Molecular, Facultad de Medicina, IDIVAL-Universidad de Cantabria, Santander 39011, Spain.
authors.forename: Gerardo
authors.initials: G
authors.lastname: Carranza
authors.affiliation: Departamento de Estructura de Macromoléculas, Centro Nacional de Biotecnología (CNB-CSIC), Madrid 28049, Spain.
authors.forename: Jaime
authors.initials: J
authors.lastname: Martín-Benito
authors.affiliation: Departamento de Biología Estructural y Computacional, Institute for Research in Biomedicine (IRB-Barcelona), Barcelona 08028, Spain Departamento de Biología Estructural, Institut de Biologia Molecular de Barcelona (IBMB-CSIC), Barcelona 08028, Spain.
authors.forename: Robert
authors.initials: R
authors.lastname: Janowski
authors.affiliation: Departamento de Biología Estructural y Computacional, Institute for Research in Biomedicine (IRB-Barcelona), Barcelona 08028, Spain Departamento de Biología Estructural, Institut de Biologia Molecular de Barcelona (IBMB-CSIC), Barcelona 08028, Spain.
authors.forename: Albert
authors.initials: A
authors.lastname: Canals
authors.affiliation: Departamento de Biología Estructural y Computacional, Institute for Research in Biomedicine (IRB-Barcelona), Barcelona 08028, Spain Departamento de Biología Estructural, Institut de Biologia Molecular de Barcelona (IBMB-CSIC), Barcelona 08028, Spain.
authors.forename: Miquel
authors.initials: M
authors.lastname: Coll
authors.affiliation: Departamento de Biología Molecular, Facultad de Medicina, IDIVAL-Universidad de Cantabria, Santander 39011, Spain.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Zabala
authors.affiliation: Departamento de Estructura de Macromoléculas, Centro Nacional de Biotecnología (CNB-CSIC), Madrid 28049, Spain juan.zabala@unican.es jmv@cnb.csic.es.
authors.forename: José María
authors.initials: JM
authors.lastname: Valpuesta
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D018360:Crystallography, X-Ray; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate; D006801:Humans; D006868:Hydrolysis; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; C469270:TBCE protein, human; D014404:Tubulin; C501073:tubulin cofactor B, human; D049452:Green Fluorescent Proteins; D006160:Guanosine Triphosphate
keywords: Chaperone; Folding cofactor; Microtubule; Protein degradation; TBCB; TBCE; Tubulin