Tubulin cofactors and Arl2 are cage-like chaperones that regulate the soluble αβ-tubulin pool for microtubule dynamics
Stanley Nithianantham,
Sinh Le,
Elbert Seto,
Weitao Jia,
Julie Leary,
Kevin D Corbett,
Jeffrey K Moore,
Jawdat Al-Bassam
Affiliations
Stanley Nithianantham
Department of Molecular Cellular Biology, University of California, Davis, Davis, United States
Sinh Le
Department of Molecular Cellular Biology, University of California, Davis, Davis, United States
Elbert Seto
Department of Molecular Cellular Biology, University of California, Davis, Davis, United States
Weitao Jia
Department of Molecular Cellular Biology, University of California, Davis, Davis, United States
Julie Leary
Department of Molecular Cellular Biology, University of California, Davis, Davis, United States
Kevin D Corbett
Ludwig Institute for Cancer Research, University of California, San Diego, San Diego, United States; Department of Cellular and Molecular Medicine, University of California, San Diego, San Diego, United States
Jeffrey K Moore
Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, United States
Jawdat Al-Bassam
Department of Molecular Cellular Biology, University of California, Davis, Davis, United States
Microtubule dynamics and polarity stem from the polymerization of αβ-tubulin heterodimers. Five conserved tubulin cofactors/chaperones and the Arl2 GTPase regulate α- and β-tubulin assembly into heterodimers and maintain the soluble tubulin pool in the cytoplasm, but their physical mechanisms are unknown. Here, we reconstitute a core tubulin chaperone consisting of tubulin cofactors TBCD, TBCE, and Arl2, and reveal a cage-like structure for regulating αβ-tubulin. Biochemical assays and electron microscopy structures of multiple intermediates show the sequential binding of αβ-tubulin dimer followed by tubulin cofactor TBCC onto this chaperone, forming a ternary complex in which Arl2 GTP hydrolysis is activated to alter αβ-tubulin conformation. A GTP-state locked Arl2 mutant inhibits ternary complex dissociation in vitro and causes severe defects in microtubule dynamics in vivo. Our studies suggest a revised paradigm for tubulin cofactors and Arl2 functions as a catalytic chaperone that regulates soluble αβ-tubulin assembly and maintenance to support microtubule dynamics.
