Tubulin Cofactors and Arl2 Are Cage-Like Chaperones That Regulate the Soluble αβ-tubulin Pool for Microtubule Dynamics

Elife. 2015 Jul 24;4:e08811. doi: 10.7554/eLife.08811.

Abstract

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.

Keywords: Arl2; GTPase; S. cerevisiae; biochemistry; biophysics; chaperone; cofactor; microtubule; structural biology; tubulin.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • ADP-Ribosylation Factors / metabolism*
  • Microscopy, Electron
  • Microtubule-Associated Proteins / metabolism*
  • Microtubules / metabolism*
  • Molecular Chaperones / metabolism*
  • Protein Multimerization*
  • Saccharomyces cerevisiae / physiology
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Tubulin / metabolism*

Substances

  • CIN1 protein, S cerevisiae
  • Microtubule-Associated Proteins
  • Molecular Chaperones
  • PAC2 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • TBCC protein, S cerevisiae
  • TBCD protein, S cerevisiae
  • TBCE protein, human
  • Tubulin
  • ARF3 protein, S cerevisiae
  • ADP-Ribosylation Factors