Cell and Developmental Biology Seminar Series: Deciphering the nature of the γ-tubulin ring complex using cryo-EM and biochemical reconstitutions

Cell and Developmental Biology Seminar Series

  • Date: Dec 1, 2020
  • Time: 15:00 - 16:00
  • Speaker: Michal Wieczorek
  • The Rockefeller University (Laboratory of Chemistry and Cell Biology)
  • Location: Max-Planck-Institut für biophysikalische Chemie (MPIBPC)
  • Room: online format - access data will be mailed before the seminar
  • Host: Dr. Melina Schuh
  • Contact: office.schuh@mpibpc.mpg.de
Cell and Developmental Biology Seminar Series: Deciphering the nature of the γ-tubulin ring complex using cryo-EM and biochemical reconstitutions
The formation of diverse microtubule cytoskeleton networks depends on the γ-tubulin ring complex (γ-TuRC). Discovered over 25 years ago, this essential multi-subunit protein complex is thought to facilitate microtubule assembly by mimicking a microtubule nucleation intermediate. However, the composition and stoichiometry of γ-TuRC constituents, as well as a molecular description of how these components come together to facilitate microtubule assembly, have remained mysterious since the discovery of the complex, severely limiting biochemical dissections of proposed functional models. In this talk, I will describe our recent work in generating a near-complete molecular model of the endogenous human γ-TuRC using cryo-EM. We find that the γ-TuRC adopts a cone-shaped structure ~30 nm in diameter, in which a unique arrangement of the γ-tubulin ring complex proteins (GCPs) 2-6 collectively position 14 copies of γ-tubulin into a quasi-helical “ring”. We discovered an unexpected structural feature that spans the lumen of the γ-TuRC and contains monomeric actin in complex with the microprotein MZT1. Using our structure of the endogenous complex as a guide, we also successfully reconstitute the γ-TuRC with ten recombinant human proteins. Remarkably, the γ-tubulin “rings” in both endogenous and reconstituted human γ-TuRCs do not match the arrangement of α/β-tubulin in the microtubule lattice, raising important questions about how the γ-TuRC regulates microtubule formation in cells. Our near-complete molecular picture of the γ-TuRC solves several long-standing puzzles in the cytoskeleton field and paves the way towards functional studies of this intriguing complex using bottom-up approaches.
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