Ring closure activates yeast [gamma]TuRC for species-specific microtubule nucleation

• Published in: Nature structural & molecular biology Vol. 22; no. 2; p. 132
• Main Authors: Kollman, Justin M, Greenberg, Charles H, Li, Sam, Moritz, Michelle, Zelter, Alex, Fong, Kimberly K, Fernandez, Jose-jesus, Sali, Andrej, Kilmartin, John, Davis, Trisha N, Agard, David A
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group 01.02.2015
• ISSN: 1545-9993; 1545-9985
• DOI: 10.1038/nsmb.2953

The γ-tubulin ring complex (γTuRC) is the primary microtubule nucleator in cells. γγTuRC is assembled from repeating γγ-tubulin small complex (γTuSC) subunits and is thought to function as a template by presenting a γ-tubulin ring that mimics microtubule geometry. However, a previous yeast γTuRC structure showed γTuSC in an open conformation that prevents matching to microtubule symmetry. By contrast, we show here that γ-tubulin complexes are in a closed conformation when attached to microtubules. To confirm the functional importance of the closed γTuSC ring, we trapped the closed state and determined its structure, showing that the γ-tubulin ring precisely matches microtubule symmetry and providing detailed insight into γTuRC architecture. Importantly, the closed state is a stronger nucleator, thus suggesting that this conformational switch may allosterically control γTuRC activity. Finally, we demonstrate that γTuRCs have a strong preference for tubulin from the same species.