CM1-driven assembly and activation of yeast ?-tubulin small complex underlies microtubule nucleation.

Microtubule (MT) nucleation is regulated by the ?-tubulin ring complex (?TuRC), conserved from yeast to humans. In Saccharomyces cerevisiae, ?TuRC is composed of seven identical ?-tubulin small complex (?TuSC) sub-assemblies, which associate helically to template MT growth. ?TuRC assembly provides a key point of regulation for the MT cytoskeleton. Here, ...
we combine crosslinking mass spectrometry, X-ray crystallography, and cryo-EM structures of both monomeric and dimeric ?TuSCs, and open and closed helical ?TuRC assemblies in complex with Spc110p to elucidate the mechanisms of ?TuRC assembly. ?TuRC assembly is substantially aided by the evolutionarily conserved CM1 motif in Spc110p spanning a pair of adjacent ?TuSCs. By providing the highest resolution and most complete views of any ?TuSC assembly, our structures allow phosphorylation sites to be mapped, surprisingly suggesting that they are mostly inhibitory. A comparison of our structures with the CM1 binding site in the human ?TuRC structure at the interface between GCP2 and GCP6 allows for the interpretation of significant structural changes arising from CM1 helix binding to metazoan ?TuRC.
Mesh Terms:
Antigens, Nuclear, Binding Sites, Calmodulin-Binding Proteins, Cryoelectron Microscopy, Crystallography, X-Ray, Cytoskeletal Proteins, Humans, Mass Spectrometry, Microtubule-Organizing Center, Microtubules, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Tubulin
Elife
Date: Dec. 05, 2020
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