The Cryo-Em Structure Of A Gamma-Tusc Elucidates Architecture And Regulation Of Minimal Microtubule Nucleation Systems

The nucleation of microtubules from alpha beta -tubulin subunits is mediated by gamma -tubulin complexes, which vary in composition across organisms. Aiming to understand how de novo microtubule formation is achieved and regulated by a minimal microtubule nucleation system, we here determined the cryo-electron microscopy structure of the heterotetrameric gamma -tubulin small complex (gamma -TuSC) from C. albicans at near-atomic resolution. Compared to the vertebrate gamma -tubulin ring complex (gamma -TuRC), we observed a vastly remodeled interface between the SPC/GCP-gamma -tubulin spokes, which stabilizes the complex and defines the gamma -tubulin arrangement. The relative positioning of gamma -tubulin subunits indicates that a conformational rearrangement of the complex is required for microtubule nucleation activity, which follows opposing directionality as predicted for the vertebrate gamma -TuRC. Collectively, our data suggest that the assembly and regulation mechanisms of gamma -tubulin complexes fundamentally differ between the microtubule nucleation systems in lower and higher eukaryotes. The nucleation of microtubules from alpha beta -tubulin subunits is mediated by gamma tubulin complexes, which vary in composition across organisms. Here, authors present the cryo-EM structure of the heterotetrameric gamma -tubulin small complex (gamma -TuSC) from C. albicans at near-atomic resolution.