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Cell. 2020 Jan 9;180(1):165-175.e16. doi: 10.1016/j.cell.2019.12.007. Epub 2019 Dec 17.

Asymmetric Molecular Architecture of the Human γ-Tubulin Ring Complex.

Author information

1
Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
2
Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA; Laboratory of Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
3
Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.
4
Laboratory of Chemistry and Cell Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA. Electronic address: kapoor@rockefeller.edu.

Abstract

The γ-tubulin ring complex (γ-TuRC) is an essential regulator of centrosomal and acentrosomal microtubule formation, yet its structure is not known. Here, we present a cryo-EM reconstruction of the native human γ-TuRC at ∼3.8 Å resolution, revealing an asymmetric, cone-shaped structure. Pseudo-atomic models indicate that GCP4, GCP5, and GCP6 form distinct Y-shaped assemblies that structurally mimic GCP2/GCP3 subcomplexes distal to the γ-TuRC "seam." We also identify an unanticipated structural bridge that includes an actin-like protein and spans the γ-TuRC lumen. Despite its asymmetric architecture, the γ-TuRC arranges γ-tubulins into a helical geometry poised to nucleate microtubules. Diversity in the γ-TuRC subunits introduces large (>100,000 Å2) surfaces in the complex that allow for interactions with different regulatory factors. The observed compositional complexity of the γ-TuRC could self-regulate its assembly into a cone-shaped structure to control microtubule formation across diverse contexts, e.g., within biological condensates or alongside existing filaments.

KEYWORDS:

GCP2; GCP3; GCP4; GCP5; GCP6; actin; microtubule nucleation; microtubules; single particle cryo-EM; γ-tubulin ring complex

PMID:
31862189
PMCID:
PMC7027161
[Available on 2021-01-09]
DOI:
10.1016/j.cell.2019.12.007

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