The conserved centrosomin motif, γTuNA, forms a dimer that directly activates microtubule nucleation by the γ-tubulin ring complex (γTuRC).

Michael Rale, Brianna Romer, Brian P. Mahon, Sophie M. Travis, Sabine Petry

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

To establish the microtubule cytoskeleton, the cell must tightly regulate when and where microtubules are nucleated. This regulation involves controlling the initial nucleation template, the γ-tubulin ring complex (γTuRC). Although γTuRC is present throughout the cytoplasm, its activity is restricted to specific sites including the centrosome and Golgi. The well-conserved γ-tubulin nucleation activator (γTuNA) domain has been reported to increase the number of microtubules (MTs) generated by γTuRCs. However, previously we and others observed that γTuNA had a minimal effect on the activity of antibody-purified Xenopus γTuRCs in vitro (Thawani et al., eLife, 2020; Liu et al., 2020). Here we instead report, based on improved versions of γTuRC, γTuNA, and our TIRF assay, the first real-time observation that γTuNA directly increases γTuRC activity in vitro, which is thus a bona fide γTuRC activator. We further validate this effect in Xenopus egg extract. Via mutation analysis, we find that γTuNA is an obligate dimer. Moreover, efficient dimerization as well as γTuNA’s L70, F75, and L77 residues are required for binding to and activation of γTuRC. Finally, we find that γTuNA’s activating effect opposes inhibitory regulation by stathmin. In sum, our improved assays prove that direct γTuNA binding strongly activates γTuRCs, explaining previously observed effects of γTuNA expression in cells and illuminating how γTuRC-mediated microtubule nucleation is regulated.

Original languageEnglish (US)
Article numbere80053
JournaleLife
Volume11
DOIs
StatePublished - Dec 2022

All Science Journal Classification (ASJC) codes

  • General Immunology and Microbiology
  • General Biochemistry, Genetics and Molecular Biology
  • General Neuroscience

Keywords

  • CM1
  • Cdk5rap2
  • Golgi
  • Microtubules
  • centrosome
  • gamma-tubulin ring complex
  • microtubule nucleation
  • single molecule TIRF
  • γTuNA

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