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Romer B, Travis SM, Mahon BP, McManus CT, Jeffrey PD, Coudray N, Raghu R, Rale MJ, Zhong ED, Bhabha G, Petry S. Conformational states of the microtubule nucleator, the γ-tubulin ring complex. bioRxiv 2023:2023.12.19.572162. [PMID: 38187763 PMCID: PMC10769196 DOI: 10.1101/2023.12.19.572162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
Microtubules (MTs) perform essential functions in the cell, and it is critical that they are made at the correct cellular location and cell cycle stage. This nucleation process is catalyzed by the γ-tubulin ring complex (γ-TuRC), a cone-shaped protein complex composed of over 30 subunits. Despite recent insight into the structure of vertebrate γ-TuRC, which shows that its diameter is wider than that of a MT, and that it exhibits little of the symmetry expected for an ideal MT template, the question of how γ-TuRC achieves MT nucleation remains open. Here, we utilized single particle cryo-EM to identify two conformations of γ-TuRC. The helix composed of 14 γ-tubulins at the top of the γ-TuRC cone undergoes substantial deformation, which is predominantly driven by bending of the hinge between the GRIP1 and GRIP2 domains of the γ-tubulin complex proteins. However, surprisingly, this deformation does not remove the inherent asymmetry of γ-TuRC. To further investigate the role of γ-TuRC conformational change, we used cryo electron-tomography (cryo-ET) to obtain a 3D reconstruction of γ-TuRC bound to a nucleated MT, providing insight into the post-nucleation state. Rigid-body fitting of our cryo-EM structures into this reconstruction suggests that the MT lattice is nucleated by spokes 2 through 14 of the γ-tubulin helix, which entails spokes 13 and 14 becoming more structured than what is observed in apo γ-TuRC. Together, our results allow us to propose a model for conformational changes in γ-TuRC and how these may facilitate MT formation in a cell.
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Affiliation(s)
- Brianna Romer
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Sophie M. Travis
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Brian P. Mahon
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- Present address: Molecular Structure and Design, Bristol Myers Squibb, Princeton, NJ, USA
| | - Collin T. McManus
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Philip D. Jeffrey
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Nicolas Coudray
- Department of Cell Biology, NYU School of Medicine, New York City, NY, USA
- Applied Bioinformatics Laboratories, NYU School of Medicine, New York, NY, USA
| | - Rishwanth Raghu
- Department of Computer Science, Princeton University, Princeton, NJ, USA
| | - Michael J. Rale
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- Present address: Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Ellen D. Zhong
- Department of Computer Science, Princeton University, Princeton, NJ, USA
| | - Gira Bhabha
- Department of Cell Biology, NYU School of Medicine, New York City, NY, USA
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
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Travis SM, Mahon BP, Huang W, Ma M, Rale MJ, Kraus J, Taylor DJ, Zhang R, Petry S. Integrated model of the vertebrate augmin complex. Nat Commun 2023; 14:2072. [PMID: 37055408 PMCID: PMC10102177 DOI: 10.1038/s41467-023-37519-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Accepted: 03/17/2023] [Indexed: 04/15/2023] Open
Abstract
Accurate segregation of chromosomes is required to maintain genome integrity during cell division. This feat is accomplished by the microtubule-based spindle. To build a spindle rapidly and with high fidelity, cells take advantage of branching microtubule nucleation, which rapidly amplifies microtubules during cell division. Branching microtubule nucleation relies on the hetero-octameric augmin complex, but lack of structure information about augmin has hindered understanding how it promotes branching. In this work, we combine cryo-electron microscopy, protein structural prediction, and visualization of fused bulky tags via negative stain electron microscopy to identify the location and orientation of each subunit within the augmin structure. Evolutionary analysis shows that augmin's structure is highly conserved across eukaryotes, and that augmin contains a previously unidentified microtubule binding site. Thus, our findings provide insight into the mechanism of branching microtubule nucleation.
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Affiliation(s)
- Sophie M Travis
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Brian P Mahon
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- Department of Structural Biology, Bristol Myers Squibb, Princeton, NJ, USA
| | - Wei Huang
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA
| | - Meisheng Ma
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, School of Medicine, St. Louis, MO, USA
- Department of Histology and Embryology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Michael J Rale
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
- Department of Cell Biology, Harvard Medical School, Boston, MA, USA
| | - Jodi Kraus
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Derek J Taylor
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA
| | - Rui Zhang
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, School of Medicine, St. Louis, MO, USA.
| | - Sabine Petry
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
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Rale MJ, Romer B, Mahon BP, Travis SM, Petry S. The conserved centrosomin motif, γTuNA, forms a dimer that directly activates microtubule nucleation by the γ-tubulin ring complex (γTuRC). eLife 2022; 11:e80053. [PMID: 36515268 PMCID: PMC9859039 DOI: 10.7554/elife.80053] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Accepted: 12/07/2022] [Indexed: 12/15/2022] Open
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.
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Affiliation(s)
- Michael J Rale
- Department of Molecular Biology, Princeton UniversityPrincetonUnited States
| | - Brianna Romer
- Department of Molecular Biology, Princeton UniversityPrincetonUnited States
| | - Brian P Mahon
- Department of Molecular Biology, Princeton UniversityPrincetonUnited States
| | - Sophie M Travis
- Department of Molecular Biology, Princeton UniversityPrincetonUnited States
| | - Sabine Petry
- Department of Molecular Biology, Princeton UniversityPrincetonUnited States
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Rale MJ, Travis S, Romer B, Mahon BP, Petry S. Cdk5rap2 dimers activate microtubule nucleation by opposing inhibitory pathways. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.2146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Thawani A, Rale MJ, Coudray N, Bhabha G, Stone HA, Shaevitz JW, Petry S. The transition state and regulation of γ-TuRC-mediated microtubule nucleation revealed by single molecule microscopy. eLife 2020; 9:e54253. [PMID: 32538784 PMCID: PMC7338055 DOI: 10.7554/elife.54253] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2019] [Accepted: 06/15/2020] [Indexed: 12/31/2022] Open
Abstract
Determining how microtubules (MTs) are nucleated is essential for understanding how the cytoskeleton assembles. While the MT nucleator, γ-tubulin ring complex (γ-TuRC) has been identified, precisely how γ-TuRC nucleates a MT remains poorly understood. Here, we developed a single molecule assay to directly visualize nucleation of a MT from purified Xenopus laevis γ-TuRC. We reveal a high γ-/αβ-tubulin affinity, which facilitates assembly of a MT from γ-TuRC. Whereas spontaneous nucleation requires assembly of 8 αβ-tubulins, nucleation from γ-TuRC occurs efficiently with a cooperativity of 4 αβ-tubulin dimers. This is distinct from pre-assembled MT seeds, where a single dimer is sufficient to initiate growth. A computational model predicts our kinetic measurements and reveals the rate-limiting transition where laterally associated αβ-tubulins drive γ-TuRC into a closed conformation. NME7, TPX2, and the putative activation domain of CDK5RAP2 h γ-TuRC-mediated nucleation, while XMAP215 drastically increases the nucleation efficiency by strengthening the longitudinal γ-/αβ-tubulin interaction.
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Affiliation(s)
- Akanksha Thawani
- Department of Chemical and Biological Engineering, Princeton UniversityPrincetonUnited States
| | - Michael J Rale
- Department of Molecular Biology, Princeton UniversityPrincetonUnited States
| | - Nicolas Coudray
- Department of Cell Biology, New York University School of MedicineNew YorkUnited States
| | - Gira Bhabha
- Department of Cell Biology, New York University School of MedicineNew YorkUnited States
| | - Howard A Stone
- Department of Mechanical and Aerospace Engineering, Princeton UniversityPrincetonUnited States
| | - Joshua W Shaevitz
- Lewis-Sigler Institute for Integrative GenomicsPrincetonUnited States
- Department of Physics, Princeton UniversityPrincetonUnited States
| | - Sabine Petry
- Department of Molecular Biology, Princeton UniversityPrincetonUnited States
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Abstract
Centrosomes are self-assembling, micron-scale, nonmembrane bound organelles that nucleate microtubules (MTs) and organize the microtubule cytoskeleton of the cell. They orchestrate critical cellular processes such as ciliary-based motility, vesicle trafficking, and cell division. Much is known about the role of the centrosome in these contexts, but we have a less comprehensive understanding of how the centrosome assembles and generates microtubules. Studies over the past 10 years have fundamentally shifted our view of these processes. Subdiffraction imaging has probed the amorphous haze of material surrounding the core of the centrosome revealing a complex, hierarchically organized structure whose composition and size changes profoundly during the transition from interphase to mitosis. New biophysical insights into protein phase transitions, where a diffuse protein spontaneously separates into a locally concentrated, nonmembrane bounded compartment, have provided a fresh perspective into how the centrosome might rapidly condense from diffuse cytoplasmic components. In this Perspective, we focus on recent findings that identify several centrosomal proteins that undergo phase transitions. We discuss how to reconcile these results with the current model of the underlying organization of proteins in the centrosome. Furthermore, we reflect on how these findings impact our understanding of how the centrosome undergoes self-assembly and promotes MT nucleation.
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Affiliation(s)
- Michael J Rale
- Department of Molecular Biology, Princeton University , Princeton, New Jersey 08544, United States
| | - Rachel S Kadzik
- Department of Molecular Biology, Princeton University , Princeton, New Jersey 08544, United States
| | - Sabine Petry
- Department of Molecular Biology, Princeton University , Princeton, New Jersey 08544, United States
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