The microtubule polymerase Stu2 promotes oligomerization of the γ-TuSC for cytoplasmic microtubule nucleation.

Judith Gunzelmann,Tien-Chen Lin,Elmar Schiebel,Diana Rüthnick,Ursula Jäkle,Annett Neuner,Wanlu Zhang

doi:10.7554/elife.39932

Judith Gunzelmann, Tien-Chen Lin + Show 5 more

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https://doi.org/10.7554/elife.39932

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Journal: eLife	Publication Date: Sep 17, 2018
Citations: 59	License type: CC BY 4.0

Affiliation: DKFZ-ZMBH Alliance, Heidelberg University

Abstract

Stu2/XMAP215/ZYG-9/Dis1/Alp14/Msps/ch-TOG family members in association with with γ-tubulin complexes nucleate microtubules, but we know little about the interplay of these nucleation factors. Here, we show that the budding yeast Stu2 in complex with the γ-tubulin receptor Spc72 nucleates microtubules in vitro without the small γ-tubulin complex (γ-TuSC). Upon γ-TuSC addition, Stu2 facilitates Spc72-γ-TuSC interaction by binding to Spc72 and γ-TuSC. Stu2 together with Spc72-γ-TuSC increases microtubule nucleation in a process that is dependent on the TOG domains of Stu2. Importantly, these activities are also important for microtubule nucleation in vivo. Stu2 stabilizes Spc72-γ-TuSC at the minus end of cytoplasmic microtubules (cMTs) and an in vivo assay indicates that cMT nucleation requires the TOG domains of Stu2. Upon γ-tubulin depletion, we observed efficient cMT nucleation away from the spindle pole body (SPB), which was dependent on Stu2. Thus, γ-TuSC restricts cMT assembly to the SPB whereas Stu2 nucleates cMTs together with γ-TuSC and stabilizes γ-TuSC at the cMT minus end.

Highlights

Microtubules (MTs) are cylindrical polymers composed of tubulin, a heterodimer of a- and b-tubulin, with b-tubulin facing the more dynamic MT plus end and a-tubulin the less dynamic MT minus end (Mitchison, 1993)
One factor that promotes MT nucleation and that resides at the MT minus end is the g-tubulin complex, which is composed of g-tubulin and additional g-tubulin complex proteins (GCPs) (Zheng et al, 1995)
We show that the purified Spc72N–Stu2 complex assembles MTs from a/b-tubulin subunits in the form of asters in the absence of g-tubulin small complex (g-TuSC)

Summary

Introduction

Microtubules (MTs) are cylindrical polymers composed of tubulin, a heterodimer of a- and b-tubulin, with b-tubulin facing the more dynamic MT plus end and a-tubulin the less dynamic MT minus end (Mitchison, 1993). One factor that promotes MT nucleation and that resides at the MT minus end is the g-tubulin complex, which is composed of g-tubulin and additional g-tubulin complex proteins (GCPs) (Zheng et al, 1995). The g-TuSC oligomerizes into a left-handed spiral upon interaction with the g-tubulin receptor protein Spc110 at the nuclear side of the yeast spindle pole body (SPB) (Geissler et al, 1996; Knop and Schiebel, 1997, 1998; Kollman et al, 2010; Nguyen et al, 1998). Through the interaction of g-tubulin with a/b-tubulin, the kinetic barrier of a/b-tubulin oligomerization is overcome and MT assembly is facilitated (Kollman et al, 2011; Roostalu and Surrey, 2017)

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