Mechanism of how augmin directly targets the γ-tubulin ring complex to microtubules.
Mechanism of how augmin directly targets the γ-tubulin ring complex to microtubules.
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DOI：
10.1083/jcb.201711090
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发表时间：
2018-07-02
期刊：
影响因子：
--
通讯作者：
Petry S
中科院分区：
文献类型：
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作者：
Song JG;King MR;Zhang R;Kadzik RS;Thawani A;Petry S
微管可以从已经存在的微管中成核出新的微管，这对于纺锤体组装很重要，并且需要蛋白质复合物augmin。Song等人现在表明augmin在先前存在的微管和形成新微管基础的g-微管蛋白环成核复合物之间起直接桥梁的作用。微管（MT）必须从精确的位置产生，以形成细胞形状和功能所需的结构框架。MT由γ-微管蛋白环复合物（γ-TuRC）成核，但仍不清楚γ-TuRC如何到达正确的位置。Augmin已被认为是γ-TuRC靶向因子，并且是MT从预先存在的MT成核所需的。为了确定augmin的结构和功能，我们从昆虫细胞中纯化了非洲爪蟾augmin。我们证明augmin足以通过体外重建将γ-TuRC靶向MT。Augmin由两个功能部分组成。一个模块（四聚体-II）是MT结合所必需的，而另一个模块（四聚体-III）与γ-TuRC相互作用。负染色电子显微镜显示，这两个四聚体适合的Y-形状的Augmin，和MT分支试验表明，都是必要的MT成核。augmin可以通过这两个四聚体直接桥接MT与γ-TuRC的发现增加了我们对MT如何从预先存在的MT成核的机理理解。
Microtubules can nucleate new microtubules from preexisting microtubules, which is important for spindle assembly and requires the protein complex augmin. Song et al. now show that augmin functions as a direct bridge between the preexisting microtubule and the g-tubulin ring nucleation complex forming the base of the new microtubule. Microtubules (MTs) must be generated from precise locations to form the structural frameworks required for cell shape and function. MTs are nucleated by the γ-tubulin ring complex (γ-TuRC), but it remains unclear how γ-TuRC gets to the right location. Augmin has been suggested to be a γ-TuRC targeting factor and is required for MT nucleation from preexisting MTs. To determine augmin’s architecture and function, we purified Xenopus laevis augmin from insect cells. We demonstrate that augmin is sufficient to target γ-TuRC to MTs by in vitro reconstitution. Augmin is composed of two functional parts. One module (tetramer-II) is necessary for MT binding, whereas the other (tetramer-III) interacts with γ-TuRC. Negative-stain electron microscopy reveals that both tetramers fit into the Y-shape of augmin, and MT branching assays reveal that both are necessary for MT nucleation. The finding that augmin can directly bridge MTs with γ-TuRC via these two tetramers adds to our mechanistic understanding of how MTs can be nucleated from preexisting MTs.