The structure of the γ-tubulin small complex:: Implications of its architecture and flexibility for microtubule nucleation
The structure of the γ-tubulin small complex:: Implications of its architecture and flexibility for microtubule nucleation
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DOI：
10.1091/mbc.e07-09-0879
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发表时间：
2008-01-01
影响因子：
3.3
通讯作者：
Agard, David A.
中科院分区：
文献类型：
--
作者：
Kollman, Justin M.;Zelter, Alex;Agard, David A.
γ-微管蛋白小分子复合体是一种进化上保守的异四聚体，对微管成核至关重要。我们用电子显微镜测定了25埃分辨率的酿酒酵母伽马-TUSC结构。Gamma-TUSC是Y形的，两个手臂连接着一个细长的身体。胶体金标记法显示，两个γ-微管蛋白位于臂末端的叶状结构中，其他组分的相对取向由体内FRET确定。不同亚群的γ-TUSC的结构表明，移动臂与复合体的其余部分之间的连接具有灵活性，导致伽马-微管蛋白的相对位置和方向发生变化。在所有的结构中，伽马微管蛋白是明显分开的，这种构型与微管晶格不相容。在分离的Gamma-TUSC中，γ-微管蛋白的分离可能在抑制其固有的微管成核活性方面发挥作用，在Gamma-TUSC被掺入更高阶的复合体或定位于微管组织中心之前，这种作用相对较弱。我们认为，需要移动臂的进一步运动才能使伽马微管蛋白在微管样相互作用中聚集在一起，并为微管生长提供模板。
The gamma-tubulin small complex (gamma-TuSC) is an evolutionarily conserved heterotetramer essential for microtubule nucleation. We have determined the structure of the Saccharomyces cerevisiae gamma-TuSC at 25-angstrom resolution by electron microscopy. gamma-TuSC is Y-shaped, with an elongated body connected to two arms. Gold labeling showed that the two gamma-tubulins are located in lobes at the ends of the arms, and the relative orientations of the other gamma-TuSC components were determined by in vivo FRET. The structures of different subpopulations of gamma-TuSC indicate flexibility in the connection between a mobile arm and the rest of the complex, resulting in variation of the relative positions and orientations of the gamma-tubulins. In all of the structures, the gamma-tubulins are distinctly separated, a configuration incompatible with the microtubule lattice. The separation of the gamma-tubulins in isolated gamma-TuSC likely plays a role in suppressing its intrinsic microtubule-nucleating activity, which is relatively weak until the gamma-TuSC is incorporated into higher order complexes or localized to microtubule-organizing centers. We propose that further movement of the mobile arm is required to bring the gamma-tubulins together in microtubule-like interactions, and provide a template for microtubule growth.