微管是細(xì)胞骨架的一個(gè)重要組成部分,在活體中通常是在一個(gè)由γ-微管蛋白復(fù)合物構(gòu)成的核心周圍以13個(gè)原始細(xì)絲(protoflilament)為一組的形式來組織的,。
這一精確的幾何是怎樣控制的仍不清楚?,F(xiàn)在,由普遍保守的核心微管核化復(fù)合物“γ-微管蛋白小復(fù)合物” (γTuSC)構(gòu)成的高級(jí)組合體(從釀酒酵母中分離出)的結(jié)構(gòu)已利用冷電子顯微鏡被確定,。該結(jié)構(gòu)為了解γTuSC是怎樣建立13重的微管蛋白對(duì)稱性的提供了線索。(生物谷Bioon.com)
生物谷推薦原文出處:
Nature doi:10.1038/nature09207
Microtubule nucleating γ-TuSC assembles structures with 13-fold microtubule-like symmetry
Justin M. Kollman,Jessica K. Polka,Alex Zelter,Trisha N. Davis& David A. Agard
Microtubules are nucleated in vivo by γ-tubulin complexes. The 300-kDa γ-tubulin small complex (γ-TuSC), consisting of two molecules of γ-tubulin and one copy each of the accessory proteins Spc97 and Spc98, is the conserved, essential core of the microtubule nucleating machinery1, 2. In metazoa multiple γ-TuSCs assemble with other proteins into γ-tubulin ring complexes (γ-TuRCs). The structure of γ-TuRC indicated that it functions as a microtubule template2, 3, 4, 5. Because each γ-TuSC contains two molecules of γ-tubulin, it was assumed that the γ-TuRC-specific proteins are required to organize γ-TuSCs to match 13-fold microtubule symmetry. Here we show that Saccharomyces cerevisiae γ-TuSC forms rings even in the absence of other γ-TuRC components. The yeast adaptor protein Spc110 stabilizes the rings into extended filaments and is required for oligomer formation under physiological buffer conditions. The 8-? cryo-electron microscopic reconstruction of the filament reveals 13 γ-tubulins per turn, matching microtubule symmetry, with plus ends exposed for interaction with microtubules, implying that one turn of the filament constitutes a microtubule template. The domain structures of Spc97 and Spc98 suggest functions for conserved sequence motifs, with implications for the γ-TuRC-specific proteins. The γ-TuSC filaments nucleate microtubules at a low level, and the structure provides a strong hypothesis for how nucleation is regulated, converting this less active form to a potent nucleator.