Kerssemakers Jacob W J, Munteanu E Laura, Laan Liedewij, Noetzel Tim L, Janson Marcel E, Dogterom Marileen
Foundation for Fundamental Research on Matter (FOM) Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.
Nature. 2006 Aug 10;442(7103):709-12. doi: 10.1038/nature04928. Epub 2006 Jun 25.
Microtubules are highly dynamic protein polymers that form a crucial part of the cytoskeleton in all eukaryotic cells. Although microtubules are known to self-assemble from tubulin dimers, information on the assembly dynamics of microtubules has been limited, both in vitro and in vivo, to measurements of average growth and shrinkage rates over several thousands of tubulin subunits. As a result there is a lack of information on the sequence of molecular events that leads to the growth and shrinkage of microtubule ends. Here we use optical tweezers to observe the assembly dynamics of individual microtubules at molecular resolution. We find that microtubules can increase their overall length almost instantaneously by amounts exceeding the size of individual dimers (8 nm). When the microtubule-associated protein XMAP215 (ref. 6) is added, this effect is markedly enhanced and fast increases in length of about 40-60 nm are observed. These observations suggest that small tubulin oligomers are able to add directly to growing microtubules and that XMAP215 speeds up microtubule growth by facilitating the addition of long oligomers. The achievement of molecular resolution on the microtubule assembly process opens the way to direct studies of the molecular mechanism by which the many recently discovered microtubule end-binding proteins regulate microtubule dynamics in living cells.
微管是高度动态的蛋白质聚合物，构成了所有真核细胞细胞骨架的关键部分。尽管已知微管由微管蛋白二聚体自组装而成，但在体外和体内，关于微管组装动力学的信息都很有限，仅限于对数千个微管蛋白亚基的平均生长和收缩速率的测量。因此，缺乏关于导致微管末端生长和收缩的分子事件序列的信息。在这里，我们使用光镊以分子分辨率观察单个微管的组装动力学。我们发现微管可以几乎瞬间增加其总长度，增加量超过单个二聚体的大小（8纳米）。当添加微管相关蛋白XMAP215（参考文献6）时，这种效应会显著增强，并且观察到长度快速增加约40 - 60纳米。这些观察结果表明，小的微管蛋白寡聚体能够直接添加到生长中的微管上，并且XMAP215通过促进长寡聚体的添加来加速微管生长。在微管组装过程中实现分子分辨率为直接研究许多最近发现的微管末端结合蛋白调节活细胞中微管动力学的分子机制开辟了道路。
