des Georges Amédée, Katsuki Miho, Drummond Douglas R, Osei Michael, Cross Robert A, Amos Linda A
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.
Nat Struct Mol Biol. 2008 Oct;15(10):1102-8. doi: 10.1038/nsmb.1482. Epub 2008 Sep 14.
In vitro studies of pure tubulin have suggested that tubulin heterodimers in cells assemble into B-lattice microtubules, where the 8-nm dimers in adjacent protofilaments are staggered by 0.9 nm. This arrangement requires the tube to close by forming a seam with an A-lattice, in which the protofilaments are staggered by 4.9 nm. Here we show that Mal3, an EB1 family tip-tracking protein, drives tubulin to assemble in vitro into exclusively 13-protofilament microtubules with a high proportion of A-lattice protofilament contacts. We present a three-dimensional cryo-EM reconstruction of a purely A-lattice microtubule decorated with Mal3, in which Mal3 occupies the groove between protofilaments and associates closely with one tubulin monomer. We propose that Mal3 promotes assembly by binding to freshly formed tubulin polymer and particularly favors any with A-lattice arrangement. These results reopen the question of microtubule structure in cells.
对纯微管蛋白的体外研究表明，细胞中的微管蛋白异二聚体组装成B晶格微管，其中相邻原纤维中的8纳米二聚体交错0.9纳米。这种排列要求微管通过与A晶格形成一个缝来闭合，在A晶格中原纤维交错4.9纳米。在此我们表明，Mal3，一种EB1家族的尖端追踪蛋白，驱动微管蛋白在体外组装成仅含13根原纤维的微管，其中A晶格原纤维接触的比例很高。我们展示了一个用Mal3装饰的纯A晶格微管的三维冷冻电镜重建，其中Mal3占据原纤维之间的凹槽并与一个微管蛋白单体紧密结合。我们提出，Mal3通过与新形成的微管蛋白聚合物结合来促进组装，并且特别青睐具有A晶格排列的聚合物。这些结果重新开启了细胞中微管结构的问题。
