Wang Hong-Wei, Nogales Eva
Howard Hughes Medical Institute, University of California Berkeley, Berkeley, California 94720-3200, USA.
Nature. 2005 Jun 16;435(7044):911-5. doi: 10.1038/nature03606.
The atomic structure of tubulin in a polymerized, straight protofilament is clearly distinct from that in a curved conformation bound to a cellular depolymerizer. The nucleotide contents are identical, and in both cases the conformation of the GTP-containing, intra-dimer interface is indistinguishable from the GDP-containing, inter-dimer contact. Here we present two structures corresponding to the start and end points in the microtubule polymerization and hydrolysis cycles that illustrate the consequences of nucleotide state on longitudinal and lateral assembly. In the absence of depolymerizers, GDP-bound tubulin shows distinctive intra-dimer and inter-dimer interactions and thus distinguishes the GTP and GDP interfaces. A cold-stable tubulin polymer with the non-hydrolysable GTP analogue GMPCPP, containing semi-conserved lateral interactions, supports a model in which the straightening of longitudinal interfaces happens sequentially, starting with a conformational change after GTP binding that straightens the dimer enough for the formation of lateral contacts into a non-tubular intermediate. Closure into a microtubule does not require GTP hydrolysis.
聚合形成的直原丝中微管蛋白的原子结构与结合细胞解聚剂的弯曲构象中的微管蛋白原子结构明显不同。核苷酸含量相同，并且在这两种情况下，含GTP的二聚体内界面的构象与含GDP的二聚体间接触的构象无法区分。在这里，我们展示了对应于微管聚合和解聚循环起点和终点的两种结构，这些结构说明了核苷酸状态对纵向和横向组装的影响。在没有解聚剂的情况下，结合GDP的微管蛋白表现出独特的二聚体内和二聚体间相互作用，从而区分了GTP和GDP界面。一种含有不可水解的GTP类似物GMPCPP且具有半保守横向相互作用的冷稳定微管蛋白聚合物，支持了这样一种模型，即纵向界面的伸直是顺序发生的，从GTP结合后的构象变化开始，这种变化使二聚体伸直，足以形成横向接触，进而形成非管状中间体。封闭形成微管并不需要GTP水解。
