Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck, University of London, London, UK.
Nat Struct Mol Biol. 2018 Jul;25(7):607-615. doi: 10.1038/s41594-018-0087-8. Epub 2018 Jul 2.
Microtubules form from longitudinally and laterally assembling tubulin α-β dimers. The assembly induces strain in tubulin, resulting in cycles of microtubule catastrophe and regrowth. This 'dynamic instability' is governed by GTP hydrolysis that renders the microtubule lattice unstable, but it is unclear how. We used a human microtubule nucleating and stabilizing neuronal protein, doublecortin, and high-resolution cryo-EM to capture tubulin's elusive hydrolysis intermediate GDP•Pi state, alongside the prehydrolysis analog GMPCPP state and the posthydrolysis GDP state with and without an anticancer drug, Taxol. GTP hydrolysis to GDP•Pi followed by Pi release constitutes two distinct structural transitions, causing unevenly distributed compressions of tubulin dimers, thereby tightening longitudinal and loosening lateral interdimer contacts. We conclude that microtubule catastrophe is triggered because the lateral contacts can no longer counteract the strain energy stored in the lattice, while reinforcement of the longitudinal contacts may support generation of force.
微管由α-β 微管蛋白二聚体纵向和横向组装而成。组装会使微管蛋白产生应变，导致微管的灾难性崩溃和再生循环。这种“动态不稳定性”受 GTP 水解的控制，使微管晶格不稳定，但尚不清楚具体原因。我们使用了一种人类微管成核和稳定神经元的蛋白——双皮质蛋白，并用高分辨率 cryo-EM 捕获了微管难以捉摸的水解中间体 GDP•Pi 状态，以及预水解类似物 GMPCPP 状态和水解后 GDP 状态，同时还结合了抗癌药物紫杉醇。GTP 水解为 GDP•Pi 后释放 Pi 构成了两个截然不同的结构转变，导致微管二聚体不均匀压缩，从而使纵向相互作用紧密，侧向相互作用变松。我们的结论是，微管的灾难性崩溃是由于侧向相互作用不再能够抵消晶格中储存的应变能，而纵向相互作用的加强可能支持力的产生。
