Department of Molecular Biology, Princeton University, Princeton, New Jersey, 08544, USA.
Department of Biomedical Engineering, Washington University, Brauer Hall, One Brookings Drive, Saint Louis, Missouri, 63130, USA.
Nat Commun. 2020 Jan 14;11(1):270. doi: 10.1038/s41467-019-14087-0.
Phase separation of substrates and effectors is proposed to enhance biological reaction rates and efficiency. Targeting protein for Xklp2 (TPX2) is an effector of branching microtubule nucleation in spindles and functions with the substrate tubulin by an unknown mechanism. Here we show that TPX2 phase separates into a co-condensate with tubulin, which mediates microtubule nucleation in vitro and in isolated cytosol. TPX2-tubulin co-condensation preferentially occurs on pre-existing microtubules, the site of branching microtubule nucleation, at the endogenous and physiologically relevant concentration of TPX2. Truncation and chimera versions of TPX2 suggest that TPX2-tubulin co-condensation enhances the efficiency of TPX2-mediated branching microtubule nucleation. Finally, the known inhibitor of TPX2, the importin-α/β heterodimer, regulates TPX2 condensation in vitro and, consequently, branching microtubule nucleation activity in isolated cytosol. Our study demonstrates how regulated phase separation can simultaneously enhance reaction efficiency and spatially coordinate microtubule nucleation, which may facilitate rapid and accurate spindle formation.
底物和效应物的相分离被提议用来提高生物反应速率和效率。靶向 Xklp2（TPX2）的蛋白质是纺锤体分支微管核形成的效应物，通过未知机制与底物微管蛋白一起发挥作用。在这里，我们表明 TPX2 相分离成与微管蛋白的共凝聚物，该共凝聚物介导体外和分离胞质溶胶中的微管核形成。TPX2-微管蛋白共凝聚物优先在预先存在的微管上发生，即在分支微管核形成的部位，在 TPX2 的内源性和生理相关浓度下。TPX2 的截断和嵌合体版本表明，TPX2-微管蛋白共凝聚物提高了 TPX2 介导的分支微管核形成的效率。最后，已知的 TPX2 抑制剂，即输入蛋白-α/β 异二聚体，调节 TPX2 体外凝聚，从而调节分离胞质溶胶中的分支微管核形成活性。我们的研究表明，受调控的相分离如何同时提高反应效率和空间协调微管核形成，这可能有助于快速和准确的纺锤体形成。
