Sturgill Emma G, Das Dibyendu Kumar, Takizawa Yoshimasa, Shin Yongdae, Collier Scott E, Ohi Melanie D, Hwang Wonmuk, Lang Matthew J, Ohi Ryoma
Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37235, USA.
Curr Biol. 2014 Oct 6;24(19):2307-13. doi: 10.1016/j.cub.2014.08.022. Epub 2014 Sep 25.
Proteins that recognize and act on specific subsets of microtubules (MTs) enable the varied functions of the MT cytoskeleton. We recently discovered that Kif15 localizes exclusively to kinetochore fibers (K-fibers) or bundles of kinetochore-MTs within the mitotic spindle. It is currently speculated that the MT-associated protein TPX2 loads Kif15 onto spindle MTs, but this model has not been rigorously tested. Here, we show that Kif15 accumulates on MT bundles as a consequence of two inherent biochemical properties. First, Kif15 is self-repressed by its C terminus. Second, Kif15 harbors a nonmotor MT-binding site, enabling dimeric Kif15 to crosslink and slide MTs. Two-MT binding activates Kif15, resulting in its accumulation on and motility within MT bundles but not on individual MTs. We propose that Kif15 targets K-fibers via an intrinsic two-step mechanism involving molecular unfolding and two-MT binding. This work challenges the current model of Kif15 regulation and provides the first account of a kinesin that specifically recognizes a higher-order MT array.
能够识别并作用于特定微管（MT）亚群的蛋白质，实现了MT细胞骨架的多种功能。我们最近发现，Kif15仅定位于有丝分裂纺锤体中的动粒纤维（K纤维）或动粒MT束。目前推测，MT相关蛋白TPX2将Kif15加载到纺锤体MT上，但该模型尚未经过严格测试。在这里，我们表明，由于两个固有的生化特性，Kif15在MT束上积累。首先，Kif15的C末端自我抑制。其次，Kif15含有一个非运动性MT结合位点，使二聚体Kif15能够交联并滑动MT。双MT结合激活Kif15，导致其在MT束上积累并在其中运动，但不在单个MT上。我们提出，Kif15通过一种内在的两步机制靶向K纤维，该机制涉及分子解折叠和双MT结合。这项工作挑战了目前Kif15调控的模型，并首次阐述了一种特异性识别高阶MT阵列的驱动蛋白。
