Department of Biochemistry, Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur St., 02-093 Warsaw, Poland.
Eur J Cell Biol. 2016 Dec;95(12):521-530. doi: 10.1016/j.ejcb.2016.08.004. Epub 2016 Aug 31.
End-binding proteins are capable of tracking the plus-ends of growing microtubules (MTs). The motor protein Ncd, a member of the kinesin-14 family, interacts with EB1 protein and becomes a non-autonomous tip-tracker. Here, we attempted to find out whether at least for Ncd, the efficient EB1-mediated tip-tracking involves the interaction of the kinesin with the MT surface. We prepared a series of Ncd tail mutants in which the MT-binding sites were altered or eliminated. Using TIRF microscopy, we characterized their behavior as tip-trackers and measured the dwell times of single molecules of EB1 and Ncd tail or its mutated forms. The mutated forms of Ncd tail exhibited tip-tracking in the presence of EB1 and the effectiveness of this process was proportional to the affinity of the mutant's tail to MT. Even though the interaction of Ncd with EB1 was weak (K∼9μM) the half saturating concentration of EB1 for tip-tracking was 7nM. The dwell time of Ncd tail in the presence of EB1 was ∼1s. The dwell time of EB1 alone was shorter (∼0.3s) and increased considerably in the presence of a large excess of Ncd tail. We demonstrated that tip-tracking of kinesin-14 occurs through several concurrent mechanisms: binding of kinesin only to EB1 located at the MT end, interaction of the kinesin molecules with a composite site formed by EB1 and the MT tip, and probably surface diffusion of the tail along MT. The second mechanism seems to play a crucial role in efficient tip-tracking.
末端结合蛋白能够追踪不断生长的微管(MT)的正极。动力蛋白 Ncd 是驱动蛋白-14 家族的成员,与 EB1 蛋白相互作用,成为非自主尖端追踪器。在这里,我们试图找出至少对于 Ncd 来说,有效的 EB1 介导的尖端追踪是否涉及到马达蛋白与 MT 表面的相互作用。我们制备了一系列 Ncd 尾部突变体,其中改变或消除了 MT 结合位点。我们使用 TIRF 显微镜对其作为尖端追踪器的行为进行了表征,并测量了 EB1 和 Ncd 尾部或其突变体形式的单分子停留时间。Ncd 尾部的突变体在 EB1 的存在下表现出尖端追踪,该过程的有效性与突变体尾部与 MT 的亲和力成正比。尽管 Ncd 与 EB1 的相互作用较弱(K∼9μM),但 EB1 用于尖端追踪的半饱和浓度为 7nM。在 EB1 存在下,Ncd 尾部的停留时间约为 1s。EB1 单独的停留时间较短(约 0.3s),但在存在大量过量的 Ncd 尾部时会大大增加。我们证明,驱动蛋白-14 的尖端追踪通过几种并发机制发生:驱动蛋白仅与位于 MT 末端的 EB1 结合,驱动蛋白分子与由 EB1 和 MT 尖端形成的复合位点相互作用,以及可能沿 MT 进行尾部的表面扩散。第二种机制似乎在有效的尖端追踪中起着至关重要的作用。
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