The Kinesin-12 Kif15 is a processive track-switching tetramer.
The Kinesin-12 Kif15 is a processive track-switching tetramer.
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DOI：
10.7554/elife.01724
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发表时间：
2014-03-25
期刊：
影响因子：
7.7
通讯作者：
McAinsh AD
中科院分区：
文献类型：
--
作者：
Drechsler H;McHugh T;Singleton MR;Carter NJ;McAinsh AD
驱动蛋白 12 马达是驱动蛋白超家族中一个研究较少的分支，其人类蛋白 (Kif15) 与纺锤体力学和染色体运动有关。在这项研究中，我们在体外重建了全长 hKif15 及其微管靶向因子 hTpx2，以深入了解电机的运行模式。我们发现 hKif15 是一种正端定向的加工同四聚体，可以抵抗高达 3.5 pN 的负载。我们进一步表明，hKif15 是第一个能够在交叉点有效切换微管轨道的驱动蛋白，使其能够导航微管网络，例如纺锤体。 hKif15 四聚体也能够交联微管，但出乎意料的是，这并不依赖于 hTpx2。相反，我们发现 hTpx2 在微管结合时抑制 hKif15 步进。我们的数据表明，hKif15 是除驱动蛋白 5 Eg5 之外的第二个四聚体纺锤体马达，并提供了对 hKif15 及其抑制剂 hTpx2 调节纺锤体微管结构的机制的见解。 DOI：http://dx.doi.org/10.7554/eLife.01724.001 在细胞分裂之前，它会产生所有染色体的额外副本，然后必须确保每个子细胞最终拥有每条染色体的一个副本。在分裂过程中，细胞中形成一种称为纺锤体的结构。这个纺锤体由称为微管的线状延伸组成，微管从细胞两端的两个极点生长。这些微管负责让染色体在细胞中间排列，然后将一半染色体拉到细胞的一端，另一半拉到另一端。然后细胞分裂成两个子细胞。两种运动蛋白（之所以如此命名，是因为它们消耗化学能沿着微管“行走”）在此过程中发挥着重要作用：Kif11 运动蛋白主要驱动纺锤体的形成，从而驱动染色体的分裂。不含 Kif11 的细胞只有在含有称为 Kif15 的第二种运动蛋白的额外拷贝时才能分裂：这表明 Kif15 可以作为 Kif11 的某种后备。正常细胞仅在需要新细胞生长或取代已死亡的旧细胞时才会分裂。另一方面，癌细胞以不受控制的方式分裂。干扰 Kif11 的药物已经被开发出来，希望它们能够阻止癌细胞分裂，但这些药物在临床测试中并不是非常有效，可能是由于 Kif15 的备份。因此，科学家希望更好地了解 Kif15 的作用可能会改善癌症治疗。德雷克斯勒等人。分离出单个 Kif15 运动蛋白，并使用先进的显微镜技术来研究它们的作用。这些实验表明，Kif15 运动蛋白可以沿着单个微管长距离移动，并且还可以在交叉点切换到不同的微管。当 Kif15 碰到位于微管上的 Tpx2 蛋白时，Kif15 的这种运动就会停止。这些蛋白质还可以一起在微管之间形成能够承受高力的连接。这些特性为了解 Kif15 如何在细胞中充当 Kif11 的备份提供了起点。未来，弄清楚 Kif11 和 Kif15 运动蛋白如何协同工作来构建纺锤体将非常重要。 DOI：http://dx.doi.org/10.7554/eLife.01724.002
Kinesin-12 motors are a little studied branch of the kinesin superfamily with the human protein (Kif15) implicated in spindle mechanics and chromosome movement. In this study, we reconstitute full-length hKif15 and its microtubule-targeting factor hTpx2 in vitro to gain insight into the motors mode of operation. We reveal that hKif15 is a plus-end-directed processive homotetramer that can step against loads of up to 3.5 pN. We further show that hKif15 is the first kinesin that effectively switches microtubule tracks at intersections, enabling it to navigate microtubule networks, such as the spindle. hKif15 tetramers are also capable of cross-linking microtubules, but unexpectedly, this does not depend on hTpx2. Instead, we find that hTpx2 inhibits hKif15 stepping when microtubule-bound. Our data reveal that hKif15 is a second tetrameric spindle motor in addition to the kinesin-5 Eg5 and provides insight into the mechanisms by which hKif15 and its inhibitor hTpx2 modulate spindle microtubule architecture. DOI: http://dx.doi.org/10.7554/eLife.01724.001 Before a cell can divide, it produces an extra copy of all its chromosomes, and it must then ensure that each daughter cell ends up with one copy of each chromosome. During the division process, a structure called the spindle forms in the cell. This spindle is made of thread-like extensions called microtubules that grow from two poles at opposite ends of the cell. These microtubules are responsible for getting the chromosomes to line up in the middle of the cell, and then pulling half of the chromosomes to one end of the cell, and half to the other end. The cell then divides into two daughter cells. Two motor proteins—so-called because they consume chemical energy to ‘walk’ along the microtubules—have important roles in this process: Kif11 motor proteins mainly drive the formation of the spindle and thus division of the chromosomes. A cell that does not contain Kif11 can only divide if it contains extra copies of a second motor protein called Kif15: this suggests that Kif15 can serve as some sort of back up for Kif11. Normal cells only divide when new cells are needed for growth or to replace old cells that have died. Cancer cells, on the other hand, divide in a way that is not controlled. Drugs that interfere with Kif11 have been developed in the hope that they will stop cancer cells dividing, but these drugs have not been very effective in clinical tests, possibly due to the Kif15 back up. Scientists hope, therefore, that a better understanding of the role of Kif15 may lead to improved cancer treatments. Drechsler et al. have isolated individual Kif15 motor proteins and used advanced microscopy techniques to study them in action. These experiments showed that Kif15 motor proteins can travel long distances along a single microtubule, and can also switch to a different microtubule at intersections. This movement of Kif15 is stopped when they bump into Tpx2 proteins, which are sitting on the microtubules. Together, these proteins can also form links between microtubules that can withstand high forces. These properties provide a starting point to understand how Kif15 can act as a back up for Kif11 in cells. In the future, it will be important to work out how Kif11 and Kif15 motor proteins work together in teams to build the spindle. DOI: http://dx.doi.org/10.7554/eLife.01724.002