The proper structural organization of the microtubule-based spindle during cell division requires the collective activity of many different types of proteins. These include non-motor microtubule-associated proteins (MAPs) whose functions include crosslinking microtubules to regulate filament sliding rates and assembling microtubule arrays. One such protein is PRC1, an essential MAP that has been shown to preferentially crosslink overlapping antiparallel microtubules at the spindle midzone. PRC1 has been proposed to act as a molecular brake, but insight into the mechanism of how PRC1 molecules function cooperatively to resist motor-driven microtubule sliding and to allow for the formation of stable midzone overlaps has been lacking. Here we employ a modified microtubule gliding assay to rupture PRC1-mediated microtubule pairs using surface-bound kinesins. We discovered that PRC1 crosslinks always reduce bundled filament sliding velocities relative to single microtubule gliding rates, and do so via two distinct emergent modes of mechanical resistance to motor-driven sliding. We term these behaviors braking and coasting, where braking events exhibit substantially slowed microtubule sliding compared to coasting events. Strikingly, braking behavior requires the formation of two distinct high-density clusters of PRC1 molecules near microtubule tips. Our results suggest a cooperative mechanism for PRC1 accumulation when under mechanical load that leads to a unique state of enhanced resistance to filament sliding and provides insight into collective protein ensemble behavior in regulating the mechanics of spindle assembly.

中文翻译：

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PRC1介导的对驱动蛋白驱动的微管网络破坏的机械抵抗的两种模式。

基于微管的纺锤体在细胞分裂过程中的适当结构组织需要许多不同类型蛋白质的共同活性。这些包括非运动微管相关蛋白（MAP），其功能包括交联微管以调节细丝滑动速率和组装微管阵列。一种这样的蛋白是PRC1，PRC1是一种必需的MAP，已显示它可以在纺锤体中部优先交联重叠的反平行微管。已经提出了PRC1起分子制动器的作用，但是缺乏对PRC1分子如何协同作用以抵抗电机驱动的微管滑动并允许形成稳定的中间区重叠的机理的见解。在这里，我们采用改良的微管滑动试验，以使用表面结合的驱动蛋白断裂PRC1介导的微管对。我们发现，PRC1交联总是降低相对于单个微管滑动速率的成束的长丝滑动速度，并通过两种不同的机械抵抗电机驱动滑动的紧急模式来实现。我们将这些行为称为制动和惯性滑行，其中制动事件与惯性滑行事件相比表现出显着减慢的微管滑动。惊人的是，制动行为要求在微管尖端附近形成两个不同的PRC1分子高密度簇。