Microtubules are cytoskeletal polymers of tubulin dimers assembled into protofilaments that constitute nanotubes undergoing periods of assembly and disassembly. Static electron micrographs suggest a structural transition of straight protofilaments into curved ones occurring at the tips of disassembling microtubules. However, these structural transitions have never been observed and the process of microtubule disassembly thus remains unclear. Here, label-free optical microscopy capable of selective imaging of the transient structural changes of protofilaments at the tip of a disassembling microtubule is introduced. Upon induced disassembly, the transition of ordered protofilaments into a disordered conformation is resolved at the tip of the microtubule. Imaging the unbinding of individual tubulin oligomers from the microtubule tip reveals transient pauses and relapses in the disassembly, concurrent with enrichment of ordered protofilament segments at the microtubule tip. These findings show that microtubule disassembly is a discrete process and suggest a mechanism of switching from the disassembly to the assembly phase.

中文翻译：

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无标签的超高分辨率显微镜揭示了可拆卸微管的纳米结构波动。

微管是微管蛋白二聚体的细胞骨架聚合物，组装成原生丝，构成经历了组装和拆卸期的纳米管。静态电子显微照片表明，在分解微管的尖端出现了直原丝的结构转变为弯曲的原丝。但是，从未观察到这些结构转变，因此微管拆卸的过程仍然不清楚。在这里，介绍了一种无标记的光学显微镜，该显微镜能够选择性成像拆卸微管尖端处原丝的瞬时结构变化。在诱导拆卸时，有序的原丝向无序构象的转变在微管的尖端被分辨。对单个微管蛋白寡聚体从微管尖端的解除结合进行成像显示，在拆卸过程中出现了短暂的停顿和复发，同时微管尖端的有序原丝节段富集。这些发现表明，微管的拆卸是一个离散的过程，并提出了从拆卸到组装阶段的转换机制。