Severing enzymes and molecular motors extract tubulin from the walls of microtubules by exerting mechanical force on subunits buried in the lattice. However, how much force is needed to remove tubulin from microtubules is not known, nor is the pathway by which subunits are removed. Using a site-specific functionalization method, we applied forces to the C-terminus of α-tubulin with an optical tweezer and found that a force of ~30 pN is required to extract tubulin from the microtubule wall. Additionally, we discovered that partial unfolding is an intermediate step in tubulin removal. The unfolding and extraction forces are similar to those generated by AAA-unfoldases. Lastly, we show that three kinesin-1 motor proteins can also extract tubulin from the microtubule lattice. Our results provide the first experimental investigation of how tubulin responds to mechanical forces exerted on its α-tubulin C-terminal tail and have implications for the mechanisms of severing enzymes and microtubule stability.

切断酶和分子马达通过对埋在晶格中的亚基施加机械力，从微管壁提取微管蛋白。然而，从微管中去除微管蛋白需要多大的力尚不清楚，亚基去除的途径也不清楚。使用位点特异性功能化方法，我们用光学镊子对 α-微管蛋白的 C 末端施加力，发现从微管壁提取微管蛋白需要约 30 pN 的力。此外，我们发现部分展开是去除微管蛋白的中间步骤。展开力和提取力类似于 AAA 展开酶产生的力。最后，我们表明三种驱动蛋白 1 运动蛋白也可以从微管晶格中提取微管蛋白。