CAMSAP and Patronin family members regulate microtubule minus-end stability and localization and thus organize noncentrosomal microtubule networks, which are essential for cell division, polarization and differentiation. Here, we found that the CAMSAP C-terminal CKK domain is widely present among eukaryotes and autonomously recognizes microtubule minus ends. Through a combination of structural approaches, we uncovered how mammalian CKK binds between two tubulin dimers at the interprotofilament interface on the outer microtubule surface. In vitro reconstitution assays combined with high-resolution fluorescence microscopy and cryo-electron tomography suggested that CKK preferentially associates with the transition zone between curved protofilaments and the regular microtubule lattice. We propose that minus-end-specific features of the interprotofilament interface at this site serve as the basis for CKK's minus-end preference. The steric clash between microtubule-bound CKK and kinesin motors explains how CKK protects microtubule minus ends against kinesin-13-induced depolymerization and thus controls the stability of free microtubule minus ends.

中文翻译：

---

CAMSAP蛋白识别和保护微管负端的结构模型

CAMSAP和Patronin家族成员调节微管负端稳定性和定位，从而组织非中心体微管网络，这对于细胞分裂，极化和分化必不可少。在这里，我们发现CAMSAP C端CKK域广泛存在于真核生物之间，并自主识别微管负端。通过结构方法的组合，我们发现了哺乳动物CKK如何在微管外表面的原丝间界面处的两个微管蛋白二聚体之间结合。体外重组分析与高分辨率荧光显微镜和低温电子断层扫描相结合，表明CKK优先与弯曲的原丝和规则的微管格之间的过渡区相关联。我们建议在此站点的protofilament接口的负端特定功能可作为CKK负端优先选择的基础。微管结合的CKK和驱动蛋白马达之间的空间冲突说明了CKK如何保护微管负端免受驱动蛋白13诱导的解聚，从而控制游离微管负端的稳定性。