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：

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CAMSAP蛋白对微管负端识别和保护的结构模型。

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、极化和分化至关重要。在这里，我们发现 CAMSAP C 末端 CKK 结构域广泛存在于真核生物中，并自主识别微管负端。通过结合结构方法，我们揭示了哺乳动物 CKK 如何在外微管表面的原丝间界面处的两个微管蛋白二聚体之间结合。体外重组分析结合高分辨率荧光显微镜和冷冻电子断层扫描表明，CKK 优先与弯曲原丝和规则微管晶格之间的过渡区相关联。我们建议该站点原丝间界面的负端特定特征作为 CKK 负端偏好的基础。微管结合的 CKK 和驱动蛋白马达之间的空间冲突解释了 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。