Telomeric shelterin complex caps chromosome ends and plays a crucial role in telomere maintenance and protection. In the fission yeast Schizosaccharomyces pombe, shelterin is composed of telomeric single- and double-stranded DNA-binding protein subcomplexes Pot1-Tpz1 and Taz1-Rap1, which are bridged by their interacting protein Poz1. However, the structure of Poz1 and how Poz1 functions as an interaction hub in the shelterin complex remain unclear. Here we report the crystal structure of Poz1 in complex with Poz1-binding motifs of Tpz1 and Rap1. The crystal structure shows that Poz1 employs two different binding surfaces to interact with Tpz1 and Rap1. Unexpectedly, the structure also reveals that Poz1 adopts a dimeric conformation. Mutational analyses suggest that proper interactions between Tpz1, Poz1, and Rap1 in the shelterin core complex are required for telomere length homeostasis and heterochromatin structure maintenance at telomeres. Structural resemblance between Poz1 and the TRFH domains of other shelterin proteins in fission yeast and humans suggests a model for the evolution of shelterin proteins.

中文翻译：

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裂变酵母粟酒裂殖酵母端粒Tpz1-Poz1-Rap1复合物的结构。

端粒庇护蛋白复合物使染色体末端加盖，并在端粒的维护和保护中起着至关重要的作用。在裂殖酵母粟酒裂殖酵母中，庇护素由端粒的单链和双链DNA结合蛋白亚复合物Pot1-Tpz1和Taz1-Rap1组成，​​它们通过相互作用的蛋白质Poz1桥接。但是，尚不清楚Poz1的结构以及Poz1如何在庇护所复合体中充当交互枢纽。在这里，我们报告Poz1的晶体结构与Tpz1和Rap1的Poz1结合基序复杂。晶体结构表明Poz1使用两个不同的结合表面与Tpz1和Rap1相互作用。出乎意料的是，该结构还揭示了Poz1采用二聚体构象。突变分析表明，Tpz1，Poz1，端粒长度的稳态和端粒异质染色质结构的维持需要庇护素核心复合物中的Rap1和Rap1。裂殖酵母和人体内Poz1与其他胶体蛋白的TRFH结构域之间的结构相似性为胶体蛋白进化提供了模型。