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美国加州大学Juli Feigon研究组的最新研究解析了四膜虫端粒酶结合CST与聚合酶α-primase的结构。2022年7月13日，国际学术期刊《自然》发表了这一成果。

在本研究中，研究人员在端粒酶全酶的基础上解析了四膜虫CST的冷冻电镜(cryo-EM)结构，在PolαPrim不存在和存在的情况下，以及单独的PolαPrim结构。冷冻电镜和核磁共振光谱表明四膜虫Ctc1的可变结合区与端粒酶亚基p50结合，这是TPP1的直系同源物。PolαPrim聚合酶亚基POLA1结合Ctc1和Stn1，其与Ctc1形成的界面是G链 DNA进入POLA1的活性位点入口。该研究提供了单个活性复合物中端粒DNA合成所需四个关键成分的结构基础-端粒酶核心核糖核蛋白、p50、CST 和 PolαPrim-提供了CST和PolαPrim招募以及G链之间切换和C链合成的见解。

据悉，端粒是线性染色体的物理末端。它们由短的双链DNA重复序列（例如嗜热四膜虫G链中的TTGGGG）、G单链3'突出端以及六种庇护蛋白：TPP1、POT1、TRF1、TRF2、RAP1和TIN2组成。TPP1和POT1与 3' 突出端相关联，POT1与G链结合，TPP1（与TIN24复合）通过与端粒逆转录酶5(TERT)的相互作用招募端粒酶。端粒DNA G链末端由端粒酶复制和维持，端粒DNA C链末端由DNA聚合酶α-primase (PolαPrim) 维持。PolαPrim活性受到异源三聚体复合物CTC1–STN1–TEN1 (CST)的激活，但将PolαPrim和CST招募到端粒末端的结构基础仍然未知。

附：英文原文

Title: Structure of Tetrahymena telomerase-bound CST with polymerase α-primase

Author: He, Yao, Song, He, Chan, Henry, Liu, Baocheng, Wang, Yaqiang, Suac, Lukas, Zhou, Z. Hong, Feigon, Juli

Issue&Volume: 2022-07-13

Abstract: Telomeres are the physical ends of linear chromosomes. They are composed of short repeating sequences (such as TTGGGG in the G-strand for Tetrahymena thermophila) of double-stranded DNA with a single-strand 3′ overhang of the G-strand and, in humans, the six shelterin proteins: TPP1, POT1, TRF1, TRF2, RAP1 and TIN21,2. TPP1 and POT1 associate with the 3′ overhang, with POT1 binding the G-strand3 and TPP1 (in complex with TIN24) recruiting telomerase via interaction with telomerase reverse transcriptase5 (TERT). The telomere DNA ends are replicated and maintained by telomerase6, for the G-strand, and subsequently DNA polymerase α–primase7,8 (PolαPrim), for the C-strand9. PolαPrim activity is stimulated by the heterotrimeric complex CTC1–STN1–TEN110,11,12 (CST), but the structural basis of the recruitment of PolαPrim and CST to telomere ends remains unknown. Here we report cryo-electron microscopy (cryo-EM) structures of Tetrahymena CST in the context of the telomerase holoenzyme, in both the absence and the presence of PolαPrim, and of PolαPrim alone. Tetrahymena Ctc1 binds telomerase subunit p50, a TPP1 orthologue, on a flexible Ctc1 binding motif revealed by cryo-EM and NMR spectroscopy. The PolαPrim polymerase subunit POLA1 binds Ctc1 and Stn1, and its interface with Ctc1 forms an entry port for G-strand DNA to the POLA1 active site. We thus provide a snapshot of four key components that are required for telomeric DNA synthesis in a single active complex—telomerase-core ribonucleoprotein, p50, CST and PolαPrim—that provides insights into the recruitment of CST and PolαPrim and the handoff between G-strand and C-strand synthesis.

DOI: 10.1038/s41586-022-04931-7

Source: https://www.nature.com/articles/s41586-022-04931-7

Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
官方网址：http://www.nature.com/
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