西湖大学申恩志和吴建平等取得重要工作进展。他们对PIWI型Argonaute蛋白切割RNA的结构进行了解析。相关研究成果2025年1月15日在线发表于《自然》杂志上。

据介绍，Argonaute蛋白分为AGO和PIWI两个进化枝。在大多数动物物种中，AGO进化枝蛋白在多种细胞类型中广泛表达，并调控正常的基因表达。相比之下，PIWI进化枝蛋白主要在配子发生过程中发挥作用，以抑制转座子并确保生育能力。这两个进化枝都利用核酸向导通过碱基配对来识别靶标，这对于启动靶标沉默至关重要，靶标沉默通常通过直接切割实现。

AGO进化枝蛋白利用一个狭窄的通道来确保向导与靶标紧密相互作用。相比之下，PIWI 蛋白具有一个更宽的通道，这可能允许在配对过程中出现错配，从而拓宽了靶标沉默能力。然而，PIWI介导的靶标切割机制仍不清楚。

研究人员发现，在与靶标结合后，PIWI 蛋白会发生从 “开放” 状态到 “锁定” 状态的构象变化，促进碱基配对并提高靶标切割效率。这种转变涉及结合通道的变窄以及PIWI相互作用 RNA-靶标双链体向MID-PIWI叶的重新定位，从而建立广泛的接触以稳定双链体。

在这个转变过程中，研究人员还鉴定出一种中间的“逗号形”构象，它可能招募GTSF1，这是一种已知的辅助蛋白，可增强PIWI的切割活性。GTSF1通过将PIWI结构域与RNA双链体连接起来，促进向锁定状态的转变，从而加快对高效靶标切割至关重要的构象变化。

总之，这一研究解释了PIWI-PIWI相互作用RNA复合物，在靶标RNA切割中发挥作用的分子机制，为PIWI蛋白的动态构象变化如何协调辅助因子，来保障配子发生提供了见解。

附：英文原文

Title: Structural insights into RNA cleavage by PIWI Argonaute

Author: Li, Zhiqing, Xu, Qikui, Zhong, Jing, Zhang, Yan, Zhang, Tianxiang, Ying, Xiaoze, Lu, Xiaoli, Li, Xiaoyi, Wan, Li, Xue, Junchao, Huang, Jing, Zhen, Ying, Zhang, Zhao, Wu, Jianping, Shen, En-Zhi

Issue&Volume: 2025-01-15

Abstract: Argonaute proteins are categorized into AGO and PIWI clades. Across most animal species, AGO-clade proteins are widely expressed in various cell types, and regulate normal gene expression1. By contrast, PIWI-clade proteins predominantly function during gametogenesis to suppress transposons and ensure fertility1,2. Both clades use nucleic acid guides for target recognition by means of base pairing, crucial for initiating target silencing, often through direct cleavage. AGO-clade proteins use a narrow channel to secure a tight guide–target interaction3. By contrast, PIWI proteins feature a wider channel that potentially allows mismatches during pairing, broadening target silencing capability4,5. However, the mechanism of PIWI-mediated target cleavage remains unclear. Here we demonstrate that after target binding, PIWI proteins undergo a conformational change from an ‘open’ state to a ‘locked’ state, facilitating base pairing and enhancing target cleavage efficiency. This transition involves narrowing of the binding channel and repositioning of the PIWI-interacting RNA–target duplex towards the MID-PIWI lobe, establishing extensive contacts for duplex stabilization. During this transition, we also identify an intermediate ‘comma-shaped’ conformation, which might recruit GTSF1, a known auxiliary protein that enhances PIWI cleavage activity6. GTSF1 facilitates the transition to the locked state by linking the PIWI domain to the RNA duplex, thereby expediting the conformational change critical for efficient target cleavage. These findings explain the molecular mechanisms underlying PIWI–PIWI-interacting RNA complex function in target RNA cleavage, providing insights into how dynamic conformational changes from PIWI proteins coordinate cofactors to safeguard gametogenesis.

DOI: 10.1038/s41586-024-08438-1

Source:https://www.nature.com/articles/s41586-024-08438-1