I-F2型CRISPR-Cas中Cas8非依赖性Cas3募集的结构基础
Structural basis of Cas8-independent Cas3 recruitment in Type I-F2 CRISPR-Cas.
摘要(中文译文)
CRISPR-Cas系统通过靶向并降解入侵遗传元件，在原核生物中提供适应性免疫。其中，I-F2型系统是最紧凑的I型CRISPR-Cas变体，其显著特征是同时完全缺失大亚基（Cas8）和小亚基（Cas11）。在其他I型系统中，Cas8对于原型间隔序列毗邻基序（PAM）的识别以及触发Cas3的招募至关重要，而Cas11则稳定Cascade骨架并在R环形成过程中引导非靶标DNA链。为阐明I-F2如何在缺失这些亚基的情况下执行干扰功能，我们解析了I-F2 Cascade与靶标DNA及Cas3结合的冷冻电镜结构。我们的结构揭示，仅由Cas5介导PAM感知，而Cas7亚基直接招募Cas3，后者采用一种适于DNA结合的解旋酶装载构象。我们展示了Cas3的解旋酶结构域和C端结构域如何捕获被置换的非靶标链，从而启动定向解旋和降解。这些发现揭示了关键的机制适应性，使得在缺乏经典大、小亚基的情况下仍能实现高效干扰，并强调了包括I-E、I-F1和I-F2在内的密切相关I型系统之间的机制多样性。这些见解为工程化改造超紧凑I-F2系统以用于基因组编辑和生物技术应用提供了结构基础。
Abstract
CRISPR-Cas systems provide adaptive immunity in prokaryotes by targeting and degrading invasive genetic elements. Among them, the Type I-F2 system represents the most compact Type I CRISPR-Cas variant, distinguished by the complete absence of both large (Cas8) and small (Cas11) subunits. In other Type I systems, Cas8 is essential for protospacer adjacent motif (PAM) recognition and for triggering Cas3 recruitment, while Cas11 stabilizes the Cascade backbone and guides the nontarget DNA strand during R-loop formation. To elucidate how I-F2 executes interference in their absence, we determined the cryo-electron microscopy structure of the I-F2 Cascade bound to target DNA and Cas3. Our structure reveals that Cas5 alone mediates PAM sensing, while Cas7 subunits directly recruit Cas3, which adopts a helicase-loaded conformation compatible with DNA engagement. We show how the helicase and C-terminal domains of Cas3 capture the displaced nontarget strand to initiate directional unwinding and degradation. These findings uncover key mechanistic adaptations that enable efficient interference without canonical large and small subunits and emphasize the mechanistic diversity among closely related Type I systems, including I-E, I-F1, and I-F2. These insights provide a structural basis for engineering the hypercompact I-F2 system for genome editing and biotechnological applications.
如何引用
AMA
Thomas Noé Perry, Christopher-Nils Mais, Mariana Sanchez-Londono, Wieland Steinchen, Pauline A Plitzko, Lennart Randau, et al. Structural basis of Cas8-independent Cas3 recruitment in Type I-F2 CRISPR-Cas.. Nucleic acids research. 2026; doi:10.1093/nar/gkag136.
APA
Thomas Noé Perry, Christopher-Nils Mais, Mariana Sanchez-Londono, Wieland Steinchen, Pauline A Plitzko, Lennart Randau, et al (2026). Structural basis of Cas8-independent Cas3 recruitment in Type I-F2 CRISPR-Cas.. Nucleic acids research. https://doi.org/10.1093/nar/gkag136
GB/T 7714
Thomas Noé Perry, Christopher-Nils Mais, Mariana Sanchez-Londono, Wieland Steinchen, Pauline A Plitzko, Lennart Randau, et al. Structural basis of Cas8-independent Cas3 recruitment in Type I-F2 CRISPR-Cas.[J]. Nucleic acids research, 2026 doi:10.1093/nar/gkag136.
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