ジャーナル: EMBO J / 年: 2024 タイトル: Structural basis for the type I-F Cas8-HNH system. 著者: Xuzichao Li / Yanan Liu / Jie Han / Lingling Zhang / Zhikun Liu / Lin Wang / Shuqin Zhang / Qian Zhang / Pengyu Fu / Hang Yin / Hongtao Zhu / Heng Zhang / 要旨: The Cas3 nuclease is utilized by canonical type I CRISPR-Cas systems for processive target DNA degradation, while a newly identified type I-F CRISPR variant employs an HNH nuclease domain from the ...The Cas3 nuclease is utilized by canonical type I CRISPR-Cas systems for processive target DNA degradation, while a newly identified type I-F CRISPR variant employs an HNH nuclease domain from the natural fusion Cas8-HNH protein for precise target cleavage both in vitro and in human cells. Here, we report multiple cryo-electron microscopy structures of the type I-F Cas8-HNH system at different functional states. The Cas8-HNH Cascade complex adopts an overall G-shaped architecture, with the HNH domain occupying the C-terminal helical bundle domain (HB) of the Cas8 protein in canonical type I systems. The Linker region connecting Cas8-NTD and HNH domains adopts a rigid conformation and interacts with the Cas7.6 subunit, enabling the HNH domain to be in a functional position. The full R-loop formation displaces the HNH domain away from the Cas6 subunit, thus activating the target DNA cleavage. Importantly, our results demonstrate that precise target cleavage is dictated by a C-terminal helix of the HNH domain. Together, our work not only delineates the structural basis for target recognition and activation of the type I-F Cas8-HNH system, but also guides further developments leveraging this system for precise DNA editing.
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A: type I-F CRISPR-associated protein Csy3 B: type I-F CRISPR-associated protein Csy3 C: type I-F CRISPR-associated protein Csy3 D: type I-F CRISPR-associated protein Csy3 E: hypothetical protein J6N51_11000 F: HNH endonuclease G: type I-F CRISPR-associated protein Csy3 H: type I-F CRISPR-associated protein Csy3 I: DNA (32-MER) J: DNA (5'-D(P*GP*TP*GP*CP*GP*GP*A)-3') L: RNA (69-MER) M: type I-F CRISPR-associated endoribonuclease Cas6/Csy4