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Mol Cell. 2019 Apr 4;74(1):132-142.e5. doi: 10.1016/j.molcel.2019.02.001. Epub 2019 Mar 11.

Structure Reveals a Mechanism of CRISPR-RNA-Guided Nuclease Recruitment and Anti-CRISPR Viral Mimicry.

Author information

1
Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, USA.
2
Department of Integrative Structural and Computational Biology, Scripps Research Institute, La Jolla, CA, USA.
3
Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA.
4
Department of Integrative Structural and Computational Biology, Scripps Research Institute, La Jolla, CA, USA. Electronic address: glander@scripps.edu.
5
Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, USA. Electronic address: bwiedenheft@gmail.com.

Abstract

Bacteria and archaea have evolved sophisticated adaptive immune systems that rely on CRISPR RNA (crRNA)-guided detection and nuclease-mediated elimination of invading nucleic acids. Here, we present the cryo-electron microscopy (cryo-EM) structure of the type I-F crRNA-guided surveillance complex (Csy complex) from Pseudomonas aeruginosa bound to a double-stranded DNA target. Comparison of this structure to previously determined structures of this complex reveals a ∼180-degree rotation of the C-terminal helical bundle on the "large" Cas8f subunit. We show that the double-stranded DNA (dsDNA)-induced conformational change in Cas8f exposes a Cas2/3 "nuclease recruitment helix" that is structurally homologous to a virally encoded anti-CRISPR protein (AcrIF3). Structural homology between Cas8f and AcrIF3 suggests that AcrIF3 is a mimic of the Cas8f nuclease recruitment helix.

KEYWORDS:

Acr; CRISPR; Cas; Cascade; Csy; anti-CRISPR; crRNA; cryo-EM; type I-F

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