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

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


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Video-Audio Media

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / immunology
  • Bacterial Proteins / metabolism*
  • CRISPR-Associated Proteins / chemistry
  • CRISPR-Associated Proteins / genetics
  • CRISPR-Associated Proteins / immunology
  • CRISPR-Associated Proteins / metabolism*
  • CRISPR-Cas Systems*
  • Clustered Regularly Interspaced Short Palindromic Repeats*
  • Cryoelectron Microscopy
  • DNA, Bacterial / chemistry
  • DNA, Bacterial / genetics
  • DNA, Bacterial / metabolism*
  • Models, Molecular
  • Molecular Mimicry*
  • Nucleic Acid Conformation
  • Protein Conformation
  • Pseudomonas aeruginosa / enzymology*
  • Pseudomonas aeruginosa / genetics
  • Pseudomonas aeruginosa / immunology
  • RNA, Bacterial / chemistry
  • RNA, Bacterial / genetics
  • RNA, Bacterial / metabolism*
  • RNA, Guide, Kinetoplastida / chemistry
  • RNA, Guide, Kinetoplastida / genetics
  • RNA, Guide, Kinetoplastida / metabolism*
  • Structure-Activity Relationship
  • Viral Proteins / chemistry
  • Viral Proteins / genetics
  • Viral Proteins / immunology
  • Viral Proteins / metabolism*


  • Bacterial Proteins
  • CRISPR-Associated Proteins
  • DNA, Bacterial
  • RNA, Bacterial
  • RNA, Guide
  • Viral Proteins