A 1.3 Å high-resolution crystal structure of an anti-CRISPR protein, AcrI E2

Biochem Biophys Res Commun. 2020 Dec 17;533(4):751-757. doi: 10.1016/j.bbrc.2020.09.067. Epub 2020 Sep 25.


As a result of bacterial infection with viruses, bacteria have developed CRISPR-Cas as an adaptive immune system, which allows them to destroy the viral genetic material introduced via infection. However, viruses have also evolved to develop multiple anti-CRISPR proteins, which are capable of inactivating the CRISPR-Cas adaptive immune system to combat bacteria. In this study, we aimed to elucidate the molecular mechanisms associated with anti-CRISPR proteins by determining a high-resolution crystal structure (1.3 Å) of Type I-E anti-CRISPR protein called AcrIE2. Our structural analysis revealed that AcrIE2 was composed of unique folds comprising five antiparallel β-sheets (β1∼β5) surrounding one α-helix (α1) in the order, β2β1α1β5β4β3. Structural comparison of AcrIE2 with a structural homolog called AcrIF9 showed that AcrIE2 contained a long and flexible β4-β5 connecting loop and a distinct surface feature. These results indicated that the inhibitory mechanism of AcrIE2 might be different from that of AcrIF9. This unique structure of AcrIE2 indicates its special mode of CRISPR-Cas inhibitory activity. Therefore, this study helps us understand the diversity in the inhibitory mechanisms of Acr family.

Keywords: AcrIE2; Adaptive immunity; CRISPR-Cas system; Crystal structure; anti-CRISPR proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • CRISPR-Associated Proteins / chemistry*
  • CRISPR-Cas Systems
  • Clustered Regularly Interspaced Short Palindromic Repeats
  • Crystallography, X-Ray
  • Models, Molecular
  • Protein Conformation, alpha-Helical
  • Protein Conformation, beta-Strand
  • Pseudomonas aeruginosa / virology*
  • Viral Proteins / chemistry*
  • Viral Proteins / metabolism


  • CRISPR-Associated Proteins
  • Viral Proteins