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Investigating the molecular mechanisms underlying the anti-CRISPR function of AcrIIA13b protein

So Yeon Lee1,2, Hyun Ho Park1,2

  • 1College of Pharmacy, Chung-Ang University, Seoul, Korea.

The FEBS Journal
|October 25, 2025
PubMed

Insights

Researchers uncovered how anti-CRISPR protein AcrIIA13b inhibits Staphylococcus aureus Cas9 (SauCas9) by blocking DNA binding. This discovery deepens our understanding of CRISPR-Cas regulation and phage-bacteria interactions.

Area of Science:

  • Molecular Biology
  • Genetics
  • Microbiology

Background:

  • CRISPR-Cas systems provide bacterial and archaeal immunity against mobile genetic elements.
  • Anti-CRISPR (Acr) proteins from phages and viruses counteract CRISPR-Cas systems.
  • Understanding Acrs is crucial for improving CRISPR-Cas genome editing safety and efficacy.

Purpose of the Study:

  • To elucidate the structural and molecular mechanisms by which AcrIIA13b inhibits Staphylococcus aureus Cas9 (SauCas9).
  • To provide insights into the regulation of CRISPR-Cas systems and the evolutionary arms race between phages and bacteria.

Main Methods:

  • X-ray crystallography to determine the structure of AcrIIA13b.
  • Biochemical assays to analyze the functional features and inhibitory activity of AcrIIA13b against SauCas9.
  • Site-directed mutagenesis to investigate the role of N-terminal amino acid residues.

Main Results:

  • The structure of AcrIIA13b was determined, revealing its interaction with SauCas9.
  • AcrIIA13b inhibits SauCas9 by blocking the Protospacer Adjacent Motif (PAM)-binding region, preventing target DNA recognition.
  • The N-terminal 15 amino acids of AcrIIA13b are critical for its dimerization and inhibitory function.

Conclusions:

  • AcrIIA13b effectively inhibits SauCas9 by sterically hindering PAM recognition.
  • The N-terminal dimerization domain of AcrIIA13b is essential for its anti-CRISPR activity.
  • These findings enhance comprehension of CRISPR-Cas inhibition mechanisms and phage-host interactions.
Keywords:
AcrIIA13bCRISPR‐Cas systemadaptive immunityanti‐CRISPRcrystal structure

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