Cas9 degradation in human cells using phage anti-CRISPR proteins

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Bacteriophages utilize anti-CRISPR (Acr) proteins to disable bacterial CRISPR-Cas immune systems for successful replication.
• Acr proteins employ diverse mechanisms to inhibit CRISPR-Cas systems.
• AcrIIA1, a known inhibitor of Streptococcus pyogenes Cas9 (SpyCas9), is encoded by various phages and plasmids.

Purpose of the Study:

• To investigate the mechanism of AcrIIA1 inhibition of CRISPR-Cas systems in human cells.
• To determine if AcrIIA1 can induce degradation of Cas9 nucleases.
• To explore the therapeutic potential of AcrIIA1-mediated Cas9 degradation.

Main Methods:

• Human cell culture experiments were performed to observe AcrIIA1 interactions with SpyCas9 and Staphylococcus aureus Cas9 (SauCas9).
• Mutagenesis of AcrIIA1 was used to identify key interaction domains responsible for Cas9 degradation.
• CRISPR-Cas9 nuclease activity was assessed in the presence of AcrIIA1.

Main Results:

• AcrIIA1 was observed to induce the degradation of SpyCas9 and SauCas9 in human cells, a novel finding for Acr proteins.
• Mutations disrupting the physical interaction between AcrIIA1 and Cas9 abolished the degradation effect.
• This suggests a mechanism dependent on direct protein-protein interaction for Cas9 degradation.

Conclusions:

• AcrIIA1 actively degrades Cas9 nucleases in human cells via direct interaction.
• Targeted degradation of Cas9 by AcrIIA1 presents a novel strategy for modulating gene editing activity.
• AcrIIA1's properties could enable the development of CRISPR-Cas proteolysis-targeting chimeras (PROTACs) for safer gene editing applications.