Backbone assignment and structural analysis of anti-CRISPR AcrIF7 from Pseudomonas aeruginosa prophages

The CRISPR-Cas system provides adaptive immunity for bacteria and archaea against invading phages and foreign plasmids. In the Class 1 CRISPR-Cas system, multi-subunit Cas proteins assemble with crRNA to bind to DNA targets. To disarm the bacterial defense system, bacteriophages evolved anti-CRISPR (Acr) proteins that actively inhibit the host CRISPR-Cas function. Here we report the backbone resonance assignments of AcrIF7 protein that inhibits the type I-F CRISPR-Cas system of Pseudomonas aeruginosa using triple-resonance nuclear magnetic resonance spectroscopy. We employed various computational methods to predict the structure and binding interface of AcrIF7, and assessed the model with experimental data. AcrIF7 binds to Cas8f protein via flexible loop regions to inhibit target DNA binding, suggesting that conformational heterogeneity is important for the Cas-Acr interaction.

Automated summary

The CRISPR-Cas system provides adaptive immunity for bacteria and archaea, but phages have evolved Acr proteins to inhibit host CRISPR-Cas function. The study reveals how AcrIF7 binds to Cas8f protein to inhibit target DNA binding, highlighting the importance of conformational heterogeneity in the Cas-Acr interaction.