Pro-CRISPR PcrIIC1-associated Cas9 system for enhanced bacterial immunity

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• CRISPR-Cas systems provide adaptive immunity in prokaryotes against foreign DNA.
• Type II Cas9 systems, particularly subtype II-C, are extensively studied but their evolutionary potential remains unclear.
• Understanding Cas9 diversity is crucial for developing new genome editing tools.

Purpose of the Study:

• To investigate the structural diversity and evolutionary trajectories of type II-C Cas9 proteins.
• To identify novel associated genes (NAGs) within Cas9 loci and their functional roles.
• To characterize a newly identified Cas9-NAG complex and its impact on CRISPR-mediated immunity.

Main Methods:

• Bioinformatic analysis of 2,062 complete Cas9 loci.
• Protein structure prediction for Cas9-associated proteins.
• Biochemical characterization of the CbCas9-PcrIIC1 complex.

Main Results:

• Three distinct structural evolutionary trajectories were identified for type II-C Cas9.
• Novel associated genes (NAGs) were frequently found in larger Cas9 loci.
• The CbCas9-PcrIIC1 complex, featuring a novel β-REC2 domain, demonstrated enhanced DNA binding, cleavage, and anti-phage activity compared to standalone CbCas9.
• PcrIIC1 acts as a pro-CRISPR factor, boosting immunity.

Conclusions:

• Type II-C Cas9 proteins exhibit diverse evolutionary paths, including the acquisition of NAGs.
• The CbCas9-PcrIIC1 complex represents a novel, enhanced CRISPR-Cas defense mechanism.
• NAGs like PcrIIC1 play a significant role in augmenting CRISPR-mediated bacterial immunity.