Rapid two-step target capture ensures efficient CRISPR-Cas9-guided genome editing

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• RNA-guided CRISPR-Cas enzymes are essential tools for programmable genome editing.
• These enzymes recognize specific DNA sequences, including a protospacer-adjacent motif (PAM), to initiate editing.
• Understanding the factors influencing editing efficiency is crucial for improving CRISPR technology.

Purpose of the Study:

• To investigate the molecular mechanisms underlying high-efficiency genome editing by CRISPR-Cas enzymes.
• To determine the impact of protospacer-adjacent motif (PAM) binding specificity on the efficiency of *S. pyogenes* Cas9 (SpyCas9).
• To elucidate the relationship between PAM recognition breadth and genome editing effectiveness.

Main Methods:

• Biochemical assays were used to assess enzyme activity and binding properties.
• Biophysical techniques were employed to analyze protein-DNA and protein-RNA interactions.
• Cell-based assays were conducted to evaluate genome editing efficiencies of *Spy*Cas9 variants.

Main Results:

• Reduced PAM specificity in *Spy*Cas9 variants resulted in persistent, non-selective DNA binding.
• These variants showed recurrent failures in stable guide RNA hybridization to the target DNA.
• Lower genome editing efficiencies were observed in cells expressing *Spy*Cas9 variants with reduced PAM specificity.

Conclusions:

• A fundamental trade-off exists between broad PAM recognition and genome editing effectiveness.
• High-efficiency RNA-guided genome editing likely involves a two-step target capture: selective PAM binding followed by rapid DNA unwinding.
• This study provides a foundational model for engineering improved CRISPR-Cas and related RNA-guided genome editors.