Direct observation of the formation of a CRISPR-Cas12a R-loop complex at the single-molecule level

Area of Science:

• Molecular Biology
• Biophysics
• CRISPR Gene Editing

Background:

• Cas12a is a CRISPR-associated enzyme involved in DNA targeting.
• R-loop formation is a key intermediate in Cas12a-mediated DNA cleavage.
• Understanding Cas12a's mechanism requires detailed analysis of its interactions with target DNA.

Purpose of the Study:

• To develop a single-molecule assay for detecting and characterizing Cas12a R-loop complex formation.
• To investigate the thermodynamic stability of the R-loop complex.
• To elucidate the role of the Cas12a Nuc domain in target recognition and R-loop assembly.

Main Methods:

• Development of an optical tweezers-based single-molecule manipulation assay.
• Utilizing DNA hairpins containing target and non-target sequences.
• Measuring forces associated with DNA hairpin unfolding and R-loop formation.

Main Results:

• Cas12a R-loop complex formation induces a two-step unfolding of a DNA hairpin.
• The non-target DNA strand exhibits loose binding and is readily released.
• The Nuc domain of Cas12a is essential for stable target binding and R-loop formation.

Conclusions:

• The Cas12a R-loop complex is thermodynamically stable.
• The Nuc domain plays a critical role in the specificity and stability of Cas12a DNA interactions.
• This study provides new insights into the molecular mechanisms of Cas12a function.