Nuc domain electrostatics drive the trans cleavage activity of CRISPR-Cas12a

The trans cleavage activity of Cas12a has been extensively used for the detection of biomolecules. Different Cas12a orthologues exhibit faster or slower trans cleavage kinetics, making some orthologues more suited for sensitive molecular detection. Ionic strength of reaction buffers and mutations that change the electrostatic environment near the RuvC active site have also been reported to strongly influence trans cleavage kinetics. Studying three commonly used Cas12a orthologues (FnCas12a, AsCas12a, and LbCas12a), we report that electrostatic interactions near the RuvC active site are critical for their trans cleavage activity. Alanine substitution of arginine and lysine residues in the Nuc domain can abolish trans cleavage while modestly reducing cis cleavage. Substitutions in the RuvC lid and substitutions to introduce positively charged residues in the Nuc could enhance both cis and trans cleavage. These Cas12a variants improved DNA detection and genome editing efficacy. Overall, this study provides a blueprint for rationally engineering the DNase activities of Cas12a.