CRISPR/Cas12a Collateral Cleavage Activity for Sensitive 3′–5′ Exonuclease Assay

This study presents a technique for detecting 3′–5′ exonuclease activity through the use of CRISPR/Cas12a. These enzymes, including 3′–5′ exonuclease (Exo III), perform crucial roles in various cellular processes and are associated with life expectancy. However, imbalances in their expression can increase susceptibility to diseases such as cancer, particularly under prolonged stress. In this study, an activator sequence of CRISPR/Cas12a was constructed on the 5′–end of a hairpin probe (HP), forming a blunt end. When the 3′–end of the HP was hydrolyzed with Exo III activity, the activator sequence of Cas12a was exposed, which led to collateral cleavage of the DNA signal probe and generated a fluorescent signal, allowing sensitive and highly specific Exo III detection. This detection principle relied on the fact that Exo III exclusively cleaves the 3′–end mononucleotide of dsDNA and does not affect ssDNA. Based on this strategy, Exo III activity was successfully assayed at 0.0073 U/mL, demonstrating high sensitivity. In addition, this technique was used to screen candidate inhibitors of Exo III activity.