Novel strategy to inhibit CRISPR/Cas13a activity by PNA/crRNA duplex and its application in MMP-2 biosensor

Abstract

Using Peptide nucleic acid (PNA), this work provides a unique approach for controlling CRISPR/Cas13a activity by RNA Inhibitory PNA (RIP). This method reduces the action of CRISPR/Cas13a by inhibiting the binding of crRNA to CRISPR/Cas13a, which was subsequently utilized to detect metalloproteinase-2 (MMP-2) activity. We carefully constructed a PNA sequence that includes a peptide sequence (Gly-Pro-Leu-Gly-Val-Arg-Gly) that is particularly cleaved by MMP-2 in the middle. When MMP-2 is not present in the system, the PNA/crRNA complex reduces crRNA binding to CRISPR/Cas13a, hence inhibiting CRISPR/Cas13a cleavage activity. When MMP-2 is present in the system, it cleaves the peptide sequence (Gly-Pro-Leu-Gly-Val-Arg-Gly) selectively and so prevents PNA from binding to crRNA, enabling crRNA to reach the "free" form. Then, in the presence of an RNA activator, crRNA may bind to CRISPR/Cas13a and stimulate its activity. CRISPR/Cas13a triggered in this manner may precisely cleave the DNA sequence containing modified -UU- bases on the electrode surface. Thus, the ferrocene (Fc) is changed away from the electrode surface at one end of the DNA, enabling for the recovery of the Electrochemiluminescence (ECL) signal from the two-dimensional material transformed on the electrode surface. As a result, MMP-2 activity was detected utilizing this technique of inhibiting crRNA activity with a detection limit of 15.56 fM. Our suggested method of inhibiting CRISPR/Cas13a activity via PNA has a broad variety of potential therapeutic applications in gene editing and the development of CRISPR/Cas13a-based biosensors.