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

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.