Supramolecular Chemistry-Assisted Electrochemical Method for the Assay of Endogenous Peptidylarginine Deiminases Activities

Peptidylarginine deiminase 4 (PAD4) is the only isoform of PADs located within the cell nucleus, which has been known to be related to several human, diseases. In this work, we have proposed an electrochemical method for the assay of endogenous PAD4 activities as well as the studies of PAD4 inhibitors by making use of the supramolecular chemistry-assisted signal labeling. Specifically, peptide probes P1 and P2, which separately contain cysteine residues and tripeptides FGG (Phe-Gly-Gly), can be self-assembled onto the surface of the gold electrode and silver nanoparticles, respectively. In the meantime, the peptide probes can be connected together through cucurbit[8]uril-mediated host guest interaction. Nevertheless, after trypsin-catalyzed digestion, FGG at the N-terminal of P1 will be removed from the electrode surface, thereby inhibiting the connection of P1 and P2. Since PAD4 catalyzes the citrullination of arginine residue within P1, trypsin-catalyzed digestion of P1 can be prohibited by the addition of PAD4. Consequently, an obvious change of the electrochemical response can be obtained from the silver nanoparticles (AgNPs) immobilized on the electrode surface. Experimental results have shown that our method can display an improved sensitivity and specificity for both PAD4 assay and inhibitor screening, which may effectively trace endogenous PAD4 and the inhibitors in the cancer cells. Therefore, our method may have great potential for the diagnosis and treatment of PAD4-related diseases in the future.