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.