Discovery of new inhibitor for the protein arginine deiminase type 4 (PAD4) by rational design of α-enolase-derived peptides

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease affecting about 0.24 % of the world population. Protein arginine deiminase type 4 (PAD4) is believed to be responsible for the occurrence of RA by catalyzing citrullination of proteins. The citrullinated proteins act as autoantigens by stimulating an immune response. Citrullinated alpha-enolase has been identified as one of the autoantigens for RA. Hence, alpha-enolase serves as a suitable template for design of potential peptide inhibitors against PAD4. The binding affinity of alpha-enolasederived peptides and PAD4 was virtually determined using PatchDock and HADDOCK docking programs. Synthesis of the designed peptides was performed using a solid phase peptide synthesis method. The inhibitory potential of each peptide was determined experimentally by PAD4 inhibition assay and IC50 measurement. PAD4 assay data show that the N-P2 peptide is the most favourable substrate among all peptides. Further modification of N-P2 by changing the Arg residue to canavanine [P2 (Cav)] rendered it an inhibitor against PAD4 by reducing the PAD4 activity to 35 % with IC50 1.39 mM. We conclude that P2 (Cav) is a potential inhibitor against PAD4 and can serve as a starting point for the development of even more potent inhibitors.

Automated summary

Rheumatoid arthritis is an inflammatory autoimmune disease affecting about 0.24% of the world population, and PAD4 is believed to be responsible for its occurrence. Peptide inhibitors designed to target PAD4 can reduce its activity, with P2 (Cav) showing potential as an inhibitor against PAD4 based on experimental data.