Discovery of specific inhibitors and activators of PADI4 to elucidate its biological role Teresa Bertran 1 , Bertran M.T. 1 , Walmsley R. 3 , Cummings T. 3 , Valle Aramburu I. 4 , Swanton T. 4 , Papayannopoulos V. 4 , Christophorou M. 3 , Walport L. J. 1, 1 Protein-Protein Interaction Laboratory, The Francis Crick Institute, London, UK, 2 Imperial College London, UK, 3 The Babraham Institute, Cambridge, UK , 4 Antimicrobial Defense Laboratory, The Francis Crick Institute, London, UK Peptidyl Arginine Deiminase 4 (PADI4) is a member of the peptidyl deiminase family of proteins that catalyse the post-translational modification of arginine to the non-canonical amino acid citrulline. PADI4 is involved in various biological processes and its dysregulation has been linked to various pathologies, including rheumatoid arthritis and a range of cancers; however, the molecular mechanisms that regulate PADI4 are poorly understood 1,2 . In consequence, the discovery of chemical tools that selectively modulate PADI4 activity is crucial to understand its biological function. The Random non-standard Peptide Integrated Discovery (RaPID) platform is a very powerful technology that enables us to screen > 1 trillion cyclic peptides against a target of interest 3,4 . We carried out three RaPID screens and identified macrocyclic peptides that bound to different conformations of PADI4 with nanomolar affinities. One of the peptides identified acts as a potent and selective PADI4 inhibitor both in vitro and in cells, while another one with no inhibitory effect was used as an affinity probe. In addition, we also identified a cyclic peptide that acts as a potent PADI4 activator at low calcium concentration. These peptides will be used as chemical tools to modulate PADI4 activity and hence elucidate its biological role. References 1. Witalison et al. Curr Drug Targets. 2015:16(7) 700-710.Christophorou M., R. Soc. Open. Sci. 2022, 9:220125
2. K. Bashiruddin et al., Curr. Opin. Chem. Biol. 2015 24, 131-138. 3. Passioura T and Suga H., Chem Commun, 2017, 53,1931.
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