Insights into peptidylarginine deiminase expression and citrullination pathways

Peptidylarginine deiminases (PADs) are calcium-dependent enzymes that mediate citrullination, an irreversible post-translational modification (PTM). PAD enzymes have received increasing attention in (patho-)physiology since multi-omics analysis accelerated their expression profiling. Here, we provide a comprehensive overview of PAD expression at the RNA and protein levels, and a list of annotated substrates per PAD isozyme. We discuss novel roles of citrullination in cellular growth, epigenetic regulation, tissue remodeling, inflammation, and cancer in mouse models and humans. Additionally, we cluster similar effects of protein deimination to offer a different perspective and improve our understanding of citrullination in health and disease. Citrullination should no longer be considered as a rare PTM, but as an important regulatory mechanism in physiology and pathology.