Protein Arginine Phosphatase (PAPs), also known as Phosphoarginine Phosphatase, is an enzyme that catalyzes the dephosphorylation of phosphoarginine residues in proteins. Protein phosphatases (PPs) are "obligatory heteromers" made up of two maximum catalytic subunits attached to a non-catalytic subunit. Arginine modification is a post-translational protein modification in gram-positive bacteria. McsB and YwIE were recently identified as phosphorylating enzymes in Bacillus Subtilis (B.Subtilis). YwIE was thought to be a protein-tyrosine-phosphatase, and McsB a tyrosine-kinase, however in 2012 Elsholz et al. showed that McsB is a protein-arginine-kinase (PAK) and YwlE is a phosphatase-arginine-phosphatase (PAP).
Many proteins rely on protein phosphatase activity for regulating their stability, localization, and interaction with other proteins. Arginine modification is a post-translational protein modification in gram-positive bacteria, and protein arginine phosphorylation regulates transcription factors, in addition to tagging rogue proteins for degradation in gram-positive bacteria. Like phosphorylation, dephosphorylation is a reversible post-translational event. It is reversible through the action of kinases (enzymes that adds a phosphate group to a protein via phosphorylation), and this antagonist activity of phosphorylation and dephosphorylation of proteins controls all aspect of prokaryotic and eukaryotic life. In general, protein phosphatases play a crucial role in cell signaling regulation in both eukaryotes and prokaryotes. They act by removing a phosphate group from proteins, and their activity counteracts that of protein kinases.