Kinetic Characterization, Inhibition, and Activity-Based Protein Profiling of Protein Arginine Methyltransferase 1

Protein arginine methyltransferases (PRMTs) are SAM-dependent enzymes that catalyze the mono- and di-methylation of peptidyl arginine residues. Although all PRMTs produce mono-methyl arginine (MMA), type I PRMTs go on to form asymmetrically dimethylated arginine (ADMA), while type II enzymes form symmetrically dimethylated arginine (SDMA). The predominant member of the PRMT family is PRMT1, as it is responsible for approximately 85% of the arginine methylation in mammalian cells. Since PRMT1 exhibits type I activity, it is the primary producer of the competitive NOS inhibitor, ADMA. Recently, dysregulated PRMT1 activity has also been implicated in the pathophysiology of breast cancer. Hence, potent inhibitors, which are highly selective for this particular isozyme, could serve as therapeutics for heart disease and cancer. However, the design of such inhibitors is impeded by a lack of information regarding this enzyme\u27s mechanism of action and in vivo function. Analyses of the substrate specificity of PRMT1 have shown that the enzyme preferentially methylates substrate peptides with positively-charged residues distal to the methylation site. Mechanistic studies have also been used to demonstrate that PRMT1 methylates its substrates in a partially-processive fashion, utilizing a rapid equilibrium random mechanism with dead-end EAP and EBQ complexes. These results aided the design and synthesis of a potent PRMT1-selective inhibitor, denoted C21. As C21 is able to covalently modify PRMT1, fluorescent and biotinylated C21 derivatives have been used as activity-based protein profiling probes for the elucidation of PRMT1 in vivo function