PRMT (Protein Arginine Methyltransferase) is a mammalian enzyme that catalyzes methylation of arginine residues in a polypeptide chain. PRMT is categorized as 3 different types. The methylation can occur as asymmetric dimethylation (ADMA, PRMT 1, 2, 3, 4, 6, and 8), symmetric dimethylation (SDMA, PRMT 7, 5 and 9) or monomethylation (MMA, PRMT 7), Type I, II and III respectively. PRMT1 generates ADMA on arginine residues of the Histone H4 N-terminal tail, which can lead to transcription of cancer-related genes. Alternatively, PRMT5 can modify the same arginine residue to produce SDMA, which represses the development of those same cancer-related genes. A better understanding of the substrate specificity of these enzymes can assist in the development of novel isozyme-specific pharmaceuticals.1 To identify these differences, we synthesized a 96-well plate of peptides based on the Histone H4 N-terminal tail, screened them against PRMT1 using a screening method previously developed in the Knuckley lab.2 This medium-throughput screen identified 7 “hit” peptide sequences and consensus sequences based on the “hit” peptides were synthesized by solid-phase peptide synthesis. Each of these consensus sequences varied at the N-terminus, while retaining the more distal positive charges of H4-16 peptide. The peptides were validated using a MTase-GloTM Methyltransferase Assay to determine if they were indeed substrates for PRMT1. The kinetic values indicate their efficiency as PRMT1 substrates and further investigations are being conducted to identify the differences in the substrate specificity regarding PRMT4 and PRMT5. These continued efforts will help us gain a better understanding of the role PRMT isozymes play in the onset of cancer, while assisting in the design of novel pharmaceuticals to battle this disease
