Kinetic analysis of human protein arginine N-methyltransferase 2: formation of monomethyl- and asymmetric dimethyl-arginine residues on histone H4.

Protein arginine N-methyltransferases (PRMTs) methylate arginine residues within proteins using S-adenosyl-L-methionine (AdoMet) to form S-adenosyl-L-homocysteine and methylarginine residues. All PRMTs produce omega-NG-monomethylarginine (MMA) residues and either asymmetric omega-N(G),N(G)-dimethylarginine (aDMA) or symmetric omega-N(G),N'(G)-dimethylarginine (sDMA) residues, referred to as Type I or Type II activity respectively. Here we report methylation activity from PRMT2 and compare it with PRMT1 activity using UPLC-MS/MS (ultra-performance liquid chromatography-tandem MS), gel electrophoresis, and thin-layer chromatography. We show that PRMT2 is a Type I enzyme and that the ratio of aDMA to MMA produced by PRMTs 1 and 2 is dependent on the substrate, regardless of rate or K(m), suggesting that the reactions for both enzymes are distributive rather than processive. Using UPLC-MS/MS we find that, for PRMT2, the dissociation constant (KAs) and K(m) of AdoMet and the Km of histone H4 are similar to values for PRMT1, whereas the PRMT2 k(cat) is 800-fold less than the PRMT1 k(cat). Although PRMT2 activity is substantially lower than PRMT1 in vitro, the fact that both enzymes selectively methylate histone H4 suggest that PRMT2, like PRMT1, may act as a transcription co-activator through this modification.

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