PRMT7 as a unique member of the protein arginine methyltransferase family: A review

Protein arginine methyltransferases (PRMTs) are found in a wide variety of eukaryotic organisms and can regulate gene expression, DNA repair, RNA splicing, and stem cell biology. In mammalian cells, nine genes encode a family of sequence-related enzymes; six of these PRMTs catalyze the formation of ω-asymmetric dimethyl derivatives, two catalyze ω-symmetric dimethyl derivatives, and only one (PRMT7) solely catalyzes ω-monomethylarginine formation. Purified recombinant PRMT7 displays a number of unique enzymatic properties including a substrate preference for arginine residues in R-X-R motifs with additional flanking basic amino acid residues and a temperature optimum well below 37 °C. Evidence has been presented for crosstalk between PRMT7 and PRMT5, where methylation of a histone H4 peptide at R17, a PRMT7 substrate, may activate PRMT5 for methylation of R3. Defects in muscle stem cells (satellite cells) and immune cells are found in mouse Prmt7 homozygous knockouts, while humans lacking PRMT7 are characterized by significant intellectual developmental delays, hypotonia, and facial dysmorphisms. The overexpression of the PRMT7 gene has been correlated with cancer metastasis in humans. Current research challenges include identifying cellular factors that control PRMT7 expression and activity, identifying the physiological substrates of PRMT7, and determining the effect of methylation on these substrates.

Biochemistry and regulation of the protein arginine methyltransferases (PRMTs)

Many key cellular processes can be regulated by the seemingly simple addition of one, or two, methyl groups to arginine residues by the nine known mammalian protein arginine methyltransferases (PRMTs). The impact that arginine methylation has on cellular well-being is highlighted by the ever growing evidence linking PRMT dysregulation to disease states, which has marked the PRMTs as prominent pharmacological targets. This review is meant to orient the reader with respect to the structural features of the PRMTs that account for catalytic activity, as well as provide a framework for understanding how these enzymes are regulated. An overview of what we understand about substrate recognition and binding is provided. Control of product specificity and enzyme processivity are introduced as necessary but flexible features of the PRMTs. Precise control of PRMT activity is a critical component to eukaryotic cell health, especially given that an arginine demethylase has not been identified. We therefore conclude the review with a comprehensive discussion of how protein arginine methylation is regulated.

Substrate specificity of human protein arginine methyltransferase 7 (PRMT7): the importance of acidic residues in the double E loop

Protein arginine methyltransferase 7 (PRMT7) methylates arginine residues on various protein substrates and is involved in DNA transcription, RNA splicing, DNA repair, cell differentiation, and metastasis. The substrate sequences it recognizes in vivo and the enzymatic mechanism behind it, however, remain to be explored. Here we characterize methylation catalyzed by a bacterially expressed GST-tagged human PRMT7 fusion protein with a broad range of peptide and protein substrates. After confirming its type III activity generating only ω-N(G)-monomethylarginine and its distinct substrate specificity for RXR motifs surrounded by basic residues, we performed site-directed mutagenesis studies on this enzyme, revealing that two acidic residues within the double E loop, Asp-147 and Glu-149, modulate the substrate preference. Furthermore, altering a single acidic residue, Glu-478, on the C-terminal domain to glutamine nearly abolished the activity of the enzyme. Additionally, we demonstrate that PRMT7 has unusual temperature dependence and salt tolerance. These results provide a biochemical foundation to understanding the broad biological functions of PRMT7 in health and disease.