The Biological Axis of Protein Arginine Methylation and Asymmetric Dimethylarginine

Abstract

Protein post-translational modifications (PTMs) in eukaryotic cells play important roles in the regulation of functionalities of the proteome and in the tempo-spatial control of cellular processes. Most PTMs enact their regulatory functions by affecting the biochemical properties of substrate proteins such as altering structural conformation, protein-protein interaction, and protein-nucleic acid interaction. Amid various PTMs, arginine methylation is widespread in all eukaryotic organisms, from yeasts to humans. Arginine methylation in many situations can drastically or subtly affect the interactions of substrate proteins with their partnering proteins or nucleic acids, thus impacting major cellular programs. Recently, arginine methylation has become an important regulator of the formation of membrane-less organelles inside cells, a phenomenon of liquid-liquid phase separation (LLPS), through altering π-cation interactions. Another unique feature of arginine methylation lies in its impact on cellular physiology through its downstream amino acid product, asymmetric dimethylarginine (ADMA). Accumulation of ADMA in cells and in the circulating bloodstream is connected with endothelial dysfunction and a variety of syndromes of cardiovascular diseases. Herein, we review the current knowledge and understanding of protein arginine methylation in regards to its canonical function in direct protein regulation, as well as the biological axis of protein arginine methylation and ADMA biology.

Keywords: ADMA; PRMT; arginine methylation; metabolism; nitric oxide.

Figure 1

The biological axis of protein arginine methylation and formation of methylarginine small molecule metabolites. Type I, II, and III PRMTs catalyze the initial monomethylation of an arginine residue at the terminal guanidinium nitrogen. Subsequently, type I and II can catalyze a second arginine methylation reaction to form the asymmetric and symmetric dimethylated arginine residues, respectively. Protein degradation of arginine methylated proteins produces the ADMA, l-NMMA, and SDMA metabolites.

Figure 2

Protein arginine methyltransferases and novel members. For all proteins, the residue numbers are based on human protein sequences. Domains are assigned based on protein alignments within PRMT family members and the examination of the crystal structure data when available. The second Rossmann fold and β-barrel domain in the C-terminal region of PRMT7 is catalytically inactive. The domains of PRMT9 are assigned based on protein alignment alone since crystal structural data is unavailable. The dashed lined α-helix and dimerization arm region in PRMT9 indicates that this is expected, but there is a lack of crystal structure data to confirm this. The dashed, checkerboard pattern in the domains of NDUFAF7 and METTL23 indicates that there is limited protein sequence similarity when compared with the Rossmann fold and β-barrel domains of the PRMTs by sequence alignment. The protein sequences can be found in UniProt: PRMT1, Q99873-3; PRMT2, P55345-1; PRMT3, O60678-1; PRMT4/CARM1, Q86X55-3; PRMT5, O14744-1; PRMT6, Q96LA8-1; PRMT7, Q9NVM4-1; PRMT8, Q9NR22-1; PRMT9, Q6P2P2-1; NDUFAF7, Q7L592-1; METTL23, Q86XA0-1.

Figure 3

Asymmetric dimethylarginine (ADMA) function and regulation. The free ADMA molecule is produced from proteolysis of proteins containing Rme2a residues. ADMA level is regulated at multiple pathways. At the protein level, type-I PRMTs and potentially PAD and arginine demethylase enzymes regulate the abundance of Rme2a in proteins. Free ADMA is metabolized by DDAH and AGXT2 enzymes. DDAH activity generates citrulline and dimethylamine. AGXT2 activity generates DMGV that is further converted to DMGB. ADMA inhibits nitric oxide (NO) synthesis by competitive binding to nitric oxide synthase (NOS). Homocysteine inhibits DDAH activity via a reactive S-nitroso-l-homocysteine adduct.