NG-Methylation of arginine residues in many nucleic-acid-binding proteins are formed post-translationally, catalysed by S-adenosylmethionine:protein-arginine N-methyltransferase in their glycine-rich and arginine-rich motifs. The amino acid sequences of the stimulator of HIV-1 TAR (Tat-responsive element) RNA-binding protein (SRB) and fibronectin also show the presence of the internal -Gly-Arg-Gly- (-GRG-) sequence, which is potentially methylatable by the methyltransferase. To investigate the sequence requirement for methylation of these proteins, several synthetic oligopeptides with different chain lengths and sequences similar to the -GRG- regions of SRB and fibronectin were synthesized. Whereas the heptapeptide AGGRGKG (residues 16-22 in SRB) served as the methyl acceptor for the methyltransferase with a Km of 50 μM, the 19-mer peptide (residues 10-28 in SRB) was methylated with a Km of 8.3 μM, indicating that a greater peptide chain length yields a better methyl acceptor. Product analysis of the methylated [methyl-14C]SRB-peptide by HPLC indicated the formation of NG-monomethylarginine and NG,NG-dimethyl(asymmetric)arginine. Synthetic peptides containing the cell attachment sequence [Arg-Gly-Asp (‘RGD’)] in fibronectin, GRGDSPK, GGRGDSPK and GGGRGDSPK, were also studied; whereas GRGDSPK was a poor methyl acceptor, the longer peptides were better methyl acceptors. To provide an understanding of the effect of methylation on fibronectin peptide, arginine-unmethylated and methylated GGRGDSPK were compared for their effect on the mitogenesis induced by β-hexosaminidase A and an agonistic antibody (mAb15) in bovine tracheal smooth-muscle cells; whereas the former inhibited 35-67% of mitogenesis at a concentration of 5-10 μM, the latter did not block mitogenesis. This lack of inhibition by the insertion of a methyl group on the arginyl residue of the cell attachment sequence might be due to the hindrance of the binding of fibronectin peptide to integrins.
Enzymic methylation of arginyl residues in -Gly-Arg-Gly- peptides
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Young-Lan HYUN, D. Betty LEW, Seung Hee PARK, Chan-Wha KIM, Woon Ki PAIK, Sangduk KIM; Enzymic methylation of arginyl residues in -Gly-Arg-Gly- peptides. Biochem J 15 June 2000; 348 (3): 573–578. doi: https://doi.org/10.1042/bj3480573
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