Synthesis of cysteine-containing dipeptides by aminoacyl-tRNA synthetases.
Arginyl-tRNA synthetase (ArgRS) catalyses AMP- and PPi-independent deacylation of Arg-tRNAArg in the presence of cysteine. A dipeptide, Arg-Cys, is a product of this deacylation reaction. Similar reaction with homocysteine yields Arg-Hcy. Arginine is a noncompetitive inhibitor of the cysteine-dependent deacylation which indicates that cysteine binds to the enzyme-Arg-tRNAArg complex at a site separate from the arginine binding site. In the presence of arginine, [14C]Arg-tRNAArg is deacylated at a rate similar to the rate of its spontaneous deacylation in solution and [14C]arginine is a product. Experiments with cysteine derivatives indicate that the -SH group is essential for the reaction whereas -NH2 and -COOH groups are not. Thioesters of arginine are formed with 3-mercaptopropionic acid, N-acetyl-L-cysteine and dithiothreitol. These data suggest that formation of the dipeptide Arg-Cys involves a thioester intermediate, S-(L-arginyl)-L-cysteine, which is not observed because of the rapid rearrangement to form a stable peptide bond. Facile intramolecular reaction results from the favorable geometric arrangement of the alpha-amino group of cysteine with respect to the thioester formed in the initial reaction. Similar reactions, yielding Ile-Cys and Val-Cys, are catalyzed by isoleucyl- and valyl-tRNA synthetases, respectively.
Jakubowski
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Department of Microbiology and Molecular Genetics, UMDNJ-New Jersey Medical School, Newark 07103, USA.
D000604:Amino Acyl-tRNA Synthetases / Q000302:isolation & purification / Q000378:metabolism*; D001126:Arginine-tRNA Ligase / Q000302:isolation & purification / Q000378:metabolism; D002250:Carbon Radioisotopes; D003001:Cloning, Molecular; D003545:Cysteine; D004151:Dipeptides / Q000096:biosynthesis*; D004926:Escherichia coli; D007533:Isoleucine-tRNA Ligase / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D012347:RNA, Transfer, Arg / Q000378:metabolism*; D011865:Radioisotope Dilution Technique; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D013379:Substrate Specificity; D014637:Valine-tRNA Ligase / Q000302:isolation & purification / Q000378:metabolism
D002250:Carbon Radioisotopes; D004151:Dipeptides; D012347:RNA, Transfer, Arg; D011994:Recombinant Proteins; D000604:Amino Acyl-tRNA Synthetases; D001126:Arginine-tRNA Ligase; D007533:Isoleucine-tRNA Ligase; D014637:Valine-tRNA Ligase; D003545:Cysteine