Arginyl-tRNA synthetase from yeast. Discrimination between 20 amino acids in aminoacylation of tRNA(Arg)-C-C-A and tRNA(Arg)-C-C-A(3'NH2).
For discrimination between arginine and 19 other amino acids in aminoacylation of tRNA(Arg)-C-C-A by arginyl-tRNA synthetase from baker's yeast, discrimination factors (D) have been determined from kcat and Km values. The lowest values were found for Trp, Cys, Lys (D = 800-8500), showing that arginine is 800-8500 times more often incorporated into tRNA(Arg)-C-C-A than noncognate acids at the same amino acid concentrations. The other noncognate amino acids exhibit D values between 10,000 and 60,000. In aminoacylation of tRNA(Arg)-C-C-A(3'NH2) discrimination factors D1 are in the range 10-600. From these values and AMP formation stoichiometry, pretransfer proof-reading factors II1 were determined; from D values and AMP stoichiometry in aminoacylation of tRNA(Arg)-C-C-A, posttransfer proof-reading factors II2 could be calculated, II1 values between 2 and 120 show that pretransfer proof-reading is the main correction step, posttransfer proof-reading (II2 approximately 1-10) plays a marginal role. Initial discrimination factors due to different Gibbs free energies of binding between arginine and the noncognate amino acids were calculated from discrimination and proof-reading factors. According to a two-step binding process, two factors (I1 and I2) were determined. They can be related to hydrophobic interaction forces and hydrogen bonds that are especially formed by the arginine side chain. A hypothetical 'stopper' model of the amino acid recognition site is discussed.
Freist
W
W
Max-Planck-Institut für Experimentelle Medizin, Abteilung Chemie, Göttingen, Federal Republic of Germany.
Sternbach
H
H
Cramer
F
F
D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D001120:Arginine; D001126:Arginine-tRNA Ligase / Q000378:metabolism*; D001665:Binding Sites; D002250:Carbon Radioisotopes; D003062:Codon; D007700:Kinetics; D012345:RNA, Transfer, Amino Acid-Specific / Q000378:metabolism*; D012347:RNA, Transfer, Arg / Q000378:metabolism*; D011865:Radioisotope Dilution Technique; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity
D002250:Carbon Radioisotopes; D003062:Codon; D012345:RNA, Transfer, Amino Acid-Specific; D012347:RNA, Transfer, Arg; D001120:Arginine; D000604:Amino Acyl-tRNA Synthetases; D001126:Arginine-tRNA Ligase