Isoleucyl-tRNA synthetase from baker's yeast. Discrimination of 20 amino acids in aminoacylation of tRNA(Ile)-C-C-3'dA; role of terminal hydroxyl groups aminoacylation of tRNA(Ile)-C-C-A.
Specificity with regard to amino acids in aminoacylation of tRNA(Ile)-C-C-3'dA by isoleucyl-tRNA synthetase is characterized by discrimination factors (D2) which are calculated from kcat and Km values. The lowest values are observed for Cys, Val, His, and Trp (D2 = 180-1700), indicating that at same amino acid concentrations isoleucine is 180-1700 times more attached to tRNA(Ile)-C-C-3'dA. The highest values are observed for Gly, Ala, Ser, Pro, Gln, Leu, Glu, and Phe (D2 = 10,000-30,000). D2 values of the other amino acids are in the range of 2000-10,000. Recognition of most amino acids is achieved in a four-step process. Two initial discrimination steps are due to different hydrophobic interactions with the binding pockets; two proof-reading steps occur on the pre- and the post-transfer stage. For nine amino acids (Ser, Asp, Asn, Val, Leu, His, Phe, Lys, Trp) post-transfer proof-reading is negligible. As a special case in discrimination of valine, one initial discrimination step and the post-transfer proof-reading step are lacking. The role of the terminal hydroxyl groups of the tRNA for post-transfer proof-reading is assigned to a simple neighbouring group effect. No preference for the 2' or 3' position in proof-reading can be postulated.
Freist
W
W
Max-Planck-Institut für Experimentelle Medizin, Abteilung Chemie, Göttingen, Federal Republic of Germany.
Sternbach
H
H
D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D007533:Isoleucine-tRNA Ligase / Q000378:metabolism*; D007700:Kinetics; D008962:Models, Theoretical; D011485:Protein Binding; D012355:RNA, Transfer, Ile / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013379:Substrate Specificity
D012355:RNA, Transfer, Ile; D000604:Amino Acyl-tRNA Synthetases; D007533:Isoleucine-tRNA Ligase