Class I tyrosyl-tRNA synthetase has a class II mode of cognate tRNA recognition.
Bacterial tyrosyl-tRNA synthetases (TyrRS) possess a flexibly linked C-terminal domain of approximately 80 residues, which has hitherto been disordered in crystal structures of the enzyme. We have determined the structure of Thermus thermophilus TyrRS at 2.0 A resolution in a crystal form in which the C-terminal domain is ordered, and confirm that the fold is similar to part of the C-terminal domain of ribosomal protein S4. We have also determined the structure at 2.9 A resolution of the complex of T.thermophilus TyrRS with cognate tRNA(tyr)(G Psi A). In this structure, the C-terminal domain binds between the characteristic long variable arm of the tRNA and the anti-codon stem, thus recognizing the unique shape of the tRNA. The anticodon bases have a novel conformation with A-36 stacked on G-34, and both G-34 and Psi-35 are base-specifically recognized. The tRNA binds across the two subunits of the dimeric enzyme and, remarkably, the mode of recognition of the class I TyrRS for its cognate tRNA resembles that of a class II synthetase in being from the major groove side of the acceptor stem.
European Molecular Biology Laboratory, Grenoble Outstation, c/o ILL, 156X, F-38042 Grenoble cedex 9, France.
Anna
A
Yaremchuk
Ivan
I
Kriklivyi
Michael
M
Tukalo
Stephen
S
Cusack
D000595:Amino Acid Sequence; D001483:Base Sequence; D003461:Crystallography; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D012343:RNA, Transfer / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D016963:Thermus thermophilus / Q000201:enzymology; D014448:Tyrosine-tRNA Ligase / Q000737:chemistry / Q000378:metabolism*
D012343:RNA, Transfer; D014448:Tyrosine-tRNA Ligase