ARCHITECTURES OF CLASS-DEFINING AND SPECIFIC DOMAINS OF GLUTAMYL-TRANSFER-RNA SYNTHETASE

The crystal structure of a class I aminoacyl-transfer RNA synthetase, glutamyl-tRNA synthetase (GluRS) from Thermus thermophilus, was solved and refined at 2.5 Angstrom resolution. The amino-terminal half of Gl uRS shows a geometrical similarity with that of Escherichia coli gluta minyl-tRNA synthetase (GlnRS) of the same subclass in class I, compris ing the class I-specific Rossmann fold domain and the intervening subc lass-specific alpha/beta domain. These domains were found to have two GluRS-specific, secondary-structure insertions, which then participate d in the specific recognition of the D and acceptor stems of tRNA(Glu) as indicated by mutagenesis analyses based on the docking properties of GluRS and tRNA. In striking contrast to the beta-barrel structure o f the GlnRS carboxyl-terminal half, the GluRS carboxyl-terminal half d isplayed an all-alpha-helix architecture, an alpha-helix cage, and mut agenesis analyses indicated that it had a role in the anticodon recogn ition.