title: Crystal structure of a non-discriminating glutamyl-tRNA synthetase.
abstract: Error-free protein biosynthesis is dependent on the reliable charging of each tRNA with its cognate amino acid. Many bacteria, however, lack a glutaminyl-tRNA synthetase. In these organisms, tRNA(Gln) is initially mischarged with glutamate by a non-discriminating glutamyl-tRNA synthetase (ND-GluRS). This enzyme thus charges both tRNA(Glu) and tRNA(Gln) with glutamate. Discriminating GluRS (D-GluRS), found in some bacteria and all eukaryotes, exclusively generates Glu-tRNA(Glu). Here we present the first crystal structure of a non-discriminating GluRS from Thermosynechococcus elongatus (ND-GluRS(Tel)) in complex with glutamate at a resolution of 2.45 A. Structurally, the enzyme shares the overall architecture of the discriminating GluRS from Thermus thermophilus (D-GluRS(Tth)). We confirm experimentally that GluRS(Tel) is non-discriminating and present kinetic parameters for synthesis of Glu-tRNA(Glu) and of Glu-tRNA(Gln). Anticodons of tRNA(Glu) (34C/UUC36) and tRNA(Gln) (34C/UUG36) differ only in base 36. The pyrimidine base of C36 is specifically recognized in D-GluRS(Tth) by the residue Arg358. In ND-GluRS(Tel) this arginine residue is replaced by glycine (Gly366) presumably allowing both cytosine and the bulkier purine base G36 of tRNA(Gln) to be tolerated. Most other ND-GluRS share this structural feature, leading to relaxed substrate specificity.
authors.affiliation: Division of Structural Biology, German Research Centre for Biotechnology (GBF), Mascheroder Weg 1, D-38124 Braunschweig, Germany.
authors.forename: Jörg O
authors.initials: JO
authors.lastname: Schulze
authors.forename: Ava
authors.initials: A
authors.lastname: Masoumi
authors.forename: Daniel
authors.initials: D
authors.lastname: Nickel
authors.forename: Martina
authors.initials: M
authors.lastname: Jahn
authors.forename: Dieter
authors.initials: D
authors.lastname: Jahn
authors.forename: Wolf-Dieter
authors.initials: WD
authors.lastname: Schubert
authors.forename: Dirk W
authors.initials: DW
authors.lastname: Heinz
mesh_terms: D000595:Amino Acid Sequence; D000926:Anticodon / Q000378:metabolism; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000201:enzymology*; D005975:Glutamate-tRNA Ligase / Q000737:chemistry*; D018698:Glutamic Acid / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary
chemical_list: D000926:Anticodon; D018698:Glutamic Acid; D005975:Glutamate-tRNA Ligase