Crystal Structure of a Non-discriminating Glutamyl-tRNA Synthetase

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• 作者：Jö ; rg O. Schulze ; Ava Masoumi ; Daniel Nickel ; Martina Jahn ; Dieter Jahn ; Wolf-Dieter Schubert and Dirk W. Heinz
• 刊名：Journal of Molecular Biology
• 出版年：2006
• 期刊代码：102_00222836
• 类别：imm
• 出版时间：1 September 2006
• 卷：361
• 期：5
• 页码：888-897
• 文件大小：834 K

摘要

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 Å. 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.