Amino Acid Discrimination by a Class I Aminoacyl-tRNA Synthetase Specified by Negative Determinants

摘要: Abstract The 2.5 A crystal structure of Escherichia coli glutaminyl-tRNA synthetase in a quaternary complex with tRNAGln, an ATP analog and glutamate reveals that the non-cognate amino acid adopts distinct binding mode within active site cleft. In contrast to cognate glutamine, one oxygen charged carboxylate group makes direct ion-pair interaction strictly conserved Arg30 residue located first half dinucleotide fold domain. nucleophilic α-carboxylate moiety is mispositioned respect both α-phosphate terminal tRNA ribose groups, suggesting component discrimination resides at catalytic step reaction. Further, other side-chain found position identical previously proposed be occupied by NH2 glutamine substrate. At this position, accepts hydrogen bonds from hydroxyl Tyr211 water molecule. These findings demonstrate specificity GlnRS cannot arise donated amide these same moieties, as suggested. Instead, functions negative determinant drive into non-productive orientation. poorly differentiated acid-binding may consequence late emergence enzyme eukaryotic lineage glutamyl-tRNA synthetases.