Recognition of tRNAs by aminoacyl-tRNA synthetases

Our present understanding of the molecular mechanisms responsible for the recognition of tRNAs by their cognate aminoacyl-tRNA synthetases (aaRS) is essentially based on three sources of information: 1) the characterization of tRNA identity determinants using in vivo and in vitro approaches, 2) the classification of synthetases from primary sequence analysis: aaRS can be partitioned into two classes according to the spatial structure of their ATP binding domain, and 3) the structural results of crystallographic investigations and solution studies. The crystal structures of three aaRS and two complexes, one of each class, are known to atomic resolution. tRNA recognition has two structural components. The interaction between the acceptor end and the active site domain is class-specific and the binding mode of the stem observed in the crystal structures of GlnRS-tRNA(Gln) and AspRS-tRNA(Asp) complexes can be generalized to their respective classes. Identity determinants located in other parts of the tRNA molecule are decoded by different domains of the enzyme. These protein modules exhibit a large structural diversity. The recognition process is then system or subgroup specific.