Aminoacyl-tRNA Synthetases: The Division into Two Classes Predicted by the Chemistry of Substrates and Enzymes

In biological systems, almost all chemical reactions are catalyzed by enzymes. In order to understand the mode of action of these biocatalysts, we need to know precise details of their structures, their active sites, and their functional groups. Most important are those parts of the protein molecule that are responsible for precise recognition of the substrates, for the specific interaction between the enzymes and their reactants. Decades can pass between the isolation of an enzyme and the determination of its exact structure by X-ray analysis. For the chemist, however, means are known by which initial information may be gathered relatively quickly: the synthesis of modified substrates and affinity labeling. During the last twenty five years these two methods have been put to the test on aminoacyl-tRNA synthetases. Today, we know enough about the structures of these enzymes to evaluate the success of this “chemistry on macromolecules,” or their substrates. Chemists have had some successes, which provided the structural analysts with valuable preliminary results.