Aminoacyl‐ tRNA Synthetases

Abstract Aminoacyl‐tRNA synthetases catalyse a key reaction in protein biosynthesis. They match the 20 amino acids to the genetic code by specifically attaching them to their adaptors, transfer ribonucleic acid (tRNA) molecules. The reaction proceeds in two steps: the amino acid is first activated by adenosine triphosphate (ATP) to form aminoacyl adenylate and then the aminoacyl group is transferred to the terminal ribose of tRNA. This family of enzymes is divided into two classes, based on the similarities in primary structure and architecture of the active site domains; the two architectures are characterised by two modes of binding of ATP, the intermediate aminoacyl adenylate and the acceptor end of tRNA, which result in two regioselectivities of amino acid attachment to the terminal ribose of the tRNA. Aminoacyl‐tRNA synthetases are modular enzymes; to the central active site module are attached various domains with diverse functions such as tRNA‐binding and amino acid editing. The primary subject of this article are structural and functional aspects of these enzymes. Key Concepts Highly specific attachment of amino acids to their corresponding adaptor molecules, the transfer ribonucleic acids. Synthetases are partitioned into two classes according to structural features of their catalytic site and their functional correlation. Class II enzymes exhibit a unique fold and bind ATP in a unique bent conformation. The two classes bind the acceptor arm of tRNA in two ways that constitute mirror images of each other. Aminoacyl‐tRNA synthetases are modular enzymes, various domains of diverse functions being attached to the active site domain. Continuous editing is part of the tRNA aminoacylation process in living organisms.