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Aminoacyl‐tRNA synthetases and the evolution of coded peptide synthesis: the Thioester World

Coded peptide synthesis must have been preceded by a prebiotic stage, in which thioesters played key roles. Fossils of the Thioester World are found in extant aminoacyl‐tRNA synthetases (AARSs). Indeed, studies of the editing function reveal that AARSs have a thiol‐binding site in their catalytic modules. The thiol‐binding site confers the ability to catalyze aminoacyl~coenzyme A thioester synthesis and peptide bond formation. Genomic comparisons show that AARSs are structurally related to proteins involved in sulfur and coenzyme A metabolisms and peptide bond synthesis. These findings point to the origin of the amino acid activation and peptide bond synthesis functions in the Thioester World and suggest that the present‐day AARSs had originated from ancestral forms that were involved in noncoded thioester‐dependent peptide synthesis.