An aminoacyl tRNA synthetase (abbreviated aaRs) is an enzyme that catalyzes the binding of a specific amino acid to a tRNA to form an aminoacyl-tRNA. The synthetase hydrolyzes ATP to bind the appropriate amino acid to the 3' hydroxyl of the tRNA molecule. It also mediates a proofreading reaction to ensure high fidelity of tRNA charging; if the tRNA is found to be improperly charged, the amino acid-tRNA bond is hydrolyzed.

Reaction:

1. amino acid + ATP → aminoacyl-AMP + PPi
2. aminoacyl-AMP + tRNA → aminoacyl-tRNA + AMP

Classes

• Class I has two common homologous peptide sequence motifs. It aminoacylates at the 2'-OH.
• Class II has three common homologous peptide sequence motifs. It aminoacylates at the 3'-OH.

The one exception to the above rule is PheRS, a class II enzyme that attaches Phenylalanine to the 2'-OH of tRNA^Phe.

EC 6.1 | Gene expression

Aminoacyl-tRNA-Synthetase | アミノアシルtRNAシンセテース