Transfer RNA - Aminoacylation

Aminoacylation

Aminoacylation is the process of adding an aminoacyl group to a compound. It produces tRNA molecules with their CCA 3' ends covalently linked to an amino acid.

Each tRNA is aminoacylated (or charged) with a specific amino acid by an aminoacyl tRNA synthetase. There is normally a single aminoacyl tRNA synthetase for each amino acid, despite the fact that there can be more than one tRNA, and more than one anticodon, for an amino acid. Recognition of the appropriate tRNA by the synthetases is not mediated solely by the anticodon, and the acceptor stem often plays a prominent role.

Reaction:

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

Sometimes, certain organisms can have one or more aminoacyl tRNA synthetases missing. This leads to mischarging of the tRNA by a chemically related amino acid. The correct amino acid is made by enzymes that modify the mischarged amino acid to the correct one.

For example, Helicobacter pylori has glutaminyl tRNA synthetase missing. Thus, glutamate tRNA synthetase mischarges tRNA-glutamine(tRNA-Gln) with glutamate. An amidotransferase then converts the acid side chain of the glutamate to the amide, forming the correctly charged gln-tRNA-Gln.