Aminoacyl-tRNA-Synthetase

Aminoacyl -tRNA synthetases ( AARS ) are enzymes that occur in all living things in the cytoplasm and are important for translation ( a part of the protein ). Its function is depending on their sequence ( in particular, its anticodon sequence) with their specific amino acids to the tRNAs is loaded. There are usually several 20 aminoacyl -tRNA synthetase molecules, one for each amino acid. Eukaryotes have an additional set of mitochondrial AARS, and plant another one in plastids. These are the main enzymes and different from each other and preferably loaded the tRNA of the respective organelles. However, archaea, cyanobacteria, but also mitochondria and plastids some tRNA does not make use of the AARS. These organisms do not have a second route for the biosynthesis of aminoacyl- tRNA.

In humans, mutations in the GARS gene ( glycyl -tRNA synthetase ) to a form of Charcot -Marie -Tooth.

The catalyzed reaction:

Structure

The division of the AARS is performed in two classes: Class 1 - AARS have a Rossmann fold, whereas Class 2 - AARS have a beta sheet.

End of the tRNA charging

Thus, a tRNA with the appropriate amino acid (AA ) can be loaded, the aminoacyl- tRNA synthetase, the AS must activate first. This is done by forming a carboxylic acid anhydride bond between the amino acid and ATP, with AS- AMP ( aminoacyl ) and pyrophosphate formed ( PPi or diphosphate ).

Now, the AS connected to the AMP may be transferred to the 3'-end of the tRNA, wherein the AMP molecule is cleaved.

The specificity and control of these aminoacylation of tRNAs is just as important for the accuracy of the protein as the anticodon - codon interaction between tRNA and mRNA on the ribosome. TRNA is loaded with the wrong amino acid in protein biosynthesis so that false amino acid is incorporated, even if the tRNA mRNA interaction is correct.

Some aminoacyl -tRNA synthetases recognize the appropriate tRNAs mainly on the basis of the anticodon. However, it was shown by mutagenesis experiments for the alanyl -tRNA synthetase that this recognizes the corresponding tRNA anticodon is not on, but based on the acceptor stem and a hairpin loop. Also, there are not for each of the 64 possible codon combinations of a specific aminoacyl -tRNA synthetase, but only one for any proteinogenic amino acid (see degenerate genetic code).

Finally, the aminoacyl -tRNA synthetase also has the ability to proofread and the binding between a "false -laden " amino acid and the tRNA also redissolved.