Aminoacyl tRNA synthetases
| Anticodon-binding domain of tRNA | |||||||||
|---|---|---|---|---|---|---|---|---|---|
leucyl-tRNA synthetase from Thermus thermophilus complexed with a post-transfer editing substrate analogue
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| Identifiers | |||||||||
| Symbol | Anticodon_2 | ||||||||
| Pfam | PF08264 | ||||||||
| InterPro | IPR013155 | ||||||||
| SCOP | 1ivs | ||||||||
| SUPERFAMILY | 1ivs | ||||||||
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| Available protein structures: | |
|---|---|
| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
| DALR anticodon binding domain 1 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
Thermus thermophilus arginyl-trna synthetase
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| Identifiers | |||||||||
| Symbol | DALR_1 | ||||||||
| Pfam | PF05746 | ||||||||
| Pfam clan | CL0258 | ||||||||
| InterPro | IPR008909 | ||||||||
| SCOP | 1bs2 | ||||||||
| SUPERFAMILY | 1bs2 | ||||||||
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| Available protein structures: | |
|---|---|
| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
| DALR anticodon binding domain 2 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
crystal structure of cysteinyl-tRNA synthetase binary complex with tRNACys
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| Identifiers | |||||||||
| Symbol | DALR_2 | ||||||||
| Pfam | PF09190 | ||||||||
| Pfam clan | CL0258 | ||||||||
| InterPro | IPR015273 | ||||||||
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| Available protein structures: | |
|---|---|
| Pfam | structures |
| PDB | RCSB PDB; PDBe; PDBj |
| PDBsum | structure summary |
An aminoacyl tRNA synthetase (aaRS) is an enzyme that attaches the appropriate amino acid onto its tRNA. It does so by catalyzing the esterification of a specific cognate amino acid or its precursor to one of all its compatible cognate tRNAs to form an aminoacyl-tRNA. In humans, the 21 different types of aa-tRNA are made by the 21 different aminoacyl-tRNA synthetases, one for each amino acid of the genetic code.
This is sometimes called "charging" or "loading" the tRNA with the amino acid. Once the tRNA is charged, a ribosome can transfer the amino acid from the tRNA onto a growing peptide, according to the genetic code. Aminoacyl tRNA therefore plays an important role in DNA translation, the expression of genes to create proteins.
As genetic efficiency evolved in higher organisms, 13 new domains with no obvious association with the catalytic activity of aaRSs genes have been added.
The synthetase first binds ATP and the corresponding amino acid (or its precursor) to form an aminoacyl-adenylate, releasing inorganic pyrophosphate (PPi). The adenylate-aaRS complex then binds the appropriate tRNA molecule's D arm, and the amino acid is transferred from the aa-AMP to either the 2'- or the 3'-OH of the last tRNA nucleotide (A76) at the 3'-end.
The mechanism can be summarized in the following reaction series:
Summing the reactions, the highly exergonic overall reaction is as follows:
Some synthetases also mediate a editing reaction to ensure high fidelity of tRNA charging. If the incorrect tRNA is added (aka. the tRNA is found to be improperly charged), the aminoacyl-tRNA bond is hydrolyzed. This can happen when two amino acids have different properties even if they have similar shapes—as is the case with Valine and Threonine.
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