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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1qf6

E.C. namethreonine---tRNA ligase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz) 6.1.1.3
CSA Homologues of 1qf6There are 99 Homologs
CSA Entries With UniProtID P0A8M3
CSA Entries With EC Number 6.1.1.3
PDBe Entry 1qf6
PDBSum Entry 1qf6
MACiE Entry 1qf6

Literature Report

Introductionthreonyl tRNA synthase from E.coli is able to catalyse the attachment of a threonine residue to its corresponding tRNA, displaying remarkable specificity as it only works on the specific amino acid and on the specific tRNA. It is part of the class II tRNA synthases, which make up approximately half of the known tRNA synthases. It is rare among class II synthases because of the presence of a Zinc ion in the active site, which is catalytic rather than structural.
MechansimThe reaction proceeds through direct nucleophilic attack from the carboxy terminal of the threonine on the alpha phosphate of ATP to form threonylAMP and releasing PPi in the process. This part of the reaction passes through a pentavalent phosphate intermediate, stabilised by Arg 363's positively charged side chain. The threonylAMP binds specifically to the Zinc ion, which therefore prevents other amino acids from forming amino acylAMPs. Placement of the tRNA anticodon allows specific transfer of the threonyl moiety to it by another nucleophilic addition elimination reaction, this time with AMP as the leaving group.
Reaction

Catalytic Sites for 1qf6

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
ArgA363363macie:sideChainPositive charge on side chain interacts electrostatically with the pentavalent phosphate intermediate thus resulting in its stabilisation, facilitating the formation of the aminoacyl AMP.

Literature References

Notes:
Sankaranarayanan R
The structure of threonyl-tRNA synthetase-tRNA(Thr) complex enlightens its repressor activity and reveals an essential zinc ion in the active site.
Cell 1999 97 371-381
PubMed: 10319817
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