Aspartate—tRNA(Asn) ligase

Aspartate---tRNAAsn ligase (EC 6.1.1.23, nondiscriminating aspartyl-tRNA synthetase) is an enzyme with systematic name L-aspartate:tRNAAsx ligase (AMP-forming).^[1]^[2]^[3] This enzyme catalyses the following chemical reaction

ATP + L-aspartate + tRNAAsx

\rightleftharpoons

AMP + diphosphate + aspartyl-tRNAAsx

The 3 substrates of this enzyme are ATP, L-asparagine, and tRNAAsx, whereas its 3 products are AMP, diphosphate, and asparaginyl-tRNAAsx.

When this enzyme acts on tRNAAsp, it catalyses the same reaction as EC 6.1.1.12, aspartate---tRNA ligase. It has, however, diminished discrimination, so that it can also form aspartyl-tRNAAsn. This relaxation of specificity has been found to result from the absence of a loop in the tRNA that specifically recognizes the third position of the anticodon [1]. This accounts for the ability of this enzyme in, for example, Thermus thermophilus, to recognize both tRNAAsp (GUC anticodon) and tRNAAsn (GUU anticodon). The aspartyl-tRNAAsn is not used in protein synthesis until it is converted by EC 6.3.5.6, asparaginyl-tRNA synthase (glutamine-hydrolysing), into asparaginyl-tRNAAsn.

This enzyme belongs to the family of ligases, to be specific those forming carbon-oxygen bonds in aminoacyl-tRNA and related compounds. The systematic name of this enzyme class is L-asparaginyl:tRNAAsx ligase (AMP-forming). This enzyme is also called nondiscriminating asparaginyl-tRNA synthetase. This enzyme participates in alanine and asparagine metabolism.

References

↑ Ibba, M.; Söll, D. (2000). "Aminoacyl-tRNA synthesis". Annu. Rev. Biochem. 69: 617–650. doi:10.1146/annurev.biochem.69.1.617. PMID 10966471.
↑ Schmitt, E.; Moulinier, L.; Fujiwara, S.; Imanaka, T.; Thierry, J.C.; Moras, D. (1998). "Crystal structure of aspartyl-tRNA synthetase from Pyrococcus kodakaraensis KOD: archaeon specificity and catalytic mechanism of adenylate formation". EMBO J. 17: 5227–5237. doi:10.1093/emboj/17.17.5227. PMC 1170850. PMID 9724658.
↑ Becker, H.D.; Kern, D. (1998). "Thermus thermophilus: a link in evolution of the tRNA-dependent amino acid amidation pathways". Proc. Natl. Acad. Sci. USA. 95: 12832–12837. doi:10.1073/pnas.95.22.12832. PMC 23616. PMID 9789000.

Enzymes: CO CS and CN ligases (EC 6.1-6.3)

6.1: Carbon-Oxygen	Aminoacyl tRNA synthetase Alanine Arginine Asparagine Aspartate Cysteine D-alanine—poly(phosphoribitol) ligase Glutamate Glutamine Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine

6.2: Carbon-Sulfur	Succinyl coenzyme A synthetase Acetyl—CoA synthetase Long-chain-fatty-acid—CoA ligase

6.3: Carbon-Nitrogen	Glutamine synthetase Ubiquitin ligase Cullin Von Hippel–Lindau tumor suppressor UBE3A Mdm2 Anaphase-promoting complex UBR1 Glutathione synthetase CTP synthetase Adenylosuccinate synthase Argininosuccinate synthase Holocarboxylase synthetase GMP synthase Asparagine synthetase Carbamoyl phosphate synthetase I II Glutamate–cysteine ligase

Enzymes

Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Catalytically perfect enzyme Coenzyme Cofactor Enzyme catalysis Enzyme kinetics Lineweaver–Burk plot Michaelis–Menten kinetics

Regulation	Allosteric regulation Cooperativity Enzyme inhibitor

Classification	EC number Enzyme superfamily Enzyme family List of enzymes

Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list)

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