View source for Aspartate—tRNA(Asn) ligase

{{Infobox enzyme
| Name       = Aspartate—tRNA<sup>Asn</sup> ligase
| EC_number  = 6.1.1.23
| CAS_number = 9027-32-1
| GO_code    =
| image      = 
| width      = 
| caption    =  
}}
'''Aspartate—tRNA<sup>Asn</sup> ligase''' ({{EnzExplorer|6.1.1.23}}, ''nondiscriminating aspartyl-tRNA synthetase'') is an [[enzyme]] with systematic name ''L-aspartate:tRNAAsx ligase (AMP-forming)''.<ref>{{cite journal | vauthors = Ibba M, Soll D | title = Aminoacyl-tRNA synthesis | journal = Annual Review of Biochemistry | volume = 69 | pages = 617–50 | date = 2000 | pmid = 10966471 | doi = 10.1146/annurev.biochem.69.1.617 }}</ref><ref>{{cite journal | vauthors = Schmitt E, Moulinier L, Fujiwara S, Imanaka T, Thierry JC, Moras D | title = Crystal structure of aspartyl-tRNA synthetase from Pyrococcus kodakaraensis KOD: archaeon specificity and catalytic mechanism of adenylate formation | journal = The EMBO Journal | volume = 17 | issue = 17 | pages = 5227–37 | date = September 1998 | pmid = 9724658 | pmc = 1170850 | doi = 10.1093/emboj/17.17.5227 }}</ref><ref>{{cite journal | vauthors = Becker HD, Kern D | title = Thermus thermophilus: a link in evolution of the tRNA-dependent amino acid amidation pathways | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 22 | pages = 12832–7 | date = October 1998 | pmid = 9789000 | pmc = 23616 | doi = 10.1073/pnas.95.22.12832 | bibcode = 1998PNAS...9512832B | doi-access = free }}</ref> This enzyme [[catalysis|catalyses]] the following [[chemical reaction]]

: ATP + L-aspartate + tRNAAsx <math>\rightleftharpoons</math> AMP + diphosphate + aspartyl-tRNAAsx

The 3 [[substrate (biochemistry)|substrates]] of this enzyme are [[adenosine triphosphate|ATP]], [[L-asparagine]], and [[tRNAAsx]], whereas its 3 [[product (chemistry)|products]] are [[adenosine monophosphate|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 [[ligase]]s, to be specific those forming carbon-oxygen bonds in aminoacyl-tRNA and related compounds.  The [[List of enzymes|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 ==
{{reflist|1}}

{{Ligases CO CS and CN}}
{{Enzymes}}
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{{DEFAULTSORT:Asparagine-tRNA(Asn) ligase}}
[[Category:EC 6.1.1]]
[[Category:Enzymes of unknown structure]]


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