The Enzyme Database

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Accepted name: glutamate—tRNAGln ligase
Reaction: ATP + L-glutamate + tRNAGlx = AMP + diphosphate + L-glutamyl-tRNAGlx
Other name(s): nondiscriminating glutamyl-tRNA synthetase
Systematic name: L-glutamate:tRNAGlx ligase (AMP-forming)
Comments: When this enzyme acts on tRNAGlu, it catalyses the same reaction as EC, glutamate—tRNA ligase. It has, however, diminished discrimination, so that it can also form glutamyl-tRNAGln. 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, Bacillus subtilis, to recognize both tRNA1Gln (UUG anticodon) and tRNAGlu (UUC anticodon) but not tRNA2Gln (CUG anticodon). The ability of this enzyme to recognize both tRNAGlu and one of the tRNAGln isoacceptors derives from their sharing a major identity element, a hypermodified derivative of U34 (5-methylaminomethyl-2-thiouridine). The glutamyl-tRNAGln is not used in protein synthesis until it is converted by EC, glutaminyl-tRNA synthase (glutamine-hydrolysing), into glutaminyl-tRNAGln.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 9068-76-2
1.  Ibba, M. and Söll, D. Aminoacyl-tRNA synthesis. Annu. Rev. Biochem. 69 (2000) 617–650. [DOI] [PMID: 10966471]
2.  Schmitt, E., Moulinier, L., Fujiwara, S., Imanaka, T., Thierry, J.C. and Moras, D. Crystal structure of aspartyl-tRNA synthetase from Pyrococcus kodakaraensis KOD: archaeon specificity and catalytic mechanism of adenylate formation. EMBO J. 17 (1998) 5227–5237. [DOI] [PMID: 9724658]
3.  Kim, S.I. and Söll, D. Major identity element of glutamine tRNAs from Bacillus subtilis and Escherichia coli in the reaction with B. subtilis glutamyl-tRNA synthetase. Mol. Cells 8 (1998) 459–465. [PMID: 9749534]
[EC created 2002]

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