EC 6.3.5.7     
Accepted name: glutaminyl-tRNA synthase (glutamine-hydrolysing)
Reaction: ATP + L-glutamyl-tRNAGln + L-glutamine = ADP + phosphate + L-glutaminyl-tRNAGln + L-glutamate (overall reaction)
(1a) L-glutamine + H2O = L-glutamate + NH3
(1b) ATP + L-glutamyl-tRNAGln = ADP + 5-phosphooxy-L-glutamyl-tRNAGln
(1c) 5-phosphooxy-L-glutamyl-tRNAGln + NH3 = L-glutaminyl-tRNAGln + phosphate
Other name(s): Glu-AdT; Glu-tRNAGln amidotransferase; glutamyl-tRNAGln amidotransferase; Glu-tRNAGln:L-glutamine amido-ligase (ADP-forming); GatCAB; GatFAB; GatDE
Systematic name: L-glutamyl-tRNAGln:L-glutamine amido-ligase (ADP-forming)
Comments: In systems lacking discernible glutamine—tRNA ligase (EC 6.1.1.18), glutaminyl-tRNAGln is formed by a two-enzyme system. In the first step, a nondiscriminating ligase (EC 6.1.1.24, glutamate—tRNAGln ligase) mischarges tRNAGln with glutamate, forming glutamyl-tRNAGln. The glutamyl-tRNAGln is not used in protein synthesis until the present enzyme converts it into glutaminyl-tRNAGln (glutamyl-tRNAGlu is not a substrate for this enzyme). A glutaminase subunit (cf. EC 3.5.1.2, glutaminase) produces an ammonia molecule that is transferred by a 30 Å tunnel to a synthase subunit, where it is ligated to the carboxy group that has been activated by phosphorylation. Some bacterial GatCAB complexes also has the activity of EC 6.3.5.6 [asparaginyl-tRNA synthase (glutamine-hydrolysing)].
References:
1.  Curnow, A.W., Tumbula, D.L., Pelaschier, J.T., Min, B. and Söll, D. Glutamyl-tRNAGln amidotransferase in Deinococcus radiodurans may be confined to asparagine biosynthesis. Proc. Natl. Acad. Sci. USA 95 (1998) 12838–12843. [PMID: 9789001]
2.  Ibba, M. and Söll, D. Aminoacyl-tRNA synthesis. Annu. Rev. Biochem. 69 (2000) 617–650. [PMID: 10966471]
3.  Raczniak, G., Becker, H.D., Min, B. and Soll, D. A single amidotransferase forms asparaginyl-tRNA and glutaminyl-tRNA in Chlamydia trachomatis. J. Biol. Chem. 276 (2001) 45862–45867. [PMID: 11585842]
4.  Horiuchi, K.Y., Harpel, M.R., Shen, L., Luo, Y., Rogers, K.C. and Copeland, R.A. Mechanistic studies of reaction coupling in Glu-tRNAGln amidotransferase. Biochemistry 40 (2001) 6450–6457. [PMID: 11371208]
5.  Feng, L., Sheppard, K., Tumbula-Hansen, D. and Soll, D. Gln-tRNAGln formation from Glu-tRNAGln requires cooperation of an asparaginase and a Glu-tRNAGln kinase. J. Biol. Chem. 280 (2005) 8150–8155. [PMID: 15611111]
6.  Nakamura, A., Yao, M., Chimnaronk, S., Sakai, N. and Tanaka, I. Ammonia channel couples glutaminase with transamidase reactions in GatCAB. Science 312 (2006) 1954–1958. [PMID: 16809541]
7.  Wu, J., Bu, W., Sheppard, K., Kitabatake, M., Kwon, S.T., Soll, D. and Smith, J.L. Insights into tRNA-dependent amidotransferase evolution and catalysis from the structure of the Aquifex aeolicus enzyme. J. Mol. Biol. 391 (2009) 703–716. [PMID: 19520089]
8.  Araiso, Y., Huot, J.L., Sekiguchi, T., Frechin, M., Fischer, F., Enkler, L., Senger, B., Ishitani, R., Becker, H.D. and Nureki, O. Crystal structure of Saccharomyces cerevisiae mitochondrial GatFAB reveals a novel subunit assembly in tRNA-dependent amidotransferases. Nucleic Acids Res. 42 (2014) 6052–6063. [PMID: 24692665]
[EC 6.3.5.7 created 2002, modified 2019]