EC 6.3.5.7

Reaction: ATP + L-glutamyl-tRNA^Gln + L-glutamine = ADP + phosphate + L-glutaminyl-tRNA^Gln + L-glutamate (overall reaction)
(1a) L-glutamine + H₂O = L-glutamate + NH₃
(1b) ATP + L-glutamyl-tRNA^Gln = ADP + 5-phosphooxy-L-glutamyl-tRNA^Gln
(1c) 5-phosphooxy-L-glutamyl-tRNA^Gln + NH₃ = L-glutaminyl-tRNA^Gln + phosphate

Other name(s): Glu-AdT; Glu-tRNA^Gln amidotransferase; glutamyl-tRNA^Gln amidotransferase; Glu-tRNA^Gln:L-glutamine amido-ligase (ADP-forming); GatCAB; GatFAB; GatDE

Systematic name: L-glutamyl-tRNA^Gln:L-glutamine amido-ligase (ADP-forming)

Comments: In systems lacking discernible glutamine—tRNA ligase (EC 6.1.1.18), glutaminyl-tRNA^Gln is formed by a two-enzyme system. In the first step, a nondiscriminating ligase (EC 6.1.1.24, glutamate—tRNA^Gln ligase) mischarges tRNA^Gln with glutamate, forming glutamyl-tRNA^Gln. The glutamyl-tRNA^Gln is not used in protein synthesis until the present enzyme converts it into glutaminyl-tRNA^Gln (glutamyl-tRNA^Glu 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]).

Links to other databases: BRENDA, EXPASY, ExplorEnz, KEGG, MetaCyc, PDB, CAS registry number: 52232-48-1

References:

1. Curnow, A.W., Tumbula, D.L., Pelaschier, J.T., Min, B. and Söll, D. Glutamyl-tRNA^Gln 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-tRNA^Gln amidotransferase. Biochemistry 40 (2001) 6450-6457. [PMID: 11371208]

5. Feng, L., Sheppard, K., Tumbula-Hansen, D. and Soll, D. Gln-tRNA^Gln formation from Glu-tRNA^Gln requires cooperation of an asparaginase and a Glu-tRNA^Gln 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]