Glutamine amidotransferase
{{Infobox protein family
| Symbol = GATase
| Name = Glutamine amidotransferase class-I
| image = PDB 1o1y EBI.jpg
| width =
| caption = crystal structure of putative glutamine amido transferase (tm1158) from thermotoga maritima at 1.70 a resolution
| Pfam = PF00117
| Pfam_clan = CL0014
| InterPro = IPR000991
| SMART =
| PROSITE = PDOC00406
| MEROPS = C44
| SCOP = 1ea0
| TCDB =
| OPM family =
| OPM protein =
| CAZy =
| CDD = cd01653
}}
In molecular biology, glutamine amidotransferases (GATase) are enzymes which catalyse the removal of the ammonia group from a glutamine molecule and its subsequent transfer to a specific substrate, thus creating a new carbon-nitrogen group on the substrate. This activity is found in a range of biosynthetic enzymes, including glutamine amidotransferase, anthranilate synthase component II, p-aminobenzoate, and glutamine-dependent carbamoyl-transferase (CPSase). Glutamine amidotransferase (GATase) domains can occur either as single polypeptides, as in glutamine amidotransferases, or as domains in a much larger multifunctional synthase protein, such as CPSase. On the basis of sequence similarities two classes of GATase domains have been identified: class-I (also known as trpG-type) and class-II (also known as purF-type).{{cite journal | vauthors = Weng ML, Zalkin H | title = Structural role for a conserved region in the CTP synthetase glutamine amide transfer domain | journal = Journal of Bacteriology | volume = 169 | issue = 7 | pages = 3023–8 | date = July 1987 | pmid = 3298209 | pmc = 212343 | doi = 10.1128/jb.169.7.3023-3028.1987}}{{cite journal | vauthors = Nyunoya H, Lusty CJ | title = Sequence of the small subunit of yeast carbamyl phosphate synthetase and identification of its catalytic domain | journal = The Journal of Biological Chemistry | volume = 259 | issue = 15 | pages = 9790–8 | date = August 1984 | pmid = 6086650 }} Class-I GATase domains are defined by a conserved catalytic triad consisting of cysteine, histidine and glutamate. Class-I GATase domains have been found in the following enzymes: the second component of anthranilate synthase and 4-amino-4-deoxychorismate (ADC) synthase; CTP synthase; GMP synthase; glutamine-dependent carbamoyl-phosphate synthase; phosphoribosylformylglycinamidine synthase II; and the histidine amidotransferase hisH.