A large group of biosynthetic enzymes are able to catalyze the removal of the
ammonia group from glutamine and then to transfer this group to a substrate to
form a new carbon-nitrogen group. This catalytic activity is known as
glutamine amidotransferase (GATase) (EC 2.4.2.-) . The GATase domain exists
either as a separate polypeptidic subunit or as part of a larger polypeptide
fused in different ways to a synthase domain. On the basis of sequence
similarities two classes of GATase domains have been identified [2,3]: class-I
(also known as trpG-type or triad) and class-II (also known as purF-type or
Ntn) (see <PDOC00406>). Class-I (or type 1) GATase domains have been found in
the following enzymes:
The second component of anthranilate synthase (AS) (EC 126.96.36.199) . AS
catalyzes the biosynthesis of anthranilate from chorismate and glutamine.
AS is generally a dimeric enzyme: the first component can synthesize
anthranilate using ammonia rather than glutamine, whereas component II
provides the GATase activity (see <PDB:1QDL; B>) . In some bacteria and
in fungi the GATase component of AS is part of a multifunctional protein
that also catalyzes other steps of the biosynthesis of tryptophan.
The second component of 4-amino-4-deoxychorismate (ADC) synthase (EC 4.1.3.
-), a dimeric prokaryotic enzyme that functions in the pathway that
catalyzes the biosynthesis of para-aminobenzoate (PABA) from chorismate and
glutamine. The second component (gene pabA) provides the GATase activity
CTP synthase (EC 188.8.131.52). CTP synthase catalyzes the final reaction in the
biosynthesis of pyrimidine, the ATP-dependent formation of CTP from UTP and
glutamine. CTP synthase is a single chain enzyme that contains two distinct
domains; the GATase domain is in the C-terminal section  (see
GMP synthase (glutamine-hydrolyzing) (EC 184.108.40.206). GMP synthase catalyzes
the ATP-dependent formation of GMP from xanthosine 5'-phosphate and
glutamine. GMP synthase is a single chain enzyme that contains two distinct
domains; the GATase domain is in the N-terminal section [6,7] (see
Glutamine-dependent carbamoyl-phosphate synthase (EC 220.127.116.11) (GD-CPSase);
an enzyme involved in both arginine and pyrimidine biosynthesis and which
catalyzes the ATP-dependent formation of carbamoyl phosphate from glutamine
and carbon dioxide. In bacteria GD-CPSase is composed of two subunits: the
large chain (gene carB) provides the CPSase activity, while the small chain
(gene carA) provides the GATase activity (see <PDB:1A9X; B>). In yeast the
enzyme involved in arginine biosynthesis is also composed of two subunits:
CPA1 (GATase), and CPA2 (CPSase). In most eukaryotes, the first three steps
of pyrimidine biosynthesis are catalyzed by a large multifunctional enzyme
(called URA2 in yeast, rudimentary in Drosophila, and CAD in mammals). The
GATase domain is located at the N-terminal extremity of this polyprotein
Phosphoribosylformylglycinamidine synthase (EC 18.104.22.168), an enzyme that
catalyzes the fourth step in the de novo biosynthesis of purines. In some
species of bacteria and archaea, FGAM synthase II is composed of two
subunits: a small chain (gene purQ) which provides the GATase activity and
a large chain (gene purL) which provides the aminator activity. In
eukaryotes and Gram-negative bacteria a single polypeptide (large type of
purL) contains a FGAM synthethase domain and the GATase as the C-terminal
domain (see <PDB:1T3T>) .
Imidazole glycerol phosphate synthase subunit hisH (EC 2.4.2.-), an enzyme
that catalyzes the fifth step in the biosynthesis of histidine (see
A triad of conserved Cys-His-Glu forms the active site, wherein the catalytic
cysteine is essential for the amidotransferase activity [7,10]. Different
structures show that the active site Cys of type 1 GATase is located at the
tip of a nucleophile elbow.
The profile we developed covers the entire GATase type 1 domain, including the
catalytic Cys in the N-terminal half of the domain and the conserved His and
Glu of the triad in the C-terminal part of the domain.
The GATase type 1 domain profile is in competition with profiles of
related domains, which include cobBQ-type GATase (see <PDOC51274>), pdxT/SNO
(see <PDOC00950>), γ-glutamyl hydrolase (see <PDOC51275>) and PfpI
endopeptidase (see <PDOC51276>).
December 2006 / Pattern removed, profile added and text revised.
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