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- ***************************************************
- * Glutamine amidotransferases class-I active site *
- ***************************************************
-
- 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.-) [1]. 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) and class-II (also known as purF-type). Class-I
- GATase domains have been found in the following enzymes:
-
- - The second component of anthranilate synthase (AS) (EC 4.1.3.27) [4]. 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. 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 function in the pathway that
- catalyzes the biosynthesis of para-aminobenzoate (PABA) from chorismate and
- glutamine. The second component (gene pabA) provides the GATase activity
- [4].
- - CTP synthase (EC 6.3.4.2). 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 [2].
- - GMP synthase (glutamine-hydrolyzing) (EC 6.3.5.2). 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 [5].
- - Glutamine-dependent carbamoyl-phosphate synthase (EC 6.3.5.5) (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. 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 [6].
- - Phosphoribosylformylglycinamidine synthase II (EC 6.3.5.3), an enzyme that
- catalyzes the fourth step in the biosynthesis of purines. In some species
- of bacteria, 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.
- - The histidine amidotransferase hisH, an enzyme that catalyzes the fifth
- step in the biosynthesis of histidine in prokaryotes.
-
- In the second component of AS a cysteine has been shown [7] to be essential
- for the amidotransferase activity. The sequence around this residue is well
- conserved in all the above GATase domains and can be used as a signature
- pattern for class-I GATase.
-
- -Consensus pattern: [PA]-[LIVMFYT]-[LIVMFY]-G-[LIVMFY]-C-[LIVMFYN]-G-x-[QE]-x-
- [LIVMFA]
- [C is the active site residue]
- -Sequences known to belong to this class detected by the pattern: ALL.
- -Other sequence(s) detected in SWISS-PROT: NONE.
-
- -Note: in the first position of the pattern Pro is found in all cases except
- in the slime mold GD-CPSase where it is replaced by Ala.
-
- -Last update: June 1994 / Pattern and text revised.
-
- [ 1] Buchanan J.M.
- Adv. Enzymol. 39:91-183(1973).
- [ 2] Weng M., Zalkin H.
- J. Bacteriol. 169:3023-3028(1987).
- [ 3] Nyunoya H., Lusty C.J.
- J. Biol. Chem. 259:9790-9798(1984).
- [ 4] Crawford I.P.
- Annu. Rev. Microbiol. 43:567-600(1989).
- [ 5] Zalkin H., Argos P., Narayana S.V.L., Tiedeman A.A., Smith J.M.
- J. Biol. Chem. 260:3350-3354(1985).
- [ 6] Davidson J.N., Chen K.C., Jamison R.S., Musmanno L.A., Kern C.B.
- BioEssays 15:157-164(1993).
- [ 7] Tso J.Y., Hermodson M.A., Zalkin H.
- J. Biol. Chem. 255:1451-1457(1980).
-