Domain

Glutamine amidotransferase type 2 domain (IPR017932)

Short name: GATase_2_dom

Domain relationships

Description

A large group of biosynthetic enzymes are able to catalyse 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) [PMID: 4355768]. 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 [PMID: 3298209, PMID: 6086650]: class-I (also known as trpG-type or triad) and class-II (also known as purF-type or Ntn). Class-II (or type 2) GATase domains have been found in the following enzymes:

  • Amido phosphoribosyltransferase (glutamine phosphoribosylpyrophosphate amidotransferase). An enzyme which catalyses the first step in purine biosynthesis, the transfer of the ammonia group of glutamine to PRPP to form 5-phosphoribosylamine (gene purF in bacteria, ADE4 in yeast).
  • Glucosamine--fructose-6-phosphate aminotransferase. This enzyme catalyses a key reaction in amino sugar synthesis, the formation of glucosamine 6-phosphate from fructose 6-phosphate and glutamine (gene glmS in Escherichia coli, nodM in Rhizobium, GFA1 in yeast).
  • Asparagine synthetase (glutamine-hydrolyzing). This enzyme is responsible for the synthesis of asparagine from aspartate and glutamine.
  • Glutamate synthase (gltS), an enzyme which participates in the ammonia assimilation process by catalysing the formation of glutamate from glutamine and 2-oxoglutarate. Glutamate synthase is a multicomponent iron-sulphur flavoprotein and three types occur which use a different electron donor: NADPH-dependent gltS (large chain), ferredoxin-dependent gltS and NADH-dependent gltS [PMID: 10357231].

The active site is formed by a cysteine present at the N-terminal extremity of the mature form of all these enzymes [PMID: 6411716, PMID: 2573597, PMID: 9575335, PMID: 15052410]. Two other conserved residues, Asn and Gly, form an oxyanion hole for stabilisation of the formed tetrahedral intermediate. An insert of ~120 residues can occur between the conserved regions [PMID: 10357231]. In some class-II GATases (for example in Bacillus subtilis or chicken amido phosphoribosyltransferase) the enzyme is synthesised with a short propeptide which is cleaved off post-translationally by a proposed autocatalytic mechanism. Nuclear-encoded Fd-dependent gltS have a longer propeptide which may contain a chloroplast-targeting peptide in addition to the propeptide that is excised on enzyme activation.

The 3-D structure of the GATase type 2 domain forms a four layer alpha/beta/beta/alpha architecture which consists of a fold similar to the N-terminal nucleophile (Ntn) hydrolases. These have the capacity for nucleophilic attack and the possibility of autocatalytic processing. The N-terminal position and the folding of the catalytic Cys differ strongly from the Cys-His-Glu triad which forms the active site of GATases of type 1.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles
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