AIR synthetase (FGAM cyclase)

protein
Name=phosphoribosylglycinamide formyltransferase, phosphoribosylglycinamide synthetase, phosphoribosylaminoimidazole synthetase
caption=


width=
HGNCid=4163
Symbol=GART
AltSymbols=PRGS, PGFT
EntrezGene=2618
OMIM=138440
RefSeq=NM_000819
UniProt=P22102
PDB=
ECnumber=2.1.2.2
Chromosome=21
Arm=q
Band=22.11
LocusSupplementaryData=

AIR synthetase is the fifth enzyme in the "de novo" synthesis of purine nucleotides. It catalyzes the reaction to form 5-aminoimidizole ribonucleotide (AIR) from formylglycinamidine-ribonucleotide FGAM. This reaction closes the ring and produces a 5-membered imidazole ring of the purine nucleus (AIR). AIR synthetase catalyzes the transfer of the oxygen of the formyl group to phosphate. It is a sequential mechanism in which ATP binds first to the enzyme and ADP is released last. This enzyme hydrolyzes ATP to activate the oxygen of the amide in order to carry out a nucleophilic attack by a nitrogen. The enzyme contains 388 amino acids and has an estimated molecular mass of 40.4 kDa.

Purine Synthesis

Purines are one of the two types of nitrogenous heterocyclic bases, which are one of the three components of the nucleotides that make up nucleic acids. Synthesis can be de novo or salvage - AIR synthetase is a component of the "de novo" pathway. The first committed step of the de novo pathway begins with phosphoribose pyrophosphate (PRPP) and the end product is inosine monophospate (IMP). IMP is eventually converted to either AMP or GMP purines. The purine ring structure is composed by the attachment of 1 or 2 atoms at a time to the ribose sugar. The "de novo" pathway tends to be conserved across most organisms.

Cowpea AIR synthetase

AIR synthetase is found in both mitochondria and plastids; the mitochondrial form has 5 more amino acids than the plastid form. [Goggin, D.E.; Lipscombe, R.; Fedorova, E.; Millar, A.H.; Mann, A.; Atkins, C.A.; Smith, P.M. Dual intracellular localization and targeting of aminoimidazole ribonucleotide synthetase in cowpea. Plant Physiol. 2003 March; 131(3): 1033-1041 ] The enzyme is encoded by a single gene in cowpeas despite the fact that it exists in different forms in plastids and mitochondria. This suggests that the different versions may be derived from a single transcript. One study proposes that there is tight transcriptional control of pur5, the gene encoding AIR synthetase. [ Smith, P.M.; Mann, A.J.; Goggin, D.E.; Atkins, C.A. AIR synthetase in cowpea nodules: a single gene product targeted to two organelles? Plant Mol Biol. 1998 April ;36(6): 811-820 ]

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