AIR carboxylase
SMART accession number:SM01001
Description: Members of this family catalyse the decarboxylation of 1-(5-phosphoribosyl)-5-amino-4-imidazole-carboxylate (AIR). This family catalyse the sixth step of de novo purine biosynthesis. Some members of this family contain two copies of this domain.
Interpro abstract (IPR000031):

Two distinct mechanisms for the production of 4-carboxy-5-aminoimidazole ribonucleotide (CAIR) in de novo purine biosynthesis are known. The first one requires PurK and PurE for the overall conversion of AIR to CAIR. In Escherichia coli, PurK and PurE exist as independent enzymes. In plants and fungi, PurK and PurE exist as domains of a fusion protein, phosphoribosylaminoimidazole carboxylase (AIR carboxilase)[(PUBMED:9219341)].

PurK, N5-carboxyaminoimidazole ribonucleotide (N5-CAIR) synthetase, catalyses the conversion of 5-aminoimidazole ribonucleotide (AIR), ATP, and bicarbonate to N5-CAIR, ADP, and Pi. PurE, N5-CAIR mutase, catalyses the reversible conversion of N5-CAIR and CAIR [(PUBMED:10074353)], the sixth step of de novo purine biosynthesis. In the presence of high concentrations of bicarbonate, PurE is reported able to convert AIR to CAIR directly and without ATP [(PUBMED:7918411)]. The crystal structure of PurE indicates a unique quaternary structure that confirms the octameric nature of the enzyme [(PUBMED:10574791)].

A second mechanism for the production of 4-carboxy-5-aminoimidazole is found, for example, in Gallus gallus PurCE [(PUBMED:7918410), (PUBMED:7918411)]. PurCE uses CO2 to carboxylate AIR in forming CAIR and will not utilise N5-CAIR as a substrate. Despite the functional differences, the bacterial PurE protein has a high degree of amino acid sequence similarity with the corresponding regions of the PurCE and yeast ADE2 [(PUBMED:9500840)] indicating a common genetic ancestry.

This domain represents the bacterial PurE and the related regions in PurCE and ADE2.

GO process:'de novo' IMP biosynthetic process (GO:0006189)
Family alignment:
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There are 6396 AIRC domains in 6377 proteins in SMART's nrdb database.

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