Phosphoribosylaminoimidazole carboxylase

Phosphoribosylaminoimidazole carboxylase (or AIR carboxylase) is an enzyme involved in nucleotide biosynthesis and in particular in purine biosynthesis. It catalyzes the conversion of 5'-phosphoribosyl-5-aminoimidazole ("AIR") into 5'-phosphoribosyl-4-carboxy-5-aminoimidazole ("CAIR") as described in the reaction:

5-aminoimidazole ribonucleotide + CO2 5'-phosphoribosyl-4-carboxy-5-aminoimidazole + 2 H+
phosphoribosylaminoimidazole carboxylase
Phosphoribosylaminoimidazole carboxylase oktamer, Human
Identifiers
EC number4.1.1.21
CAS number9032-04-6
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / QuickGO
phosphoribosylaminoimidazole carboxylase, phosphoribosylaminoimidazole succinocarboxamide synthetase
Identifiers
SymbolPAICS
Alt. symbolsPAIS
NCBI gene10606
HGNC8587
OMIM172439
RefSeqNM_006452
UniProtP22234
Other data
EC number4.1.1.21
LocusChr. 4 pter-q21

In plants and fungi

Phosphoribosylaminoimidazole carboxylase is a fusion protein in plants and fungi, but consists of two non-interacting proteins in bacteria, PurK and PurE.

The crystal structure of PurE indicates a unique quaternary structure that confirms the octameric nature of the enzyme.[1]

In Escherichia coli

In the bacterium Escherichia coli the reaction is catalyzed in two steps carried out by two separate enzymes, PurK and PurE.

PurK, N5-carboxyaminoimidazole ribonucleotide synthetase, catalyzes the conversion of 5-aminoimidazole ribonucleotide ("AIR"), ATP, and bicarbonate to N5-carboxyaminoimidazole ribonucleotide ("N5-CAIR"), ADP, and Pi.

PurE, N5-carboxyaminoimidazole ribonucleotide mutase, converts N5-CAIR to CAIR, 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. Some members of this family contain two copies of this domain.[2]

References
  1. Ealick SE, Stubbe J, Kappock TJ, Mathews II (1999). "Crystal structure of Escherichia coli PurE, an unusual mutase in the purine biosynthetic pathway". Structure. 7 (11): 1395–1406. doi:10.1016/S0969-2126(00)80029-5. PMID 10574791.
  2. Meyer E, Stubbe J, Kappock TJ, Osuji C (1999). "Evidence for the direct transfer of the carboxylate of N5-carboxyaminoimidazole ribonucleotide (N5-CAIR) to generate 4-carboxy-5-aminoimidazole ribonucleotide catalyzed by Escherichia coli PurE, an N5-CAIR mutase". Biochemistry. 38 (10): 3012–3018. doi:10.1021/bi9827159. PMID 10074353.
This article incorporates text from the public domain Pfam and InterPro: IPR000031


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