Taxonomic distribution of proteins containing AIRC domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing AIRC domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Crystal structure of Escherichia coli PurE, an unusual mutase in thepurine biosynthetic pathway.

Mathews II, Kappock TJ, Stubbe J, Ealick SE
Structure. 1999; 7: 1395-406

BACKGROUND: Conversion of 5-aminoimidazole ribonucleotide (AIR) to4-carboxyaminoimidazole ribonucleotide (CAIR) in Escherichia coli requirestwo proteins - PurK and PurE. PurE has recently been shown to be a mutasethat catalyzes the unusual rearrangement of N(5)-carboxyaminoimidazoleribonucleotide (N(5)-CAIR), the PurK reaction product, to CAIR. PurEs fromhigher eukaryotes are homologous to E. coli PurE, but use AIR and CO(2) assubstrates to produce CAIR directly. RESULTS: The 1.50 A crystal structureof PurE reveals an octameric structure with 422 symmetry. A centralthree-layer (alphabetaalpha) sandwich domain and a kinked C-terminal helixform the folded structure of the monomeric unit. The structure reveals acleft at the interface of two subunits and near the C-terminal helix of athird subunit. Co-crystallization experiments with CAIR confirm this to bethe mononucleotide-binding site. The nucleotide is bound predominantly toone subunit, with conserved residues from a second subunit making up onewall of the cleft. CONCLUSIONS: The crystal structure of PurE reveals aunique quaternary structure that confirms the octameric nature of theenzyme. An analysis of the native crystal structure, in conjunction withsequence alignments and studies of co-crystals of PurE with CAIR, revealsthe location of the active site. The environment of the active site andthe analysis of conserved residues between the two classes of PurEssuggests a model for the differences in their substrate specificities andthe relationship between their mechanisms.