Catalyzes the conversion of N5-carboxyaminoimidazole ribonucleotide (N5-CAIR) to 4-carboxy-5-aminoimidazole ribonucleotide (CAIR). 5-carboxyamino-1-(5-phospho-D-ribosyl)imidazole + H(+) = 5-amino-1-(5-phospho-D-ribosyl)imidazole-4-carboxylate Purine metabolism; IMP biosynthesis via de novo pathway; 5-amino-1-(5-phospho-D-ribosyl)imidazole-4-carboxylate from 5-amino-1-(5-phospho-D-ribosyl)imidazole (N5-CAIR route): step 2/2. Was identified as a high-confidence drug target. Belongs to the AIR carboxylase family. Class I subfamily.