Structure of N5-carboxyaminoimidazole ribonucleotide synthase (PurK) from Bacillus anthracis.

The apo structure of N 5-carboxyaminoimidazole ribonucleotide synthase (PurK) from Bacillus anthracis (baPurK) with Mg2+ in the active site is reported at 1.96 A resolution. PurK is an enzyme in the purine-biosynthetic pathway, unique to prokaryotes, that converts 5-aminoimidazole ribonucleotide to N 5-carboxyaminoimidazole ribonucleotide and has been suggested as a potential antimicrobial drug target. Two interesting features of baPurK are a flexible B-loop (residues 149/150–157) that is in close contact with the active site and the binding of Mg2+ to the active site without additional ligands.