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

The apo structure of N⁵-carboxyaminoimidazole ribonucleotide synthase (PurK) from Bacillus anthracis (baPurK) with Mg²⁺ in the active site is reported at 1.96 Å resolution. PurK is an enzyme in the purine-biosynthetic pathway, unique to prokaryotes, that converts 5-aminoimidazole ribonucleotide to N⁵-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.