Abstract
The nitro group is an important functional group found in the nitroimidazoles, antibiotic therapeutics for anaerobic pathogens. In the biosynthetic pathway to the nitroimidazole antibiotic azomycin, a nitro-forming enzyme RohS—a member of the heme-oxygenase-like dimetal/domain-containing oxidase/oxygenase (HDO) family—catalyzes a six-electron oxidation of 2-aminoimidazole to 2-nitroimidazole. Here, we present the 2.20 Å resolution crystal structure of RohS and identify a potential active site pocket consisting of seven key residues important for metal coordination. By comparing the structures and sequences of two RohS homologs—one functionally active and one inactive—we convert the inactive RohS to its active form, thus revealing a key residue for metal coordination in RohS catalysis. Altogether, our work provides a structural basis for further mechanistic investigation of this six-electron oxidation process and provides insight into the expanding repertoire of the HDO protein family and nitro-formation N-oxygenases.