The reducing component BoxA of benzoyl-coenzyme A epoxidase from Azoarcus evansii is a [4Fe-4S] protein

► BoxA acts as reductase in the benzoyl-CoA oxidizing epoxidase enzyme system BoxAB. ► Homodimeric BoxA harbors an FAD and two [4Fe-4S] clusters per protein monomer. ► The [4Fe-4S] clusters degrade with traces of O2, but could be reconstituted in vitro. ► BoxAB(C) represent a new subclass of bacterial multicomponent monooxygenases (BMO). ► Compared to BMOs, BoxA is the only dimeric reductase with FAD and [4Fe-4S] centers.