Lactococcus lactis is one of the few organisms with two dihydroorotate dehydrogenases, DHODs, A and B [1]. The B enzyme is a prototype for DHODs in Gram-positive bacteria that use NAD+ as the second substrate. DHODB is a hetero-tetramer composed of a central homodimer of PyrDB subunits resembling the DHODA structure and two PyrK subunits along with three different cofactors: FMN, FAD, and a [2Fe-2S] cluster. The [2Fe-2S] iron-sulfur cluster binds to this C-terminal domain of the PyrK subunit, which is at the interface between the flavin and NAD binding domains and contains three beta-strands. The four cysteine residues at the N-terminal part of this domain are the ones that bind, in pairs, to the iron-sulfur cluster. The conformation of the whole molecule means that the iron-sulfur cluster is localised in a well-ordered part of this domain close to the FAD binding site [1]. The FAD and and NAD binding domains are FAD_binding_6, Pfam:PF00970 and NAD_binding_1, Pfam:PF00175.

1: Structure of dihydroorotate dehydrogenase B: electron transfer between two flavin groups bridged by an iron-sulphur cluster. Rowland P, Norager S, Jensen KF, Larsen S; Structure. 2000;8:1227-1238. PMID:11188687