This family includes Escherichia coli and Pseudomonas aeruginosa bacterioferritin-associated ferredoxin BFD which binds an [2Fe-2S] cluster and appears to interact with bacterioferritin (E. coli BFR/YheA and P. aeruginosa BfrB), a dynamic regulator of intracellular iron levels. It has been suggested that BFD and bacterioferritin form an electron transfer complex which may participate in the iron storage or iron immobilization functions of bacterioferritin. For Pseudomonas aeruginosa, it has been shown that mobilization of Fe3+ stored in BfrB requires interaction with BFD, which transfers electrons to reduce Fe3+ in the internal cavity of BfrB for subsequent release of Fe2+. The stability of BFD may be aided by an anion-binding site found within this domain. In addition to BFD, the BFD-like [2Fe-2S]-binding domain is found in a variety of proteins such as the large subunit of NADH-dependent nitrite reductase and the Cu+ chaperone CopZ. It comprises a helix-turn-helix fold, and binds an [2Fe-2S] cluster via 4 highly-conserved Cys residues, found in loops between the alpha-helices. For the class of proteins having a BFD-like [2Fe-2S]-binding domain, the Cys residues are organized in a unique C-X2-C-X31-35-C-X2-9-C-arrangement. [2Fe-2S] clusters are sulfide-linked diiron centers, a primary role for which is electron transport.
Jiyao W et al.(2023). "The conserved domain database in 2023.",