Electronic structures of a [4Fe-4S] cluster, [Fe4S4(SCH3)3(CH3COO)], in dark-operative protochlorophyllide oxidoreductase (DPOR)

► Redox potentials of the [4Fe-4S] clusters are sensitive to the terminal ligands. ► NB cluster can be a better electron-donor than conventional [4Fe-4S] clusters in DPOR. ► This redox character of the NB cluster can explain why Asp36 is essential in DPOR. ► The unknown ligand of the [4Fe-4S] cluster in the D36A mutant is a chloride ion.