Crystallographic analysis of the intact metal centres [3Fe–4S]1+/0 and [4Fe–4S]2+/1+ in a Zn2+-containing ferredoxin

Detailed structural models of di-cluster seven-iron ferredoxins constitute a valuable resource for folding and stability studies relating the metal cofactors’ role in protein stability. The here reported, hemihedric twinned crystal structure at 2.0 Å resolution from Acidianus ambivalens ferredoxin, shows an integral 103 residues, physiologically relevant native form composed by a N-terminal extension comprising a His/Asp Zn2+ site and the ferredoxin (βαβ)2 core, which harbours intact clusters I and II, a [3Fe–4S]1+/0 and a [4Fe–4S]2+/1+ centres. This is in contrast with the previously available ferredoxin structure from Sulfolofus tokodai, which was obtained from an artificial oxidative conversion with two [3Fe–4S]1+/0 centres and poor definition around cluster II.