Redox-dependent conformational changes of a proximal [4Fe–4S] cluster in Hyb-type [NiFe]-hydrogenase to protect the active site from O2

Citrobacter sp. S-77 [NiFe]-hydrogenase harbors a standard [4Fe–4S] cluster proximal to the Ni–Fe active site. The presence of relocatable water molecules and a flexible aspartate enables the [4Fe–4S] to display redox-dependent conformational changes. These structural features are proposed to be the key aspects that protect the active site from O2 attack.