This is the C-terminal domain found in Hydrogen maturase F (HydF) present in Thermotoga neapolitana. HydF is a GTPase, containing an FeS cluster-binding motif, that is able to are able to activate HydA produced so that HydA can drive the reversible reduction of protons to molecular H2. This domain is known as domain III, and is primarily responsible for homotetramer formation. Interactions between the two FeS cluster-binding domains worth noting are the interactions between beta-2 strands, the initial part of the long loop that connects strand beta-2 to strand beta-3, and the loop that connects strand beta-1 to helix alpha-3. There are three highly conserved cysteine residues (Cys-302, Cys-353, and Cys-356) that represent the FeS cluster-binding site which form a superficial pocket [1].

1: Crystal structure of HydF scaffold protein provides insights into [FeFe]-hydrogenase maturation. Cendron L, Berto P, D'Adamo S, Vallese F, Govoni C, Posewitz MC, Giacometti GM, Costantini P, Zanotti G; J Biol Chem. 2011;286:43944-43950. PMID:22057316