Iron-sulfur proteins NiFe hydrogenase

Two [Fe] hydrogenase structures have so far been determined from C. pasteurianum (Cp) (Peters et al. 1998) and D. desulfuricans (Dd) (Nicolet et al. 1999). They have in common a large domain, which contains the catalytic site and three [4Fe-4S] iron sulfur clusters. The catalytic site and the closest (proximal) cluster are deeply buried inside the protein between two domains (or lobes), with access to a third, ferredoxin-like, domain that contains the two remaining (medial and distal) clusters. By contrast with [NiFe] hydrogenases the proximal [4Fe-4S] cluster is directly bridged to the bin-uclear active site by a cysteic thiolate (Fig. 6.12). 

Figure 8.3 Outline reaction cycle of NiFe hydrogenase.The minimal hydrogenase is depicted, consisting of the [NiFe] centre in the large subunit, and the proximal [4Fe-4S] cluster (C) in the small subunit.The reaction is written in the direction of the oxidation of H2. Electrons are transferred out through the other iron-sulfur clusters to an acceptor protein (not shown).The equivalent states of the NiFe centre B, SR, R and C are indicated. Reduced centres are shaded. Electron transfers are accompanied by transfers of hydrons (not shown).

Others decorate sensitive proteins with sacrificial atoms,... T. Goris et al. A unique iron-sulfur cluster is crucial for oxygen tolerance of a [NiFe]-hydrogenase. 2011. Nat Chem Biol. 7(5), p. 310. DOI 10.1038/nchembio.555. 

Figure 6.10 The catalytic site of [NiFe] and [NiFeSe] hydrogenases in oxidised inactive (top) and reduced active (bottom) states. Note the three non-protein diatomic ligands to the iron.The site bridging the Ni and Fe is occupied by an oxygen or sulfur species in the most oxidised states and probably by a hydride or molecular hydrogen in the most reduced states.

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