Taxonomic distribution of proteins containing Fe_hyd_SSU domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing Fe_hyd_SSU domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Hydrogenases: hydrogen-activating enzymes.

Frey M
Chembiochem. 2002; 3: 153-60

Desulfovibrio desulfuricans iron hydrogenase: the structure shows unusualcoordination to an active site Fe binuclear center.

Nicolet Y, Piras C, Legrand P, Hatchikian CE, Fontecilla-Camps JC
Structure. 1999; 7: 13-23

BACKGROUND: Many microorganisms have the ability to either oxidizemolecular hydrogen to generate reducing power or to produce hydrogen inorder to remove low-potential electrons. These reactions are catalyzed bytwo unrelated enzymes: the Ni-Fe hydrogenases and the Fe-onlyhydrogenases. RESULTS: We report here the structure of the heterodimericFe-only hydrogenase from Desulfovibrio desulfuricans - the first for thisclass of enzymes. With the exception of a ferredoxin-like domain, thestructure represents a novel protein fold. The so-called H cluster of theenzyme is composed of a typical [4Fe-4S] cubane bridged to a binuclearactive site Fe center containing putative CO and CN ligands and onebridging 1, 3-propanedithiol molecule. The conformation of the subunitscan be explained by the evolutionary changes that have transformedmonomeric cytoplasmic enzymes into dimeric periplasmic enzymes. Plausibleelectron- and proton-transfer pathways and a putative channel for theaccess of hydrogen to the active site have been identified. CONCLUSIONS:The unrelated active sites of Ni-Fe and Fe-only hydrogenases have severalcommon features: coordination of diatomic ligands to an Fe ion; a vacantcoordination site on one of the metal ions representing a possiblesubstrate-binding site; a thiolate-bridged binuclear center; and plausibleproton- and electron-transfer pathways and substrate channels. Thediatomic coordination to Fe ions makes them low spin and favors low redoxstates, which may be required for catalysis. Complex electron paramagneticresonance signals typical of Fe-only hydrogenases arise from magneticinteractions between the [4Fe-4S] cluster and the active site binuclearcenter. The paucity of protein ligands to this center suggests that it wasimported from the inorganic world as an already functional unit.