NifH/frxC family (IPR000392)

Short name: NifH/frxC

Overlapping homologous superfamilies

Family relationships


This entry includes the bacterial nitrogenase iron protein NifH [PMID: 6327620], chloroplast encoded chlL (or frxC) [PMID: 2491672], and archaeal Ni-sirohydrochlorin a,c-diamide reductive cyclase complex component CfbC [PMID: 28225763].

Nitrogenase (EC: is responsible for biological nitrogen fixation. Nitrogenase is an oligomeric complex which consists of two components: component 1 which contains the active site for the reduction of nitrogen to ammonia and component 2 (also called the iron protein) [PMID: 2672439, PMID: 6327620]. Component 2 is a homodimer of a protein (gene nifH) which binds a single 4Fe-4S iron sulfur cluster. In the nitrogen fixation process NifH is first reduced by a protein such as ferredoxin; the reduced protein then transfers electrons to component 1 with the concomitant consumption of ATP [PMID: 6327620].

There are a number of conserved regions in the sequence of these proteins: in the N-terminal section there is an ATP-binding site motif 'A' (P-loop) and in the central section there are two conserved cysteines which have been shown, in NifH, to be the ligands of the 4Fe-4S cluster.

Protochlorophyllide reductase is involved in light-independent chlorophyll biosynthesis. The light-independent reaction uses Mg-ATP and reduced ferredoxin to reduce ring D of protochlorophyllide (Pchlide) to form chlorophyllide a (Chlide). This enzyme complex is composed of three subunits: ChlL, ChlN and ChlB. ChlL (also known as frxC) is present as a homodimer, and binds one 4Fe-4S cluster per dimer. The conserved domains, including the ATP-binding motif and the Fe-S binding motif found in the three subunits, are similar to those in nitrogenases [PMID: 16889380].

GO terms

Biological Process

GO:0055114 oxidation-reduction process

Molecular Function

GO:0005524 ATP binding
GO:0016491 oxidoreductase activity

Cellular Component

No terms assigned in this category.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.
PROSITE profiles