• Prosthetic group features
• Nitrogenase reaction
• Nitrogenase in enzyme databases
• Fe protein in motif databases
• Fe protein in alignment databases
• Fe protein in 3­D databases
• References

Iron-sulphur cluster	Formal oxidation/spin states
[Fe4S4](SCys)4	Active species: [Fe4S4]0 (S=4); [Fe4S4]+ (S=1/2; S=3/2); [Fe4S4]2+ (S=0)
[Fe2S2](SCys)4	Inactive species: [Fe2S2]2+ (S=0)

Biological nitrogen fixation, i.e. reduction of molecular nitrogen to ammonia (1), is catalysed by the nitrogenase enzyme system (EC 1.18.6.1). Molybdenum nitrogenase (Mo­nitrogenase), which is found in all nitrogen fixing organisms, consists of two components: component I [nitrogenase molybdenum-iron (MoFe) protein or dinitrogenase], and component II [nitrogenase iron (Fe) protein or dinitrogenase reductase] [1] (see list of reviews on structure and function of Mo­nitrogenase).

N2 + 8H+ + 8e¯ + 16MgATP 2NH3 + H2 + 16MgADP + 16Pi

(1)

The 3­D structure of Azotobacter vinelandii nitrogenase Fe protein has been determined [3]. This protein is a dimer of two identical subunits that coordinate a single [Fe₄S₄] cluster (see Figure 1NIP a). Each subunit folds as a single /ß type domain, which together symmetrically ligate the surface exposed [Fe₄S₄] cluster through two cysteines from each subunit (Figure 1NIP b). A single bound ADP molecule is located in the interface region between the two subunits.

                                ,-----.
                                |     |
   Subunit A         +H3N--···--C     C--···--COO¯
                                 \   /
                                [Fe4S4]
                                 /   \
   Subunit B         ¯OOC--···--C     C--···--NH3+
                                |     |
                                `-----'

It has been shown that an unusual [Fe₄S₄] to [Fe₂S₂] cluster conversion in nitrogenase Fe protein is induced by an treatment with an iron chelator or by thionine­oxidation [4, 5].

Nitrogenase in enzyme databases

ENZYME	LIGAND	BRENDA	Official name
1.18.6.1	1.18.6.1	1.18.6.1	Nitrogenase

Fe protein in motif databases

PRINTS ID	PRINTS AC	PROSITE/BLOCKS ID	PROSITE AC	BLOCKS AC
NITROGNASEII	PR00091	NIFH_FRXC_1 NIFH_FRXC_2	PS00746 PS00692	BL00746

Fe protein in alignment databases

Protein Superfamily	Pfam	LPFC 3­D alignment
00214; nitrogenase iron protein	PF00142; fer4_NifH	-

PDB	scop	BSM	RELI Base	Header	¹
1cp2	-	1cp2	-	Nitrogenase Fe protein; Clostridium pasteurianum	-
1n2c	1n2c	1n2c	1n2c	Nitrogenase complex (2:1 complex of homodimeric Fe protein and 2ß2 heterotetrameric MoFe protein) (complex with ADP, AlF4¯, Ca2+, Mg2+ and 3­hydroxy3­carboxy­adipic acid); Azotobacter vinelandii	-
1nip	1nip	1nip	1nip	Nitrogenase Fe protein (complex with Mg2+ and ADP); Azotobacter vinelandii	MMS93146

¹ Macromolecular Structures abstract. Full text is available to BioMedNet Members

References

1. Kim, J. and Rees, D.C. (1994) Nitrogenase and biological nitrogen fixation. Biochemistry 33, 389-397.
2. Seefeldt, L.C., Morgan, T.V., Dean, D.R. and Mortenson, L.E. (1992) Mapping the site(s) of MgATP and MgADP interaction with the nitrogenase of Azotobacter vinelandii. Lysine 15 of the iron protein plays a major role in MgATP interaction. J. Biol. Chem. 267, 6680-6688.
3. Georgiadis, M.M., Jr., Komiya, H., Chakrabarti, P., Woo, D., Kornuc, J.J. and Rees, D.C. (1992) Crystallographic structure of the nitrogenase iron protein from Azotobacter vinelandii. Science 257, 1653-1659.
4. Anderson, G.L. and Howard, J.B. (1984) Reactions with the oxidized iron protein of Azotobacter vinelandii nitrogenase: formation of a 2Fe center. Biochemistry 23, 2118-2122.
5. Fu, W.G., Morgan, T.V., Mortenson, L.E. and Johnson, M.K. (1991) Resonance Raman studies of the [4Fe-4S] to [2Fe-2S] cluster conversion in the iron protein of nitrogenase. FEBS Lett. 284, 165-168.

Bibliography on structural studies of Mo­nitrogenase component II

Reviews on Mo­nitrogenase