TSRI's main web site PROMISE mirror at TSRI Metalloprotein DB site Created: 5 May 1996
Last modified: 3 February 1999

Fe4S4 / Fe3S4 proteins
Iron-sulphur cluster Formal oxidation states
[Fe4S4]Cys4 image
[Fe4S4](SgammaCys)4
[Fe4S4]+; [Fe4S4]2+; [Fe4S4]3+
[Fe4S4]Cys3His(Ndelta) image
[Fe4S4](SgammaCys)3NdeltaHis
[Fe4S4]+; [Fe4S4]2+
[Fe4S4]Cys3His(Nepsilon) image
[Fe4S4](SgammaCys)3NepsilonHis
[Fe4S4]+; [Fe4S4]2+
[Fe4S4]Cys3COOH image
[Fe4S4](SgammaCys)3OdeltaAsp
[Fe4S4]+; [Fe4S4]2+
Fe4S4 image
[Fe4S4](SgammaCys)3(H2O)n
[Fe4S4]+; [Fe4S4]2+; [Fe4S4]3+
[Fe3S4] image
[Fe3S4](SgammaCys)3
[Fe3S4]2-; [Fe3S4]0; [Fe3S4]+

Iron-sulphur proteins are characterised by the presence of polymetallic systems containing sulphide ions, in which the iron ions have variable oxidation states. One of the most common polymetallic systems, [Fe4S4], is characterised by four iron ions and four sulphide ions placed at the vertices of a cubane­type structure, coordinated by four cysteinyl ligands [1]. The [Fe4S4] electron­transfer proteins ([Fe4S4] ferredoxins) may be further subdivided into low­potential (bacterial­type) and high­potential (HiPIP) ferredoxins. Low­ and high­potential ferredoxins are related by the following redox scheme [2]:

The formal oxidation numbers of the iron ions can be [2Fe3+, 2Fe2+] or [1Fe3+, 3Fe2+] in low­potential ferredoxins. The oxidation numbers of the iron ions in high­potential ferredoxins can be [3Fe3+, 1Fe2+] or [2Fe3+, 2Fe2+].

There are proteins containing an [Fe3S4] centre, in which one iron is missing from the [Fe4S4] core. Three sulphide ions bridge two iron ions each, while the fourth sulphide bridges three iron ions. Their formal oxidation states may vary from [Fe3S4]+ (all­Fe3+ form) to [Fe3S4]2- (all­Fe2+ form) [3].

In a number of iron-sulphur proteins, the [Fe4S4] cluster can be reversibly converted by oxidation and loss of one iron ion to a [Fe3S4] cluster. E.g., the inactive form of aconitase possesses an [Fe3S4] and is activated by addition of Fe2+ and reductant [4].

Fe4S4 / Fe3S4 proteins in PROMISE

PROMISE ID Description
ACONITASE Aconitases, iron­responsive element binding proteins (IRE­BP), and alpha­isopropylmalate isomerases
AOR Aldehyde ferredoxin oxidoreductase family
BACFRDX Bacterial­type mono­, di­ and polycluster ferredoxins
DMSOR DMSO reductase family
ENDONUCLEASE3 Endonuclease III
FEHASE Iron hydrogenases
GPATASE Glutamine PRPP amidotransferase
HIPIP High potential iron-sulphur proteins
NIFE Nickel-iron hydrogenase
NITROGENASE1 Mo­nitrogenase component I
NITROGENASE2 Mo­nitrogenase component II
PRISMANE `Prismane' proteins
SIROHAEM Sirohaem-Fe4S4 enzymes (including sulphite reductases and assimilatory nitrite reductases)
TMADH Trimethylamine dehydrogenase

Fe4S4 / Fe3S4 proteins in enzyme databases

Enzyme cofactors LIGAND electron transport proteins
ENZYME LIGAND Code Description
  • Iron
  • Iron-sulfur
  • Non­heme iron
  • Iron
  • Iron-sulfur
  • Sulfur
    		•  C00138 Reduced ferredoxin
    C00139 Oxidized ferredoxin

    Fe4S4 / Fe3S4 proteins in motif databases

    PRINTS ID PRINTS AC PROSITE/BLOCKS ID PROSITE AC BLOCKS AC
    3FE4SFRDOXIN PR00352
    -
    -
    -
    4FE4SFRDOXIN PR00353 4FE4S_FERREDOXIN PS00198 BL00198
    7FE8SFRDOXIN PR00354
    ACONITASE PR00415 ACONITASE PS00450 BL00450
    -
    -
    		 ENDONUCLEASE_III_1
    ENDONUCLEASE_III_2    		 PS00764
    PS01155    		 BL00764
    -
    -
    		 GATASE_TYPE_II PS00443 BL00443
    HIPIPFRDOXIN PR00374 HIPIP PS00596 BL00596
    NIHGNASESMLL PR00614
    -
    -
    -
    -
    -
    		 NITROGENASE_1_1
    NITROGENASE_1_2    		 PS00699
    PS00090    		 BL00699
    NITROGNASEII PR00091 NIFH_FRXC_1
    NIFH_FRXC_2    		 PS00746
    PS00692    		 BL00746
    -
    -
    		 PUR_PYR_PR_TRANSFER PS00103 BL00103
    SIROHAEM PR00397 NIR_SIR PS00365 BL00365

    HET groups in PDB (at BSM)

    HET group Description Formula HET group Description Formula
    F3S
    		[Fe3S4] cluster Fe3S4
    F4S
    		[Fe4S4] cluster Fe4S4
    FS3
    		[Fe3S4] cluster Fe3S4
    FS4
    		[Fe4S4] cluster Fe4S4
    CLF
    		P­cluster of Mo­nitrogenase component I Fe8S7
    CLP*
    		 P­cluster of Mo­nitrogenase component I Fe8S8*

    * The [Fe8S8] cluster model appears to be wrong.

    Fe4S4 / Fe3S4 proteins in 3­D databases

    Ferredoxins Enzymes

    References

    1. Bertini, I., Ciurli, S. and Luchinat, C. (1995) The electronic structure of FeS centers in proteins and models. A contribution to the understanding of their electron transfer properties. Structure and Bonding 83, 1-53.
    2. Cowan, J.A. (1993) Inorganic Biochemistry: An Introduction. VCH Publishers, New York.
    3. Duff, J.L.C., Breton, J.L.J., Butt, J.N., Armstrong, F.A. and Thomson, A.J. (1996) Novel redox chemistry of [3Fe-4S] clusters: Electrochemical characterization of the all­Fe(II) form of the [3Fe-4S] cluster generated reversibly in various proteins and its spectroscopic investigation in Sulfolobus acidocaldarius ferredoxin. J. Am. Chem. Soc. 118, 8593-8603.
    4. Rouault, T.A. and Klausner, R.D. (1996) Iron-sulfur clusters as biosensors of oxidants and iron. Trends Biochem. Sci. 21, 174-177.