TSRI's main web site PROMISE mirror at TSRI Metalloprotein DB site Created: 22 May 1997
Last modified: 1 February 1999

Mononuclear iron proteins

 Mononuclear iron proteins can be classified according to their biological function, by Fe centre type, by type and number of prosthetic centres, and by sequence similarity. In the Fe(Cys)4 proteins, tetracoordinate iron is bound to four cysteines [1]; these proteins, which are involved in electron transfer, contain the simplest form of iron centre - they are often included in the group of iron-sulphur proteins even though they do not bind inorganic sulphur.

A number of enzymes contain active sites where mononuclear iron is bound to residues other than Cys. Among the mononuclear iron enzymes with known 3­D structures, the common features are [2]:

  1. Iron is penta­ or hexacoordinate
  2. At least two His ligands
  3. At least one coordination site is vacant or occupied by solvent
  4. Ability to activate dioxygen Nitrile hydratase contain a novel iron centre coordinated by three Cys thiolates and two mainchain amide nitrogen atoms [3].

    Mononuclear iron proteins by function

    Function Protein class
    Catalysis Oxidoreductases
    • alpha­keto acid­dependent oxygenases
    • Aromatic amino acid hydroxylases
    • Aromatic­ring­cleavage dioxygenases
    • Fe-superoxide dismutase
    • Isopenicillin N synthase
    • Lipoxygenases
    • Nitrile hydratase
    • Rieske oxygenases
    Electron transfer
  5. Desulforedoxin
  6. Rubredoxins

  7. Photosynthetic reaction centres

    8. Mononuclear iron proteins by Fe centre type

    Mononuclear iron centre Protein class
    FeCys4 image
    Fe(SgammaCys)4
  8. Fe(Cys)4 proteins
    9. 2His-Fe-Glu centre

    Fe(NepsilonHis)2OepsilonGlu·2H2O
  9. Aromatic amino acid hydroxylases
  10. Extradiol aromatic­ring­cleavage dioxygenases
    		11.
    NDO Fe centre image
    Fe(NepsilonHis)2OdeltaAsp·H2O
  11. Aromatic­ring­hydroxylating dioxygenases
    		12.
    Fe(Cys)(His)4 image
    FeSgammaCysNdeltaHis(NepsilonHis)3
  12. Desulfoferrodoxin (centre II)
    13. Fe-SOD Fe centre

    Fe(NepsilonHis)3OdeltaAspH2O
  13. Fe-superoxide dismutase
    		14.
    34PCD Fe centre

    Fe(NepsilonHis)2(OetaTyr)2OH
  14. Intradiol aromatic­ring­cleavage dioxygenases
    		15.
    IPNS Fe centre

    Fe(NepsilonHis)2OdeltaAspOepsilonGln·2H2O
  15. Isopenicillin N synthase
    		16.
    plant lipoxygenase Fe centre

    Fe(NepsilonHis)3OCOO¯IleOdeltaAsnOH
  16. Lipoxygenases (plant)
    		17.
    mammalian lipoxygenase Fe centre

    Fe(NepsilonHis)3NdeltaHisOCOO¯IleOH
  17. Lipoxygenases (mammalian)
    		18.
    NHASE Fe-OH centre

    (SgammaCys)3(Nalpha)2OH
  18. Nitrile hydratase
    		19.
    PRC Fe centre

    Fe(NepsilonHis)4OepsilonGlu
  19. Photosynthetic reaction centres of purple bacteria
    		20.

    Mononuclear iron proteins by type and number of prosthetic centres

    Mononuclear iron proteins
    Simple Complex

    Mononuclear iron proteins in motif databases

    PRINTS ID PRINTS AC PROSITE/BLOCKS ID PROSITE AC BLOCKS AC
    -
    -
    		 EXTRADIOL_DIOXYGENAS PS00082 BL00082
    -
    -
    		 INTRADIOL_DIOXYGENAS PS00083 BL00083
    IPNSYNTHASE PR00682 IPNS1
    IPNS2    		 PS00185
    PS00186    		 BL00185
    LIPOXYGENASE PR00087 LIPOXYGENASE_1
    LIPOXYGENASE_2    		 PS00711
    PS00081    		 BL00711
    MAMLPOXGNASE PR00467
    PLTLPOXGNASE PR00468
    REACTNCENTRE PR00256 REACTION_CENTER PS00244 BL00244
    RNGDIOXGNASE PR00090 RING_HYDROXYL_ALPHA PS00570 BL00570
    RUBREDOXIN PR00163 RUBREDOXIN PS00202 BL00202
    -
    -
    		 SOD_MN PS00088 BL00088

    Mononuclear iron proteins in PROMISE
    PROMISE ID Description
    AAAOH Aromatic amino acid hydroxylases
    AOR Aldehyde ferredoxin oxidoreductase family
    ARHD Aromatic­ring­hydroxylating dioxygenases
    DESULFOREDOXIN Desulforedoxin­type Fe(Cys)4 proteins
    DFX Desulfoferrodoxin
    EARCD Extradiol aromatic­ring­cleavage dioxygenases
    FESOD Fe-superoxide dismutase
    IARCD Intradiol aromatic­ring­cleavage dioxygenases
    IPNS Isopenicillin N synthase
    LIPOXYGENASE Lipoxygenases
    NHASE Nitrile hydratase
    PRCPB Photosynthetic reaction centres of purple bacteria
    RIESKE Rieske iron-sulphur proteins
    RUBREDOXIN Rubredoxin­type Fe(Cys)4 proteins
    RUBRERYTHRIN Rubrerythrin

    HET groups in PDB (at BSM)

    HET group Description Formula HET group Description Formula
    FE
    		Iron(III) ion Fe3+
    FE2
    		Iron(II) ion Fe2+
    MN
    		Manganese ion Mn2+ or Mn3+
    ZN
    		Zinc ion Zn2+

    Mononuclear iron proteins in 3­D databases

    Electron­transfer proteins Enzymes
  20. Desulforedoxin
  21. Photosynthetic reaction centres of purple bacteria
  22. Rubredoxins
  23. Rubrerythrin
  24. Aromatic amino acid hydroxylases
  25. Extradiol aromatic­ring­cleavage dioxygenases
  26. Intradiol aromatic­ring­cleavage dioxygenases
  27. Isopenicillin N synthase
  28. Lipoxygenases
  29. Nitrile hydratase

    30. 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. Que, L., Jr. and Ho, R.Y.N. (1996) Dioxygen activation by enzymes with mononuclear non­heme iron active sites. Chem. Rev. 96, 2607-2624.
    3. Huang, W., Jia, J., Cummings, J., Nelson, M., Schneider, G. and Lindqvist, Y. (1997) Crystal structure of nitrile hydratase reveals a novel iron centre in a novel fold. Structure 5, 691-699.
    General references on mononuclear iron proteins