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Last modified: 22 December 1998

Fe-superoxide dismutase
Mononuclear iron centre Iron ligand(s) Formal iron
oxidation/spin states
Fe-SOD Fe centre

Fe(NepsilonHis)3OdeltaAspH2O
3 × NepsilonHis;

eta1­OdeltaAsp;

H2O or OH¯

FeII (S = 2);

FeIII (S = 5/2)

Superoxide dismutases (SODs) are antioxidant metalloenzymes catalysing the redox disproportionatin (dismutation) of superoxide radical, O2·¯ (1):

It is generally accepted that in all SODs the metal ion (M) catalyses dismutation of the superoxide radical through a cyclic oxidation­reduction mechanism: Four classes of SODs are known, distinguished by the metal prosthetic group: Cu/Zn, Fe, Mn and Ni. Fe- and Mn-SODs constitute a structural family [1, 2]. Fe- and Mn-SODs are unequally distributed throughout the kingdoms of living organisms and are located in different cellular compartments [3]. In particular, Fe-SOD is found in obligate anaerobes and aerobic diazotrophs (exclusively), facultative aerobes (exclusively or together with Mn-SOD), in the cytosol of cyanobacteria, in the chloroplast stroma of higher plants and in protozoa (cf. Mn-SOD). Fe-SOD and Mn-SOD from some organisms (e.g. Escherichia coli) exhibit almost absolute metal specificity [4], while other enzymes, such as `cambialistic' SOD from Propionibacterium shermanii, are active with either metal [5]. Fe- and Mn-SODs occur as homodimers or homotetramers.

The 3­D structures of several Fe-SODs have been determined [6-10]. The monomers fold into two domains. The N­terminal domain consists of two long antiparallel alpha­helices. The C­terminal domain contains a central ß­sheet formed by three antiparallel ß­strands with 4-6 surrounding alpha­helices. The iron atom is liganded by two residues from each of N­terminal helices and two residues from the loops in the C­terminal domain.

The active site iron is pentacoordinate, with the metal ligands (Nepsilon of three conserved His residues, Odelta of the conserved Asp residue and a water molecule) arranged in distorted trigonal bipyramidal geometry. The first His residue and a solvent molecule fill the two axial positions. In the azide-FeIII-SOD complex, the iron becomes hexacoordinate with distorted octahedral geometry, with azide coordinated trans to Asp ligand [7]. The table below lists the mononuclear iron environment residues in known 3­D structures.

Enzyme Quaternary
structure		 Mononuclear iron environment residues PDB code Ref.
Aquifex pyrophilus Fe-SOD tetramer
His­27
His­81
Asp­163
His­167
-
[6]
Escherichia coli Fe-SOD dimer
His­26
His­73
Asp­156
His­160
1isa
1isb
1isc
[7]
Mycobacterium tuberculosis Fe-SOD tetramer
His­28
His­76
Asp­160
His­164
1ids
[8]
Pseudomonas ovalis Fe-SOD dimer
His­26
His­74
Asp­156
His­160
3sdp
[9]
Propionibacterium freudenreichii cambialistic SOD tetramer
His­27
His­75
Asp­161
His­165
1ar5 1avm
[10]

Fe-SOD in enzyme databases

ENZYME LIGAND BRENDA Official name Alternative names
1.15.1.1 1.15.11.1 1.15.1.1 Superoxide dismutase Ferrisuperoxide dismutase; Fe-SOD

Fe-SOD in motif databases

PRINTS ID PRINTS AC PROSITE/BLOCKS ID PROSITE AC BLOCKS AC
-
-
 SOD_MN PS00088 BL00088

Fe-SOD in alignment databases

Protein Superfamily Pfam LPFC 3­D alignment
00206; superoxide dismutase (Fe/Mn)
PF00081; sodfe
-

Fe-SOD in 3­D databases

Fe-superoxide dismutase contain a single iron atom per monomer.

PDB MSD scop BSMRELI
Base		 Header MMS Abstract ¹
1ar5 1ar5 1ar5 1ar5 1ar5 Cambialistic superoxide dismutase [Fe(III) bound]; Propionibacterium freudenreichii subspec. Shermanii
-
1avm 1avm 1avm 1avm 1avm Cambialistic superoxide dismutase [Fe(III) bound] (complex with azide); Propionibacterium freudenreichii subspec. Shermanii, strain PZ3
-
1ids 1ids 1ids 1ids 1ids Fe(III)-superoxide dismutase; Mycobacterium tuberculosis (recombinant form expressed in Mycobacterium vaccae)
-
1isa 1isa 1isa 1isa 1isa Fe(II)-superoxide dismutase; Escherichia coli
-
1isb 1isb 1isb 1isb 1isb Fe(III)-superoxide dismutase; Escherichia coli
-
1isc 1isc 1isc 1isc 1isc Fe(III)-superoxide dismutase (complex with azide); Escherichia coli
-
3sdp 3sdp 3sdp 3sdp 3sdp Fe(III)-superoxide dismutase; Pseudomonas ovalis
-

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

References

  1. Parker, M.W., Blake, C.C., Barra, D., Bossa, F., Schinina, M.E., Bannister, W.H. and Bannister, J.V. (1987) Structural identity between the iron­ and manganese­containing superoxide dismutases. Protein Engineering 1, 393-397.
  2. Parker, M.W. and Blake, C.C. (1988) Iron­ and manganese­containing superoxide dismutases can be distinguished by analysis of their primary structures. FEBS Lett. 229, 377-382.
  3. Grace, S.C. (1990) Phylogenetic distribution of superoxide dismutase supports an endosymbiotic origin for chloroplasts and mitochondria. Life Sci. 47, 1875-1886.
  4. Beyer, W.F., Jr., Reynolds, J.A. and Fridovich, I. (1989) Differences between the manganese­ and the iron­containing superoxide dismutases of Escherichia coli detected through sedimentation equilibrium, hydrodynamic, and spectroscopic studies. Biochemistry 28, 4403-4409.
  5. Sehn, A.P. and Meier, B. (1994) Regulation of an in vivo metal­exchangeable superoxide dismutase from Propionibacterium shermanii exhibiting activity with different metal cofactors. Biochem. J. 304, 803-808.
  6. Lim, J.­H., Yu, Y.G., Han, Y.S., Cho, S., Ahn, B.­Y., Kim, S.­H. and Cho, Y. (1997) The crystal structure of an Fe-superoxide dismutase from the hyperthermophile Aquifex pyrophilus at 1.9 Å resolution: Structural basis for thermostability. J. Mol. Biol. 270, 259-274.
  7. Lah, M.S., Dixon, M.M., Pattridge, K.A., Stallings, W.C., Fee, J.A. and Ludwig, M.L. (1995) Structure-function in Escherichia coli iron superoxide dismutase: Comparisons with the manganese enzyme from Thermus thermophilus. Biochemistry 34, 1646-1660.
  8. Cooper, J.B., McIntyre, K., Badasso, M.O., Wood, S.P., Zhang, Y., Garbe, T.R. and Young, D. (1995) X­ray structure analysis of the iron­dependent superoxide dismutase from Mycobacterium tuberculosis at 2.0 Å resolution reveals novel dimer-dimer interactions. J. Mol. Biol. 246, 531-544.
  9. Stoddard, B.L., Howell, P.L., Ringe, D. and Petsko, G.A. (1990a) The 2.1­Å resolution structure of iron superoxide dismutase from Pseudomonas ovalis. Biochemistry 29, 8885-8893.
  10. Schmidt, M., Meier, B. and Parak, F. (1996) X­ray structure of the cambialistic superoxide dismutase from Propionibacterium shermanii active with Fe or Mn. J. Biol. Inorg. Chem. 1, 532-541.
Bibliography on structural studies of Fe-superoxide dismutase
Reviews on superoxide dismutases