Superoxide reductase
Neelareductase, or superoxide reductase, from the thermophilic Archaea Pyrococcus furiosus, is able to catalyse the conversion of the superoxide radical O*- into the less toxic product hydrogen peroxide. It shares this ability with a number of homologous proteins from anaerobic bacteria and archaea where the removal of the superoxide radical, a product of anaerobic respiration in these organisms, is essential for their survival. It is part of a family of mononuclear non-haem iron containing proteins, which all have the iron coordinated with a pentacoordinate 4 His Cys motif and a variable 6th ligand.
Reference Protein and Structure
- Sequence
-
P82385
(1.15.1.2)
(Sequence Homologues) (PDB Homologues)
- Biological species
-
Pyrococcus furiosus DSM 3638 (Archaea)
- PDB
-
1do6
- CRYSTAL STRUCTURE OF SUPEROXIDE REDUCTASE IN THE OXIDIZED STATE AT 2.0 ANGSTROM RESOLUTION
(2.0 Å)
- Catalytic CATH Domains
-
2.60.40.730
(see all for 1do6)
- Cofactors
- Iron(2+) (1), Iron(3+) (1)
Enzyme Mechanism
Introduction
The iron centre is able to reduce the superoxide radical to hydrogen peroxide, ultimately accepting electrons from a NADPH coupled oxidoreductase, thus transferring the electrons from NADPH to the superoxide radical. In doing so, the reduced iron centre Fe(II) gives an electron to the superoxide with concomitant protonation by Lys 15. This produces an intermediate Fe(III) hydroperoxide species which picks up another proton allowing hydrogen peroxide release, assisted by the binding of Glu 14 to the Fe (III) centre to replace the oxygen of the hydroperoxide as a ligand. Regeneration of the catalytic Fe (II) ion is then achieved by the donation of electrons from an NADPH oxidoreductase.
Catalytic Residues Roles
UniProt | PDB* (1do6) | ||
Glu14 | Glu14A | Acts as the 6th iron ligand when in the Fe (III) form, thus protecting this form from being reduced, and allowing hydrogen peroxide to leave the complex. | nucleophile, metal ligand, electrostatic stabiliser |
Lys15 | Lys15A | Protonates the superoxide radical to allow it to accept an electron from the iron centre, thus forming the hydroperoxide intermediate. | proton donor |
Chemical Components
coordination to a metal ion, electron transfer, redox reaction, proton transfer, intermediate formation, overall product formed, native state of enzyme regenerated, intermediate terminatedReferences
- Abreu IA et al. (2001), J Biol Chem, 276, 38995-39001. The Mechanism of Superoxide Scavenging byArchaeoglobus fulgidus Neelaredoxin. DOI:10.1074/jbc.m103232200. PMID:11489883.
- Silaghi-Dumitrescu R et al. (2003), Inorg Chem, 42, 446-456. Computational Study of the Non-Heme Iron Active Site in Superoxide Reductase and Its Reaction with Superoxide. DOI:10.1021/ic025684l.
- Emerson JP et al. (2002), Biochemistry, 41, 4348-4357. Kinetics and Mechanism of Superoxide Reduction by Two-Iron Superoxide Reductase fromDesulfovibriovulgaris†. DOI:10.1021/bi0119159. PMID:11914081.
- Yeh AP et al. (2000), Biochemistry, 39, 2499-2508. Structures of the Superoxide Reductase fromPyrococcus furiosusin the Oxidized and Reduced States†,‡. DOI:10.1021/bi992428k. PMID:10704199.
Step 1. The superoxide radical binds to the iron centre, oxidising Fe(II) to Fe(III).
Download: Image, Marvin FileCatalytic Residues Roles
Residue | Roles |
---|---|
His16A | metal ligand |
His41A | metal ligand |
His47A | metal ligand |
Cys111A | metal ligand |
His114A | metal ligand |
Chemical Components
coordination to a metal ion, electron transfer, redox reactionCatalytic Residues Roles
Residue | Roles |
---|---|
His41A | metal ligand |
His47A | metal ligand |
Cys111A | metal ligand |
His114A | metal ligand |
Glu14A | electrostatic stabiliser |
Lys15A | proton donor |
Chemical Components
proton transfer, intermediate formationStep 3. The hydroperoxy intermediate is protonated again and released from the iron centre by Glu14. The Fe(II) centre is subsequently regenerated by the donation of electrons from an NADPH oxidoreductase.
Download: Image, Marvin FileCatalytic Residues Roles
Residue | Roles |
---|---|
Glu14A | metal ligand |
His16A | metal ligand |
His41A | metal ligand |
His47A | metal ligand |
Cys111A | metal ligand |
His114A | metal ligand |
Glu14A | nucleophile |