Rubredoxin

Rubredoxins are a class of low-molecular-weight iron-containing proteins found in sulfur-metabolizing bacteria and archaea. Sometimes rubredoxins are classified as iron-sulfur proteins; however, in contrast to iron-sulfur proteins, rubredoxins do not contain inorganic sulfide. Like cytochromes, ferredoxins and Rieske proteins, rubredoxins participate in electron transfer in biological systems.

tructure

The 3-D structures of a number of rubredoxins have been solved. The fold belongs to the α+β class, with 2 α-helices and 2-3 β-strands. Rubredoxin active site contains an iron ion which is coordinated by the sulfurs of four conserved cysteine residues forming an almost regular tetrahedron. This is sometimes denoted as a [1Fe-0S] or an Fe₁S₀ system, in analogy to the nomenclature for iron-sulfur proteins.

Rubredoxins perform one-electron transfer processes. The central iron atom changes between the +2 and +3 oxidation states. In both oxidation states, the metal remains high spin, which helps to minimize structural changes. The reduction potential of a rubredoxin is typically in the range +50 mV to -50 mV.

This iron-sulphur protein is an electron carrier, and it is easy to distinguish its metallic centre changes: the oxidized state is reddish (due to a ligand metal charge transfer), while the reduced state is colourless (because the electron transition has an energy of the infrared level, which is imperceptible for the human eye).

Rubredoxin in some biochemical reactions

EC number|1.14.15.2 camphor 1,2-monooxygenase [(+)-camphor,reduced-rubredoxin:oxygen oxidoreductase (1,2-lactonizing)] : (+)-bornane-2,5-dione + reduced rubredoxin + O₂ = 5-oxo-1,2-campholide + oxidized rubredoxin + H₂OEC number|1.14.15.3 alkane 1-monooxygenase (alkane,reduced-rubredoxin:oxygen 1-oxidoreductase): octane + reduced rubredoxin + O₂ = 1-octanol + oxidized rubredoxin + H₂OEC number|1.15.1.2 superoxide reductase (rubredoxin:superoxide oxidoreductase): reduced rubredoxin + superoxide + 2 H⁺ = rubredoxin + H₂O₂EC number|1.18.1.1 rubredoxin—NAD⁺ reductase (rubredoxin:NAD⁺ oxidoreductase): reduced rubredoxin + NAD⁺ = oxidized rubredoxin + NADH + H⁺EC number|1.18.1.4 rubredoxin—NAD(P)⁺ reductase (rubredoxin:NAD(P)⁺ oxidoreductase): reduced rubredoxin + NAD(P)⁺ = oxidized rubredoxin + NAD(P)H + H⁺

ee also

* Bioinorganic chemistry
* Iron-sulfur protein
* Ferredoxin
* Cytochrome
* Rieske protein

References

* Stephen J. Lippard, Jeremy M. Berg, "Principles of Bioinorganic Chemistry", University Science Books, 1994, ISBN 0-935702-72-5
* J.J.R. Fraústo da Silva and R.J.P. Williams, "The biological chemistry of the elements: The inorganic chemistry of life", 2nd Edition, Oxford University Press, 2001, ISBN 0-19-850848-4

External links

* - X-ray structure of rubredoxin from "Clostridium pasteurianum"
* - neutron diffraction structure of rubredoxin from "Pyrococcus furiosus"
* - InterPro entry for rubredoxin
* [http://faculty.washington.edu/stenkamp/rubre.html A Little Iron-Sulfur Protein]