Symbol Rubredoxin Pfam clan CL0045 PROSITE PDOC00179 | Pfam PF00301 InterPro IPR004039 SCOP 7rxn | |
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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.
Contents
Structure
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. While the vast majority of rubredoxins are soluble, there exists a membrane-bound rubredoxin referred to as rubredoxin A in oxygenic photoautotrophs.
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 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 1.14.15.3 alkane 1-monooxygenase (alkane,reduced-rubredoxin:oxygen 1-oxidoreductase)
octane + reduced rubredoxin + O2 = 1-octanol + oxidized rubredoxin + H2OEC 1.15.1.2 superoxide reductase (rubredoxin:superoxide oxidoreductase)
reduced rubredoxin + superoxide + 2 H+ = rubredoxin + H2O2EC 1.18.1.1 rubredoxin—NAD+ reductase (rubredoxin:NAD+ oxidoreductase)
reduced rubredoxin + NAD+ = oxidized rubredoxin + NADH + H+EC 1.18.1.4 rubredoxin—NAD(P)+ reductase (rubredoxin:NAD(P)+ oxidoreductase)
reduced rubredoxin + NAD(P)+ = oxidized rubredoxin + NAD(P)H + H+