T. Imai et al., Characterization and cloning of an extremely thermostable, Pyrococcus furiosus-type 4Fe ferredoxin from Thermococcus profundus, J BIOCHEM, 130(5), 2001, pp. 649-655
An extremely thermostable [4Fe-4S] ferredoxin was isolated under anaerobic
conditions from a hyperthermophilic archaeon Thermococcus profundus, and th
e ferredoxin gene was cloned and sequenced. The nucleotide sequence of the
ferredoxin gene shows the ferredoxin to comprise 62 amino acid residues wit
h a sequence similar to those of many bacterial and archaeal 4Fe (3Fe) ferr
edoxins. The unusual Fe-S cluster type, which was identified in the resonan
ce Raman and EPR spectra, has three cysteines and one aspartate as the clus
ter ligands, as in the Pyrococcus furiosus 4Fe_ferredoxin. Under aerobic co
nditions, a ferredoxin was purified that contains a [3Fe-4S] cluster as the
major Fe-S cluster and a small amount of the [4Fe-4S] cluster. Its N-termi
nal amino acid se-quence is the same as that of the anaerobically-purified
ferredoxin up to the 26th residue. These results indicate that the 4Fe ferr
edoxin was degraded to 3Fe ferredoxin during aerobic purification. The aero
bically-purified ferredoxin was reversibly converted back to the [4Fe-4S] f
erredoxin by the addition of ferrous ions under reducing conditions. The an
aerobically-purified [4Fe-4S] ferredoxin is quite stable; little degradtion
was observed over 20 h at 100 degreesC, while the half-life of the aerobic
ally-purified ferredoxin is 10 h at 100 degreesC. Both the anaerobically- a
nd aerobically-purified ferredoxins were found to function as electron acce
ptors for the pyruvate-ferredoxin oxidoreductase purified from the same arc
haeon.