Functional and evolutionary implications of a [3Fe-4S] cluster of the dicluster-type ferredoxin from the thermoacidophilic archaeon, Sulfolobus sp. strain 7.
The dicluster-type ferredoxin is a key electron carrier in the cytoplasm of the aerobic and thermoacidophilic archaeon, Sulfolobus sp. strain 7, and contains 1 aspartate and 7 cysteine residues as possible ligands to two FeS clusters. The optical, electron paramagnetic resonance (EPR), and cyclic voltammetric studies suggest the presence of one each of [3Fe-4S]1+,0 (-280 mV) and [4Fe-4S]2+,1+ (-530 mV) clusters in the purified Sulfolobus ferredoxin, and the lower potential [4Fe-4S] center was scarcely reducible by excess dithionite even at pH 9. While the Sulfolobus ferredoxin has been known to function as an electron acceptor of 2-oxoacid:ferredoxin oxidoreductase (Kerscher, L., Nowitzki, S., and Oesterhelt, D. (1982) Eur. J. Biochem. 128, 223-230), it is not known whether one or both of two clusters is reduced during the steady-state turnover of the enzyme. Here we show by combinations of the optical and EPR spectroscopies that only the higher potential [3Fe-4S] cluster is reduced at the physiological pH during the steady-state turnover of the purified 2-oxoacid:ferredoxin oxidoreductase at 50 degrees C. The functional significance and evolutionary implications of the [3Fe-4S] center in dicluster-type ferredoxins are discussed.
Iwasaki
T
T
Department of Life Science, Tokyo Institute of Technology, Yokohama, Japan.
Wakagi
T
T
Isogai
Y
Y
Tanaka
K
K
Iizuka
T
T
Oshima
T
T
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D005075:Biological Evolution; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D055095:Optics and Photonics; D016944:Sulfolobus / Q000378:metabolism*
D001426:Bacterial Proteins; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins