Sulredoxin: a novel iron-sulfur protein of the thermoacidophilic archaeon Sulfolobus sp. strain 7 with a Rieske-type [2Fe-2S] center

Abstract

A novel pink [2Fe-2S] protein has been purified from the cytosol fraction of the thermoacidophilic archaeon Sulfolobus sp. strain 7 (originally named Sulfolobus acidocaldarius 7) and called ''sulredoxin. ' The plant-type [2Fe-2S] ferredoxins have midpoint redox potentials ranging from Ϫ230 to Ϫ450 mV (35) and serve as low-potential, single-electron carriers from the photosystem I reaction center to various ferredoxin-dependent oxidoreductases in cyanobacteria and chloroplasts of plants (21,35). Their redox centers, namely, the plant ferredoxin-type [2Fe-2S] clusters, coordinate to the proteins by four sulfide ligands contributed by four cysteine residues and give a low-temperature electron paramagnetic resonance (EPR) signal only in the reduced state, with an average g-factor (g av ) of around 1.96 (28, 29). Essentially similar ferredoxins have also been isolated from the mammalian adrenal mitochondria (adrenodoxin), purple bacteria, and the extremely halophilic archaea, which participate in the cytochrome P-450-dependent steroid-hydroxylating system, nitrogen fixation system, and coenzyme A-acylating 2-oxoacid-oxidizing system, respectively (35).Another class of the [2Fe-2S] cluster-containing FeS proteins comprises the respiratory Rieske proteins, which are an important constituent of the cytochrome bc (bc 1 /b 6 f) complex (respiratory complex III) of the aerobic respiratory and photosynthetic systems (28, 34). They have relatively high midpoint redox potentials ranging from Ϫ150 to ϩ350 mV and elicit a characteristic EPR signal with an unusually low g av of ϳ1.91 in the reduced state, as well as red-shifted visible spectra in the oxidized state. The [2Fe-2S] clusters of several ferredoxins involved in the bacterial dioxygenase systems also have spectral properties more similar to those of the Rieske-type FeS proteins than those of the plant-type ferredoxins (28). These spectral properties are due most likely to the asymmetrical ligand environments; extensive analyses of the Riesketype [2Fe-2S] clusters of Thermus thermophilus respiratory Rieske protein (8) and Pseudomonas cepacia phthalate dioxygenase (3) suggested that one iron atom of the FeS cluster coordinated to the protein by two sulfide ligands contributed by two cysteine residues, while the other coordinated by two ␦-nitrogens of the imidazole rings contributed by two histidine residues (5, 9, 13, 23).Sulfolobus sp. strain 7 (originally named Sulfolobus acidocaldarius 7) is a typical aerobic and thermoacidophilic archaeon that grows optimally at pH 2.5 to 3 and at 75 to 80ЊC (36). Chemoheterotrophically grown cells acquire biological energy by aerobic respiration rather than simple fermentation (22,36), and the aerobic respiratory chain, which is coupled to the oxidative tricarboxylic acid cycle at the level of succinate (17), contains the unusual membrane-bound terminal cytochrome oxidase system; it consists solely of a-and b-type but no c-type cytochromes (17,36,37), and the presence of a respiratory Rieske FeS protein or its analog has not been r...

Molecular and phylogenetic characterization of isopropylmalate dehydrogenase of a thermoacidophilic archaeon, Sulfolobus sp. strain 7

“…IPMDH is a homotetramer, supporting the earlier proposal (40). While prokaryotic IPMDHs and eubacterial NADP-dependent ICDH are homodimeric (12,18,37). The mitochondrial NAD-dependent ICDHs are either tetrameric (33,41) or octameric (21).…”

Engineering a Three-cysteine, One-histidine Ligand Environment into a New Hyperthermophilic Archaeal Rieske-type [2Fe-2S] Ferredoxin from Sulfolobus solfataricus

“…2B and 3A). Interestingly the cluster reduction potential of ARF is significantly more negative than that of S. tokodaii sulredoxin, another archaeal water-soluble Rieske protein (E m,low pH ϳ ϩ190 mV) (28,29), suggesting operation of multiple soluble Rieske-type proteins in the Sulfolobus redox system; ARF likely plays a redox role in an unknown electron transfer sequence, perhaps involved in biodegradation of alkene or aromatic compounds at high temperature.…”

“…Sulredoxin was purified from the soluble fraction of S. tokodaii strain 7 (formerly Sulfolobus sp. strain 7; JCM 10545T (34)) as described previously (28,35). Other chemicals mentioned in this study were of analytical grade.…”

Role of cytochrome b562 in the archaeal aerobic respiratory chain of Sulfolobus sp. strain 7

“…strain 7 was cultivated at pH 2.5-3 and 75-80°C harvested in the early to middle exponential phase of growth, and the intact membrane was prepared by French press treatment ( -20 mg of protein/ml) [8]. In some experiments, the membrane fraction was treated with 4% (w/v) sodium cholate in 40 mM potassium phosphate buffer, pH 6.8, which efficiently removed some weakly associated membrane proteins including a 'g, = 1.91' Rieske FeS protein of unknown function [8,12], but not the cognate succinate :caldariellaquinone oxidoreductase (the respiratory complex II) [14] and the terminal oxidase supercomplex [8]. The material collected by ultracentrifugation and made in 40 mM potassium phosphate buffer, pH 6.8, was used as the 'cholate-treated membrane'.…”