Purification and characterization of the Rieske iron‐sulfur protein from the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius

The Archaeal SoxABCD Complex Is a Proton Pump in Sulfolobus acidocaldarius

“…Despite the lack of cytochrome c (11,14) Sulfolobus membranes oxidize cytochrome c from horse heart in a cyanide-sensitive manner. Since it was shown that the membrane-residing Rieske-FeS proteins of Sulfolobus can accept electrons from cytochrome c (18,61), it is very likely that this activity is artifactual; as shown previously (61), the Rieske-FeS centers are reoxidized by the terminal oxidases also in intact membranes under aerobic conditions. Consequently, the cytochrome c oxidase activity vanishes during the purification of the SoxABCD quinol oxidase.…”

“…Although the Sulfolobus Rieske protein (SoxL (18)) presumably has no genuine cytochrome c binding domain, a sufficient rate of redox equilibration between both components is obviously possible (18). The back-transfer of electrons from the Rieske protein to quinone is thermodynamically compensated for by the large free energy change of the quinol oxidase reaction catalyzed by the integrated SoxABCD complex.…”

“…It has been shown that in isolated form one of the two Rieske-FeS proteins from Sulfolobus membranes (18,40) can readily equilibrate electrons between cytochrome c and ubiquinone analogs. Further, we have demonstrated that the reduced Rieske-FeS protein can be reoxidized by the detergent-solubilized SoxABCD complex, which inherently contains bound caldariella quinone.…”

“…In this work, we report on a method for isolation of the intact SoxABCD complex from membranes of S. acidocaldarius as well as for its successful reconstitution as a proton pump into archaeal lipid vesicles. This has been achieved by co-reconstitution with the SoxL Rieske-FeS protein from Sulfolobus (18), thereby permitting construction of a system that allowed energization of the membranes by reductant pulses from only one side; thus, the problem of randomized orientation of pumps could be overcome, and H ϩ /e Ϫ stoichiometries could be determined. Based on comparative sequence analyses, the data suggest that the single entity form of the enzyme is unlikely to pump protons, whereas the integrated SoxABCD complex is a proton pump very likely operating by an alternate pumping mechanism, eventually involving a Q cycle.…”

Isolation, Characterisation and Crystallisation of a Water‐Soluble Fragment of the Rieske Iron‐Sulfur Protein of Bovine Heart Mitochondrial bc1 Complex

“…Subsequently, the iron-sulfur protein has been isolated from various bc, complexes (Hurt et al, 1981 ;Engel et al, 1983;Shimomura et al, 1984;Schagger et al, 1987;Degli Esposti et al, 1990;Gonzklez-Halphen et al, 1991). In addition, Rieske proteins have been isolated-from Therrnus therrnophilus where no bc, complex has yet been identified (Fee et al, 1984) and from the archaeon Sulfolobus acidocaldarius which does not contain any c-type cytochromes and therefore no bc, complex (Schmidt et al, 1995).…”