Rieske iron sulfur cluster

Figure 18-8 Stereoscopic ribbon diagrams of the chicken bc1 complex (A) The native dimer. The molecular twofold axis runs vertically between the two monomers. Quinones, phospholipids, and detergent molecules are not shown for clarity. The presumed membrane bilayer is represented by a gray band. (B) Isolated close-up view of the two conformations of the Rieske protein (top and long helix at right) in contact with cytochrome b (below), with associated heme groups and bound inhibitors, stigmatellin, and antimycin. The isolated heme of cytochrome c, (left, above) is also shown. (C) Structure of the intermembrane (external surface) domains of the chicken bcx complex. This is viewed from within the membrane, with the transmembrane helices truncated at roughly the membrane surface. Ball-and-stick models represent the heme group of cytochrome cy the Rieske iron-sulfur cluster, and the disulfide cysteines of subunit 8. SU, subunit cyt, cytochrome. From Zhang et al.105...

C. Movement of the Extrinsic Rieske Iron-Sulfur-Cluster Domain during Electron Transfer...658... 

Naphthalene dioxygenase consists of three components, which form an electron transfer chain an NADH-dependent flavoprotein reductase, a ferredoxin containing two [2Fe2S] Rieske iron-sulfur clusters, and a Rieske oxygenase containing both a [2Fe2S] Rieske iron-sulfiir cluster and a mononuclear iron(II) center in the enzyme active site. ° ... 

In summary, it appears that the protein has to adopt the correct fold before the Rieske cluster can be inserted. The correct folding will depend on the stability of the protein the Rieske protein from the thermoacidophilic archaebacterium Sulfolobus seems to be more stable than Rieske proteins from other bacteria so that the Rieske cluster can be inserted into the soluble form of the protein during expression with the help of the chaperonins. If the protein cannot adopt the correct fold, the result will be either no cluster or a distorted iron sulfur cluster, perhaps using the two cysteines that form the disulfide bridge in correctly assembled Rieske proteins. 

Studies (see, e.g., (101)) indicate that photosynthesis originated after the development of respiratory electron transfer pathways (99, 143). The photosynthetic reaction center, in this scenario, would have been created in order to enhance the efficiency of the already existing electron transport chains, that is, by adding a light-driven cycle around the cytochrome be complex. The Rieske protein as the key subunit in cytochrome be complexes would in this picture have contributed the first iron-sulfur center involved in photosynthetic mechanisms (since on the basis of the present data, it seems likely to us that the first photosynthetic RC resembled RCII, i.e., was devoid of iron—sulfur clusters). 

In the hydrogenosomal membranes, EPR spectra showed no trace of the highly characteristic features of the iron-sulfur clusters of complex I (NADH ubiquinone reductase) and the Rieske protein of complex III of the mitochondrial respiratory chain. This is consistent with the absence of... 

In this text, iron-sulfur clusters are discussed because they appear in proteins and enzymes (1) cytochrome b(6)f, Rieske [2Fe-2S] cluster (Section 7.5 and Figure 7.26) (2) cytochrome bci, Rieske [2Fe-2S] cluster (Section 7.6 and Figure 7.30) and (3) aconitase, [4Fe-4S] cluster (Section 7.9.2.1, and Figure 7.50). The iron-sulfur protein (ISP) component of the cytochrome b(6)f and cytochrome bci complexes, now called the Rieske ISP, was first discovered and isolated by John S. Rieske and co-workers in 1964 (in the cytochrome bci complex). More information about the RISP is found in Section 7.5.1. Section 7.9.2 briefly discusses other proteins with iron-sulfur clusters—rubredoxins, ferrodoxins, and the enzyme nitrogenase. The nitrogenase enzyme was the subject of Chapter 6 in the hrst edition of this text— see especially the first edition s Section 6.3 for a discussion of iron-sulfur clusters. In this second edition, information on iron-sulfur clusters in nitrogenase is found in Section 3.6.4. See Table 3.2 and the descriptive examples discussed in Section 3.6.4. 

It is noteworthy that except for the Rieske center in Complex III, Complexes I and 11 are home to all the iron-sulfur clusters in the mitochondrial electron transfer chain and consequently most of the iron-containing carriers in the entire sequence. Hibbs subsequently showed that CAM-injured cells lose a substantial portion of their total intracellular iron (Hibbs et al., 1984) [later studies specifically identified loss of mitochondrial iron (Wharton et al., 1988)] and Drapier and Hibbs (1986) showed that the activity of another iron-sulfur-containing enzyme, aconitase, is also lost. In early 1987 Hibbs reported that the cytostatic actions of CAMs requires the presence of only one component in culture medium, L-arginine (Hibbs et al., 1987b). Thus, the stage was set for the discovery of a unique reactive species that targets intracellular iron, produced by CAMs. 

Functions of iron-sulfur enzymes. Numerous iron-sulfur clusters are present within the membrane-bound electron transport chains discussed in Chapter 18. Of special interest is the Fe2S2 cluster present in a protein isolated from the cytochrome be complex (complex III) of mitochondria. First purified by Rieske et al.,307 this protein is often called the Rieske iron-sulfur protein 308 Similar proteins are found in cytochrome be complexes of chloroplasts.125 300 309 310 In... 

Figure 16-18 Mossbauer X-ray absorption spectra of iron-sulfur clusters. (See Chapter 23 for a brief description of the method.) Quadrupole doublets are indicated by brackets and isomer shifts are marked by triangles. (A) [Fe2S2]1+ cluster of the Rieske protein from Pseudomonas mendocina, at temperature T = 200 K. (B) [Fe3S4]1+ state of D. gigas ferre-doxin II, T = 90 K. (C) [Fe3S4]° state of D. gigas ferredoxin II, T = 15 K. (D) [Fe4S4]2+ cluster of E. coli FNR protein, T = 4.2 K. (E) [Fe4S4]1+ cluster of E. coli sulfite reductase, T = 110 K. From Beinert et al.260...

The bcf complexes form dimers in the membrane with molecular masses of approximately 480 kDa (mitochondria) and 130 kDa (bacteria), respectively. Each monomer has 10-13 membrane spanning helices, depending on the number of noncatalytic subunits. The membrane spanning helices of cytochrome b are in the center of the structure and form the dimer interface while the other membrane spanning helices are located around cytochrome b. Cytochrome c and the Rieske iron sulfur protein both have water soluble domains containing the redox centers, heme ci and the [2Fe-2S] cluster, respectively. These domains are at the outside of the iimer mitochondrial membrane, i.e., in the intermembrane space, and bound to the membrane via membrane spanning helices acting as membrane anchors. 

Denke, E., Merbitz-Zahradnik, T., Hatzfeld, O. M., Snyder, C. H., Link, T. A., and Trumpower, B. L., 1998, Alteration of the midpoint potential and catalytic activity of the rieske iron-sulfur protein by changes of amino acids forming hydrogen bonds to the iron-sulfur cluster, J. Biol. Chem. 273 9085n9093. 

Rieske iron-sulfur protein An iron-sulfur protein of the mitochondrial respiratory chain, in which the [2FE-2S] cluster is coordinated to two sulfur ligands from cysteine and two imidazole ligands from histidine. The term is also applied to similar proteins isolated from photosynthetic organisms and microorganisms and other proteins containing [2Fe-2S] clusters with similar coordination. 

Cytochromes, as components of electron transfer chains, must interact with the other components, accepting electrons from reduced donor molecules and transferring them to appropriate acceptors. In the respiratory chain of the mitochondria, the ubiquinolxytochrome c oxidoreductase, QCR or cytochrome bc complex, transfers electrons coming from Complexes 1 and 11 to cytochrome c. The bc complex oxidises a membrane-localised ubiquinol the redox process is coupled to the translocation of protons across the membrane, in the so-called proton-motive Q cycle, which is presented in a simplified form in Figure 13.14. This cycle was first proposed by Peter Mitchell 30 years ago and substantially confirmed experimentally since then. The Q cycle in fact consists of two turnovers of QH2 (Figure 13.14). In both turnovers, the lipid-soluble ubiquinol (QH2) is oxidized in a two-step reoxidation in which the semiquinone CoQ is a stable intermediate, at the intermembrane face of the mitochondrial inner membrane. It transfers one electron to the Rieske iron—sulfur protein (ISP), one electron to one of the two cytochrome b haems (bi), while two protons are transferred to the intermembrane space. In both of the Q cycles, the cytochrome bi reduces cytochrome bfj while the Reiske iron—sulfur cluster reduces cytochrome c/. The cytochrome ci in turn reduces the water-soluble cytochrome c, which transfers its electrons to the terminal oxidase, cytochrome c oxidase, described above. In one of the two Q cycles, reduced cytochrome bf reduces Q to the semiquinone, which is then reduced to QH2 by the second reduced cytochrome bn- The protons required for this step are derived from the matrix side of the membrane. The overall outcome of the two CoQ cycles (10) (/ — matrix o — intermembrane space) is... 

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