Rieske-type proteins dioxygenase

Sequences of proteins containing Rieske-type clusters have been deduced from the complete operons of several dioxygenases these dioxygenases require electrons from NAD(P)H to convert aromatic compounds to cis-arene diols. The water-soluble dioxygenase systems consist of a reductase and a terminal dioxygenase many dioxygenases also contain a [2Fe-2S] ferredoxin (20). The terminal oxygenases contain a Rieske-type cluster and the ferredoxins may contain either a Rieske-type or a 4-cysteine coordinated [2Fe-2S] cluster. 

The coordination of the Rieske cluster in the a subunit of benzene dioxygenase has been studied by site-directed mutagenesis. The replacement of His 98 or His 119 (corresponding to His 83/104 in NDO) by Cys resulted in a protein that was unable to coordinate a normal Rieske-type cluster (53). In the mutant His 98 Cys, a novel EPR spectrum with av = 1-94 was detected that is intermediate between... 

Extinction Coefficients and Ellipticities of the Rieske Protein from Bovine Heart bc Complex (ISF) and of the Rieske-Type Ferredoxin from Benzene Dioxygenase (FiIbed)... 

X-ray absorption spectroscopy has been performed on the isolated Rieske protein from bovine heart mitochondrial bc complex 69) as well as on the Rieske-type cluster in Burkholderia cepacia phthalate dioxygenase (PDO) (72). The analysis performed by Powers et al. 69) was significantly hampered by the fact that the presence of two histidine ligands was not fully recognized therefore, only the results obtained with the dioxygenase where the mononuclear iron has been depleted will be considered here. Table VII gives a comparison of the distances obtained from the fit of the EXAFS spectra assuming an idealized Rieske model and of the distances in the crystal structures... 

NDO can be classified as class III dioxygenase the electron transfer chain involves a Rieske-type ferredoxin. Electrons enter NDO through the Rieske-type cluster of the dioxygenase. Kauppi et al. (11) have suggested that the binding site of NDO for the ferredoxin involves the 6 strands 10 and 12 of the Rieske domain as well as residues from the catalytic domain that form a depression in the protein surface close to Cys 101, which is a ligand of the Rieske cluster. In Rieske proteins from be complexes, access to this side of the cluster is blocked by an acidic surface residue (Asp 152 in the ISF, Glu 120 in RFS). 

A wide range of soluble redox enzymes contain one or more intrinsic [2Fe-2S]2+ +, [3Fe-4S]+ , or [4Fe S]2+ + clusters that function in electron transport chains to transfer electrons to or from nonheme Fe, Moco/Wco, corrinoid, flavin, thiamine pyrophosphate (TPP), Fe S cluster containing, or NiFe active sites. Many have been structurally and spectroscopically characterized and only a few of the most recent examples of each type are summarized here. Dioxygenases that function in the dihydroxylation of aromatics such as benzene, toluene, benzoate, naphthalene, and phthalate contain a Rieske-type [2Fe-2S] + + cluster that serves as the immediate electron donor to the monomeric nonheme Fe active site see Iron Proteins with Mononuclear Active Sites). The xanthine oxidase family of molybdoenzymes see Molybdenum MPT-containing Enzymes) contain two [2Fe-2S] + + clusters that mediate electron transfer between the Moco active site and the Other soluble molybdoen-... 

An excellent example of the powerful combination of ENDOR with isotopic labeling studies is found in the identification of histidine ligands in the Rieske-type 2Fe-2S iron-sulfur protein of phthalate dioxygenase (PDO). As shown in Fig. 12, the X-band " N cw ENDOR spectrum of natural-abundance PDO shows a broad pattern of N resonances that by... 

Dioxygenases are nonheme Rieske-type NAD(P)H-dependent enzymes that introduce both atoms of molecular oxygen into their substrates. The multicomponent enzyme systems are composed of a catalytic oxygenase component and one- or two-electron transfer proteins, including a flavoprotein reductase, and in some cases a ferredoxin that mediates electron transfer from the reductase to the oxygenase component ([3] Figure 17.1). 

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