Rieske-type cluster

In order to get an insight into the diversity of proteins that may contain a Rieske or Rieske-type cluster, a database search was performed in the following way. 

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. 

In order to check whether the occurrence of the Rieske-type sequence motif is unique for the assimilatory nitrite reductase from Bacillus subtilis, the sequences of other assimilatory nitrite reductases were searched for the presence of the four putative ligands of Rieske-type clusters. A well-conserved sequence pattern... 

The X-ray structures of three water-soluble proteins containing a Rieske or Rieske-type cluster have been reported so far (Fig. 2) ... 

Early mutational studies of the Rieske protein from 6ci complexes have been performed with the intention of identifying the ligands of the Rieske cluster. These studies have shown that the four conserved cysteine residues as well as the two conserved histidine residues are essential for the insertion of the [2Fe-2S] cluster (44, 45). Small amounts of a Rieske cluster with altered properties were obtained in Rhodobacter capsulatus when the second cysteine in the cluster binding loop II (Cys 155, corresponding to Cys 160 in the bovine ISF) was replaced by serine (45). The fact that all four cysteine residues are essential in Rieske clusters from be complexes, but that only two cysteines are conserved in Rieske-type clusters, led to the suggestion that the Rieske protein may contain a disulfide bridge the disulfide bridge was finally shown to exist in the X-ray structure (9). 

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... 

The CD spectra reveal several distinct features that are highly significant for both Rieske and Rieske-type clusters. The CD spectra of the oxidized proteins show two positive bands between 310 and 350 nm, a negative band at 375-380 nm, and a set of positive bands between 400 and 500 nm. The CD spectra of the reduced proteins show positive bands at 314 nm, a negative band at 384-390 nm and a negative band around 500 nm. 

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... 

Hyperfine Coupling Values of the Nitrogen Ligands of Rieske and Rieske-Type Clusters Determined by ENDOR and ESEEM Spectroscopy... 

While the redox potentials of Rieske clusters are above -1-100 mV at pH 7, values between 100 and 150 mV have been determined for the redox potentials of Rieske-type clusters (Table XI). Several 4-cysteine coordinated [2Fe-2S] clusters have redox potentials similar to those of Rieske-type clusters, for example, the [2Fe-2S] clusters of the dioxygenase reductases [compilation in (104)]-, therefore, the redox potential is not useful for distinguishing between Rieske-type and ferredoxin-type clusters. 

Although the redox potential of Rieske-type clusters is approximately 400 mV lower than that of Rieske clusters, it is 300 mV more positive than the redox potential of plant-type ferredoxins (approximately -400 mV). Multiple factors have been considered to be essential for the redox potential of iron sulfur proteins ... 

Rieske-type clusters are found in aromatic-ring hydroxylating dioxygenase systems (20). These enzymes catalyze the conversion of different aromatic compounds into cis-arene diols ... 

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). 

Unlike Rieske clusters in be complexes, Rieske-type clusters are involved only in electron transfer and not in substrate binding or cataly-... 

Since their discovery, Rieske proteins have been the object of numerous studies aimed at gaining insight into the molecular basis of their unique properties. These studies not only have shed light on Rieske and Rieske-type clusters, but also have contributed to the understanding of iron sulfur proteins in general. 

By the application of modem spectroscopic techniques and through the recent availability of high-resolution structural information, several issues could be resolved, in particular the nature of the ligands of the Rieske cluster. Now that stmctures are available, the research will focus on new questions in order to provide a better understanding of the electronic properties of Rieske and Rieske-type clusters as well as of their function ... 

How are the spectroscopic and electrochemical properties of Rieske and Rieske-type clusters related to their structure ... 

What is the interaction between the Rieske-type cluster and the catalytic iron site of dioxygenases ... 

Gurbiel, R. J., Batie, C. J., Sivaraja, M., True, A. E., Fee, J. A., Hoffman, B. M., and Ballou, D. P., 1989, Electron-nuclear double resonance spectroscopy of 15N-enriched phthalate dioxygenase from Pseudomonas cepacia proves that two histidines are coordinated to the [2Fe-2S] Rieske-type clusters, Biochemistry 28 4861n4871. 

---