Desulfovibrio, cytochrome

THE CYTOCHROMES C3 ARE CLASS III C-TYPE CYTOCHROMES (l) that were originally isolated in 1954 from Desulfovibrio (2, 3). Although widely distributed amongst the Desulfovibrio, cytochromes c3 have only recently been found in other species for example, in the purple phototrophic bacterium H1R (T. E. Meyer, personal communication) and in Desulfuromonas aeetoxi-... 

Although reduction of chromate Cr to Cr has been observed in a number of bacteria, these are not necessarily associated with chromate resistance. For example, reduction of chromate has been observed with cytochrome Cj in Desulfovibrio vulgaris (Lovley and Phillips 1994), soluble chromate reductase has been purified from Pseudomonas putida (Park et al. 2000), and a membrane-bound reductase has been purified from Enterobacter cloacae (Wang et al. 1990). The flavoprotein reductases from Pseudomonas putida (ChrR) and Escherichia coli (YieF) have been purified and can reduce Cr(VI) to Cr(III) (Ackerley et al. 2004). Whereas ChrR generated a semi-quinone and reactive oxygen species, YieR yielded no semiquinone, and is apparently an obligate four-electron reductant. It could therefore present a suitable enzyme for bioremediation. 

Postgate (51) observed a high concentration of a type of cytochrome, designated cytochrome cz, in the strictly anaerobic sulfate-reducing bacterium, Desul/ovibrio. The cytochrome Cz Desulfovibrio vulgaris has been shown to possess a very low redox potential (—0.205 V), two heme groups per mole and a sequence which implies two half sections, each of which binds a heme group (52). 

Although electron transfers in biological systems are generally expected to be non-adiabatic, it is possible for some intramolecular transfers to be close to the adiabatic limit, particularly in proteins where several redox centers are held in a very compact arrangement. This situation is found for example in cytochromes C3 of sulfate-reducing bacteria which contain four hemes in a 13 kDa molecule [10, 11], or in Escherichia coli sulfite reductase where the distance between the siroheme iron and the closest iron of a 4Fe-4S cluster is only 4.4 A [12]. It is interesting to note that a very fast intramolecular transfer rate of about 10 s was inferred from resonance Raman experiments performed in Desulfovibrio vulgaris Miyazaki cytochrome Cj [13]. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

By interesting coincidence, the old dogma that cytochromes are not present in anaerobes was demolished by discovery, at about the same time, of c-type cytochromes in Desulfovibrio and anoxygenic photosynthetic bacteria (Kamen and Vernon 1955). 

Barton LL, editor. 1995. Sulfate-reducing bacteria. New York Plenum Press. Blanchard L, Marion D, Pollock B, et al. 1993. Overexpression of Desulfovibrio vulgaris Hildenborough cytochrome C553 in Desulfovibrio desulfuricans G200 evidence of conformational heterogeneity in the oxidized protein by NMR. Eur J Biochem 218 293-301. 

Kitamura M, Mizugai K,Taniguchi M, et al. 1995. A gene encoding a cytochrome c oxidase-like protein is located closely to the cytochrome c-553 gene in the anaerobic bacterium, Desulfovibrio vulgaris (Miyazaki F). Microbiol Immunol 39 75-80. 

Ozawa K, Mogi T, Suzuki M, et al. 1997. Membrane-bound cytochromes in a sulfate-reducing strict anaerobe Desulfovibrio vulgaris Miyazaki F. Anaerobe 3 339 6. 

Pollock WBR, Voordouw G. 1994. Molecular biology of c-type cytochromes from Desulfovibrio vulgaris Hildenborough. Biochimie 76 554-60. 

Rapp-Giles BJ, Casalot L, English RS, et al. 2000. Cytochrome mutants of Desulfovibrio desulfuricans. Appl Environ Microbiol 66 671-7. 

Voordouw G, Pollock WBR, Bruschi M, et al. 1990. Functional expression of Desulfovibrio vulgaris Hildenborough cytochrome Cj in Desulfovibrio desulfuri-cans following conjngational gene transfer from Escherichia coli. J Bacteriol 172 6122-6. 

Figure 8.1. Redox proteins catalyzing electron transfer from hydrogen to sulfate in Desulfovibrio. The cytoplasmic uptake of protons associated with the reduction of sulfate is not shown. Hyd, hydrogenase cyctcs, cytochrome C3 HmcA, HmcB, HmcC, HmcE, HmcF, components of the Hmc complex IM, inner membrane OM, outer membrane.

Matias PM, Coelho R, Pereira lA, et al. 1999. The primary and three-dimensional structures of a nine haem cytochrome c from Desulfovibrio desulfuricans ATCC 2111A reveal a new member of the Hmc family. Structure 7 119-30. 

Pereira lAC, Romao CV, Xavier AV, et al. 1998. Electron transfer between hydrogenases and mono- and multiheme cytochromes in Desulfovibrio spp. J Biol Inorg Chem 3 494-8. 

Several proteins were reported to function as enzymes for the dissimilatory reduction of metals and nonessential elements. As Usted in Table 16.4, the most frequently reported proteins involved in metal reduction are the cytochromes from sulfate-reducing bacteria. The focus on these cytochromes supports the initial papers by Lovley and colleagues in which they reported that reduced cytochrome Cs from Desulfovibrio vulgaris Hildenborough reduces uranyl salts (Lovley et al. 1993a) and chromate (Lovley and PhUhps 1994). 

Lovley DR, Phillips EJP. 1994. Reduction of chromate by Desulfovibrio vulgaris and its C3 cytochrome. Appl Environ Microbiol 60 726-8. 

Frazao, C., Sieker, L., Sheldrick, G. M., Famzin, V.,LeGall,J. and Carrondo, M. A. (1999). Ab initio structure solution of a dimeric cytochrome c3 from Desulfovibrio gigas containing disulfide bridges. /. Biol. Inorg. Chem. 4, 162-165. 

Another property that distinguishes various cytochromes is the redox potential E ° (Table 6-8), which in this discussion is given for pH 7.0. Cytochromes carry electrons between other oxidoreductase proteins of widely varying values of E°. Because of the various heme environments cytochromes have greatly differing values of E°, allowing them to function in many different biochemical systems. 97a/97b For mitochondrial cytochrome c the value of E ° is + 0.265 V but for the closely related cytochrome/of chloroplasts it is +0.365 V and for cytochrome c3 of Desulfovibrio about -0.330 V. There is more than an 0.6-volt difference between E ° ... 

Most cytochromes have only one heme group per polypeptide chain,112 but the 115-residue cytochrome c3 from the sulfate-reducing bacterium Desulfovibrio binds four hemes (Fig. 16-8C).104,113 115 Each one seems to have a different redox potential in the -0.20 to -0.38 V range.114 Another c-type cytochrome, also from Desulfovibrio, contains six hemes in a much larger 66-kDa protein and functions as a nitrite reductase.116... 

B) a subunit of the dimeric cytochrome c from Rhodospirillum molischianum (C) cytochrome c3 from Desulfovibrio desulfuricans. (A) and (B) courtesy of Salemme 101... 

Fe Desulfovibrio vulgaris, Hildenborough strain Periplasm, soluble H2 consumption/ production 46 + 10 [H] + 2[4Fe-4S] Multiheme cytochrome c... 

In the photosynthetic and mitochondrial membranes the components of the transmembrane electron transport chain are not linked with covalent bonds, but fixed in a protein matrix. An example of such an arrangement of the electron transport chain in an artificial system can be found in papers by Tabushi et al. [244, 245], which deal with the dark electron transfer across the lipid membranes containing the dimers of cytochrome c3 from Desulfovibrio vulgaris. The dimer size is about 60 A, i.e. it somewhat exceeds the membrane thickness. This enables electron to move across the membrane via the cytochrome along the chain of hem fragments embedded in the protein. However, the characteristic time of the transmembrane electron transfer by this method is rather long (about 10 s). 

Matias PM, Soares CM, Saraiva LM, Coelho R, Morals J, Le Gall J, Carrondo MA (2001) [NiFe] hydrogenase from Desulfovibrio desulfuricans ATCC 27774 gene sequencing, three-dimensional structure determination and refinement at 1.8 A and modelling studies of its interaction with the tetrahaem cytochrome. J. Biol. Inorg. Chem. 6 63-81... 

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