Bacterial ferredoxin

Bacterial ferredoxins. Bacterial ferredoxin was first described in 1962 by Mortenson et al. (p who found a low-molecular iron protein involved in electron transfer of pyruvate hydrogenase and nitrogenase in C. pasteurianum. Subsequently, a number of ferredoxins have been found lii widely different types of bacteria such as photosynthetic bacteria and N2-fixing bacteria. These bacterial type ferredoxins have molecular... 

It was pointed out previously that both bacterial and plant fer-redoxins are colored proteins in the oxidized state. Fig. 3 shows the visible and ultraviolet absorption spectra of a bacterial (C. pasteurianum) and plant (spinach) ferredoxin. Bacterial ferredoxin shows a single peak in the visible region at 390 m(r and a peak in the ultraviolet region at about 280 mp. with a shoulder at 300 mp. The relative height of the peak at 280 mp to the shoulder at 300 mp varies among preparations from different bacteria generally the peak at 280 mp predominates (Loven-berg, Buchanan, and Rabinowitz (65) Bachofen and Arnon (12)). Plant... 

Figure 8.39 Fourier transformed Fe extended X-ray absorption fine structure (EXAFS) and retransformation, after applying a 0.9-3.5 A filter window, of (a) a rubredoxin, (b) a plant ferredoxin and (c) a bacterial ferredoxin, whose structures are also shown. (Reproduced, with permission, Ifom Teo, B. K. and Joy, D. C. (Eds), EXAFS Spectroscopy, p. 15, Plenum, New York, 1981)...

Iron Sulfur Compounds. Many molecular compounds (18—20) are known in which iron is tetrahedraHy coordinated by a combination of thiolate and sulfide donors. Of the 10 or more stmcturaHy characterized classes of Fe—S compounds, the four shown in Figure 1 are known to occur in proteins. The mononuclear iron site REPLACE occurs in the one-iron bacterial electron-transfer protein mbredoxin. The [2Fe—2S] (10) and [4Fe—4S] (12) cubane stmctures are found in the 2-, 4-, and 8-iron ferredoxins, which are also electron-transfer proteins. The [3Fe—4S] voided cubane stmcture (11) has been found in some ferredoxins and in the inactive form of aconitase, the enzyme which catalyzes the stereospecific hydration—rehydration of citrate to isocitrate in the Krebs cycle. In addition, enzymes are known that contain either other types of iron sulfur clusters or iron sulfur clusters that include other metals. Examples include nitrogenase, which reduces N2 to NH at a MoFe Sg homocitrate cluster carbon monoxide dehydrogenase, which assembles acetyl-coenzyme A (acetyl-CoA) at a FeNiS site and hydrogenases, which catalyze the reversible reduction of protons to hydrogen gas. 

A second example is that of an Ala-to-Cys mutation, which causes the fonnation of a rare SH S hydrogen bond between the cysteine and a redox site sulfur and a 50 mV decrease in redox potential (and vice versa) in the bacterial ferredoxins [73]. Here, the side chain contribution of the cysteine is significant however, a backbone shift can also contribute depending on whether the nearby residues allow it to happen. Site-specific mutants have confirmed the redox potential shift [76,77] and the side chain conformation of cysteine but not the backbone shift in the case with crystal structures of both the native and mutant species [78] the latter can be attributed to the specific sequence of the ferre-doxin studied [73]. 

Figure 25.9 Some non-haem iron proteins (a) rubredoxin in which the single Fe is coordinated, almost tetra-hedrally, to 4 cysteine-sulfurs, (b) plant ferredoxin, [Fe2S2(S-Cys)4], (c) [Fe4S4(S-Cys)4] cube of bacterial ferredoxins. (This is in fact distorted, the Fe4 and S4 making up the two interpenetrating tetrahedra, of which the latter is larger than the former).

The use of direct electrochemical methods (cyclic voltammetry Pig. 17) has enabled us to measure the thermodynamic parameters of isolated water-soluble fragments of the Rieske proteins of various bci complexes (Table XII)). (55, 92). The values determined for the standard reaction entropy, AS°, for both the mitochondrial and the bacterial Rieske fragments are similar to values obtained for water-soluble cytochromes they are more negative than values measured for other electron transfer proteins (93). Large negative values of AS° have been correlated with a less exposed metal site (93). However, this is opposite to what is observed in Rieske proteins, since the cluster appears to be less exposed in Rieske-type ferredoxins that show less negative values of AS° (see Section V,B). 

Fig. 1. Iron-sulfur clusters basic building blocks. In most cases the iron is tetrahe-drally coordinated by sulfur from cysteinyl residues (and labile sulfur). Variability on coordination is allowed (see text). A, Rubredoxin type FeS4 (simplest cluster, no labile sulfur) B, plant-type ferredoxin [2Fe-2S] C, bacterial ferredoxin [3Fe-4S] D, bacterial ferredoxin and HiPIP [4Fe-4S] E, novel cluster [4Fe-2S, 20] ( hybrid cluster ).

Dorner E, M Boll (2002) Properties of 2-oxoglutarate ferredoxin oxidoreductase from Thauera aromatica and its role in enzymatic reduction of the aromatic ring. J Bacterial 184 3975-3983. 

Roy R, S Mukund, GJ Schut, DM Dunn, R Weiss, MWW Adams (1999) Purification and molecular characterization of the tungsten-containing formaldehyde ferredoxin oxidoreductase from the hyperthermophilic archaeon Pyrococcus furiosus the third of a putative five-member tungstoenzyme family. J Bacterial. 181 1171-1180. 

Directly related to the single Fe4S4 proteins are the bacterial 8Fe ferredoxins, which contain two Fe4S4 units (FW 6000), Figure 26.52... 

The last class of iron-sulfur proteins to be considered is that of the bacterial 7Fe ferredoxins, which contain both an Fe3S4 and an Fe4S4 cluster. Figure 28 shows the molecular structure of that from Azotobacter vinelandii (FW — 12 700).53... 

Artificial cell-free systems have been investigated, to test models of photosynthetic production of H2. Benemann et al. (1973) demonstrated that it was possible to produce H2 and O2 by combining chloroplasts from green plants and bacterial hydrogenase, with ferredoxin as the intermediate electron carrier ... 

Ferredoxins (Fds) are widespread in the three domains of life and an abundance of sequence data and structural information are available for Fds isolated from several sources. In particular, the bacterial type Fds are small electron-transfer proteins that posses cubane xFe-yS clusters attached to the protein matrix by Fe ligation of Cys via a conserved consensus ligating sequence. The archaeal type ferredoxins are water-soluble electron acceptors for the acyl-coenzyme A forming 2-oxoacid/ferredoxin oxidoreductase, a key enzyme involved in the central archaeal metabolic pathways. Fds have been distinguished according to the number of iron and inorganic sulphur atoms, 2Fe-2S, 4Fe-4S/3Fe-4S (Fig. Ib-d) and Zn-containing Fds. 

Ferredoxins from thermoacidophilic archaea such as Thermoplasma acidophi-lum and Sulfolobus sp. contain, in addition to one 3Fe-4S (cluster I) and one 4Fe-4S (cluster II) cluster, one zinc centre tetrahedrally co-ordinated to three histidines in the N-terminal region and to one aspartate in the ferredoxin core domain. These Fds contain an unusually long N-terminal extension region of unknown function, which was not detected in other bacterial type Fds. Upon oxidative degradation of Fd from Sulfolobus sp. strain 7 (Fopt = 80 cluster II is selectively converted into a cubane 3Fe-4S,... 

At this point it may be valuable to digress a moment and discuss the state-of-the-knowledge in the field of Fe-S proteins by the ntid-1970 s. At this time there were three known structures found in nature, IFe as represented by rubredoxin, the [2Fe-2S] cluster as represented by plant ferredoxins, and the [4Fe-4S] cluster as found in many bacterial ferredoxins (24). The schematic structures and selected properties are listed in Table I. 

Other Iron Compounds of Biological Interest.—The valency of iron in a range of ferredoxin extracts has been determined by ESCA. The structure of the Fe—S complex in a bacterial ferredoxin has been determined. The iron and sulphur atoms occupy alternate corners of a cube and four more sulphur atoms project from the iron atoms.Admission of oxygen to a neutral solution of Fe and excess penicillamine gives a red bis-complex, which is relatively stable in aqueous solution at room temperature. Quantitative... 

An abbreviation for Ifigh-potential iron-sulfur protein, which is now regarded as a ferredoxin. In its role as a bacterial electron transfer component, this [4Fe-4S] cluster protein can undergo interconversion to the [4Fe-4S] and [4Fe-4S] states. 

This enzyme [EC 1.14.99.15] catalyzes the reaction of 4-methoxybenzoate with AH2 and dioxygen to produce 4-hydroxybenzoate, formaldehyde. A, and water. The bacterial enzyme consists of a ferredoxin-type protein and an iron-sulfur fiavoprotein (FMN). 4-Ethoxyben-zoate, A-methyl-4-aminobenzoate, and toluate can serve as substrates as well. The fungal enzyme acts best on ver-atrate. 

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