Three-dimensional structures ferredoxin

The aldehyde ferredoxin oxidoreductase from the hyperthermophile Pyrococcus furiosus was the first molybdopterin-dependent enzyme for which a three-dimensional structure became available.683,684 The tungstoenzyme resembles that of the related molybdo-enzyme (Fig. 16-31). A similar ferredoxin-dependent enzyme reduces glyceraldehyde-3-phosphate.685 Another member of the tungstoenzyme aldehyde oxidoreductase family is carboxylic acid reductase, an enzyme found in certain acetogenic clostridia. It is able to use reduced ferredoxin to convert unactivated carboxylic acids into aldehydes, even though E° for the acetaldehyde/acetate couple is -0.58 V.686... 

The soluble electron carriers released from the reaction centers into the cytoplasm of bacteria or into the stroma of chloroplasts are reduced single-electron carriers. Bacterial ferredoxin with two Fe4S4 clusters is formed by bacteria if enough iron is present. In its absence flavodoxin (Chapter 15), which may carry either one or two electrons, is used. In chloroplasts the carrier is the soluble chloroplast ferredoxin (Fig. 16-16,C), which contains one Fe2S2 center. Reduced ferredoxin transfers electrons to NADP+ (Eq. 15-28) via ferredoxin NADP oxidoreductase, a flavoprotein of known three-dimensional structure.367 369... 

Chloroplast ferredoxin containing the [(2Fe-2S)-(S-Cys)4] cluster is one common type of iron-sulfur protein. Another [2Fe-2S]-type protein is the Rieske iron-sulfur protein, present in the Cyt >6/complex as well as the Cyt Ac, complex. The pair of iron atoms in the cluster ofthe Rieske iron-sulfur protein are bound to two cysteine and two histidine residues, in addition to two sulfur atoms. The three-dimensional structures of ferredoxins and that of the Rieske iron-sulfur protein have been determined by X-ray crystallography (see Chapters 34 and 35, respectively, for the structure ofthe chloroplast ferredoxin and the Rieske iron-sulfur protein). The sulfide ions in iron-sulfur proteins urt acid-labile this provides a simple means for detecting the iron-sulfur proteins, as the sulfide is released as H2S upon acidification. The oxidized and reduced states of iron-sulfur clusters differ by just one unit of formal charge, corresponding to and Fe. Iron-sulfurproteins are commonly characterized by optical absorption, circular-dichro-... 

The bacterial ferredoxin from Pseudomonas aerogenes [now called Peptococcus assaccharolyticus] (P. a.) was crystallized and its three-dimensional structure first determined by Adman, Sieker and Jensen ° at 2.8 A resolution in 1973. The backbone structure model of P. aerogenes ferredoxin (abbreviated as P.a.-Fd) is shown in Fig. 9, below. The shape of the molecule is approximately a prolate ellipsoid, with a minor axis of 22 A and a major axis of 27 A, and with the centers of the two [4Fe 4S] clusters 12 A apart. 

As seen from the amino-acid sequence for PsaC in Fig. 7 and that for the P. aerogenes ferredoxin in Fig. 9, cysteines 11, 14, 17 and 58 coordinate to FeS-B and cysteines 21, 48, 51 and 54 to FeS-A. The three-dimensional structure of the P. aerogenes ferredoxin may be utilized to show the cysteine coordination patterns for the two [4Fe 4S] clusters in the chloroplast PsaC subunit. Taking the two cysteine binding motifs. 

Fig. 15. Three-dimensional structure of Anabaena ferredoxin in ribbon representation. The five strands of p-pleated sheet are labeled A to E. Figure source Holden, Jackson, Jacobson, Hurley, Tollin, Oh, Skjedal, Chae, Cheng, Xia and Markley (1993) Structure-function studies of[2Fe-2S] ferredoxins. J Bioenerg Biomembr 26 72.

Fig. 17 (B) shows flash-induced absorbance changes measured at 480 as well as 580 nm. The anteima transients described above were again subtracted to yield the net signals. These new results show more clearly complete electron transfer from photosystem I to ferredoxin. Furthermore, some new features emerge in the transients at 580 nm. At higher time resolution, Setif and Bottin found three fast, first-order components in the absorbance changes with ty, of 500 ns, 20 jus and 100 jus, respectively. Separately measured spectra in the 460-600 nm region show that the three phases are all attributable to electron transfer from [FeS-A/B] to Fd. The different phases have been accounted for on the basis of structurally different, Fd-binding sites in the PS-I reaction center Possible sites may be seen in the newly determined, three-dimensional structure of the PS-I reaction center . ...

Fig. 20. Top stereogram of the three-dimensional structure of spinach Fd NADP reductase (FNR) with the p-strands shown as arrows, the o-helices as spirals, and FAD and 2 -phospho-5 -AMP as ball-and-stick models Bottom topological diagram for FNR, with the p-strands shown as arrows, and the a-helices as rectangles. Figure source Karplus and Bruns (1994) Structure-function relations for ferredoxin reductase. J Bioenerg Biomembr 26 92 and Karplus, Daniels and Herriotf (1991) Atomic structure of ferredoxin-NADP reductase Prototype for a structurally novel flavoenzyme family. Science 251 62.

N Krau, W Hinrichs, I Witt, P Fromme, W Pritzkow, Z Dauter, C Betzel, KS Wilson, HT Witt and W Saenger (1993) Three-dimensional structure of system I of photosynthesis at 6 resolution. Nature 361 326-331 G Zanetti and G Merati (1987) Interaction between photosystem I and ferredoxin. EurJ Biochem 169 143-6 AL Zilber and R Malkin (1988) Ferredoxin cross-links to a 22 kDa subunit of photosystem I. Plant Physiol 88 810-814... 

In contrast to the large amount of the three-dimensional structural data available in the literature, little is known about the physiological fimction of Rd. Typically, Rds exhibit redox potentials in the range of —60 to OmV [24], and are commonly assmned to be involved in electron transfer processes. It has bear demonstrated that Rd can replace ferredoxin as an electron carrier in certain electron transfer reactions [3]. Furthermore, Rd from the aerobe P. oleovorans was proposed to participate in the ctj-hydroxylation of fatty acids and hydrocarbons by transferring electrons to an alkane hydroxylase [7, 25]. Rd isolated from D. gigas was also shown to be involved in the formation of ATP from the degradation of polyglucose in the presence of... 

The three-dimensional structure of Sulfolobus sp. ferredoxin contains two [3Fe-4S] clusters and corresponds to the 6Fe form. Determined with the as-isolated zinc-containing ferredoxin which contains one [3Fe-4S] cluster, one [4Fe-4S] cluster, and one isolated zinc center. ... 

An unexpected result from X-ray structural analysis is that two [3Fe-4S] clusters and one isolated zinc center are observed in the three-dimensional structure determined at 2.0-A resolution cluster II was found as a cubane [3Fe-4S] cluster and was connected to the polypeptide chain by three cysteinyl residues, Cys-55, Cys-83, and Cys-89 (Fig. 2). The presence of two [3Fe-4S] clusters is very unusual in the bacterial-type dicluster ferredoxins. Biochemical and spectroscopic analyses of Sulfolobus sp. ferredoxin have shown that this 6Fe-containing species is an artifact of the crystallization procedure after protein isolation. Thus, the crystal structure provides the first structural evidence for a [4Fe-4S] [3Fe-4S] cluster conversion at the cluster n site in the dicluster-type ferredoxins. Interestingly, a potential ligand for a fourth site, Cys-86, is not bound in the crystal structure at 2.0-A resolution. In addition, the polypeptide conformation in vicinity of the cubane [3Fe-4S] cluster II and Cys-86 is reportedly an intermediate form between the [3Fe-4S] and [4Fe-4S] cluster conformations. ... 

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