Peptococcus aerogenes ferredoxin

Figure 3. Amino add sequence of Peptococcus aerogenes ferredoxin.

Fe-xS] ferredoxins, 33 54-55 rubredoxin, 33 44-51 hydrophobic effect, 33 60-62 significance, 33 40-44 metal complexes of, 7 218-220 model complexes, catalysis by, 33 61-62 Peptococcus aerogenes ferredoxin, structure, 38 242, 244-245... 

Adman E, Watenpaugh KD, Jensen LH (1975) NH S hydrogen-bonds in Peptococcus-aerogenes ferredoxin, Clostridium pasteurianum rubredoxin, and Chromatium high potential iron protein. Proc Natl Acad Sci USA 72 4854 1858... 

Fig. 14. Stereo ribbon structure of Peptococcus aerogenes ferredoxin showing the two [4Fe-4S] clusters. The C terminal and positions of the two prolines (P) are also indicated. This illustration was kindly provided by Larry Sieker (University of Washington, Seattle)...

Fig. 2. Protein backbone representations of (a) the 2[4Fe-4S] ferredoxin from Peptococcus aerogenes, (b) the proposed structure of the FA/FB-binding protein of PSl based on the 4 A crystsd structure (25), and (c) the [3Fe-4S][4Fe-4S] ferredoxin from Sulfolo-bus acidocaldarius. Ligands to clusters Fa and Fb, important residues as well as the loop extension (see text) EU e highlighted in darker gray.

Fig. 3. Sequence comparison of the FA/FB-binding subunits of PSl from tobacco and the RC of green sulfur bacteria with that of the 2[4Fe-4S] ferredoxin from Peptococcus aerogenes. Cysteine ligands to the right-hand cluster in the three structures of Fig. 2 (i.e., cluster Fb for the case of the FA/FB-protein) are marked by open boxes Emd residues ligating the left-hand cluster by hatched boxes.

Figure 26 X-Ray structure of the active site of the 8Fe ferredoxin of Peptococcus aerogenes...

From the biological area, iron-sulfur clusters in biomolecules such as rubredoxin mononuclear Fe-S clusters (Rao et at., 1972), plant-type ferredoxin 2Fe-2S clusters (Johnson, 1975) and bacterial-type ferredoxin 4Fe-2S clusters (Thompson et at., 1974) are readily distinguished from one another by their Mossbauer spectra. The temperature dependence of relaxation effects can provide information about the types of internuclear interaction and can even lead to estimates of the distance between paramagnetic sites, for example, the two 4Fe-4S clusters in ferredoxin in Peptococcus aerogenes (Adman etal., 1973). 

Ferredoxins with (8Fe + 8S have also been reported in C. pasteuri-C. thermosaccharolyticum, Peptococcus aerogenes, Peptostrepto-... 

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. 

The [4 Fe-4 S] cores have been one of the most intriguing inorganic structures involved in biological systems. Carter et al. (1977) 191 demonstrated that the same basic structure is present in the two [4 Fe—4 S] centers of the 8 Fe ferredoxin of Peptococcus aerogenes (E 0 = - 400 mV)2) and in the high potential iron protein (HiPIP) isolated from the purple photosynthetic bacterium Chromatium vinosum... 

Promotion of protein electrochemistry by multi-charged counter ions shows several interesting features. A typical case, illustrated in Fig. 7, concerns the 2[4Fe-4S] ferredoxin from Clostridium pasteurianum. This is a low-potential electron carrier (MW approx. 6000) that carries a large overall negative charge, possibly as high as — 10 for the fully oxidized state. Structurally, it is very similar to the ferredoxin from Peptococcus aerogenes (see Fig. 14). Voltammetry at PGE... 

Four structural classes of Fe-S centre have been identified to date these are depicted in Fig. 13. All of them feature high-spin tetrahedral Fe(II) or Fe(III) coordinated typically by four sulfur donors. Apart from the monomeric centre found in proteins known as rubredoxins, they are all clusters that contain both protein donors and inorganic bridging (p) sulfido ligands. Most of our knowledge stems from studies made on the small electron-transport proteins known as ferredoxins (Fd s) and from work on model compounds. Figure 14 shows the structure of a ferredoxin isolated from the anaerobe Peptococcus aerogenes [165]. 

Since the discovery of [3Fe-4S] clusters, it has frequently been argued [173] that they must, in many cases, be artifacts produced by degradation of [4Fe-4S] during isolation and exposure to air. Oxidation is probably a key factor since Clostridium pasteurianum 2[4Fe-4S] ferredoxin (whose structure and properties are analogous to Peptococcus aerogenes Fd) is converted [173,180], upon treat-... 

The structures of the active sites of 4-Fe and 8-Fe Ferredoxins has been univocally established by X-ray diffraction methods. Proteins of the 4-Fe type contain the [Fe4S4(S-Cys)4] site with a cubane-like structure as that illustrated schematically in Fig. 5.2. The structure of HP from Chromatium vinosum has been determined for two oxidation levels, HP ed and HPox- In both cases the active sites are tetranuclear clusters as shown in Fig. 5.2. Characteristic structural parameters for such centers can be observed in Fig. 5.3 where they are reproduced beside those of some synthetic analogues. As illustrated in Fig. 5.4, in the 8-Fe Fdox from Peptococcus aerogenes there are-two identical tetranuclear active centers which are separated by about 12 A. They are dimensionally very similar to the site in HP ed-... 

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