Cytochromes, Iron-Sulfur, and Copper Proteins Mediating Electron Transfer from the Cyt bc1 Complex to Photosynthetic Reaction Center Complexes

Meyer, Terrance E.; Donohue, Timothy J.

doi:10.1007/0-306-47954-0_34

Cited by 21 publications

(18 citation statements)

References 147 publications

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“…In H. halophila, this electron carrier is a high-potential iron sulfur protein (HiPIP) (13). The redox potential of this HiPIP [E m ϭ ϩ165 mV (13)] turned out to be substantially lower than that of other purple bacterial HiPIPs (14) and instead falls within the range of potentials generally observed for electron donors to RCs in phototrophs using MK as pool quinone (15). Because no purple bacterium operating its photosynthetic chain on MK has been described thus far, this finding is surprising.…”

Section: Resultsmentioning

confidence: 98%

Menaquinone as pool quinone in a purple bacterium

Schoepp‐Cothenet

Lieutaud

Baymann

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

109

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Purple bacteria have thus far been considered to operate lightdriven cyclic electron transfer chains containing ubiquinone (UQ) as liposoluble electron and proton carrier. We show that in the purple ␥-proteobacterium Halorhodospira halophila, menaquinone-8 (MK-8) is the dominant quinone component and that it operates in the QB-site of the photosynthetic reaction center (RC). The redox potentials of the photooxidized pigment in the RC and of the Rieske center of the bc1 complex are significantly lower (Em ‫؍‬ ؉270 mV and ؉110 mV, respectively) than those determined in other purple bacteria but resemble those determined for species containing MK as pool quinone. These results demonstrate that the photosynthetic cycle in H. halophila is based on MK and not on UQ. This finding together with the unusual organization of genes coding for the bc1 complex in H. halophila suggests a specific scenario for the evolutionary transition of bioenergetic chains from the low-potential menaquinones to higher-potential UQ in the proteobacterial phylum, most probably induced by rising levels of dioxygen 2.5 billion years ago. This transition appears to necessarily proceed through bioenergetic ambivalence of the respective organisms, that is, to work both on MK-and on UQ-pools. The establishment of the corresponding low-and high-potential chains was accompanied by duplication and redox optimization of the bc1 complex or at least of its crucial subunit oxidizing quinols from the pool, the Rieske protein. Evolutionary driving forces rationalizing the empirically observed redox tuning of the chain to the quinone pool are discussed.electron transport ͉ evolution ͉ photosynthesis C hemiosmotic energy-converting mechanisms in all life on this planet are variations on a strikingly conserved theme. Electrons derived from reduced substrates enter a chain of membrane-integral and/or associated enzymes and are channeled on toward terminal electron-accepting substrates. Some of the free energy available during individual electron-transfer steps is stored in a transmembrane proton motive gradient. Mitchell (1) proposed a general mechanism for coupling electron transfer to proton translocation, which accounts for the majority of these systems. In this mechanism, electrons travel through 2 types of carrier ''arms'' back and forth across the energetic membrane. In an ''electrogenic arm,'' electrons move alone across the membrane from the positively to the negatively charged side, building up an electric field. Via a ''neutral arm,'' electrons travel in the opposite direction, along with protons. Placing electrogenic and neutral arms in series leads to net proton translocation across the membrane.Without exception, the chemiosmotic neutral arms involve diffusion of small, lipophilic molecules across the energetic membrane. In all bioenergetic systems except methanogenesis, these molecules are quinones that diffuse in the lipid bilayer. The bulk of these diffusing quinones electrochemically connecting redox enzymes is called the quinone pool, to disti...

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Section: Resultsmentioning

confidence: 98%

Menaquinone as pool quinone in a purple bacterium

Schoepp‐Cothenet

Lieutaud

Baymann

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

109

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“…Yet, cyt c y homologs have been encountered in P. denitrificans (43), B. japonicum (4), Nitrobacter vinogradskyi (28), R. sphaeroides (49), and possibly Rhodospirillum rubrum (27a). Their presence is also anticipated in many other phototrophic bacteria, especially in those apparently lacking the soluble electron carrier cyt c 2 , such as members of the genera Rhodoferax, Rhodocyclus, Chromatium, Ectothiorhodospira, and Heliobacterium (26). Thus, it could be argued that electron transfer via cyt c y to the RC is more efficient during multiple turnovers because of the lack of any diffusible periplasmic components (19,33,45).…”

Section: Discussionmentioning

confidence: 96%

Cytochrome c(y) of Rhodobacter capsulatus is attached to the cytoplasmic membrane by an uncleaved signal sequence-like anchor

et al. 1997

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During the photosynthetic growth of Rhodobacter capsulatus, electrons are conveyed from the cytochrome (cyt) bc 1 complex to the photochemical reaction center by either the periplasmic cyt c 2 or the membrane-bound cyt c y . Cyt c y is a member of a recently established subclass of bipartite c-type cytochromes consisting of an amino (N)-terminal domain functioning as a membrane anchor and a carboxyl (C)-terminal domain homologous to cyt c of various sources. Structural homologs of cyt c y have now been found in several bacterial species, including Rhodobacter sphaeroides. In this work, a C-terminally epitope-tagged and functional derivative of R. capsulatus cyt c y was purified from intracytoplasmic membranes to homogeneity. Analyses of isolated cyt c y indicated that its spectral and thermodynamic properties are very similar to those of other c-type cytochromes, in particular to those from bacterial and plant mitochondrial sources. Amino acid sequence determination for purified cyt c y revealed that its signal sequence-like N-terminal portion is uncleaved; hence, it is anchored to the membrane. To demonstrate that the N-terminal domain of cyt c y is indeed its membrane anchor, this sequence was fused to the N terminus of cyt c 2 . The resulting hybrid cyt c (MA-c 2 ) remained membrane bound and was able to support photosynthetic growth of R. capsulatus in the absence of the cyt c y and c 2 . Therefore, cyt c 2 can support cyclic electron transfer during photosynthetic growth in either a freely diffusible or a membraneanchored form. These findings should now allow for the first time the comparison of electron transfer properties of a given electron carrier when it is anchored to the membrane or is freely diffusible in the periplasm.

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“…C. vinosum c8 is 44% identical to R aeruginosa ex and is 51 % identical to the Azotobacter vinelandii protein (Ambler, 1991). Cytochrome c, from Hydrogenobacter thernzophilus (Sanbongi et al, 1989(Sanbongi et al, , 1991 starts and ends at the same positions as C. vinosum c-551 (49% similarity) and also requires a single residue deletion at position 78 as do the A. vinelandii and R aeruginosa cytochromes. Several amino acid residues characteristic of cytochromes c, also occur in C. vinosum cytochrome c-55 1 : e.g.…”

Section: Discussionmentioning

confidence: 99%

“…5 ) but no one has demonstrated its role in photosynthesis. The only type of cytochrome that has been clearly demonstrated to be the electron-donor partner of the photoreaction cen-69.5 ter is the cytochrome c, from the non-sulfur bacteria Rhodobacter sphaeroides and Rhodobacter capsulatus (Donohue et al, 1988;Jenney and Daldal, 1993;Wang et al, 1994;Meyer and Donohue, 1995). C. vinosum, which in contrast with the latter bacteria has a tetrahaem cytochrome associated with its reaction center, may consequently have a cytochrome donor different from a c,-like protein.…”

Section: Discussionmentioning

confidence: 99%

A High‐Potential Soluble Cytochrome C ‐551 from the Purple Phototrophic Bacterium Chromatium vinosum is Homologous to Cytochrome C₈ from Denitrifying Pseudomonads

Samyn

Smet

Driessche

et al. 1996

European Journal of Biochemistry

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A minor cytochrome c-551 component of Chromatium vinosum was previously found to efficiently couple electron transfer between the cytochrome bc, complex and the photosynthetic reaction center. We have now determined the amino acid sequence of this cytochrome c-551 and find that it is homologous to cytochrome cx (formerly called Pseudomonas cytochrome c-551). It is most similar to Methylophilus methylotrophus, Rhodocyclus tenuis, and Azotobacter vinelandii cytochromes c, (respectively, 57 %, 52 % and 51%). The C. vinosum cytochrome c, has a single residue insertion relative to Pseudomonas and Azotobacter cytochromes cx. It has fewer charged residues than its homologs and is essentially neutral, which may explain why it is less soluble than the others. The cytochromes cx are only very distantly related to the cytochromes c2 found in other species of purple bacteria which are much larger in size and which usually mediate electron transfer between the cytochrome be, complex and the reaction center. The photosynthetic pathway in Chromatium thus appears to be radically different from that in purple non-sulfur bacteria.

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Cytochromes, Iron-Sulfur, and Copper Proteins Mediating Electron Transfer from the Cyt bc1 Complex to Photosynthetic Reaction Center Complexes

Cited by 21 publications

References 147 publications

Menaquinone as pool quinone in a purple bacterium

Menaquinone as pool quinone in a purple bacterium

Cytochrome c(y) of Rhodobacter capsulatus is attached to the cytoplasmic membrane by an uncleaved signal sequence-like anchor

A High‐Potential Soluble Cytochrome C ‐551 from the Purple Phototrophic Bacterium Chromatium vinosum is Homologous to Cytochrome C₈ from Denitrifying Pseudomonads

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Cytochromes, Iron-Sulfur, and Copper Proteins Mediating Electron Transfer from the Cyt bc1 Complex to Photosynthetic Reaction Center Complexes

Cited by 21 publications

References 147 publications

Menaquinone as pool quinone in a purple bacterium

Menaquinone as pool quinone in a purple bacterium

Cytochrome c(y) of Rhodobacter capsulatus is attached to the cytoplasmic membrane by an uncleaved signal sequence-like anchor

A High‐Potential Soluble Cytochrome C ‐551 from the Purple Phototrophic Bacterium Chromatium vinosum is Homologous to Cytochrome C8 from Denitrifying Pseudomonads

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A High‐Potential Soluble Cytochrome C ‐551 from the Purple Phototrophic Bacterium Chromatium vinosum is Homologous to Cytochrome C₈ from Denitrifying Pseudomonads