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Hager-Braun, Christine; Jarosch, Ursula; Hauska, Günter; Nitschke, Wolfgang; Riedel, A.

doi:10.1023/a:1005787209977

Cited by 20 publications

(4 citation statements)

References 22 publications

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“…8A. The obtained spectral shapes were basically identical to those reported previously in C. tepidum, C. vivrioforme, and C. limicola as well (31)(32)(33)(34). Although the signals in the resonance region at around g z ϭ 2.07 were extremely noisy, the interacting spectra detected at a high magnetic field were clear enough for a comparison of the wild-type and mutant strains.…”

Section: Fig 3 Sds-page Analysis Of the Isolated Rc Complexessupporting

confidence: 84%

Function of a PscD Subunit in a Homodimeric Reaction Center Complex of the Photosynthetic Green Sulfur Bacterium Chlorobium tepidum Studied by Insertional Gene Inactivation

Tsukatani

Miyamoto

Itoh

et al. 2004

Journal of Biological Chemistry

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The PscD subunit in the homodimeric "type I" photosynthetic reaction center (RC) complex of the green sulfur bacterium Chlorobium tepidum was disrupted by insertional mutagenesis of its relevant pscD gene. This is the first report on the use of the direct mutagenic approach into the RC-related genes in green sulfur bacteria. The RC complex of C. tepidum is supposed to form a homodimer of two identical PscA subunits together with three other subunits: PscB (F A /F B -containing protein), PscC (cytochrome c z ), and PscD. PscD shows a relatively low but significant similarity in its amino acid sequence to PsaD in the photosystem I of plants and cyanobacteria. We studied the biochemical and spectroscopic properties of a mutant lacking PscD in order to elucidate its unknown function. 1) The RC complex isolated from the mutant cells showed no band corresponding to PscD on SDS-PAGE analysis. 2) The growth rate of the PscD-less mutant was slower than that of the wildtype cells at low light intensities. 3) Time-resolved fluorescence spectra at 77 K revealed prolonged decay times of the fluorescence from bacteriochlorophyll c on the antenna chlorosome and from bacteriochlorophyll a on the Fenna-Matthews-Olson antenna protein in the mutant cells. The loss of PscD led to a much slower energy transfer from the antenna pigments to the special pair bacteriochlorophyll a (P840). 4) The mutant strain exhibited slightly less activity of ferredoxin-mediated NADP ؉ photoreduction compared with that in the wild-type strain. The extent of suppression, however, was less significant than that reported in the PsaD-less mutants of cyanobacterial photosystem I. The evolutionary relationship between PscD and PsaD was also discussed based on a structural homology modeling of the former.Photosynthetic organisms convert light energy into electrochemical free energy by carrying out a series of light-driven electron transfer reactions. This process, which is fundamental for life, is mediated by reaction center (RC) 1 complexes. The RCs are primarily grouped into two types based on their terminal electron acceptors, type I (FeS-type) RCs and type II (quinone-type) RCs. Purple photosynthetic bacteria contain only type II RCs, which do not evolve oxygen, whereas oxygenic cyanobacteria and plants utilize both type I (photosystem I) and type II (photosystem II) RCs, which are connected in-line through the b 6 f complex. Green sulfur bacteria and heliobacteria have unique type I RCs, so-called "homodimeric" RCs, which are made of two identical core polypeptides.The "heterodimeric" type I and II RCs, which are found in all photosynthetic organisms other than green sulfur bacteria and heliobacteria, consist of a set of two partially different core polypeptides that produce a slightly asymmetric arrangement of cofactors. A three-dimensional structure of the heterodimeric RC was first obtained from the type II RC of the purple bacterium Blastochloris viridis in 1985 (1). Recently, those of photosystem I and II RCs from the thermophilic cyanobacterium Sy...

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Section: Fig 3 Sds-page Analysis Of the Isolated Rc Complexessupporting

confidence: 84%

Function of a PscD Subunit in a Homodimeric Reaction Center Complex of the Photosynthetic Green Sulfur Bacterium Chlorobium tepidum Studied by Insertional Gene Inactivation

Tsukatani

Miyamoto

Itoh

et al. 2004

Journal of Biological Chemistry

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“…In the membranes and RC complex of green sulfur bacteria, the ESR spectra of photoaccumulated F X - have been shown with low signal-to-noise ratios ( − ). The spectrum of F X - with a g z of 2.17, a g y of 1.92, and a g x of 1.77 has been identified by its characteristic low-field peak and high-field trough (), as observed in PS I ( , ).…”

Section: Discussionmentioning

confidence: 99%

ESR Signal of the Iron−Sulfur Center F_Xand Its Function in the Homodimeric Reaction Center ofHeliobacterium modesticaldum^,

et al. 2006

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Electron transfer in the membranes and the type I reaction center (RC) core protein complex isolated from Heliobacterium modesticaldum was studied by optical and ESR spectroscopy. The RC is a homodimer of PshA proteins. In the isolated membranes, illumination at 14 K led to accumulation of a stable ESR signal of the reduced iron-sulfur center F(B)(-) in the presence of dithiothreitol, and an additional 20 min illumination at 230 K induced the spin-interacting F(A)(-)/F(B)(-) signal at 14 K. During illumination at 5 K in the presence of dithionite, we detected a new transient signal with the following values: g(z)= 2.040, g(y)= 1.911, and g(x)= 1.896. The signal decayed rapidly with a 10 ms time constant after the flash excitation at 5 K and was attributed to the F(X)(-)-type center, although the signal shape was more symmetrical than that of F(X)(-) in photosystem I. In the purified RC core protein, laser excitation induced the absorption change of a special pair, P800. The flash-induced P800(+) signal recovered with a fast 2-5 ms time constant below 150 K, suggesting charge recombination with F(X)(-). Partial destruction of the RC core protein complex by a brief exposure to air increased the level of the P800(+)A(0)(-) state that gave a lifetime (t(1/2)) of 100 ns at 77 K. The reactions of F(X) and quinone were discussed on the basis of the three-dimensional structural model of RC that predicts the conserved F(X)-binding site and the quinone-binding site, which is more hydrophilic than that in the photosystem I RC.

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“…Results from special TRIPLE spectroscopy suggest that a 2-methylnaphthoquinone radical could photoaccumulate at 205 K in a membrane fraction from Chlorobium limicola (14). However, electron transfer kinetic measurements have not provided to this point any clear evidence for the involvement of quinone in the main electron transfer pathway in PS-C. With regard to iron-sulfur clusters, the presence of two clusters in PS-C (equivalent to F A and F B of PSI) was easily detected by EPR spectroscopy (10,15,16, and references therein), but only small signals ascribed to F X have been observed (10,15,17).…”

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confidence: 99%

Electron Transfer Kinetics in Purified Reaction Centers from the Green Sulfur Bacterium Chlorobium tepidum Studied by Multiple-Flash Excitation

et al. 1999

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Reaction center preparations from the green sulfur bacterium Chlorobium tepidum, which contain monoheme cytochrome c, were studied by flash-absorption spectroscopy in the near-UV, visible, and near-infrared regions. The decay kinetics of the photooxidized primary donor P840(+), together with the amount of photooxidized cytochrome c, were analyzed along a series of four flashes spaced by 1 ms: 95% of the P840(+) was reduced by cytochrome c with a t(1/2) of approximately 65 micros after the first flash, 80% with a t(1/2) of approximately 100 micros after the second flash, and 23% with a t(1/2) of approximately 100 micros after the third flash; after the fourth flash, almost no cytochrome c oxidation occurred. The observed rates, the establishment of redox equilibrium after each flash, and the total amount of photooxidizable cytochrome c are consistent with the presence of two equivalent cytochrome c molecules per photooxidizable P840. The data are well fitted assuming a standard free energy change DeltaG degrees of -53 meV for electron transfer from one cytochrome c to P840(+), DeltaG degrees being independent of the oxidation state of the other cytochrome c. These observations support a model with two monoheme cytochromes c which are symmetrically arranged around the reaction center core. From the ratio of menaquinone-7 to the bacteriochlorophyll pigment absorbing at 663 nm, it was estimated that our preparations contain 0.6-1.2 menaquinone-7 molecules per reaction center. However, no transient signal due to menaquinone could be observed between 360 and 450 nm in the time window from 10 ns to 4 micros. No recombination reaction between the primary partners P840(+) and A(0)(-) could be detected under normal conditions. Such a recombination was observed (t(1/2) approximately 19 ns) under highly reducing conditions or after accumulation of three electrons on the acceptor side during a series of flashes, showing that the secondary acceptors can stabilize three electrons. From our data, there is no evidence for involvement of menaquinone in charge separation in the reaction center of green sulfur bacteria.

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Cited by 20 publications

References 22 publications

Function of a PscD Subunit in a Homodimeric Reaction Center Complex of the Photosynthetic Green Sulfur Bacterium Chlorobium tepidum Studied by Insertional Gene Inactivation

Function of a PscD Subunit in a Homodimeric Reaction Center Complex of the Photosynthetic Green Sulfur Bacterium Chlorobium tepidum Studied by Insertional Gene Inactivation

ESR Signal of the Iron−Sulfur Center F_Xand Its Function in the Homodimeric Reaction Center ofHeliobacterium modesticaldum^,

Electron Transfer Kinetics in Purified Reaction Centers from the Green Sulfur Bacterium Chlorobium tepidum Studied by Multiple-Flash Excitation

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Untitled

Cited by 20 publications

References 22 publications

Function of a PscD Subunit in a Homodimeric Reaction Center Complex of the Photosynthetic Green Sulfur Bacterium Chlorobium tepidum Studied by Insertional Gene Inactivation

Function of a PscD Subunit in a Homodimeric Reaction Center Complex of the Photosynthetic Green Sulfur Bacterium Chlorobium tepidum Studied by Insertional Gene Inactivation

ESR Signal of the Iron−Sulfur Center FXand Its Function in the Homodimeric Reaction Center ofHeliobacterium modesticaldum,

Electron Transfer Kinetics in Purified Reaction Centers from the Green Sulfur Bacterium Chlorobium tepidum Studied by Multiple-Flash Excitation

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ESR Signal of the Iron−Sulfur Center F_Xand Its Function in the Homodimeric Reaction Center ofHeliobacterium modesticaldum^,