Electron Transfer Dynamics of <i>Rhodopseudomonas </i><i>viridis</i> Reaction Centers with a Modified Binding Site for the Accessory Bacteriochlorophyll

Arlt, T.; Dohse, Barbara; Schmidt, Stefan; Wachtveitl, Josef; Laussermair, E.; Zinth, Wolfgang; Oesterhelt, Dieter

doi:10.1021/bi960185f

Cited by 47 publications

(38 citation statements)

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“…It has been suggested that the principal reaction that is influenced by the electric field is the step P*B L →P + B L − [18]. In all of the M210 mutant reaction centers there is a change in the E m of the P/P + couple, which would be expected to change the driving force for P* decay by changing the standard free‐energy of the P + B L − state, which is thought to be the first radical pair state formed during transmembrane electron transfer [68–70]. In the YM210F, YM210L and YM210W reaction centers, the observed slowing of the rate of P* decay is consistent with the measured increase in the midpoint potential of the P/P + couple in these mutants, the trend being that the effect on the rate gets larger as the change in E m increases.…”

Section: Discussionmentioning

confidence: 99%

Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Rotterdam

Westerhoff²,

Visschers³

et al. 2001

European Journal of Biochemistry

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Transduction of free-energy by Rhodobacter sphaeroides reaction-center-light-harvesting-complex-1 (RCLH1) was quantified. RCLH1 complexes were reconstituted into liposomal membranes. The capacity of the RCLH1 complex to build up a proton motive force was examined at a range of incident light intensities, and induced proton permeabilities, in the presence of artificial electron donors and acceptors. Experiments were also performed with RCLH1 complexes in which the midpoint potential of the reaction center primary donor was modified over an 85-mV range by replacement of the tyrosine residue at the M210 position of the reaction center protein by histidine, phenylalanine, leucine or tryptophan. The intrinsic driving force with which the reaction center pumped protons tended to decrease as the midpoint potential of the primary donor was increased. This observation is discussed in terms of the control of the energetics of the first steps in light-driven electron transfer on the thermodynamic efficiency of the bacterial photosynthetic process. The light intensity at which half of the maximal proton motive force was generated, increased with increasing proton permeability of the membrane. This presents the first direct evidence for so-called backpressure control exerted by the proton motive force on steady-state cyclic electron transfer through and coupled proton pumping by the bacterial reaction center.Keywords: thermodynamics; bacterial photosynthesis; electron transport; reaction center; proton motive force.The fundamental event in photosynthesis is the conversion of light-energy into (Gibbs) free-energy of protons. This process of energy transduction takes place in plants, algae and certain species of bacteria. The transmembrane electron transfer, or charge separation, process occurs in specialized pigment±protein complexes collectively known as photosynthetic reaction centers. The best understood reaction center is that of the purple photosynthetic bacteria, and in particular of the bacterium Rhodobacter sphaeroides. Not only the atomic structure of this reaction center is known [1±3] but it has also been subjected to intensive spectroscopic study. The reaction center (RC) is intimately associated with the LH1 light-harvesting complex, to form the so-called RCLH1`core' complex.In RCLH1 core complexes, the photosynthetic process is initiated by the absorption of a photon, usually by the bacteriochlorophyll (Bchl) or carotenoid molecules of the LH1 antenna that are present in excess over the reaction center pigments. Excitation energy captured by the antenna pigments is transferred to the reaction center on the timescale of a few tens of picoseconds [4], creating the first singlet excited state of the reaction center primary donor, P, (P*) and so transforming P into a powerful reductant that is capable of reducing the adjacent cofactors.Transmembrane electron transfer is a multistep reaction involving the donation of an electron to the (Q A ) ubiquinone-A located within the reaction center protein on the opposite sid...

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Section: Discussionmentioning

confidence: 99%

Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Rotterdam

Westerhoff²,

Visschers³

et al. 2001

European Journal of Biochemistry

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“…Charge recombination of P þ H A occurs on the 10-ns timescale in the wild-type and very likely involves formation of P þ B A as an intermediate (27,32). In fact, in some mutants, the standard free energies of P þ B A and P þ H A are probably close enough that the charge-separated state present at 10 ps is likely an equilibrium mixture (23,33,34). One possibility is that on the 20-ps timescale in M210YD the free-energy difference between P þ H A and P þ B A is much smaller than in the wild-type, allowing very fast recombination of P þ H A via P þ B A -(see below).…”

Section: M210yd Mutant Rcs Undergo Fast Charge Recombination and Multmentioning

confidence: 99%

Protein Dielectric Environment Modulates the Electron-Transfer Pathway in Photosynthetic Reaction Centers

Guo

Woodbury

Lin

2012

Biophysical Journal

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The replacement of tyrosine by aspartic acid at position M210 in the photosynthetic reaction center of Rhodobacter sphaeroides results in the generation of a fast charge recombination pathway that is not observed in the wild-type. Apparently, the initially formed charge-separated state (cation of the special pair, P, and anion of the A-side bacteriopheophytin, H(A)) can decay rapidly via recombination through the neighboring bacteriochlorophyll (B(A)) soon after formation. The charge-separated state then relaxes over tens of picoseconds and recombination slows to the hundreds-of-picoseconds or nanosecond timescale. This dielectric relaxation results in a time-dependent blue shift of B(A)(-) absorption, which can be monitored using transient absorbance measurements. Protein dynamics also appear to modulate the electron transfer between H(A) and the next electron carrier, Q(A) (a ubiquinone). The kinetics of this reaction are complex in the mutant, requiring two kinetic terms, and the spectra associated with the two terms are distinct; a red shift of the H(A) ground-state bleaching is observed between the shorter and longer H(A)-to-Q(A) electron-transfer phases. The kinetics appears to be pH-independent, suggesting a negligible contribution of static heterogeneity originating from protonation/deprotonation in the ground state. A dynamic model based on the energy levels of the two early charge-separated states, P(+)B(A)(-) and P(+)H(A)(-), has been developed in which the energetics of these states is modulated by fast protein dielectric relaxations and this in turn alters both the kinetic complexity of the reaction and the reaction pathway.

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“…The reaction generates a P ϩ H Ϫ ion pair with a time constant of ϳ3 ps at room temperature, and it becomes even faster at cryogenic temperatures (Woodbury et al, 1985;Breton et al, 1988;Fleming et al, 1988). Recent experimental work has provided increasing support for the view that charge separation occurs in two distinct steps (Holzapfel et al, 1990;Arlt et al, 1993Arlt et al, , 1996Shkuropatov and Shuvalov, 1996;Maiti et al, 1994;Schmidt et al, 1994Schmidt et al, , 1995Heller et al, 1995Heller et al, , 1996Kirmaier et al, 1995a,b;Holzwarth and Muller, 1996;Van Brederode et al, 1996;Kennis et al, 1997). In the first step, P* probably transfers an electron to a neighboring bacteriochlorophyll (B), forming a P ϩ B Ϫ ion pair; in the second step, an electron moves from B Ϫ to H:…”

Section: Introductionmentioning

confidence: 99%

“…However, P ϩ H Ϫ appears to be created much closer in energy to P* and to relax toward its final level on both the picosecond and nanosecond time scales (Woodbury and Parson, 1984;Ogrodnik et al, 1988;Peloquin et al, 1994;Holzwarth and Muller, 1996). Measurements of the kinetics of charge separation in mutant or chemically modified reaction centers suggest that ⌬G°for the formation of P ϩ B Ϫ in wild-type reaction centers is on the order of Ϫ0.4 to Ϫ2 kcal/mol (Nagarajan et al, 1993;Jia et al, 1993;Hamm et al, 1993;Shkuropatov and Shuvalov, 1996;Schmidt et al, 1994;Huber et al, 1995;Arlt et al, 1996;Heller et al, 1996;Bixon et al, 1996;Van Brederode et al, 1996;Kennis et al, 1997). Electrostatics and molecular dynamics/free energy perturbation (FEP) calculations based on the crystallographic structure of the reaction center have put P ϩ B Ϫ ϳ3 kcal/mol below P*, with an estimated uncertainty of Ϯ3 kcal/mol Warshel et al, 1994;Alden et al, 1995Alden et al, , 1996a.…”

Section: Introductionmentioning

confidence: 99%

Reorganization Energy of the Initial Electron-Transfer Step in Photosynthetic Bacterial Reaction Centers

Parson

Chu

Warshel

1998

Biophysical Journal

109

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The reorganization energy (lambda) for electron transfer from the primary electron donor (P*) to the adjacent bacteriochlorophyll (B) in photosynthetic bacterial reaction centers is explored by molecular-dynamics simulations. Relatively long (40 ps) molecular-dynamics trajectories are used, rather than free energy perturbation techniques. When the surroundings of the reaction center are modeled as a membrane, lambda for P* B --> P+ B- is found to be approximately 1.6 kcal/mol. The results are not sensitive to the treatment of the protein's ionizable groups, but surrounding the reaction center with water gives higher values of lambda (approximately 6.5 kcal/mol). In light of the evidence that P+ B- lies slightly below P* in energy, the small lambda obtained with the membrane model is consistent with the speed and temperature independence of photochemical charge separation. The calculated reorganization energy is smaller than would be expected if the molecular dynamics trajectories had sampled the full conformational space of the system. Because the system does not relax completely on the time scale of electron transfer, the lambda obtained here probably is more pertinent than the larger value that would be obtained for a fully equilibrated system.

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Electron Transfer Dynamics of Rhodopseudomonas viridis Reaction Centers with a Modified Binding Site for the Accessory Bacteriochlorophyll

Cited by 47 publications

References 48 publications

Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Pumping capacity of bacterial reaction centers and backpressure regulation of energy transduction

Protein Dielectric Environment Modulates the Electron-Transfer Pathway in Photosynthetic Reaction Centers

Reorganization Energy of the Initial Electron-Transfer Step in Photosynthetic Bacterial Reaction Centers

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