Charge Recombination and Protein Dynamics in Bacterial Photosynthetic Reaction Centers Entrapped in a Sol-Gel Matrix

Kriegl, Jan M.; Forster, Florian K.; Nienhaus, G. Ulrich

doi:10.1016/s0006-3495(03)74613-x

Cited by 38 publications

(37 citation statements)

References 94 publications

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“…The cuvette containing the sample was attached to the cold finger of a closed-cycle helium refrigerator. Light-induced charge recombination kinetics were monitored in the Soret region of the BChl molecules at 436 nm, as described previously (9,10).…”

Section: Methodsmentioning

confidence: 99%

“…Illumination was switched on at selected temperatures during cooling to 10 K. With this illumination, RC molecules were kept in the charge-separated state for Ն95% of the time during cooling (9,10). After arrival at 10 K, samples were warmed in the dark with a ramp rate of 4.7 mK͞s for both dark-and light-adapted samples.…”

Section: Methodsmentioning

confidence: 99%

“…Proteins fluctuate thermally among many different conformations and respond to charge rearrangements with structural relaxations on time scales ranging from (below) picoseconds to (at least) seconds. These motions can strongly affect the ET parameters and hence the ET rates (8)(9)(10). For studying biological ET, the photosynthetic reaction center (RC) of the purple bacterium Rhodobacter sphaeroides is a superb model system.…”

mentioning

confidence: 99%

“…21) were used in this work. Bacterial growth, RC purification, and removal of the secondary quinone were performed as described previously (10,(21)(22)(23).…”

mentioning

confidence: 99%

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Structural, dynamic, and energetic aspects of long-range electron transfer in photosynthetic reaction centers

Kriegl

Nienhaus

2003

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

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Intramolecular electron transfer within proteins plays an essential role in biological energy transduction. Electron donor and acceptor cofactors are bound in the protein matrix at specific locations, and protein-cofactor interactions as well as protein conformational changes can markedly influence the electron transfer rates. To assess these effects, we have investigated charge recombination from the primary quinone acceptor to the special pair bacteriochlorophyll dimer in wild-type reaction centers of Rhodobacter sphaeroides and four mutants with widely modified free energy gaps. After light-induced charge separation, the recombination kinetics were measured in the light-and dark-adapted forms of the protein from 10 to 300 K. The data were analyzed by using the spin-boson model, which allowed us to self-consistently determine the electronic coupling energy, the distribution of energy gaps, the spectral density of phonons, and the reorganization energy. The analysis revealed slow changes of the energy gap after charge separation. Interesting correlations of the control parameters governing electron transfer were found and related to structural and dynamic properties of the protein.T he bioenergetic pathways of living systems involve a multitude of electron transfer (ET) reactions. Within large protein-cofactor complexes, electrons tunnel between donor and acceptor sites over substantial distances (5-30 Å). In the weak coupling regime, the ET rate coefficient is obtained from perturbation theory as (1-4)where ប and V denote Planck's constant divided by 2 and the electronic coupling matrix element, respectively. The thermally averaged Franck-Condon factor, FC, represents the probability of forming a resonant complex between donor and acceptor. This quantity can be calculated in various ways, based on classical, semiclassical, or quantum-mechanical theories (4). In the celebrated classical Marcus theory (1),with Boltzmann's constant, k B , and absolute temperature, T. The free energy difference between the reactant and product states, , the nuclear reorganization energy, , and the electronic coupling, V, are the three system parameters that govern the ET rate. From these quantities, only the driving force, , is directly accessible to measurement, e.g., by delayed fluorescence (5), redox titration (6), or voltammetry (7). The other two parameters can be determined only indirectly from kinetic data and are difficult to disentangle in practice. The intrinsic flexibility of proteins adds an interesting dynamic aspect to the ET reaction. Proteins fluctuate thermally among many different conformations and respond to charge rearrangements with structural relaxations on time scales ranging from (below) picoseconds to (at least) seconds. These motions can strongly affect the ET parameters and hence the ET rates (8-10). For studying biological ET, the photosynthetic reaction center (RC) of the purple bacterium Rhodobacter sphaeroides is a superb model system. This membrane-spanning, 120-kDa, protein-pigment complex consists...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

“…21) were used in this work. Bacterial growth, RC purification, and removal of the secondary quinone were performed as described previously (10,(21)(22)(23).…”

mentioning

confidence: 99%

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Structural, dynamic, and energetic aspects of long-range electron transfer in photosynthetic reaction centers

Kriegl

Nienhaus

2003

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

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“…2 and 3 also exhibit hydration-shell-coupled motions. Such motions dominate, for instance, the response of photosynthetic reaction center proteins to internal charge separation, where the sensitivity to hydration has been quantified (37)(38)(39). ''Hydration shell'' in this case likely refers to buried water.…”

Section: The ␤-Relaxation In Proteinsmentioning

confidence: 99%

Bulk-solvent and hydration-shell fluctuations, similar to α- and β-fluctuations in glasses, control protein motions and functions

Fenimore

Frauenfelder²,

McMahon³

et al. 2004

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

498

504

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The concept that proteins exist in numerous different conformations or conformational substates, described by an energy landscape, is now accepted, but the dynamics is incompletely explored. We have previously shown that large-scale protein motions, such as the exit of a ligand from the protein interior, follow the dielectric fluctuations in the bulk solvent. Here, we demonstrate, by using mean-square displacements (msd) from Mö ssbauer and neutron P roteins are the molecules that perform most biological functions, from storage of dioxygen (O 2 ) to enzyme catalysis. A central goal of protein science is to relate structure, dynamics, and function. Although investigations of protein structures and functions are well organized industries, protein dynamics is still in its infancy. Dynamics studies are best performed on proteins whose structures and functions are well known, e.g., myoglobin (Mb), the protein that gives muscles their red color. A hybrid picture of Mb is shown in Fig. 1. The lower part displays a piece of the protein backbone, namely, three ␣-helices. The upper part presents a space-filling view of the protein atoms. The active center, a heme group with a central iron atom, is red. Two cavities are also shown, Xe1 and the heme cavity. The protein is surrounded by the hydration shell, one to two layers of water, and is embedded in the bulk solvent. In Mb's role as an oxygenstorage protein, O 2 enters the protein, stays some time in Xe1, then binds at the heme iron (1). CO follows a similar path through the protein. The structure of Mb shows no permanent channel that leads from the outside to either Xe1 or the heme pocket or from Xe1 to the heme pocket. Thus, structural fluctuations are necessary for function (2).Fluctuations imply that Mb possesses numerous different conformations, called conformational substates (CS) (3). The different CS can be described by an energy landscape (EL) (4), the central concept in the folding (5), dynamics, and function of proteins. The EL is a construct in Ϸ3N dimensions, where N is the number of atoms forming the protein and the hydration shell. A substate is a point in this hyperspace, and structural fluctuations are represented by jumps between points. Initially, we assumed that protein conformations could be organized into a simple, rough EL (1). Experiments showed, however, that there are wells within wells within wells, and an organization of the EL with several tiers of decreasing free-energy barriers ensued (6). The top tier, denoted by CS0, contains a small number of CS with different structures that can have different functions: in A 0 Mb is involved in NO enzymatics; in A 1 it acts as an oxygen-storage system (7). Each of the CS0 substates can assume a very large number of CS1, called statistical substates. They perform the same function but with different rates. Here, we will show that the statistical substates comprise two tiers, CS1␣ and CS1␤. Fluctuations between CS1␣ substates are slaved to the solvent motions and involve sizeable structural changes (8). ...

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Multifrequency EPR on Photosynthetic Systems

Misra

Möbius

Savitsky³

2011

Multifrequency Electron Paramagnetic Resonance

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Charge Recombination and Protein Dynamics in Bacterial Photosynthetic Reaction Centers Entrapped in a Sol-Gel Matrix

Cited by 38 publications

References 94 publications

Structural, dynamic, and energetic aspects of long-range electron transfer in photosynthetic reaction centers

Structural, dynamic, and energetic aspects of long-range electron transfer in photosynthetic reaction centers

Bulk-solvent and hydration-shell fluctuations, similar to α- and β-fluctuations in glasses, control protein motions and functions

Multifrequency EPR on Photosynthetic Systems

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