Analysis of the Kinetics of P+HA– Recombination in Membrane-Embedded Wild-Type and Mutant Rhodobacter sphaeroides Reaction Centers between 298 and 77 K Indicates That the Adjacent Negatively Charged QA Ubiquinone Modulates the Free Energy of P+HA– and May Influence the Rate of the Protein Dielectric Response

Gibasiewicz, Krzysztof; Pajzderska, Maria; Dobek, A.; Brettel, Klaus; Jones, Michael R.

doi:10.1021/jp4011235

Cited by 6 publications

(13 citation statements)

References 45 publications

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“…6 ) and are consistent with the relative amplitudes of the two phases of charge recombination shown in Fig. 5 e–h b Data taken from Gibasiewicz et al ( 2013b ) c For two-exponential fits τ av = ( τ 1 A 1 + τ 2 A 2 )/( A 1 + A 2 ). The estimated experimental error of the fit parameters obtained for the nanosecond experiment is ±20 %…”

Section: Resultssupporting

confidence: 82%

“…Preparation of samples and instrumentation for nanosecond transient absorption measurements were described previously (Byrdin et al 2009 ; Gibasiewicz et al 2013b ). In brief, RC-only membranes were diluted to OD 800nm,1.5mm ≈ 0.5 in Tris–HCl buffer (pH 8.2) containing ~0.0001 % β-dodecyl maltoside (β-DM), ~50 % glycerol (v/v), 20 mM sodium ascorbate, and 12 mM o -phenanthroline.…”

Section: Methodsmentioning

confidence: 99%

“…In membrane-bound WT Rba. sphaeroides RCs, the overall characteristic lifetime of this process was estimated to be τ 12 = 3.7 ± 0.4 ns with no evident temperature dependence between 78 K and room temperature (RT) (Gibasiewicz et al 2013b ). For isolated Rba.…”

Section: Introductionmentioning

confidence: 99%

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Weak temperature dependence of P + H A − recombination in mutant Rhodobacter sphaeroides reaction centers

et al. 2016

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In contrast with findings on the wild-type Rhodobacter sphaeroides reaction center, biexponential P+HA− → PHA charge recombination is shown to be weakly dependent on temperature between 78 and 298 K in three variants with single amino acids exchanged in the vicinity of primary electron acceptors. These mutated reaction centers have diverse overall kinetics of charge recombination, spanning an average lifetime from ~2 to ~20 ns. Despite these differences a protein relaxation model applied previously to wild-type reaction centers was successfully used to relate the observed kinetics to the temporal evolution of the free energy level of the state P+HA− relative to P+BA−. We conclude that the observed variety in the kinetics of charge recombination, together with their weak temperature dependence, is caused by a combination of factors that are each affected to a different extent by the point mutations in a particular mutant complex. These are as follows: (1) the initial free energy gap between the states P+BA− and P+HA−, (2) the intrinsic rate of P+BA− → PBA charge recombination, and (3) the rate of protein relaxation in response to the appearance of the charge separated states. In the case of a mutant which displays rapid P+HA− recombination (ELL), most of this recombination occurs in an unrelaxed protein in which P+BA− and P+HA− are almost isoenergetic. In contrast, in a mutant in which P+HA− recombination is relatively slow (GML), most of the recombination occurs in a relaxed protein in which P+HA− is much lower in energy than P+HA−. The weak temperature dependence in the ELL reaction center and a YLH mutant was modeled in two ways: (1) by assuming that the initial P+BA− and P+HA− states in an unrelaxed protein are isoenergetic, whereas the final free energy gap between these states following the protein relaxation is large (~250 meV or more), independent of temperature and (2) by assuming that the initial and final free energy gaps between P+BA− and P+HA− are moderate and temperature dependent. In the case of the GML mutant, it was concluded that the free energy gap between P+BA− and P+HA− is large at all times.Electronic supplementary materialThe online version of this article (doi:10.1007/s11120-016-0239-9) contains supplementary material, which is available to authorized users.

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Section: Resultssupporting

confidence: 82%

Section: Methodsmentioning

confidence: 99%

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Weak temperature dependence of P + H A − recombination in mutant Rhodobacter sphaeroides reaction centers

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“…We were thus able to measure in a single experiment the complete charge separation and recombination dynamics of carotenoid-containing R. sphaeroides RCs. Our results are in good agreement with previous experiments reported earlier but using different experimental approaches suited either to long [15,16] or short [12,17] time scales. Furthermore, our results exhibit an improved signal-to-noise ratio despite an acquisition time of only a few minutes.…”

supporting

confidence: 93%

“…The solid line is a three-exponential fit that yields time constants equal to 2.0 ns (53%), 8 ns (42%), and 43 ns (5%). Our results are in good agreement with previously reported results obtained using lowrepetition-rate continuous-probe experiments [15,16], where the multiphasic kinetics were interpreted in terms of a gradual stabilization of the P H − L state. Our high time resolution and excellent signal-to-noise ratio furthermore allow us to more precisely determine the rate and relative amplitude of the fastest component, which presumably reflects recombination from the unrelaxed state.…”

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confidence: 93%

Arbitrary-detuning asynchronous optical sampling pump-probe spectroscopy of bacterial reaction centers

et al. 2013

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A recently reported variant of asynchronous optical sampling compatible with arbitrary unstabilized laser repetition rates is applied to pump-probe spectroscopy. This makes possible the use of a 5.1 MHz chirped pulse oscillator as the pump laser, thus extending the available time window to almost 200 ns with a time resolution as good as about 320 fs. The method is illustrated with the measurement in a single experiment of the complete charge transfer dynamics of the reaction center from Rhodobacter sphaeroides.

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Temperature dependence of nanosecond charge recombination in mutant Rhodobacter sphaeroides reaction centers: modelling of the protein dynamics

Gibasiewicz

Pajzderska

Białek

et al. 2021

Photochem Photobiol Sci

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We investigated the influence of a range of factors—temperature, redox midpoint potential of an electron carrier, and protein dynamics—on nanosecond electron transfer within a protein. The model reaction was back electron transfer from a bacteriopheophytin anion, HA−, to an oxidized primary electron donor, P+, in a wild type Rhodobacter sphaeroides reaction center (RC) with a permanently reduced secondary electron acceptor (quinone, QA−). Also used were two modified RCs with single amino acid mutations near the monomeric bacteriochlorophyll, BA, located between P and HA. Both mutant RCs showed significant slowing down of this back electron transfer reaction with decreasing temperature, similar to that observed with the wild type RC, but contrasting with a number of single point mutant RCs studied previously. The observed similarities and differences are explained in the framework of a (P+BA− ↔ P+HA−) equilibrium model with an important role played by protein relaxation. The major cause of the observed temperature dependence, both in the wild type RC and in the mutant proteins, is a limitation in access to the thermally activated pathway of charge recombination via the state P+BA− at low temperatures. The data indicate that in all RCs both charge recombination pathways, the thermally activated one and a direct one without involvement of the P+BA− state, are controlled by the protein dynamics. It is concluded that the modifications of the protein environment affect the overall back electron transfer kinetics primarily by changing the redox potential of BA and not by changing the protein relaxation dynamics.

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Cited by 6 publications

References 45 publications

Weak temperature dependence of P + H A − recombination in mutant Rhodobacter sphaeroides reaction centers

Weak temperature dependence of P + H A − recombination in mutant Rhodobacter sphaeroides reaction centers

Arbitrary-detuning asynchronous optical sampling pump-probe spectroscopy of bacterial reaction centers

Temperature dependence of nanosecond charge recombination in mutant Rhodobacter sphaeroides reaction centers: modelling of the protein dynamics

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