Showing papers by "Rienk van Grondelle published in 2006"
TL;DR: Experimental and theoretical studies of energy transfer in the photosynthetic light-harvesting complexes LH1, LH2, and LHCII performed during the past decade since the discovery of high-resolution structure are overviewed.
Abstract: We overview experimental and theoretical studies of energy transfer in the photosynthetic light-harvesting complexes LH1, LH2, and LHCII performed during the past decade since the discovery of high-resolution structure of these complexes. Experimental findings obtained with various spectroscopic techniques makes possible a modelling of the excitation dynamics at a quantitative level. The modified Redfield theory allows a precise assignment of the energy transfer pathways together with a direct visualization of the whole excitation dynamics where various regimes from a coherent motion of delocalized exciton to a hopping of localized excitations are superimposed. In a single complex it is possible to observe the switching between these regimes driven by slow conformational motion (as we demonstrate for LH2). Excitation dynamics under quenched conditions in higher-plant complexes is discussed.
444 citations
TL;DR: This work shows that photoactivation of BLUF domains proceeds by means of a radical-pair mechanism, driven by electron and proton transfer from the protein to the flavin, resulting in the transient formation of anionic and neutral flavin radical species that finally result in the long-lived signaling state on a 100-ps timescale.
Abstract: BLUF (blue light sensing using FAD) domains constitute a recently discovered class of photoreceptor proteins found in bacteria and eukaryotic algae, where they control a range of physiological responses including photosynthesis gene expression, photophobia, and negative phototaxis. Other than in well known photoreceptors such as the rhodopsins and phytochromes, BLUF domains are sensitive to light through an oxidized flavin rather than an isomerizable cofactor. To understand the physicochemical basis of BLUF domain photoactivation, we have applied femtosecond transient absorption spectroscopy to the Slr1694 BLUF domain of Synechocystis PCC6803. We show that photoactivation of BLUF domains proceeds by means of a radical-pair mechanism, driven by electron and proton transfer from the protein to the flavin, resulting in the transient formation of anionic and neutral flavin radical species that finally result in the long-lived signaling state on a 100-ps timescale. A pronounced deuteration effect is observed on the lifetimes of the intermediate radical species, indicating that proton movements underlie their molecular transformations. We propose a photoactivation mechanism that involves a successive rupture of hydrogen bonds between a conserved tyrosine and glutamine by light-induced electron transfer from tyrosine to flavin and between the glutamine and flavin by subsequent protonation at flavin N5. These events allow a reorientation of the conserved glutamine, resulting in a switching of the hydrogen-bond network connecting the chromophore to the protein, followed by radical-pair recombination, which locks the glutamine in place. It is suggested that the redox potential of flavin generally defines the light sensitivity of flavin-binding photoreceptors.
209 citations
TL;DR: A transient absorption spectroscopic study on a model system made up of a zinc phthalocyanine molecule covalently linked to carotenoids with 9, 10, or 11 conjugated carbon-carbon double bonds shows that acarotenoid can act as an acceptor of Pc excitation energy, thereby shortening its singlet excited-state lifetime.
Abstract: Under excess illumination, plant photosystem II dissipates excess energy through the quenching of chlorophyll fluorescence, a process known as nonphotochemical quenching. Activation of nonphotochemical quenching has been linked to the conversion of a carotenoid with a conjugation length of nine double bonds (violaxanthin) into an 11-double-bond carotenoid (zeaxanthin). It has been suggested that the increase in the conjugation length turns the carotenoid from a nonquencher into a quencher of chlorophyll singlet excited states, but unequivocal evidence is lacking. Here, we present a transient absorption spectroscopic study on a model system made up of a zinc phthalocyanine (Pc) molecule covalently linked to carotenoids with 9, 10, or 11 conjugated carbon–carbon double bonds. We show that a carotenoid can act as an acceptor of Pc excitation energy, thereby shortening its singlet excited-state lifetime. The conjugation length of the carotenoid is critical to the quenching process. Remarkably, the addition of only one double bond can turn the carotenoid from a nonquencher into a very strong quencher. By studying the solvent polarity dependence of the quenching using target analysis of the time-resolved data, we show that the quenching proceeds through energy transfer from the excited Pc to the optically forbidden S1 state of the carotenoid, coupled to an intramolecular charge-transfer state. The mechanism for excess energy dissipation in photosystem II is discussed in view of the insights obtained on this simple model system.
132 citations
TL;DR: The rate of ground-state recovery of the BLUF domain of AppA follows Arrhenius kinetics, which suggests that this domain itself does not undergo large structural changes upon illumination and that the structural transitions in full-length AppA are dominated by interdomain rearrangements.
Abstract: AppA, a transcriptional antirepressor, regulates the steady expression of photosynthesis genes in Rhodobacter sphaeroides in response to high-intensity blue light and to redox signals. Its blue-light sensing is mediated by an N-terminal BLUF domain, a member of a novel flavin fold. The photocycle of this domain (AppA5-125) includes formation of a slightly red-shifted long-lived signaling state, which is formed directly from the singlet excited state of the flavin on a subnanosecond time scale [Gauden et al. (2005) Biochemistry 44, 3653−3662]. The red shift of the absorption spectrum of this signaling state has been attributed to a rearrangement of its hydrogen-bonding interactions with the surrounding apoprotein. In this study we have characterized an AppA mutant with an altered aromatic amino acid: W104F. This mutant exhibits an increased lifetime of the singlet excited state of the flavin chromophore. Most strikingly, however, it shows a 1.5-fold increase in its quantum yield of signaling state formati...
103 citations
TL;DR: It is demonstrated that experimentally observed quasistable conformational states are characterized by excitation energy transfer regimes varying from a coherent wavelike motion of a delocalized exciton to a hopping-type motion of the wavepacket and self-trapped excitations that do not move from their localization site.
99 citations
TL;DR: Two new models are proposed that can describe both the time-resolved and the intensity-dependent data of the electronic excited-state manifold of the carotenoid rhodopin glucoside in the light-harvesting 2 complex isolated from Rhodopseudomonas acidophila and adequately fit the measured data.
Abstract: Dispersed transient absorption spectra collected at variable excitation intensities in combination with time-resolved signals were used to explore the underlying connectivity of the electronic excited-state manifold of the carotenoid rhodopin glucoside in the light-harvesting 2 complex isolated from Rhodopseudomonas acidophila. We find that the S* state, which was recently identified as an excited state in carotenoids bound in bacterial light-harvesting complexes, exhibits a different response to the increase of excitation intensity than the S1 state, which suggests that the models used so far to describe the excited states of carotenoids are incomplete. We propose two new models that can describe both the time-resolved and the intensity-dependent data; the first postulates that S1 and S* are not populated in parallel after the decay of the initially excited S2 state but instead result from the excitation of distinct ground-state subpopulations. The second model introduces a resonantly enhanced light-indu...
99 citations
TL;DR: The excited and ground electronic states manifold of peridinin has been reconstructed using target analysis; this approach combined with the measured multipulse spectroscopic data allows us to estimate the spectra and time scales of the corresponding transient states.
Abstract: Optical pump-induced dynamics of the highly asymmetric carotenoid peridinin in methanol was studied by dispersed pump−probe, pump−dump−probe, and pump−repump−probe transient absorption spectroscopy in the visible region. Dispersed pump−probe measurements show that the decay of the initially excited S2 state populates two excited states, the S1 and the intramolecular charge-transfer (ICT) state, at a ratio determined by the excitation wavelength. The ensuing spectral evolution occurs on the time scale of a few picoseconds and suggests the equilibration of these states. Dumping the stimulated emission of the ICT state with an additional 800-nm pulse after 400- and 530-nm excitation preferentially removes the ICT state contribution from the broad excited-state absorption, allowing for its spectral characterization. At the same time, an unrelaxed ground-state species, which has a subpicosecond lifetime, is populated. The application of the 800-nm pulse at early times, when the S2 state is still populated, led...
96 citations
TL;DR: The results demonstrate that the properties of the S1/ICT state specific for carbonyl carotenoids is the key to ensure the effective harvesting of photons in the 500-600 nm region, which is of vital importance to underwater organisms.
Abstract: Carbonyl carotenoids are important constituents of the antenna complexes of marine organisms. These carotenoids possess an excited state with a charge-transfer character (intramolecular charge transfer state, ICT), but many details of the carotenoid to chlorophyll energy transfer mechanisms are as yet poorly understood. Here, we employ femtosecond transient absorption spectroscopy to study energy transfer pathways in the intrinsic light-harvesting complex (LHC) of dinoflagellates, which contains the carbonyl carotenoid peridinin. Carotenoid to chlorophyll energy transfer efficiency is about 90% in the 530-550 nm region, where the peridinin S2 state transfers energy with an efficiency of 25-50%. The rest proceeds via the S1/ICT channel, and the major S1/ICT-mediated energy transfer pathway utilizes the relaxed S1/ICT state and occurs with a time constant of 2.6 ps. Below 525 nm, the overall energy transfer efficiency drops because of light absorption by another carotenoid, diadinoxanthin, that contributes only marginally to energy transfer. Instead, its role is likely to be photoprotection. In addition to the peridinin-Chl-a energy transfer, it was shown that energy transfer also occurs between the two chlorophyll species in LHC, Chl-c2, and Chl-a. The time constant characterizing the Chl-c2 to Chl-a energy transfer is 1.4 ps. The results demonstrate that the properties of the S1/ICT state specific for carbonyl carotenoids is the key to ensure the effective harvesting of photons in the 500-600 nm region, which is of vital importance to underwater organisms.
78 citations
TL;DR: It is proposed that formation of the A696 state involves hydride transfer from NADPH to form a charge transfer complex, and a catalytic mechanism of POR is suggested in which Pchlide absorbs a photon, creating a transient charge separation across the C-17–C-18 double bond.
60 citations
TL;DR: An investigation of energy migration dynamics in intact cells of the photosynthetic cryptophyte Rhodomonas CS24 using analyses of steady-state and time-resolved fluorescence anisotropy measurements shows an almost equal distribution of excitation energy from PE545 to both photosystem I (PSI) and photosystem II (PSII), whose trap times correspond well to those obtained from experiments on isolated photosystems.
Abstract: We report an investigation of energy migration dynamics in intact cells of the photosynthetic cryptophyte Rhodomonas CS24 using analyses of steady-state and time-resolved fluorescence anisotropy measurements. By fitting a specific model to the fluorescence data, we obtain three time scales (17, 58, and 113 ps) by which the energy is transferred from phycoerythrin 545 (PE545) to the membrane-associated chlorophylls (Chls). We propose that these time scales reflect both an angular distribution of PE545 around the photosystems and the relative orientations of the donor dihydrobiliverdin (DBV) bilin and the acceptor Chl. Contrary to investigations of the isolated antenna complex, it is demonstrated that energy transfer from PE545 does not occur from a single-emitting bilin, but rather both the peripheral dihydrobiliverdin (DBV) chromophores in PE545 appear to be viable donors of excitation energy to the membrane-bound proteins. The model shows an almost equal distribution of excitation energy from PE545 to both photosystem I (PSI) and photosystem II (PSII), whose trap times correspond well to those obtained from experiments on isolated photosystems.
55 citations
01 Jan 2006
TL;DR: In this article, long wavelength chlorophylls (LWCs) are located in the Photosystem I (PS I) core complex, whereas in plants and algae they are distributed between the PS I core and the light-harvesting complexes (LHC I).
Abstract: Summary In cyanobacteria, long wavelength chlorophylls (LWC) are located in the Photosystem I (PS I) core complex, whereas in plants and algae they are distributed between the PS I core and the light-harvesting complexes (LHC I). LWC are most probably aggregates of (excitonically) coupled chlorophylls, mainly dimers or trimers. The total number of LWC is rather small (≤10% of the total chlorophylls). Depending on their location in the PS I antenna and their distance from P700, they can play a crucial role in the kinetics of energy transfer and in the trapping of the excitation energy by charge separation. Energy absorbed by LWC is transferred uphill to P700 with high efficiency at room temperature, thereby increasing the cross-section for the absorption of red light. LWC are involved also in the dissipation of excess energy, thus protecting the reaction center. Under physiological conditions, the excitations within the PS I antenna are nearly thermally equilibrated over the different spectral forms and the excitation energy is efficiently trapped via charge separation in the reaction center. When the photochemistry in the reaction center is blocked, the excitations migrate to the LWC and are quenched either by P700 + or by the P700 triplet state depending on the state of P700.
TL;DR: The origin and characteristics of the circular dichroism (CD) spectrum of various light-harvesting 1 (LH1) complexes is investigated, and the shape of the absorption and CD spectra and the structure of the LH1 complex are contemplated.
Abstract: In this work, we investigate the origin and characteristics of the circular dichroism (CD) spectrum of various light-harvesting 1 (LH1) complexes. The near-infrared (NIR) CD signal of these core antennae is strongly nonconservative, and the nature of this nonconservativity is under examination in this paper. So far, on the basis of the high-resolution structures of LH2, we have been able to model the absorption and CD spectra in the bacteriochlorophyll (BChl) QY and QX regions of LH2 (Georgakopoulou et al., Biophys. J. 2002, 82, 2184−2197), as well as in the carotenoid region (Georgakopoulou et al., Biophys. J. 2004, 87, 3010−3022). We proceed by applying the same modeling method in order to reproduce the LH1 spectra. We assume a ring of dimers in a perfect circular arrangement with 16-fold symmetry, and account for all excitonic interactions within the ring. Because LH1 complexes exhibit QY and QX CD signals of very low intensity, higher transitions can easily affect these regions. Therefore, we expand t...
TL;DR: Different jumping behavior is observed for single complexes of different types investigated with the same equivalent excitation intensity, and the differences in spectral diffusion are associated with subtle differences of the binding pocket of B850 pigments and the structural flexibility of the different types of complexes.
TL;DR: The rate constants for energy transfer and decay of the fluorescence were very similar, indicating that structurally the three isoforms are highly homologous and that probably none of them play a more significant role in light-harvesting and energy transfer.
Abstract: In this article we report the characterization of the energy transfer process in the reconstituted isoforms of the plant light-harvesting complex II. Homotrimers of recombinant Lhcb1 and Lhcb2 and monomers of Lhcb3 were compared to native trimeric complexes. We used low-intensity femtosecond transient absorption (TA) and time-resolved fluorescence measurements at 77 K and at room temperature, respectively, to excite the complexes selectively in the chlorophyll b absorption band at 650 nm with 80 fs pulses and on the high-energy side of the chlorophyll a absorption band at 662 nm with 180 fs pulses. The subsequent kinetics was probed at 30-35 different wavelengths in the region from 635 to 700 nm. The rate constants for energy transfer were very similar, indicating that structurally the three isoforms are highly homologous and that probably none of them play a more significant role in light-harvesting and energy transfer. No signature has been found in the transient absorption measurements at 77 K for Lhcb3 which might suggest that this protein acts as a relative energy sink of the excitations in heterotrimers of Lhcb1/Lhcb2/Lhcb3. Minor differences in the amplitudes of some of the rate constants and in the absorption and fluorescence properties of some pigments were observed, which are ascribed to slight variations in the environment surrounding some of the chromophores depending on the isoform. The decay of the fluorescence was also similar for the three isoforms and multi-exponential, characterized by two major components in the ns regime and a minor one in the ps regime. In agreement with previous transient absorption measurements on native LHC II complexes, Chl b --> Chl a energy transfer exhibited very fast channels but at the same time a slow component (ps). The Chls absorbing at around 660 nm exhibited both fast energy transfer which we ascribe to transfer from 'red' Chl b towards 'red' Chl a and slow transfer from 'blue' Chl a towards 'red' Chl a. The results are discussed in the context of the new available atomic models for LHC II.
TL;DR: This work presents and discusses the single-molecule fluorescence spectra of a variety of species of light-harvesting complexes: LH2 of Rhodopseudomonas acidophila, Rhodobacter sphaeroides, and Rhodospirillum molischianum and LH1 of Rhodob bacteria.
TL;DR: A molecular dyad is designed and synthesized in which the carotenoid acts both as an antenna for the fullerene and as an electron transfer partner, which leads to charge separation on the subpicosecond time scale and on the ps time scale.
Abstract: We have designed and synthesized a molecular dyad comprising a carotenoid pigment linked to a fullerene derivative (C–C60) in which the carotenoid acts both as an antenna for the fullerene and as an electron transfer partner Ultrafast transient absorption spectroscopy was carried out on the dyad in order to investigate energy transfer and charge separation pathways and efficiencies upon excitation of the carotenoid moiety When the dyad is dissolved in hexane energy transfer from the carotenoid S2 state to the fullerene takes place on an ultrafast (sub 100 fs) timescale and no intramolecular electron transfer was detected When the dyad is dissolved in toluene, the excited carotenoid decays from its excited states both by transferring energy to the fullerene and by forming a charge-separated C˙+–C60˙− The charge-separated state is also formed from the excited fullerene following energy transfer from the carotenoid These pathways lead to charge separation on the subpicosecond time scale (possibly from the S2 state and the vibrationally excited S1 state of the carotenoid), on the ps time scale (55 ps) from the relaxed S1 state of the carotenoid, and from the excited state of C60 in 235 ps The charge-separated state lives for 13 ns and recombines to populate both the low-lying carotenoid triplet state and the dyad ground state
TL;DR: This study, combined with the theoretical approach of the companion paper, provide a complete explanation of the origin of the nonconservative NIR CD spectra of LH1 and B820.
Abstract: Absorption and circular dichroism (CD) spectra of light-harvesting (LH)1 complexes from the purple bacteria Rhodobacter (Rba.) sphaeroides and Rhodospirillum (Rsp.) rubrum are presented. The complexes exhibit very low intensity, highly nonconservative, near-infrared (NIR) CD spectra. Absorption and CD spectra from several mutant and reconstituted LH1 complexes, with the carotenoid neurosporene and the precursor phytoene replacing the wild-type (WT) carotenoids, are also examined. The experiments show that the position of the carotenoid bands as well as the bacteriochlorophyll (BChl)/carotenoid ratio affect the NIR CD spectra: bluer bands and larger ratios make the NIR CD signal more conservative. Modeling results that support this finding are presented. This study, combined with the theoretical approach of the companion paper, where modeling of such complexes is presented and discussed in detail, provide a complete explanation of the origin of the nonconservative NIR CD spectra of LH1 and B820.
TL;DR: The experimental conditions that are required for incoherent effects to contribute to control experimental signals are discussed, with particular emphasis on pulse intensities, and it is shown that the optimization of a ratio of conservative signals is required to exclude saturation effects from coherent control studies.
Abstract: Dispersed multipump-probe (PPP) spectroscopy was used to explore the role of saturation, annihilation, and structured pulses in recent coherent control experiments on the light-harvesting 2 complex from Rhodopseudomonas acidophila (Herek et al. Nature 2002, 417, 533). We discuss the complimentary aspects between the PPP technique and coherent control studies, in particular the ability to dissect complicated pulse structures and the utility in exploring incoherent mechanisms. With the aid of a simple multistate model involving only population dynamics, we illustrate how the optimized structured pulses may be explained in terms of an interplay between excited-state populations, saturation, and annihilation. Furthermore, we discuss the experimental conditions that are required for incoherent effects to contribute to control experimental signals, with particular emphasis on pulse intensities, and show that the optimization of a ratio of conservative signals (i.e., not modulated by external dynamics) is required to exclude saturation effects from coherent control studies.
TL;DR: "natural" (occurring in the absence of excitation) spectral diffusion after a spectral jump has occurred is investigated, which is suggested to be due to a natural conformational development of the pigment-protein complex, which so far has not been observed for this type of complex at the single-molecule level.
Abstract: We have employed the technique of single-molecule fluorescence microspectroscopy to investigate the spontaneous conformational evolution of individual peripheral LH2 complexes from the purple bacterium Rhodopseudomonas acidophila. Fluorescence microscopy is a sensitive tool, which allows the spectral changes of single complexes to be monitored on a time scale from 0.1 s to many minutes. Here we have investigated "natural" (occurring in the absence of excitation) spectral diffusion after a spectral jump has occurred. In a quarter of all the observed spectral jumps recorded with the LH2 complexes, a further spontaneous evolution occurs, in the absence of illumination, that results in the formation of a different spectroscopic state. We suggest that this is due to a natural conformational development of the pigment-protein complex, which so far has not been observed for this type of complex at the single-molecule level. The functional significance of such structural rearrangements is not yet clear but may be associated with the necessity for the light-harvesting complexes to adjust their shape in the densely packed photosynthetic membrane.
31 Jul 2006
TL;DR: In this article, the interplay between excited-state dynamics, saturation, and annihilation phenomena in the LH2 protein from Rhodopseudomonas acidophila generates structured pulses in optimal control experiments.
Abstract: Dispersed transient absorption and multi-pump spectroscopies were used to illustrate how the interplay between excited-state dynamics, saturation, and annihilation phenomena in the LH2 protein from Rhodopseudomonas acidophila generates structured pulses in optimal control experiments.
01 Jan 2006
TL;DR: This chapter uses femtosecond transient absorption spectroscopy to investigate the photochemical events that lead to the formation of the redshifted signaling state in the AppA and Synechocystis Slr1694 BLUF domains.
Abstract: Blue-light sensing using FAD (BLUF) domains are a distinct family of flavin-binding photoreceptors that show no significant relationship to other sensor proteins in sequence or structure. AppA is a two-component protein that can sense blue light at its N-terminal domain, and oxygen tension at its cysteine-rich C-terminal domain, and is shown to control photosynthesis gene expression in response to high-intensity blue-light irradiation and variation of the oxygen tension. This chapter uses femtosecond transient absorption spectroscopy to investigate the photochemical events that lead to the formation of the redshifted signaling state in the AppA and Synechocystis Slr1694 BLUF domains. The time-resolved data are globally analyzed in terms of a kinetic scheme with sequentially interconverting species. The global analysis procedure indicates that six components are required for an adequate description of the time-resolved data.