Papers by Rienk Van Grondelle
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2004
The electric-field induced absorption changes (Stark effect) of reconstituted light-harvesting co... more The electric-field induced absorption changes (Stark effect) of reconstituted light-harvesting complex II (LHCII) in different oligomerisation states-monomers and trimers-with different xanthophyll content have been probed at 77 K. The Stark spectra of the reconstituted control samples, containing the xanthophylls lutein and neoxanthin, are very similar to previously reported spectra of native LHCII. Reconstituted LHCII, containing lutein but no neoxanthin, shows a similar electrooptical response in the Chl a region, but the Stark signal of Chl b around 650 nm amounts to at most approximately 25% of that of the control samples. We conclude that neoxanthin strongly modifies the electronic states of the nearby Chl b molecules causing a large electrooptical response at 650 nm stemming from one or more Chls b in the control samples. Ambiguities about the assignment of several bands in the Soret region [Biochim. Biophys. Acta 1605 (2003) 83] are resolved and the striking difference in electric field response between the two lutein molecules is confirmed. The Stark effect in the carotenoid spectral region in both control and neoxanthin-deficient samples is almost identical, showing that the neoxanthin Stark signal is small and much less intense than the lutein Stark signal.
The Journal of Physical Chemistry B, 2013
Structure-based calculations are combined with quantitative modeling of spectra and energy transf... more Structure-based calculations are combined with quantitative modeling of spectra and energy transfer dynamics to detemine the energy transfer scheme of the PE545 principal light-harvesting antenna of the cryptomonad Rhodomonas CS24. We use a recently developed quantum-mechanics/molecular mechanics (QM/MM) method that allows us to account for pigment-protein interactions at atomic detail in site energies, transition dipole moments, and electronic couplings. In addition, conformational flexibility of the pigment-protein complex is accounted for through molecular dynamics (MD) simulations. We find that conformational disorder largely smoothes the large energetic differences predicted from the crystal structure between the pseudosymmetric pairs PEB50/61C-PEB50/61D and PEB82C-PEB82D. Moreover, we find that, in contrast to chlorophyll-based photosynthetic complexes, pigment composition and conformation play a major role in defining the energy ladder in the PE545 complex, rather than specific pigment-protein interactions. This is explained by the remarkable conformational flexibility of the eight bilin pigments in PE545, characterized by a quasi-linear arrangement of four pyrrole units. The MD-QM/MM site energies allow us to reproduce the main features of the spectra, and minor adjustments of the energies of the three red-most pigments DBV19A, DBV19B, and PEB82D allow us to model the spectra of PE545 with a similar quality compared to our original model (model E from Novoderezhkin et al. Biophys. J.2010, 99, 344), which was extracted from the spectral and kinetic fit. Moreover, the fit of the transient absorption kinetics is even better in the new structure-based model. The largest difference between our previous and present results is that the MD-QM/MM calculations predict a much smaller gap between the PEB50/61C and PEB50/61D sites, in better accord with chemical intuition. We conclude that the current adjusted MD-QM/MM energies are more reliable in order to explore the spectral properties and energy transfer dynamics in the PE545 complex.
Biophysical Journal, 2010
We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolat... more We model the spectra and excitation dynamics in the phycobiliprotein antenna complex PE545 isolated from the unicellular photosynthetic cryptophyte algae Rhodomonas CS24. The excitonic couplings between the eight bilins are calculated using the CIS/6-31G method. The site energies are extracted from a simultaneous fit of the absorption, circular dichroism, fluorescence, and excitation anisotropy spectra together with the transient absorption kinetics using the modified Redfield approach. Quantitative fit of the data enables us to assign the eight exciton components of the spectra and build up the energy transfer picture including pathways and timescales of energy relaxation, thus allowing a visualization of excitation dynamics within the complex.
Journal of the American Chemical Society, Jan 18, 2017
The purple bacterial core light harvesting antenna-reaction center (LH1-RC) complex is the simple... more The purple bacterial core light harvesting antenna-reaction center (LH1-RC) complex is the simplest system able to achieve the entire primary function of photosynthesis. During the past decade, a variety of photosynthetic proteins were studied by a powerful technique, two-dimensional electronic spectroscopy (2DES). However, little attention has been paid to LH1-RC, although its reversible uphill energy transfer, trapping, and backward detrapping processes, represent a crucial step in the early photosynthetic reaction dynamics. Thus, in this work, we employed 2DES to study two LH1-RC complexes of Thermochromatium (Tch.) tepidum. By direct observation of detrapping, the complex reversible process was clearly identified and an overall scheme of the excitation evolution in LH1-RC was obtained.
Scientific reports, Jan 9, 2016
Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria i... more Energy transfer and trapping in the light harvesting antennae of purple photosynthetic bacteria is an ultrafast process, which occurs with a quantum efficiency close to unity. However the mechanisms behind this process have not yet been fully understood. Recently it was proposed that low-lying energy dark states, such as charge transfer states and polaron pairs, play an important role in the dynamics and directionality of energy transfer. However, it is difficult to directly detect those states because of their small transition dipole moment and overlap with the B850/B870 exciton bands. Here we present a new experimental approach, which combines the selectivity of two-dimensional electronic spectroscopy with the availability of genetically modified light harvesting complexes, to reveal the presence of those dark states in both the genetically modified and the wild-type light harvesting 2 complexes of Rhodopseudomonas palustris. We suggest that Nature has used the unavoidable charge ...
Biophysical Journal, 2004
Wavelength-and time-resolved fluorescence experiments have been performed on the photoactive yell... more Wavelength-and time-resolved fluorescence experiments have been performed on the photoactive yellow protein, the E46Q mutant, the hybrids of these proteins containing a nonisomerizing ''locked'' chromophore, and the native and locked chromophores in aqueous solution. The ultrafast dynamics of these six systems is compared and spectral signatures of isomerization and solvation are discussed. We find that the ultrafast red-shifting of fluorescence is associated mostly with solvation dynamics, whereas isomerization manifests itself as quenching of fluorescence. The observed multiexponential quenching of the protein samples differs from the single-exponential lifetimes of the chromophores in solution. The locked chromophore in the protein environment decays faster than in solution. This is due to additional channels of excited-state energy dissipation via the covalent and hydrogen bonds with the protein environment. The observed large dispersion of quenching timescales observed in the protein samples that contain the native pigment favors both an inhomogeneous model and an excited-state barrier for isomerization.
For the antioxidant effect of lipoic acid, reduction to dihydrolipoic acid is considered to be im... more For the antioxidant effect of lipoic acid, reduction to dihydrolipoic acid is considered to be important. Dihydrolipoamide dehydrogenase (LipHD) preferentially reduces R-lipoic acid and in a subsequent reaction, the R-dihydrolipoic acid formed may non-enzymatically reduce S-lipoic acid. Using circular dichroism (CD) spectroscopy, the second order rate constant of the latter reaction was determined (k 2 = 15 M −1 sec −1). In vitro, it was found that S-lipoic acid is reduced by LipDH using R-lipoic acid as a catalyst. The non-enzymatic dithiol-disulfide reaction leads to synergistic reduction of the enan-tiomers which can explain the higher antioxidant activity of racemic lipoic acid found in vivo (Maitra et al. Biochem. Biophys. Res. Commun. 221:422–429, 1996) in comparison to the enantiomers. Lipoic acid is therapeutically active in several diseases via antioxi-dant activity. These findings suggest that racemic lipoic acid can be therapeutically more active than the separate enantiomers. Chirality 9:362–366, 1997.
Chirality, Jan 1, 1997
For the antioxidant effect of lipoic acid, reduction to dihydrolipoic acid is considered to be im... more For the antioxidant effect of lipoic acid, reduction to dihydrolipoic acid is considered to be important. Dihydrolipoamide dehydrogenase (LipHD) preferentially reduces R-lipoic acid and in a subsequent reaction, the R-dihydrolipoic acid formed may non-enzymatically reduce S-lipoic acid. Using circular dichroism (CD) spectroscopy, the second order rate constant of the latter reaction was determined (k 2 = 15 M −1 sec −1 ). In vitro, it was found that S-lipoic acid is reduced by LipDH using R-lipoic acid as a catalyst. The non-enzymatic dithiol-disulfide reaction leads to synergistic reduction of the enantiomers which can explain the higher antioxidant activity of racemic lipoic acid found in vivo (Maitra et al. Biochem. Biophys. Res. Commun. 221:422-429, 1996) in comparison to the enantiomers. Lipoic acid is therapeutically active in several diseases via antioxidant activity. These findings suggest that racemic lipoic acid can be therapeutically more active than the separate enantiomers. Chirality 9: 362-366, 1997.
2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC, 2013
ABSTRACT In this work we studied an artificial supramolecule composed of a carotenoids (Car) with... more ABSTRACT In this work we studied an artificial supramolecule composed of a carotenoids (Car) with 10 conjugated double bonds linked to a phthalocyanine (Pc), mimicking the light harvesting unity. We follow the selective excitation of Car, monitoring the ultrafast rise of the Pc population. The Car→Pc ET process occurs from the bright Car S2 excited state and competes with an internal conversion (IC) process towards the lower-lying dark Car S1 excited state. To establish the relative weight of these two deactivation pathways, we performed pump-probe experiments with sub-20-fs temporal resolution on the isolated Car and on the dyad and compared the excited state dynamics. In addition, following selective excitation of the Pc, we have identified the spectral signatures of the S1 excited state of the Car which appear within the ≈50-fs time resolution of our measurement. This strongly indicates excited state coupling between the S1 state of Car and the S1 state of Pc, with important implications for the regulation of photosynthetic activity.
Analytical Biochemistry, 1990
Proceedings of The National Academy of Sciences, 2004
Photosynthesis relies on the delicate interplay between a specific set of membrane-bound pigment-... more Photosynthesis relies on the delicate interplay between a specific set of membrane-bound pigment-protein complexes that harvest and transport solar energy, execute charge separation, and conserve the energy. We have investigated the organization of the light-harvesting (LH) and reaction-center (RC) complexes in native bacterial photosynthetic membranes of the purple bacterium Rhodobacter sphaeroides by using polarized light spectroscopy, linear dichroism (LD) on oriented membranes. These LD measurements show that in native membranes, which contain LH2 as the major energy absorber, the RC-LH1-PufX complexes are highly organized in a way similar to that which we found previously for a mutant lacking LH2. The relative contribution of LH1 and LH2 light-harvesting complexes to the LD spectrum shows that LH2 preferentially resides in highly curved parts of the membrane. Combining the spectroscopic data with our recent atomic force microscopy (AFM) results, we propose an organization for this photosynthetic membrane that features domains containing linear arrays of RC-LH1-PufX complexes interspersed with LH2 complexes and some LH2 found in separate domains. The study described here allows the simultaneous assessment of both global and local structural information on the organization of intact, untreated membranes. membrane organization ͉ photosynthesis ͉ polarized spectroscopy This paper was submitted directly (Track II) to the PNAS office.
The Journal of Physical Chemistry B, 2013
Bacteriochlorophyll a with Ni 2+ replacing the central Mg 2+ ion was used as an ultrafast excitat... more Bacteriochlorophyll a with Ni 2+ replacing the central Mg 2+ ion was used as an ultrafast excitation energy dissipation center in reconstituted bacterial LH1 complexes. B870, a carotenoid-less LH1 complex, and B880, an LH1 complex containing spheroidene, were obtained via reconstitution from the subunits isolated from chromatophores of Rhodospirillum rubrum. Ni-substituted bacteriochlorophyll a added to the reconstitution mixture partially substituted the native pigment in both forms of LH1. The excited-state dynamics of the reconstituted LH1 complexes were probed by femtosecond pump−probe transient absorption spectroscopy in the visible and near-infrared spectral region. Spheroidene-binding B880 containing no excitation dissipation centers displayed complex dynamics in the time range of 0.1−10 ps, reflecting internal conversion and intersystem crossing in the carotenoid, exciton relaxation in BChl complement, and energy transfer from carotenoid to the latter. In B870, some aggregation-induced excitation energy quenching was present. The binding of Ni-BChl a to both B870 and B880 resulted in strong quenching of the excited states with main deexcitation lifetime of ca. 2 ps. The LH1 excited-state lifetime could be modeled with an intrinsic decay time constant in Ni-substituted bacteriochlorophyll a of 160 fs. The presence of carotenoid in LH1 did not influence the kinetics of energy trapping by Ni-BChl unless the carotenoid was directly excited, in which case the kinetics was limited by a slower carotenoid S 1 to bacteriochlorophyll energy transfer.
Photochemistry and Photobiology, 1993
The present study describes the construction of a Rhodobacter sphaeroides light-harvesting (LH2) ... more The present study describes the construction of a Rhodobacter sphaeroides light-harvesting (LH2) mutant in which the charged residue BLys23 is changed by site-directed mutagenesis to a Gln residue, and the characterization of the resulting mutant complex by a range of spectroscopic techniques. In the 77 K absorption spectrum of the mutant, the peak equivalent to the 850 nm peak in the wild-type membrane is blue-shifted by approximately 18 nm to 837 nm; except for this blue-shift, the 77 K fluorescence excitation and emission spectra and the circular dichroism spectrum of the mutant are very similar to the equivalent spectra from the witd-type membranes, suggesting that the mutation pLys23 -Gln probably does not cause any major changes in the conformation or aggregation state of these membranes. Possible causes of the 18 nm blue-shift in the absorption spectrum are discussed.
The Journal of Physical Chemistry B, 2008
The membrane-intrinsic light harvesting complex from the diatom Cyclotella meneghiniana, fucoxant... more The membrane-intrinsic light harvesting complex from the diatom Cyclotella meneghiniana, fucoxanthin chlorophyll-a/c 2 protein (FCP), is characterized by Stark spectroscopy to obtain a quantitative measure of the excited-state dipolar properties of the constituent pigments. The electrooptical properties of the carotenoid fucoxanthin (Fx), the primary light harvester in FCP, were determined from the Stark spectrum measured in a MeTHF glass (77 K) and compared to the results from electronic-structure calculations. On photon absorption by Fx, a 17 D change in the static dipole moment (|Δμ ⃗ | exp ), and a somewhat larger |Δμ ⃗ | exp at the red edge, are measured for the S 0 → S 2 transition. The significant change in dipolar properties demonstrates that Fx undergoes photoinduced charge transfer (CT), and underscores the influence of the S 2 state on the polarity-dependent excited-state dynamics of Fx that has so far been attributed to, and discussed in terms of, the S 0 and the S 1 /ICT states. MNDO-PSDCI and SACCI-CISD calculations indicate that the -like state intrinsically possesses a dipole moment much smaller than the -like state, suggesting that solvent fields promote the mixing of these two states and accounts for the large dipole moments measured here for the S 0 → S 2 transition. These CT properties of the -like state of Fx, which are further enhanced in the protein, underpin its photosynthetic capabilities for light harvesting and energy transfer (ET). In FCP, the CT properties of the Fx's vary according to the energetic position: between 450 and 500 nm there appear to be two sets of Fx's that exhibit |Δμ ⃗ | exp values on the order of 5 and 15 D, whereas the red-most Fx's, that are very efficient in ET to chlorophyll-a (Chl-a), exhibit strikingly large |Δμ ⃗ | exp values on the order of 40 D. Such magnitudes of |ΔΔμ ⃗ | exp suggest a mechanism to enhance Coulombic coupling to promote ET from the S 2 state
Nature, Jan 27, 1992
Light energy for photosynthesis is collected by the antenna system, creating an excited state whi... more Light energy for photosynthesis is collected by the antenna system, creating an excited state which migrates energetically 'downhill'. To achieve efficient migration of energy the antenna is populated with a series of pigments absorbing at progressively redshifted wavelengths. This variety in absorbing species in vivo has been created in a biosynthetically economical fashion by modulating the absorbance behaviour of one kind of (bacterio)chlorophyll molecule. This modulation is poorly understood but has been ascribed to pigment-pigment and pigment-protein interactions. We have examined the relationship between aromatic residues in antenna polypeptides and pigment absorption, by studying the effects of site-directed mutagenesis on a bacterial antenna complex. A clear correlation was observed between the absorbance of bacteriochlorophyll a and the presence of two tyrosine residues, alpha Tyr44 and alpha Tyr45, in the alpha subunit of the peripheral light-harvesting complex of ...
Biochemistry, 1998
In this paper, we report the circular dichroism (CD) spectra of two types of LH2 -only mutants of... more In this paper, we report the circular dichroism (CD) spectra of two types of LH2 -only mutants of Rhodobacter sphaeroides. In the first, only the wild type LH2 is present, while in the second, the B800 binding site of LH2 has been either destabilized or removed. For the first time, we have identified a band in the CD spectrum of LH2, located at ∼780 nm, that can be ascribed to the high exciton component of the B850 band. The experimental spectra have been modeled by theoretical calculations. On this basis, the average interaction strength between monomers in the B850 ring can be estimated to be approximately 300 cm -1 . In addition, we suggest that in LH2 of Rb. sphaeroides the angles made by the Q y transitions of the B850 BChls with respect to the plane of the ring are slightly different from those calculated from the crystal structure of the Rhodopseudomonas acidophila LH2 complex.
Chemical Physics Letters, 1993
Absorption and fluorescence excitation spectra of various LH2 antenna complexes of two purple bac... more Absorption and fluorescence excitation spectra of various LH2 antenna complexes of two purple bacteria at low temperature ( 1.2 and 4.2 K) have been measured, and energy transfer rates within these complexes have been determined by spectra holeburning. The systems studied were membranes of a wild-type strain of Rhodobacter sphaeroides, membrane samples from four LHZ-only strains containing specifically mutated LH2 complexes of the same bacterium, and the isolated BSOO-820 complex of Rhodopseudomonas acidophila (strain 7050). The mutants exhibit blue-shifted B850 absorption bands with their spectral positions depending on the specific amino acid residues replaced in the a-polypeptide sequence. Energy transfer rates from BSOO to B850 (or to their respectively blue-shifted bands) have been obtained by hole-burning experiments in the B800 band. The mutants of Rb. sphaeroides and the LH2 complex of Rps. acidophila yielded transfer times similar to those of the B800-850 complex of Rb. sphaeroufes. These values, which for the various complexes vary between 1.7 and 2.5 ps in the wavelength region from 798 to 805 nm, do not decrease monotonically with the spectral distance between the bands. Various models based on Forster's energy transfer mechanism are discussed, of which only one is consistent with the results. In this model the energy is assumed to be transferred not directly from the Q, O-O band of B800 to that of the (blue-shifted) B850, but indirectly through the excitation of a vibrational mode.
Chemical Physics Letters, 2002
The absorption and stimulated emission changes in the first 535 ps of the PYP photocycle can be d... more The absorption and stimulated emission changes in the first 535 ps of the PYP photocycle can be described by four life times of 0.7, 6.3, and 220 ps and long lived. Two intermediates, I 0 and I z 0 , were identified. We did not obtain indications for a significant excitation wavelength dependent primary photochemistry as found in low temperature absorption spectroscopy. The anisotropy of the primary photoproduct I 0 and its successor I z 0 amounts to 0.3 -significantly lower than that of the bleached ground state (0.4). This distinctive change of the transition dipole moment orientation in the product state (24°) reflects changes of the chromophore geometry and electron density distribution caused by the photoisomerisation. Ó
Chemical Physics Letters, 1997
... reaction, in which the excited RC first gives rise to the charge separated state PB,~HA which... more ... reaction, in which the excited RC first gives rise to the charge separated state PB,~HA which in turn develops to the state P+BAHA. ... The detection of the fluorescence light was with a cooled S1 photo-multiplier tube (Thorn EMI 9206B) using the single photon counting technique. ...
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Papers by Rienk Van Grondelle