| 1. |
- Wadsten, Pia, 1969, et al.
(författare)
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Lipidic sponge phase crystallization of membrane proteins.
- 2006
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Ingår i: Journal of molecular biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 364:1, s. 44-53
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Tidskriftsartikel (refereegranskat)abstract
- Bicontinuous lipidic cubic phases can be used as a host for growing crystals of membrane proteins. Since the cubic phase is stiff, handling is difficult and time-consuming. Moreover, the conventional cubic phase may interfere with the hydrophilic domains of membrane proteins due to the limited size of the aqueous pores. Here, we introduce a new crystallization method that makes use of a liquid analogue of the cubic phase, the sponge phase. This phase facilitates a considerable increase in the allowed size of aqueous domains of membrane proteins, and is easily generalised to a conventional vapour diffusion crystallisation experiment, including the use of nanoliter drop crystallization robots. The appearance of the sponge phase was confirmed by visual inspection, small-angle X-ray scattering and NMR spectroscopy. Crystals of the reaction centre from Rhodobacter sphaeroides were obtained by a conventional hanging-drop experiment, were harvested directly without the addition of lipase or cryoprotectant, and the structure was refined to 2.2 Angstroms resolution. In contrast to our earlier lipidic cubic phase reaction centre structure, the mobile ubiquinone could be built and refined. The practical advantages of the sponge phase make it a potent tool for crystallization of membrane proteins.
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| 2. |
- Wöhri, Annemarie, 1976, et al.
(författare)
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A Lipidic-Sponge Phase Screen for Membrane Protein Crystallization
- 2008
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Ingår i: Structure. - : Elsevier BV. - 0969-2126 .- 1878-4186. ; 16:7, s. 1003-1009
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Tidskriftsartikel (refereegranskat)abstract
- A major current deficit in structural biology is the lack of high-resolution structures of eukaryotic membrane proteins, many of which are key drug targets for the treatment of disease. Numerous eukaryotic membrane proteins require specific lipids for their stability and activity, and efforts to crystallize and solve the structures of membrane proteins that do not address the issue of lipids frequently end in failure rather than success. To help address this problem, we have developed a sparse matrix crystallization screen consisting of 48 lipidic-sponge phase conditions. Sponge phases form liquid lipid bilayer environments which are suitable for conventional hanging- and sitting-drop crystallization experiments. Using the sponge phase screen, we obtained crystals of several different membrane proteins from bacterial and eukaryotic sources. We also demonstrate how the screen may be manipulated by incorporating specific lipids such as cholesterol; this modification led to crystals being recovered from a bacterial photosynthetic core complex.
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| 3. |
- Camacho Dejay, Rafael, et al.
(författare)
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Fluorescence polarization measures energy funneling in single light-harvesting antennas-LH2 vs conjugated polymers.
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Numerous approaches have been proposed to mimic natural photosynthesis using artificial antenna systems, such as conjugated polymers (CPs), dendrimers, and J-aggregates. As a result, there is a need to characterize and compare the excitation energy transfer (EET) properties of various natural and artificial antennas. Here we experimentally show that EET in single antennas can be characterized by 2D polarization imaging using the single funnel approximation. This methodology addresses the ability of an individual antenna to transfer its absorbed energy towards a single pool of emissive states, using a single parameter called energy funneling efficiency (ε). We studied individual peripheral antennas of purple bacteria (LH2) and single CP chains of 20 nm length. As expected from a perfect antenna, LH2s showed funneling efficiencies close to unity. In contrast, CPs showed lower average funneling efficiencies, greatly varying from molecule to molecule. Cyclodextrin insulation of the conjugated backbone improves EET, increasing the fraction of CPs possessing ε = 1. Comparison between LH2s and CPs shows the importance of the protection systems and the protein scaffold of LH2, which keep the chromophores in functional form and at such geometrical arrangement that ensures excellent EET.
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| 4. |
- Herek, Jennifer, et al.
(författare)
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Quantum control of energy flow in light harvesting.
- 2002
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 417:6888, s. 533-535
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Tidskriftsartikel (refereegranskat)abstract
- Coherent light sources have been widely used in control schemes that exploit quantum interference effects to direct the outcome of photochemical processes. The adaptive shaping of laser pulses is a particularly powerful tool in this context: experimental output as feedback in an iterative learning loop refines the applied laser field to render it best suited to constraints set by the experimenter. This approach has been experimentally implemented to control a variety of processes, but the extent to which coherent excitation can also be used to direct the dynamics of complex molecular systems in a condensed-phase environment remains unclear. Here we report feedback-optimized coherent control over the energy-flow pathways in the light-harvesting antenna complex LH2 from Rhodopseudomonas acidophila, a photosynthetic purple bacterium. We show that phases imprinted by the light field mediate the branching ratio of energy transfer between intra- and intermolecular channels in the complex's donor acceptor system. This result illustrates that molecular complexity need not prevent coherent control, which can thus be extended to probe and affect biological functions.
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| 5. |
- Karki, Khadga Jung, et al.
(författare)
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Before Förster. Initial excitation in photosynthetic light harvesting.
- 2019
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Ingår i: Chemical Science. - 2041-6539. ; 10, s. 7923-7928
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Tidskriftsartikel (refereegranskat)abstract
- Electronic 2D spectroscopy allows nontrivial quantum effects to be explored in unprecedented detail. Here, we apply recently developed fluorescence detected coherent 2D spectroscopy to study the light harvesting antenna 2 (LH2) of photosynthetic purple bacteria. We report double quantum coherence 2D spectra which show clear cross peaks indicating correlated excitations. Similar results are found for rephasing and nonrephasing signals. Analysis of signal generating quantum pathways leads to the conclusion that, contrary to the currently prevailing physical picture, the two weakly coupled pigment rings of LH2 share the initial electronic excitation leading to quantum mechanical correlation between the two clearly separate absorption bands. These results are general and have consequences for the interpretation of initially created excited states not only in photosynthesis but in all light absorbing systems composed of weakly interacting pigments where the excitation transfer is commonly described by using Förster theory. Being able to spectrally resolve the nonequilibrium dynamics immediately following photoabsorption may provide a glimpse to the systems' transition into the Förster regime.
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| 6. |
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| 7. |
- Macpherson, Alisdair N, et al.
(författare)
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Efficient Energy Transfer from the Carotenoid S2 State in a Photosynthetic Light-Harvesting Complex
- 2001
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Ingår i: Biophysical Journal. ; 80:2, s. 923-30
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Tidskriftsartikel (refereegranskat)abstract
- Previously, the spatial arrangement of the carotenoid and bacteriochlorophyll molecules in the peripheral light-harvesting (LH2) complex from Rhodopseudomonas acidophila strain 10050 has been determined at high resolution. Here, we have time resolved the energy transfer steps that occur between the carotenoid's initial excited state and the lowest energy group of bacteriochlorophyll molecules in LH2. These kinetic data, together with the existing structural information, lay the foundation for understanding the detailed mechanisms of energy transfer involved in this fundamental, early reaction in photosynthesis. Remarkably, energy transfer from the rhodopin glucoside S2 state, which has an intrinsic lifetime of ~120 fs, is by far the dominant pathway, with only a minor contribution from the longer-lived S1 state.
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| 8. |
- Schröter, Marco, et al.
(författare)
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Origin of the Two Bands in the B800 Ring and Their Involvement in the Energy Transfer Network of Allochromatium vinosum
- 2018
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:6, s. 1340-1345
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial photosynthesis features robust and adaptable energy-harvesting processes in which light-harvesting proteins play a crucial role. The peripheral light-harvesting complex of the purple bacterium Allochromatium vinosum is particularly distinct, featuring a double peak structure in its B800 absorption band. Two hypotheses - not necessarily mutually exclusive - concerning the origin of this splitting have been proposed; either two distinct B800 bacteriochlorophyll site energies are involved, or an excitonic dimerization of bacteriochlorophylls within the B800 ring takes place. Through the use of two-dimensional electronic spectroscopy, we present unambiguous evidence that excitonic interaction shapes the split band. We further identify and characterize all of the energy transfer pathways within this complex by using a global kinetic fitting procedure. Our approach demonstrates how the combination of two-dimensional spectral resolution and self-consistent fitting allows for extraction of information on light-harvesting processes, which would otherwise be inaccessible due to signal congestion.
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| 9. |
- Thyrhaug, Erling, et al.
(författare)
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Intraband dynamics and exciton trapping in the LH2 complex of Rhodopseudomonas acidophila
- 2021
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:4
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Tidskriftsartikel (refereegranskat)abstract
- Over the last several decades, the light-harvesting protein complexes of purple bacteria have been among the most popular model systems for energy transport in excitonic systems in the weak and intermediate intermolecular coupling regime. Despite this extensive body of scientific work, significant questions regarding the excitonic states and the photo-induced dynamics remain. Here, we address the low-temperature electronic structure and excitation dynamics in the light-harvesting complex 2 of Rhodopseudomonas acidophila by two-dimensional electronic spectroscopy. We find that, although at cryogenic temperature energy relaxation is very rapid, exciton mobility is limited over a significant range of excitation energies. This points to the presence of a sub-200 fs, spatially local energy-relaxation mechanism and suggests that local trapping might contribute substantially more in cryogenic experiments than under physiological conditions where the thermal energy is comparable to or larger than the static disorder.
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| 10. |
- Tubasum, Sumera, et al.
(författare)
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Evidence of excited state localization and static disorder in LH2 investigated by 2D-polarization single-molecule imaging at room temperature.
- 2013
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:45, s. 19862-19869
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional polarization fluorescence imaging of single light harvesting complexes 2 (LH2) of Rps. acidophila was carried out to investigate the polarization properties of excitation and fluorescence emission simultaneously, at room temperature. In two separate experiments we excited LH2 with a spectrally narrow laser line matched to the absorption bands of the two chromophore rings, B800 and B850, thereby indirectly and directly triggering fluorescence of the B850 exciton state. A correlation analysis of the polarization modulation depths in excitation and emission for a large number of single complexes was performed. Our results show, in comparison to B800, that the B850 ring is a more isotropic absorber due to the excitonic nature of its excited states. At the same time, we observed a strong tendency for LH2 to emit with dipolar character, from which preferential localization of the emissive exciton, stable for minutes, is inferred. We argue that the observed effects can consistently be explained by static energetic disorder and/or deformation of the complex, with possible involvement of exciton self-trapping.
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