Chlorosomes of green photosynthetic bacteria are large light-harvesting complexes enabling these organisms to survive at extremely low-light conditions. Bacteriochlorophylls found in chlorosomes self-organize and are ideal candidates for use in biomimetic light-harvesting in artificial photosynthesis and other applications for solar energy utilization. Here we report on the construction and characterization of an artificial antenna consisting of bacteriochlorophyll c co-aggregated with β-carotene, which is used to extend the light-harvesting spectral range, and bacteriochlorophyll a, which acts as a final acceptor for excitation energy. Efficient energy transfer between all three components was observed by means of fluorescence spectroscopy. The efficiency varies with the β-carotene content, which increases the average distance between the donor and acceptor in both energy transfer steps. The efficiency ranges from 89 to 37% for the transfer from β-carotene to bacteriochlorophyll c, and from 93 to 69% for the bacteriochlorophyll c to bacteriochlorophyll a step. A significant part of this study was dedicated to a development of methods for determination of energy transfer efficiency. These methods may be applied also for study of chlorosomes and other pigment complexes.

• Klíčová slova
• Artificial light-harvesting antenna, Bacteriochlorophyll aggregates, Chlorosomes, Efficiency of excitation energy transfer, Fluorescence spectroscopy,
• MeSH
• bakteriální proteiny metabolismus   MeSH
• bakteriochlorofyl A * chemie   MeSH
• bakteriochlorofyly * chemie   MeSH
• beta-karoten MeSH
• fotosyntéza MeSH
• přenos energie MeSH
• světlosběrné proteinové komplexy chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriochlorofyl A * MeSH
• bakteriochlorofyly * MeSH
• beta-karoten MeSH
• světlosběrné proteinové komplexy MeSH

The sensitized phosphorescence of Tb3+ is often used for the assessment of the ion binding to various chelating agents or natural Ca2+-binding proteins. The detailed structure of the Tb3+ excitation spectrum gives a special advantage for analysis; any extra absorption peak can be easily detected which provides simple and direct evidence that resonance energy transfer occurs. By employing the Tb3+ phosphorescence, we characterized the Ca2+-binding sites of two related peptides - self-processing module of the FrpC protein produced by bacterium Neisseria meningitidis and the shorter peptide derived from FrpC. Here we show that while the increase of direct Tb3+ excitation at 243 nm generally corresponds to Tb3+ association with various binding sites, the excitation enhancement in the 250-300 nm band signifies Tb3+-binding in the close proximity of aromatic residues. We demonstrate that the presence of resonance energy transfer could be easily detected by inspecting Tb3+ excitation spectra. Additionally, we show that the high level of specificity of Tb3+ steady state detection on the spectral level could be reached at very low Tb3+ concentrations by taking advantage of its narrow phosphorescence emission maximum at 545 nm and subtracting the averaged autofluorescence intensities outside this peak, namely at 525 and 565 nm.

• Klíčová slova
• Calcium-binding site, Energy transfer, Excitation Spectrum, Protein fluorescence, Terbium phosphorescence, Tryptophan,
• Publikační typ
• časopisecké články MeSH

The structure of phycobiliproteins of the cyanobacterium Acaryochloris marina was investigated in buffer solution at physiological temperatures, i.e. under the same conditions applied in spectroscopic experiments, using small angle neutron scattering. The scattering data of intact phycobiliproteins in buffer solution containing phosphate can be well described using a cylindrical shape with a length of about 225Å and a diameter of approximately 100Å. This finding is qualitatively consistent with earlier electron microscopy studies reporting a rod-like shape of the phycobiliproteins with a length of about 250 (M. Chen et al., FEBS Letters 583, 2009, 2535) or 300Å (J. Marquart et al., FEBS Letters 410, 1997, 428). In contrast, phycobiliproteins dissolved in buffer lacking phosphate revealed a splitting of the rods into cylindrical subunits with a height of 28Å only, but also a pronounced sample aggregation. Complementary small angle neutron and X-ray scattering experiments on phycocyanin suggest that the cylindrical subunits may represent either trimeric phycocyanin or trimeric allophycocyanin. Our findings are in agreement with the assumption that a phycobiliprotein rod with a total height of about 225Å can accommodate seven trimeric phycocyanin subunits and one trimeric allophycocyanin subunit, each of which having a height of about 28Å. The structural information obtained by small angle neutron and X-ray scattering can be used to interpret variations in the low-energy region of the 4.5K absorption spectra of phycobiliproteins dissolved in buffer solutions containing and lacking phosphate, respectively.

• Klíčová slova
• Acaryochloris marina, Excitation energy transfer, Phycobiliproteins, Small angle X-ray scattering, Small angle neutron scattering,
• MeSH
• difrakce rentgenového záření MeSH
• fykobiliproteiny chemie   MeSH
• maloúhlový rozptyl * MeSH
• neutronová difrakce MeSH
• přenos energie * MeSH
• sinice chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fykobiliproteiny MeSH

We formulate a classical pure dephasing system-bath interaction model in a full correspondence to the well-studied quantum model of natural light-harvesting antennae. The equations of motion of our classical model not only represent the correct classical analogy to the quantum description of excitonic systems, but they also have exactly the same functional form. We demonstrate derivation of classical dissipation and relaxation tensor in second order perturbation theory. We find that the only difference between the classical and quantum descriptions is in the interpretation of the state and in certain limitations imposed on the parameters of the model by classical physics. The effects of delocalization, transfer pathway interference, and the transition from coherent to diffusive transfer can be found already in the classical realm. The only qualitatively new effect occurring in quantum systems is the preference for a downhill energy transfer and the resulting possibility of trapping the energy in the lowest energy state.

• MeSH
• fotosyntéza * MeSH
• kvantová teorie MeSH
• přenos energie MeSH
• světlosběrné proteinové komplexy chemie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• světlosběrné proteinové komplexy MeSH

Carotenoids are crucial for photosynthesis, playing key roles in light harvesting and photoprotection. In this study, spheroidene and bacteriochlorophyll a (Bchl a) were reconstituted into the chromatophores of the carotenoidless mutant Rhodobacter sphaeroides R26.1, resulting in the preparation of high-quality LH2 complexes. Global and target analyses of transient absorption data revealed that incorporating B800 Bchl a significantly enhances excitation energy transfer (EET) efficiency from carotenoids to Bchl a. EET predominantly occurs from the carotenoid S2 state, with additional pathways from the S1 state observed in native LH2. Unique relaxation dynamics were identified, including the generation of the carotenoid S* state in reconstituted LH2 with both spheroidene and B800 Bchl a and the formation of the carotenoid T1 state in reconstituted LH2. These findings underscore the critical influence of pigment composition and spatial organization on energy transfer mechanisms. They provide valuable insights into the molecular interplay that governs excitation energy transfer in photosynthetic light-harvesting systems.

• Klíčová slova
• B800 bacteriochlorophyll a, carotenoid, light-harvesting, photoprotection, purple photosynthetic bacteria, reconstitution,
• MeSH
• bakteriální proteiny metabolismus   genetika   chemie   MeSH
• bakteriochlorofyl A * metabolismus   chemie   MeSH
• fotosyntéza MeSH
• karotenoidy * metabolismus   chemie   MeSH
• přenos energie * MeSH
• Rhodobacter sphaeroides * metabolismus   genetika   MeSH
• světlosběrné proteinové komplexy * metabolismus   chemie   genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriochlorofyl A * MeSH
• karotenoidy * MeSH
• světlosběrné proteinové komplexy * MeSH

The peripheral light-harvesting antenna complex (LH2) of purple photosynthetic bacteria is an ideal testing ground for models of structure-function relationships due to its well-determined molecular structure and ultrafast energy deactivation. It has been the target for numerous studies in both theory and ultrafast spectroscopy; nevertheless, certain aspects of the convoluted relaxation network of LH2 lack a satisfactory explanation by conventional theories. For example, the initial carotenoid-to-bacteriochlorophyll energy transfer step necessary on visible light excitation was long considered to follow the Förster mechanism, even though transfer times as short as 40 femtoseconds (fs) have been observed. Such transfer times are hard to accommodate by Förster theory, as the moderate coupling strengths found in LH2 suggest much slower transfer within this framework. In this study, we investigate LH2 from Phaeospirillum (Ph.) molischianum in two types of transient absorption experiments-with narrowband pump and white-light probe resulting in 100 fs time resolution, and with degenerate broadband 10 fs pump and probe pulses. With regard to the split Qx band in this system, we show that vibronically mediated transfer explains both the ultrafast carotenoid-to-B850 transfer, and the almost complete lack of transfer to B800. These results are beyond Förster theory, which predicts an almost equal partition between the two channels.

• Klíčová slova
• Excitation energy transfer, Excitons, LH2, Photosynthesis, Ultrafast spectroscopy,
• MeSH
• bakteriochlorofyly metabolismus   MeSH
• časové faktory MeSH
• Fourierova analýza MeSH
• karotenoidy metabolismus   MeSH
• lasery MeSH
• přenos energie * MeSH
• Proteobacteria metabolismus   MeSH
• spektrofotometrie ultrafialová MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• bakteriochlorofyly MeSH
• karotenoidy MeSH
• světlosběrné proteinové komplexy MeSH

Photosynthetic organisms had to evolve diverse mechanisms of light-harvesting to supply photosynthetic apparatus with enough energy. Cryptophytes represent one of the groups of photosynthetic organisms combining external and internal antenna systems. They contain one type of immobile phycobiliprotein located at the lumenal side of the thylakoid membrane, together with membrane-bound chlorophyll a/c antenna (CAC). Here we employ femtosecond transient absorption spectroscopy to study energy transfer pathways in the CAC proteins of cryptophyte Rhodomonas salina. The major CAC carotenoid, alloxanthin, is a cryptophyte-specific carotenoid, and it is the only naturally-occurring carotenoid with two triple bonds in its structure. In order to explore the energy transfer pathways within the CAC complex, three excitation wavelengths (505, 590, and 640 nm) were chosen to excite pigments in the CAC antenna. The excitation of Chl c at either 590 or 640 nm proves efficient energy transfer between Chl c and Chl a. The excitation of alloxanthin at 505 nm shows an active pathway from the S2 state with efficiency around 50%, feeding both Chl a and Chl c with approximately 1:1 branching ratio, yet, the S1-route is rather inefficient. The 57 ps energy transfer time to Chl a gives ~25% efficiency of the S1 channel. The low efficiency of the S1 route renders the overall carotenoid-Chl energy transfer efficiency low, pointing to the regulatory role of alloxanthin in the CAC antenna.

• Klíčová slova
• Carotenoids, Cryptophyte, Energy transfer, Light harvesting, Photosynthesis, Ultrafast spectroscopy,
• MeSH
• chlorofyl metabolismus   MeSH
• Cryptophyta fyziologie   MeSH
• fykobiliproteiny metabolismus   MeSH
• přenos energie * MeSH
• xanthofyly metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• alloxanthin MeSH Prohlížeč
• chlorofyl MeSH
• fykobiliproteiny MeSH
• xanthofyly MeSH

Fluorescence resonance energy transfer (FRET) in combination with quantum dots (QDs) and their superior properties has enabled designing of the new and improved sensors. In this review, the latest novelties in development and application of FRET nanosensors employing QDs are presented. QDs offer several advantages over organic dyes - broad excitation spectra, narrow defined tunable emission peak, longer fluorescence lifetime, resistance to photobleaching and 10-100 times higher molar extinction coefficient. These properties of QDs allow multicolor QDs to be excited from one source by common fluorescent dyes without emission signal overlap and results in brighter probes comparing to conventional fluorophores. Due to these benefits, QD-FRET-based nanosensors gained a wide spread popularity in a variety of scientific areas. These sensors are most frequently applied in the domain of the nucleic acid and enzyme activity detection. Other applications are detection of peptides and low-molecular compounds, environmental pollutants, viruses, microorganisms and their toxins, QD-FRET-based immunoassays, and pH sensors.

• Klíčová slova
• Enzyme, Fluorescence resonance energy transfer, Nucleic acid, Quantum dots, Sensor,
• MeSH
• analýza selhání vybavení MeSH
• biosenzitivní techniky přístrojové vybavení   MeSH
• biotest přístrojové vybavení   MeSH
• design vybavení MeSH
• kvantové tečky * MeSH
• nanotechnologie přístrojové vybavení   MeSH
• rezonanční přenos fluorescenční energie přístrojové vybavení   MeSH
• sekvenční analýza DNA přístrojové vybavení   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH

Higher plants defend themselves from bursts of intense light via the mechanism of Non-Photochemical Quenching (NPQ). It involves the Photosystem II (PSII) antenna protein (LHCII) adopting a conformation that favors excitation quenching. In recent years several structural models have suggested that quenching proceeds via energy transfer to the optically forbidden and short-lived S 1 states of a carotenoid. It was proposed that this pathway was controlled by subtle changes in the relative orientation of a small number of pigments. However, quantum chemical calculations of S 1 properties are not trivial and therefore its energy, oscillator strength and lifetime are treated as rather loose parameters. Moreover, the models were based either on a single LHCII crystal structure or Molecular Dynamics (MD) trajectories about a single minimum. Here we try and address these limitations by parameterizing the vibronic structure and relaxation dynamics of lutein in terms of observable quantities, namely its linear absorption (LA), transient absorption (TA) and two-photon excitation (TPE) spectra. We also analyze a number of minima taken from an exhaustive meta-dynamical search of the LHCII free energy surface. We show that trivial, Coulomb-mediated energy transfer to S 1 is an unlikely quenching mechanism, with pigment movements insufficiently pronounced to switch the system between quenched and unquenched states. Modulation of S 1 energy level as a quenching switch is similarly unlikely. Moreover, the quenching predicted by previous models is possibly an artifact of quantum chemical over-estimation of S 1 oscillator strength and the real mechanism likely involves short-range interaction and/or non-trivial inter-molecular states.

• Klíčová slova
• LHCII, carotenoid, energy-dissipation, non-photochemical quenching (NPQ), photosystem (PSII), transient absorption,
• Publikační typ
• časopisecké články MeSH

The excitation energy transfer (EET) from the bacteriochlorophyll (BChl) Soret band to the second excited state(s) (S2) of carotenoids in pigment-protein complexes of purple bacteria was investigated. The efficiency of EET was determined, based on fluorescence excitation and absorption spectra of chromatophores, peripheral light-harvesting complexes (LH2), core complexes (LH1-RC), and pigments in solution. Carotenoid-containing and carotenoid-less samples were compared: LH1-RC and LH2 from Allochromatium minutissimum, Ectothiorhodospira haloalkaliphila, and chromatophores from Rhodobacter sphaeroides and Rhodospirillum rubrum wild type and carotenoid-free strains R-26 and G9. BChl-to-carotenoid EET was absent, or its efficiency was less than the accuracy of the measurements of ∼5%. Quantum chemical calculations support the experimental results: The transition dipole moments of spatially close carotenoid/BChl pairs were found to be nearly orthogonal. The structural arrangements suggest that Soret EET may be lacking for the studied systems, however, EET from carotenoids to Qx appears to be possible.

• MeSH
• bakteriochlorofyly MeSH
• Chromatiaceae MeSH
• Ectothiorhodospira MeSH
• fluorescenční spektrometrie MeSH
• fotosyntetické reakční centrum - proteinové komplexy * metabolismus   MeSH
• karotenoidy MeSH
• přenos energie MeSH
• Proteobacteria metabolismus   MeSH
• Rhodobacter sphaeroides * metabolismus   MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriochlorofyly MeSH
• fotosyntetické reakční centrum - proteinové komplexy * MeSH
• karotenoidy MeSH
• světlosběrné proteinové komplexy MeSH