A quenching mechanism mediated by the orange carotenoid protein (OCP) is one of the ways cyanobacteria protect themselves against photooxidative stress. Here, we present a femtosecond spectroscopic study comparing OCP and RCP (red carotenoid protein) samples binding different carotenoids. We confirmed significant changes in carotenoid configuration upon OCP activation reported by Leverenz et al. (Science 348:1463-1466. doi: 10.1126/science.aaa7234 , 2015) by comparing the transient spectra of OCP and RCP. The most important marker of these changes was the magnitude of the transient signal associated with the carotenoid intramolecular charge-transfer (ICT) state. While OCP with canthaxanthin exhibited a weak ICT signal, it increased significantly for canthaxanthin bound to RCP. On the contrary, a strong ICT signal was recorded in OCP binding echinenone excited at the red edge of the absorption spectrum. Because the carbonyl oxygen responsible for the appearance of the ICT signal is located at the end rings of both carotenoids, the magnitude of the ICT signal can be used to estimate the torsion angles of the end rings. Application of two different excitation wavelengths to study OCP demonstrated that the OCP sample contains two spectroscopically distinct populations, none of which is corresponding to the photoactivated product of OCP.

• Klíčová slova
• Intramolecular charge-transfer state, Non-photochemical quenching, Orange carotenoid protein, Red carotenoid protein, Ultrafast spectroscopy,
• MeSH
• karotenoidy analýza   MeSH
• sinice chemie   MeSH
• spektrální analýza metody   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• karotenoidy MeSH

The major light-harvesting complex of Amphidinium (A.) carterae, chlorophyll-a-chlorophyll-c 2-peridinin-protein complex (acpPC), was studied using ultrafast pump-probe spectroscopy at low temperature (60 K). An efficient peridinin-chlorophyll-a energy transfer was observed. The stimulated emission signal monitored in the near-infrared spectral region was stronger when redder part of peridinin pool was excited, indicating that these peridinins have the S1/ICT (intramolecular charge-transfer) state with significant charge-transfer character. This may lead to enhanced energy transfer efficiency from "red" peridinins to chlorophyll-a. Contrary to the water-soluble antenna of A. carterae, peridinin-chlorophyll-a protein, the energy transfer rates in acpPC were slower under low-temperature conditions. This fact underscores the influence of the protein environment on the excited-state dynamics of pigments and/or the specificity of organization of the two pigment-protein complexes.

• MeSH
• blízká infračervená spektroskopie * MeSH
• časové faktory MeSH
• chlorofyl a MeSH
• chlorofyl metabolismus   MeSH
• Dinoflagellata metabolismus   MeSH
• elektrony MeSH
• karotenoidy metabolismus   MeSH
• kinetika MeSH
• nízká teplota * MeSH
• přenos energie MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chlorofyl a MeSH
• chlorofyl MeSH
• karotenoidy MeSH
• peridinin MeSH Prohlížeč
• světlosběrné proteinové komplexy MeSH

Carotenoids are known to offer protection against the potentially damaging combination of light and oxygen encountered by purple phototrophic bacteria, but the efficiency of such protection depends on the type of carotenoid. Rhodobacter sphaeroides synthesizes spheroidene as the main carotenoid under anaerobic conditions whereas, in the presence of oxygen, the enzyme spheroidene monooxygenase catalyses the incorporation of a keto group forming spheroidenone. We performed ultrafast transient absorption spectroscopy on membranes containing reaction center-light-harvesting 1-PufX (RC-LH1-PufX) complexes and showed that when oxygen is present the incorporation of the keto group into spheroidene, forming spheroidenone, reconfigures the energy transfer pathway in the LH1, but not the LH2, antenna. The spheroidene/spheroidenone transition acts as a molecular switch that is suggested to twist spheroidenone into an s-trans configuration increasing its conjugation length and lowering the energy of the lowest triplet state so it can act as an effective quencher of singlet oxygen. The other consequence of converting carotenoids in RC-LH1-PufX complexes is that S(2)/S(1)/triplet pathways for spheroidene is replaced with a new pathway for spheroidenone involving an activated intramolecular charge-transfer (ICT) state. This strategy for RC-LH1-PufX-spheroidenone complexes maintains the light-harvesting cross-section of the antenna by opening an active, ultrafast S(1)/ICT channel for energy transfer to LH1 Bchls while optimizing the triplet energy for singlet oxygen quenching. We propose that spheroidene/spheroidenone switching represents a simple and effective photoprotective mechanism of likely importance for phototrophic bacteria that encounter light and oxygen.

• MeSH
• bakteriální proteiny chemie   metabolismus   MeSH
• bakteriochlorofyly chemie   metabolismus   MeSH
• buněčná membrána metabolismus   MeSH
• karotenoidy chemie   metabolismus   MeSH
• kyslík metabolismus   MeSH
• molekulární struktura MeSH
• přenos energie účinky záření   MeSH
• Proteobacteria chemie   metabolismus   MeSH
• Rhodobacter sphaeroides chemie   metabolismus   MeSH
• spektrofotometrie MeSH
• světlo MeSH
• světlosběrné proteinové komplexy chemie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriochlorofyly MeSH
• karotenoidy MeSH
• kyslík MeSH
• PufX protein, Rhodobacter MeSH Prohlížeč
• spheroidene MeSH Prohlížeč
• spheroidenone MeSH Prohlížeč
• světlosběrné proteinové komplexy MeSH

Carotenoids are naturally occurring pigments that absorb light in the spectral region in which the sun irradiates maximally. These molecules transfer this energy to chlorophylls, initiating the primary photochemical events of photosynthesis. Carotenoids also regulate the flow of energy within the photosynthetic apparatus and protect it from photoinduced damage caused by excess light absorption. To carry out these functions in nature, carotenoids are bound in discrete pigment-protein complexes in the proximity of chlorophylls. A few three-dimensional structures of these carotenoid complexes have been determined by X-ray crystallography. Thus, the stage is set for attempting to correlate the structural information with the spectroscopic properties of carotenoids to understand the molecular mechanism(s) of their function in photosynthetic systems. In this Account, we summarize current spectroscopic data describing the excited state energies and ultrafast dynamics of purified carotenoids in solution and bound in light-harvesting complexes from purple bacteria, marine algae, and green plants. Many of these complexes can be modified using mutagenesis or pigment exchange which facilitates the elucidation of correlations between structure and function. We describe the structural and electronic factors controlling the function of carotenoids as energy donors. We also discuss unresolved issues related to the nature of spectroscopically dark excited states, which could play a role in light harvesting. To illustrate the interplay between structural determinations and spectroscopic investigations that exemplifies work in the field, we describe the spectroscopic properties of four light-harvesting complexes whose structures have been determined to atomic resolution. The first, the LH2 complex from the purple bacterium Rhodopseudomonas acidophila, contains the carotenoid rhodopin glucoside. The second is the LHCII trimeric complex from higher plants which uses the carotenoids lutein, neoxanthin, and violaxanthin to transfer energy to chlorophyll. The third, the peridinin-chlorophyll-protein (PCP) from the dinoflagellate Amphidinium carterae, is the only known complex in which the bound carotenoid (peridinin) pigments outnumber the chlorophylls. The last is xanthorhodopsin from the eubacterium Salinibacter ruber. This complex contains the carotenoid salinixanthin, which transfers energy to a retinal chromophore. The carotenoids in these pigment-protein complexes transfer energy with high efficiency by optimizing both the distance and orientation of the carotenoid donor and chlorophyll acceptor molecules. Importantly, the versatility and robustness of carotenoids in these light-harvesting pigment-protein complexes have led to their incorporation in the design and synthesis of nanoscale antenna systems. In these bioinspired systems, researchers are seeking to improve the light capture and use of energy from the solar emission spectrum.

• MeSH
• chlorofyl chemie   metabolismus   MeSH
• Dinoflagellata chemie   metabolismus   MeSH
• Eukaryota metabolismus   MeSH
• fotosyntéza * fyziologie   MeSH
• glukosidy MeSH
• glykosidy MeSH
• karotenoidy * chemie   metabolismus   MeSH
• lutein chemie   metabolismus   MeSH
• přenos energie MeSH
• Rhodopseudomonas metabolismus   MeSH
• světlo MeSH
• světlosběrné proteinové komplexy * chemie   metabolismus   MeSH
• tylakoidy metabolismus   MeSH
• xanthofyly metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• chlorofyl MeSH
• glukosidy MeSH
• glykosidy MeSH
• karotenoidy * MeSH
• lutein MeSH
• neoxanthin MeSH Prohlížeč
• peridinin MeSH Prohlížeč
• rhodopin glucoside MeSH Prohlížeč
• salinixanthin MeSH Prohlížeč
• světlosběrné proteinové komplexy * MeSH
• violaxanthin MeSH Prohlížeč
• xanthofyly MeSH

Xanthorhodopsin of the extremely halophilic bacterium Salinibacter ruber represents a novel antenna system. It consists of a carbonyl carotenoid, salinixanthin, bound to a retinal protein that serves as a light-driven transmembrane proton pump similar to bacteriorhodopsin of archaea. Here we apply the femtosecond transient absorption technique to reveal the excited-state dynamics of salinixanthin both in solution and in xanthorhodopsin. The results not only disclose extremely fast energy transfer rates and pathways, they also reveal effects of the binding site on the excited-state properties of the carotenoid. We compared the excited-state dynamics of salinixanthin in xanthorhodopsin and in NaBH(4)-treated xanthorhodopsin. The NaBH(4) treatment prevents energy transfer without perturbing the carotenoid binding site, and allows observation of changes in salinixanthin excited-state dynamics related to specific binding. The S(1) lifetimes of salinixanthin in untreated and NaBH(4)-treated xanthorhodopsin were identical (3 ps), confirming the absence of the S(1)-mediated energy transfer. The kinetics of salinixanthin S(2) decay probed in the near-infrared region demonstrated a change of the S(2) lifetime from 66 fs in untreated xanthorhodopsin to 110 fs in the NaBH(4)-treated protein. This corresponds to a salinixanthin-retinal energy transfer time of 165 fs and an efficiency of 40%. In addition, binding of salinixanthin to xanthorhodopsin increases the population of the S(*) state that decays in 6 ps predominantly to the ground state, but a small fraction (<10%) of the S(*) state generates a triplet state.

• MeSH
• absorpce MeSH
• bakteriální proteiny chemie   metabolismus   MeSH
• borohydridy farmakologie   MeSH
• glykosidy chemie   metabolismus   MeSH
• karotenoidy chemie   metabolismus   MeSH
• kinetika MeSH
• methanol MeSH
• přenos energie * MeSH
• rhodopsiny mikrobiální chemie   metabolismus   MeSH
• spektrální analýza MeSH
• vazebná místa MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• bakteriální proteiny MeSH
• borohydridy MeSH
• glykosidy MeSH
• karotenoidy MeSH
• methanol MeSH
• rhodopsiny mikrobiální MeSH
• salinixanthin MeSH Prohlížeč
• sodium borohydride MeSH Prohlížeč
• xanthorhodopsin, Salinibacter MeSH Prohlížeč

We use femtosecond transient absorption spectroscopy to study chlorophyll (Chl)-Chl energy transfer in the peridinin-chlorophyll protein (PCP) reconstituted with mixtures of either chlorophyll b (Chlb) and Chld or Chla and bacteriochlorophyll a (BChla). Analysis of absorption and transient absorption spectra demonstrated that reconstitution with chlorophyll mixtures produces a significant fraction of PCP complexes that contains a different Chl in each domain of the PCP monomer. The data also suggest that binding affinity of Chla is less than that of the other three Chl species. By exciting the Chl species lying at higher energy, we obtained energy transfer times of 40 +/- 5 ps (Chlb-Chld) and 59 +/- 3 ps (Chla-BChla). The experimental values match those obtained from the Förster equation, 36 and 50 ps, respectively, showing that energy transfer proceeds via the Förster mechanism. Excitation of peridinin in the PCP complex reconstituted with Chla/BChla mixture provided time constants of 2.6 and 0.4 ps for the peridinin-Chla and peridinin-BChla energy transfer, matching those obtained from studies of PCP complexes reconstituted with single chlorophyll species.

• MeSH
• chemické modely * MeSH
• chlorofyl chemie   účinky záření   MeSH
• dávka záření MeSH
• karotenoidy chemie   účinky záření   MeSH
• počítačová simulace MeSH
• přenos energie účinky záření   MeSH
• světlo MeSH
• vazba proteinů účinky záření   MeSH
• vazebná místa účinky záření   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chlorofyl MeSH
• karotenoidy MeSH
• peridinin MeSH Prohlížeč