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Malina T, Bína D, Collins AM, Alster J, Pšenčík J. Efficient two-step excitation energy transfer in artificial light-harvesting antenna based on bacteriochlorophyll aggregates. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY. B, BIOLOGY 2024; 254:112891. [PMID: 38555841 DOI: 10.1016/j.jphotobiol.2024.112891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 02/21/2024] [Accepted: 02/28/2024] [Indexed: 04/02/2024]
Abstract
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.
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Affiliation(s)
- Tomáš Malina
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
| | - David Bína
- Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic & Biology Centre, Czech Academy of Sciences, České Budějovice, Czech Republic
| | - Aaron M Collins
- Department of Environmental and Physical Sciences, Southern New Hampshire University, Manchester, NH, USA
| | - Jan Alster
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
| | - Jakub Pšenčík
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic.
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Yakovlev AG, Taisova AS. Quenching of bacteriochlorophyll a triplet state by carotenoids in the chlorosome baseplate of green bacterium Chloroflexus aurantiacus. Phys Chem Chem Phys 2024; 26:8815-8823. [PMID: 38421198 DOI: 10.1039/d4cp00287c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/02/2024]
Abstract
To capture weak light fluxes, green photosynthetic bacteria have unique structures - chlorosomes, consisting of 104-5 molecules of bacteriochlorophyll (BChl) c, d, e. Chlorosomes are attached to the cytoplasmic membrane through the baseplate, a paracrystalline protein structure containing BChl a and carotenoids (Car). The most important function of Car is the quenching of triplet states of BChl, which prevents the formation of singlet oxygen and thereby provides photoprotection. In our work, we studied the dynamics of the triplet states of BChl a and Car in the baseplate of Chloroflexus aurantiacus chlorosomes using picosecond differential spectroscopy. BChl a of the baseplate was excited into the Qy band at 810 nm, and the corresponding absorption changes were recorded in the range of 420-880 nm. It was found that the formation of the Car triplet state occurs in ∼1.3 ns, which is ∼3 times faster than the formation of this state in the peripheral antenna of C. aurantiacus according to literature data. The Car triplet state was recorded by the characteristic absorption band T1 → Tn at ∼550 nm. Simultaneously with the appearance of absorption T1 → Tn, there was a bleaching of the singlet absorption of Car in the region of 400-500 nm. Theoretical modeling made it possible to estimate the characteristic time of formation of the triplet state of BChl a as ∼0.5 ns. It is shown that the experimental data are well described by the sequential scheme of formation and quenching of the BChl a triplet state: BChl a* → BChl aT → CarT. Thus, carotenoids from green bacteria effectively protect the baseplate from possible damage by singlet oxygen.
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Affiliation(s)
- Andrei G Yakovlev
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Leninskie Gory, Moscow 119991, Russian Federation.
| | - Alexandra S Taisova
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Leninskie Gory, Moscow 119991, Russian Federation.
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Yakovlev AG, Taisova AS, Fetisova ZG. Dynamic Stark effect in β and γ carotenes induced by photoexcitation of bacteriochlorophyll c in chlorosomes from Chloroflexus aurantiacus. PHOTOSYNTHESIS RESEARCH 2022; 154:291-302. [PMID: 36115930 DOI: 10.1007/s11120-022-00942-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 07/20/2022] [Indexed: 06/15/2023]
Abstract
Chlorosomes of green bacteria can be considered as a prototype of future artificial light-harvesting devices due to their unique property of self-assembly of a large number of bacteriochlorophyll (BChl) c/d/e molecules into compact aggregates. The presence of carotenoids (Cars) in chlorosomes is very important for photoprotection, light harvesting and structure stabilization. In this work, we studied for the first time the electrochromic band shift (Stark effect) in Cars of the phototrophic filamentous green bacterium Chloroflexus (Cfx.) aurantiacus induced by fs light excitation of the main pigment, BChl c. The high accuracy of the spectral measurements permitted us to extract a small wavy spectral feature, which, obviously, can be associated with the dynamic shift of the Car absorption band. A global analysis of spectroscopy data and theoretical modeling of absorption spectra showed that near 60% of Cars exhibited a red Stark shift of ~ 25 cm-1 and the remaining 40% exhibited a blue shift. We interpreted this finding as evidence of various orientations of Car in chlorosomes. We estimated the average value of the light-induced electric field strength in the place of Car molecules as ~ 106 V/cm and the average distance between Car and the neighboring BChl c as ~ 10 Å. We concluded that the dynamics of the Car electrochromic band shift mainly reflected the dynamics of exciton migration through the chlorosome toward the baseplate within ~ 1 ps. Our work has unambiguously shown that Cars are sensitive indicators of light-induced internal electric fields in chlorosomes.
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Affiliation(s)
- Andrei G Yakovlev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 119991, Moscow, Russian Federation.
| | - Alexandra S Taisova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 119991, Moscow, Russian Federation
| | - Zoya G Fetisova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 119991, Moscow, Russian Federation
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Yakovlev AG, Taisova AS, Fetisova ZG. Femtosecond excited-state dynamics in chlorosomal carotenoids of the photosynthetic bacterium Chloroflexus aurantiacus revealed by near infrared pump-probe spectroscopy. Phys Chem Chem Phys 2021; 23:12761-12770. [PMID: 34042141 DOI: 10.1039/d1cp00927c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In photosynthetic green bacteria, chlorosomes provide light harvesting with high efficiency. Chlorosomal carotenoids (Cars) participate in light harvesting together with the main pigment, bacteriochlorophyll (BChl) c/d/e. In the present work, we studied the excited-state dynamics in Cars from Chloroflexus (Cfx.) aurantiacus chlorosomes by near infrared pump-probe spectroscopy with 25 fs temporal resolution at room temperature. The S2 state of Cars was excited at a wavelength of ∼520 nm, and the absorption changes were probed at 860-1000 nm where the excited state absorption (ESA) of the Cars S2 state occurred. Global analysis of the spectroscopy data revealed an ultrafast (∼15 fs) and large (>130 nm) red shift of the S2 ESA spectrum together with the well-known S2 → S1 IC (∼190 fs) and Cars → BChl c EET (∼120 fs). The S2 lifetime was found to be ∼74 fs. Our findings are in line with earlier results on the excited-state dynamics in Cars in vitro. To explain the extremely fast S2 dynamics, we have tentatively proposed two alternative schemes. The first scheme assumed the formation of a vibrational wavepacket in the S2 state, the motion of which caused a dynamical red shift of the S2 ESA spectrum. The second scheme assumed the presence of two potential minima in the S2 state and incoherent energy transfer between them.
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Affiliation(s)
- Andrei G Yakovlev
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Leninskie Gory, 119991, Moscow, Russian Federation.
| | - Alexandra S Taisova
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Leninskie Gory, 119991, Moscow, Russian Federation.
| | - Zoya G Fetisova
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Leninskie Gory, 119991, Moscow, Russian Federation.
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Utilization of blue-green light by chlorosomes from the photosynthetic bacterium Chloroflexus aurantiacus: Ultrafast excitation energy conversion and transfer. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2021; 1862:148396. [PMID: 33581107 DOI: 10.1016/j.bbabio.2021.148396] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 02/01/2021] [Accepted: 02/05/2021] [Indexed: 01/14/2023]
Abstract
Chlorosomes of photosynthetic green bacteria are unique molecular assemblies providing efficient light harvesting followed by multi-step transfer of excitation energy to reaction centers. In each chlorosome, 104-105 bacteriochlorophyll (BChl) c/d/e molecules are organized by self-assembly into high-ordered aggregates. We studied the early-time dynamics of the excitation energy flow and energy conversion in chlorosomes isolated from Chloroflexus (Cfx.) aurantiacus bacteria by pump-probe spectroscopy with 30-fs temporal resolution at room temperature. Both the S2 state of carotenoids (Cars) and the Soret states of BChl c were excited at ~490 nm, and absorption changes were probed at 400-900 nm. A global analysis of spectroscopy data revealed that the excitation energy transfer (EET) from Cars to BChl c aggregates occurred within ~100 fs, and the Soret → Q energy conversion in BChl c occurred faster within ~40 fs. This conclusion was confirmed by a detailed comparison of the early exciton dynamics in chlorosomes with different content of Cars. These processes are accompanied by excitonic and vibrational relaxation within 100-270 fs. The well-known EET from BChl c to the baseplate BChl a proceeded on a ps time-scale. We showed that the S1 state of Cars does not participate in EET. We discussed the possible presence (or absence) of an intermediate state that might mediates the Soret → Qy internal conversion in chlorosomal BChl c. We discussed a possible relationship between the observed exciton dynamics and the structural heterogeneity of chlorosomes.
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Triplet state quenching of bacteriochlorophyll c aggregates in a protein-free environment of a chlorosome interior. Chem Phys 2020. [DOI: 10.1016/j.chemphys.2019.110542] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Cardona T, Sánchez‐Baracaldo P, Rutherford AW, Larkum AW. Early Archean origin of Photosystem II. GEOBIOLOGY 2019; 17:127-150. [PMID: 30411862 PMCID: PMC6492235 DOI: 10.1111/gbi.12322] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Revised: 10/03/2018] [Accepted: 10/11/2018] [Indexed: 05/09/2023]
Abstract
Photosystem II is a photochemical reaction center that catalyzes the light-driven oxidation of water to molecular oxygen. Water oxidation is the distinctive photochemical reaction that permitted the evolution of oxygenic photosynthesis and the eventual rise of eukaryotes. At what point during the history of life an ancestral photosystem evolved the capacity to oxidize water still remains unknown. Here, we study the evolution of the core reaction center proteins of Photosystem II using sequence and structural comparisons in combination with Bayesian relaxed molecular clocks. Our results indicate that a homodimeric photosystem with sufficient oxidizing power to split water had already appeared in the early Archean about a billion years before the most recent common ancestor of all described Cyanobacteria capable of oxygenic photosynthesis, and well before the diversification of some of the known groups of anoxygenic photosynthetic bacteria. Based on a structural and functional rationale, we hypothesize that this early Archean photosystem was capable of water oxidation to oxygen and had already evolved protection mechanisms against the formation of reactive oxygen species. This would place primordial forms of oxygenic photosynthesis at a very early stage in the evolutionary history of life.
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Affiliation(s)
- Tanai Cardona
- Department of Life SciencesImperial College LondonLondonUK
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Khoroshyy P, Bína D, Gardian Z, Litvín R, Alster J, Pšenčík J. Quenching of chlorophyll triplet states by carotenoids in algal light-harvesting complexes related to fucoxanthin-chlorophyll protein. PHOTOSYNTHESIS RESEARCH 2018; 135:213-225. [PMID: 28669083 DOI: 10.1007/s11120-017-0416-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Accepted: 06/16/2017] [Indexed: 06/07/2023]
Abstract
We have used time-resolved absorption and fluorescence spectroscopy with nanosecond resolution to study triplet energy transfer from chlorophylls to carotenoids in a protective process that prevents the formation of reactive singlet oxygen. The light-harvesting complexes studied were isolated from Chromera velia, belonging to a group Alveolata, and Xanthonema debile and Nannochloropsis oceanica, both from Stramenopiles. All three light-harvesting complexes are related to fucoxanthin-chlorophyll protein, but contain only chlorophyll a and no chlorophyll c. In addition, they differ in the carotenoid content. This composition of the complexes allowed us to study the quenching of chlorophyll a triplet states by different carotenoids in a comparable environment. The triplet states of chlorophylls bound to the light-harvesting complexes were quenched by carotenoids with an efficiency close to 100%. Carotenoid triplet states were observed to rise with a ~5 ns lifetime and were spectrally and kinetically homogeneous. The triplet states were formed predominantly on the red-most chlorophylls and were quenched by carotenoids which were further identified or at least spectrally characterized.
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Affiliation(s)
- Petro Khoroshyy
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, 121 16, Prague 2, Czech Republic
| | - David Bína
- Biological Centre, Czech Academy of Sciences, 370 05, České Budějovice, Czech Republic
- Faculty of Science, University of South Bohemia, 370 05, České Budějovice, Czech Republic
| | - Zdenko Gardian
- Biological Centre, Czech Academy of Sciences, 370 05, České Budějovice, Czech Republic
- Faculty of Science, University of South Bohemia, 370 05, České Budějovice, Czech Republic
| | - Radek Litvín
- Biological Centre, Czech Academy of Sciences, 370 05, České Budějovice, Czech Republic
- Faculty of Science, University of South Bohemia, 370 05, České Budějovice, Czech Republic
| | - Jan Alster
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, 121 16, Prague 2, Czech Republic
| | - Jakub Pšenčík
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, 121 16, Prague 2, Czech Republic.
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Magdaong NCM, Blankenship RE. Photoprotective, excited-state quenching mechanisms in diverse photosynthetic organisms. J Biol Chem 2018; 293:5018-5025. [PMID: 29298897 DOI: 10.1074/jbc.tm117.000233] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Light-harvesting complexes (LHCs) serve a dual role in photosynthesis, depending on the prevailing light conditions. In low light, they ensure photosynthetic efficiency by maximizing the light absorption cross-section and subsequent energy storage. Under excess light conditions, LHCs perform photoprotective quenching functions to prevent harmful chemical species such as triplet chlorophyll and singlet oxygen from forming and damaging the photosynthetic apparatus. In this Minireview, various photoprotective quenching mechanisms that have been identified in different photosynthetic organisms are surveyed and summarized, and implications for improving photosynthetic productivity are briefly discussed.
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Affiliation(s)
- Nikki Cecil M Magdaong
- From the Departments of Biology and Chemistry and.,the Photosynthetic Antenna Research Center, Washington University in Saint Louis, St. Louis, Missouri 63130
| | - Robert E Blankenship
- From the Departments of Biology and Chemistry and .,the Photosynthetic Antenna Research Center, Washington University in Saint Louis, St. Louis, Missouri 63130
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Kvíčalová Z, Alster J, Hofmann E, Khoroshyy P, Litvín R, Bína D, Polívka T, Pšenčík J. Triplet–triplet energy transfer from chlorophylls to carotenoids in two antenna complexes from dinoflagellate Amphidinium carterae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:341-9. [DOI: 10.1016/j.bbabio.2016.01.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Revised: 01/08/2016] [Accepted: 01/17/2016] [Indexed: 11/24/2022]
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Pšenčík J, Butcher SJ, Tuma R. Chlorosomes: Structure, Function and Assembly. THE STRUCTURAL BASIS OF BIOLOGICAL ENERGY GENERATION 2014. [DOI: 10.1007/978-94-017-8742-0_5] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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Abstract
Chlorosomes are large light-harvesting complexes found in three phyla of anoxygenic photosynthetic bacteria. Chlorosomes are primarily composed of self-assembling pigment aggregates. In addition to the main pigment, bacteriochlorophyll c, d, or e, chlorosomes also contain variable amounts of carotenoids. Here, we use X-ray scattering and electron cryomicroscopy, complemented with absorption spectroscopy and pigment analysis, to compare the morphologies, structures, and pigment compositions of chlorosomes from Chloroflexus aurantiacus grown under two different light conditions and Chlorobaculum tepidum. High-purity chlorosomes from C. aurantiacus contain about 20% more carotenoid per bacteriochlorophyll c molecule when grown under low light than when grown under high light. This accentuates the light-harvesting function of carotenoids, in addition to their photoprotective role. The low-light chlorosomes are thicker due to the overall greater content of pigments and contain domains of lamellar aggregates. Experiments where carotenoids were selectively extracted from intact chlorosomes using hexane proved that they are located in the interlamellar space, as observed previously for species belonging to the phylum Chlorobi. A fraction of the carotenoids are localized in the baseplate, where they are bound differently and cannot be removed by hexane. In C. tepidum, carotenoids cannot be extracted by hexane even from the chlorosome interior. The chemical structure of the pigments in C. tepidum may lead to π-π interactions between carotenoids and bacteriochlorophylls, preventing carotenoid extraction. The results provide information about the nature of interactions between bacteriochlorophylls and carotenoids in the protein-free environment of the chlorosome interior.
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Kulminskaya NV, Pedersen MØ, Bjerring M, Underhaug J, Miller M, Frigaard NU, Nielsen JT, Nielsen NC. In Situ Solid-State NMR Spectroscopy of Protein in Heterogeneous Membranes: The Baseplate Antenna Complex of Chlorobaculum tepidum. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201201160] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Kulminskaya NV, Pedersen MØ, Bjerring M, Underhaug J, Miller M, Frigaard NU, Nielsen JT, Nielsen NC. In situ solid-state NMR spectroscopy of protein in heterogeneous membranes: the baseplate antenna complex of Chlorobaculum tepidum. Angew Chem Int Ed Engl 2012; 51:6891-5. [PMID: 22685072 DOI: 10.1002/anie.201201160] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2012] [Revised: 05/16/2012] [Indexed: 11/06/2022]
Abstract
A clever combination: an in situ solid-state NMR analysis of CsmA proteins in the heterogeneous environment of the photoreceptor of Chlorobaculum tepidum is reported. Using different combinations of 2D and 3D solid-state NMR spectra, 90 % of the CsmA resonances are assigned and provide on the basis of chemical shift data information about the structure and conformation of CsmA in the CsmA-bacteriochlorophyll a complex.
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Alster J, Polívka T, Arellano JB, Hříbek P, Vácha F, Hála J, Pšenčík J. Self-assembly and energy transfer in artificial light-harvesting complexes of bacteriochlorophyll c with astaxanthin. PHOTOSYNTHESIS RESEARCH 2012; 111:193-204. [PMID: 21833799 DOI: 10.1007/s11120-011-9670-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Accepted: 07/02/2011] [Indexed: 05/31/2023]
Abstract
Chlorosomes, the light-harvesting antennae of green photosynthetic bacteria, are based on large aggregates of bacteriochlorophyll molecules. Aggregates with similar properties to those in chlorosomes can also be prepared in vitro. Several agents were shown to induce aggregation of bacteriochlorophyll c in aqueous environments, including certain lipids, carotenes, and quinones. A key distinguishing feature of bacteriochlorophyll c aggregates, both in vitro and in chlorosomes, is a large (>60 nm) red shift of their Q(y) absorption band compared with that of the monomers. In this study, we investigate the self-assembly of bacteriochlorophyll c with the xanthophyll astaxanthin, which leads to the formation of a new type of complexes. Our results indicate that, due to its specific structure, astaxanthin molecules competes with bacteriochlorophylls for the bonds involved in the aggregation, thus preventing the formation of any significant red shift compared with pure bacteriochlorophyll c in aqueous buffer. A strong interaction between both the types of pigments in the developed assemblies, is manifested by a rather efficient (~40%) excitation energy transfer from astaxanthin to bacteriochlorophyll c, as revealed by fluorescence excitation spectroscopy. Results of transient absorption spectroscopy show that the energy transfer is very fast (<500 fs) and proceeds through the S(2) state of astaxanthin.
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Affiliation(s)
- J Alster
- Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16, Praha, Czech Republic
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Alster J, Polívka T, Arellano J, Chábera P, Vácha F, Pšenčík J. β-Carotene to bacteriochlorophyll c energy transfer in self-assembled aggregates mimicking chlorosomes. Chem Phys 2010. [DOI: 10.1016/j.chemphys.2010.02.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Pedersen MØ, Linnanto J, Frigaard NU, Nielsen NC, Miller M. A model of the protein-pigment baseplate complex in chlorosomes of photosynthetic green bacteria. PHOTOSYNTHESIS RESEARCH 2010; 104:233-243. [PMID: 20077007 DOI: 10.1007/s11120-009-9519-y] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2009] [Accepted: 12/16/2009] [Indexed: 05/28/2023]
Abstract
In contrast to photosynthetic reaction centers, which share the same structural architecture, more variety is found in the light-harvesting antenna systems of phototrophic organisms. The largest antenna system described, so far, is the chlorosome found in anoxygenic green bacteria, as well as in a recently discovered aerobic phototroph. Chlorosomes are the only antenna system, in which the major light-harvesting pigments are organized in self-assembled supramolecular aggregates rather than on protein scaffolds. This unique feature is believed to explain why some green bacteria are able to carry out photosynthesis at very low light intensities. Encasing the chlorosome pigments is a protein-lipid monolayer including an additional antenna complex: the baseplate, a two-dimensional paracrystalline structure containing the chlorosome protein CsmA and bacteriochlorophyll a (BChl a). In this article, we review current knowledge of the baseplate antenna complex, which physically and functionally connects the chlorosome pigments to the reaction centers via the Fenna-Matthews-Olson protein, with special emphasis on the well-studied green sulfur bacterium Chlorobaculum tepidum (previously Chlorobium tepidum). A possible role for the baseplate in the biogenesis of chlorosomes is discussed. In the final part, we present a structural model of the baseplate through combination of a recent NMR structure of CsmA and simulation of circular dichroism and optical spectra for the CsmA-BChl a complex.
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Affiliation(s)
- Marie Ø Pedersen
- Center for Insoluble Protein Structures, Interdisciplinary Nanoscience Center, Aarhus University, Langelandsgade 140, Arhus C, Aarhus, Denmark
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Fuciman M, Chábera P, Župčanová A, Hříbek P, Arellano JB, Vácha F, Pšenčík J, Polívka T. Excited state properties of aryl carotenoids. Phys Chem Chem Phys 2010; 12:3112-20. [DOI: 10.1039/b921384h] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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Structure of chlorosomes from the green filamentous bacterium Chloroflexus aurantiacus. J Bacteriol 2009; 191:6701-8. [PMID: 19717605 DOI: 10.1128/jb.00690-09] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The green filamentous bacterium Chloroflexus aurantiacus employs chlorosomes as photosynthetic antennae. Chlorosomes contain bacteriochlorophyll aggregates and are attached to the inner side of a plasma membrane via a protein baseplate. The structure of chlorosomes from C. aurantiacus was investigated by using a combination of cryo-electron microscopy and X-ray diffraction and compared with that of Chlorobi species. Cryo-electron tomography revealed thin chlorosomes for which a distinct crystalline baseplate lattice was visualized in high-resolution projections. The baseplate is present only on one side of the chlorosome, and the lattice dimensions suggest that a dimer of the CsmA protein is the building block. The bacteriochlorophyll aggregates inside the chlorosome are arranged in lamellae, but the spacing is much greater than that in Chlorobi species. A comparison of chlorosomes from different species suggested that the lamellar spacing is proportional to the chain length of the esterifying alcohols. C. aurantiacus chlorosomes accumulate larger quantities of carotenoids under high-light conditions, presumably to provide photoprotection. The wider lamellae allow accommodation of the additional carotenoids and lead to increased disorder within the lamellae.
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Olson TL, van de Meene AML, Francis JN, Pierson BK, Blankenship RE. Pigment analysis of "Candidatus Chlorothrix halophila," a green filamentous anoxygenic phototrophic bacterium. J Bacteriol 2007; 189:4187-95. [PMID: 17369304 PMCID: PMC1913391 DOI: 10.1128/jb.01712-06] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Accepted: 02/27/2007] [Indexed: 11/20/2022] Open
Abstract
The pigment composition of "Candidatus Chlorothrix halophila," a filamentous anoxygenic phototrophic bacterium found in Baja California Sur, Mexico, was determined. Previous work showed that bacteriochlorophyll c (BChl c) was the major pigment in "Ca. Chlorothrix halophila," but it was not clear if this bacterium also contains BChl a (J. A. Klappenbach and B. K. Pierson, Arch. Microbiol. 181:17-25, 2004). Here we show that in addition to BChl c, a small amount of a pigment that is spectrally indistinguishable from BChl a is present in cell extracts of "Ca. Chlorothrix halophila." Nevertheless, the BChl a-like pigment from "Ca. Chlorothrix halophila" has a different molecular weight and a different high-performance liquid chromatography elution time than BChl a from other photosynthetic bacteria. Based on mass spectrometry and other spectroscopic analysis, we determined that the BChl a-like pigment in "Ca. Chlorothrix halophila" contains a tetrahydrogeranylgeraniol tail rather than the phytol tail that is present in BChl a. The carotenoids and major BChl c homologs in "Ca. Chlorothrix halophila" were also identified. BChls c were found to be farnesol esterified and geranylgeraniol esterified.
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Affiliation(s)
- Tien Le Olson
- Department of Biology and Chemistry, Arizona State University, Tempe, AZ 85287, USA
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Arellano JB, Bernt Melø T, Borrego CM, Naqvi KR. Bacteriochlorophyll e Monomers, but Not Aggregates, Sensitize Singlet Oxygen: Implications for a Self-photoprotection Mechanism in Chlorosomes¶. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2002)0760373bembna2.0.co2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Arellano JB, Bernt Melø T, Borrego CM, Garcia-Gil J, Naqvi KR. Nanosecond Laser Photolysis Studies of Chlorosomes and Artificial Aggregates Containing Bacteriochlorophyll e: Evidence for the Proximity of Carotenoids and Bacteriochlorophyll a in Chlorosomes from Chlorobium phaeobacteroides strain CL1401¶. Photochem Photobiol 2007. [DOI: 10.1562/0031-8655(2000)0720669nlpsoc2.0.co2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Klinger P, Arellano JB, Vácha F, Hála J, PšenčíK J. Effect of Carotenoids and Monogalactosyl Diglyceride on Bacteriochlorophyll c Aggregates in Aqueous Buffer: Implications for the Self-assembly of Chlorosomes¶. Photochem Photobiol 2007. [DOI: 10.1111/j.1751-1097.2004.tb00131.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Kim H, Li H, Maresca JA, Bryant DA, Savikhin S. Triplet exciton formation as a novel photoprotection mechanism in chlorosomes of Chlorobium tepidum. Biophys J 2007; 93:192-201. [PMID: 17434948 PMCID: PMC1914439 DOI: 10.1529/biophysj.106.103556] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Chlorosomes comprise thousands of bacteriochlorophylls (BChl c, d, or e) in a closely packed structure surrounded by a lipid-protein envelope and additionally contain considerable amounts of carotenoids, quinones, and BChl a. It has been suggested that carotenoids in chlorosomes provide photoprotection by rapidly quenching triplet excited states of BChl via a triplet-triplet energy transfer mechanism that prevents energy transfer to oxygen and the formation of harmful singlet oxygen. In this work we studied triplet energy transfer kinetics and photodegradation of chlorosomes isolated from wild-type Chlorobium tepidum and from genetically modified species with different types of carotenoids and from a carotenoid-free mutant. Supporting a photoprotective function of carotenoids, carotenoid-free chlorosomes photodegrade approximately 3 times faster than wild-type chlorosomes. However, a significant fraction of the BChls forms a long-lived, triplet-like state that does not interact with carotenoids or with oxygen. We propose that these states are triplet excitons that form due to triplet-triplet interaction between the closely packed BChls. Numerical exciton simulations predict that the energy of these triplet excitons may fall below that of singlet oxygen and triplet carotenoids; this would prevent energy transfer from triplet BChl. Thus, the formation of triplet excitons in chlorosomes serves as an alternative photoprotection mechanism.
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Affiliation(s)
- Hanyoup Kim
- Department of Physics, Purdue University, West Lafayette, Indiana, USA
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Klinger P, Arellano JB, Vácha F, Hála J, Psencík J. Effect of carotenoids and monogalactosyl diglyceride on bacteriochlorophyll c aggregates in aqueous buffer: implications for the self-assembly of chlorosomes. Photochem Photobiol 2006; 80:572-8. [PMID: 15623345 DOI: 10.1562/0031-8655(2004)080<0572:eocamd>2.0.co;2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Aggregation of bacteriochlorophyll (BChl) c from chlorosomes, the main light-harvesting complex of green bacteria, has been studied in aqueous buffer. Unlike other chlorophyll-like molecules, BChl c is rather soluble in aqueous buffer, forming dimers. When BChl c is mixed with carotenoids (Car), the BChl c Qy transition is further redshifted, in respect to that of monomers and dimers. The results suggest that Car are incorporated in the aggregates and induce further aggregation of BChl c. The redshift of the BChl c Qy band is proportional to the Car concentration. In contrast, the mixture of bacteriochlorophyllide (BChlide) c, which lacks the nonpolar esterifying alcohol, does not form aggregates with Car in aqueous buffer or nonpolar solvents. Instead, the position of the BChlide c Qy transition remains unshifted in respect to that of the monomeric molecule, and Car precipitates with the course of time in aqueous buffer. Similar effects on both BChl c and BChlide c are also observed when monogalactosyl diglyceride (MGDG), which forms the monolayer envelope of chlorosomes, is used instead of (or together with) Car. The results show that the hydrophobic interactions of the BChl c esterifying alcohols with themselves and the nonpolar carbon skeleton of Car, or the fatty acid tails of MGDG, are essential driving forces for BChl aggregation in chlorosomes.
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Affiliation(s)
- Pavel Klinger
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
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Frigaard NU, Bryant DA. Chlorosomes: Antenna Organelles in Photosynthetic Green Bacteria. MICROBIOLOGY MONOGRAPHS 2006. [DOI: 10.1007/7171_021] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Frigaard NU, Bryant DA. Seeing green bacteria in a new light: genomics-enabled studies of the photosynthetic apparatus in green sulfur bacteria and filamentous anoxygenic phototrophic bacteria. Arch Microbiol 2004; 182:265-76. [PMID: 15340781 DOI: 10.1007/s00203-004-0718-9] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2004] [Revised: 07/21/2004] [Accepted: 07/22/2004] [Indexed: 10/26/2022]
Abstract
Based upon their photosynthetic nature and the presence of a unique light-harvesting antenna structure, the chlorosome, the photosynthetic green bacteria are defined as a distinctive group in the Bacteria. However, members of the two taxa that comprise this group, the green sulfur bacteria (Chlorobi) and the filamentous anoxygenic phototrophic bacteria ("Chloroflexales"), are otherwise quite different, both physiologically and phylogenetically. This review summarizes how genome sequence information facilitated studies of the biosynthesis and function of the photosynthetic apparatus and the oxidation of inorganic sulfur compounds in two model organisms that represent these taxa, Chlorobium tepidum and Chloroflexus aurantiacus. The genes involved in bacteriochlorophyll (BChl) c and carotenoid biosynthesis in these two organisms were identified by sequence homology with known BChl a and carotenoid biosynthesis enzymes, gene cluster analysis in Cfx. aurantiacus, and gene inactivation studies in Chl. tepidum. Based on these results, BChl a and BChl c biosynthesis is similar in the two organisms, whereas carotenoid biosynthesis differs significantly. In agreement with its facultative anaerobic nature, Cfx. aurantiacus in some cases apparently produces structurally different enzymes for heme and BChl biosynthesis, in which one enzyme functions under anoxic conditions and the other performs the same reaction under oxic conditions. The Chl. tepidum mutants produced with modified BChl c and carotenoid species also allow the functions of these pigments to be studied in vivo.
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Affiliation(s)
- Niels-Ulrik Frigaard
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16801, USA.
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Frigaard NU, Maresca JA, Yunker CE, Jones AD, Bryant DA. Genetic manipulation of carotenoid biosynthesis in the green sulfur bacterium Chlorobium tepidum. J Bacteriol 2004; 186:5210-20. [PMID: 15292122 PMCID: PMC490927 DOI: 10.1128/jb.186.16.5210-5220.2004] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2004] [Accepted: 05/14/2004] [Indexed: 11/20/2022] Open
Abstract
The green sulfur bacterium Chlorobium tepidum is a strict anaerobe and an obligate photoautotroph. On the basis of sequence similarity with known enzymes or sequence motifs, nine open reading frames encoding putative enzymes of carotenoid biosynthesis were identified in the genome sequence of C. tepidum, and all nine genes were inactivated. Analysis of the carotenoid composition in the resulting mutants allowed the genes encoding the following six enzymes to be identified: phytoene synthase (crtB/CT1386), phytoene desaturase (crtP/CT0807), zeta-carotene desaturase (crtQ/CT1414), gamma-carotene desaturase (crtU/CT0323), carotenoid 1',2'-hydratase (crtC/CT0301), and carotenoid cis-trans isomerase (crtH/CT0649). Three mutants (CT0180, CT1357, and CT1416 mutants) did not exhibit a discernible phenotype. The carotenoid biosynthetic pathway in C. tepidum is similar to that in cyanobacteria and plants by converting phytoene into lycopene using two plant-like desaturases (CrtP and CrtQ) and a plant-like cis-trans isomerase (CrtH) and thus differs from the pathway known in all other bacteria. In contrast to the situation in cyanobacteria and plants, the construction of a crtB mutant completely lacking carotenoids demonstrates that carotenoids are not essential for photosynthetic growth of green sulfur bacteria. However, the bacteriochlorophyll a contents of mutants lacking colored carotenoids (crtB, crtP, and crtQ mutants) were decreased from that of the wild type, and these mutants exhibited a significant growth rate defect under all light intensities tested. Therefore, colored carotenoids may have both structural and photoprotection roles in green sulfur bacteria. The ability to manipulate the carotenoid composition so dramatically in C. tepidum offers excellent possibilities for studying the roles of carotenoids in the light-harvesting chlorosome antenna and iron-sulfur-type (photosystem I-like) reaction center. The phylogeny of carotenogenic enzymes in green sulfur bacteria and green filamentous bacteria is also discussed.
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Affiliation(s)
- Niels-Ulrik Frigaard
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
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Granzhan A, Penzkofer A, Hauska G. Photo-degradation of bacteriochlorophyll c in intact cells and extracts from Chlorobium tepidum. J Photochem Photobiol A Chem 2004. [DOI: 10.1016/j.jphotochem.2004.03.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Polívka T, Sundström V. Ultrafast dynamics of carotenoid excited States-from solution to natural and artificial systems. Chem Rev 2004; 104:2021-71. [PMID: 15080720 DOI: 10.1021/cr020674n] [Citation(s) in RCA: 638] [Impact Index Per Article: 31.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tomás Polívka
- Department of Chemical Physics, Lund University, Box 124, SE-221 00 Lund, Sweden.
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Arellano JB, Melø TB, Fyfe PK, Cogdell RJ, Naqvi KR. Multichannel Flash Spectroscopy of the Reaction Centers of Wild-type and Mutant Rhodobacter sphaeroides: BacteriochlorophyllB-mediated Interaction Between the Carotenoid Triplet and the Special Pair†¶. Photochem Photobiol 2004. [DOI: 10.1562/0031-8655(2004)79<68:mfsotr>2.0.co;2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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32
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Kakitani Y, Rondonuwu FS, Mizoguchi T, Watanabe Y, Koyama Y. Energy Dissipations in Chlorosomes: Emission from the Qy State Following Singlet−Singlet and Triplet−Triplet Annihilation Reactions in the Cylindrical Aggregate and Its Reversible Dissociation into the Piggy-Back Dimers. J Phys Chem B 2003. [DOI: 10.1021/jp0300288] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yoshinori Kakitani
- Department of Chemistry and Department of Physics, Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan, and Department of Bioscience and Biotechnology, Ritsumeikan University, Nojihigashi, Kusatsu 525-8577, Japan
| | - Ferdy S. Rondonuwu
- Department of Chemistry and Department of Physics, Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan, and Department of Bioscience and Biotechnology, Ritsumeikan University, Nojihigashi, Kusatsu 525-8577, Japan
| | - Tadashi Mizoguchi
- Department of Chemistry and Department of Physics, Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan, and Department of Bioscience and Biotechnology, Ritsumeikan University, Nojihigashi, Kusatsu 525-8577, Japan
| | - Yasutaka Watanabe
- Department of Chemistry and Department of Physics, Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan, and Department of Bioscience and Biotechnology, Ritsumeikan University, Nojihigashi, Kusatsu 525-8577, Japan
| | - Yasushi Koyama
- Department of Chemistry and Department of Physics, Faculty of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan, and Department of Bioscience and Biotechnology, Ritsumeikan University, Nojihigashi, Kusatsu 525-8577, Japan
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Psencík J, Ma YZ, Arellano JB, Hála J, Gillbro T. Excitation energy transfer dynamics and excited-state structure in chlorosomes of Chlorobium phaeobacteroides. Biophys J 2003; 84:1161-79. [PMID: 12547796 PMCID: PMC1302692 DOI: 10.1016/s0006-3495(03)74931-5] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The excited-state relaxation within bacteriochlorophyll (BChl) e and a in chlorosomes of Chlorobium phaeobacteroides has been studied by femtosecond transient absorption spectroscopy at room temperature. Singlet-singlet annihilation was observed to strongly influence both the isotropic and anisotropic decays. Pump intensities in the order of 10(11) photons x pulse(-1) x cm(-2) were required to obtain annihilation-free conditions. The most important consequence of applied very low excitation doses is an observation of a subpicosecond process within the BChl e manifold (approximately 200-500 fs), manifesting itself as a rise in the red part of the Q(y) absorption band of the BChl e aggregates. The subsequent decay of the kinetics measured in the BChl e region and the corresponding rise in the baseplate BChl a is not single-exponential, and at least two components are necessary to fit the data, corresponding to several BChl e-->BChl a transfer steps. Under annihilation-free conditions, the anisotropic kinetics show a generally slow decay within the BChl e band (10-20 ps) whereas it decays more rapidly in the BChl a region ( approximately 1 ps). Analysis of the experimental data gives a detailed picture of the overall time evolution of the energy relaxation and energy transfer processes within the chlorosome. The results are interpreted within an exciton model based on the proposed structure.
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Affiliation(s)
- Jakub Psencík
- Department of Chemistry, Biophysical Chemistry, Umeå University, S-901 87 Umeå, Sweden.
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Arellano JB, Melø TB, Borrego CM, Naqvi KR. Bacteriochlorophyll e monomers, but not aggregates, sensitize singlet oxygen: implications for a self-photoprotection mechanism in chlorosomes. Photochem Photobiol 2002; 76:373-80. [PMID: 12405142 DOI: 10.1562/0031-8655(2002)076<0373:bembna>2.0.co;2] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Sensitization of singlet delta oxygen (O2(1delta(g))) by bacteriochlorophyll e (BChle) has been investigated to gain a better understanding of the photoprotection mechanism(s) operating in chlorosomes of green photosynthetic bacteria. The sensitization process has been studied in media where BChle forms monomers (acetone and aqueous solutions containing 0.5% Triton X-100 [TX]) and in systems where BChle aggregates, namely, aqueous solutions containing 0.003% monogalactosyl diglyceride (MGDG) and chlorosomes(control as well as hexanol perturbed) from Chlorobium phaeobacteroides strain CL1401. In Ar-purged acetone, BChle triplets (BChle triplets) have a lifetime of a few tens of microseconds; however, in air-saturated acetone, quenching of BChle triplets by ground-state oxygen (O2(3sigma(-)g)) and formation of O2(1delta(g)) take place. The O2(1delta(g)) so formed is susceptible to quenching by BChle0, a ground-state BChle molecule. A Stern-Volmer analysis reveals a linear fit between the decay rate of O2(1delta(g)) and the BChle concentration. The rate constants for the quenching of O2(1delta(g)) by BChle0 and for the deactivation of O2(1delta(g)) by the solvent come out to be kq = (1.4 +/- 0.1) x 10(9) M(-1) s(-1) and k0 = (18.5 +/- 0.7) x 10(3) s(-1), respectively. The absolute quantum yield of O2(1delta(g)) sensitization by BChle monomers is 0.65 +/- 0.15 in air-saturated acetone. In aqueous phase, the triplet lifetime of BChle aggregates in native or hexanol-perturbed chlorosomes shortens by more than two orders of magnitude when compared with the triplet lifetime of BChle monomers in 0.5% TX solution (a few hundreds of microseconds). Quenching by carotenoids (Car) makes only a minor contribution to the decay of BChle triplets in aggregates. Because O2(1delta(g)) sensitization by BChle triplets could be detected neither in MGDG aggregates nor in chlorosomes (control as well as hexanol perturbed), it is concluded that (1) this process is highly likely when BChle is present as a monomer but not when it is tightly packed in artificial aggregates or in chlorosomes; and (2) Car, though vital for the baseplate BChla, are dispensable for BChle.
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Affiliation(s)
- Juan B Arellano
- Department of Physics, Norwegian University of Science and Technology, Trondheim.
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Arellano JB, Melø TB, Borrego CM, Garcia-Gil J, Naqvi KR. Nanosecond laser photolysis studies of chlorosomes and artificial aggregates containing bacteriochlorophyll e: evidence for the proximity of carotenoids and bacteriochlorophyll a in chlorosomes from Chlorobium phaeobacteroides strain CL1401. Photochem Photobiol 2000; 72:669-75. [PMID: 11107853 DOI: 10.1562/0031-8655(2000)072<0669:nlpsoc>2.0.co;2] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Time-resolved, laser-induced changes in absorbance, delta A(lambda; t), have been recorded with a view to probing pigment-pigment interactions in chlorosomes (control as well as carotenoid-depleted) and artificial aggregates of bacteriochlorophyll e (BChle). Control chlorosomes were isolated from Chlorobium phaeobacteroides strain CL1401, whose chromophores comprise BChle, bacteriochlorophyll a (BChla) and several carotenoid (Car) pigments; Car-depleted chlorosomes, from cells grown in cultures containing 2-hydroxybiphenyl. Artificial aggregates were prepared by dispersing BChle in aqueous phase in the presence of monogalactosyl diglyceride. In chlorosomes delta A(lambda; t) shows, besides a signal attributable to triplet Car (with a half-life of about 4 microseconds), signals in the Qy regions of both BChl. The BChla signal decays at the same rate as the Car signal, which is explained by postulating that some Car are in intimate contact with some baseplate BChla pigments, and that when a ground-state Car changes into a triplet Car, the absorption spectrum of its BChla neighbors undergoes a concomitant change (termed transient environment-induced perturbation). The signal in the Qy-region of BChle behaves differently: its amplitude falls, under reducing conditions, by more than a factor of two during the first 0.5 microsecond (a period during which the Car signal suffers negligible diminution), and is much smaller under nonreducing conditions. The BChle signal is also attributed to transient environment-induced perturbation, but in this case the perturber is a BChle photoproduct (probably a triplet or a radical ion). The absence of long-lived BChle triplets in all three systems, and of long-lived BChla triplets in chlorosomes, indicates that BChle in densely packed assemblies is less vulnerable to photodamage than monomeric BChle and that, in chlorosome, BChla rather than BChle needs, and receives, photoprotection from an adjacent Car.
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Affiliation(s)
- J B Arellano
- Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
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