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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. Q-band hyperchromism and B-band hypochromism of bacteriochlorophyll c as a tool for investigation of the oligomeric structure of chlorosomes of the green photosynthetic bacterium Chloroflexus aurantiacus. PHOTOSYNTHESIS RESEARCH 2020; 146:95-108. [PMID: 31939070 DOI: 10.1007/s11120-019-00707-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 12/31/2019] [Indexed: 06/10/2023]
Abstract
Chlorosomes of green photosynthetic bacteria are the most amazing example of long-range ordered natural light-harvesting antennae. Chlorosomes are the largest among all known photosynthetic light-harvesting structures (~ 104-105 pigments in the aggregated state). The chlorosomal bacteriochlorophyll (BChl) c/d/e molecules are organized via self-assembly and do not require proteins to provide a scaffold for efficient light harvesting. Despite numerous investigations, a consensus regarding the spatial structure of chlorosomal antennae has not yet been reached. In the present work, we studied hyperchromism/hypochromism in the chlorosomal BChl c Q/B absorption bands of the green photosynthetic bacterium Chloroflexus (Cfx.) aurantiacus. The chlorosomes were isolated from cells grown under different light intensities and therefore, as we discovered earlier, they had different sizes of both BChl c antennae and their unit building blocks. We have shown experimentally that the Q-/B-band hyperchromism/hypochromism is proportional to the size of the chlorosomal antenna. We explained theoretically these findings in terms of excitonic intensity borrowing between the Q and B bands for the J-/H-aggregates of the BChls. The theory developed by Gülen (Photosynth Res 87:205-214, 2006) showed the dependence of the Q-/B-band hyperchromism/hypochromism on the structure of the aggregates. For the model of exciton-coupled BChl c linear chains within a unit building block, the theory predicted an increase in the hyperchromism/hypochromism with the increase in the number of molecules per chain and a decrease in it with the increase in the number of chains. It was previously shown that this model ensured a good fit with spectroscopy experiments and approximated the BChl c low packing density in vivo. The presented experimental and theoretical studies of the Q-/B-band hyperchromism/hypochromism permitted us to conclude that the unit building block of Cfx. aurantiacus chlorosomes comprises of several short BChl c chains.This conclusion is in accordance with previous linear and nonlinear spectroscopy studies on Cfx. aurantiacus chlorosomes.
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Affiliation(s)
- Andrei G Yakovlev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991.
| | - Alexandra S Taisova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991
| | - Zoya G Fetisova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991.
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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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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: 35] [Impact Index Per Article: 5.8] [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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Yakovlev A, Taisova A, Arutyunyan A, Shuvalov V, Fetisova Z. Variability of aggregation extent of light-harvesting pigments in peripheral antenna of Chloroflexus aurantiacus. PHOTOSYNTHESIS RESEARCH 2017; 133:343-356. [PMID: 28361448 DOI: 10.1007/s11120-017-0374-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2016] [Accepted: 03/21/2017] [Indexed: 06/07/2023]
Abstract
The stationary ground state and femtosecond time-resolved absorption spectra as well as spectra of circular dichroism were measured at room temperature using freshly prepared samples of chlorosomes isolated from fresh cultures of the green bacterium Chloroflexus aurantiacus. Cultures were grown by using as inoculum the same seed culture but under different light conditions. All measured spectra clearly showed the red shift of BChl c Qy bands (up to 5 nm) for low-light chlorosomes as compared to high-light ones, together with concomitant narrowing of these bands and increasing of their amplitudes. The sizes of the unit BChl c aggregates of the high-light-chlorosomes and the low-light ones were estimated. The fit of all experimental spectra was obtained within the framework of our model proposed before (Fetisova et al., Biophys J 71:995-101, 1996). The model assumes that a unit building block of the BChl c antenna has a form of a tubular aggregate of L = 6 linear single or double exciton-coupled pigment chains within a rod element, with the pigment packing density, approximating that in vivo. The simultaneous fit of all experimental spectra gave the number of pigments in each individual linear pigment chain N = 4 and N = 6 for the high-light and the low-light BChl c unit building blocks, respectively. The size of a unit building block in the BChl c antenna was found to vary from L × N = 24 to L × N = 36 exciton-coupled BChl c molecules being governed by the growth-light intensity. All sets of findings for Chloroflexus aurantiacus chlorosomes demonstrated the biologically expedient light-controlled variability, predicted by us, of the extent of BChl c aggregation within a unit building block in this antenna.
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Affiliation(s)
- Andrei Yakovlev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991.
| | - Alexandra Taisova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991
| | - Alexander Arutyunyan
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991
| | - Vladimir Shuvalov
- Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region, Russian Federation, 142290
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991
| | - Zoya Fetisova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow, Russian Federation, 119991.
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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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Yakovlev A, Novoderezhkin V, Taisova A, Shuvalov V, Fetisova Z. Orientation of B798 BChl a Q y transition dipoles in Chloroflexus aurantiacus chlorosomes: polarized transient absorption spectroscopy studies. PHOTOSYNTHESIS RESEARCH 2015; 125:31-42. [PMID: 25515768 DOI: 10.1007/s11120-014-0060-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Accepted: 11/16/2014] [Indexed: 06/04/2023]
Abstract
Isotropic and anisotropic pump-probe spectra of Cfx. aurantiacus chlorosomes were measured on the fs-through ps-time scales for the B798 BChl a Q y band upon direct excitation of the B798 band at T = 293 K and T = 90 K. Upon direct excitation of the B798 band, the anisotropy parameter value r(λ) was constant within the whole BChl a Q y band at any delay time at both temperatures. The value of the anisotropy parameter r decayed from r = 0.4 at both temperatures (at 200 fs delay time after excitation) to the steady-state values r = 0.1 at T = 293 K and to r = 0.09 at T = 90 K (at 30 ÷ 100 ps delay time after excitation). The results were considered within the framework of the model of uniaxial orientation distribution of BChl-a transition dipoles within a single Cfx. aurantiacus chlorosome. This implies that the B798 BChl a Q y transition dipoles, randomly distributed around the normal to the baseplate plane, form the angle θ with the plane. For this model, the theoretical dependence of the steady-state anisotropy parameter r on the angle θ was derived. According to the theoretical dependence r(θ), the angle θ corresponding to the experimental steady-state value r = 0.1 at T = 293 K was found to equal 55°. As the temperature drops to 90 K, the angle θ decreases to 54°.
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Affiliation(s)
- Andrei Yakovlev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 119991, Moscow, Russian Federation
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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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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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Oostergetel GT, van Amerongen H, Boekema EJ. The chlorosome: a prototype for efficient light harvesting in photosynthesis. PHOTOSYNTHESIS RESEARCH 2010; 104:245-55. [PMID: 20130996 PMCID: PMC2882566 DOI: 10.1007/s11120-010-9533-0] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Accepted: 01/16/2010] [Indexed: 05/18/2023]
Abstract
Three phyla of bacteria include phototrophs that contain unique antenna systems, chlorosomes, as the principal light-harvesting apparatus. Chlorosomes are the largest known supramolecular antenna systems and contain hundreds of thousands of BChl c/d/e molecules enclosed by a single membrane leaflet and a baseplate. The BChl pigments are organized via self-assembly and do not require proteins to provide a scaffold for efficient light harvesting. Their excitation energy flows via a small protein, CsmA embedded in the baseplate to the photosynthetic reaction centres. Chlorosomes allow for photosynthesis at very low light intensities by ultra-rapid transfer of excitations to reaction centres and enable organisms with chlorosomes to live at extraordinarily low light intensities under which no other phototrophic organisms can grow. This article reviews several aspects of chlorosomes: the supramolecular and molecular organizations and the light-harvesting and spectroscopic properties. In addition, it provides some novel information about the organization of the baseplate.
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Affiliation(s)
- Gert T. Oostergetel
- Biophysical Chemistry, Groningen Biomolecular Sciences & Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Herbert van Amerongen
- Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, The Netherlands
| | - Egbert J. Boekema
- Biophysical Chemistry, Groningen Biomolecular Sciences & Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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Psencík J, Torkkeli M, Zupcanová A, Vácha F, Serimaa RE, Tuma R. The lamellar spacing in self-assembling bacteriochlorophyll aggregates is proportional to the length of the esterifying alcohol. PHOTOSYNTHESIS RESEARCH 2010; 104:211-219. [PMID: 20306134 DOI: 10.1007/s11120-010-9541-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2009] [Accepted: 02/24/2010] [Indexed: 05/29/2023]
Abstract
Chlorosomes from green photosynthetic bacteria are large photosynthetic antennae containing self-assembling aggregates of bacteriochlorophyll c, d, or e. The pigments within chlorosomes are organized in curved lamellar structures. Aggregates with similar optical properties can be prepared in vitro, both in polar as well as non-polar solvents. In order to gain insight into their structure we examined hexane-induced aggregates of purified bacteriochlorophyll c by X-ray scattering. The bacteriochlorophyll c aggregates exhibit scattering features that are virtually identical to those of native chlorosomes demonstrating that the self-assembly of these pigments is fully encoded in their chemical structure. Thus, the hexane-induced aggregates constitute an excellent model to study the effects of chemical structure on assembly. Using bacteriochlorophyllides transesterified with different alcohols we have established a linear relationship between the esterifying alcohol length and the lamellar spacing. The results provide a structural basis for lamellar spacing variability observed for native chlorosomes from different species. A plausible physiological role of this variability is discussed. The X-ray scattering also confirmed the assignments of peaks, which arise from the crystalline baseplate in the native chlorosomes.
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Affiliation(s)
- Jakub Psencík
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic.
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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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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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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, 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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Blankenship RE, Matsuura K. Antenna Complexes from Green Photosynthetic Bacteria. LIGHT-HARVESTING ANTENNAS IN PHOTOSYNTHESIS 2003. [DOI: 10.1007/978-94-017-2087-8_6] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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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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