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Hirozo Ohoka - One of the best experts on this subject based on the ideXlab platform.

  • sulfur oxidation in mutants of the photosynthetic green sulfur bacterium Chlorobium tepidum devoid of cytochrome c 554 and soxb
    Photosynthesis Research, 2009
    Co-Authors: Chihiro Azai, Yusuke Tsukatani, Jiro Harada, Hirozo Ohoka
    Abstract:

    A mutant devoid of cytochrome c-554 (CT0075) in Chlorobium tepidum (syn. Chlorobaculum tepidum) exhibited a decreased growth rate but normal growth yield when compared to the wild type. From quantitative determinations of sulfur compounds in media, the mutant was found to oxidize thiosulfate more slowly than the wild type but completely to sulfate as the wild type. This indicates that cytochrome c-554 would increase the rate of thiosulfate oxidation by serving as an efficient electron carrier but is not indispensable for thiosulfate oxidation itself. On the other hand, mutants in which a portion of the soxB gene (CT1021) was replaced with the aacC1 cassette did not grow at all in a medium containing only thiosulfate as an electron source. They exhibited partial growth yields in media containing only sulfide when compared to the wild type. This indicates that SoxB is not only essential for thiosulfate oxidation but also responsible for sulfide oxidation. An alternative electron carrier or electron transfer path would thus be operating between the Sox system and the reaction center in the mutant devoid of cytochrome c-554. Cytochrome c-554 might function in any other pathway(s) as well as the thiosulfate oxidation one, since even green sulfur bacteria that cannot oxidize thiosulfate contain a cycA gene encoding this electron carrier.

  • parallel electron donation pathways to cytochrome cz in the type i homodimeric photosynthetic reaction center complex of Chlorobium tepidum
    Biochimica et Biophysica Acta, 2008
    Co-Authors: Yusuke Tsukatani, Shigeru Itoh, Toru Kondo, Chihiro Azai, Hirozo Ohoka
    Abstract:

    Abstract We studied the regulation mechanism of electron donations from menaquinol:cytochrome c oxidoreductase and cytochrome c -554 to the type I homodimeric photosynthetic reaction center complex of the green sulfur bacterium Chlorobium tepidum . We measured flash-induced absorption changes of multiple cytochromes in the membranes prepared from a mutant devoid of cytochrome c -554 or in the reconstituted membranes by exogenously adding cytochrome c -555 purified from Chlorobium limicola . The results indicated that the photo-oxidized cytochrome c z bound to the reaction center was rereduced rapidly by cytochrome c -555 as well as by the menaquinol:cytochrome c oxidoreductase and that cytochrome c -555 did not function as a shuttle-like electron carrier between the menaquinol:cytochrome c oxidoreductase and cytochrome c z . It was also shown that the rereduction rate of cytochrome c z by cytochrome c -555 was as high as that by the menaquinol:cytochrome c oxidoreductase. The two electron-transfer pathways linked to sulfur metabolisms seem to function independently to donate electrons to the reaction center.

  • bifurcated electron donations from quinol oxidoreductase and soluble cyca to cytochrome cz of the photosynthetic reaction center complex in the green sulfur bacterium Chlorobium tepidum
    2008
    Co-Authors: Chihiro Azai, Yusuke Tsukatani, Ryo Miyamoto, Shigeru Itoh, Toru Kondo, Hiroumi Murakami, Hirozo Ohoka
    Abstract:

    In The Photosynthetic Green Sulfur Bacterium Chlorobium tepidum, The Photo-Oxidized Primary Electron Donor P840+ Is Rapidly Rereduced By Cytochrome CZ, One Of Subunits Of The Reaction Center Complex. The Oxidized Cytochrome CZ Can Be Rereduced By Either Soluble Low-Molecular-Weight Cytochrome C, Cyca, Or Membrane-Bound Quinol Oxidoreductase Directly. By Setting Up The Reconstitution System Using Membranes Prepared From A Mutant Devoid Of Cyca, We Investigated The Photosynthetic Electron Transfer Pathways When Both Of Them Co-Exist As They Do In Vivo. It Was Found That Quinol Oxidoreductase Never Donates Electrons To Cyca When It Can Donate To Cytochrome CZ, Making A Clear Contrast With The Case In Purple Bacteria Where Cytochrome Bc 1 Complex Donates Electrons To Cytochorme C2. The Analysis Of Photosynthetic Growth Profiles Using Mutants Defective In Sulfur Oxidations Suggests That Quinol Oxidoreductase And Cyca Serve As Electron Carriers In The Two Different Pathways, That Is, The Sulfide And Thiosulfate Oxidation One, Respectively.

  • soluble cytochrome c 554 cyca is not essential for photosynthetic electron transfer in Chlorobium tepidum
    FEBS Letters, 2006
    Co-Authors: Yusuke Tsukatani, Ryo Miyamoto, Shigeru Itoh, Hirozo Ohoka
    Abstract:

    Abstract We constructed a mutant lacking soluble cytochrome c -554 (CycA) by disruption of the cycA gene in the green sulfur bacterium Chlorobium tepidum . The mutant grew phototrophically with a growth rate slower than that of the wild type, suggesting that CycA is not essential for photosynthetic electron transfer even though CycA is known to work as an electron donor to the reaction center. The re-reduction of photo-oxidized cytochrome c z by quinol oxidoreductase was inhibited almost completely by the addition of stigmatellin in the mutant cells. This result indicates that, in the mutant cells, the linear electron transfer can occur from the quinol oxidoreductase to cytochrome c z , and to reaction center P840 with no participation of CycA.

  • crystallization and preliminary x ray diffraction study of bchu a methyltransferase from Chlorobium tepidum involved in bacteriochlorophyll c biosynthesis
    Acta Crystallographica Section F-structural Biology and Crystallization Communications, 2005
    Co-Authors: Jiro Harada, Hitoshi Tamiaki, Hirozo Ohoka, Kei Wada, Hitomi Yamaguchi, Keiichi Fukuyama
    Abstract:

    The S-adenosylmethionine-dependent methyltransferase BchU is an enzyme involved in the bacteriochlorophyll c biosynthetic pathway and catalyzes methylation at the C-20 position of the chlorin moiety. Recombinant Chlorobium tepidum BchU overproduced in Escherichia coli was purified and crystallized by the hanging-drop vapour-diffusion method using ammonium sulfate as a precipitant. The crystals belonged to the hexagonal space group P6122 or P6522, with unit-cell parameters a = b = 81.5, c = 250.7 A. A native data set was collected to 2.27 A resolution using synchrotron radiation at SPring-8.

Georgios Tsiotis - One of the best experts on this subject based on the ideXlab platform.

  • Membrane proteome of the green sulfur bacterium Chlorobium tepidum (syn. Chlorobaculum tepidum) analyzed by gel-based and gel-free methods
    Photosynthesis Research, 2010
    Co-Authors: Kalliopi Kouyianou, Michalis Aivaliotis, Kris Gevaert, Michael Karas, Georgios Tsiotis
    Abstract:

    Chlorobium tepidum is a Gram-negative bacterium of the green sulfur phylum ( Chlorobia ). Chlorobia are obligate anaerobic photolithoautotrophs that are widely distributed in aquatic environments where anoxic layers containing reduced sulfur compounds are exposed to light. The envelope of C. tepidum is a complex organelle composed of the outer membrane, the periplasm–peptidoglycan layer, and the cytoplasmic membrane. In addition to the outer and plasma membranes, C. tepidum contains chlorosomes attached to the cytoplasmic side of the plasma membrane. Each cellular compartment has a unique set of proteins, called sub-proteome. An important aim of proteome analysis is to study the level of the expressed genes and their response to environmental changes. Membrane protein studies are of primary importance to understand how nutrients are transported inside the cell, how toxic molecules are exported, and the mechanisms of photosynthesis and energy metabolism.

  • an alternative strategy for the membrane proteome analysis of the green sulfur bacterium Chlorobium tepidum using blue native page and 2 d page on purified membranes
    Journal of Proteome Research, 2007
    Co-Authors: Michalis Aivaliotis, Michael Karas, Georgios Tsiotis
    Abstract:

    To avoid the specific problems concerning intrinsic membrane proteins in proteome analysis, an alternative strategy is described that is complementary to previous investigations using 2-D polyacrylamide gel electrophoresis (PAGE) techniques. The strategy involves (a) obtaining purified preparations of the membranes from Chlorobium tepidum by washing with 2 M NaBr, which removed membrane-associated soluble proteins and membrane-associated organelles; (b) separation of membrane protein complexes using 1-D Blue-native polyacrylamide gel electrophoresis (BN-PAGE) after solubilization with n-dodecyl-β-d-maltoside (DDM); (c) combination of the BN with Tricine-SDS-PAGE; (d) high-throughput mass spectrometric analysis after gel band excision, in-gel digestion, and MALDI target spotting; and (e) protein identification from mixtures of tryptic peptides by peptide mass fingerprinting. Using this approach, we identified 143 different proteins, 70 of which have not been previously reported using 2-D PAGE techniques. M...

  • proteomic analysis of chlorosome depleted membranes of the green sulfur bacterium Chlorobium tepidum
    Proteomics, 2006
    Co-Authors: Michalis Aivaliotis, Michael Karas, Winfried Haase, Georgios Tsiotis
    Abstract:

    Green sulfur bacteria are obligate anaerobic phototrophs, which in addition to outer and plasma membranes contain chlorosomes. The analysis of the membrane proteome of Chlorobium tepidum from chlorosome-depleted membranes is described in this study. The membranes were purified by sucrose density centrifugation and characterized by 1-DE and 2-DE coupled with MS, absorption spectroscopy, and electron microscopy. 1-DE and 2-DE were employed to analyze the membrane proteins and to characterize the capabilities of the methods. Solubilization of the membrane proteins prior to 2-DE was improved by using a series of zwitterionic detergents. Based on the resolved spots after 2-DE, the combination of amidosulfobetaine 14 with Triton X-100 is more efficient than the combination of CHAPS, N-decyl-N,N-dimethyl-3-ammonio-1-propane sulfonate, and Triton X-100. From the application of 1-DE and 2-DE, 167 and 202 unique proteins were identified, respectively, using PMF by MALDI-TOF MS. Both methods resulted in the detection of 291 different proteins of which only 88 were predicted membrane proteins, indicating the limitation of membrane protein detection after separation with electrophoresis methods. In addition, 53 of these proteins were identified as outer membrane proteins.

  • membrane proteome analysis of the green sulfur bacterium Chlorobium tepidum
    Electrophoresis, 2004
    Co-Authors: Michalis Aivaliotis, Michael Karas, Carsten Corvey, Irene Tsirogianni, Georgios Tsiotis
    Abstract:

    An extensive proteomic approach relies on the possibility to visualize and analyze various types of proteins, including membrane proteins, which are rarely detectable on two-dimensional electrophoresis gels. In this study, different methods were employed for the enrichment of membrane proteins from Chlorobium tepidum prior to analysis with two-dimensional electrophoresis (2-DE). Isolated membranes were solubilized with Triton X-100 and from the supernatant we identified 58 unique proteins. The use of ionic sodium dodecyl sulfate (SDS) for protein solubilization, combined with acetone precipitation, resulted in an improved 2-DE pattern and the total number of the identified proteins was increased to 117. The use of acetone for protein precipitation improved the results by extracting compounds potentially deleterious to the resolution of 2-DE. However, the additional proteins detected by the use of SDS are in the majority more difficult to solubilize than less hydrophobic proteins. Further our attempts for selective extraction of the outer membrane proteins using the acid glycine method allowed the identification of 37 proteins of which 14 were predicted to have a signal sequence indicating their localization in the periplasmic space or in the outer membrane.

  • Isolation and Characterization of an Outer Membrane Protein of Chlorobium tepidum
    Photosynthesis research, 2004
    Co-Authors: Michalis Aivaliotis, Elefteria Neofotistou, Hervé-w. Rémigy, Georgios Tsimpinos, Ariel Lustig, Friedrich Lottspeich, Georgios Tsiotis
    Abstract:

    A protein was isolated from membranes of the green sulfur bacterium Chlorobium tepidum. This protein was characterized by gel electrophoresis, gel filtration, analytical ultracentrifugation and amino acid sequencing. The molecular weight of the purified protein was shown to be 26 kDa by SDS-PAGE. HPLC gelfiltration, SDS-PAGE and analytical ultracentrifugation are consistent with the presence of a homogenous protein in the preparations. Amino acid analysis was obtained from the isolated protein after fragmentation with Lys-C, trypsin and cyanogen bromide. The cleavage pattern resulting from these treatments combined with Edman sequencing yield a sequence allowing the identification of an integral membrane agglutinin in Chl. tepidum.

Donald A. Bryant - One of the best experts on this subject based on the ideXlab platform.

  • long range organization of bacteriochlorophyll in chlorosomes of Chlorobium tepidum investigated by cryo electron microscopy
    FEBS Letters, 2007
    Co-Authors: Gert T Oostergetel, Donald A. Bryant, Aline Gomez Maqueo Chew, Michael Reus, Egbert J Boekema, Alfred R. Holzwarth
    Abstract:

    Intact chlorosomes of Chlorobium tepidum were embedded in amorphous ice layers and examined by cryo-electron microscopy to study the long-range organization of bacteriochlorophyll (BChl) layers. End-on views reveal that chlorosomes are composed of several multi-layer tubules of variable diameter (20–30 nm) with some locally undulating non-tubular lamellae in between. The multi-layered tubular structures are more regular and larger in a C. tepidum mutant that only synthesizes [8-ethyl, 12-methyl]-BChl d. Our data show that wild-type C. tepidum chlorosomes do not have a highly regular, long-range BChl c layer organization and that they contain several multi-layered tubules rather than single-layer tubules or exclusively undulating lamellae as previously proposed.

  • x ray scattering and electron cryomicroscopy study on the effect of carotenoid biosynthesis to the structure of Chlorobium tepidum chlorosomes
    Biophysical Journal, 2007
    Co-Authors: Teemu P Ikonen, Niels-ulrik Frigaard, Donald A. Bryant, Jakub Psencik, Pasi Laurinmaki, Sarah J Butcher, Ritva Serimaa, Roman Tuma
    Abstract:

    Chlorosomes, the main antenna complexes of green photosynthetic bacteria, were isolated from null mutants of Chlorobium tepidum, each of which lacked one enzyme involved in the biosynthesis of carotenoids. The effects of the altered carotenoid composition on the structure of the chlorosomes were studied by means of x-ray scattering and electron cryomicroscopy. The chlorosomes from each mutant strain exhibited a lamellar arrangement of the bacteriochlorophyll c aggregates, which are the major constituents of the chlorosome interior. However, the carotenoid content and composition had a pronounced effect on chlorosome biogenesis and structure. The results indicate that carotenoids with a sufficiently long conjugated system are important for the biogenesis of the chlorosome baseplate. Defects in the baseplate structure affected the shape of the chlorosomes and were correlated with differences in the arrangement of lamellae and spacing between the lamellar planes of bacteriochlorophyll aggregates. In addition, comparisons among the various mutants enabled refinement of the assignments of the x-ray scattering peaks. While the main scattering peaks come from the lamellar structure of bacteriochlorophyll c aggregates, some minor peaks may originate from the paracrystalline arrangement of CsmA in the baseplate.

  • triplet exciton formation as a novel photoprotection mechanism in chlorosomes of Chlorobium tepidum
    Biophysical Journal, 2007
    Co-Authors: Hanyoup Kim, Donald A. Bryant, Julia A. Maresca, Sergei Savikhin
    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 ∼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.

  • two genes encoding new carotenoid modifying enzymes in the green sulfur bacterium Chlorobium tepidum
    Journal of Bacteriology, 2006
    Co-Authors: Julia A. Maresca, Donald A. Bryant
    Abstract:

    The green sulfur bacterium Chlorobium tepidum produces chlorobactene as its primary carotenoid. Small amounts of chlorobactene are hydroxylated by the enzyme CrtC and then glucosylated and acylated to produce chlorobactene glucoside laurate. The genes encoding the enzymes responsible for these modifications of chlorobactene, CT1987, and CT0967, have been identified by comparative genomics, and these genes were insertionally inactivated in C. tepidum to verify their predicted function. The gene encoding chlorobactene glucosyltransferase (CT1987) has been named cruC, and the gene encoding chlorobactene lauroyltransferase (CT0967) has been named cruD. Homologs of these genes are found in the genomes of all sequenced green sulfur bacteria and filamentous anoxygenic phototrophs as well as in the genomes of several nonphotosynthetic bacteria that produce similarly modified carotenoids. The other bacteria in which these genes are found are not closely related to green sulfur bacteria or to one another. This suggests that the ability to synthesize modified carotenoids has been a frequently transferred trait.

  • molecular contacts for chlorosome envelope proteins revealed by cross linking studies with chlorosomes from Chlorobium tepidum
    Biochemistry, 2006
    Co-Authors: Niels-ulrik Frigaard, Donald A. Bryant
    Abstract:

    Chlorosomes are unique light-harvesting antennae found in two phyla of green bacteria: Chlorobi and Chloroflexi. In the green sulfur bacterium Chlorobium tepidum, 10 proteins (CsmA, CsmB, CsmC, CsmD, CsmE, CsmF, CsmH, CsmI, CsmJ, and CsmX) exist in the chlorosome envelope. Chlorosomes from the wild type and mutants lacking a single chlorosome protein were cross-linked with the zero-length cross-linker 1-ethyl-3-[3-(dimethylamino)propyl]carbodiimide (EDC) and analyzed by gel electrophoresis. Similar cross-linking products were observed when the time and temperature were varied or when EDC was replaced with glutaraldehyde. Specific interactions between chlorosome proteins in cross-linked products were identified by immunoblotting with polyclonal antibodies raised against recombinant chlorosome proteins. We confirmed these interactions by demonstrating that these products were missing in appropriate mutants. Confirming the location of CsmA in the paracrystalline baseplate, cross-linking showed that CsmA forms dimers, trimers, and homomultimers as large as dodecamers and that CsmA directly interacts with the Fenna-Matthews-Olson protein. Cross-linking further suggests that the precursor form of CsmA is inserted near the edges of the baseplate, where CsmA and pre-CsmA interact with CsmB and CsmF. Several chlorosome proteins, including CsmA, CsmC, CsmD, CsmH, CsmI, CsmJ, and CsmX, were shown to exist as homomultimers in the chlorosome envelope. On the basis of the structural information obtained from these cross-linking experiments, a model for the locations and interactions of the proteins of the chlorosome envelope is proposed.

Robert E Blankenship - One of the best experts on this subject based on the ideXlab platform.

  • excitonic energy landscape of the y16f mutant of the Chlorobium tepidum fenna matthews olson fmo complex high resolution spectroscopic and modeling studies
    Journal of Physical Chemistry B, 2018
    Co-Authors: Anton Khmelnitskiy, Robert E Blankenship, Rafael G Saer, Ryszard Jankowiak
    Abstract:

    We report high-resolution (low-temperature) absorption, emission, and nonresonant/resonant hole-burned (HB) spectra and results of excitonic calculations using a non-Markovian reduced density matrix theory (with an improved algorithm for parameter optimization in heterogeneous samples) obtained for the Y16F mutant of the Fenna–Matthews–Olson (FMO) trimer from the green sulfur bacterium Chlorobium tepidum. We show that the Y16F mutant is a mixture of FMO complexes with three independent low-energy traps (located near 817, 821, and 826 nm), in agreement with measured composite emission and HB spectra. Two of these traps belong to mutated FMO subpopulations characterized by significantly modified low-energy excitonic states. Hamiltonians for the two major subpopulations (Sub821 and Sub817) provide new insight into extensive changes induced by the single-point mutation in the vicinity of BChl 3 (where tyrosine Y16 was replaced with phenylalanine F16). The average decay time(s) from the higher exciton state(s)...

  • Excitonic Energy Landscape of the Y16F Mutant of the Chlorobium tepidum Fenna–Matthews–Olson (FMO) Complex: High Resolution Spectroscopic and Modeling Studies
    2018
    Co-Authors: Anton Khmelnitskiy, Robert E Blankenship, Rafael G Saer, Ryszard Jankowiak
    Abstract:

    We report high-resolution (low-temperature) absorption, emission, and nonresonant/resonant hole-burned (HB) spectra and results of excitonic calculations using a non-Markovian reduced density matrix theory (with an improved algorithm for parameter optimization in heterogeneous samples) obtained for the Y16F mutant of the Fenna–Matthews–Olson (FMO) trimer from the green sulfur bacterium Chlorobium tepidum. We show that the Y16F mutant is a mixture of FMO complexes with three independent low-energy traps (located near 817, 821, and 826 nm), in agreement with measured composite emission and HB spectra. Two of these traps belong to mutated FMO subpopulations characterized by significantly modified low-energy excitonic states. Hamiltonians for the two major subpopulations (Sub821 and Sub817) provide new insight into extensive changes induced by the single-point mutation in the vicinity of BChl 3 (where tyrosine Y16 was replaced with phenylalanine F16). The average decay time(s) from the higher exciton state(s) in the Y16F mutant depends on frequency and occurs on a picosecond time scale

  • the structure of the fmo protein from Chlorobium tepidum at 2 2 a resolution
    Photosynthesis Research, 2003
    Co-Authors: A Camaraartigas, Robert E Blankenship, James P Allen
    Abstract:

    The bacteriochlorophyll protein, or FMO protein, from Chlorobium tepidum, which serves as a light-harvesting complex and directs light energy from the chlorosomes attached to the cell membrane to the reaction center has been crystallized in a new space group. The crystals belong to the cubic space group P4(3)32 and the structure has been refined to a resolution 2.2 A with a R factor of 19.7%. The electron density maps show that the structure is composed of two beta sheets that surround seven bacteriochlorophylls as previously reported (Li et al. (1997) J Mol Biol 271: 456-471). The availability of the new data allows a more accurate refinement of the pigment-protein complex including identification of bound solvent molecules. Several structural differences probably contribute to the observed spectroscopic differences between the FMO proteins from Cb. tepidum and Prosthecochloris aestuarii, including differences in the planarity of corresponding tetrapyrroles. A citrate molecule is found on the surface of each protein subunit of the trimer from Cb. tepidum. However, the citrate molecule is over 15 A from any bacteriochlorophyll. The presence of the citrate probably does not contribute to the function of the protein although it does contribute to the crystallization as it interacts with a crystallographically related trimer. Among the 236 water molecules found in the protein are four that appear to play a special role in the properties of bacteriochlorophyll 2, as this tetrapyrrole is coordinated by one of these water molecules and the waters form a hydrogen-bonded network that leads to the surface of the protein.

  • high pressure and stark hole burning studies of chlorosome antennas from Chlorobium tepidum
    Biophysical Journal, 2000
    Co-Authors: M Ratsep, Ryszard Jankowiak, C S Young, Robert E Blankenship, G J Small
    Abstract:

    Abstract Results from high-pressure and Stark hole-burning experiments on isolated chlorosomes from the green sulfur bacterium Chlorobium tepidum are presented, as well as Stark hole-burning data for bacteriochlorophyll c (BChl c ) monomers in a poly(vinyl butyral) copolymer film. Large linear pressure shift rates of −0.44 and −0.54cm −1 /MPa were observed for the chlorosome BChl c Q y -band at 100K and the lowest Q y -exciton level at 12K, respectively. It is argued that approximately half of the latter shift rate is due to electron exchange coupling between BChl c molecules. The similarity between the above shift rates and those observed for the B875 and B850 BChl a rings of the light-harvesting complexes of purple bacteria is emphasized. For BChl c monomer, ƒΔ μ =0.35 D, where Δ μ is the dipole moment change for the Q y transition and ƒ is the local field correction factor. The data establish that Δ μ is dominated by the matrix-induced contribution. The change in polarizability (Δ α ) for the Q y transition of the BChl c monomer is estimated at 19A 3 , which is essentially identical to that of the Chl a monomer. Interestingly, no Stark effects were observed for the lowest exciton level of the chlorosomes (maximum Stark field of 10 5 V/cm). Possible explanations for this are given, and these include consideration of structural models for the chlorosome BChl c aggregates.

  • transient absorption spectroscopy of energy transfer and trapping processes in the reaction center complex of Chlorobium tepidum
    Journal of Physical Chemistry B, 1998
    Co-Authors: Hirozo Ohoka, Shoichiro Kamei, Hiroshi Matsubara, Su Lin, Paula I Van Noort, Robert E Blankenship
    Abstract:

    Reaction center complexes from the green sulfur bacterium Chlorobium tepidum were examined using picosecond absorption difference spectroscopy at room temperature. The complexes include the core proteins containing the primary electron donor P840 and associated core antenna pigments and also include some of the Fenna−Matthews−Olson (FMO) antenna protein. Upon excitation at 590 nm, long-lived absorption difference changes were observed that are interpreted to arise from a combination of the excited FMO protein and the P840-containing complex. Most of the FMO protein does not transfer energy to the core in this preparation. Excitation at 840 nm directly into the core complex gave an overall excited-state decay of 35 ps, forming the long-lived charge-separated state P840+A0- and no excited FMO complex. No antenna components were observed with absorption at wavelengths longer than the primary donor, in contrast to the situation in the related reaction centers from heliobacteria and photosystem I.

Mette Miller - One of the best experts on this subject based on the ideXlab platform.

  • the three dimensional structure of csma a small antenna protein from the green sulfur bacterium Chlorobium tepidum
    FEBS Letters, 2008
    Co-Authors: Marie Ostergaard Pedersen, Mette Miller, Jarl Underhaug, Jens Dittmer, Niels Christian Nielsen
    Abstract:

    The structure of the chlorosome baseplate protein CsmA from Chlorobium tepidum in a 1:1 chloroform:methanol solution was determined using liquid-state NMR spectroscopy. The data reveal that the 59-residue protein is predominantly α-helical with a long helical domain extending from residues V6 to L36, containing a putative bacteriochlorophyll a binding domain, and a short helix in the C-terminal part extending from residues M41 to G49. These elements are compatible with a model of CsmA having the long N-terminal α-helical stretch immersed into the lipid monolayer confining the chlorosome and the short C-terminal helix protruding outwards, thus available for interaction with the Fenna–Matthews–Olson antenna protein.

  • chlorosome lipids from Chlorobium tepidum characterization and quantification of polar lipids and wax esters
    Photosynthesis Research, 2008
    Co-Authors: Peder Grove Sorensen, Mette Miller
    Abstract:

    We have extracted polar lipids and waxes from isolated chlorosomes from the green sulfur bacterium Chlorobium tepidum and determined the fatty acid composition of each lipid class. Polar lipids amounted to 4.8 mol per 100 mol bacteriochlorophyll in the chlorosomes, while non-polar lipids (waxes) were present at a ratio of 5.9 mol per 100 mol bacteriochlorophyll. Glycolipids constitute 60 % of the polar lipids while phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine, and an aminoglycosphingolipid make up respectively 15, 3, 8 and 12 %. A novel glycolipid was identified as a rhamnose derivative of monogalactosyldiacylglycerol, while the other major glycolipid was monogalactosyldiacylglycerol. Tetradecanoic acid was the major fatty acid in the aminoglycosphingolipid, while the other polar lipids contained predominantly hexandecanoic acid. The chlorosome waxes are esters of unbranched fatty acids and fatty alcohols with 14 or 16 carbon atoms, joined to form molecules with between 28 and 32 carbon atoms. The stoichiometry between lipids and bacteriochlorophyll suggests that much of the chlorosome surface is covered by protein.

  • a reconstituted light harvesting complex from the green sulfur bacterium Chlorobium tepidum containing csma and bacteriochlorophyll a
    Biochemistry, 2008
    Co-Authors: Marie Ostergaard Pedersen, Dorte Bjerre Steensgaard, Lan Pham, Mette Miller
    Abstract:

    Green sulfur bacteria possess two light-harvesting antenna systems, the chlorosome and the Fenna-Matthews-Olson (FMO) protein. In addition to self-aggregated bacteriochlorophyll (BChl) c, chlorosomes of Chlorobium tepidum contain a small amount of BChl a (ratio 100:1). The chlorosomal BChl a is associated with CsmA, a 6.2 kDa protein that accounts for more than 50% of the protein content of chlorosomes. This CsmA-BChl a complex is located in the chlorosome baseplate with the hydrophilic C-terminal part of CsmA in contact with the FMO protein. CsmA was purified from Chl. tepidum. Isolated chlorosomes were lyophilized and extracted with chloroform/methanol (1:1, v/v). The extract was further purified using gel filtration and reverse-phase HPLC and the purity of the preparation confirmed by SDS-PAGE. Mass spectrometric analysis showed an m/z of 6154.8, in agreement with the calculated mass of the csmA gene product after C-terminal processing. CD spectroscopy of the isolated protein showed that the main structural motif was an alpha-helix. We have reconstituted the isolated CsmA protein with BChl a in micelles of n-octyl beta-d-glucopyranoside. The resulting preparation reproduced the spectral characteristics of the CsmA-BChl a complex present in the chlorosome baseplate.

  • Effect of Alkaline Treatment on Bacteriochlorophyll a, Quinones and Energy Transfer in Chlorosomes from Chlorobium tepidum and Chlorobium phaeobacteroides
    Photochemistry and Photobiology, 2008
    Co-Authors: Cornelis A. Van Walree, Yumiko Sakuragi, Dorte Bjerre Steensgaard, Carola S. Bösinger, Niels-ulrik Frigaard, Raymond P. Cox, Alfred R. Holzwarth, Mette Miller
    Abstract:

    — Chlorosomes isolated from two types of green sulfur bacteria, Chlorobium tepidum which contains bacteriochlorophyll c (BChl c) and the BChl e-containing Chlorobium phaeobacteroides, were subjected to alkaline treatment (pH 12.7 at 40°C for 20 min). This caused selective degradation of BChl a, whereas BChl c or e were not affected. Chlorobiumquinone in the Chlorosomes was partially degraded by the alkaline treatment but menaquinone was unchanged. Fluorescence decay kinetics showed that alkaline treatment disrupted energy transfer from BChl c or e to BChl a under reducing conditions. However, this did not give rise to any substantial increase in the excited state lifetime of BChl e in C. phaeobacteroides Chlorosomes, while for C. tepidum a decrease in the BChl c lifetime was found. The steady-state fluorescence of chlorosomes is highly dependent on the redox potential such that emission is quenched in oxidizing environments. Alkaline treatment diminished this quenching effect and caused a doubling in the BChl c or e emission intensity under aerobic conditions. Single-photon timing experiments confirmed that alkaline treatment inhibits the energy trapping process operative under aerobic conditions. These effects of alkaline treatment on the fluorescence intensity and decay kinetics are likely to be related to the depletion in BChl a or in Chlorobiumquinone or a combination of these.

  • The light-harvesting antenna of Chlorobium tepidum: Interactions between the FMO protein and the major chlorosome protein CsmA studied by surface plasmon resonance
    Photosynthesis Research, 2006
    Co-Authors: Marie Ostergaard Pedersen, Raymond P. Cox, Jonas Borch, Peter Højrup, Mette Miller
    Abstract:

    Green sulfur bacteria possess two external light-harvesting antenna systems, the chlorosome and the FMO protein, which participate in a sequential energy transfer to the reaction centers embedded in the cytoplasmic membrane. However, little is known about the physical interaction between these two antenna systems. We have studied the interaction between the major chlorosome protein, CsmA, and the FMO protein in Chlorobium tepidum using surface plasmon resonance (SPR). Our results show an interaction between the FMO protein and an immobilized synthetic peptide corresponding to 17 amino acids at the C terminal of CsmA. This interaction is dependent on the presence of a motif comprising six amino acids that are highly conserved in all the currently available CsmA protein sequences.