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Cryo-EM structures of the Synechocystis sp. PCC 6803 cytochrome b6f complex with and without the regulatory PetP subunit. Biochem J 2022; 479:1487-1503. [PMID: 35726684 PMCID: PMC9342900 DOI: 10.1042/bcj20220124] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2022] [Revised: 06/01/2022] [Accepted: 06/21/2022] [Indexed: 11/17/2022]
Abstract
In oxygenic photosynthesis, the cytochrome b6f (cytb6f) complex links the linear electron transfer (LET) reactions occurring at photosystems I and II and generates a transmembrane proton gradient via the Q-cycle. In addition to this central role in LET, cytb6f also participates in a range of processes including cyclic electron transfer (CET), state transitions and photosynthetic control. Many of the regulatory roles of cytb6f are facilitated by auxiliary proteins that differ depending upon the species, yet because of their weak and transient nature the structural details of these interactions remain unknown. An apparent key player in the regulatory balance between LET and CET in cyanobacteria is PetP, a ∼10 kDa protein that is also found in red algae but not in green algae and plants. Here, we used cryogenic electron microscopy to determine the structure of the Synechocystis sp. PCC 6803 cytb6f complex in the presence and absence of PetP. Our structures show that PetP interacts with the cytoplasmic side of cytb6f, displacing the C-terminus of the PetG subunit and shielding the C-terminus of cytochrome b6, which binds the heme cn cofactor that is suggested to mediate CET. The structures also highlight key differences in the mode of plastoquinone binding between cyanobacterial and plant cytb6f complexes, which we suggest may reflect the unique combination of photosynthetic and respiratory electron transfer in cyanobacterial thylakoid membranes. The structure of cytb6f from a model cyanobacterial species amenable to genetic engineering will enhance future site-directed mutagenesis studies of structure-function relationships in this crucial ET complex.
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Gisriel CJ, Wang J, Brudvig GW, Bryant DA. Opportunities and challenges for assigning cofactors in cryo-EM density maps of chlorophyll-containing proteins. Commun Biol 2020; 3:408. [PMID: 32733087 PMCID: PMC7393486 DOI: 10.1038/s42003-020-01139-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2020] [Accepted: 07/10/2020] [Indexed: 01/21/2023] Open
Abstract
The accurate assignment of cofactors in cryo-electron microscopy maps is crucial in determining protein function. This is particularly true for chlorophylls (Chls), for which small structural differences lead to important functional differences. Recent cryo-electron microscopy structures of Chl-containing protein complexes exemplify the difficulties in distinguishing Chl b and Chl f from Chl a. We use these structures as examples to discuss general issues arising from local resolution differences, properties of electrostatic potential maps, and the chemical environment which must be considered to make accurate assignments. We offer suggestions for how to improve the reliability of such assignments. In this Perspective, Christopher Gisriel et al. discuss the challenges in accurate assignment of co-factors in cryo-EM, particularly for chlorophylls. They explore the factors that lead to misassignment and offer suggestions for improving reliability of cryo-EM-based assignments.
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Affiliation(s)
| | - Jimin Wang
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Gary W Brudvig
- Department of Chemistry, Yale University, New Haven, CT, 06520, USA.,Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Donald A Bryant
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA.,Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT, 59717, USA
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3
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The Complex Transcriptional Response of Acaryochloris marina to Different Oxygen Levels. G3-GENES GENOMES GENETICS 2017; 7:517-532. [PMID: 27974439 PMCID: PMC5295598 DOI: 10.1534/g3.116.036855] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Ancient oxygenic photosynthetic prokaryotes produced oxygen as a waste product, but existed for a long time under an oxygen-free (anoxic) atmosphere, before an oxic atmosphere emerged. The change in oxygen levels in the atmosphere influenced the chemistry and structure of many enzymes that contained prosthetic groups that were inactivated by oxygen. In the genome of Acaryochloris marina, multiple gene copies exist for proteins that are normally encoded by a single gene copy in other cyanobacteria. Using high throughput RNA sequencing to profile transcriptome responses from cells grown under microoxic and hyperoxic conditions, we detected 8446 transcripts out of the 8462 annotated genes in the Cyanobase database. Two-thirds of the 50 most abundant transcripts are key proteins in photosynthesis. Microoxic conditions negatively affected the levels of expression of genes encoding photosynthetic complexes, with the exception of some subunits. In addition to the known regulation of the multiple copies of psbA, we detected a similar transcriptional pattern for psbJ and psbU, which might play a key role in the altered components of photosystem II. Furthermore, regulation of genes encoding proteins important for reactive oxygen species-scavenging is discussed at genome level, including, for the first time, specific small RNAs having possible regulatory roles under varying oxygen levels.
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Simon DP, Anila N, Gayathri K, Sarada R. Heterologous expression of β-carotene hydroxylase in Dunaliella salina by Agrobacterium -mediated genetic transformation. ALGAL RES 2016. [DOI: 10.1016/j.algal.2016.06.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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5
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Chauvet AAP, Agarwal R, Haddad AA, van Mourik F, Cramer WA. Photo-induced oxidation of the uniquely liganded heme f in the cytochrome b6f complex of oxygenic photosynthesis. Phys Chem Chem Phys 2016; 18:12983-91. [PMID: 27108913 PMCID: PMC4990003 DOI: 10.1039/c6cp01592a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The ultrafast behavior of the ferrous heme f from the cytochrome b6f complex of oxygenic photosynthesis is revealed by means of transient absorption spectroscopy. Benefiting from the use of microfluidic technologies for handling the sample as well as from a complementary frame-by-frame analysis of the heme dynamics, the different relaxation mechanisms from vibrationally excited states are disentangled and monitored via the shifts of the heme α-absorption band. Under 520 nm laser excitation, about 85% of the heme f undergoes pulse-limited photo-oxidation (<100 fs), with the electron acceptor being most probably one of the adjacent aromatic amino acid residues. After charge recombination in 5.3 ps, the residual excess energy is dissipated in 3.6 ps. In a parallel pathway, the remaining 15% of the hemes directly relax from their excited state in 2.5 ps. In contrast to a vast variety of heme-proteins, including the homologous heme c1 from the cytochrome bc1 complex, there is no evidence that heme f photo-dissociates from its axial ligands. Due to its unique binding, with histidine and an unusual tyrosine as axial ligands, the heme f exemplifies a dependence of ultrafast dynamics on the structural environment.
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Affiliation(s)
- Adrien A P Chauvet
- Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Spectroscopie Ultrarapide (LSU), ISIC, Faculté des Sciences de Base and Lausanne Centre for Ultrafast Science (LACUS), Station 6, 1015 Lausanne, Switzerland.
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Vladkova R. Chlorophyllais the crucial redox sensor and transmembrane signal transmitter in the cytochromeb6fcomplex. Components and mechanisms of state transitions from the hydrophobic mismatch viewpoint. J Biomol Struct Dyn 2015; 34:824-54. [DOI: 10.1080/07391102.2015.1056551] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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7
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Hasan SS, Zakharov SD, Chauvet A, Stadnytskyi V, Savikhin S, Cramer WA. A map of dielectric heterogeneity in a membrane protein: the hetero-oligomeric cytochrome b6f complex. J Phys Chem B 2014; 118:6614-25. [PMID: 24867491 PMCID: PMC4067154 DOI: 10.1021/jp501165k] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
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The
cytochrome b6f complex,
a member of the cytochrome bc family that
mediates energy transduction in photosynthetic and respiratory membranes,
is a hetero-oligomeric complex that utilizes two pairs of b-hemes in a symmetric dimer to accomplish trans-membrane
electron transfer, quinone oxidation–reduction, and generation
of a proton electrochemical potential. Analysis of electron storage
in this pathway, utilizing simultaneous measurement of heme reduction,
and of circular dichroism (CD) spectra, to assay heme–heme
interactions, implies a heterogeneous distribution of the dielectric
constants that mediate electrostatic interactions between the four
hemes in the complex. Crystallographic information was used to determine
the identity of the interacting hemes. The Soret band CD signal is
dominated by excitonic interaction between the intramonomer b-hemes, bn and bp, on the electrochemically negative and positive sides
of the complex. Kinetic data imply that the most probable pathway
for transfer of the two electrons needed for quinone oxidation–reduction
utilizes this intramonomer heme pair, contradicting the expectation
based on heme redox potentials and thermodynamics, that the two higher
potential hemes bn on different monomers
would be preferentially reduced. Energetically preferred intramonomer
electron storage of electrons on the intramonomer b-hemes is found to require heterogeneity of interheme dielectric
constants. Relative to the medium separating the two higher potential
hemes bn, a relatively large dielectric
constant must exist between the intramonomer b-hemes,
allowing a smaller electrostatic repulsion between the reduced hemes.
Heterogeneity of dielectric constants is an additional structure–function
parameter of membrane protein complexes.
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Affiliation(s)
- S Saif Hasan
- Department of Biological Sciences and ‡Department of Physics, Purdue University , West Lafayette, Indiana 47907, United States
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Domonkos I, Kis M, Gombos Z, Ughy B. Carotenoids, versatile components of oxygenic photosynthesis. Prog Lipid Res 2013; 52:539-61. [PMID: 23896007 DOI: 10.1016/j.plipres.2013.07.001] [Citation(s) in RCA: 141] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Revised: 07/19/2013] [Accepted: 07/19/2013] [Indexed: 12/13/2022]
Abstract
Carotenoids (CARs) are a group of pigments that perform several important physiological functions in all kingdoms of living organisms. CARs serve as protective agents, which are essential structural components of photosynthetic complexes and membranes, and they play an important role in the light harvesting mechanism of photosynthesizing plants and cyanobacteria. The protection against reactive oxygen species, realized by quenching of singlet oxygen and the excited states of photosensitizing molecules, as well as by the scavenging of free radicals, is one of the main biological functions of CARs. X-ray crystallographic localization of CARs revealed that they are present at functionally and structurally important sites of both the PSI and PSII reaction centers. Characterization of a CAR-less cyanobacterial mutant revealed that while the absence of CARs prevents the formation of PSII complexes, it does not abolish the assembly and function of PSI. CAR molecules assist in the formation of protein subunits of the photosynthetic complexes by gluing together their protein components. In addition to their aforementioned indispensable functions, CARs have a substantial role in the formation and maintenance of proper cellular architecture, and potentially also in the protection of the translational machinery under stress conditions.
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Affiliation(s)
- Ildikó Domonkos
- Institute of Plant Biology, Biological Research Centre of Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged, Hungary
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Kallas T. Cytochrome b 6 f Complex at the Heart of Energy Transduction and Redox Signaling. PHOTOSYNTHESIS 2012. [DOI: 10.1007/978-94-007-1579-0_21] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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10
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Sozer O, Komenda J, Ughy B, Domonkos I, Laczkó-Dobos H, Malec P, Gombos Z, Kis M. Involvement of carotenoids in the synthesis and assembly of protein subunits of photosynthetic reaction centers of Synechocystis sp. PCC 6803. PLANT & CELL PHYSIOLOGY 2010; 51:823-35. [PMID: 20231245 DOI: 10.1093/pcp/pcq031] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The crtB gene of Synechocystis sp. PCC 6803, encoding phytoene synthase, was inactivated in the Delta crtH mutant to generate a carotenoidless Delta crtH/B double mutant. Delta crtH mutant cells were used because they had better transformability than wild-type cells, most probably due to their adaptation to partial carotenoid deficiency. Cells of the Delta crtH/B mutant were light sensitive and could grow only under light-activated heterotrophic growth conditions in the presence of glucose. Carotenoid deficiency did not significantly affect the cellular content of phycobiliproteins while the chlorophyll content of the mutant cells decreased. The mutant cells exhibited no oxygen-evolving activity, suggesting the absence of photochemically active PSII complexes. This was confirmed by 2D electrophoresis of photosynthetic membrane complexes. Analyses identified only a small amount of a non-functional PSII core complex lacking CP43, while the monomeric and dimeric PSII core complexes were absent. On the other hand, carotenoid deficiency did not prevent formation of the cytochrome b(6)f complex and PSI, which predominantly accumulated in the monomeric form. Radioactive labeling revealed very limited synthesis of inner PSII antennae, CP47 and especially CP43. Thus, carotenoids are indispensable constituents of the photosynthetic apparatus, being essential not only for antioxidative protection but also for the efficient synthesis and accumulation of photosynthetic proteins and especially that of PSII antenna subunits.
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Affiliation(s)
- Ozge Sozer
- Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary
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11
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The Biosynthetic pathway for synechoxanthin, an aromatic carotenoid synthesized by the euryhaline, unicellular cyanobacterium Synechococcus sp. strain PCC 7002. J Bacteriol 2008; 190:7966-74. [PMID: 18849428 DOI: 10.1128/jb.00985-08] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The euryhaline, unicellular cyanobacterium Synechococcus sp. strain PCC 7002 produces the dicyclic aromatic carotenoid synechoxanthin (chi,chi-caroten-18,18'-dioic acid) as a major pigment (>15% of total carotenoid) and when grown to stationary phase also accumulates small amounts of renierapurpurin (chi,chi-carotene) (J. E. Graham, J. T. J. Lecomte, and D. A. Bryant, J. Nat. Prod. 71:1647-1650, 2008). Two genes that were predicted to encode enzymes involved in the biosynthesis of synechoxanthin were identified by comparative genomics, and these genes were insertionally inactivated in Synechococcus sp. strain PCC 7002 to verify their function. The cruE gene (SYNPCC7002_A1248) encodes beta-carotene desaturase/methyltransferase, which converts beta-carotene to renierapurpurin. The cruH gene (SYNPCC7002_A2246) encodes an enzyme that is minimally responsible for the hydroxylation/oxidation of the C-18 and C-18' methyl groups of renierapurpurin. Based on observed and biochemically characterized intermediates, a complete pathway for synechoxanthin biosynthesis is proposed.
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12
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Isorenieratene biosynthesis in green sulfur bacteria requires the cooperative actions of two carotenoid cyclases. J Bacteriol 2008; 190:6384-91. [PMID: 18676669 DOI: 10.1128/jb.00758-08] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The cyclization of lycopene to gamma- or beta-carotene is a major branch point in the biosynthesis of carotenoids in photosynthetic bacteria. Four families of carotenoid cyclases are known, and each family includes both mono- and dicyclases, which catalyze the formation of gamma- and beta-carotene, respectively. Green sulfur bacteria (GSB) synthesize aromatic carotenoids, of which the most commonly occurring types are the monocyclic chlorobactene and the dicyclic isorenieratene. Recently, the cruA gene, encoding a conserved hypothetical protein found in the genomes of all GSB and some cyanobacteria, was identified as a lycopene cyclase. Further genomic analyses have found that all available fully sequenced genomes of GSB encode an ortholog of cruA. Additionally, the genomes of all isorenieratene-producing species of GSB encode a cruA paralog, now named cruB. The cruA gene from the chlorobactene-producing GSB species Chlorobaculum tepidum and both cruA and cruB from the brown-colored, isorenieratene-producing GSB species Chlorobium phaeobacteroides strain DSM 266(T) were heterologously expressed in lycopene- and neurosporene-producing strains of Escherichia coli, and the cruB gene of Chlorobium clathratiforme strain DSM 5477(T) was also heterologously expressed in C. tepidum by inserting the gene at the bchU locus. The results show that CruA is probably a lycopene monocyclase in all GSB and that CruB is a gamma-carotene cyclase in isorenieratene-producing species. Consequently, the branch point for the synthesis of mono- and dicyclic carotenoids in GSB seems to be the modification of gamma-carotene, rather than the cyclization of lycopene as occurs in cyanobacteria.
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Maresca JA, Graham JE, Bryant DA. The biochemical basis for structural diversity in the carotenoids of chlorophototrophic bacteria. PHOTOSYNTHESIS RESEARCH 2008; 97:121-40. [PMID: 18535920 DOI: 10.1007/s11120-008-9312-3] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2008] [Accepted: 05/14/2008] [Indexed: 05/15/2023]
Abstract
Ongoing work has led to the identification of most of the biochemical steps in carotenoid biosynthesis in chlorophototrophic bacteria. In carotenogenesis, a relatively small number of modifications leads to a great diversity of carotenoid structures. This review examines the individual steps in the pathway, discusses how each contributes to structural diversity among carotenoids, and summarizes recent progress in elucidating the biosynthetic pathways for carotenoids in chlorophototrophs.
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Affiliation(s)
- Julia A Maresca
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA
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14
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Yan J, Dashdorj N, Baniulis D, Yamashita E, Savikhin S, Cramer WA. On the Structural Role of the Aromatic Residue Environment of the Chlorophyll a in the Cytochrome b6f Complex. Biochemistry 2008; 47:3654-61. [PMID: 18302324 DOI: 10.1021/bi702299b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Jiusheng Yan
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Naranbaatar Dashdorj
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Danas Baniulis
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Eiki Yamashita
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Sergei Savikhin
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - William A. Cramer
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
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Reisinger V, Hertle AP, Plöscher M, Eichacker LA. Cytochrome b6f is a dimeric protochlorophyll a binding complex in etioplasts. FEBS J 2008; 275:1018-24. [PMID: 18221490 DOI: 10.1111/j.1742-4658.2008.06268.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The cytochrome b6f complex is a dimeric protein complex that is of central importance for photosynthesis to carry out light driven electron and proton transfer in chloroplasts. One molecule of chlorophyll a was found to associate per cytochrome b6f monomer and the structural or functional importance of this is discussed. We show that etioplasts which are devoid of chlorophyll a already contain dimeric cytochrome b6f. However, the phytylated chlorophyll precursor protochlorophyll a, and not chlorophyll a, is associated with subunit b6. The data imply that a phytylated tetrapyrrol is an essential structural requirement for assembly of cytochrome b6f.
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Abstract
Crystal structures and their implications for function are described for the energy transducing hetero-oligomeric dimeric cytochrome b6f complex of oxygenic photosynthesis from the thermophilic cyanobacterium, Mastigocladus laminosus, and the green alga, Chlamydomonas reinhardtii. The complex has a cytochrome b core and a central quinone exchange cavity, defined by the two monomers that are very similar to those in the respiratory cytochrome bc1 complex. The pathway of quinol/quinone (Q/QH2) transfer emphasizes the labyrinthine internal structure of the complex, including an 11x12 A portal through which Q/QH2, containing a 45-carbon isoprenoid chain, must pass. Three prosthetic groups are present in the b6f complex that are not found in the related bc1 complex: a chlorophyll (Chl) a, a beta-carotene, and a structurally unique covalently bound heme that does not possess amino acid side chains as axial ligands. It is hypothesized that this heme, exposed to the cavity and a neighboring plastoquinone and close to the positive surface potential of the complex, can function in cyclic electron transport via anionic ferredoxin.
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Affiliation(s)
- William A Cramer
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-2054, USA.
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Schneider D, Volkmer T, Rögner M. PetG and PetN, but not PetL, are essential subunits of the cytochrome b6f complex from Synechocystis PCC 6803. Res Microbiol 2006; 158:45-50. [PMID: 17224258 DOI: 10.1016/j.resmic.2006.10.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2006] [Revised: 08/10/2006] [Accepted: 10/03/2006] [Indexed: 10/23/2022]
Abstract
The cytochrome b(6)f complex consists of four large core subunits and an additional four low molecular weight subunits, the function of which is elusive thus far. Here we sought to determine whether small subunits PetG, PetL, and PetN are essential for a cyanobacterial cytochrome b(6)f complex. We found that only PetL is dispensable, whereas PetG and PetN appear to be essential. Possible roles of the small cytochrome b(6)f complex subunits are discussed, and observations from our study are compared with previous findings.
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Affiliation(s)
- Dirk Schneider
- Institut für Biochemie und Molekularbiologie, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Strasse 19, 79104 Freiburg, Germany
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Volkmer T, Schneider D, Bernát G, Kirchhoff H, Wenk SO, Rögner M. Ssr2998 of Synechocystis sp. PCC 6803 is involved in regulation of cyanobacterial electron transport and associated with the cytochrome b6f complex. J Biol Chem 2006; 282:3730-7. [PMID: 17166849 DOI: 10.1074/jbc.m604948200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To analyze the function of a protein encoded by the open reading frame ssr2998 in Synechocystis sp. PCC 6803, the corresponding gene was disrupted, and the generated mutant strain was analyzed. Loss of the 7.2-kDa protein severely reduced the growth of Synechocystis, especially under high light conditions, and appeared to impair the function of the cytochrome b6 f complex. This resulted in slower electron donation to cytochrome f and photosystem 1 and, concomitantly, over-reduction of the plastoquinone pool, which in turn had an impact on the photosystem 1 to photosystem 2 stoichiometry and state transition. Furthermore, a 7.2-kDa protein, encoded by the open reading frame ssr2998, was co-isolated with the cytochrome b6 f complex from the cyanobacterium Synechocystis sp. PCC 6803. ssr2998 seems to be structurally and functionally associated with the cytochrome b6 f complex from Synechocystis, and the protein could be involved in regulation of electron transfer processes in Synechocystis sp. PCC 6803.
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Affiliation(s)
- Thomas Volkmer
- Biochemie der Pflanzen, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
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Zuo P, Li BX, Zhao XH, Wu YS, Ai XC, Zhang JP, Li LB, Kuang TY. Ultrafast carotenoid-to-chlorophyll singlet energy transfer in the cytochrome b6f complex from Bryopsis corticulans. Biophys J 2006; 90:4145-54. [PMID: 16565047 PMCID: PMC1459505 DOI: 10.1529/biophysj.105.076612] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ultrafast carotenoid-to-chlorophyll (Car-to-Chl) singlet excitation energy transfer in the cytochrome b(6)f (Cyt b(6)f) complex from Bryopsis corticulans is investigated by the use of femtosecond time-resolved absorption spectroscopy. For all-trans-alpha-carotene free in n-hexane, the lifetimes of the two low-lying singlet excited states, S(1)(2A(g)(-)) and S(2)(1B(u)(+)), are determined to be 14.3 +/- 0.4 ps and 230 +/- 10 fs, respectively. For the Cyt b(6)f complex, to which 9-cis-alpha-carotene is bound, the lifetime of the S(1)(2A(g)(-)) state remains unchanged, whereas that of the S(2)(1B(u)(+)) state is significantly reduced. In addition, a decay-to-rise correlation between the excited-state dynamics of alpha-carotene and Chl a is clearly observed. This spectroscopic evidence proves that the S(2)(1B(u)(+)) state is able to transfer electronic excitations to the Q(x) state of Chl a, whereas the S(1)(2A(g)(-)) state remains inactive. The time constant and the partial efficiency of the energy transfer are determined to be 240 +/- 40 fs and (49 +/- 4)%, respectively, which supports the overall efficiency of 24% determined with steady-state fluorescence spectroscopy. A scheme of the alpha-carotene-to-Chl a singlet energy transfer is proposed based on the excited-state dynamics of the pigments.
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Affiliation(s)
- Ping Zuo
- State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People's Republic of China
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Alric J, Pierre Y, Picot D, Lavergne J, Rappaport F. Spectral and redox characterization of the heme ci of the cytochrome b6f complex. Proc Natl Acad Sci U S A 2005; 102:15860-5. [PMID: 16247018 PMCID: PMC1276102 DOI: 10.1073/pnas.0508102102] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Absorption spectra of the purified cytochrome b(6)f complex from Chlamydomonas reinhardtii were monitored as a function of the redox potential. Four spectral and redox components were identified: in addition to heme f and the two b hemes, the fourth component must be the new heme c(i) (also denoted x) recently discovered in the crystallographic structures. This heme is covalently attached to the protein, but has no amino acid axial ligand. It is located in the plastoquinone-reducing site Q(i) in the immediate vicinity of a b heme. Each heme titrated as a one-electron Nernst curve, with midpoint potentials at pH 7.0 of -130 mV and -35 mV (hemes b), +100 mV (heme c(i)), and +355 mV (heme f). The reduced minus oxidized spectrum of heme c(i) consists of a broad absorption increase centered approximately 425 nm. Its potential has a dependence of -60 mV/pH unit, implying that the reduced form binds one proton in the pH 6-9 range. The Q(i) site inhibitor 2-n-nonyl-4-hydroxyquinoline N-oxide, a semiquinone analogue, induces a shift of this potential by about -225 mV. The spectrum of c(i) matches the absorption changes previously observed in vivo for an unknown redox center denoted "G." The data are discussed with respect to the effect of the membrane potential on the electron transfer equilibrium between G and heme b(H) found in earlier experiments.
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Affiliation(s)
- Jean Alric
- Unité Mixte de Recherche 7099, Centre National de la Recherche Scientifique-Université Paris 7, France
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