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Biswas S, Niedzwiedzki DM, Pakrasi HB. Energy dissipation efficiency in the CP43 assembly intermediate complex of photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2023; 1864:148982. [PMID: 37146928 DOI: 10.1016/j.bbabio.2023.148982] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 04/10/2023] [Accepted: 04/20/2023] [Indexed: 05/07/2023]
Abstract
Photosystem II in oxygenic organisms is a large membrane bound rapidly turning over pigment protein complex. During its biogenesis, multiple assembly intermediates are formed, including the CP43-preassembly complex (pCP43). To understand the energy transfer dynamics in pCP43, we first engineered a His-tagged version of the CP43 in a CP47-less strain of the cyanobacterium Synechocystis 6803. Isolated pCP43 from this engineered strain was subjected to advanced spectroscopic analysis to evaluate its excitation energy dissipation characteristics. These included measurements of steady-state absorption and fluorescence emission spectra for which correlation was tested with Stepanov relation. Comparison of fluorescence excitation and absorptance spectra determined that efficiency of energy transfer from β-carotene to chlorophyll a is 39 %. Time-resolved fluorescence images of pCP43-bound Chl a were recorded on streak camera, and fluorescence decay dynamics were evaluated with global fitting. These demonstrated that the decay kinetics strongly depends on temperature and buffer used to disperse the protein sample and fluorescence decay lifetime was estimated in 3.2-5.7 ns time range, depending on conditions. The pCP43 complex was also investigated with femtosecond and nanosecond time-resolved absorption spectroscopy upon excitation of Chl a and β-carotene to reveal pathways of singlet excitation relaxation/decay, Chl a triplet dynamics and Chl a → β-carotene triplet state sensitization process. The latter demonstrated that Chl a triplet in the pCP43 complex is not efficiently quenched by carotenoids. Finally, detailed kinetic analysis of the rise of the population of β-carotene triplets determined that the time constant of the carotenoid triplet sensitization is 40 ns.
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Affiliation(s)
- Sandeep Biswas
- Department of Biology, Washington University, St. Louis, MO 63130, USA.
| | - Dariusz M Niedzwiedzki
- Center for Solar Energy and Energy Storage, Washington University, St. Louis, MO 63130, USA; Department of Energy, Environmental & Chemical Engineering, Washington University, St. Louis, MO 63130, USA.
| | - Himadri B Pakrasi
- Department of Biology, Washington University, St. Louis, MO 63130, USA.
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A novel species of the marine cyanobacterium Acaryochloris with a unique pigment content and lifestyle. Sci Rep 2018; 8:9142. [PMID: 29904088 PMCID: PMC6002478 DOI: 10.1038/s41598-018-27542-7] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 06/01/2018] [Indexed: 01/01/2023] Open
Abstract
All characterized members of the ubiquitous genus Acaryochloris share the unique property of containing large amounts of chlorophyll (Chl) d, a pigment exhibiting a red absorption maximum strongly shifted towards infrared compared to Chl a. Chl d is the major pigment in these organisms and is notably bound to antenna proteins structurally similar to those of Prochloron, Prochlorothrix and Prochlorococcus, the only three cyanobacteria known so far to contain mono- or divinyl-Chl a and b as major pigments and to lack phycobilisomes. Here, we describe RCC1774, a strain isolated from the foreshore near Roscoff (France). It is phylogenetically related to members of the Acaryochloris genus but completely lacks Chl d. Instead, it possesses monovinyl-Chl a and b at a b/a molar ratio of 0.16, similar to that in Prochloron and Prochlorothrix. It differs from the latter by the presence of phycocyanin and a vestigial allophycocyanin energetically coupled to photosystems. Genome sequencing confirmed the presence of phycobiliprotein and Chl b synthesis genes. Based on its phylogeny, ultrastructural characteristics and unique pigment suite, we describe RCC1774 as a novel species that we name Acaryochloris thomasi. Its very unusual pigment content compared to other Acaryochloris spp. is likely related to its specific lifestyle.
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Wang P, Grimm B. Organization of chlorophyll biosynthesis and insertion of chlorophyll into the chlorophyll-binding proteins in chloroplasts. PHOTOSYNTHESIS RESEARCH 2015; 126:189-202. [PMID: 25957270 DOI: 10.1007/s11120-015-0154-5] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/30/2015] [Indexed: 05/23/2023]
Abstract
Oxygenic photosynthesis requires chlorophyll (Chl) for the absorption of light energy, and charge separation in the reaction center of photosystem I and II, to feed electrons into the photosynthetic electron transfer chain. Chl is bound to different Chl-binding proteins assembled in the core complexes of the two photosystems and their peripheral light-harvesting antenna complexes. The structure of the photosynthetic protein complexes has been elucidated, but mechanisms of their biogenesis are in most instances unknown. These processes involve not only the assembly of interacting proteins, but also the functional integration of pigments and other cofactors. As a precondition for the association of Chl with the Chl-binding proteins in both photosystems, the synthesis of the apoproteins is synchronized with Chl biosynthesis. This review aims to summarize the present knowledge on the posttranslational organization of Chl biosynthesis and current attempts to envision the proceedings of the successive synthesis and integration of Chl into Chl-binding proteins in the thylakoid membrane. Potential auxiliary factors, contributing to the control and organization of Chl biosynthesis and the association of Chl with the Chl-binding proteins during their integration into photosynthetic complexes, are discussed in this review.
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Affiliation(s)
- Peng Wang
- Institute of Biology/Plant Physiology, Humboldt-University Berlin, Philippstraße 13, 10115, Berlin, Germany
| | - Bernhard Grimm
- Institute of Biology/Plant Physiology, Humboldt-University Berlin, Philippstraße 13, 10115, Berlin, Germany.
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Mella-Flores D, Six C, Ratin M, Partensky F, Boutte C, Le Corguillé G, Marie D, Blot N, Gourvil P, Kolowrat C, Garczarek L. Prochlorococcus and Synechococcus have Evolved Different Adaptive Mechanisms to Cope with Light and UV Stress. Front Microbiol 2012; 3:285. [PMID: 23024637 PMCID: PMC3441193 DOI: 10.3389/fmicb.2012.00285] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Accepted: 07/19/2012] [Indexed: 11/13/2022] Open
Abstract
Prochlorococcus and Synechococcus, which numerically dominate vast oceanic areas, are the two most abundant oxygenic phototrophs on Earth. Although they require solar energy for photosynthesis, excess light and associated high UV radiations can induce high levels of oxidative stress that may have deleterious effects on their growth and productivity. Here, we compared the photophysiologies of the model strains Prochlorococcus marinus PCC 9511 and Synechococcus sp. WH7803 grown under a bell-shaped light/dark cycle of high visible light supplemented or not with UV. Prochlorococcus exhibited a higher sensitivity to photoinactivation than Synechococcus under both conditions, as shown by a larger drop of photosystem II (PSII) quantum yield at noon and different diel patterns of the D1 protein pool. In the presence of UV, the PSII repair rate was significantly depressed at noon in Prochlorococcus compared to Synechococcus. Additionally, Prochlorococcus was more sensitive than Synechococcus to oxidative stress, as shown by the different degrees of PSII photoinactivation after addition of hydrogen peroxide. A transcriptional analysis also revealed dramatic discrepancies between the two organisms in the diel expression patterns of several genes involved notably in the biosynthesis and/or repair of photosystems, light-harvesting complexes, CO(2) fixation as well as protection mechanisms against light, UV, and oxidative stress, which likely translate profound differences in their light-controlled regulation. Altogether our results suggest that while Synechococcus has developed efficient ways to cope with light and UV stress, Prochlorococcus cells seemingly survive stressful hours of the day by launching a minimal set of protection mechanisms and by temporarily bringing down several key metabolic processes. This study provides unprecedented insights into understanding the distinct depth distributions and dynamics of these two picocyanobacteria in the field.
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Affiliation(s)
- Daniella Mella-Flores
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
- Departamento de Ecología, Facultad de Ciencias Biologicas, Pontificia Universidad Catolica de ChileSantiago, Chile
| | - Christophe Six
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
| | - Morgane Ratin
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
| | - Frédéric Partensky
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
| | - Christophe Boutte
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
| | - Gildas Le Corguillé
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- CNRS, FR 2424, Service Informatique et GénomiqueRoscoff, France
| | - Dominique Marie
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
| | - Nicolas Blot
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
- Laboratoire Microorganismes: Génome et Environnement, Clermont Université, Université Blaise PascalClermont-Ferrand, France
- Laboratoire Microorganismes: Génome et Environnement, CNRS, UMR 6023Aubière, France
| | - Priscillia Gourvil
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
| | - Christian Kolowrat
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
- Center for Doctoral Studies, University of ViennaVienna, Austria
| | - Laurence Garczarek
- Station Biologique, UPMC-Université Paris VIRoscoff, France
- Groupe Plancton Océanique, CNRS, UMR 7144Roscoff, France
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Light Stress Proteins in Viruses, Cyanobacteria and Photosynthetic Eukaryota. PHOTOSYNTHESIS 2012. [DOI: 10.1007/978-94-007-1579-0_14] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
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The Extended Light-Harvesting Complex (LHC) Protein Superfamily: Classification and Evolutionary Dynamics. FUNCTIONAL GENOMICS AND EVOLUTION OF PHOTOSYNTHETIC SYSTEMS 2012. [DOI: 10.1007/978-94-007-1533-2_11] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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Abstract
Energy conversion of sunlight by photosynthetic organisms has changed Earth and life on it. Photosynthesis arose early in Earth's history, and the earliest forms of photosynthetic life were almost certainly anoxygenic (non-oxygen evolving). The invention of oxygenic photosynthesis and the subsequent rise of atmospheric oxygen approximately 2.4 billion years ago revolutionized the energetic and enzymatic fundamentals of life. The repercussions of this revolution are manifested in novel biosynthetic pathways of photosynthetic cofactors and the modification of electron carriers, pigments, and existing and alternative modes of photosynthetic carbon fixation. The evolutionary history of photosynthetic organisms is further complicated by lateral gene transfer that involved photosynthetic components as well as by endosymbiotic events. An expanding wealth of genetic information, together with biochemical, biophysical, and physiological data, reveals a mosaic of photosynthetic features. In combination, these data provide an increasingly robust framework to formulate and evaluate hypotheses concerning the origin and evolution of photosynthesis.
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Engelken J, Brinkmann H, Adamska I. Taxonomic distribution and origins of the extended LHC (light-harvesting complex) antenna protein superfamily. BMC Evol Biol 2010; 10:233. [PMID: 20673336 PMCID: PMC3020630 DOI: 10.1186/1471-2148-10-233] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Accepted: 07/30/2010] [Indexed: 11/26/2022] Open
Abstract
Background The extended light-harvesting complex (LHC) protein superfamily is a centerpiece of eukaryotic photosynthesis, comprising the LHC family and several families involved in photoprotection, like the LHC-like and the photosystem II subunit S (PSBS). The evolution of this complex superfamily has long remained elusive, partially due to previously missing families. Results In this study we present a meticulous search for LHC-like sequences in public genome and expressed sequence tag databases covering twelve representative photosynthetic eukaryotes from the three primary lineages of plants (Plantae): glaucophytes, red algae and green plants (Viridiplantae). By introducing a coherent classification of the different protein families based on both, hidden Markov model analyses and structural predictions, numerous new LHC-like sequences were identified and several new families were described, including the red lineage chlorophyll a/b-binding-like protein (RedCAP) family from red algae and diatoms. The test of alternative topologies of sequences of the highly conserved chlorophyll-binding core structure of LHC and PSBS proteins significantly supports the independent origins of LHC and PSBS families via two unrelated internal gene duplication events. This result was confirmed by the application of cluster likelihood mapping. Conclusions The independent evolution of LHC and PSBS families is supported by strong phylogenetic evidence. In addition, a possible origin of LHC and PSBS families from different homologous members of the stress-enhanced protein subfamily, a diverse and anciently paralogous group of two-helix proteins, seems likely. The new hypothesis for the evolution of the extended LHC protein superfamily proposed here is in agreement with the character evolution analysis that incorporates the distribution of families and subfamilies across taxonomic lineages. Intriguingly, stress-enhanced proteins, which are universally found in the genomes of green plants, red algae, glaucophytes and in diatoms with complex plastids, could represent an important and previously missing link in the evolution of the extended LHC protein superfamily.
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Scanlan DJ, Ostrowski M, Mazard S, Dufresne A, Garczarek L, Hess WR, Post AF, Hagemann M, Paulsen I, Partensky F. Ecological genomics of marine picocyanobacteria. Microbiol Mol Biol Rev 2009; 73:249-99. [PMID: 19487728 PMCID: PMC2698417 DOI: 10.1128/mmbr.00035-08] [Citation(s) in RCA: 446] [Impact Index Per Article: 29.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Marine picocyanobacteria of the genera Prochlorococcus and Synechococcus numerically dominate the picophytoplankton of the world ocean, making a key contribution to global primary production. Prochlorococcus was isolated around 20 years ago and is probably the most abundant photosynthetic organism on Earth. The genus comprises specific ecotypes which are phylogenetically distinct and differ markedly in their photophysiology, allowing growth over a broad range of light and nutrient conditions within the 45 degrees N to 40 degrees S latitudinal belt that they occupy. Synechococcus and Prochlorococcus are closely related, together forming a discrete picophytoplankton clade, but are distinguishable by their possession of dissimilar light-harvesting apparatuses and differences in cell size and elemental composition. Synechococcus strains have a ubiquitous oceanic distribution compared to that of Prochlorococcus strains and are characterized by phylogenetically discrete lineages with a wide range of pigmentation. In this review, we put our current knowledge of marine picocyanobacterial genomics into an environmental context and present previously unpublished genomic information arising from extensive genomic comparisons in order to provide insights into the adaptations of these marine microbes to their environment and how they are reflected at the genomic level.
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Affiliation(s)
- D J Scanlan
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom.
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Liang X, Qiao D, Huang M, Yi X, Bai L, Xu H, Wei L, Zeng J, Cao Y. Identification of a gene encoding the light-harvesting chlorophyll a/b proteins of photosystem I in green alga Dunaliella salina. ACTA ACUST UNITED AC 2007; 19:137-45. [PMID: 17852332 DOI: 10.1080/10425170701447614] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
There are four LhcII genes of Dunaliella salina have been submitted to the database of GenBank. However, little is known about Lhca genes of this green alga, although this knowledge might be available to study the composition and phylogenesis of Lhc gene family. Recently, one Lhca gene was been cloned from the green alga D. salina by PCR amplification using degenerate primers. This cDNA, designated as DsLhca1, contains an open reading frame encoded a protein of 222 amino acids with a calculated molecular mass of 27.8 kDa. DsLhca1 is predicted to contain three transmembrane domains and a N-terminal chloroplast transit peptide (cTP) with length of 33 amino acids. The genomic sequence of DsLhca1 is composed of five introns. The deduced polypeptide sequence of this gene showed a lower degree of identity (less than 30%) with LHCII proteins from D. salina. But its homology to Lhca proteins of other algae (Volvox carteri Lhca_AF110786) was higher with pairwise identities of up to 67.1%. Phylogenetic analysis indicated that DsLhcal protein cannot be assigned to any types of Lhca proteins in higher plants or in Chlamydomonas reinhardtii.
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Affiliation(s)
- Xue Liang
- Key Laboratory of Bio-resources and Eco-environment, Ministry of Education (Sichuan University), Sichuan Public Experimental Platform of Bioinformatics and Metabolic Engineering, Sichuan 610064, P R. China.
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Mulkidjanian AY, Koonin EV, Makarova KS, Mekhedov SL, Sorokin A, Wolf YI, Dufresne A, Partensky F, Burd H, Kaznadzey D, Haselkorn R, Galperin MY. The cyanobacterial genome core and the origin of photosynthesis. Proc Natl Acad Sci U S A 2006; 103:13126-31. [PMID: 16924101 PMCID: PMC1551899 DOI: 10.1073/pnas.0605709103] [Citation(s) in RCA: 187] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Comparative analysis of 15 complete cyanobacterial genome sequences, including "near minimal" genomes of five strains of Prochlorococcus spp., revealed 1,054 protein families [core cyanobacterial clusters of orthologous groups of proteins (core CyOGs)] encoded in at least 14 of them. The majority of the core CyOGs are involved in central cellular functions that are shared with other bacteria; 50 core CyOGs are specific for cyanobacteria, whereas 84 are exclusively shared by cyanobacteria and plants and/or other plastid-carrying eukaryotes, such as diatoms or apicomplexans. The latter group includes 35 families of uncharacterized proteins, which could also be involved in photosynthesis. Only a few components of cyanobacterial photosynthetic machinery are represented in the genomes of the anoxygenic phototrophic bacteria Chlorobium tepidum, Rhodopseudomonas palustris, Chloroflexus aurantiacus, or Heliobacillus mobilis. These observations, coupled with recent geological data on the properties of the ancient phototrophs, suggest that photosynthesis originated in the cyanobacterial lineage under the selective pressures of UV light and depletion of electron donors. We propose that the first phototrophs were anaerobic ancestors of cyanobacteria ("procyanobacteria") that conducted anoxygenic photosynthesis using a photosystem I-like reaction center, somewhat similar to the heterocysts of modern filamentous cyanobacteria. From procyanobacteria, photosynthesis spread to other phyla by way of lateral gene transfer.
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Affiliation(s)
- Armen Y. Mulkidjanian
- *School of Physics, University of Osnabrück, D-49069 Osnabrück, Germany
- A. N. Belozersky Institute of Physico–Chemical Biology, Moscow State University, Moscow 119899, Russia
| | - Eugene V. Koonin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894
| | - Kira S. Makarova
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894
| | - Sergey L. Mekhedov
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894
| | - Alexander Sorokin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894
| | - Yuri I. Wolf
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894
| | - Alexis Dufresne
- Station Biologique, Unité Mixte de Recherche 7144, Centre National de la Recherche Scientifique et Université Paris 6, BP74, F-29682 Roscoff Cedex, France
| | - Frédéric Partensky
- Station Biologique, Unité Mixte de Recherche 7144, Centre National de la Recherche Scientifique et Université Paris 6, BP74, F-29682 Roscoff Cedex, France
| | - Henry Burd
- Integrated Genomics, Inc., Chicago, IL 60612; and
| | | | - Robert Haselkorn
- **Department of Molecular Genetics and Cell Biology, University of Chicago, 920 East 58th Street, Chicago, IL 60637
| | - Michael Y. Galperin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894
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Bailey S, Mann NH, Robinson C, Scanlan DJ. The occurrence of rapidly reversible non-photochemical quenching of chlorophyll a fluorescence in cyanobacteria. FEBS Lett 2005; 579:275-80. [PMID: 15620726 DOI: 10.1016/j.febslet.2004.11.091] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2004] [Revised: 11/18/2004] [Accepted: 11/18/2004] [Indexed: 10/26/2022]
Abstract
Cyanobacteria have previously been considered to differ fundamentally from plants and algae in their regulation of light harvesting. We show here that in fact the ecologically important marine prochlorophyte, Prochlorococcus, is capable of forming rapidly reversible non-photochemical quenching of chlorophyll a fluorescence (NPQf or qE) as are freshwater cyanobacteria when they employ the iron stress induced chlorophyll-based antenna, IsiA. For Prochlorococcus, the capacity for NPQf is greater in high light-adapted strains, except during iron starvation which allows for increased quenching in low light-adapted strains. NPQf formation in freshwater cyanobacteria is accompanied by deep Fo quenching which increases with prolonged iron starvation.
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Affiliation(s)
- Shaun Bailey
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
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Melkozernov AN, Blankenship RE. Structural and functional organization of the peripheral light-harvesting system in photosystem I. PHOTOSYNTHESIS RESEARCH 2005; 85:33-50. [PMID: 15977058 DOI: 10.1007/s11120-004-6474-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2004] [Accepted: 11/19/2004] [Indexed: 05/03/2023]
Abstract
This review centers on the structural and functional organization of the light-harvesting system in the peripheral antenna of Photosystem I (LHC I) and its energy coupling to the Photosystem I (PS I) core antenna network in view of recently available structural models of the eukaryotic Photosystem I-LHC I complex, eukaryotic LHC II complexes and the cyanobacterial Photosystem I core. A structural model based on the 3D homology of Lhca4 with LHC II is used for analysis of the principles of pigment arrangement in the LHC I peripheral antenna, for prediction of the protein ligands for the pigments that are unique for LHC I and for estimates of the excitonic coupling in strongly interacting pigment dimers. The presence of chlorophyll clusters with strong pigment-pigment interactions is a structural feature of PS I, resulting in the characteristic red-shifted fluorescence. Analysis of the interactions between the PS I core antenna and the peripheral antenna leads to the suggestion that the specific function of the red pigments is likely to be determined by their localization with respect to the reaction center. In the PS I core antenna, the Chl clusters with a different magnitude of low energy shift contribute to better spectral overlap of Chls in the reaction center and the Chls of the antenna network, concentrate the excitation around the reaction center and participate in downhill enhancement of energy transfer from LHC II to the PS I core. Chlorophyll clusters forming terminal emitters in LHC I are likely to be involved in photoprotection against excess energy.
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Affiliation(s)
- Alexander N Melkozernov
- Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, Tempe, AZ, 85287-1604, USA.
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