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Conrad W. Mullineaux - One of the best experts on this subject based on the ideXlab platform.
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Phycobilisome Mobility and Its Role in the Regulation of Light Harvesting in Red Algae.
Plant physiology, 2014Co-Authors: Radek Kaňa, Eva Kotabová, Martin Lukeš, Štěpán Papáček, Ctirad Matonoha, Lu-ning Liu, Ondřej Prášil, Conrad W. MullineauxAbstract:Red algae represent an evolutionarily important group that gave rise to the whole red clade of photosynthetic organisms. They contain a unique combination of light-harvesting systems represented by a membrane-bound antenna and by Phycobilisomes situated on thylakoid membrane surfaces. So far, very little has been revealed about the mobility of their Phycobilisomes and the regulation of their light-harvesting system in general. Therefore, we carried out a detailed analysis of Phycobilisome dynamics in several red alga strains and compared these results with the presence (or absence) of photoprotective mechanisms. Our data conclusively prove Phycobilisome mobility in two model mesophilic red alga strains, Porphyridium cruentum and Rhodella violacea. In contrast, there was almost no Phycobilisome mobility in the thermophilic red alga Cyanidium caldarium that was not caused by a decrease in lipid desaturation in this extremophile. Experimental data attributed this immobility to the strong Phycobilisome-photosystem interaction that highly restricted Phycobilisome movement. Variations in Phycobilisome mobility reflect the different ways in which light-harvesting antennae can be regulated in mesophilic and thermophilic red algae. Fluorescence changes attributed in cyanobacteria to state transitions were observed only in mesophilic P. cruentum with mobile Phycobilisomes, and they were absent in the extremophilic C. caldarium with immobile Phycobilisomes. We suggest that state transitions have an important regulatory function in mesophilic red algae; however, in thermophilic red algae, this process is replaced by nonphotochemical quenching.
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Distinct roles of CpcG1-Phycobilisome and CpcG2-Phycobilisome in state transitions in a cyanobacterium Synechocystis sp. PCC 6803
Photosynthesis research, 2009Co-Authors: Kumiko Kondo, Conrad W. Mullineaux, Masahiko IkeuchiAbstract:State transitions in cyanobacteria regulate the relative energy transfer from Phycobilisome to photosystem I and II. Although it has been shown that Phycobilisome mobility is essential for Phycobilisome-dependent state transitions, the biochemical mechanism is not known. Previously we reported that two distinct forms of Phycobilisome are assembled with different CpcG copies, which have been referred to as “rod-core linker,” in a cyanobacterium Synechocystis sp. PCC 6803. CpcG2-Phycobilisome is devoid of a typical central core, while CpcG1-Phycobilisome is equivalent to the conventional Phycobilisome supercomplex. Here, we demonstrated that the cpcG1 disruptant has a severe specific defect in the Phycobilisome-dependent state transition. However, fluorescence recovery after photobleaching measurements showed no obvious difference in Phycobilisome mobility between the wild type and the cpcG1 disruptant. This suggests that both CpcG1 and CpcG2 Phycobilisomes have an unstable interaction with the reaction centres. However, only CpcG1 Phycobilisomes are involved in state transitions. This suggests that state transitions require the Phycobilisome core.
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Phycobilisome-reaction centre interaction in cyanobacteria
Photosynthesis research, 2007Co-Authors: Conrad W. MullineauxAbstract:The Phycobilisome is a remarkable light-harvesting antenna that combines high efficiency with functional flexibility and the ability to capture light across a broad spectral range. A combination of biochemical, structural and spectroscopic studies has given an excellent picture of the structure and function of isolated Phycobilisomes. However, we still know remarkably little about the interaction of the Phycobilisome with the thylakoid membrane and the reaction centres. This article will discuss the various current ideas about this question and explain the things we need to know more about. As a working model, I propose that the Phycobilisome is attached to the membrane by multiple weak charge–charge interactions with lipid head-groups and/or proteins, and that the core-membrane linker polypeptide ApcE provides a flexible surface allowing interaction with multiple membrane components.
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the psbu subunit of photosystem ii stabilizes energy transfer and primary photochemistry in the Phycobilisome photosystem ii assembly of synechocystis sp pcc 6803
Biochemistry, 2005Co-Authors: John Veerman, Conrad W. Mullineaux, Fiona K Bentley, Julian J Eatonrye, Sergei Vasilev, Doug BruceAbstract:The PsbU subunit of photosystem II (PSII) is one of three extrinsic polypeptides associated with stabilizing the oxygen evolving machinery of photosynthesis in cyanobacteria. We investigated the influence of PsbU on excitation energy transfer and primary photochemistry by spectroscopic analysis of a PsbU-less (or ΔPsbU) mutant. The absence of PsbU was found to have multiple effects on the excited state dynamics of the Phycobilisome and PSII. ΔPsbU cells exhibited decreased variable fluorescence when excited with light absorbed primarily by allophycocyanin but not when excited with light absorbed primarily by chlorophyll a. Fluorescence emission spectra at 77 K showed evidence for impaired energy transfer from the allophycocyanin terminal Phycobilisome emitters to PSII. Picosecond fluorescence decay kinetics revealed changes in both allophycocyanin and PSII associated decay components. These changes were consistent with a decrease in the coupling of Phycobilisomes to PSII and an increase in the number of c...
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Phycobilisome Diffusion Is Required for Light-State Transitions in Cyanobacteria
Plant physiology, 2004Co-Authors: Sarah Joshua, Conrad W. MullineauxAbstract:Phycobilisomes are the major accessory light-harvesting complexes of cyanobacteria and red algae. Studies using fluorescence recovery after photobleaching on cyanobacteria in vivo have shown that the Phycobilisomes are mobile complexes that rapidly diffuse on the thylakoid membrane surface. By contrast, the PSII core complexes are completely immobile. This indicates that the association of Phycobilisomes with reaction centers must be transient and unstable. Here, we show that when cells of the cyanobacterium Synechococcus sp. PCC7942 are immersed in buffers of high osmotic strength, the diffusion coefficient for the Phycobilisomes is greatly decreased. This suggests that the interaction between Phycobilisomes and reaction centers becomes much less transient under these conditions. We discuss the possible reasons for this. State transitions are a rapid physiological adaptation mechanism that regulates the way in which absorbed light energy is distributed between PSI and PSII. Immersing cells in high osmotic strength buffers inhibits state transitions by locking cells into whichever state they were in prior to addition of the buffer. The effect on state transitions is induced at the same buffer concentrations as the effect on Phycobilisome diffusion. This implies that Phycobilisome diffusion is required for state transitions. The main physiological role for Phycobilisome mobility may be to allow such flexibility in light harvesting.
Diana Kirilovsky - One of the best experts on this subject based on the ideXlab platform.
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Changing Color for Photoprotection: The Orange Carotenoid Protein
Trends in Plant Science, 2019Co-Authors: Fernando Muzzopappa, Diana KirilovskyAbstract:Under high irradiance, light becomes dangerous for photosynthetic organisms and they must protect themselves. Cyanobacteria have developed a simple mechanism, involving a photoactive soluble carotenoid protein, the orange carotenoid protein (OCP), which increases thermal dissipation of excess energy by interacting with the cyanobacterial antenna, the Phycobilisome. Here, we summarize our knowledge of the OCP-related photoprotective mechanism, including the remarkable progress that has been achieved in recent years on OCP photoactivation and interaction with Phycobilisomes, as well as with the fluorescence recovery protein, which is necessary to end photoprotection. A recently discovered unique mechanism of carotenoid transfer between soluble proteins related to OCP is also described.
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Different roles for ApcD and ApcF in Synechococcus elongatus and Synechocystis sp. PCC 6803 Phycobilisomes
Biochimica biophysica acta (BBA) - Bioenergetics, 2019Co-Authors: Pablo I. Calzadilla, Fernando Muzzopappa, Pierre Sétif, Diana KirilovskyAbstract:The Phycobilisome, the cyanobacterial light harvesting complex, is a huge phycobiliprotein containing extramembrane complex, formed by a core from which rods radiate. The Phycobilisome has evolved to efficiently absorb sun energy and transfer it to the photosystems via the last energy acceptors of the Phycobilisome, ApcD and ApcE. ApcF also affects energy transfer by interacting with ApcE. In this work we studied the role of ApcD and ApcF in energy transfer and state transitions in Synechococcus elongatus and Synechocystis PCC6803. Our results demonstrate that these proteins have different roles in both processes in the two strains. The lack of ApcD and ApcF inhibits state transitions in Synechocystis but not in S. elongatus. In addition, lack of ApcF decreases energy transfer to both photosystems only in Synechocystis, while the lack of ApcD alters energy transfer to photosystem I only in S. elongatus. Thus, conclusions based on results obtained in one cyanobacterial strain cannot be systematically transferred to other strains and the putative role(s) of Phycobilisomes in state transitions need to be reconsidered.
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Modulating energy arriving at photochemical reaction centers: orange carotenoid protein-related photoprotection and state transitions.
Photosynthesis Research, 2015Co-Authors: Diana KirilovskyAbstract:Photosynthetic organisms tightly regulate the energy arriving to the reaction centers in order to avoid photodamage or imbalance between the photosystems. To this purpose, cyanobacteria have developed mechanisms involving relatively rapid (seconds to minutes) changes in the photosynthetic apparatus. In this review, two of these processes will be described: orange carotenoid protein(OCP)-related photoprotection and state transitions which optimize energy distribution between the two photosystems. The photoactive OCP is a light intensity sensor and an energy dissipater. Photoactivation depends on light intensity and only the red-active OCP form, by interacting with Phycobilisome cores, increases thermal energy dissipation at the level of the antenna. A second protein, the "fluorescence recovery protein", is needed to recover full antenna capacity under low light conditions. This protein accelerates OCP conversion to the inactive orange form and plays a role in dislodging the red OCP protein from the Phycobilisome. The mechanism of state transitions is still controversial. Changes in the redox state of the plastoquinone pool induce movement of Phycobilisomes and/or photosystems leading to redistribution of energy absorbed by Phycobilisomes between PSII and PSI and/or to changes in excitation energy spillover between photosystems. The different steps going from the induction of redox changes to movement of Phycobilisomes or photosystems remain to be elucidated.
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light induced energy dissipation in iron starved cyanobacteria roles of ocp and isia proteins
The Plant Cell, 2007Co-Authors: Adjele Wilson, Clemence Boulay, Annegret Wilde, Cheryl A Kerfeld, Diana KirilovskyAbstract:In response to iron deficiency, cyanobacteria synthesize the iron stress–induced chlorophyll binding protein IsiA. This protein protects cyanobacterial cells against iron stress. It has been proposed that the protective role of IsiA is related to a blue light–induced nonphotochemical fluorescence quenching (NPQ) mechanism. In iron-replete cyanobacterial cell cultures, strong blue light is known to induce a mechanism that dissipates excess absorbed energy in the Phycobilisome, the extramembranal antenna of cyanobacteria. In this photoprotective mechanism, the soluble Orange Carotenoid Protein (OCP) plays an essential role. Here, we demonstrate that in iron-starved cells, blue light is unable to quench fluorescence in the absence of the Phycobilisomes or the OCP. By contrast, the absence of IsiA does not affect the induction of fluorescence quenching or its recovery. We conclude that in cyanobacteria grown under iron starvation conditions, the blue light–induced nonphotochemical quenching involves the Phycobilisome OCP–related energy dissipation mechanism and not IsiA. IsiA, however, does seem to protect the cells from the stress generated by iron starvation, initially by increasing the size of the photosystem I antenna. Subsequently, the IsiA converts the excess energy absorbed by the Phycobilisomes into heat through a mechanism different from the dynamic and reversible light-induced NPQ processes.
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a soluble carotenoid protein involved in Phycobilisome related energy dissipation in cyanobacteria
The Plant Cell, 2006Co-Authors: Adjele Wilson, Ghada Ajlani, Cheryl A Kerfeld, Jeanmarc Verbavatz, Imre Vass, Diana KirilovskyAbstract:Photosynthetic organisms have developed multiple protective mechanisms to survive under high-light conditions. In plants, one of these mechanisms is the thermal dissipation of excitation energy in the membrane-bound chlorophyll antenna of photosystem II. The question of whether or not cyanobacteria, the progenitor of the chloroplast, have an equivalent photoprotective mechanism has long been unanswered. Recently, however, evidence was presented for the possible existence of a mechanism dissipating excess absorbed energy in the Phycobilisome, the extramembrane antenna of cyanobacteria. Here, we demonstrate that this photoprotective mechanism, characterized by blue light–induced fluorescence quenching, is indeed Phycobilisome-related and that a soluble carotenoid binding protein, ORANGE CAROTENOID PROTEIN (OCP), encoded by the slr1963 gene in Synechocystis PCC 6803, plays an essential role in this process. Blue light is unable to quench fluorescence in the absence of Phycobilisomes or OCP. The fluorescence quenching is not ΔpH-dependent, and it can be induced in the absence of the reaction center II or the chlorophyll antenna, CP43 and CP47. Our data suggest that OCP, which strongly interacts with the thylakoids, acts as both the photoreceptor and the mediator of the reduction of the amount of energy transferred from the Phycobilisomes to the photosystems. These are novel roles for a soluble carotenoid protein.
Frédéric Partensky - One of the best experts on this subject based on the ideXlab platform.
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Adaptation to Blue Light in Marine Synechococcus Requires MpeU, an Enzyme with Similarity to Phycoerythrobilin Lyase Isomerases
Frontiers in Microbiology, 2017Co-Authors: Rania M. Mahmoud, David M. Kehoe, Joseph E. Sanfilippo, Adam A. Nguyen, Johann A. Strnat, Frédéric Partensky, Laurence Garczarek, Nabil Abo El Kassem, Wendy M. SchluchterAbstract:Marine Synechococcus has successfully adapted to environments with different light colors, which likely contributes to this genus being the second most abundant group of microorganisms worldwide. Populations of Synechococcus that grow in deep, blue ocean waters contain large amounts of the blue-light absorbing chromophore phycourobilin (PUB) in their light harvesting complexes (Phycobilisomes). Here, we show that all Synechococcus strains adapted to blue light possess a gene called mpeU. MpeU is structurally similar to phycobilin lyases, enzymes that ligate chromophores to phycobiliproteins. Interruption of mpeU caused a reduction in PUB content, impaired Phycobilisome assembly and reduced growth rate more strongly in blue than green light. When mpeU was reintroduced in the mpeU mutant background, the mpeU-less phenotype was complemented in terms of PUB content and Phycobilisome content. Fluorescence spectra of mpeU mutant cells and purified Phycobilisomes revealed red-shifted phycoerythrin emission peaks, likely indicating a defect in chromophore ligation to phycoerythrin-I (PE-I) or phycoerythrin-II (PE-II). Our results suggest that MpeU is a lyase-isomerase that attaches a phycoerythrobilin to a PEI or PEII subunit and isomerizes it to PUB. MpeU is therefore an important determinant in adaptation of Synechococcus spp. to capture photons in blue light environments throughout the world’s oceans.
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adaptation to blue light in marine synechococcus requires mpeu an enzyme with similarity to phycoerythrobilin lyase isomerases
Frontiers in Microbiology, 2017Co-Authors: Rania M. Mahmoud, David M. Kehoe, Joseph E. Sanfilippo, Adam A. Nguyen, Johann A. Strnat, Frédéric Partensky, Laurence Garczarek, Nabil Abo El Kassem, Wendy M. SchluchterAbstract:Marine Synechococcus cyanobacteria have successfully adapted to environments with different light colors, which likely contributes to this genus being the second most abundant photosynthetic microorganism worldwide. Populations of Synechococcus that grow in deep, blue ocean waters contain large amounts of the blue-light absorbing chromophore phycourobilin (PUB) in their light harvesting complexes (Phycobilisomes). Here we show that all Synechococcus strains adapted to blue light possess a gene called mpeU. MpeU is structurally similar to phycobilin lyases, enzymes that ligate chromophores to phycobiliproteins. Interruption of mpeU caused a reduction in PUB content, produced impaired Phycobilisomes and reduced growth rate more strongly in blue than green light. When mpeU was reintroduced in the mpeU mutant background, the mpeU-less phenotype was complemented in terms of PUB content and Phycobilisome content. Fluorescence spectra of mpeU mutant cells and purified Phycobilisomes revealed red-shifted phycoerythrin emission peaks, likely indicating a defect in chromophore ligation to phycoerythrin-I (PE-I) or phycoerythrin-II (PE-II). Our results suggest that MpeU is a lyase-isomerase that attaches a phycoerythrobilin to a PEI or PEII subunit and isomerizes it to PUB. MpeU is therefore an important determinant in adaptation of Synechococcus spp. to capture photons in blue light environments throughout the world’s oceans.
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Diversity and evolution of Phycobilisomes in marine Synechococcusspp.: a comparative genomics study
Genome Biology, 2007Co-Authors: Christophe Six, Jean-claude Thomas, Laurence Garczarek, Martin Ostrowski, Alexis Dufresne, Nicolas Blot, David J Scanlan, Frédéric PartenskyAbstract:Background Marine Synechococcus owe their specific vivid color (ranging from blue-green to orange) to their large extrinsic antenna complexes called Phycobilisomes, comprising a central allophycocyanin core and rods of variable phycobiliprotein composition. Three major pigment types can be defined depending on the major phycobiliprotein found in the rods (phycocyanin, phycoerythrin I or phycoerythrin II). Among strains containing both phycoerythrins I and II, four subtypes can be distinguished based on the ratio of the two chromophores bound to these phycobiliproteins. Genomes of eleven marine Synechococcus strains recently became available with one to four strains per pigment type or subtype, allowing an unprecedented comparative genomics study of genes involved in Phycobilisome metabolism. Results By carefully comparing the Synechococcus genomes, we have retrieved candidate genes potentially required for the synthesis of phycobiliproteins in each pigment type. This includes linker polypeptides, phycobilin lyases and a number of novel genes of uncharacterized function. Interestingly, strains belonging to a given pigment type have similar Phycobilisome gene complements and organization, independent of the core genome phylogeny (as assessed using concatenated ribosomal proteins). While phylogenetic trees based on concatenated allophycocyanin protein sequences are congruent with the latter, those based on phycocyanin and phycoerythrin notably differ and match the Synechococcus pigment types. Conclusion We conclude that the Phycobilisome core has likely evolved together with the core genome, while rods must have evolved independently, possibly by lateral transfer of Phycobilisome rod genes or gene clusters between Synechococcus strains, either via viruses or by natural transformation, allowing rapid adaptation to a variety of light niches.
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Diversity and evolution of Phycobilisomes in marine Synechococcus spp.: a comparative genomics study
Genome Biology, 2007Co-Authors: Christophe Six, Jean-claude Thomas, Laurence Garczarek, Martin Ostrowski, Alexis Dufresne, Nicolas Blot, David J Scanlan, Frédéric PartenskyAbstract:Background: Marine Synechococcus owe their specific vivid color (ranging from blue-green to orange) to their large extrinsic antenna complexes called Phycobilisomes, comprising a central allophycocyanin core and rods of variable phycobiliprotein composition. Three major pigment types can be defined depending on the major phycobiliprotein found in the rods (phycocyanin, phycoerythrin I or phycoerythrin II). Among strains containing both phycoerythrins I and II, four subtypes can be distinguished based on the ratio of the two chromophores bound to these phycobiliproteins. Genomes of eleven marine Synechococcus strains recently became available with one to four strains per pigment type or subtype, allowing an unprecedented comparative genomics study of genes involved in Phycobilisome metabolism. Results: By carefully comparing the Synechococcus genomes, we have retrieved candidate genes potentially required for the synthesis of phycobiliproteins in each pigment type. This includes linker polypeptides, phycobilin lyases and a number of novel genes of uncharacterized function. Interestingly, strains belonging to a given pigment type have similar Phycobilisome gene complements and organization, independent of the core genome phylogeny (as assessed using concatenated ribosomal proteins). While phylogenetic trees based on concatenated allophycocyanin protein sequences are congruent with the latter, those based on phycocyanin and phycoerythrin notably differ and match the Synechococcus pigment types. Conclusion: We conclude that the Phycobilisome core has likely evolved together with the core genome, while rods must have evolved independently, possibly by lateral transfer of Phycobilisome rod genes or gene clusters between Synechococcus strains, either via viruses or by natural transformation, allowing rapid adaptation to a variety of light niches.
Wendy M. Schluchter - One of the best experts on this subject based on the ideXlab platform.
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Adaptation to Blue Light in Marine Synechococcus Requires MpeU, an Enzyme with Similarity to Phycoerythrobilin Lyase Isomerases
Frontiers in Microbiology, 2017Co-Authors: Rania M. Mahmoud, David M. Kehoe, Joseph E. Sanfilippo, Adam A. Nguyen, Johann A. Strnat, Frédéric Partensky, Laurence Garczarek, Nabil Abo El Kassem, Wendy M. SchluchterAbstract:Marine Synechococcus has successfully adapted to environments with different light colors, which likely contributes to this genus being the second most abundant group of microorganisms worldwide. Populations of Synechococcus that grow in deep, blue ocean waters contain large amounts of the blue-light absorbing chromophore phycourobilin (PUB) in their light harvesting complexes (Phycobilisomes). Here, we show that all Synechococcus strains adapted to blue light possess a gene called mpeU. MpeU is structurally similar to phycobilin lyases, enzymes that ligate chromophores to phycobiliproteins. Interruption of mpeU caused a reduction in PUB content, impaired Phycobilisome assembly and reduced growth rate more strongly in blue than green light. When mpeU was reintroduced in the mpeU mutant background, the mpeU-less phenotype was complemented in terms of PUB content and Phycobilisome content. Fluorescence spectra of mpeU mutant cells and purified Phycobilisomes revealed red-shifted phycoerythrin emission peaks, likely indicating a defect in chromophore ligation to phycoerythrin-I (PE-I) or phycoerythrin-II (PE-II). Our results suggest that MpeU is a lyase-isomerase that attaches a phycoerythrobilin to a PEI or PEII subunit and isomerizes it to PUB. MpeU is therefore an important determinant in adaptation of Synechococcus spp. to capture photons in blue light environments throughout the world’s oceans.
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adaptation to blue light in marine synechococcus requires mpeu an enzyme with similarity to phycoerythrobilin lyase isomerases
Frontiers in Microbiology, 2017Co-Authors: Rania M. Mahmoud, David M. Kehoe, Joseph E. Sanfilippo, Adam A. Nguyen, Johann A. Strnat, Frédéric Partensky, Laurence Garczarek, Nabil Abo El Kassem, Wendy M. SchluchterAbstract:Marine Synechococcus cyanobacteria have successfully adapted to environments with different light colors, which likely contributes to this genus being the second most abundant photosynthetic microorganism worldwide. Populations of Synechococcus that grow in deep, blue ocean waters contain large amounts of the blue-light absorbing chromophore phycourobilin (PUB) in their light harvesting complexes (Phycobilisomes). Here we show that all Synechococcus strains adapted to blue light possess a gene called mpeU. MpeU is structurally similar to phycobilin lyases, enzymes that ligate chromophores to phycobiliproteins. Interruption of mpeU caused a reduction in PUB content, produced impaired Phycobilisomes and reduced growth rate more strongly in blue than green light. When mpeU was reintroduced in the mpeU mutant background, the mpeU-less phenotype was complemented in terms of PUB content and Phycobilisome content. Fluorescence spectra of mpeU mutant cells and purified Phycobilisomes revealed red-shifted phycoerythrin emission peaks, likely indicating a defect in chromophore ligation to phycoerythrin-I (PE-I) or phycoerythrin-II (PE-II). Our results suggest that MpeU is a lyase-isomerase that attaches a phycoerythrobilin to a PEI or PEII subunit and isomerizes it to PUB. MpeU is therefore an important determinant in adaptation of Synechococcus spp. to capture photons in blue light environments throughout the world’s oceans.
Laurence Garczarek - One of the best experts on this subject based on the ideXlab platform.
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Adaptation to Blue Light in Marine Synechococcus Requires MpeU, an Enzyme with Similarity to Phycoerythrobilin Lyase Isomerases
Frontiers in Microbiology, 2017Co-Authors: Rania M. Mahmoud, David M. Kehoe, Joseph E. Sanfilippo, Adam A. Nguyen, Johann A. Strnat, Frédéric Partensky, Laurence Garczarek, Nabil Abo El Kassem, Wendy M. SchluchterAbstract:Marine Synechococcus has successfully adapted to environments with different light colors, which likely contributes to this genus being the second most abundant group of microorganisms worldwide. Populations of Synechococcus that grow in deep, blue ocean waters contain large amounts of the blue-light absorbing chromophore phycourobilin (PUB) in their light harvesting complexes (Phycobilisomes). Here, we show that all Synechococcus strains adapted to blue light possess a gene called mpeU. MpeU is structurally similar to phycobilin lyases, enzymes that ligate chromophores to phycobiliproteins. Interruption of mpeU caused a reduction in PUB content, impaired Phycobilisome assembly and reduced growth rate more strongly in blue than green light. When mpeU was reintroduced in the mpeU mutant background, the mpeU-less phenotype was complemented in terms of PUB content and Phycobilisome content. Fluorescence spectra of mpeU mutant cells and purified Phycobilisomes revealed red-shifted phycoerythrin emission peaks, likely indicating a defect in chromophore ligation to phycoerythrin-I (PE-I) or phycoerythrin-II (PE-II). Our results suggest that MpeU is a lyase-isomerase that attaches a phycoerythrobilin to a PEI or PEII subunit and isomerizes it to PUB. MpeU is therefore an important determinant in adaptation of Synechococcus spp. to capture photons in blue light environments throughout the world’s oceans.
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adaptation to blue light in marine synechococcus requires mpeu an enzyme with similarity to phycoerythrobilin lyase isomerases
Frontiers in Microbiology, 2017Co-Authors: Rania M. Mahmoud, David M. Kehoe, Joseph E. Sanfilippo, Adam A. Nguyen, Johann A. Strnat, Frédéric Partensky, Laurence Garczarek, Nabil Abo El Kassem, Wendy M. SchluchterAbstract:Marine Synechococcus cyanobacteria have successfully adapted to environments with different light colors, which likely contributes to this genus being the second most abundant photosynthetic microorganism worldwide. Populations of Synechococcus that grow in deep, blue ocean waters contain large amounts of the blue-light absorbing chromophore phycourobilin (PUB) in their light harvesting complexes (Phycobilisomes). Here we show that all Synechococcus strains adapted to blue light possess a gene called mpeU. MpeU is structurally similar to phycobilin lyases, enzymes that ligate chromophores to phycobiliproteins. Interruption of mpeU caused a reduction in PUB content, produced impaired Phycobilisomes and reduced growth rate more strongly in blue than green light. When mpeU was reintroduced in the mpeU mutant background, the mpeU-less phenotype was complemented in terms of PUB content and Phycobilisome content. Fluorescence spectra of mpeU mutant cells and purified Phycobilisomes revealed red-shifted phycoerythrin emission peaks, likely indicating a defect in chromophore ligation to phycoerythrin-I (PE-I) or phycoerythrin-II (PE-II). Our results suggest that MpeU is a lyase-isomerase that attaches a phycoerythrobilin to a PEI or PEII subunit and isomerizes it to PUB. MpeU is therefore an important determinant in adaptation of Synechococcus spp. to capture photons in blue light environments throughout the world’s oceans.
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Diversity and evolution of Phycobilisomes in marine Synechococcusspp.: a comparative genomics study
Genome Biology, 2007Co-Authors: Christophe Six, Jean-claude Thomas, Laurence Garczarek, Martin Ostrowski, Alexis Dufresne, Nicolas Blot, David J Scanlan, Frédéric PartenskyAbstract:Background Marine Synechococcus owe their specific vivid color (ranging from blue-green to orange) to their large extrinsic antenna complexes called Phycobilisomes, comprising a central allophycocyanin core and rods of variable phycobiliprotein composition. Three major pigment types can be defined depending on the major phycobiliprotein found in the rods (phycocyanin, phycoerythrin I or phycoerythrin II). Among strains containing both phycoerythrins I and II, four subtypes can be distinguished based on the ratio of the two chromophores bound to these phycobiliproteins. Genomes of eleven marine Synechococcus strains recently became available with one to four strains per pigment type or subtype, allowing an unprecedented comparative genomics study of genes involved in Phycobilisome metabolism. Results By carefully comparing the Synechococcus genomes, we have retrieved candidate genes potentially required for the synthesis of phycobiliproteins in each pigment type. This includes linker polypeptides, phycobilin lyases and a number of novel genes of uncharacterized function. Interestingly, strains belonging to a given pigment type have similar Phycobilisome gene complements and organization, independent of the core genome phylogeny (as assessed using concatenated ribosomal proteins). While phylogenetic trees based on concatenated allophycocyanin protein sequences are congruent with the latter, those based on phycocyanin and phycoerythrin notably differ and match the Synechococcus pigment types. Conclusion We conclude that the Phycobilisome core has likely evolved together with the core genome, while rods must have evolved independently, possibly by lateral transfer of Phycobilisome rod genes or gene clusters between Synechococcus strains, either via viruses or by natural transformation, allowing rapid adaptation to a variety of light niches.
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Diversity and evolution of Phycobilisomes in marine Synechococcus spp.: a comparative genomics study
Genome Biology, 2007Co-Authors: Christophe Six, Jean-claude Thomas, Laurence Garczarek, Martin Ostrowski, Alexis Dufresne, Nicolas Blot, David J Scanlan, Frédéric PartenskyAbstract:Background: Marine Synechococcus owe their specific vivid color (ranging from blue-green to orange) to their large extrinsic antenna complexes called Phycobilisomes, comprising a central allophycocyanin core and rods of variable phycobiliprotein composition. Three major pigment types can be defined depending on the major phycobiliprotein found in the rods (phycocyanin, phycoerythrin I or phycoerythrin II). Among strains containing both phycoerythrins I and II, four subtypes can be distinguished based on the ratio of the two chromophores bound to these phycobiliproteins. Genomes of eleven marine Synechococcus strains recently became available with one to four strains per pigment type or subtype, allowing an unprecedented comparative genomics study of genes involved in Phycobilisome metabolism. Results: By carefully comparing the Synechococcus genomes, we have retrieved candidate genes potentially required for the synthesis of phycobiliproteins in each pigment type. This includes linker polypeptides, phycobilin lyases and a number of novel genes of uncharacterized function. Interestingly, strains belonging to a given pigment type have similar Phycobilisome gene complements and organization, independent of the core genome phylogeny (as assessed using concatenated ribosomal proteins). While phylogenetic trees based on concatenated allophycocyanin protein sequences are congruent with the latter, those based on phycocyanin and phycoerythrin notably differ and match the Synechococcus pigment types. Conclusion: We conclude that the Phycobilisome core has likely evolved together with the core genome, while rods must have evolved independently, possibly by lateral transfer of Phycobilisome rod genes or gene clusters between Synechococcus strains, either via viruses or by natural transformation, allowing rapid adaptation to a variety of light niches.