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Ara AM, D'Haene S, van Grondelle R, Wahadoszamen M. Unveiling large charge transfer character of PSII in an iron-deficient cyanobacterial membrane: A Stark fluorescence spectroscopy study. Photosynth Res 2024:10.1007/s11120-024-01099-1. [PMID: 38619701 DOI: 10.1007/s11120-024-01099-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 03/25/2024] [Indexed: 04/16/2024]
Abstract
In this work, we applied Stark fluorescence spectroscopy to an iron-stressed cyanobacterial membrane to reveal key insights about the electronic structures and excited state dynamics of the two important pigment-protein complexes, IsiA and PSII, both of which prevail simultaneously within the membrane during iron deficiency and whose fluorescence spectra are highly overlapped and hence often hardly resolved by conventional fluorescence spectroscopy. Thanks to the ability of Stark fluorescence spectroscopy, the fluorescence signatures of the two complexes could be plausibly recognized and disentangled. The systematic analysis of the SF spectra, carried out by employing standard Liptay formalism with a realistic spectral deconvolution protocol, revealed that the IsiA in an intact membrane retains almost identical excited state electronic structures and dynamics as compared to the isolated IsiA we reported in our earlier study. Moreover, the analysis uncovered that the excited state of the PSII subunit of the intact membrane possesses a significantly large CT character. The observed notably large magnitude of the excited state CT character may signify the supplementary role of PSII in regulative energy dissipation during iron deficiency.
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Affiliation(s)
- Anjue Mane Ara
- Department of Physics, Jagannath University, Dhaka, 1100, Bangladesh
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands
| | - Sandrine D'Haene
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands
| | - Rienk van Grondelle
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands
| | - Md Wahadoszamen
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, The Netherlands.
- Department of Physics, University of Dhaka, Dhaka, 1000, Bangladesh.
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Ara AM, Ahmed MK, D'Haene S, van Roon H, Ilioaia C, van Grondelle R, Wahadoszamen M. Absence of far-red emission band in aggregated core antenna complexes. Biophys J 2021; 120:1680-1691. [PMID: 33675767 DOI: 10.1016/j.bpj.2021.02.037] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 01/31/2021] [Accepted: 02/22/2021] [Indexed: 10/22/2022] Open
Abstract
Reported herein is a Stark fluorescence spectroscopy study performed on photosystem II core antenna complexes CP43 and CP47 in their native and aggregated states. The systematic mathematical modeling of the Stark fluorescence spectra with the aid of conventional Liptay formalism revealed that induction of aggregation in both the core antenna complexes via detergent removal results in a single quenched species characterized by a remarkably broad and inhomogenously broadened emission lineshape peaking around 700 nm. The quenched species possesses a fairly large magnitude of charge-transfer character. From the analogy with the results from aggregated peripheral antenna complexes, the quenched species is thought to originate from the enhanced chlorophyll-chlorophyll interaction due to aggregation. However, in contrast, aggregation of both core antenna complexes did not produce a far-red emission band at ∼730 nm, which was identified in most of the aggregated peripheral antenna complexes. The 730-nm emission band of the aggregated peripheral antenna complexes was attributed to the enhanced chlorophyll-carotenoid (lutein1) interaction in the terminal emitter locus. Therefore, it is very likely that the no occurrence of the far-red band in the aggregated core antenna complexes is directly related to the absence of lutein1 in their structures. The absence of the far-red band also suggests the possibility that aggregation-induced conformational change of the core antenna complexes does not yield a chlorophyll-carotenoid interaction associated energy dissipation channel.
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Affiliation(s)
- Anjue Mane Ara
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, the Netherlands; Department of Physics, Jagannath University, Dhaka, Bangladesh
| | | | - Sandrine D'Haene
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, the Netherlands
| | - Henny van Roon
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, the Netherlands
| | - Cristian Ilioaia
- Institute for Integrative Biology of the Cell, CEA, CNRS, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Rienk van Grondelle
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, the Netherlands
| | - Md Wahadoszamen
- Biophysics of Photosynthesis, Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, Amsterdam, the Netherlands; Department of Physics, University of Dhaka, Dhaka, Bangladesh.
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Szewczyk S, Giera W, D'Haene S, van Grondelle R, Gibasiewicz K. Comparison of excitation energy transfer in cyanobacterial photosystem I in solution and immobilized on conducting glass. Photosynth Res 2017; 132:111-126. [PMID: 27696181 PMCID: PMC5387024 DOI: 10.1007/s11120-016-0312-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 09/26/2016] [Indexed: 05/21/2023]
Abstract
Excitation energy transfer in monomeric and trimeric forms of photosystem I (PSI) from the cyanobacterium Synechocystis sp. PCC 6803 in solution or immobilized on FTO conducting glass was compared using time-resolved fluorescence. Deposition of PSI on glass preserves bi-exponential excitation decay of ~4-7 and ~21-25 ps lifetimes characteristic of PSI in solution. The faster phase was assigned in part to photochemical quenching (charge separation) of excited bulk chlorophylls and in part to energy transfer from bulk to low-energy (red) chlorophylls. The slower phase was assigned to photochemical quenching of the excitation equilibrated over bulk and red chlorophylls. The main differences between dissolved and immobilized PSI (iPSI) are: (1) the average excitation decay in iPSI is about 11 ps, which is faster by a few ps than for PSI in solution due to significantly faster excitation quenching of bulk chlorophylls by charge separation (~10 ps instead of ~15 ps) accompanied by slightly weaker coupling of bulk and red chlorophylls; (2) the number of red chlorophylls in monomeric PSI increases twice-from 3 in solution to 6 after immobilization-as a result of interaction with neighboring monomers and conducting glass; despite the increased number of red chlorophylls, the excitation decay accelerates in iPSI; (3) the number of red chlorophylls in trimeric PSI is 4 (per monomer) and remains unchanged after immobilization; (4) in all the samples under study, the free energy gap between mean red (emission at ~710 nm) and mean bulk (emission at ~686 nm) emitting states of chlorophylls was estimated at a similar level of 17-27 meV. All these observations indicate that despite slight modifications, dried PSI complexes adsorbed on the FTO surface remain fully functional in terms of excitation energy transfer and primary charge separation that is particularly important in the view of photovoltaic applications of this photosystem.
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Affiliation(s)
- Sebastian Szewczyk
- Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614, Poznan, Poland
| | - Wojciech Giera
- Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614, Poznan, Poland
| | - Sandrine D'Haene
- Department of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
| | - Rienk van Grondelle
- Department of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
| | - Krzysztof Gibasiewicz
- Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614, Poznan, Poland.
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Wahadoszamen M, D'Haene S, Ara AM, Romero E, Dekker JP, Grondelle RV, Berera R. Identification of common motifs in the regulation of light harvesting: The case of cyanobacteria IsiA. Biochim Biophys Acta 2015; 1847:486-492. [PMID: 25615585 DOI: 10.1016/j.bbabio.2015.01.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Revised: 11/27/2014] [Accepted: 01/12/2015] [Indexed: 10/24/2022]
Abstract
When cyanobacteria are grown under iron-limited or other oxidative stress conditions the iron stress inducible pigment-protein IsiA is synthesized in variable amounts. IsiA accumulates in aggregates inside the photosynthetic membrane that strongly dissipate chlorophyll excited state energy. In this paper we applied Stark fluorescence (SF) spectroscopy at 77K to IsiA aggregates to gain insight into the nature of the emitting and energy dissipating state(s). Our study shows that two emitting states are present in the system, one emitting at 684 nm and the other emitting at about 730 nm. The new 730 nm state exhibits strongly reduced fluorescence (F) together with a large charge transfer character. We discuss these findings in the light of the energy dissipation mechanisms involved in the regulation of photosynthesis in plants, cyanobacteria and diatoms. Our results suggest that photosynthetic organisms have adopted common mechanisms to cope with the deleterious effects of excess light under unfavorable growth conditions.
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Affiliation(s)
- Md Wahadoszamen
- Biophysics of Photosynthesis/Physics of Energy, Department of Physics Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands; Department of Physics, University of Dhaka, Dhaka 1000, Bangladesh.
| | - Sandrine D'Haene
- Biophysics of Photosynthesis/Physics of Energy, Department of Physics Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands
| | - Anjue Mane Ara
- Biophysics of Photosynthesis/Physics of Energy, Department of Physics Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands; Department of Physics, Jagannath University, Dhaka 1100, Bangladesh
| | - Elisabet Romero
- Biophysics of Photosynthesis/Physics of Energy, Department of Physics Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands
| | - Jan P Dekker
- Biophysics of Photosynthesis/Physics of Energy, Department of Physics Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands
| | - Rienk van Grondelle
- Biophysics of Photosynthesis/Physics of Energy, Department of Physics Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands
| | - Rudi Berera
- Biophysics of Photosynthesis/Physics of Energy, Department of Physics Astronomy, Faculty of Sciences, VU University Amsterdam, The Netherlands.
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Wilson A, Kinney JN, Zwart PH, Punginelli C, D'Haene S, Perreau F, Klein MG, Kirilovsky D, Kerfeld CA. Structural determinants underlying photoprotection in the photoactive orange carotenoid protein of cyanobacteria. J Biol Chem 2010; 285:18364-75. [PMID: 20368334 PMCID: PMC2881762 DOI: 10.1074/jbc.m110.115709] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2010] [Revised: 03/21/2010] [Indexed: 01/14/2023] Open
Abstract
The photoprotective processes of photosynthetic organisms involve the dissipation of excess absorbed light energy as heat. Photoprotection in cyanobacteria is mechanistically distinct from that in plants; it involves the orange carotenoid protein (OCP), a water-soluble protein containing a single carotenoid. The OCP is a new member of the family of blue light-photoactive proteins; blue-green light triggers the OCP-mediated photoprotective response. Here we report structural and functional characterization of the wild type and two mutant forms of the OCP, from the model organism Synechocystis PCC6803. The structural analysis provides high resolution detail of the carotenoid-protein interactions that underlie the optical properties of the OCP, unique among carotenoid-proteins in binding a single pigment per polypeptide chain. Collectively, these data implicate several key amino acids in the function of the OCP and reveal that the photoconversion and photoprotective responses of the OCP to blue-green light can be decoupled.
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Affiliation(s)
- Adjele Wilson
- From the Commissariat à l'Energie Atomique, Institut de Biologie et Technologies de Saclay, and
- CNRS, URA 2906, 91191 Gif sur Yvette, France
| | - James N. Kinney
- the Joint Genome Institute, United States Department of Energy, Walnut Creek, California 94598
| | - Petrus H. Zwart
- the Joint Genome Institute, United States Department of Energy, Walnut Creek, California 94598
| | - Claire Punginelli
- From the Commissariat à l'Energie Atomique, Institut de Biologie et Technologies de Saclay, and
- CNRS, URA 2906, 91191 Gif sur Yvette, France
| | - Sandrine D'Haene
- From the Commissariat à l'Energie Atomique, Institut de Biologie et Technologies de Saclay, and
- CNRS, URA 2906, 91191 Gif sur Yvette, France
| | - François Perreau
- the Institut Jean-Pierre Bourgin, UMR 1318 INRA-AgroParisTech, INRA Versailles-Grignon, Route de Saint Cyr, F-78026 Versailles, France, and
| | - Michael G. Klein
- the Joint Genome Institute, United States Department of Energy, Walnut Creek, California 94598
| | - Diana Kirilovsky
- From the Commissariat à l'Energie Atomique, Institut de Biologie et Technologies de Saclay, and
- CNRS, URA 2906, 91191 Gif sur Yvette, France
| | - Cheryl A. Kerfeld
- the Joint Genome Institute, United States Department of Energy, Walnut Creek, California 94598
- the Department of Plant and Microbial Biology, University of California, Berkeley, California 94720
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van der Weij-de Wit CD, Ihalainen JA, van de Vijver E, D'Haene S, Matthijs HC, van Grondelle R, Dekker JP. Fluorescence quenching of IsiA in early stage of iron deficiency and at cryogenic temperatures. Biochimica et Biophysica Acta (BBA) - Bioenergetics 2007; 1767:1393-400. [DOI: 10.1016/j.bbabio.2007.10.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2007] [Revised: 09/14/2007] [Accepted: 10/02/2007] [Indexed: 10/22/2022]
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Ihalainen JA, D'Haene S, Yeremenko N, van Roon H, Arteni AA, Boekema EJ, van Grondelle R, Matthijs HCP, Dekker JP. Aggregates of the chlorophyll-binding protein IsiA (CP43') dissipate energy in cyanobacteria. Biochemistry 2005; 44:10846-53. [PMID: 16086587 DOI: 10.1021/bi0510680] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In many natural habitats, growth of cyanobacteria may be limited by a low concentration of iron. Cyanobacteria respond to this condition by expressing a number of iron-stress-inducible genes, of which the isiA gene encodes a chlorophyll-binding protein known as IsiA or CP43'. IsiA monomers assemble into ring-shaped polymers that encircle trimeric or monomeric photosystem I (PSI), or are present in supercomplexes without PSI, in particular upon prolonged iron starvation. In this report, we present steady-state and time-resolved fluorescence measurements of isolated IsiA aggregates that have been purified from an iron-starved psaFJ-minus mutant of Synechocystis PCC 6803. We show that these aggregates have a fluorescence quantum yield of approximately 2% compared to that of chlorophyll a in acetone, and that the dominating fluorescence lifetimes are 66 and 210 ps, more than 1 order of magnitude shorter than that of free chlorophyll a. Comparison of the temperature dependence of the fluorescence yields and spectra of the isolated aggregates and of the cells from which they were obtained suggests that these aggregates occur naturally in the iron-starved cells. We suggest that IsiA aggregates protect cyanobacterial cells against the deleterious effects of light.
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Affiliation(s)
- Janne A Ihalainen
- Division of Physics and Astronomy, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
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Kouril R, Yeremenko N, D'Haene S, Oostergetel GT, Matthijs HCP, Dekker JP, Boekema EJ. Supercomplexes of IsiA and photosystem I in a mutant lacking subunit PsaL. Biochim Biophys Acta 2005; 1706:262-6. [PMID: 15694354 DOI: 10.1016/j.bbabio.2004.11.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2004] [Revised: 11/22/2004] [Accepted: 11/22/2004] [Indexed: 11/30/2022]
Abstract
The cyanobacterium Synechocystis PCC 6803 grown under short-term iron-deficient conditions assembles a supercomplex consisting of a trimeric Photosystem I (PSI) complex encircled by a ring of 18 IsiA complexes. Furthermore, it has been shown that single or double rings of IsiA with up to 35 copies in total can surround monomeric PSI. Here we present an analysis by electron microscopy and image analysis of the various PSI-IsiA supercomplexes from a Synechocystis PCC 6803 mutant lacking the PsaL subunit after short- and long-term iron-deficient growth. In the absence of PsaL, the tendency to form complexes with IsiA is still strong, but the average number of complete rings is lower than in the wild type. The majority of IsiA copies binds into partial double rings at the side of PsaF/J subunits rather than in complete single or double rings, which also cover the PsaL side of the PSI monomer. This indicates that PsaL facilitates the formation of IsiA rings around PSI monomers but is not an obligatory structural component in the formation of PSI-IsiA complexes.
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Affiliation(s)
- Roman Kouril
- Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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Kouril R, Arteni AA, Lax J, Yeremenko N, D'Haene S, Rögner M, Matthijs HCP, Dekker JP, Boekema EJ. Structure and functional role of supercomplexes of IsiA and Photosystem I in cyanobacterial photosynthesis. FEBS Lett 2005; 579:3253-7. [PMID: 15943969 DOI: 10.1016/j.febslet.2005.03.051] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/29/2005] [Indexed: 10/25/2022]
Abstract
Cyanobacteria express large quantities of the iron stress-inducible protein IsiA under iron deficiency. IsiA can assemble into numerous types of single or double rings surrounding Photosystem I. These supercomplexes are functional in light-harvesting, empty IsiA rings are effective energy dissipaters. Electron microscopy studies of these supercomplexes show that Photosystem I trimers bind 18 IsiA copies in a single ring, whereas monomers may bind up to 35 copies in two rings. Work on mutants indicates that the PsaF/J and PsaL subunits facilitate the formation of closed rings around Photosystem I monomers but are not obligatory components in the formation of Photosystem I-IsiA supercomplexes.
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Affiliation(s)
- Roman Kouril
- Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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Yeremenko N, Kouril R, Ihalainen JA, D'Haene S, van Oosterwijk N, Andrizhiyevskaya EG, Keegstra W, Dekker HL, Hagemann M, Boekema EJ, Matthijs HCP, Dekker JP. Supramolecular organization and dual function of the IsiA chlorophyll-binding protein in cyanobacteria. Biochemistry 2004; 43:10308-13. [PMID: 15301529 DOI: 10.1021/bi048772l] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A significant part of global primary productivity is provided by cyanobacteria, which are abundant in most marine and freshwater habitats. In many oceanographic regions, however, the concentration of iron can be so low that it limits growth. Cyanobacteria respond to this condition by expressing a number of iron stress inducible genes, of which the isiA gene encodes a chlorophyll-binding protein known as IsiA or CP43'. It was recently shown that 18 IsiA proteins encircle trimeric photosystem I (PSI) under iron-deficient growth conditions. We report here that after prolonged growth of Synechocystis PCC 6803 in an iron-deficient medium, the number of bound IsiA proteins can be much higher than previously known. The largest complexes bind 12-14 units in an inner ring and 19-21 units in an outer ring around a PSI monomer. Fluorescence excitation spectra indicate an efficient light harvesting function for all PSI-bound chlorophylls. We also find that IsiA accumulates in cyanobacteria in excess of what is needed for functional light harvesting by PSI, and that a significant part of IsiA builds supercomplexes without PSI. Because the further decline of PSI makes photosystem II (PSII) increasingly vulnerable to photooxidation, we postulate that the surplus synthesis of IsiA shields PSII from excess light. We suggest that IsiA plays a surprisingly versatile role in cyanobacteria, by significantly enhancing the light harvesting ability of PSI and providing photoprotection for PSII.
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Affiliation(s)
- Nataliya Yeremenko
- Aquatic Microbiology, Institute of Biodiversity and Ecosystem Dynamics, Faculty of Science, Universiteit van Amsterdam, Nieuwe Achtergracht 127, 1018 WS Amsterdam, The Netherlands
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11
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Kouril R, Yeremenko N, D'Haene S, Yakushevska AE, Keegstra W, Matthijs HCP, Dekker JP, Boekema EJ. Photosystem I trimers from Synechocystis PCC 6803 lacking the PsaF and PsaJ subunits bind an IsiA ring of 17 units. Biochim Biophys Acta 2004; 1607:1-4. [PMID: 14556907 DOI: 10.1016/j.bbabio.2003.08.002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We report a structural characterization by electron microscopy and image analysis of a supramolecular complex consisting of Photosystem I (PSI) and the chlorophyll-binding protein IsiA from a mutant of the cyanobacterium Synechocystis PCC 6803 lacking the PsaF and PsaJ subunits. The circular complex consists of a central PSI trimer surrounded by a ring of 17 IsiA units, one less than in the wild-type supercomplex. We conclude that PsaF and PsaJ are not obligatory for the binding of the IsiA ring, and that the size of the PSI complex determines the number of IsiA units in the ring. The resulting number of 17 copies implies that each PSI monomer has a different association to the IsiA ring.
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Affiliation(s)
- Roman Kouril
- Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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12
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Andrizhiyevskaya EG, Schwabe TME, Germano M, D'Haene S, Kruip J, van Grondelle R, Dekker JP. Spectroscopic properties of PSI-IsiA supercomplexes from the cyanobacterium Synechococcus PCC 7942. Biochim Biophys Acta 2002; 1556:265-72. [PMID: 12460685 DOI: 10.1016/s0005-2728(02)00371-7] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The cyanobacterium Synechococcus PCC 7942 grown under iron starvation assembles a supercomplex consisting of a trimeric Photosystem I (PSI) complex encircled by a ring of 18 CP43' or IsiA light-harvesting complexes [Nature 412 (2001) 745]. Here we present a spectroscopic characterization by temperature-dependent absorption and fluorescence spectroscopy, site-selective fluorescence spectroscopy at 5 K, and circular dichroism of isolated PSI-IsiA, PSI and IsiA complexes from this cyanobacterium grown under iron starvation. The results suggest that the IsiA ring increases the absorption cross-section of PSI by about 100%. Each IsiA subunit binds about 16-17 chlorophyll a (Chl a) molecules and serves as an efficient antenna for PSI. Each of the monomers of the trimeric PSI complex contains two red chlorophylls, which presumably give rise to one exciton-coupled dimer and at 5 K absorb and fluoresce at 703 and 713 nm, respectively. The spectral properties of these C-703 chlorophylls are not affected by the presence of the IsiA antenna ring. The spectroscopic properties of the purified IsiA complexes are similar to those of the related CP43 complex from plants, except that the characteristic narrow absorption band of CP43 at 682.5 nm is missing in IsiA.
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Affiliation(s)
- Elena G Andrizhiyevskaya
- Division of Physics and Astronomy, Institute of Molecular Biological Science, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
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