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Agostini A, Shen G, Bryant DA, Golbeck JH, van der Est A, Carbonera D. Optically detected magnetic resonance and mutational analysis reveal significant differences in the photochemistry and structure of chlorophyll f synthase and photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2023; 1864:149002. [PMID: 37562512 DOI: 10.1016/j.bbabio.2023.149002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 07/24/2023] [Accepted: 07/31/2023] [Indexed: 08/12/2023]
Abstract
In cyanobacteria that undergo far red light photoacclimation (FaRLiP), chlorophyll (Chl) f is produced by the ChlF synthase enzyme, probably by photo-oxidation of Chl a. The enzyme forms homodimeric complexes and the primary amino acid sequence of ChlF shows a high degree of homology with the D1 subunit of photosystem II (PSII). However, few details of the photochemistry of ChlF are known. The results of a mutational analysis and optically detected magnetic resonance (ODMR) data from ChlF are presented. Both sets of data show that there are significant differences in the photochemistry of ChlF and PSII. Mutation of residues that would disrupt the donor side primary electron transfer pathway in PSII do not inhibit the production of Chl f, while alteration of the putative ChlZ, P680 and QA binding sites rendered ChlF non-functional. Together with previously published transient EPR and flash photolysis data, the ODMR data show that in untreated ChlF samples, the triplet state of P680 formed by intersystem crossing is the primary species generated by light excitation. This is in contrast to PSII, in which 3P680 is only formed by charge recombination when the quinone acceptors are removed or chemically reduced. The triplet states of a carotenoid (3Car) and a small amount of 3Chl f are also observed by ODMR. The polarization pattern of 3Car is consistent with its formation by triplet energy transfer from ChlZ if the carotenoid molecule is rotated by 15° about its long axis compared to the orientation in PSII. It is proposed that the singlet oxygen formed by the interaction between molecular oxygen and 3P680 might be involved in the oxidation of Chl a to Chl f.
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Affiliation(s)
- Alessandro Agostini
- Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131, Padova, Italy; Biology Centre, Czech Academy of Sciences, Institute of Plant Molecular Biology, Branišovská 31, 370 05 Ceske Budejovice, Czech Republic
| | - Gaozhong Shen
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, 16802, USA
| | - Donald A Bryant
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, 16802, USA
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, 16802, USA; Department of Chemistry, The Pennsylvania State University, University Park, 16802, USA
| | - Art van der Est
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock, Way, St. Catharines, ON L2S 3A1, Canada.
| | - Donatella Carbonera
- Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131, Padova, Italy.
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2
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Mohamed A, Nishi S, Kawakami K, Shen JR, Itoh S, Fukumura H, Shibata Y. Exciton quenching by oxidized chlorophyll Z across the two adjacent monomers in a photosystem II core dimer. PHOTOSYNTHESIS RESEARCH 2022; 154:277-289. [PMID: 35976595 DOI: 10.1007/s11120-022-00948-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2022] [Accepted: 07/31/2022] [Indexed: 06/15/2023]
Abstract
This study aimed to clarify (1) which pigment in a photosystem II (PSII) core complex is responsible for the 695-nm emission at 77 K and (2) the molecular basis for the oxidation-induced fluorescence quenching in PSII. Picosecond time-resolved fluorescence dynamics was compared between the dimeric and monomeric PSII with and without addition of an oxidant. The results indicated that the excitation-energy flow to the 695-nm-emitting chlorophyll (Chl) at 36 K and 77 K was hindered upon monomerization, clearly demonstrating significant exciton migration from the Chls on one monomer to the 695-nm-emitting pigment on the adjacent monomer. Oxidation of the redox-active Chl, which is named ChlZ caused almost equal quenching of the 684-nm and 695-nm emission bands in the dimer, and lower quenching of the 695-nm band in the monomer. These results suggested two possible scenarios responsible for the 695-nm emission band: (A) Chl11-13 pair and the oxidized ChlZD1 work as the 695-nm emitting Chl and the quenching site, respectively, and (B) Chl29 and the oxidized ChlZD2 work as the 695-nm emitting Chl and the quenching site, respectively.
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Affiliation(s)
- Ahmed Mohamed
- Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki Aza Aoba, Aoba-Ku, Sendai, 980-8578, Japan
- Centre Énergie Matériaux Télécommunications, Institut National de la Recherche Scientifique, 1650, Boul. Lionel-Boulet, Varennes, QC, J3X 1S2, Canada
| | - Shunsuke Nishi
- Division of Material Science (Physics), Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan
| | - Keisuke Kawakami
- Biostructural Mechanism Laboratory, RIKEN Spring-8 Center, Hyogo, 679-5148, Japan
| | - Jian-Ren Shen
- Research Institute for Interdisciplinary Science, and Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530, Japan
| | - Shigeru Itoh
- Division of Material Science (Physics), Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602, Japan
| | - Hiroshi Fukumura
- Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki Aza Aoba, Aoba-Ku, Sendai, 980-8578, Japan
- Department of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001, Leuven, Belgium
| | - Yutaka Shibata
- Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki Aza Aoba, Aoba-Ku, Sendai, 980-8578, Japan.
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Müh F, Zouni A. Structural basis of light-harvesting in the photosystem II core complex. Protein Sci 2020; 29:1090-1119. [PMID: 32067287 PMCID: PMC7184784 DOI: 10.1002/pro.3841] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2020] [Revised: 02/06/2020] [Accepted: 02/06/2020] [Indexed: 12/20/2022]
Abstract
Photosystem II (PSII) is a membrane-spanning, multi-subunit pigment-protein complex responsible for the oxidation of water and the reduction of plastoquinone in oxygenic photosynthesis. In the present review, the recent explosive increase in available structural information about the PSII core complex based on X-ray crystallography and cryo-electron microscopy is described at a level of detail that is suitable for a future structure-based analysis of light-harvesting processes. This description includes a proposal for a consistent numbering scheme of protein-bound pigment cofactors across species. The structural survey is complemented by an overview of the state of affairs in structure-based modeling of excitation energy transfer in the PSII core complex with emphasis on electrostatic computations, optical properties of the reaction center, the assignment of long-wavelength chlorophylls, and energy trapping mechanisms.
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Affiliation(s)
- Frank Müh
- Department of Theoretical Biophysics, Institute for Theoretical Physics, Johannes Kepler University Linz, Linz, Austria
| | - Athina Zouni
- Humboldt-Universität zu Berlin, Institute for Biology, Biophysics of Photosynthesis, Berlin, Germany
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4
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Wlodarczyk LM, Snellenburg JJ, Dekker JP, Stokkum IHM. Development of fluorescence quenching in Chlamydomonas reinhardtii upon prolonged illumination at 77 K. PHOTOSYNTHESIS RESEARCH 2018; 137:503-513. [PMID: 29948747 PMCID: PMC6182390 DOI: 10.1007/s11120-018-0534-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 06/11/2018] [Indexed: 06/08/2023]
Abstract
Low-temperature fluorescence measurements are frequently used in photosynthesis research to assess photosynthetic processes. Upon illumination of photosystem II (PSII) frozen to 77 K, fluorescence quenching is observed. In this work, we studied the light-induced quenching in intact cells of Chlamydomonas reinhardtii at 77 K using time-resolved fluorescence spectroscopy with a streak camera setup. In agreement with previous studies, global analysis of the data shows that prolonged illumination of the sample affects the nanosecond decay component of the PSII emission. Using target analysis, we resolved the quenching on the PSII-684 compartment which describes bulk chlorophyll molecules of the PSII core antenna. Further, we quantified the quenching rate constant and observed that as the illumination proceeds the accumulation of the quencher leads to a speed up of the fluorescence decay of the PSII-684 compartment as the decay rate constant increases from about 3 to 4 ns- 1. The quenching on PSII-684 leads to indirect quenching of the compartments PSII-690 and PSII-695 which represent the red chlorophyll of the PSII core. These results explain past and current observations of light-induced quenching in 77 K steady-state and time-resolved fluorescence spectra.
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Affiliation(s)
- Lucyna M Wlodarczyk
- LaserLaB, Department of Physics and Astronomy, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
| | - Joris J Snellenburg
- LaserLaB, Department of Physics and Astronomy, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
| | - Jan P Dekker
- LaserLaB, Department of Physics and Astronomy, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands
| | - Ivo H M Stokkum
- LaserLaB, Department of Physics and Astronomy, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
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Dumas L, Zito F, Auroy P, Johnson X, Peltier G, Alric J. Structure-Function Analysis of Chloroplast Proteins via Random Mutagenesis Using Error-Prone PCR. PLANT PHYSIOLOGY 2018; 177:465-475. [PMID: 29703866 PMCID: PMC6001340 DOI: 10.1104/pp.17.01618] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 03/31/2018] [Indexed: 05/14/2023]
Abstract
Site-directed mutagenesis of chloroplast genes was developed three decades ago and has greatly advanced the field of photosynthesis research. Here, we describe a new approach for generating random chloroplast gene mutants that combines error-prone polymerase chain reaction of a gene of interest with chloroplast complementation of the knockout Chlamydomonas reinhardtii mutant. As a proof of concept, we targeted a 300-bp sequence of the petD gene that encodes subunit IV of the thylakoid membrane-bound cytochrome b6f complex. By sequencing chloroplast transformants, we revealed 149 mutations in the 300-bp target petD sequence that resulted in 92 amino acid substitutions in the 100-residue target subunit IV sequence. Our results show that this method is suited to the study of highly hydrophobic, multisubunit, and chloroplast-encoded proteins containing cofactors such as hemes, iron-sulfur clusters, and chlorophyll pigments. Moreover, we show that mutant screening and sequencing can be used to study photosynthetic mechanisms or to probe the mutational robustness of chloroplast-encoded proteins, and we propose that this method is a valuable tool for the directed evolution of enzymes in the chloroplast.
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Affiliation(s)
- Louis Dumas
- Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Aix-Marseille Université, Unité Mixte de Recherche 7265, BIAM, Commissariat à l'Energie Atomique Cadarache, 13115 Saint-Paul-lez-Durance, France
| | - Francesca Zito
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires, Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7099, University Paris Diderot, Sorbonne Paris Cité, PSL Research University, F-75005 Paris, France
| | - Pascaline Auroy
- Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Aix-Marseille Université, Unité Mixte de Recherche 7265, BIAM, Commissariat à l'Energie Atomique Cadarache, 13115 Saint-Paul-lez-Durance, France
| | - Xenie Johnson
- Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Aix-Marseille Université, Unité Mixte de Recherche 7265, BIAM, Commissariat à l'Energie Atomique Cadarache, 13115 Saint-Paul-lez-Durance, France
| | - Gilles Peltier
- Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Aix-Marseille Université, Unité Mixte de Recherche 7265, BIAM, Commissariat à l'Energie Atomique Cadarache, 13115 Saint-Paul-lez-Durance, France
| | - Jean Alric
- Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, Commissariat à l'Energie Atomique, Centre National de la Recherche Scientifique, Aix-Marseille Université, Unité Mixte de Recherche 7265, BIAM, Commissariat à l'Energie Atomique Cadarache, 13115 Saint-Paul-lez-Durance, France jean.alric@cea
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6
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Reinot T, Chen J, Kell A, Jassas M, Robben KC, Zazubovich V, Jankowiak R. On the Conflicting Estimations of Pigment Site Energies in Photosynthetic Complexes: A Case Study of the CP47 Complex. ANALYTICAL CHEMISTRY INSIGHTS 2016; 11:35-48. [PMID: 27279733 PMCID: PMC4892206 DOI: 10.4137/aci.s32151] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 04/10/2016] [Accepted: 04/26/2016] [Indexed: 01/14/2023]
Abstract
We focus on problems with elucidation of site energies
(E0n) for photosynthetic complexes (PSCs) in order to raise some genuine concern regarding the conflicting estimations propagating in the literature. As an example, we provide a stern assessment of the site energies extracted from fits to optical spectra of the widely studied CP47 antenna complex of photosystem II from spinach, though many general comments apply to other PSCs as well. Correct values of
E0n for chlorophyll (Chl) a in CP47 are essential for understanding its excitonic structure, population dynamics, and excitation energy pathway(s). To demonstrate this, we present a case study where simultaneous fits of multiple spectra (absorption, emission, circular dichroism, and nonresonant hole-burned spectra) show that several sets of parameters can fit the spectra very well. Importantly, we show that variable emission maxima (690–695 nm) and sample-dependent bleaching in nonresonant hole-burning spectra reported in literature could be explained, assuming that many previously studied CP47 samples were a mixture of intact and destabilized proteins. It appears that the destabilized subpopulation of CP47 complexes could feature a weakened hydrogen bond between the 131-keto group of Chl29 and the PsbH protein subunit, though other possibilities cannot be entirely excluded, as discussed in this work. Possible implications of our findings are briefly discussed.
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Affiliation(s)
- Tonu Reinot
- Department of Chemistry, Kansas State University, Manhattan, KS, USA
| | - Jinhai Chen
- Department of Chemistry, Kansas State University, Manhattan, KS, USA
| | - Adam Kell
- Department of Chemistry, Kansas State University, Manhattan, KS, USA
| | - Mahboobe Jassas
- Department of Chemistry, Kansas State University, Manhattan, KS, USA
| | - Kevin C Robben
- Department of Chemistry, Kansas State University, Manhattan, KS, USA
| | | | - Ryszard Jankowiak
- Department of Chemistry, Kansas State University, Manhattan, KS, USA.; Department of Physics, Kansas State University, Manhattan, KS, USA
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7
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Mohamed A, Nagao R, Noguchi T, Fukumura H, Shibata Y. Structure-Based Modeling of Fluorescence Kinetics of Photosystem II: Relation between Its Dimeric Form and Photoregulation. J Phys Chem B 2016; 120:365-76. [PMID: 26714062 DOI: 10.1021/acs.jpcb.5b09103] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A photosystem II-enriched membrane (PSII-em) consists of the PSII core complex (PSII-cc) which is surrounded by peripheral antenna complexes. PSII-cc consists of two core antenna (CP43 and CP47) and the reaction center (RC) complex. Time-resolved fluorescence spectra of a PSII-em were measured at 77 K. The data were globally analyzed with a new compartment model, which has a minimum number of compartments and is consistent with the structure of PSII-cc. The reliability of the model was investigated by fitting the data of different experimental conditions. From the analysis, the energy-transfer time constants from the peripheral antenna to CP47 and CP43 were estimated to be 20 and 35 ps, respectively. With an exponential time constant of 320 ps, the excitation energy was estimated to accumulate in the reddest chlorophyll (Red Chl), giving a 692 nm fluorescence peak. The excited state on the Red Chl was confirmed to be quenched upon the addition of an oxidant, as reported previously. The calculations based on the Förster theory predicted that the excitation energy on Chl29 is quenched by ChlZD1(+), which is a redox active but not involved in the electron-transfer chain, located in the D1 subunit of RC, in the other monomer with an exponential time constant of 75 ps. This quenching pathway is consistent with our structure-based simulation of PSII-cc, which assigned Chl29 as the Red Chl. On the other hand, the alternative interpretation assigning Chl26 as the Red Chl was not excluded. The excited Chl26 was predicted to be quenched by another redox active ChlZD2(+) in the D2 subunit of RC in the same monomer unit with an exponential time constant of 88 ps.
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Affiliation(s)
- Ahmed Mohamed
- Department of Chemistry, Graduate School of Science, Tohoku University , Aramaki Aza Aoba, Aoba-Ku, Sendai 980-8578, Japan
| | - Ryo Nagao
- Division of Material Science (Physics), Graduate School of Science, Nagoya University , Furo-Cho, Chikusa-Ku, Nagoya 464-8602, Japan
| | - Takumi Noguchi
- Division of Material Science (Physics), Graduate School of Science, Nagoya University , Furo-Cho, Chikusa-Ku, Nagoya 464-8602, Japan
| | - Hiroshi Fukumura
- Department of Chemistry, Graduate School of Science, Tohoku University , Aramaki Aza Aoba, Aoba-Ku, Sendai 980-8578, Japan
| | - Yutaka Shibata
- Department of Chemistry, Graduate School of Science, Tohoku University , Aramaki Aza Aoba, Aoba-Ku, Sendai 980-8578, Japan
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8
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Narzi D, Bovi D, De Gaetano P, Guidoni L. Dynamics of the Special Pair of Chlorophylls of Photosystem II. J Am Chem Soc 2015; 138:257-64. [PMID: 26587662 DOI: 10.1021/jacs.5b10523] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cholophylls are at the basis of the photosynthetic energy conversion mechanisms in algae, plants, and cyanobacteria. In photosystem II, the photoproduced electrons leave a special pair of chlorophylls (namely, P(D1) and P(D2)) that becomes cationic. This oxidizing pair [P(D1),P(D2)](+), in turn, triggers a cascade of oxidative events, eventually leading to water splitting and oxygen evolution. In the present work, using quantum mechanics/molecular mechanics calculations, we investigate the electronic structure and the dynamics of the P(D1)P(D2) special pair in both its oxidized and reduced states. In agreement with previously reported static calculations, the symmetry between the two chlorophylls was found to be broken, the positive charge being preferentially located on P(D1). Nevertheless, this study reveals for the first time that large charge fluctuations occur along dynamics, temporarily inverting the charge preference for the two branches. Finally, a vibrational analysis pinpointed that such charge fluctuations are strongly coupled to specific modes of the special pair.
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Chen J, Kell A, Acharya K, Kupitz C, Fromme P, Jankowiak R. Critical assessment of the emission spectra of various photosystem II core complexes. PHOTOSYNTHESIS RESEARCH 2015; 124:253-265. [PMID: 25832780 DOI: 10.1007/s11120-015-0128-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2014] [Accepted: 03/23/2015] [Indexed: 06/04/2023]
Abstract
We evaluate low-temperature (low-T) emission spectra of photosystem II core complexes (PSII-cc) previously reported in the literature, which are compared with emission spectra of PSII-cc obtained in this work from spinach and for dissolved PSII crystals from Thermosynechococcus (T.) elongatus. This new spectral dataset is used to interpret data published on membrane PSII (PSII-m) fragments from spinach and Chlamydomonas reinhardtii, as well as PSII-cc from T. vulcanus and intentionally damaged PSII-cc from spinach. This study offers new insight into the assignment of emission spectra reported on PSII-cc from different organisms. Previously reported spectra are also compared with data obtained at different saturation levels of the lowest energy state(s) of spinach and T. elongatus PSII-cc via hole burning in order to provide more insight into emission from bleached and/or photodamaged complexes. We show that typical low-T emission spectra of PSII-cc (with closed RCs), in addition to the 695 nm fluorescence band assigned to the intact CP47 complex (Reppert et al. J Phys Chem B 114:11884-11898, 2010), can be contributed to by several emission bands, depending on sample quality. Possible contributions include (i) a band near 690-691 nm that is largely reversible upon temperature annealing, proving that the band originates from CP47 with a bleached low-energy state near 693 nm (Neupane et al. J Am Chem Soc 132:4214-4229, 2010; Reppert et al. J Phys Chem B 114:11884-11898, 2010); (ii) CP43 emission at 683.3 nm (not at 685 nm, i.e., the F685 band, as reported in the literature) (Dang et al. J Phys Chem B 112:9921-9933, 2008; Reppert et al. J Phys Chem B 112:9934-9947, 2008); (iii) trap emission from destabilized CP47 complexes near 691 nm (FT1) and 685 nm (FT2) (Neupane et al. J Am Chem Soc 132:4214-4229, 2010); and (iv) emission from the RC pigments near 686-687 nm. We suggest that recently reported emission of single PSII-cc complexes from T. elongatus may not represent intact complexes, while those obtained for T. elongatus presented in this work most likely represent intact PSII-cc, since they are nearly indistinguishable from emission spectra obtained for various PSII-m fragments.
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Affiliation(s)
- Jinhai Chen
- Department of Chemistry, Kansas State University, Manhattan, KS, 66506, USA
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10
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Zhang L, Silva DA, Zhang H, Yue A, Yan Y, Huang X. Dynamic protein conformations preferentially drive energy transfer along the active chain of the photosystem II reaction centre. Nat Commun 2014; 5:4170. [PMID: 24954746 PMCID: PMC4083425 DOI: 10.1038/ncomms5170] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 05/20/2014] [Indexed: 11/11/2022] Open
Abstract
One longstanding puzzle concerning photosystem II, a core component of photosynthesis, is that only one of the two symmetric branches in its reaction centre is active in electron transfer. To investigate the effect of the photosystem II environment on the preferential selection of the energy transfer pathway (a prerequisite for electron transfer), we have constructed an exciton model via extensive molecular dynamics simulations and quantum mechanics/molecular mechanics calculations based on a recent X-ray structure. Our results suggest that it is essential to take into account an ensemble of protein conformations to accurately compute the site energies. We identify the cofactor CLA606 of active chain as the most probable site for the energy excitation. We further pinpoint a number of charged protein residues that collectively lower the CLA606 site energy. Our work provides insights into the understanding of molecular mechanisms of the core machinery of the green-plant photosynthesis. Cofactor-mediated energy and electron transfer in photosystem II occurs preferentially through one branch of the reaction centre, despite there being a symmetric path available. Here, the authors use computational methods to determine the influence of protein conformation on this selectivity.
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Affiliation(s)
- Lu Zhang
- Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Daniel-Adriano Silva
- 1] Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [2]
| | - Houdao Zhang
- Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Alexander Yue
- Division of Biomedical Engineering, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - YiJing Yan
- 1] Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [2] Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China
| | - Xuhui Huang
- 1] Department of Chemistry, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [2] Division of Biomedical Engineering, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong [3] Centre of Systems Biology and Human Health, Institute for Advance Study and School of Science, Hong Kong University of Science and Technology, Kowloon, Hong Kong
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11
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Acharya K, Zazubovich V, Reppert M, Jankowiak R. Primary electron donor(s) in isolated reaction center of photosystem II from Chlamydomonas reinhardtii. J Phys Chem B 2012; 116:4860-70. [PMID: 22462595 DOI: 10.1021/jp302849d] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Isolated reaction centers (RCs) from wild-type Chlamydomonas (C.) reinhardtii of Photosystem II (PSII), at different levels of intactness, were studied to provide more insight into the nature of the charge-separation (CS) pathway(s). We argue that previously studied D1/D2/Cytb559 complexes (referred to as RC680), with ChlD1 serving as the primary electron donor, contain destabilized D1 and D2 polypeptides and, as a result, do not provide a representative model system for the intact RC within the PSII core. The shapes of nonresonant transient hole-burned (HB) spectra obtained for more intact RCs (referred to as RC684) are very similar to P(+)QA(-) - PQA absorbance difference and triplet minus singlet spectra measured in PSII core complexes from Synechocystis PCC 6803 [Schlodder et al. Philos. Trans. R. Soc. London, Ser. B2008, 363, 1197]. We show that in the RC684 complexes, both PD1 and ChlD1 may serve as primary electron donors, leading to two different charge separation pathways. Resonant HB spectra cannot distinguish the CS times corresponding to different paths, but it is likely that the zero-phonon holes (ZPHs) observed in the 680-685 nm region (corresponding to CS times of ∼1.4-4.4 ps) reveal the ChlD1 pathway; conversely, the observation of charge-transfer (CT) state(s) in RC684 (in the 686-695 nm range) and the absence of ZPHs at λB > 685 nm likely stem from the PD1 pathway, for which CS could be faster than 1 ps. This is consistent with the finding of Krausz et al. [Photochem. Photobiol. Sci.2005, 4, 744] that CS in intact PSII core complexes can be initiated at low temperatures with fairly long-wavelength excitation. The lack of a clear shift of HB spectra as a function of excitation wavelength within the red-tail of the absorption (i.e., 686-695 nm) and the absence of ZPHs suggest that the lowest-energy CT state is largely homogeneously broadened. On the other hand, in usually studied destabilized RCs, that is, RC680, for which CT states have never been experimentally observed, ChlD1 is the most likely electron donor.
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Affiliation(s)
- Khem Acharya
- Department of Chemistry and ‡Department of Physics, Kansas State University , Manhattan, Kansas 66506, United States
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Acharya K, Neupane B, Zazubovich V, Sayre RT, Picorel R, Seibert M, Jankowiak R. Site energies of active and inactive pheophytins in the reaction center of Photosystem II from Chlamydomonas reinhardtii. J Phys Chem B 2012; 116:3890-9. [PMID: 22397491 DOI: 10.1021/jp3007624] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
It is widely accepted that the primary electron acceptor in various Photosystem II (PSII) reaction center (RC) preparations is pheophytin a (Pheo a) within the D1 protein (Pheo(D1)), while Pheo(D2) (within the D2 protein) is photochemically inactive. The Pheo site energies, however, have remained elusive, due to inherent spectral congestion. While most researchers over the past two decades placed the Q(y)-states of Pheo(D1) and Pheo(D2) bands near 678-684 and 668-672 nm, respectively, recent modeling [Raszewski et al. Biophys. J. 2005, 88, 986 - 998; Cox et al. J. Phys. Chem. B 2009, 113, 12364 - 12374] of the electronic structure of the PSII RC reversed the assignment of the active and inactive Pheos, suggesting that the mean site energy of Pheo(D1) is near 672 nm, whereas Pheo(D2) (~677.5 nm) and Chl(D1) (~680 nm) have the lowest energies (i.e., the Pheo(D2)-dominated exciton is the lowest excited state). In contrast, chemical pigment exchange experiments on isolated RCs suggested that both pheophytins have their Q(y) absorption maxima at 676-680 nm [Germano et al. Biochemistry 2001, 40, 11472 - 11482; Germano et al. Biophys. J. 2004, 86, 1664 - 1672]. To provide more insight into the site energies of both Pheo(D1) and Pheo(D2) (including the corresponding Q(x) transitions, which are often claimed to be degenerate at 543 nm) and to attest that the above two assignments are most likely incorrect, we studied a large number of isolated RC preparations from spinach and wild-type Chlamydomonas reinhardtii (at different levels of intactness) as well as the Chlamydomonas reinhardtii mutant (D2-L209H), in which the active branch Pheo(D1) is genetically replaced with chlorophyll a (Chl a). We show that the Q(x)-/Q(y)-region site energies of Pheo(D1) and Pheo(D2) are ~545/680 nm and ~541.5/670 nm, respectively, in good agreement with our previous assignment [Jankowiak et al. J. Phys. Chem. B 2002, 106, 8803 - 8814]. The latter values should be used to model excitonic structure and excitation energy transfer dynamics of the PSII RCs.
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Affiliation(s)
- K Acharya
- Department of Chemistry, Kansas State University, Manhattan, Kansas 66506, United States
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Shinopoulos KE, Brudvig GW. Cytochrome b₅₅₉ and cyclic electron transfer within photosystem II. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2011; 1817:66-75. [PMID: 21864501 DOI: 10.1016/j.bbabio.2011.08.002] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Revised: 08/06/2011] [Accepted: 08/08/2011] [Indexed: 11/18/2022]
Abstract
Cytochrome b₅₅₉ (Cyt b₅₅₉), β-carotene (Car), and chlorophyll (Chl) cofactors participate in the secondary electron-transfer pathways in photosystem II (PSII), which are believed to protect PSII from photodamage under conditions in which the primary electron-donation pathway leading to water oxidation is inhibited. Among these cofactors, Cyt b₅₅₉ is preferentially photooxidized under conditions in which the primary electron-donation pathway is blocked. When Cyt b₅₅₉ is preoxidized, the photooxidation of several of the 11 Car and 35 Chl molecules present per PSII is observed. In this review, the discovery of the secondary electron donors, their structures and electron-transfer properties, and progress in the characterization of the secondary electron-transfer pathways are discussed. This article is part of a Special Issue entitled: Photosystem II.
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Listening to PS II: Enthalpy, entropy, and volume changes. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2011; 104:357-65. [DOI: 10.1016/j.jphotobiol.2011.03.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2010] [Revised: 03/05/2011] [Accepted: 03/08/2011] [Indexed: 11/17/2022]
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Croce R, van Amerongen H. Light-harvesting and structural organization of Photosystem II: From individual complexes to thylakoid membrane. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2011; 104:142-53. [DOI: 10.1016/j.jphotobiol.2011.02.015] [Citation(s) in RCA: 114] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 02/16/2011] [Accepted: 02/17/2011] [Indexed: 10/18/2022]
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Romero E, van Stokkum IHM, Novoderezhkin VI, Dekker JP, van Grondelle R. Two Different Charge Separation Pathways in Photosystem II. Biochemistry 2010; 49:4300-7. [DOI: 10.1021/bi1003926] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Elisabet Romero
- Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
| | - Ivo H. M. van Stokkum
- Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
| | - Vladimir I. Novoderezhkin
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Leninsky Gory, 119992 Moscow, Russia
| | - Jan P. Dekker
- Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
| | - Rienk van Grondelle
- Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
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Seibert M. Picosecond spectroscopy of the isolated reaction centers from the photosystems of oxygenic photosynthesis--ten years (1987-1997) of fun : a tribute to Michael R. Wasielewski on his 60th birthday. PHOTOSYNTHESIS RESEARCH 2010; 103:1-6. [PMID: 19924560 DOI: 10.1007/s11120-009-9505-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2009] [Accepted: 10/24/2009] [Indexed: 05/28/2023]
Abstract
Mike Wasielewski's pioneering work on Photosystem II photochemistry has an important place in the history of photosynthesis; we are proud to have been associated with him in making those first measurements. Here, we present our association and publications with him, and provide some of the history behind this research.
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Litvin R, Bina D, Vacha F. Room temperature photooxidation of beta-carotene and peripheral chlorophyll in photosystem II reaction centre. PHOTOSYNTHESIS RESEARCH 2008; 98:179-87. [PMID: 18770011 DOI: 10.1007/s11120-008-9339-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Accepted: 07/23/2008] [Indexed: 05/26/2023]
Abstract
Differential kinetic absorption spectra were measured during actinic illumination of photosystem II reaction centres and core complexes in the presence of electron acceptors silicomolybdate and ferricyanide. The spectra of samples with ferricyanide differ from those with both ferricyanide and silicomolybdate. Near-infrared spectra show temporary beta-carotene and peripheral chlorophyll oxidation during room temperature actinic illumination. Peripheral chlorophyll is photooxidized even after decay of beta-carotene oxidation activity and significant reduction of beta-carotene content in both reaction centres and photosystem II core complexes. Besides, new carotenoid cation is observed after about 1 s of actinic illumination in the reaction centres when silicomolybdate is present. Similar result was observed in PSII core complexes. HPLC analyses of illuminated reaction centres reveal several novel carotenoids, whereas no new carotenoid species were observed in HPLC of illuminated core complexes. Our data support the proposal that pigments of inner antenna are a sink of cations originating in the photosystem II reaction centre.
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Affiliation(s)
- Radek Litvin
- Biology Centre of AVCR, vvi, Institute of Plant Molecular Biology, Ceske Budejovice, Czech Republic
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Function of two beta-carotenes near the D1 and D2 proteins in photosystem II dimers. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1767:79-87. [PMID: 17123463 DOI: 10.1016/j.bbabio.2006.10.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2006] [Revised: 10/11/2006] [Accepted: 10/12/2006] [Indexed: 10/24/2022]
Abstract
The antenna proteins in photosystem II (PSII) not only promote energy transfer to the photosynthetic reaction center (RC) but provide also an efficient cation sink to re-reduce chlorophyll a if the electron transfer (ET) from the Mn-cluster is inhibited. Using the newest PSII dimer crystal structure (3.0 A resolution), in which 11 beta-carotene molecules (Car) and 14 lipids are visible in the PSII monomer, we calculated the redox potentials (Em) of one-electron oxidation for all Car (Em(Car)) by solving the Poisson-Boltzmann equation. In each PSII monomer, the D1 protein harbors a previously unlocated Car (CarD1) in van der Waals contact with the chlorin ring of ChlZ(D1). Each CarD1 in the PSII dimer complex is located in the interface between the D1 and CP47 subunits, together with another four Car of the other PSII monomer and several lipid molecules. The proximity of Car bridging between CarD1 and plastoquinone/Q(A) may imply a direct charge recombination of Car+Q(A)-. The calculated Em(CarD1) and Em(ChlZ(D1)) are, respectively, 83 and 126 mV higher than Em(CarD2) and Em(ChlZ(D2)), which could explain why CarD2+ and ChlZ(D2)+ are observed rather than the corresponding CarD1+ and ChlZ(D1)+.
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Holzwarth AR, Müller MG, Reus M, Nowaczyk M, Sander J, Rögner M. Kinetics and mechanism of electron transfer in intact photosystem II and in the isolated reaction center: pheophytin is the primary electron acceptor. Proc Natl Acad Sci U S A 2006; 103:6895-900. [PMID: 16641109 PMCID: PMC1458990 DOI: 10.1073/pnas.0505371103] [Citation(s) in RCA: 231] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The mechanism and kinetics of electron transfer in isolated D1/D2-cyt(b559) photosystem (PS) II reaction centers (RCs) and in intact PSII cores have been studied by femtosecond transient absorption and kinetic compartment modeling. For intact PSII, a component of approximately 1.5 ps reflects the dominant energy-trapping kinetics from the antenna by the RC. A 5.5-ps component reflects the apparent lifetime of primary charge separation, which is faster by a factor of 8-12 than assumed so far. The 35-ps component represents the apparent lifetime of formation of a secondary radical pair, and the approximately 200-ps component represents the electron transfer to the Q(A) acceptor. In isolated RCs, the apparent lifetimes of primary and secondary charge separation are approximately 3 and 11 ps, respectively. It is shown (i) that pheophytin is reduced in the first step, and (ii) that the rate constants of electron transfer in the RC are identical for PSII cores and for isolated RCs. We interpret the first electron transfer step as electron donation from the primary electron donor Chl(acc D1). Thus, this mechanism, suggested earlier for isolated RCs at cryogenic temperatures, is also operative in intact PSII cores and in isolated RCs at ambient temperature. The effective rate constant of primary electron transfer from the equilibrated RC* excited state is 170-180 ns(-1), and the rate constant of secondary electron transfer is 120-130 ns(-1).
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Affiliation(s)
- A R Holzwarth
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim a.d. Ruhr, Germany.
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Liu W, Lu Y, Liu Y, Liu K, Yan Y, Kong J, Xu C, Qian S. Effect of the in situ electrochemical oxidation on the pigment–protein arrangement and energy transfer in light-harvesting complex from Rhodobacter sphaeroides 601. Biochem Biophys Res Commun 2006; 340:505-11. [PMID: 16380087 DOI: 10.1016/j.bbrc.2005.12.034] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2005] [Accepted: 12/05/2005] [Indexed: 11/20/2022]
Abstract
The oxidation of bacteriochlorophylls (BChls) in peripheral light-harvesting complexes (LH2) from Rhodobacter sphaeroides was investigated by spectroelectrochemistry of absorption, fluorescence emission, and femtosecond (fs) pump-probe, with the aim obtaining information about the effect of in situ electrochemical oxidation on the pigment-protein arrangement and energy transfer within LH2. The experimental results revealed that: (a) the generation of the BChl radical cation in both B800 and B850 rings dramatically induced bleaching of the characteristic absorption in the NIR region and quenching of the fluorescence emission from the B850 ring for the electrochemical oxidized LH2; (b) the BChl-B850 radical cation might act as an additional channel to compete with the unoxidized BChl-B850 molecules for rapidly releasing the excitation energy, however the B800-B850 energy transfer rate remained almost unchanged during the oxidation process.
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Affiliation(s)
- Weimin Liu
- Physics Department, Fudan University, Shanghai 200433, China
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Xiong L, Sayre RT. Engineering the chloroplast encoded proteins of chlamydomonas. PHOTOSYNTHESIS RESEARCH 2004; 80:411-9. [PMID: 16328837 DOI: 10.1023/b:pres.0000030458.98624.37] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Over a decade ago (1988), John Boynton and colleagues successfully transformed the chloroplast genome of chlamydomonas for the first time by complementation of a chloroplast deletion mutant. Since the first demonstration of chloroplast transformation the function and structure of many chloroplast encoded subunits of the photosynthetic apparatus has been characterized by site-directed mutagenesis. With the completion of the sequencing of the Chlamydomonas chloroplast genome the genetic tools are now in hand to characterize structure-function relationships for each of the chloroplast-encoded proteins of the photosynthetic apparatus.
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Affiliation(s)
- Ling Xiong
- Department of Plant Biology, Ohio State University, Columbus, OH, 43210, USA
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Minagawa J, Takahashi Y. Structure, function and assembly of Photosystem II and its light-harvesting proteins. PHOTOSYNTHESIS RESEARCH 2004; 82:241-63. [PMID: 16143838 DOI: 10.1007/s11120-004-2079-2] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2003] [Accepted: 07/19/2004] [Indexed: 05/02/2023]
Abstract
Photosystem II (PSII) is a multisubunit chlorophyll-protein complex that drives electron transfer from water to plastoquinone using energy derived from light. In green plants, the native form of PSII is surrounded by the light-harvesting complex (LHCII complex) and thus it is called the PSII-LHCII supercomplex. Over the past several years, understanding of the structure, function, and assembly of PSII and LHCII complexes has increased considerably. The unicellular green alga Chlamydomonas reinhardtii has been an excellent model organism to study PSII and LHCII complexes, because this organism grows heterotrophically and photoautotrophically and it is amenable to biochemical, genetic, molecular biological and recombinant DNA methodology. Here, the genes encoding and regulating components of the C. reinhardtii PSII-LHCII supercomplex have been thoroughly catalogued: they include 15 chloroplast and 20 nuclear structural genes as well as 13 nuclear genes coding for regulatory factors. This review discusses these molecular genetic data and presents an overview of the structure, function and assembly of PSII and LHCII complexes.
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Affiliation(s)
- Jun Minagawa
- Institute of Low Temperature Science, Hokkaido University, N19 W8, Sapporo, 060-0819, Japan,
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Vasil'ev S, Brudvig GW, Bruce D. The X-ray structure of photosystem II reveals a novel electron transport pathway between P680, cytochrome b559 and the energy-quenching cation, ChlZ+. FEBS Lett 2003; 543:159-63. [PMID: 12753925 DOI: 10.1016/s0014-5793(03)00442-3] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
When water oxidation by photosystem II (PSII) is impaired, an oxidized chlorophyll (Chl(Z)(+)) is formed that quenches excitation and may prevent photodamage. Both the identification of this Chl(+) and the mechanism of its oxidation and reduction are controversial. Using the available X-ray structures of PSII we calculated the efficiency of two proposed quenchers, Chl(Z)(+)(D1) and Chl(Z)(+)(D2). Of these two, only Chl(Z)(+)(D1) can quench to the degree observed experimentally. We also identify a chain of closely spaced pigments in the structure from Thermosynechococcus vulcanus that we propose to form a novel electron transport pathway between Chl(Z)(D1), beta-carotene, P680(+) and cytochrome b(559).
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Affiliation(s)
- Sergej Vasil'ev
- Department of Biological Sciences, Brock University, L2S 3A1, St. Catharines, ON, Canada
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Seibert M, Wasielewski MR. The isolated Photosystem II reaction center: first attempts to directly measure the kinetics of primary charge separation. PHOTOSYNTHESIS RESEARCH 2003; 76:263-8. [PMID: 16228586 DOI: 10.1023/a:1024986307839] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Direct measurements of the intrinsic rate of primary charge separation in the isolated Photosystem II (PS II) reaction center complex had to await the availability of suitable, stabilized reaction center materials as well as sophisticated femtosecond transient absorption spectroscopic techniques. The events that led to the first direct measurements of the primary charge separation act in PS II and discussions of the results thereafter are chronicled in this brief historical review.
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Affiliation(s)
- Michael Seibert
- National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO, 80401-3393, USA,
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Telfer A. What is beta-carotene doing in the photosystem II reaction centre? Philos Trans R Soc Lond B Biol Sci 2002; 357:1431-39; discussion 1439-40, 1469-70. [PMID: 12437882 PMCID: PMC1693050 DOI: 10.1098/rstb.2002.1139] [Citation(s) in RCA: 171] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
During photosynthesis carotenoids normally serve as antenna pigments, transferring singlet excitation energy to chlorophyll, and preventing singlet oxygen production from chlorophyll triplet states, by rapid spin exchange and decay of the carotenoid triplet to the ground state. The presence of two beta-carotene molecules in the photosystem II reaction centre (RC) now seems well established, but they do not quench the triplet state of the primary electron-donor chlorophylls, which are known as P(680). The beta-carotenes cannot be close enough to P(680) for triplet quenching because that would also allow extremely fast electron transfer from beta-carotene to P(+)(680), preventing the oxidation of water. Their transfer of excitation energy to chlorophyll, though not very efficient, indicates close proximity to the chlorophylls ligated by histidine 118 towards the periphery of the two main RC polypeptides. The primary function of the beta-carotenes is probably the quenching of singlet oxygen produced after charge recombination to the triplet state of P(680). Only when electron donation from water is disturbed does beta-carotene become oxidized. One beta-carotene can mediate cyclic electron transfer via cytochrome b559. The other is probably destroyed upon oxidation, which might trigger a breakdown of the polypeptide that binds the cofactors that carry out charge separation.
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Affiliation(s)
- Alison Telfer
- Wolfson Laboratories, Department of Biological Sciences, Imperial College of Science, Technology and Medicine, London SW7 2AY, UK.
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Fyfe PK, Jones MR, Heathcote P. Insights into the evolution of the antenna domains of Type-I and Type-II photosynthetic reaction centres through homology modelling. FEBS Lett 2002; 530:117-23. [PMID: 12387877 DOI: 10.1016/s0014-5793(02)03436-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The (bacterio)chlorophylls of photosynthetic antenna and reaction centre complexes are bound to the protein via a fifth, axial ligand to the central magnesium atom. A number of the amino acids identified as providing such ligands are conserved between the large antenna of the cyanobacterial Type-I reaction centre and smaller antennas of the Type-I reaction centres of green sulphur bacteria and heliobacteria, and these numbers match closely the estimated number of antenna bacteriochlorophylls in the latter. The possible organisation of the antenna in the latter reaction centres is discussed, as is the mechanism by which the more pigment-rich antenna of the cyanobacterial reaction centre evolved. The homology modelling approach is also extended to the six-helix antenna proteins CP47 and CP43 associated with the Photosystem II reaction centre.
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Affiliation(s)
- Paul K Fyfe
- Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, UK
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Xiong J, Bauer CE. A cytochrome b origin of photosynthetic reaction centers: an evolutionary link between respiration and photosynthesis. J Mol Biol 2002; 322:1025-37. [PMID: 12367526 DOI: 10.1016/s0022-2836(02)00822-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The evolutionary origin of photosynthetic reaction centers has long remained elusive. Here, we use sequence and structural analysis to demonstrate an evolutionary link between the cytochrome b subunit of the cytochrome bc(1) complex and the core polypeptides of the photosynthetic bacterial reaction center. In particular, we have identified an area of significant sequence similarity between a three contiguous membrane-spanning domain of cytochrome b, which contains binding sites for two hemes, and a three contiguous membrane-spanning domain in the photosynthetic reaction center core subunits, which contains binding sites for cofactors such as (bacterio)chlorophylls, (bacterio)pheophytin and a non-heme iron. Three of the four heme ligands in cytochrome b are found to be conserved with the cofactor ligands in the reaction center polypeptides. Since cytochrome b and reaction center polypeptides both bind tetrapyrroles and quinones for electron transfer, the observed sequence, functional and structural similarities can best be explained with the assumption of a common evolutionary origin. Statistical analysis further supports a distant but significant homologous relationship. On the basis of previous evolutionary analyses that established a scenario that respiration evolved prior to photosynthesis, we consider it likely that cytochrome b is the evolutionary precursor for type II reaction center apoproteins. With a structural analysis confirming a common evolutionary origin of both type I and type II reaction centers, we further propose a novel "reaction center apoprotein early" hypothesis to account for the development of photosynthetic reaction center holoproteins.
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Affiliation(s)
- Jin Xiong
- Department of Biology, Texas A&M University, College Station, TX 77843, USA
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