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Luo L, Martin AP, Tandoh EK, Chistoserdov A, Slipchenko LV, Savikhin S, Xu W. Impact of Peripheral Hydrogen Bond on Electronic Properties of the Primary Acceptor Chlorophyll in the Reaction Center of Photosystem I. Int J Mol Sci 2024; 25:4815. [PMID: 38732034 PMCID: PMC11084960 DOI: 10.3390/ijms25094815] [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] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2024] [Revised: 04/18/2024] [Accepted: 04/24/2024] [Indexed: 05/13/2024] Open
Abstract
Photosystem I (PS I) is a photosynthetic pigment-protein complex that absorbs light and uses the absorbed energy to initiate electron transfer. Electron transfer has been shown to occur concurrently along two (A- and B-) branches of reaction center (RC) cofactors. The electron transfer chain originates from a special pair of chlorophyll a molecules (P700), followed by two chlorophylls and one phylloquinone in each branch (denoted as A-1, A0, A1, respectively), converging in a single iron-sulfur complex Fx. While there is a consensus that the ultimate electron donor-acceptor pair is P700+A0-, the involvement of A-1 in electron transfer, as well as the mechanism of the very first step in the charge separation sequence, has been under debate. To resolve this question, multiple groups have targeted electron transfer cofactors by site-directed mutations. In this work, the peripheral hydrogen bonds to keto groups of A0 chlorophylls have been disrupted by mutagenesis. Four mutants were generated: PsaA-Y692F; PsaB-Y667F; PsaB-Y667A; and a double mutant PsaA-Y692F/PsaB-Y667F. Contrary to expectations, but in agreement with density functional theory modeling, the removal of the hydrogen bond by Tyr → Phe substitution was found to have a negligible effect on redox potentials and optical absorption spectra of respective chlorophylls. In contrast, Tyr → Ala substitution was shown to have a fatal effect on the PS I function. It is thus inferred that PsaA-Y692 and PsaB-Y667 residues have primarily structural significance, and their ability to coordinate respective chlorophylls in electron transfer via hydrogen bond plays a minor role.
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Affiliation(s)
- Lujun Luo
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA; (L.L.)
| | - Antoine P. Martin
- Department of Physics, Purdue University, West Lafayette, IN 47907, USA
| | - Elijah K. Tandoh
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA; (L.L.)
| | - Andrei Chistoserdov
- Department of Biology, University of Louisiana at Lafayette, Lafayette, LA 70504, USA
| | | | - Sergei Savikhin
- Department of Physics, Purdue University, West Lafayette, IN 47907, USA
| | - Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA; (L.L.)
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Mäusle SM, Agarwala N, Eichmann VG, Dau H, Nürnberg DJ, Hastings G. Nanosecond time-resolved infrared spectroscopy for the study of electron transfer in photosystem I. Photosynth Res 2024; 159:229-239. [PMID: 37420121 PMCID: PMC10991071 DOI: 10.1007/s11120-023-01035-9] [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] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Accepted: 06/21/2023] [Indexed: 07/09/2023]
Abstract
Microsecond time-resolved step-scan FTIR difference spectroscopy was used to study photosystem I (PSI) from Thermosynechococcus vestitus BP-1 (T. vestitus, formerly known as T. elongatus) at 77 K. In addition, photoaccumulated (P700+-P700) FTIR difference spectra were obtained at both 77 and 293 K. The FTIR difference spectra are presented here for the first time. To extend upon these FTIR studies nanosecond time-resolved infrared difference spectroscopy was also used to study PSI from T. vestitus at 296 K. Nanosecond infrared spectroscopy has never been used to study PSI samples at physiological temperatures, and here it is shown that such an approach has great value as it allows a direct probe of electron transfer down both branches in PSI. In PSI at 296 K, the infrared flash-induced absorption changes indicate electron transfer down the B- and A-branches is characterized by time constants of 33 and 364 ns, respectively, in good agreement with visible spectroscopy studies. These time constants are associated with forward electron transfer from A1- to FX on the B- and A-branches, respectively. At several infrared wavelengths flash-induced absorption changes at 296 K recover in tens to hundreds of milliseconds. The dominant decay phase is characterized by a lifetime of 128 ms. These millisecond changes are assigned to radical pair recombination reactions, with the changes being associated primarily with P700+ rereduction. This conclusion follows from the observation that the millisecond infrared spectrum is very similar to the photoaccumulated (P700+-P700) FTIR difference spectrum.
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Affiliation(s)
- Sarah M Mäusle
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany
| | - Neva Agarwala
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA
- Department of Chemistry, Georgia State University, Atlanta, GA, 30303, USA
| | - Viktor G Eichmann
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany
| | - Holger Dau
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
| | - Dennis J Nürnberg
- Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195, Berlin, Germany.
- Dahlem Centre of Plant Sciences, Freie Universität Berlin, Berlin, Germany.
| | - Gary Hastings
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA.
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Agarwala N, Makita H, Hastings G. Time-resolved FTIR difference spectroscopy for the study of photosystem I with high potential naphthoquinones incorporated into the A 1 binding site. Biochim Biophys Acta Bioenerg 2023; 1864:148918. [PMID: 36116485 DOI: 10.1016/j.bbabio.2022.148918] [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: 07/12/2022] [Revised: 09/08/2022] [Accepted: 09/11/2022] [Indexed: 11/28/2022]
Abstract
Time-resolved step-scan Fourier transform infrared difference spectroscopy has been used to study cyanobacterial photosystem I photosynthetic reaction centers from Synechocystis sp. PCC 6803 (S6803) with four high-potential, 1,4-naphthoquinones incorporated into the A1 binding site. The high-potential naphthoquinones are 2-chloro-, 2-bromo-, 2,3-dichloro- and 2,3-dibromo-1,4-naphthoquinone. "Foreign minus native" double difference spectra (DDS) were constructed by subtracting difference spectra for native photosystem I (with phylloquinone in the A1 binding site) from corresponding spectra obtained using photosystem I with the different quinones incorporated. To help assess and assign bands in the difference and double difference spectra, density functional theory based vibrational frequency calculations for the different quinones in solvent, or in the presence of a single asymmetric H- bond to either a water molecule or a peptide backbone NH group, were undertaken. Calculated and experimental spectra agree best for the peptide backbone asymmetrically H- bonded system. By comparing multiple sets of double difference spectra, several new bands for the native quinone (phylloquinone) are identified. By comparing calculated and experimental spectra we conclude that the mono-substituted halogenated NQs can occupy the binding site in either of two different orientations, with the chlorine or bromine atom being either ortho or meta to the H- bonded CO group.
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Affiliation(s)
- Neva Agarwala
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, USA
| | - Hiroki Makita
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, USA
| | - Gary Hastings
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, USA.
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Song Y, Sechrist R, Nguyen HH, Johnson W, Abramavicius D, Redding KE, Ogilvie JP. Excitonic structure and charge separation in the heliobacterial reaction center probed by multispectral multidimensional spectroscopy. Nat Commun 2021; 12:2801. [PMID: 33990569 DOI: 10.1038/s41467-021-23060-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Accepted: 04/09/2021] [Indexed: 12/29/2022] Open
Abstract
Photochemical reaction centers are the engines that drive photosynthesis. The reaction center from heliobacteria (HbRC) has been proposed to most closely resemble the common ancestor of photosynthetic reaction centers, motivating a detailed understanding of its structure-function relationship. The recent elucidation of the HbRC crystal structure motivates advanced spectroscopic studies of its excitonic structure and charge separation mechanism. We perform multispectral two-dimensional electronic spectroscopy of the HbRC and corresponding numerical simulations, resolving the electronic structure and testing and refining recent excitonic models. Through extensive examination of the kinetic data by lifetime density analysis and global target analysis, we reveal that charge separation proceeds via a single pathway in which the distinct A0 chlorophyll a pigment is the primary electron acceptor. In addition, we find strong delocalization of the charge separation intermediate. Our findings have general implications for the understanding of photosynthetic charge separation mechanisms, and how they might be tuned to achieve different functional goals. The primary energy conversion step in photosynthesis, charge separation, takes place in the reaction center. Here the authors investigate the heliobacterial reaction center using multispectral two-dimensional electronic spectroscopy, identifying the primary electron acceptor and revealing the charge separation mechanism.
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Agarwala N, Makita H, Luo L, Xu W, Hastings G. Reversible inhibition and reactivation of electron transfer in photosystem I. Photosynth Res 2020; 145:97-109. [PMID: 32447611 DOI: 10.1007/s11120-020-00760-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2020] [Accepted: 05/12/2020] [Indexed: 06/11/2023]
Abstract
In photosystem I (PSI) complexes at room temperature electron transfer from A1- to FX is an order of magnitude faster on the B-branch compared to the A-branch. One factor that might contribute to this branch asymmetry in time constants is TrpB673 (Thermosynechococcus elongatus numbering), which is located between A1B and FX. The corresponding residue on the A-branch, between A1A and FX, is GlyA693. Here, microsecond time-resolved step-scan FTIR difference spectroscopy at 77 K has been used to study isolated PSI complexes from wild type and TrpB673Phe mutant (WB673F mutant) cells from Synechocystis sp. PCC 6803. WB673F mutant cells require glucose for growth and are light sensitive. Photoaccumulated FTIR difference spectra indicate changes in amide I and II protein vibrations upon mutation of TrpB673 to Phe, indicating the protein environment near FX is altered upon mutation. In the WB673F mutant PSI samples, but not in WT PSI samples, the phylloquinone molecule that occupies the A1 binding site is likely doubly protonated following long periods of repetitive flash illumination at room temperature. PSI with (doubly) protonated quinone in the A1 binding site are not functional in electron transfer. However, electron transfer functionality can be restored by incubating the light-treated mutant PSI samples in the presence of added phylloquinone.
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Affiliation(s)
- Neva Agarwala
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA
| | - Hiroki Makita
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA
| | - Lujun Luo
- Department of Chemistry, University of Louisiana At Lafayette, Lafayette, LA, 70503, USA
| | - Wu Xu
- Department of Chemistry, University of Louisiana At Lafayette, Lafayette, LA, 70503, USA
| | - Gary Hastings
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, 30303, USA.
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Makita H, Hastings G. Time-resolved FTIR difference spectroscopy for the study of quinones in the A 1 binding site in photosystem I: Identification of neutral state quinone bands. Biochim Biophys Acta Bioenerg 2020; 1861:148173. [PMID: 32059842 DOI: 10.1016/j.bbabio.2020.148173] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 02/05/2020] [Accepted: 02/10/2020] [Indexed: 11/24/2022]
Abstract
Infrared absorption bands associated with the neutral state of quinones in the A1 binding site in photosystem I (PSI) have been difficult to identify in the past. This problem is addressed here, where time-resolved step-scan FTIR difference spectroscopy at 77 K has been used to study PSI with six different quinones incorporated into the A1 binding site. (P700+A1- - P700A1) and (A1- - A1) FTIR difference spectra (DS) were obtained for PSI with the different quinones incorporated, and several double-difference spectra (DDS) were constructed from the DS. From analysis of the DS and DDS, in combination with density functional theory based vibrational frequency calculations of the quinones, the neutral state bands of the incorporated quinones are identified and assigned. For neutral PhQ in the A1 binding site, infrared absorption bands were identified near 1665 and 1635 cm-1, that are due to the C1O and C4O stretching vibrations of the incorporated PhQ, respectively. These assignments indicate a 30 cm-1 separation between the C1O and C4O modes, considerably less than the ~80 cm-1 found for similar modes of PhQ-. The C4O mode downshifts due to hydrogen bonding, so the suggestion is that hydrogen bonding is weaker for the neutral state compared to the anion state, indicating radical-induced proton dynamics associated with the quinone in the A1 binding site in PSI.
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Affiliation(s)
- Hiroki Makita
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA
| | - Gary Hastings
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA.
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Makita H, Hastings G. Time-resolved step-scan FTIR difference spectroscopy for the study of photosystem I with different benzoquinones incorporated into the A1 binding site. Biochimica et Biophysica Acta (BBA) - Bioenergetics 2018; 1859:1199-1206. [DOI: 10.1016/j.bbabio.2018.08.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 08/16/2018] [Accepted: 08/21/2018] [Indexed: 11/28/2022]
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Akhtar P, Zhang C, Liu Z, Tan HS, Lambrev PH. Excitation transfer and trapping kinetics in plant photosystem I probed by two-dimensional electronic spectroscopy. Photosynth Res 2018; 135:239-250. [PMID: 28808836 DOI: 10.1007/s11120-017-0427-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Accepted: 08/01/2017] [Indexed: 05/24/2023]
Abstract
Photosystem I is a robust and highly efficient biological solar engine. Its capacity to utilize virtually every absorbed photon's energy in a photochemical reaction generates great interest in the kinetics and mechanisms of excitation energy transfer and charge separation. In this work, we have employed room-temperature coherent two-dimensional electronic spectroscopy and time-resolved fluorescence spectroscopy to follow exciton equilibration and excitation trapping in intact Photosystem I complexes as well as core complexes isolated from Pisum sativum. We performed two-dimensional electronic spectroscopy measurements with low excitation pulse energies to record excited-state kinetics free from singlet-singlet annihilation. Global lifetime analysis resolved energy transfer and trapping lifetimes closely matches the time-correlated single-photon counting data. Exciton energy equilibration in the core antenna occurred on a timescale of 0.5 ps. We further observed spectral equilibration component in the core complex with a 3-4 ps lifetime between the bulk Chl states and a state absorbing at 700 nm. Trapping in the core complex occurred with a 20 ps lifetime, which in the supercomplex split into two lifetimes, 16 ps and 67-75 ps. The experimental data could be modelled with two alternative models resulting in equally good fits-a transfer-to-trap-limited model and a trap-limited model. However, the former model is only possible if the 3-4 ps component is ascribed to equilibration with a "red" core antenna pool absorbing at 700 nm. Conversely, if these low-energy states are identified with the P700 reaction centre, the transfer-to-trap-model is ruled out in favour of a trap-limited model.
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Affiliation(s)
- Parveen Akhtar
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
- Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, Szeged, 6726, Hungary
| | - Cheng Zhang
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Zhengtang Liu
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore
| | - Howe-Siang Tan
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore, 637371, Singapore.
| | - Petar H Lambrev
- Biological Research Centre, Hungarian Academy of Sciences, Temesvári krt. 62, Szeged, 6726, Hungary.
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Badshah SL, Sun J, Mula S, Gorka M, Baker P, Luthra R, Lin S, van der Est A, Golbeck JH, Redding KE. Mutations in algal and cyanobacterial Photosystem I that independently affect the yield of initial charge separation in the two electron transfer cofactor branches. Biochimica et Biophysica Acta (BBA) - Bioenergetics 2018; 1859:42-55. [DOI: 10.1016/j.bbabio.2017.10.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 10/16/2017] [Accepted: 10/17/2017] [Indexed: 01/02/2023]
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Makita H, Hastings G. Inverted-region electron transfer as a mechanism for enhancing photosynthetic solar energy conversion efficiency. Proc Natl Acad Sci U S A 2017; 114:9267-72. [PMID: 28814630 DOI: 10.1073/pnas.1704855114] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
In all photosynthetic organisms, light energy is used to drive electrons from a donor chlorophyll species via a series of acceptors across a biological membrane. These light-induced electron-transfer processes display a remarkably high quantum efficiency, indicating a near-complete inhibition of unproductive charge recombination reactions. It has been suggested that unproductive charge recombination could be inhibited if the reaction occurs in the so-called inverted region. However, inverted-region electron transfer has never been demonstrated in any native photosynthetic system. Here we demonstrate that the unproductive charge recombination in native photosystem I photosynthetic reaction centers does occur in the inverted region, at both room and cryogenic temperatures. Computational modeling of light-induced electron-transfer processes in photosystem I demonstrate a marked decrease in photosynthetic quantum efficiency, from 98% to below 72%, if the unproductive charge recombination process does not occur in the inverted region. Inverted-region electron transfer is therefore demonstrated to be an important mechanism contributing to efficient solar energy conversion in photosystem I. Inverted-region electron transfer does not appear to be an important mechanism in other photosystems; it is likely because of the highly reducing nature of photosystem I, and the energetic requirements placed on the pigments to operate in such a regime, that the inverted-region electron transfer mechanism becomes important.
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Makita H, Hastings G. Modeling electron transfer in photosystem I. Biochimica et Biophysica Acta (BBA) - Bioenergetics 2016; 1857:723-33. [DOI: 10.1016/j.bbabio.2016.03.015] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 03/13/2016] [Accepted: 03/15/2016] [Indexed: 11/26/2022]
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Makita H, Zhao N, Hastings G. Time-resolved visible and infrared difference spectroscopy for the study of photosystem I with different quinones incorporated into the A1 binding site. Biochimica et Biophysica Acta (BBA) - Bioenergetics 2015; 1847:343-54. [DOI: 10.1016/j.bbabio.2014.12.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Revised: 12/12/2014] [Accepted: 12/15/2014] [Indexed: 11/22/2022]
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Abstract
Fourier transform infrared difference spectroscopy (FTIR DS) has been widely used to study the structural details of electron transfer cofactors (and their binding sites) in many types of photosynthetic protein complexes. This review focuses in particular on work that has been done to investigate the A₁cofactor in photosystem I photosynthetic reaction centers. A review of this subject area last appeared in 2006 [1], so only work undertaken since then will be covered here. Following light excitation of intact photosystem I particles the P700⁺A⁻(1) secondary radical pair state is formed within 100ps. This state decays within 300ns at room temperature, or 300μs at 77K. Given the short-lived nature of this state, it is not easily studied using "static" photo-accumulation FTIR difference techniques at either temperature. Time-resolved techniques are required. This article focuses on the use of time-resolved step-scan FTIR DS for the study of the P700⁺A⁻(1) state in intact photosystem I. Up until now, only our group has undertaken studies in this area. So, in this article, recent work undertaken in our lab is described, where we have used low-temperature (77K), microsecond time-resolved step-scan FTIR DS to study the P700⁺A⁻(1) state in photosystem I. In photosystem I a phylloquinone molecule occupies the A₁binding site. However, different quinones can be incorporated into the A1 binding site, and here work is described for photosystem I particles with plastoquinone-9, 2-phytyl naphthoquinone and 2-methyl naphthoquinone incorporated into the A₁binding site. Studies in which ¹⁸O isotope labeled phylloquinone has been incorporated into the A1 binding site are also discussed. To fully characterize PSI particles with different quinones incorporated into the A1 binding site nanosecond to millisecond visible absorption spectroscopy has been shown to be of considerable value, especially so when undertaken using identical samples under identical conditions to that used in time-resolved step-scan FTIR measurements. In this article the latest work that has been undertaken using both visible and infrared time resolved spectroscopies on the same sample will be described. Finally, vibrational spectroscopic data that has been obtained for phylloquinone in the A1 binding site in photosystem I is compared to corresponding data for ubiquinone in the QA binding site in purple bacterial reaction centers. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.
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Affiliation(s)
- Gary Hastings
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA
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Abstract
We demonstrate the ability of two-dimensional electronic spectroscopy (2DES) to
map ultrafast energy transfer and dynamics in two systems: the pigment–protein
complex photosystem I (PSI) and aggregates of the conjugated polymer
poly(3-hexylthiophene) (P3HT). A detailed description of our experimental set-up
and data processing procedure is also given.
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Anna JM, Ostroumov EE, Maghlaoui K, Barber J, Scholes GD. Two-Dimensional Electronic Spectroscopy Reveals Ultrafast Downhill Energy Transfer in Photosystem I Trimers of the Cyanobacterium Thermosynechococcus elongatus. J Phys Chem Lett 2012; 3:3677-84. [PMID: 26291095 DOI: 10.1021/jz3018013] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Two-dimensional electronic spectroscopy (2DES) was used to investigate the ultrafast energy-transfer dynamics of trimeric photosystem I of the cyanobacterium Thermosynechococcus elongatus. We demonstrate the ability of 2DES to resolve dynamics in a large pigment-protein complex containing ∼300 chromophores with both high frequency and time resolution. Monitoring the waiting-time-dependent changes of the line shape of the inhomogeneously broadened Qy(0-0) transition, we directly observe downhill energy equilibration on the 50 fs time scale.
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Affiliation(s)
- Jessica M Anna
- †Department of Chemistry, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
| | - Evgeny E Ostroumov
- †Department of Chemistry, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
| | - Karim Maghlaoui
- ‡Division of Molecular Bioscience, Department of Life Sciences, Imperial College London, Sir Ernst Chain Building - Wolfson Laboratories, South Kensington Campus, London, SW7 2AZ, United Kingdom
| | - James Barber
- ‡Division of Molecular Bioscience, Department of Life Sciences, Imperial College London, Sir Ernst Chain Building - Wolfson Laboratories, South Kensington Campus, London, SW7 2AZ, United Kingdom
| | - Gregory D Scholes
- †Department of Chemistry, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, Canada
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Abstract
In Photosystem 1 (PS1), phylloquinone (PhQ) acts as a secondary electron acceptor from chlorophyll ec(3) and also as an electron donor to the iron-sulfur cluster F(X). PS1 possesses two virtually equivalent branches of electron transfer (ET) cofactors from P(700) to F(X), and the lifetime of the semiquinone intermediate displays biphasic kinetics, reflecting ET along the two different branches. PhQ in PS1 serves only as an intermediate in ET and is not normally fully reduced to the quinol form. This is in contrast to PS2, in which plastoquinone (PQ) is doubly reduced to plastoquinol (PQH(2)) as the terminal electron acceptor. We purified PS1 particles from the menD1 mutant of Chlamydomonas reinhardtii that cannot synthesize PhQ, resulting in replacement of PhQ by PQ in the quinone-binding pocket. The magnitude of the stable flash-induced P(700)(+) signal of menD1 PS1, but not wild-type PS1, decreased during a train of laser flashes, as it was replaced by a ~30 ns back-reaction from the preceding radical pair (P(700)(+)A(0)(-)). We show that this process of photoinactivation is due to double reduction of PQ in the menD1 PS1 and have characterized the process. It is accelerated at lower pH, consistent with a rate-limiting protonation step. Moreover, a point mutation (PsaA-L722T) in the PhQ(A) site that accelerates ET to F(X) ~2-fold, likely by weakening the sole H-bond to PhQ(A), also accelerates the photoinactivation process. The addition of exogenous PhQ can restore activity to photoinactivated PS1 and confer resistance to further photoinactivation. This process also occurs with PS1 purified from the menB PhQ biosynthesis mutant of Synechocystis PCC 6803, demonstrating that it is a general phenomenon in both prokaryotic and eukaryotic PS1.
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Affiliation(s)
- Michael D McConnell
- Department of Chemistry and Biochemistry and Center for Bioenergy and Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, United States.
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Chauhan D, Folea IM, Jolley CC, Kouřil R, Lubner CE, Lin S, Kolber D, Wolfe-Simon F, Golbeck JH, Boekema EJ, Fromme P. A Novel Photosynthetic Strategy for Adaptation to Low-Iron Aquatic Environments. Biochemistry 2011; 50:686-92. [DOI: 10.1021/bi1009425] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Devendra Chauhan
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, United States
| | - I. Mihaela Folea
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Craig C. Jolley
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, United States
| | - Roman Kouřil
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | | | - Su Lin
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, United States
| | - Dorota Kolber
- Monterey Bay Aquarium Research Institute, Moss Landing, California 95039, United States
| | - Felisa Wolfe-Simon
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, United States
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
| | - John H. Golbeck
- Department of Biochemistry and Molecular Biology
- Department of Chemistry
| | - Egbert J. Boekema
- Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Petra Fromme
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, United States
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18
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Jung H, Gulis G, Gupta S, Redding K, Gosztola DJ, Wiederrecht GP, Stroscio MA, Dutta M. Optical and Electrical Measurement of Energy Transfer between Nanocrystalline Quantum Dots and Photosystem I. J Phys Chem B 2010; 114:14544-9. [DOI: 10.1021/jp102291e] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hyeson Jung
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
| | - Galina Gulis
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
| | - Subhadra Gupta
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
| | - Kevin Redding
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
| | - David J. Gosztola
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
| | - Gary P. Wiederrecht
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
| | - Michael A. Stroscio
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
| | - Mitra Dutta
- Department of Electrical Engineering, Department of Bioengineering, and Department of Physics, The University of Illinois at Chicago, Illinois 60607, Department of Metallurgy and Materials Engineering, The University of Alabama, Alabama 35487, Department of Chemistry and Biochemistry, Arizona State University, Arizona 85287, and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439
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19
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Abstract
Photosynthesis is the major process that converts solar energy into chemical energy on Earth. Two and a half billion years ago, the ancestors of cyanobacteria were able to use water as electron source for the photosynthetic process, thereby evolving oxygen and changing the atmosphere of our planet Earth. Two large membrane protein complexes, Photosystems I and II, catalyze the primary step in this energy conversion, the light-induced charge separation across the photosynthetic membrane. This chapter describes and compares the structure of two Photosystems and discusses their function in respect to the mechanism of light harvesting, electron transfer and water splitting.
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Affiliation(s)
- Petra Fromme
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA.
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20
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Gibasiewicz K, Ramesh VM, Lin S, Redding K, Woodbury NW, Webber AN. Two equilibration pools of chlorophylls in the Photosystem I core antenna of Chlamydomonas reinhardtii. Photosynth Res 2007; 92:55-63. [PMID: 17611814 DOI: 10.1007/s11120-006-9125-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2006] [Accepted: 12/11/2006] [Indexed: 05/16/2023]
Abstract
Femtosecond transient absorption spectroscopy was applied for a comparative study of excitation decay in several different Photosystem I (PSI) core preparations from the green alga Chlamydomonas reinhardtii. For PSI cores with a fully interconnected network of chlorophylls, the excitation energy was equilibrated over a pool of chlorophylls absorbing at approximately 683 nm, independent of excitation wavelength [Gibasiewicz et al. J Phys Chem B 105:11498-11506, 2001; J Phys Chem B 106:6322-6330, 2002]. In preparations with impaired connectivity between chlorophylls, we have found that the spectrum of chlorophylls connected to the reaction center (i.e., with approximately 20 ps decay time) over which the excitation is equilibrated becomes excitation-wavelength-dependent. Excitation at 670 nm is finally equilibrated over chlorophylls absorbing at approximately 675 nm, whereas excitation at 695 nm or 700 nm is equilibrated over chlorophylls absorbing at approximately 683 nm. This indicates that in the vicinity of the reaction center there are two spectrally different and spatially separated pools of chlorophylls that are equally capable of effective excitation energy transfer to the reaction center. We propose that they are related to the two groups of central PSI core chlorophylls lying on the opposite sides of reaction center.
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Affiliation(s)
- Krzysztof Gibasiewicz
- School of Life Sciences, Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, AZ 85287-4501, USA.
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21
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Ramesh VM, Gibasiewicz K, Lin S, Bingham SE, Webber AN. Replacement of the methionine axial ligand to the primary electron acceptor A0 slows the A0− reoxidation dynamics in Photosystem I. Biochimica et Biophysica Acta (BBA) - Bioenergetics 2007; 1767:151-60. [PMID: 17316554 DOI: 10.1016/j.bbabio.2006.12.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2006] [Revised: 11/28/2006] [Accepted: 12/22/2006] [Indexed: 12/01/2022]
Abstract
The recent crystal structure of photosystem I (PSI) from Thermosynechococcus elongatus shows two nearly symmetric branches of electron transfer cofactors including the primary electron donor, P(700), and a sequence of electron acceptors, A, A(0) and A(1), bound to the PsaA and PsaB heterodimer. The central magnesium atoms of each of the putative primary electron acceptor chlorophylls, A(0), are unusually coordinated by the sulfur atom of methionine 688 of PsaA and 668 of PsaB, respectively. We [Ramesh et al. (2004a) Biochemistry 43:1369-1375] have shown that the replacement of either methionine with histidine in the PSI of the unicellular green alga Chlamydomonas reinhardtii resulted in accumulation of A(0)(-) (in 300-ps time scale), suggesting that both the PsaA and PsaB branches are active. This is in contrast to cyanobacterial PSI where studies with methionine-to-leucine mutants show that electron transfer occurs predominantly along the PsaA branch. In this contribution we report that the change of methionine to either leucine or serine leads to a similar accumulation of A(0)(-) on both the PsaA and the PsaB branch of PSI from C. reinhardtii, as we reported earlier for histidine mutants. More importantly, we further demonstrate that for all the mutants under study, accumulation of A(0)(-) is transient, and that reoxidation of A(0)(-) occurs within 1-2 ns, two orders of magnitude slower than in wild type PSI, most likely via slow electron transfer to A(1). This illustrates an indispensable role of methionine as an axial ligand to the primary acceptor A(0) in optimizing the rate of charge stabilization in PSI. A simple energetic model for this reaction is proposed. Our findings support the model of equivalent electron transfer along both cofactor branches in Photosystem I.
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Affiliation(s)
- V M Ramesh
- School of Life Sciences, Arizona State University, Tempe, PO BOX 874501, AZ 85287-4501, USA
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22
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Holzwarth AR, Müller MG, Niklas J, Lubitz W. Ultrafast transient absorption studies on photosystem I reaction centers from Chlamydomonas reinhardtii. 2: mutations near the P700 reaction center chlorophylls provide new insight into the nature of the primary electron donor. Biophys J 2006; 90:552-65. [PMID: 16258055 PMCID: PMC1367060 DOI: 10.1529/biophysj.105.059824] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2005] [Accepted: 10/03/2005] [Indexed: 11/18/2022] Open
Abstract
The energy transfer and charge separation kinetics in several core Photosystem I particles of Chlamydomonas reinhardtii with point mutations around the PA and PB reaction center chlorophylls (Chls) have been studied using ultrafast transient absorption spectroscopy in the femtosecond to nanosecond time range to characterize the influence on the early electron transfer processes. The data have been analyzed in terms of kinetic compartment models. The adequate description of the transient absorption kinetics requires three different radical pairs in the time range up to approximately 100 ps. Also a charge recombination process from the first radical pair back to the excited state is present in all the mutants, as already shown previously for the wild-type (Müller, M. G., J. Niklas, W. Lubitz, and A. R. Holzwarth. 2003. Biophys. J. 85:3899-3922; and Holzwarth, A. R., M. G. Müller, J. Niklas, and W. Lubitz. 2005. J. Phys. Chem. B. 109:5903-59115). In all mutants, the primary charge separation occurs with the same effective rate constant within the error limits as in the wild-type (>>350 ns(-1)), which implies an intrinsic rate constant of charge separation of <1 ps(-1). The rate constant of the secondary electron transfer process is slowed down by a factor of approximately 2 in the mutant B-H656C, which lacks the ligand to the central metal of Chl PB. For the mutant A-T739V, which breaks the hydrogen bond to the keto carbonyl of Chl PA, only a slight slowing down of the secondary electron transfer is observed. Finally for mutant A-W679A, which has the Trp near the PA Chl replaced, either no pronounced effect or, at best, a slight increase on the secondary electron transfer rate constants is observed. The effective charge recombination rate constant is modified in all mutants to some extent, with the strongest effect observed in mutant B-H656C. Our data strongly suggest that the Chls of the PA and PB pair, constituting what is traditionally called the "primary electron donor P700", are not oxidized in the first electron transfer process, but rather only in the secondary electron transfer step. We thus propose a new electron transfer mechanism for Photosystem I where the accessory Chl(s) function as the primary electron donor(s) and the A0 Chl(s) are the primary electron acceptor(s). This new mechanism also resolves in a straightforward manner the difficulty with the previous mechanism, where an electron would have to overcome a distance of approximately 14 A in <1 ps in a single step. If interpreted within a scheme of single-sided electron transfer, our data suggest that the B-branch is the active branch, although parallel A-branch activity cannot be excluded. All the mutations do affect to a varying extent the energy difference between the reaction center excited state RC* and the first radical pair and thus affect the rate constant of charge recombination. It is interesting to note that the new mechanism proposed is in fact analogous to the electron transfer mechanism in Photosystem II, where the accessory Chl also plays the role of the primary electron donor, rather than the special Chl pair P680 (Prokhorenko, V. and A. R. Holzwarth. 2000. J. Phys. Chem. B. 104:11563-11578).
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Affiliation(s)
- Alfred R Holzwarth
- Max-Planck-Institut für Bioanorganische Chemie, D-45470 Mülheim an der Ruhr, Germany.
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23
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Sarkisov OM, Gostev FE, Shelaev IV, Novoderezhkin VI, Gopta OA, Mamedov MD, Semenov AY, Nadtochenko VA. Long-lived coherent oscillations of the femtosecond transients in cyanobacterial photosystem I. Phys Chem Chem Phys 2006; 8:5671-8. [PMID: 17149488 DOI: 10.1039/b605660a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [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: 01/28/2023]
Abstract
The pulsed excitation of electronic levels coupled to specific nuclear modes by a 26 fs laser pulse at 706 nm creates a wavepacket in the nuclear space of photopystem I (PS I) of Synechocystis sp. strain PCC 6803 both in the ground state and in the one-exciton manifold. Fourier transform of transient decay curves shows several low frequency peaks. The most prominent Power Spectral Density (PSD) peaks are at omega = 49 cm(-1) and omega = 88 cm(-1). The peculiarity of the coherent wavepacket in the PS I of S. sp. strain PCC 6803 is the unique, long-lived 49 cm(-1) and 88 cm(-1) oscillations with decay times up to 10 ps. It was suggested that such a long-lived coherence is determined by a contribution of the ground state wavepacket. The dependence of these two PSD peaks on the probe wavelength resembles the profile of the transient absorption spectra of PS I. The pump-probe signal in the Soret region reflects the dynamics of the ground state wavepacket created by pulsed excitation of the Q(y)-band. It was shown that the multimode Brownian oscillator model allows a quantitative fit of the oscillatory patterns of the pump-probe signal to be obtained.
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Affiliation(s)
- Oleg M Sarkisov
- N N Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosigin str 4, Moscow, Russia
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24
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Melkozernov AN, Kargul J, Lin S, Barber J, Blankenship RE. Spectral and kinetic analysis of the energy coupling in the PS I-LHC I supercomplex from the green alga Chlamydomonas reinhardtii at 77 K. Photosynth Res 2005; 86:203-15. [PMID: 16172939 DOI: 10.1007/s11120-005-4118-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Accepted: 03/18/2005] [Indexed: 05/04/2023]
Abstract
Energy transfer processes in the chlorophyll antenna of the PS I-LHCI supercomplexes from the green alga Chlamydomonas reinhardtii have been studied at 77 K using transient absorption spectroscopy with multicolor excitation in the 640-670 nm region. Comparison of the kinetic data obtained at low and room temperatures indicates that the slow approximately approximately 100 ps excitation equilibration phase that is characteristic of energy coupling of the LHCI peripheral antenna to the PS I core at physiological temperatures (Melkozernov AN, Kargul J, Lin S, Barber J and Blankenship RE (2004) J Phys Chem B 108: 10547-10555) is not observed in the excitation dynamics of the PS I-LHCI supercomplex at 77 K. This suggests that at low temperatures the peripheral antenna is energetically uncoupled from the PS I core antenna. Under these conditions the observed kinetic phases on the time scales from subpicoseconds to tens of picoseconds represent the superposition of the processes occurring independently in the PS I core antenna and the Chl a/b containing LHCI antenna. In the PS I-LHCI supercomplex with two uncoupled antennas the excitation is channeled to the excitation sinks formed at low temperature by clusters of red pigments. A better spectral resolution of the transient absorption spectra at 77 K results in detection of two DeltaA bands originating from the rise of photobleaching on the picosecond time scale of two clearly distinguished pools of low energy absorbing Chls in the PS I-LHCI supercomplex. The first pool of low energy pigments absorbing at 687 nm is likely to originate from the red pigments in the LHCI where the Lhca1 protein is most abundant. The second pool at 697 nm is suggested to result either from the structural interaction of the LHCI and the PS I core or from other Lhca proteins in the antenna. The kinetic data are discussed based on recent structural models of the PS I-LHCI. It is proposed that the uncoupling of pigment pools may be a control mechanism that regulates energy flow in Photosystem I.
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Affiliation(s)
- Alexander N Melkozernov
- Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, Tempe, AZ 85287-1604, USA.
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25
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Abstract
Photosystem I is one of the most fascinating membrane protein complexes for which a structure has been determined. It functions as a bio-solar energy converter, catalyzing one of the first steps of oxygenic photosynthesis. It captures the light of the sun by means of a large antenna system, consisting of chlorophylls and carotenoids, and transfers the energy to the center of the complex, driving the transmembrane electron transfer from plastoquinone to ferredoxin. Cyanobacterial Photosystem I is a trimer consisting of 36 proteins to which 381 cofactors are non-covalently attached. This review discusses the complex function of Photosystem I based on the structure of the complex at 2.5 A resolution as well as spectroscopic and biochemical data.
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26
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Dashdorj N, Xu W, Cohen RO, Golbeck JH, Savikhin S. Asymmetric electron transfer in cyanobacterial Photosystem I: charge separation and secondary electron transfer dynamics of mutations near the primary electron acceptor A0. Biophys J 2004; 88:1238-49. [PMID: 15542554 PMCID: PMC1305126 DOI: 10.1529/biophysj.104.050963] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Point mutations were introduced near the primary electron acceptor sites assigned to A0 in both the PsaA and PsaB branches of Photosystem I in the cyanobacterium Synechocystis sp. PCC 6803. The residues Met688PsaA and Met668PsaB, which provide the axial ligands to the Mg2+ of the eC-A3 and eC-B3 chlorophylls, were changed to leucine and asparagine (chlorophyll notation follows Jordan et al., 2001). The removal of the ligand is expected to alter the midpoint potential of the A0/A0- redox pair and result in a change in the intrinsic charge separation rate and secondary electron transfer kinetics from A0- to A1. The dynamics of primary charge separation and secondary electron transfer were studied at 690 nm and 390 nm in these mutants by ultrafast optical pump-probe spectroscopy. The data reveal that mutations in the PsaB branch do not alter electron transfer dynamics, whereas mutations in the PsaA branch have a distinct effect on electron transfer, slowing down both the primary charge separation and the secondary electron transfer step (the latter by a factor of 3-10). These results suggest that electron transfer in cyanobacterial Photosystem I is asymmetric and occurs primarily along the PsaA branch of cofactors.
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27
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Wang R, Sivakumar V, Johnson TW, Hastings G. FTIR difference spectroscopy in combination with isotope labeling for identification of the carbonyl modes of P700 and P700+ in photosystem I. Biophys J 2004; 86:1061-73. [PMID: 14747341 PMCID: PMC1303899 DOI: 10.1016/s0006-3495(04)74181-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [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: 11/29/2022] Open
Abstract
Room temperature, light induced (P700(+)-P700) Fourier transform infrared (FTIR) difference spectra have been obtained using photosystem I (PS I) particles from Synechocystis sp. PCC 6803 that are unlabeled, uniformly (2)H labeled, and uniformly (15)N labeled. Spectra were also obtained for PS I particles that had been extensively washed and incubated in D(2)O. Previously, we have found that extensive washing and incubation of PS I samples in D(2)O does not alter the (P700(+)-P700) FTIR difference spectrum, even with approximately 50% proton exchange. This indicates that the P700 binding site is inaccessible to solvent water. Upon uniform (2)H labeling of PS I, however, the (P700(+)-P700) FTIR difference spectra are considerably altered. From spectra obtained using PS I particles grown in D(2)O and H(2)O, a ((1)H-(2)H) isotope edited double difference spectrum was constructed, and it is shown that all difference bands associated with ester/keto carbonyl modes of the chlorophylls of P700 and P700(+) downshift 4-5/1-3 cm(-1) upon (2)H labeling, respectively. It is also shown that the ester and keto carbonyl modes of the chlorophylls of P700 need not be heterogeneously distributed in frequency. Finally, we find no evidence for the presence of a cysteine mode in our difference spectra. The spectrum obtained using (2)H labeled PS I particles indicates that a negative difference band at 1698 cm(-1) is associated with at least two species. The observed (15)N and (2)H induced band shifts strongly support the idea that the two species are the 13(1) keto carbonyl modes of both chlorophylls of P700. We also show that a negative difference band at approximately 1639 cm(-1) is somewhat modified in intensity, but unaltered in frequency, upon (2)H labeling. This indicates that this band is not associated with a strongly hydrogen bonded keto carbonyl mode of one of the chlorophylls of P700.
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Affiliation(s)
- Ruili Wang
- Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA
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28
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Müller MG, Niklas J, Lubitz W, Holzwarth AR. Ultrafast transient absorption studies on Photosystem I reaction centers from Chlamydomonas reinhardtii. 1. A new interpretation of the energy trapping and early electron transfer steps in Photosystem I. Biophys J 2004; 85:3899-922. [PMID: 14645079 PMCID: PMC1303691 DOI: 10.1016/s0006-3495(03)74804-8] [Citation(s) in RCA: 153] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The energy transfer and charge separation kinetics in core Photosystem I (PSI) particles of Chlamydomonas reinhardtii has been studied using ultrafast transient absorption in the femtosecond-to-nanosecond time range. Although the energy transfer processes in the antenna are found to be generally in good agreement with previous interpretations, we present evidence that the interpretation of the energy trapping and electron transfer processes in terms of both kinetics and mechanisms has to be revised substantially as compared to current interpretations in the literature. We resolved for the first time i), the transient difference spectrum for the excited reaction center state, and ii), the formation and decay of the primary radical pair and its intermediate spectrum directly from measurements on open PSI reaction centers. It is shown that the dominant energy trapping lifetime due to charge separation is only 6-9 ps, i.e., by a factor of 3 shorter than assumed so far. The spectrum of the first radical pair shows the expected strong bleaching band at 680 nm which decays again in the next electron transfer step. We show furthermore that the early electron transfer processes up to approximately 100 ps are more complex than assumed so far. Several possibilities are discussed for the intermediate redox states and their sequence which involve oxidation of P700 in the first electron transfer step, as assumed so far, or only in the second electron transfer step, which would represent a fundamental change from the presently assumed mechanism. To explain the data we favor the inclusion of an additional redox state in the electron transfer scheme. Thus we distinguish three different redox intermediates on the timescale up to 100 ps. At this level no final conclusion as to the exact mechanism and the nature of the intermediates can be drawn, however. From comparison of our data with fluorescence kinetics in the literature we also propose a reversible first charge separation step which has been excluded so far for open PSI reaction centers. For the first time an ultrafast 150-fs equilibration process, occurring among exciton states in the reaction center proper, upon direct excitation of the reaction center at 700 nm, has been resolved. Taken together the data call for a fundamental revision of the present understanding of the energy trapping and early electron transfer kinetics in the PSI reaction center. Due to the fact that it shows the fastest trapping time observed so far of any intact PSI particle, the PSI core of C. reinhardtii seems to be best suited to further characterize the electron transfer steps and mechanisms in the reaction center of PSI.
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Affiliation(s)
- Marc G Müller
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstr 34-36, D-45470 Mülheim ad Ruhr, Germany
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29
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Abstract
Fourier transform infrared spectroscopy (FTIR) difference spectroscopy in combination with deuterium exchange experiments has been used to study the photo-oxidation of P740, the primary electron donor in photosystem I from Acaryochloris marina. Comparison of (P740(+)-P740) and (P700(+)-P700) FTIR difference spectra show that P700 and P740 share many structural similarities. However, there are several distinct differences also: 1), The (P740(+)-P740) FTIR difference spectrum is significantly altered upon proton exchange, considerably more so than the (P700(+)-P700) FTIR difference spectrum. The P740 binding pocket is therefore more accessible than the P700 binding pocket. 2), Broad, "dimer" absorption bands are observed for both P700(+) and P740(+). These bands differ significantly in substructure, however, suggesting differences in the electronic organization of P700(+) and P740(+). 3), Bands are observed at 2727(-) and 2715(-) cm(-1) in the (P740(+)-P740) FTIR difference spectrum, but are absent in the (P700(+)-P700) FTIR difference spectrum. These bands are due to formyl CH modes of chlorophyll d. Therefore, P740 consists of two chlorophyll d molecules. Deuterium-induced modification of the (P740(+)-P740) FTIR difference spectrum indicates that only the highest frequency 13(3) ester carbonyl mode of P740 downshifts, indicating that this ester mode is weakly H-bonded. In contrast, the highest frequency ester carbonyl mode of P700 is free from H-bonding. Deuterium-induced changes in (P740(+)-P740) FTIR difference spectrum could also indicate that one of the chlorophyll d 3(1) carbonyls of P740 is hydrogen bonded.
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Affiliation(s)
- Velautham Sivakumar
- Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA
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30
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Abstract
Femtosecond excitation of the red edge of the chlorophyll a Q(Y) transition band in photosystem I (PSI), with light of wavelength > or = 700 nm, leads to wide transient (subpicosecond) absorbance changes: positive DeltaA between 635 and 665 nm, and four negative DeltaA bands at 667, 675, 683, and 695 nm. Here we compare the transient absorbance changes after excitation at 700, 705, and 710 nm at 20 K in several PSI preparations of Chlamydomonas reinhardtii where amino acid ligands of the primary donor, primary acceptor, or connecting chlorophylls have been mutated. Most of these mutations influence the spectrum of the absorbance changes. This supports the view that the chlorophylls of the electron transfer chain as well as the connecting chlorophylls are engaged in the observed absorbance changes. The wide absorption spectrum of the electron transfer chain revealed by the transient measurements may contribute to the high efficiency of energy trapping in photosystem 1. Exciton calculations, based on the recent PSI structure, allow an assignment of the DeltaA bands to particular chlorophylls: the bands at 675 and 695 nm to the dimers of primary acceptor and accessory chlorophyll and the band at 683 nm to the connecting chlorophylls. The subpicosecond transient absorption bands decay may reflect rapid charge separation in the PSI reaction center.
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Affiliation(s)
- Krzysztof Gibasiewicz
- Department of Plant Biology and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601 USA
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31
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Melkozernov AN, Kargul J, Lin S, Barber J, Blankenship RE. Energy Coupling in the PSI−LHCI Supercomplex from the Green Alga Chlamydomonas reinhardtii,. J Phys Chem B 2004. [DOI: 10.1021/jp049375n] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Alexander N. Melkozernov
- Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, and Wolfson Laboratories, Department of Biological Sciences, Imperial College, London SW7 2AY, U.K
| | - Joanna Kargul
- Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, and Wolfson Laboratories, Department of Biological Sciences, Imperial College, London SW7 2AY, U.K
| | - Su Lin
- Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, and Wolfson Laboratories, Department of Biological Sciences, Imperial College, London SW7 2AY, U.K
| | - James Barber
- Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, and Wolfson Laboratories, Department of Biological Sciences, Imperial College, London SW7 2AY, U.K
| | - Robert E. Blankenship
- Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, and Wolfson Laboratories, Department of Biological Sciences, Imperial College, London SW7 2AY, U.K
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Nakamura A, Akai M, Yoshida E, Taki T, Watanabe T. Reversed-phase HPLC determination of chlorophyll a' and phylloquinone in Photosystem I of oxygenic photosynthetic organisms. Universal existence of one chlorophyll a' molecule in Photosystem I. Eur J Biochem 2003; 270:2446-58. [PMID: 12755700 DOI: 10.1046/j.1432-1033.2003.03616.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Chlorophyll (Chl) a', the C132-epimer of Chl a, is a constituent of the primary electron donor (P700) of Photosystem (PS) I of a thermophilic cyanobacterium Synechococcus (Thermosynechococcus) elongatus, as was recently demonstrated by X-ray crystallography. To determine whether PS I of oxygenic photosynthetic organisms universally contains one molecule of Chl a', pigment compositions of thylakoid membranes and PS I complexes isolated from the cyanobacteria T. elongatus and Synechocystis sp. PCC 6803, the green alga Chlamydomonas reinhardtii, and the green plant spinach, were examined by simultaneous detection of phylloquinone (the secondary electron acceptor of PS I) and Chl a' by reversed-phase HPLC. The results were compared with the Chl a/P700 ratio determined spectrophotometrically. The Chl a'/PS I ratios of thylakoid membranes and PS I were about 1 for all the organisms examined, and one Chl a' molecule was found in PS I even after most of the peripheral subunits were removed. Chl a' showed a characteristic extraction behaviour significantly different from the bulk Chl a in acetone/methanol extraction upon varying the mixing ratio. These findings confirm that a single Chl a' molecule in P700 is the universal feature of PS I of the Chl a-based oxygenic photosynthetic organisms.
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Fromme P, Schlodder E, Jansson S. Structure and Function of the Antenna System in Photosystem I. In: Green BR, Parson WW, editors. Light-Harvesting Antennas in Photosynthesis. Dordrecht: Springer Netherlands; 2003. pp. 253-79. [DOI: 10.1007/978-94-017-2087-8_8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2023]
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Gibasiewicz K, Ramesh VM, Lin S, Woodbury NW, Webber AN. Excitation Dynamics in Eukaryotic PS I from Chlamydomonas reinhardtii CC 2696 at 10 K. Direct Detection of the Reaction Center Exciton States. J Phys Chem B 2002. [DOI: 10.1021/jp014608l] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Krzysztof Gibasiewicz
- Department of Plant Biology, Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe Arizona 85287-1601, USA and Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61−614 Poznań, Poland
| | - V. M. Ramesh
- Department of Plant Biology, Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe Arizona 85287-1601, USA and Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61−614 Poznań, Poland
| | - Su Lin
- Department of Plant Biology, Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe Arizona 85287-1601, USA and Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61−614 Poznań, Poland
| | - Neal W. Woodbury
- Department of Plant Biology, Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe Arizona 85287-1601, USA and Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61−614 Poznań, Poland
| | - Andrew N. Webber
- Department of Plant Biology, Department of Chemistry and Biochemistry and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe Arizona 85287-1601, USA and Department of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61−614 Poznań, Poland
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Gibasiewicz K, Ramesh VM, Melkozernov AN, Lin S, Woodbury NW, Blankenship RE, Webber AN. Excitation Dynamics in the Core Antenna of PS I from Chlamydomonas reinhardtii CC 2696 at Room Temperature. J Phys Chem B 2001. [DOI: 10.1021/jp012089g] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Krzysztof Gibasiewicz
- Department of Plant Biology, Department of Chemistry and Biochemistry, and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, and Institute of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
| | - V. M. Ramesh
- Department of Plant Biology, Department of Chemistry and Biochemistry, and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, and Institute of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
| | - Alexander N. Melkozernov
- Department of Plant Biology, Department of Chemistry and Biochemistry, and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, and Institute of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
| | - Su Lin
- Department of Plant Biology, Department of Chemistry and Biochemistry, and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, and Institute of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
| | - Neal W. Woodbury
- Department of Plant Biology, Department of Chemistry and Biochemistry, and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, and Institute of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
| | - Robert E. Blankenship
- Department of Plant Biology, Department of Chemistry and Biochemistry, and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, and Institute of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
| | - Andrew N. Webber
- Department of Plant Biology, Department of Chemistry and Biochemistry, and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1601, and Institute of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland
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Abstract
The primary electron donor of photosystem I, P700, is a chlorophyll species that in its excited state has a potential of approximately -1.2 V. The precise chemical composition and electronic structure of P700 is still unknown. Recent evidence indicates that P700 is a dimer of one chlorophyll (Chl) a and one Chl a'. The Chl a' and Chl a are axially coordinated by His residues provided by protein subunits PsaA and PsaB, respectively. The Chl a', but not the Chl a, is also H-bonded to the protein. The H-bonding is likely responsible for selective insertion of Chl a' into the reaction center. EPR studies of P700(+*) in frozen solution and single crystals indicate a large asymmetry in the electron spin and charge distribution towards one Chl of the dimer. Molecular orbital calculations indicate that H-bonding will specifically stabilize the Chl a'-side of the dimer, suggesting that the unpaired electron would predominantly reside on the Chl a. This is supported by results of specific mutagenesis of the PsaA and PsaB axial His residues, which show that only mutations of the PsaB subunit significantly alter the hyperfine coupling constants associated with a single Chl molecule. The PsaB mutants also alter the microwave induced triplet-minus-singlet spectrum indicating that the triplet state is localized on the same Chl. Excitonic coupling between the two Chl a of P700 is weak due to the distance and overlap of the porphyrin planes. Evidence of excitonic coupling is found in PsaB mutants which show a new bleaching band at 665 nm that likely represents an increased intensity of the upper exciton band of P700. Additional properties of P700 that may give rise to its unusually low potential are discussed.
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Affiliation(s)
- A N Webber
- Department of Plant Biology and Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe 85287-1601, USA.
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Abstract
In plants and cyanobacteria, the primary step in oxygenic photosynthesis, the light induced charge separation, is driven by two large membrane intrinsic protein complexes, the photosystems I and II. Photosystem I catalyses the light driven electron transfer from plastocyanin/cytochrome c(6) on the lumenal side of the membrane to ferredoxin/flavodoxin at the stromal side by a chain of electron carriers. Photosystem I of Synechococcus elongatus consists of 12 protein subunits, 96 chlorophyll a molecules, 22 carotenoids, three [4Fe4S] clusters and two phylloquinones. Furthermore, it has been discovered that four lipids are intrinsic components of photosystem I. Photosystem I exists as a trimer in the native membrane with a molecular mass of 1068 kDa for the whole complex. The X-ray structure of photosystem I at a resolution of 2.5 A shows the location of the individual subunits and cofactors and provides new information on the protein-cofactor interactions. [P. Jordan, P. Fromme, H.T. Witt, O. Klukas, W. Saenger, N. Krauss, Nature 411 (2001) 909-917]. In this review, biochemical data and results of biophysical investigations are discussed with respect to the X-ray crystallographic structure in order to give an overview of the structure and function of this large membrane protein.
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Affiliation(s)
- P Fromme
- Max Volmer Laboratorium für Biophysikalische Chemie Institut für Chemie, Technische Universität Berlin, Germany.
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Melkozernov AN, Lin S, Blankenship RE, Valkunas L. Spectral inhomogeneity of photosystem I and its influence on excitation equilibration and trapping in the cyanobacterium Synechocystis sp. PCC6803 at 77 K. Biophys J 2001; 81:1144-54. [PMID: 11463655 PMCID: PMC1301583 DOI: 10.1016/s0006-3495(01)75771-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [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: 10/21/2022] Open
Abstract
Ultrafast transient absorption spectroscopy was used to probe excitation energy transfer and trapping at 77 K in the photosystem I (PSI) core antenna from the cyanobacterium Synechocystis sp. PCC 6803. Excitation of the bulk antenna at 670 and 680 nm induces a subpicosecond energy transfer process that populates the Chl a spectral form at 685--687 nm within few transfer steps (300--400 fs). On a picosecond time scale equilibration with the longest-wavelength absorbing pigments occurs within 4-6 ps, slightly slower than at room temperature. At low temperatures in the absence of uphill energy transfer the energy equilibration processes involve low-energy shifted chlorophyll spectral forms of the bulk antenna participating in a 30--50-ps process of photochemical trapping of the excitation by P(700). These spectral forms might originate from clustered pigments in the core antenna and coupled chlorophylls of the reaction center. Part of the excitation is trapped on a pool of the longest-wavelength absorbing pigments serving as deep traps at 77 K. Transient hole burning of the ground-state absorption of the PSI with excitation at 710 and 720 nm indicates heterogeneity of the red pigment absorption band with two broad homogeneous transitions at 708 nm and 714 nm (full-width at half-maximum (fwhm) approximately 200--300 cm(-1)). The origin of these two bands is attributed to the presence of two chlorophyll dimers, while the appearance of the early time bleaching bands at 683 nm and 678 nm under excitation into the red side of the absorption spectrum (>690 nm) can be explained by borrowing of the dipole strength by the ground-state absorption of the chlorophyll a monomers from the excited-state absorption of the dimeric red pigments.
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Affiliation(s)
- A N Melkozernov
- Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe, Arizona 85287-1604, USA
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Abstract
Photosystem I is the light-driven plastocyanin-ferredoxin oxidoreductase in the thylakoid membranes of cyanobacteria and chloroplasts. In recent years, sophisticated spectroscopy, molecular genetics, and biochemistry have been used to understand the light conversion and electron transport functions of photosystem I. The light-harvesting complexes and internal antenna of photosystem I absorb photons and transfer the excitation energy to P700, the primary electron donor. The subsequent charge separation and electron transport leads to the reduction of ferredoxin. The photosystem I proteins are responsible for the precise arrangement of cofactors and determine redox properties of the electron transfer centers. With the availability of genomic information and the structure of photosystem I, one can now probe the functions of photosystem I proteins and cofactors. The strong reductant produced by photosystem I has a central role in chloroplast metabolism, and thus photosystem I has a critical role in the metabolic networks and physiological responses in plants.
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Affiliation(s)
- Parag R Chitnis
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011; e-mail:
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Abstract
The excitation transport and trapping kinetics of core antenna-reaction center complexes from photosystem I of wild-type Synechocystis sp. PCC 6803 were investigated under annihilation-free conditions in complexes with open and closed reaction centers. For closed reaction centers, the long-component decay-associated spectrum (DAS) from global analysis of absorption difference spectra excited at 660 nm is essentially flat (maximum amplitude <10(-5) absorbance units). For open reaction centers, the long-time spectrum (which exhibits photobleaching maxima at approximately 680 and 700 nm, and an absorbance feature near 690 nm) resembles one previously attributed to (P700(+) - P700). For photosystem I complexes excited at 660 nm with open reaction centers, the equilibration between the bulk antenna and far-red chlorophylls absorbing at wavelengths >700 nm is well described by a single DAS component with lifetime 2.3 ps. For closed reaction centers, two DAS components (2.0 and 6.5 ps) are required to fit the kinetics. The overall trapping time at P700 ( approximately 24 ps) is very nearly the same in either case. Our results support a scenario in which the time constant for the P700 --> A(0) electron transfer is 9-10 ps, whereas the kinetics of the subsequent A(0) --> A(1) electron transfer are still unknown.
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Affiliation(s)
- S Savikhin
- Ames Laboratory, U. S. Department of Energy, Ames, Iowa 50011, USA
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Abstract
Ultrafast dynamics of excitation transfer in the Photosystem I (PSI) core antenna from the cyanobacterium Synechocystis sp. PCC 6803 were detected at 77 K by using femtosecond transient absorption spectroscopy with selective excitation at 700, 695, and 710 nm. At low temperature, the efficiency of uphill energy transfer in the core antenna significantly decreases. As a result, the spectral profile of the PSI equilibrated antenna shifts to lower energies because of a change of chlorophyll (Chl) excited-state distribution. Observed on a 2-ns time scale, P700 photooxidation spectra are largely excitation wavelength independent. In the early time spectra, excitation of P700 induces transient photobleaching at 698 nm accompanied by a resonant photobleaching band at 683 nm decaying within 250-300 fs. Chemical oxidation of P700 does not affect the transient band at 683 nm. This band is also present in 200-fs spectra induced by selective excitation of Chls at 710 nm (red pigments C708), which suggests that this high-energy transition may reflect an excitonic interaction between pigments of the reaction center and closely located red pigments. Possible candidates for the interacting molecules in the 4-angstroms crystal structure of cyanobacterial PSI are discussed.
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Affiliation(s)
- A N Melkozernov
- Department of Chemistry and Biochemistry, Center for the Study of Early Events in Photosynthesis, Arizona State University, Tempe 85287-1604, USA
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Karapetyan NV, Holzwarth AR, Rögner M. The photosystem I trimer of cyanobacteria: molecular organization, excitation dynamics and physiological significance. FEBS Lett 1999; 460:395-400. [PMID: 10556505 DOI: 10.1016/s0014-5793(99)01352-6] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.3] [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: 11/17/2022]
Abstract
The photosystem I complex organized in cyanobacterial membranes preferentially in trimeric form participates in electron transport and is also involved in dissipation of excess energy thus protecting the complex against photodamage. A small number of longwave chlorophylls in the core antenna of photosystem I are not located in the close vicinity of P700, but at the periphery, and increase the absorption cross-section substantially. The picosecond fluorescence kinetics of trimers resolved the fastest energy transfer components reflecting the equilibration processes in the core antenna at different redox states of P700. Excitation kinetics in the photosystem I bulk antenna is nearly trap-limited, whereas excitation trapping from longwave chlorophyll pools is diffusion-limited and occurs via the bulk antenna. Charge separation in the photosystem I reaction center is the fastest of all known reaction centers.
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Affiliation(s)
- N V Karapetyan
- A.N. Bakh Institute of Biochemistry, Russian Academy of Sciences, 117071, Moscow, Russia.
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Abstract
Ultrafast primary processes in the trimeric photosystem I core antenna-reaction center complex of the cyanobacterium Synechocystis sp. PCC 6803 have been examined in pump-probe experiments with approximately 100 fs resolution. A global analysis of two-color profiles, excited at 660 nm and probed at 5 nm intervals from 650 to 730 nm, reveals 430 fs kinetics for spectral equilibration among bulk antenna chlorophylls. At least two lifetime components (2.0 and 6.5 ps in our analysis) are required to describe equilibration of bulk chlorophylls with far red-absorbing chlorophylls (>700 nm). Trapping at P700 occurs with 24-ps kinetics. The multiphasic bulk left arrow over right arrow red equilibration kinetics are intriguing, because prior steady-state spectral studies have suggested that the core antenna in Synechocystis sp. contains only one red-absorbing chlorophyll species (C708). The disperse kinetics may arise from inhomogeneous broadening in C708. The one-color optical anisotropy at 680 nm (near the red edge of the bulk antenna) decays with 590 fs kinetics; the corresponding anisotropy at 710 nm shows approximately 3.1 ps kinetics. The latter may signal equilibration among symmetry-equivalent red chlorophylls, bound to different monomers within trimeric photosystem I.
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Affiliation(s)
- S Savikhin
- Ames Laboratory-U.S. Department of Energy, Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
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Soukoulis V, Savikhin S, Xu W, Chitnis PR, Struve WS. Electronic spectra of PS I mutants: the peripheral subunits do not bind red chlorophylls in Synechocystis sp. PCC 6803. Biophys J 1999; 76:2711-5. [PMID: 10233085 PMCID: PMC1300240 DOI: 10.1016/s0006-3495(99)77423-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [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: 11/17/2022] Open
Abstract
Steady-state fluorescence and absorption spectra have been obtained in the Qy spectral region (690-780 nm and 600-750 nm, respectively) for several subunit-deficient photosystem I mutants from the cyanobacterium Synechocystis sp. PCC 6803. The 77 K fluorescence spectra of the wild-type and subunit-deficient mutant photosystem I particles are all very similar, peaking at approximately 720 nm with essentially the same excitation spectrum. Because emission from far-red chlorophylls absorbing near 708 nm dominates low-temperature fluorescence in Synechocystis sp., these pigments are not coordinated to any the subunits PsaF, Psa I, PsaJ, PsaK, PsaL, or psaM. The room temperature (wild-type-mutant) absorption difference spectra for trimeric mutants lacking the PsaF/J, PsaK, and PsaM subunits suggest that these mutants are deficient in core antenna chlorophylls (Chls) absorbing near 685, 670, 675, and 700 nm, respectively. The absorption difference spectrum for the PsaF/J/I/L-deficient photosystem I complexes at 5 K reveals considerably more structure than the room-temperature spectrum. The integrated absorbance difference spectra (when normalized to the total PS I Qy spectral area) are comparable to the fractions of Chls bound by the respective (groups of) subunits, according to the 4-A density map of PS I from Synechococcus elongatus. The spectrum of the monomeric PsaL-deficient mutant suggests that this subunit may bind pigments absorbing near 700 nm.
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Affiliation(s)
- V Soukoulis
- Ames Laboratory, U.S. Department of Energy, and Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
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Abstract
Forward electron transfer in photosystem I from Synechocystis sp. PCC 6803 has been studied in the picosecond time range with transient absorption spectroscopy in the blue and near-UV spectral regions. From the direct measurement, at 380-390 nm, of the reduction kinetics of the phylloquinone secondary acceptor A1 and from the absence of spectral evolution between 100 ps and 2 ns, we conclude that electron transfer, from the chlorophyll a primary acceptor A0, to A1 occurs directly and completely with a time constant of about 30 ps.
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Affiliation(s)
- K Brettel
- Section de Bioénergétique and CNRS URA 2096, DBCM, CEA Saclay, Gif-sur-Yvette, France.
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Affiliation(s)
- M Hippler
- Departments of Molecular Biology and Plant Biology, University of Geneva, 30 Quai Ernest Ansermet, 1211 Geneva-4, Switzerland
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Pålsson LO, Flemming C, Gobets B, van Grondelle R, Dekker JP, Schlodder E. Energy transfer and charge separation in photosystem I: P700 oxidation upon selective excitation of the long-wavelength antenna chlorophylls of Synechococcus elongatus. Biophys J 1998; 74:2611-22. [PMID: 9591685 PMCID: PMC1299601 DOI: 10.1016/s0006-3495(98)77967-6] [Citation(s) in RCA: 128] [Impact Index Per Article: 4.9] [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: 02/07/2023] Open
Abstract
Photosystem I of the cyanobacterium Synechococcus elongatus contains two spectral pools of chlorophylls called C-708 and C-719 that absorb at longer wavelengths than the primary electron donor P700. We investigated the relative quantum yields of photochemical charge separation and fluorescence as a function of excitation wavelength and temperature in trimeric and monomeric photosystem I complexes of this cyanobacterium. The monomeric complexes are characterized by a reduced content of the C-719 spectral form. At room temperature, an analysis of the wavelength dependence of P700 oxidation indicated that all absorbed light, even of wavelengths of up to 750 nm, has the same probability of resulting in a stable P700 photooxidation. Upon cooling from 295 K to 5 K, the nonselectively excited steady-state emission increased by 11- and 16-fold in the trimeric and monomeric complexes, respectively, whereas the quantum yield of P700 oxidation decreased 2.2- and 1.7-fold. Fluorescence excitation spectra at 5 K indicate that the fluorescence quantum yield further increases upon scanning of the excitation wavelength from 690 nm to 710 nm, whereas the quantum yield of P700 oxidation decreases significantly upon excitation at wavelengths longer than 700 nm. Based on these findings, we conclude that at 5 K the excited state is not equilibrated over the antenna before charge separation occurs, and that approximately 50% of the excitations reach P700 before they become irreversibly trapped on one of the long-wavelength antenna pigments. Possible spatial organizations of the long-wavelength antenna pigments in the three-dimensional structure of photosystem I are discussed.
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Affiliation(s)
- L O Pålsson
- Department of Physics and Astronomy, Institute of Molecular Biological Sciences, Vrije Universiteit, Amsterdam, The Netherlands
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