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Sukhanov AA, Mamedov MD, Milanovsky GE, Salikhov KM, Semenov AY. Changes in the Electron Transfer Symmetry in the Photosystem I Reaction Centers upon Removal of Iron-Sulfur Clusters. BIOCHEMISTRY. BIOKHIMIIA 2022; 87:1109-1118. [PMID: 36273879 DOI: 10.1134/s0006297922100042] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2022] [Revised: 08/09/2022] [Accepted: 08/16/2022] [Indexed: 06/16/2023]
Abstract
In photosynthetic reaction centers of intact photosystem I (PSI) complexes from cyanobacteria, electron transfer at room temperature occurs along two symmetrical branches of redox cofactors A and B at a ratio of ~3 : 1 in favor of branch A. Previously, this has been indirectly demonstrated using pulsed absorption spectroscopy and more directly by measuring the decay modulation frequencies of electron spin echo signals (electron spin echo envelope modulation, ESEEM), which allows to determine the distance between the separated charges of the primary electron donor P700+ and phylloquinone acceptors A1A- and A1B- in the symmetric redox cofactors branches A and B. In the present work, these distances were determined using ESEEM in PSI complexes lacking three 4Fe-4S clusters, FX, FA, and FB, and the PsaC protein subunit (the so-called P700-A1 core), in which phylloquinone molecules A1A and A1B serve as the terminal electron acceptors. It was shown that in the P700-A1 core preparations, the average distance between the centers of the P700+A1- ion-radical pair at a temperature of 150 K in an aqueous glycerol solution and in a dried trehalose matrix, as well as in a trehalose matrix at 280 K, is ~25.5 Å, which corresponds to the symmetrical electron transfer along the A and B branches of redox cofactors at a ratio of 1 : 1. Possible reasons for the change in the electron transfer symmetry in PSI upon removal of the PsaC subunit and 4Fe-4S clusters FX, FA, and FB are discussed.
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Affiliation(s)
- Andrey A Sukhanov
- Zavoisky Physical-Technical Institute, FRC Kazan Scientific Center, Russian Academy of Sciences, Kazan, 420029, Russia
| | - Mahir D Mamedov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia
| | - Georgy E Milanovsky
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia
| | - Kev M Salikhov
- Zavoisky Physical-Technical Institute, FRC Kazan Scientific Center, Russian Academy of Sciences, Kazan, 420029, Russia
| | - Alexey Yu Semenov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia.
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2
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Mathis P, Sage E, Byrdin M. Pushing the limits of flash photolysis to unravel the secrets of biological electron and proton transfer. Photochem Photobiol Sci 2022; 21:1533-1544. [DOI: 10.1007/s43630-021-00134-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/05/2021] [Indexed: 11/25/2022]
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3
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Cherepanov DA, Shelaev IV, Gostev FE, Nadtochenko VA, Xu W, Golbeck JH, Semenov AY. Symmetry breaking in photosystem I: ultrafast optical studies of variants near the accessory chlorophylls in the A- and B-branches of electron transfer cofactors. Photochem Photobiol Sci 2021; 20:1209-1227. [PMID: 34478050 DOI: 10.1007/s43630-021-00094-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 08/18/2021] [Indexed: 11/25/2022]
Abstract
Femtosecond absorption spectroscopy of Photosystem I (PS I) complexes from the cyanobacterium Synechocystis sp. PCC 6803 was carried out on three pairs of complementary amino acid substitutions located near the second pair of chlorophyll molecules Chl2A and Chl2B (also termed A-1A and A-1B). The absorption dynamics at delays of 0.1-500 ps were analyzed by decomposition into discrete decay-associated spectra and continuously distributed exponential components. The multi-exponential deconvolution of the absorption changes revealed that the electron transfer reactions in the PsaA-N600M, PsaA-N600H, and PsaA-N600L variants near the B-branch of cofactors are similar to those of the wild type, while the PsaB-N582M, PsaB-N582H, and PsaB-N582L variants near the A-branch of cofactors cause significant alterations of the photochemical processes, making them heterogeneous and poorly described by a discrete exponential kinetic model. A redistribution of the unpaired electron between the second and the third monomers Chl2A/Chl2B and Chl3A/Chl3B was identified in the time range of 9-20 ps, and the subsequent reduction of A1 was identified in the time range of 24-70 ps. In the PsaA-N600L and PsaB-N582H/L variants, the reduction of A1 occurred with a decreased quantum yield of charge separation. The decreased quantum yield correlates with a slowing of the phylloquinone A0 → A1 reduction, but not with the initial transient spectra measured at the shortest time delay. The results support a branch competition model, where the electron is sheared between Chl2A-Chl3A and Chl2B-Chl3B cofactors before its transfer to phylloquinone in either A1A or A1B sites.
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Affiliation(s)
- Dmitry A Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation.
| | - Ivan V Shelaev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation
| | - Fedor E Gostev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation
| | - Victor A Nadtochenko
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation.,Department of Chemistry, Lomonosov Moscow State University, Leninskiye Gory 1-3, Moscow, 119991, Russian Federation
| | - Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA, 70504, USA
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16801, USA.,Department of Chemistry, The Pennsylvania State University, University Park, PA, 16801, USA
| | - Alexey Yu Semenov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina St. 4, Moscow, 117977, Russian Federation.,A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, 1, Moscow, 119992, Russian Federation
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Cherepanov DA, Shelaev IV, Gostev FE, Petrova A, Aybush AV, Nadtochenko VA, Xu W, Golbeck JH, Semenov AY. Primary charge separation within the structurally symmetric tetrameric Chl 2AP AP BChl 2B chlorophyll exciplex in photosystem I. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2021; 217:112154. [PMID: 33636482 DOI: 10.1016/j.jphotobiol.2021.112154] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Revised: 01/05/2021] [Accepted: 02/12/2021] [Indexed: 12/01/2022]
Abstract
In Photosystem I (PS I), the role of the accessory chlorophyll (Chl) molecules, Chl2A and Chl2B (also termed A-1A and A-1B), which are directly adjacent to the special pair P700 and fork into the A- and B-branches of electron carriers, is incompletely understood. In this work, the Chl2A and Chl2B transient absorption ΔA0(λ) at a time delay of 100 fs was identified by ultrafast pump-probe spectroscopy in three pairs of PS I complexes from Synechocystis sp. PCC 6803 with residues PsaA-N600 or PsaB-N582 (which ligate Chl2B or Chl2A through a H2O molecule) substituted by Met, His, and Leu. The ΔA0(λ) spectra were quantified using principal component analysis, the main component of which was interpreted as a mutation-induced shift of the equilibrium between the excited state of primary donor P700⁎ and the primary charge-separated state P700+Chl2-. This equilibrium is shifted to the charge-separated state in wild-type PS I and to the excited P700 in the PS I complexes with the substituted ligands to the Chl2A and Chl2B monomers. The results can be rationalized within the framework of an adiabatic model in which the P700 is electronically coupled with the symmetrically arranged monomers Chl2A and Chl2B; such a structure can be considered a symmetric tetrameric exciplex Chl2APAPBChl2B, in which the excited state (Chl2APAPBChl2B)* is mixed with two charge-transfer states P700+Chl2A- and P700+Chl2B-. The electron redistribution between the two branches in favor of the A-branch apparently takes place in the picosecond time scale after reduction of the Chl2A and Chl2B monomers.
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Affiliation(s)
- Dmitry A Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia.
| | - Ivan V Shelaev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia
| | - Fedor E Gostev
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia
| | - Anastasia Petrova
- A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Leninskie gory, 1, Building 40, Russia
| | - Arseniy V Aybush
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia
| | - Victor A Nadtochenko
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia; Department of Chemistry, Lomonosov Moscow State University, Leninskiye Gory 1-3, Moscow 119991, Russian Federation
| | - Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA 70504, USA
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16801, USA; Department of Chemistry, The Pennsylvania State University, University Park, PA 16801, USA
| | - Alexey Yu Semenov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Kosygina st., 4, Russia; A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Leninskie gory, 1, Building 40, Russia
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Gorka M, Cherepanov DA, Semenov AY, Golbeck JH. Control of electron transfer by protein dynamics in photosynthetic reaction centers. Crit Rev Biochem Mol Biol 2020; 55:425-468. [PMID: 32883115 DOI: 10.1080/10409238.2020.1810623] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Trehalose and glycerol are low molecular mass sugars/polyols that have found widespread use in the protection of native protein states, in both short- and long-term storage of biological materials, and as a means of understanding protein dynamics. These myriad uses are often attributed to their ability to form an amorphous glassy matrix. In glycerol, the glass is formed only at cryogenic temperatures, while in trehalose, the glass is formed at room temperature, but only upon dehydration of the sample. While much work has been carried out to elucidate a mechanistic view of how each of these matrices interact with proteins to provide stability, rarely have the effects of these two independent systems been directly compared to each other. This review aims to compile decades of research on how different glassy matrices affect two types of photosynthetic proteins: (i) the Type II bacterial reaction center from Rhodobacter sphaeroides and (ii) the Type I Photosystem I reaction center from cyanobacteria. By comparing aggregate data on electron transfer, protein structure, and protein dynamics, it appears that the effects of these two distinct matrices are remarkably similar. Both seem to cause a "tightening" of the solvation shell when in a glassy state, resulting in severely restricted conformational mobility of the protein and associated water molecules. Thus, trehalose appears to be able to mimic, at room temperature, nearly all of the effects on protein dynamics observed in low temperature glycerol glasses.
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Affiliation(s)
- Michael Gorka
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA
| | - Dmitry A Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia.,A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - Alexey Yu Semenov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russia.,A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University, Moscow, Russia
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA.,Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
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Multiple pathways of charge recombination revealed by the temperature dependence of electron transfer kinetics in cyanobacterial photosystem I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:601-610. [DOI: 10.1016/j.bbabio.2019.06.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Revised: 05/22/2019] [Accepted: 06/15/2019] [Indexed: 11/20/2022]
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7
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Cherepanov DA, Milanovsky GE, Gopta OA, Balasubramanian R, Bryant DA, Semenov AY, Golbeck JH. Electron–Phonon Coupling in Cyanobacterial Photosystem I. J Phys Chem B 2018; 122:7943-7955. [DOI: 10.1021/acs.jpcb.8b03906] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Dmitry A. Cherepanov
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Leninskye Gory,
1, Building 40, 119992 Moscow, Russia
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 117977 Moscow, Russia
| | - Georgy E. Milanovsky
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Leninskye Gory,
1, Building 40, 119992 Moscow, Russia
| | - Oksana A. Gopta
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Leninskye Gory,
1, Building 40, 119992 Moscow, Russia
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 328 Frear Laboratory, University Park, Pennsylvania 16802, United States
| | - Ramakrishnan Balasubramanian
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 328 Frear Laboratory, University Park, Pennsylvania 16802, United States
| | - Donald A. Bryant
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 328 Frear Laboratory, University Park, Pennsylvania 16802, United States
- Department of Chemistry and Biochemistry, Montana State University, 103 Chemistry and Biochemistry Building, PO Box 173400, Bozeman, Montana 59717, United States
| | - Alexey Yu. Semenov
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Leninskye Gory,
1, Building 40, 119992 Moscow, Russia
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Kosygina st., 4, 117977 Moscow, Russia
| | - John H. Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, 328 Frear Laboratory, University Park, Pennsylvania 16802, United States
- Department of Chemistry, The Pennsylvania State University, 328 Frear Laboratory, University Park, Pennsylvania 16802, United States
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Cherepanov DA, Milanovsky GE, Petrova AA, Tikhonov AN, Semenov AY. Electron Transfer through the Acceptor Side of Photosystem I: Interaction with Exogenous Acceptors and Molecular Oxygen. BIOCHEMISTRY (MOSCOW) 2018; 82:1249-1268. [PMID: 29223152 DOI: 10.1134/s0006297917110037] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
This review considers the state-of-the-art on mechanisms and alternative pathways of electron transfer in photosynthetic electron transport chains of chloroplasts and cyanobacteria. The mechanisms of electron transport control between photosystems (PS) I and II and the Calvin-Benson cycle are considered. The redistribution of electron fluxes between the noncyclic, cyclic, and pseudocyclic pathways plays an important role in the regulation of photosynthesis. Mathematical modeling of light-induced electron transport processes is considered. Particular attention is given to the electron transfer reactions on the acceptor side of PS I and to interactions of PS I with exogenous acceptors, including molecular oxygen. A kinetic model of PS I and its interaction with exogenous electron acceptors has been developed. This model is based on experimental kinetics of charge recombination in isolated PS I. Kinetic and thermodynamic parameters of the electron transfer reactions in PS I are scrutinized. The free energies of electron transfer between quinone acceptors A1A/A1B in the symmetric redox cofactor branches of PS I and iron-sulfur clusters FX, FA, and FB have been estimated. The second-order rate constants of electron transfer from PS I to external acceptors have been determined. The data suggest that byproduct formation of superoxide radical in PS I due to the reduction of molecular oxygen in the A1 site (Mehler reaction) can exceed 0.3% of the total electron flux in PS I.
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Affiliation(s)
- D A Cherepanov
- Lomonosov Moscow State University, Belozersky Institute of Physico-Chemical Biology, Moscow, 119992, Russia.
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Milanovsky GE, Petrova AA, Cherepanov DA, Semenov AY. Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors. PHOTOSYNTHESIS RESEARCH 2017; 133:185-199. [PMID: 28352992 DOI: 10.1007/s11120-017-0366-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 03/01/2017] [Indexed: 05/09/2023]
Abstract
The reduction kinetics of the photo-oxidized primary electron donor P700 in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P700, secondary quinone acceptor A1, iron-sulfur clusters and external electron donor and acceptors - methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl2NQ) and oxygen. PS I complexes containing various quinones in the A1-binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl2NQ) as well as F X-core complexes, depleted of terminal iron-sulfur F A/F B clusters, were studied. The acceleration of charge recombination in F X-core complexes by PhQ/PQ substitution indicates that backward ET from the iron-sulfur clusters involves quinone in the A1-binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P700+ reduction with the kinetic model. The free energy gap ΔG 0 between F X and F A/F B clusters was estimated as -130 meV. The driving force of ET from A1 to F X was determined as -50 and -220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A1A-site, this reaction was found to be endergonic (ΔG 0 = +75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis-Menten kinetics. The second-order rate constants of ET from F A/F B, F X and Cl2NQ in the A1-site of PS I to external acceptors were estimated. The side production of superoxide radical in the A1-site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.
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Affiliation(s)
- Georgy E Milanovsky
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia
| | - Anastasia A Petrova
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia
| | - Dmitry A Cherepanov
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia.
- A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russia.
| | - Alexey Yu Semenov
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russia.
- N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia.
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Santabarbara S, Galuppini L, Casazza AP. Bidirectional electron transfer in the reaction centre of photosystem I. JOURNAL OF INTEGRATIVE PLANT BIOLOGY 2010; 52:735-749. [PMID: 20666929 DOI: 10.1111/j.1744-7909.2010.00977.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In the past decade light-induced electron transfer reactions in photosystem I have been the subject of intensive investigations that have led to the elucidation of some unique characteristics, the most striking of which is the existence of two parallel, functional, redox active cofactors chains. This process is generally referred to as bidirectional electron transfer. Here we present a review of the principal evidences that have led to the uncovering of bidirectionality in the reaction centre of photosystem I. A special focus is dedicated to the results obtained combining time-resolved spectroscopic techniques, either difference absorption or electron paramagnetic resonance, with molecular genetics, which allows, through modification of the binding of redox active cofactors with the reaction centre subunits, an effect on their physical-chemical properties.
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Srinivasan N, Golbeck JH. Protein–cofactor interactions in bioenergetic complexes: The role of the A1A and A1B phylloquinones in Photosystem I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:1057-88. [DOI: 10.1016/j.bbabio.2009.04.010] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2009] [Revised: 04/14/2009] [Accepted: 04/22/2009] [Indexed: 10/20/2022]
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Antonkine ML, Koay MS, Epel B, Breitenstein C, Gopta O, Gärtner W, Bill E, Lubitz W. Synthesis and characterization of de novo designed peptides modelling the binding sites of [4Fe–4S] clusters in photosystem I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:995-1008. [DOI: 10.1016/j.bbabio.2009.03.007] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Revised: 02/23/2009] [Accepted: 03/09/2009] [Indexed: 10/21/2022]
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Santabarbara S, Jasaitis A, Byrdin M, Gu F, Rappaport F, Redding K. Additive effect of mutations affecting the rate of phylloquinone reoxidation and directionality of electron transfer within photosystem I. Photochem Photobiol 2009; 84:1381-7. [PMID: 19067959 DOI: 10.1111/j.1751-1097.2008.00458.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Optical pump-probe spectroscopy in the nanosecond-microsecond timescale has been used to study the electron transfer reactions taking place within the Photosystem I reaction center of intact Chlamydomonas reinhardtii cells. The biphasic kinetics of phylloquinone (PhQ) reoxidation were investigated in double mutants that combine a mutation (PsaA-Y696F) near the primary acceptor chlorophyll, ec3A, with those near PhQA (PsaA-S692A, PsaA-W697F). The PsaA-S692A and PsaA-W697F mutations selectively lengthened the 200 ns lifetime component observed in the wild-type (WT). The reverse similar 20 ns component was unaltered in the single mutant, both in terms of lifetime and relative amplitude. However, both double mutants possessed a reverse similar 20 ns component (PhQB(-) reoxidation) with increased amplitude compared with the WT and the individual PhQA mutants. The component assigned to PhQA(-) reoxidation was slowed, like the individual PhQA mutants, and of lower amplitude, as observed in the single ec3A mutant. Hence, the effects of these mutations are almost entirely additive, providing strong support for the previously proposed bidirectional electron transfer model, which attributes the reverse similar 20 and reverse similar 200 ns phases to reoxidation of PhQB or PhQA, respectively. Moreover, in all the mutants investigated, it was also possible to observe an intermediate (approximately 180 ns) component, as previously reported for mutants of the PhQ(A) binding pocket (Biochim. Biophys. Acta [2006] 1757, 1529-1538), which we have tentatively attributed to forward electron transfer between the iron-sulfur clusters FX and FA/B.
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Gong XM, Hochman Y, Lev T, Bunker G, Carmeli C. The structure of genetically modified iron-sulfur cluster F(x) in photosystem I as determined by X-ray absorption spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1787:97-104. [PMID: 19081389 DOI: 10.1016/j.bbabio.2008.11.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2008] [Revised: 11/05/2008] [Accepted: 11/11/2008] [Indexed: 11/28/2022]
Abstract
Photosystem I (PS I) mediates light-induced electron transfer from P700 through a chlorophyll a, a quinone and a [4Fe-4S] iron-sulfur cluster F(X), located on the core subunits PsaA/B to iron-sulfur clusters F(A/B) on subunit PsaC. Structure function relations in the native and in the mutant (psaB-C565S/D566E) of the cysteine ligand of F(X) cluster were studied by X-ray absorption spectroscopy (EXAFS) and transient spectroscopy. The structure of F(X) was determined in PS I lacking clusters F(A/B) by interruption of the psaC2 gene of PS I in the cyanobacterium Synechocystis sp PCC 6803. PsaC-deficient mutant cells assembled the core subunits of PS I which mediated electron transfer mostly to the phylloquinone. EXAFS analysis of the iron resolved a [4Fe-4S] cluster in the native PsaC-deficient PS I. Each iron had 4 sulfur and 3 iron atoms in the first and second shells with average Fe-S and Fe-Fe distances of 2.27 A and 2.69 A, respectively. In the C565S/D566E serine mutant, one of the irons of the cluster was ligated to three oxygen atoms with Fe-O distance of 1.81 A. The possibility that the structural changes induced an increase in the reorganization energy that consequently decreased the rate of electron transfer from the phylloquinone to F(X) is discussed.
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Affiliation(s)
- Xiao-Min Gong
- Department of Biochemistry, Tel Aviv University, Tel Aviv 69978, Israel
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Bender SL, Keough JM, Boesch SE, Wheeler RA, Barry BA. The Vibrational Spectrum of the Secondary Electron Acceptor, A1, in Photosystem I. J Phys Chem B 2008; 112:3844-52. [DOI: 10.1021/jp0775146] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Shana L. Bender
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332, and Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - James M. Keough
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332, and Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - Scott E. Boesch
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332, and Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - Ralph A. Wheeler
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332, and Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
| | - Bridgette A. Barry
- Department of Chemistry and Biochemistry and the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332, and Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019
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16
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Rappaport F, Diner BA, Redding K. Optical Measurements of Secondary Electron Transfer in Photosystem I. PHOTOSYSTEM I 2006. [DOI: 10.1007/978-1-4020-4256-0_16] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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17
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Santabarbara S, Heathcote P, Evans MCW. Modelling of the electron transfer reactions in Photosystem I by electron tunnelling theory: The phylloquinones bound to the PsaA and the PsaB reaction centre subunits of PS I are almost isoenergetic to the iron–sulfur cluster FX. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1708:283-310. [PMID: 15975545 DOI: 10.1016/j.bbabio.2005.05.001] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2004] [Revised: 04/12/2005] [Accepted: 05/03/2005] [Indexed: 10/25/2022]
Abstract
Photosystem I is a large macromolecular complex located in the thylakoid membranes of chloroplasts and in cyanobacteria that catalyses the light driven reduction of ferredoxin and oxidation of plastocyanin. Due to the very negative redox potential of the primary electron transfer cofactors accepting electrons, direct estimation by redox titration of the energetics of the system is hampered. However, the rates of electron transfer reactions are related to the thermodynamic properties of the system. Hence, several spectroscopic and biochemical techniques have been employed, in combination with the classical Marcus theory for electron transfer tunnelling, in order to access these parameters. Nevertheless, the values which have been presented are very variable. In particular, for the case of the tightly bound phylloquinone molecule A(1), the values of the redox potentials reported in the literature vary over a range of about 350 mV. Previous models of Photosystem I have assumed a unidirectional electron transfer model. In the present study, experimental evidence obtained by means of time resolved absorption, photovoltage, and electron paramagnetic resonance measurements are reviewed and analysed in terms of a bi-directional kinetic model for electron transfer reactions. This model takes into consideration the thermodynamic equilibrium between the iron-sulfur centre F(X) and the phylloquinone bound to either the PsaA (A(1A)) or the PsaB (A(1B)) subunit of the reaction centre and the equilibrium between the iron-sulfur centres F(A) and F(B). The experimentally determined decay lifetimes in the range of sub-picosecond to the microsecond time domains can be satisfactorily simulated, taking into consideration the edge-to-edge distances between redox cofactors and driving forces reported in the literature. The only exception to this general behaviour is the case of phylloquinone (A(1)) reoxidation. In order to describe the reported rates of the biphasic decay, of about 20 and 200 ns, associated with this electron transfer step, the redox potentials of the quinones are estimated to be almost isoenergetic with that of the iron sulfur centre F(X). A driving force in the range of 5 to 15 meV is estimated for these reactions, being slightly exergonic in the case of the A(1B) quinone and slightly endergonic, in the case of the A(1A) quinone. The simulation presented in this analysis not only describes the kinetic data obtained for the wild type samples at room temperature and is consistent with estimates of activation energy by the analysis of temperature dependence, but can also explain the effect of the mutations around the PsaB quinone binding pocket. A model of the overall energetics of the system is derived, which suggests that the only substantially irreversible electron transfer reactions are the reoxidation of A(0) on both electron transfer branches and the reduction of F(A) by F(X).
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Affiliation(s)
- Stefano Santabarbara
- School of Biological Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK.
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18
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Ishikita H, Knapp EW. Redox potential of quinones in both electron transfer branches of photosystem I. J Biol Chem 2003; 278:52002-11. [PMID: 12972408 DOI: 10.1074/jbc.m306434200] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The redox potentials of the two electron transfer (ET) active quinones in the central part of photosystem I (PSI) were determined by evaluating the electrostatic energies from the solution of the Poisson-Boltzmann equation based on the crystal structure. The calculated redox potentials are -531 mV for A1A and -686 mV for A1B. From these results we conclude the following. (i) Both branches are active with a much faster ET in the B-branch than in the A-branch. (ii) The measured lifetime of 200-290 ns of reduced quinones agrees with the estimate for the A-branch and corroborates with an uphill ET from this quinone to the iron-sulfur cluster as observed in recent kinetic measurements. (iii) The electron paramagnetic resonance spectroscopic data refer to the A-branch quinone where the corresponding ET is uphill in energy. The negative redox potential of A1 in PSI is primarily because of the influence from the negatively charged FX, in contrast to the positive shift on the quinone redox potential in bacterial reaction center and PSII that is attributed to the positively charged non-heme iron atom. The conserved residue Asp-B575 changes its protonation state after quinone reduction. The difference of 155 mV in the quinone redox potentials of the two branches were attributed to the conformation of the backbone with a large contribution from Ser-A692 and Ser-B672 and to the side chain of Asp-B575, whose protonation state couples differently with the formation of the quinone radicals.
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Affiliation(s)
- Hiroshi Ishikita
- Department of Biology, Chemistry, and Pharmacy, Institute of Chemistry, Free University of Berlin, Takustrasse 6, Berlin D-14195, Germany
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19
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Gong XM, Agalarov R, Brettel K, Carmeli C. Control of electron transport in photosystem I by the iron-sulfur cluster FX in response to intra- and intersubunit interactions. J Biol Chem 2003; 278:19141-50. [PMID: 12626505 DOI: 10.1074/jbc.m301808200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Photosystem I (PS I) is a transmembranal multisubunit complex that mediates light-induced electron transfer from plactocyanine to ferredoxin. The electron transfer proceeds from an excited chlorophyll a dimer (P700) through a chlorophyll a (A0), a phylloquinone (A1), and a [4Fe-4S] iron-sulfur cluster FX, all located on the core subunits PsaA and PsaB, to iron-sulfur clusters FA and FB, located on subunit PsaC. Earlier, it was attempted to determine the function of FX in the absence of FA/B mainly by chemical dissociation of subunit PsaC. However, not all PsaC subunits could be removed from the PS I preparations by this procedure without partially damaging FX. We therefore removed subunit PsaC by interruption of the psaC2 gene of PS I in the cyanobacterium Synechocystis sp. PCC 6803. Cells could not grow under photosynthetic conditions when subunit PsaC was deleted, yet the PsaC-deficient mutant cells grew under heterotrophic conditions and assembled the core subunits of PS I in which light-induced electron transfer from P700 to A1 occurred. The photoreduction of FX was largely inhibited, as seen from direct measurement of the extent of electron transfer from A1 to FX. From the crystal structure it can be seen that the removal of subunits PsaC, PsaD, and PsaE in the PsaC-deficient mutant resulted in the braking of salt bridges between these subunits and PsaB and PsaA and the formation of a net of two negative surface charges on PsaA/B. The potential induced on FX by these surface charges is proposed to inhibit electron transport from the quinone. In the complete PS I complex, replacement of a cysteine ligand of FX by serine in site-directed mutation C565S/D566E in subunit PsaB caused an approximately 10-fold slow down of electron transfer from the quinone to FX without much affecting the extent of this electron transfer compared with wild type. Based on these and other results, we propose that FX might have a major role in controlling electron transfer through PS I.
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Affiliation(s)
- Xiao-Min Gong
- Department of Biochemistry, Tel Aviv University, Tel Aviv 69978, Israel
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20
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Shinkarev VP, Zybailov B, Vassiliev IR, Golbeck JH. Modeling of the P700+ charge recombination kinetics with phylloquinone and plastoquinone-9 in the A1 site of photosystem I. Biophys J 2002; 83:2885-97. [PMID: 12496065 PMCID: PMC1302373 DOI: 10.1016/s0006-3495(02)75298-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Light activation of photosystem I (PS I) induces electron transfer from the excited primary electron donor P700 (a special pair of chlorophyll a/a' molecules) to three iron-sulfur clusters, F(X), F(A), and F(B) via acceptors A(0) (a monomeric chlorophyll a) and A(1) (phylloquinone). PS I complexes isolated from menA and menB mutants contain plastoquinone-9 rather than phylloquinone in the A(1) site and show altered rates of forward electron transfer from A to [F(A)/F(B)] and altered rates of back electron transfer from [F(A)/F(B)](-) to P700+ (Semenov, A. Y., et al., J. Biol. Chem. 275:23429-23438, 2000). To identify the modified electron transfer steps, we studied the kinetics of flash-induced P700+ reduction in PS I that contains either an intact set or a subset of iron-sulfur clusters F(X), F(A), and F(B) and with the A(1) binding site occupied by phylloquinone or plastoquinone-9. A modeling of the forward and backward electron transfer kinetics in P700-F(A)/F(B) complexes, P700-F(X) cores, and P700-A(1) cores shows that the replacement of phylloquinone by plastoquinone-9 induces a decrease in the free energy gap between A(1) and F(A)/F(B) from approximately -205 mV in wild-type PS I to approximately -70 mV in menA PS I. The +135 mV increase in the midpoint potential of A(1) explains the acceleration in the rate of P700+ dark reduction in menA PS I, and the resulting uphill electron transfer from A(1) to F(X) in menA PS I explains the absence of a contribution from F to the reduction of P700+. This fully quantitative description of PS I relates electron transfer rates, equilibrium constants, and redox potentials, and can be used to predict changes in these parameters upon substitution of electron transfer cofactors.
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Affiliation(s)
- Vladimir P Shinkarev
- Department of Biochemistry, University of Illinois at Urbana-Chamnpaign, 156 Davenport Hall, 607 Mathews Avenue, Urbana, IL 61801-3838, USA.
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21
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Shen G, Antonkine ML, van der Est A, Vassiliev IR, Brettel K, Bittl R, Zech SG, Zhao J, Stehlik D, Bryant DA, Golbeck JH. Assembly of photosystem I. II. Rubredoxin is required for the in vivo assembly of F(X) in Synechococcus sp. PCC 7002 as shown by optical and EPR spectroscopy. J Biol Chem 2002; 277:20355-66. [PMID: 11914374 DOI: 10.1074/jbc.m201104200] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The rubA gene was insertionally inactivated in Synechococcus sp. PCC 7002, and the properties of photosystem I complexes were characterized spectroscopically. X-band EPR spectroscopy at low temperature shows that the three terminal iron-sulfur clusters, F(X), F(A), and F(B), are missing in whole cells, thylakoids, and photosystem (PS) I complexes of the rubA mutant. The flash-induced decay kinetics of both P700(+) in the visible and A(1)- in the near-UV show that charge recombination occurs between P700(+) and A(1)- in both thylakoids and PS I complexes. The spin-polarized EPR signal at room temperature from PS I complexes also indicates that forward electron transfer does not occur beyond A(1). In agreement, the spin-polarized X-band EPR spectrum of P700(+) A(1)- at low temperature shows that an electron cycle between A(1)- and P700(+) occurs in a much larger fraction of PS I complexes than in the wild-type, wherein a relatively large fraction of the electrons promoted are irreversibly transferred to [F(A)/F(B)]. The electron spin polarization pattern shows that the orientation of phylloquinone in the PS I complexes is identical to that of the wild type, and out-of-phase, spin-echo modulation spectroscopy shows the same P700(+) to A(1)- center-to-center distance in photosystem I complexes of wild type and the rubA mutant. In contrast to the loss of F(X), F(B), and F(A), the Rieske iron-sulfur protein and the non-heme iron in photosystem II are intact. It is proposed that rubredoxin is specifically required for the assembly of the F(X) iron-sulfur cluster but that F(X) is not required for the biosynthesis of trimeric P700-A(1) cores. Since the PsaC protein requires the presence of F(X) for binding, the absence of F(A) and F(B) may be an indirect result of the absence of F(X).
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Affiliation(s)
- Gaozhong Shen
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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22
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Abstract
This mini-review focuses on recent experimental results and questions, which came up since the last more comprehensive reviews on the subject. We include a brief discussion of the different techniques used for time-resolved studies of electron transfer in photosystem I (PS I) and relate the kinetic results to new structural data of the PS I reaction centre.
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Affiliation(s)
- K Brettel
- Section de Bioénergétique and CNRS URA 2096, Département de Biologie Cellulaire et Moléculaire, CEA Saclay, 91191 Cedex, Gif-sur-Yvette, France.
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23
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Boudreaux B, MacMillan F, Teutloff C, Agalarov R, Gu F, Grimaldi S, Bittl R, Brettel K, Redding K. Mutations in both sides of the photosystem I reaction center identify the phylloquinone observed by electron paramagnetic resonance spectroscopy. J Biol Chem 2001; 276:37299-306. [PMID: 11489879 DOI: 10.1074/jbc.m102327200] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The core of photosystem I (PS1) is composed of the two related integral membrane polypeptides, PsaA and PsaB, which bind two symmetrical branches of cofactors, each consisting of two chlorophylls and a phylloquinone, that potentially link the primary electron donor and the tertiary acceptor. In an effort to identify amino acid residues near the phylloquinone binding sites, all tryptophans and histidines that are conserved between PsaA and PsaB in the region of the 10th and 11th transmembrane alpha-helices were mutated in Chlamydomonas reinhardtii. The mutant PS1 reaction centers appear to assemble normally and possess photochemical activity. An electron paramagnetic resonance (EPR) signal attributed to the phylloquinone anion radical (A(1)(-)) can be observed either transiently or after illumination of reaction centers with pre-reduced iron-sulfur clusters. Mutation of PsaA-Trp(693) to Phe resulted in an inability to photo-accumulate A(1)(-), whereas mutation of the analogous tryptophan in PsaB (PsaB-Trp(673)) did not produce this effect. The PsaA-W693F mutation also produced spectral changes in the time-resolved EPR spectrum of the P(700)(+) A(1)(-) radical pair, whereas the analogous mutation in PsaB had no observable effect. These observations indicate that the A(1)(-) phylloquinone radical observed by EPR occupies the phylloquinone-binding site containing PsaA-Trp(693). However, mutation of either tryptophan accelerated charge recombination from the terminal Fe-S clusters.
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Affiliation(s)
- B Boudreaux
- Department of Chemistry, University of Alabama, Tuscaloosa, Alabama 35487, USA
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24
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Muhiuddin IP, Heathcote P, Carter S, Purton S, Rigby SE, Evans MC. Evidence from time resolved studies of the P700(.+)/A1(.-) radical pair for photosynthetic electron transfer on both the PsaA and PsaB branches of the photosystem I reaction centre. FEBS Lett 2001; 503:56-60. [PMID: 11513854 DOI: 10.1016/s0014-5793(01)02696-5] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Kinetic analysis using pulsed electron paramagnetic resonance (EPR) of photosynthetic electron transfer in the photosystem I reaction centres of Synechocystis 6803, in wild-type Chlamydomonas reinhardtii, and in site directed mutants of the phylloquinone binding sites in C. reinhardtii, indicates that electron transfer from the reaction centre primary electron donor, P700, to the iron-sulphur centres, Fe-S(X/A/B), can occur through either the PsaA or PsaB side phylloquinone. At low temperature reaction centres are frozen in states which allow electron transfer on one side of the reaction centre only. A fraction always donates electrons to the PsaA side quinone, the remainder to the PsaB side.
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Affiliation(s)
- I P Muhiuddin
- Department of Biology, University College London, UK
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25
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Guergova-Kuras M, Boudreaux B, Joliot A, Joliot P, Redding K. Evidence for two active branches for electron transfer in photosystem I. Proc Natl Acad Sci U S A 2001; 98:4437-42. [PMID: 11274371 PMCID: PMC31853 DOI: 10.1073/pnas.081078898] [Citation(s) in RCA: 222] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
All photosynthetic reaction centers share a common structural theme. Two related, integral membrane polypeptides sequester electron transfer cofactors into two quasi-symmetrical branches, each of which incorporates a quinone. In type II reaction centers [photosystem (PS) II and proteobacterial reaction centers], electron transfer proceeds down only one of the branches, and the mobile quinone on the other branch is used as a terminal acceptor. PS I uses iron-sulfur clusters as terminal acceptors, and the quinone serves only as an intermediary in electron transfer. Much effort has been devoted to understanding the unidirectionality of electron transport in type II reaction centers, and it was widely thought that PS I would share this feature. We have tested this idea by examining in vivo kinetics of electron transfer from the quinone in mutant PS I reaction centers. This transfer is associated with two kinetic components, and we show that mutation of a residue near the quinone in one branch specifically affects the faster component, while the corresponding mutation in the other branch specifically affects the slower component. We conclude that both electron transfer branches in PS I are active.
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Affiliation(s)
- M Guergova-Kuras
- Institut de Biologie Physico-Chimique, Centre National de la Recherche Scientifique, UPR 1261, 13 Rue Pierre et Marie Curie, 75005 Paris, France
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26
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Shinkarev VP, Vassiliev IR, Golbeck JH. A kinetic assessment of the sequence of electron transfer from F(X) to F(A) and further to F(B) in photosystem I: the value of the equilibrium constant between F(X) and F(A). Biophys J 2000; 78:363-72. [PMID: 10620300 PMCID: PMC1300644 DOI: 10.1016/s0006-3495(00)76599-4] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The x-ray structure analysis of photosystem I (PS I) crystals at 4-A resolution (Schubert et al., 1997, J. Mol. Biol. 272:741-769) has revealed the distances between the three iron-sulfur clusters, labeled F(X), F(1), and F(2), which function on the acceptor side of PS I. There is a general consensus concerning the assignment of the F(X) cluster, which is bound to the PsaA and PsaB polypeptides that constitute the PS I core heterodimer. However, the correspondence between the acceptors labeled F(1) and F(2) on the electron density map and the F(A) and F(B) clusters defined by electron paramagnetic resonance (EPR) spectroscopy remains controversial. Two recent studies (Diaz-Quintana et al., 1998, Biochemistry. 37:3429-3439;, Vassiliev et al., 1998, Biophys. J. 74:2029-2035) provided evidence that F(A) is the cluster proximal to F(X), and F(B) is the cluster that donates electrons to ferredoxin. In this work, we provide a kinetic argument to support this assignment by estimating the rates of electron transfer between the iron-sulfur clusters F(X), F(A), and F(B). The experimentally determined kinetics of P700(+) dark relaxation in PS I complexes (both F(A) and F(B) are present), HgCl(2)-treated PS I complexes (devoid of F(B)), and P700-F(X) cores (devoid of both F(A) and F(B)) from Synechococcus sp. PCC 6301 are compared with the expected dependencies on the rate of electron transfer, based on the x-ray distances between the cofactors. The analysis, which takes into consideration the asymmetrical position of iron-sulfur clusters F(1) and F(2) relative to F(X), supports the F(X) --> F(A) --> F(B) --> Fd sequence of electron transfer on the acceptor side of PS I. Based on this sequence of electron transfer and on the observed kinetics of P700(+) reduction and F(X)(-) oxidation, we estimate the equilibrium constant of electron transfer between F(X) and F(A) at room temperature to be approximately 47. The value of this equilibrium constant is discussed in the context of the midpoint potentials of F(X) and F(A), as determined by low-temperature EPR spectroscopy.
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Affiliation(s)
- V P Shinkarev
- Department of Plant Biology, University of Illinois, Urbana, Illinois 61801, USA
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27
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Vassiliev IR, Yu J, Jung YS, Schulz R, Ganago AO, McIntosh L, Golbeck JH. The cysteine-proximal aspartates in the Fx-binding niche of photosystem I. Effect of alanine and lysine replacements on photoautotrophic growth, electron transfer rates, single-turnover flash efficiency, and EPR spectral properties. J Biol Chem 1999; 274:9993-10001. [PMID: 10187775 DOI: 10.1074/jbc.274.15.9993] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The FX electron acceptor in Photosystem I (PS I) is a highly electronegative (Em = -705 mV) interpolypeptide [4Fe-4S] cluster ligated by cysteines 556 and 565 on PsaB and cysteines 574 and 583 on PsaA in Synechocystis sp. PCC 6803. An aspartic acid is adjacent to each of these cysteines on PsaB and adjacent to the proline-proximal cysteine on PsaA. We investigated the effect of D566PsaB and D557PsaB on electron transfer through FX by changing each aspartate to the neutral alanine or to the positively charged lysine either singly (D566APsaB, D557APsaB, D566KPsaB, and D557KPsaB) or in pairs (D557APsaB/D566APsaB and D557KPsaB/D566APsaB). All mutants except for D557KPsaB/D566APsaB grew photoautotrophically, but the growth of D557KPsaB and D557APsaB/D566APsaB was impaired under low light. The doubling time was increased, and the chlorophyll content per cell was lower in D557KPsaB and D557APsaB/D566APsaB relative to the wild type and the other mutants. Nevertheless, the rates of NADP+ photoreduction in PS I complexes from all mutants were no less than 75% of that of the wild type. The kinetics of back-reaction of the electron acceptors on a single-turnover flash showed efficient electron transfer to the terminal acceptors FA and FB in PS I complexes from all mutants. The EPR spectrum of FX was identical to that in the wild type in all but the single and double D566APsaB mutants, where the high-field resonance was shifted downfield. We conclude that the impaired growth of some of the mutants is related to a reduced accumulation of PS I rather than to photosynthetic efficiency. The chemical nature and the charge of the amino acids adjacent to the cysteine ligands on PsaB do not appear to be significant factors in the efficiency of electron transfer through FX.
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Affiliation(s)
- I R Vassiliev
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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28
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Brettel K, Vos MH. Spectroscopic resolution of the picosecond reduction kinetics of the secondary electron acceptor A1 in photosystem I. FEBS Lett 1999; 447:315-7. [PMID: 10214969 DOI: 10.1016/s0014-5793(99)00317-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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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29
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Mamedov MD, Gourovskaya KN, Vassiliev IR, Golbeck JH. Electrogenicity accompanies photoreduction of the iron-sulfur clusters F(A) and F(B) in photosystem I. FEBS Lett 1998; 431:219-23. [PMID: 9708906 DOI: 10.1016/s0014-5793(98)00759-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Photovoltage responses accompanying electron transfer on the acceptor side of photosystem I (PS I) were investigated in proteoliposomes containing PS I complexes from the cyanobacterium Synechococcus sp. PCC 6301 using a direct electrometrical technique. The relative contributions of the F(X) --> F(B) and the F(X) --> F(A) electron transfer reactions to the overall electrogenicity were elucidated by comparing the sodium dithionite-induced decrease in the magnitude of the total photoelectric responses in control and in F(B)-less (HgCl2-treated) PS I complexes. The results obtained suggest that the electrogenesis on the acceptor side of PS I is related to electron transfers between both F(X) and F(A) and F(A) and F(B). Based on the electrogenic nature of the latter reaction in PS I complexes, we conclude that F(A) rather than F(B) is the acceptor proximal to F(X).
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Affiliation(s)
- M D Mamedov
- Department of Photobiochemistry, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia
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30
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Polm M, Brettel K. Secondary pair charge recombination in photosystem I under strongly reducing conditions: temperature dependence and suggested mechanism. Biophys J 1998; 74:3173-81. [PMID: 9635770 PMCID: PMC1299657 DOI: 10.1016/s0006-3495(98)78023-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Photoinduced electron transfer in photosystem I (PS I) proceeds from the excited primary electron donor P700 (a chlorophyll a dimer) via the primary acceptor A0 (chlorophyll a) and the secondary acceptor A1 (phylloquinone) to three [4Fe-4S] clusters, Fx, FA, and FB. Prereduction of the iron-sulfur clusters blocks electron transfer beyond A1. It has been shown previously that, under such conditions, the secondary pair P700+A1- decays by charge recombination with t1/2 approximately 250 ns at room temperature, forming the P700 triplet state (3P700) with a yield exceeding 85%. This reaction is unusual, as the secondary pair in other photosynthetic reaction centers recombines much slower and forms directly the singlet ground state rather than the triplet state of the primary donor. Here we studied the temperature dependence of secondary pair recombination in PS I from the cyanobacterium Synechococcus sp. PCC6803, which had been illuminated in the presence of dithionite at pH 10 to reduce all three iron-sulfur clusters. The reaction P700+A1- --> 3P700 was monitored by flash absorption spectroscopy. With decreasing temperature, the recombination slowed down and the yield of 3P700 decreased. In the range between 303 K and 240 K, the recombination rates could be described by the Arrhenius law with an activation energy of approximately 170 meV. Below 240 K, the temperature dependence became much weaker, and recombination to the singlet ground state became the dominating process. To explain the fast activated recombination to the P700 triplet state, we suggest a mechanism involving efficient singlet to triplet spin evolution in the secondary pair, thermally activated repopulation of the more closely spaced primary pair P700+A0- in a triplet spin configuration, and subsequent fast recombination (intrinsic rate on the order of 10(9) s(-1)) forming 3P700.
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Affiliation(s)
- M Polm
- Section de Bioénergétique and CNRS-URA 2096, Département de Biologie Cellulaire et Moléculaire, CEA Saclay, Gif-sur-Yvette, France
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[7] Comparison of in Vitro and in Vivo mutants of PsaC in photosystem I: Protocols for mutagenesis and techniques for analysis. Methods Enzymol 1998. [DOI: 10.1016/s0076-6879(98)97009-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Yu J, Vassiliev IR, Jung YS, Golbeck JH, McIntosh L. Strains of synechocystis sp. PCC 6803 with altered PsaC. I. Mutations incorporated in the cysteine ligands of the two [4Fe-4S] clusters FA and FB of photosystem I. J Biol Chem 1997; 272:8032-9. [PMID: 9065476 DOI: 10.1074/jbc.272.12.8032] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Two [4Fe-4S] clusters, FA and FB, function as terminal electron carriers in Photosystem I (PS I), a thylakoid membrane-bound protein-pigment complex. To probe the function of these two clusters in photosynthetic electron transport, site-directed mutants were created in the transformable cyanobacterium Synechocystis sp. PCC 6803. Cysteine ligands in positions 14 or 51 to FB and FA, respectively, were replaced with aspartate, serine, or alanine, and the effect on the genetic, physiological, and biochemical characteristics of PS I complexes from the mutant strains were studied. All mutant strains were unable to grow photoautotrophically, and compared with wild type, mixotrophic growth was inhibited under normal light intensity. The mutant cells supported lower rates of whole-chain photosynthetic electron transport. Thylakoids isolated from the aspartate and serine mutants have lower levels of PS I subunits PsaC, PsaD, and PsaE and lower rates of PS I-mediated substrate photoreduction compared with the wild type. The alanine and double aspartate mutants have no detectable levels PsaC, PsaD, and PsaE. Electron transfer rates, measured by cytochrome c6-mediated NADP+ photoreduction, were lower in purified PS I complexes from the aspartate and serine mutants. By measuring the P700(+) kinetics after a single turnover flash, a large percentage of the backreaction in the aspartate and serine mutants was found to be derived from A1 and FX, indicating an inefficiency at the FX --> FA/FB electron transfer step. The alanine and double aspartate mutants failed to show any backreaction from [FA/FB]-. These results indicate that the various mutations of the cysteine 14 and 51 ligands to FB and FA affect biogenesis and electron transfer differently depending on the type of substitution, and that the effects of mutations on biogenesis and function can be biochemically separated and analyzed.
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Affiliation(s)
- J Yu
- DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824-1312, USA
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Electron transfer and arrangement of the redox cofactors in photosystem I. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 1997. [DOI: 10.1016/s0005-2728(96)00112-0] [Citation(s) in RCA: 380] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Jung YS, Vassiliev IR, Qiao F, Yang F, Bryant DA, Golbeck JH. Modified ligands to FA and FB in photosystem I. Proposed chemical rescue of a [4Fe-4S] cluster with an external thiolate in alanine, glycine, and serine mutants of PsaC. J Biol Chem 1996; 271:31135-44. [PMID: 8940111 DOI: 10.1074/jbc.271.49.31135] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The FB and FA electron acceptors in Photosystem I (PS I) are [4Fe-4S] clusters ligated by cysteines provided by PsaC. In a previous study (Mehari, T., Qiao, F., Scott, M. P., Nellis, D., Zhao, J., Bryant, D., and Golbeck, J. H. (1995) J. Biol. Chem. 270, 28108-28117), we showed that when cysteines 14 and 51 were replaced with serine or alanine, the free proteins contained a S = 1/2, [4Fe-4S] cluster at the unmodified site and a mixed population of S = 1/2, [3Fe-4S] and S = 3/2, [4Fe-4S] clusters at the modified site. We show here that these mutant PsaC proteins can be rebound to P700-FX cores, resulting in fully functional PS I complexes. The low temperature EPR spectra of the C14XPsaC.PS I complexes (where X = S, A, or G) show the photoreduction of a wild-type FA cluster and a modified FB' cluster, the latter with g values of 2.115, 1.899, and 1.852 and linewidths of 110, 70, and 85 MHz. Since neither alanine nor glycine contains a suitable side group, an external thiolate provided by beta-mercaptoethanol has likely been recruited to supply the requisite ligand to the [4Fe-4S] cluster. The EPR spectrum of the C51SPsaC.PS I complex differs from that of the C51APsaC.PS I or C51GPsaC.PS I complexes by the presence of an additional set of resonances, which may be derived from the serine oxygen-ligated cluster. In all other mutant PS I complexes, a wild-type spin-coupled interaction spectrum appears when FA and FB are simultaneously reduced. Single turnover flash studies indicate approximately 50% efficient electron transfer to FA/FB in the C14SPsaC.PS I, C51SPsaC.PS I, C14GPsaC.PS I, and C51GPsaC.PS I mutants and less than 40% in the C14APsaC.PS I and C51APsaC.PS I mutants, compared with approximately 76% in the PS I core reconstructed with wild-type PsaC. These data are consistent with the measurements of the rates of cytochrome c6-NADP+ reductase activity, indicating lower rates in the alanine mutants. It is proposed that the chemical rescue of a [4Fe-4S] cluster with a recruited external thiolate at the modified site allows the mutant PsaC proteins to rebind to PS I and to function in forward electron transfer.
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Affiliation(s)
- Y S Jung
- Department of Biochemistry, and Center for Biological Chemistry, George W. Beadle Center, University of Nebraska, Lincoln, Nebraska 68588-0664, USA.
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