1
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Kim Y, Mitchell Z, Lawrence J, Morozov D, Savikhin S, Slipchenko LV. Predicting Mutation-Induced Changes in the Electronic Properties of Photosynthetic Proteins from First Principles: The Fenna-Matthews-Olson Complex Example. J Phys Chem Lett 2023; 14:7038-7044. [PMID: 37524046 DOI: 10.1021/acs.jpclett.3c01461] [Citation(s) in RCA: 1] [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: 08/02/2023]
Abstract
Multiscale molecular modeling is utilized to predict optical absorption and circular dichroism spectra of two single-point mutants of the Fenna-Matthews-Olson photosynthetic pigment-protein complex. The modeling approach combines classical molecular dynamics simulations with structural refinement of photosynthetic pigments and calculations of their excited states in a polarizable protein environment. The only experimental input to the modeling protocol is the X-ray structure of the wild-type protein. The first-principles modeling reproduces changes in the experimental optical spectra of the considered mutants, Y16F and Q198V. Interestingly, the Q198V mutation has a negligible effect on the electronic properties of the targeted bacteriochlorophyll a pigment. Instead, the electronic properties of several other pigments respond to this mutation. The molecular modeling demonstrates that a single-point mutation can induce long-range effects on the protein structure, while extensive structural changes near a pigment do not necessarily lead to significant changes in the electronic properties of that pigment.
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Affiliation(s)
- Yongbin Kim
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Zach Mitchell
- Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | - Jack Lawrence
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Dmitry Morozov
- Nanoscience Center and Department of Chemistry, University of Jyväskylä, P.O. Box 35, 40014 Jyväskylä, Finland
| | - Sergei Savikhin
- Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | - Lyudmila V Slipchenko
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
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2
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Ezhov R, Ravari AK, Palenik M, Loomis A, Meira DM, Savikhin S, Pushkar Y. Photoexcitation of Fe 3 O Nodes in MOF Drives Water Oxidation at pH=1 When Ru Catalyst Is Present. ChemSusChem 2023; 16:e202202124. [PMID: 36479638 DOI: 10.1002/cssc.202202124] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 12/01/2022] [Indexed: 06/17/2023]
Abstract
Artificial photosynthesis strives to convert the energy of sunlight into sustainable, eco-friendly solar fuels. However, systems with light-driven water oxidation reaction (WOR) at pH=1 are rare. Broadly used [Ru(bpy)3 ]2+ (bpy=2,2'-bipyridine) photosensitizer has a fixed +1.23 V potential which is insufficient to drive most water oxidation catalysts (WOCs) in acid, while Fe2 O3 , featuring the highly oxidizing holes, is not stable at low pH. Here, the key examples of Fe-based metal-organic framework (MOF) water oxidation photoelectrocatalysts active at pH=1 are presented. Fe-MIL-126 and Fe MOF-dcbpy structures were formed with 4,4'-biphenyl dicarboxylate (bpdc), 2,2'-bipyridine-5,5'-dicarboxylate (dcbpy) linkers and their mixtures. Presence of dcbpy linkers allows integration of metal-based catalysts via coordination to 2,2'-bipyridine fragments. Fe-based MOFs were doped with Ru-based precursors to achieve highly active MOFs bearing [Ru(bpy)(dcbpy)(H2 O)2 ]2+ WOC. Materials were analyzed with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infra-red (FTIR) spectroscopy, resonance Raman, X-ray absorption spectroscopy, fs optical pump-probe, electron paramagnetic resonance (EPR), diffuse reflectance and electric conductivity measurements and were modeled by band structure calculations. It is shown that under reaction conditions, FeIII and RuIII oxidation states are present, indicating rate-limiting electron transfer in MOF. Fe3 O nodes emerge as photosensitizers able to drive prolonged O2 evolution in acid. Further developments are possible via MOF's linker modification for enhanced light absorption, electrical conductivity, reduced MOF solubility in acid, Ru-WOC modification for faster WOC catalysis, or Ru-WOC substitution to 3d metal-based systems. The findings give further insight for development of light-driven water splitting systems based on Earth-abundant metals.
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Affiliation(s)
- Roman Ezhov
- Department of Physics and Astronomy, Purdue University, West Lafayette, 47907, USA
| | - Alireza K Ravari
- Department of Physics and Astronomy, Purdue University, West Lafayette, 47907, USA
| | - Mark Palenik
- US Naval Research Laboratory, Washington, 20375, USA
| | - Alexander Loomis
- Department of Physics and Astronomy, Purdue University, West Lafayette, 47907, USA
| | | | - Sergei Savikhin
- Department of Physics and Astronomy, Purdue University, West Lafayette, 47907, USA
| | - Yulia Pushkar
- Department of Physics and Astronomy, Purdue University, West Lafayette, 47907, USA
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3
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Watanabe Y, Washer BM, Zeller M, Savikhin S, Slipchenko LV, Wei A. Copper(I)-Pyrazolate Complexes as Solid-State Phosphors: Deep-Blue Emission through a Remote Steric Effect. J Am Chem Soc 2022; 144:10186-10192. [PMID: 35594145 DOI: 10.1021/jacs.1c13462] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We describe a novel manifestation of rigidochromic behavior in a series of tetranuclear Cu(I)-pyrazolate (Cu4pz4) macrocycles, with implications for solid-state luminescence at deep-blue wavelengths (<460 nm). The Cu4pz4 emissions are remarkably sensitive to structural effects far from the luminescent core: when 3,5-di-tert-butylpyrazoles are used as bridging ligands, adding a C4 substituent can induce a blue shift of more than 100 nm. X-ray crystal and computational analyses reveal that C4 units influence the conformational behavior of adjacent tert-butyl groups, with a subsequent impact on the global conformation of the Cu4pz4 complex. Emissions are mediated primarily through a cluster-centered triplet (3CC) state; compression of the Cu4 cluster into a nearly close-packed geometry prevents the reorganization of its excited-state structure and preserves the 3CC energy at a high level. The remote steric effect may thus offer alternative strategies toward the design of phosphors with rigid excited-state geometries.
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Affiliation(s)
- Yuichiro Watanabe
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Benjamin M Washer
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Matthias Zeller
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Sergei Savikhin
- Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | - Lyudmila V Slipchenko
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Alexander Wei
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States.,School of Materials Engineering, Purdue University, 701 W. Stadium Avenue, West Lafayette, Indiana 47907, United States
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4
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Zakharov SD, Savikhin S, Misumi Y, Kurisu G, Cramer WA. Isothermal titration calorimetry of membrane protein interactions: FNR and the cytochrome b 6f complex. Biophys J 2022; 121:300-308. [PMID: 34902329 PMCID: PMC8790201 DOI: 10.1016/j.bpj.2021.12.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 06/03/2021] [Accepted: 12/09/2021] [Indexed: 01/21/2023] Open
Abstract
Ferredoxin-NADP+ reductase (FNR) was previously inferred to bind to the cytochrome b6f complex in the electron transport chain of oxygenic photosynthesis. In the present study, this inference has been examined through analysis of the thermodynamics of the interaction between FNR and the b6f complex. Isothermal titration calorimetry (ITC) was used to characterize the physical interaction of FNR with b6f complex derived from two plant sources (Spinacia oleracea and Zea maize). ITC did not detect a significant interaction of FNR with the b6f complex in detergent solution nor with the complex reconstituted in liposomes. A previous inference of a small amplitude but defined FNR-b6f interaction is explained by FNR interaction with micelles of the undecyl β-D maltoside (UDM) detergent micelles used to purify b6f. Circular dichroism, employed to analyze the effect of detergent on the FNR structure, did not reveal significant changes in secondary or tertiary structures of FNR domains in the presence of UDM detergent. However, thermodynamic analysis implied a significant decrease in an interaction between the N-terminal FAD-binding and C-terminal NADP+-binding domains of FNR caused by detergent. The enthalpy, ΔHo, and the entropy, ΔSo, associated with FNR unfolding decreased four-fold in the presence of 1 mM UDM at pH 6.5. In addition to the conclusion regarding the absence of a binding interaction of significant amplitude between FNR and the b6f complex, these studies provide a precedent for consideration of significant background protein-detergent interactions in ITC analyses involving integral membrane proteins.
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Affiliation(s)
| | - Sergei Savikhin
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana
| | - Yuko Misumi
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana
| | - Genji Kurisu
- Institute for Protein Research, Osaka University, Suita, Osaka
| | - William A Cramer
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana.
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5
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Kurashov V, Milanovsky G, Luo L, Martin A, Semenov AY, Savikhin S, Cherepanov DA, Golbeck JH, Xu W. Conserved residue PsaB-Trp673 is essential for high-efficiency electron transfer between the phylloquinones and the iron-sulfur clusters in Photosystem I. Photosynth Res 2021; 148:161-180. [PMID: 33991284 DOI: 10.1007/s11120-021-00839-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2021] [Accepted: 04/23/2021] [Indexed: 06/12/2023]
Abstract
Despite the high level of symmetry between the PsaA and PsaB polypeptides in Photosystem I, some amino acids pairs are strikingly different, such as PsaA-Gly693 and PsaB-Trp673, which are located near a cluster of 11 water molecules between the A1A and A1B quinones and the FX iron-sulfur cluster. In this work, we changed PsaB-Trp673 to PsaB-Phe673 in Synechocystis sp. PCC 6803. The variant contains ~ 85% of wild-type (WT) levels of Photosystem I but is unable to grow photoautotrophically. Both time-resolved and steady-state optical measurements show that in the PsaB-W673F variant less than 50% of the electrons reach the terminal iron-sulfur clusters FA and FB; the majority of the electrons recombine from A1A- and A1B-. However, in those reaction centers which pass electrons forward the transfer is heterogeneous: a minor population shows electron transfer rates from A1A- and A1B- to FX slightly slower than that of the WT, whereas a major population shows forward electron transfer rates to FX slowed to the ~ 10 µs time range. Competition between relatively similar forward and backward rates of electron transfer from the quinones to the FX cluster account for the relatively low yield of long-lived charge separation in the PsaB-W673F variant. A higher water content and its increased mobility observed in MD simulations in the interquinone cavity of the PsaB-W673F variant shifts the pK of PsaB-Asp575 and allows its deprotonation in situ. The heterogeneity found may be rooted in protonation state of PsaB-Asp575, which controls whether electron transfer can proceed beyond the phylloquinone cofactors.
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Affiliation(s)
- Vasily Kurashov
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA
| | - George Milanovsky
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Leninskie Gory, 1, Building 40, Moscow, Russia, 119992
| | - Lujun Luo
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA, 70504, USA
| | - Antoine Martin
- Department of Physics, Purdue University, West Lafayette, IN, USA
| | - Alexey Yu Semenov
- A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University, Leninskie Gory, 1, Building 40, Moscow, Russia, 119992
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina st, 4, Moscow, Russia, 117977
| | - Sergei Savikhin
- Department of Physics, Purdue University, West Lafayette, IN, USA
| | - Dmitry A Cherepanov
- N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Kosygina st, 4, Moscow, Russia, 117977.
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA.
- Department of Chemistry, The Pennsylvania State University, University Park, PA, 16802, USA.
| | - Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, LA, 70504, USA.
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6
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Kim Y, Morozov D, Stadnytskyi V, Savikhin S, Slipchenko LV. Predictive First-Principles Modeling of a Photosynthetic Antenna Protein: The Fenna-Matthews-Olson Complex. J Phys Chem Lett 2020; 11:1636-1643. [PMID: 32013435 DOI: 10.1021/acs.jpclett.9b03486] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [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: 06/10/2023]
Abstract
High efficiency of light harvesting in photosynthetic pigment-protein complexes is governed by evolutionary-perfected protein-assisted tuning of individual pigment properties and interpigment interactions. Due to the large number of spectrally overlapping pigments in a typical photosynthetic complex, experimental methods often fail to unambiguously identify individual chromophore properties. Here, we report a first-principles-based modeling protocol capable of predicting properties of pigments in protein environment to a high precision. The technique was applied to successfully uncover electronic properties of the Fenna-Matthews-Olson (FMO) pigment-protein complex. Each of the three subunits of the FMO complex contains eight strongly coupled bacteriochlorophyll a (BChl a) pigments. The excitonic structure of FMO can be described by an electronic Hamiltonian containing excitation (site) energies of BChl a pigments and electronic couplings between them. Several such Hamiltonians have been developed in the past based on the information from various spectroscopic measurements of FMO; however, fine details of the excitonic structure and energy transfer in FMO, especially assignments of short-lived high-energy sites, remain elusive. Utilizing polarizable embedding quantum mechanics/molecular mechanics with the effective fragment potentials, we computed the electronic Hamiltonian of FMO that is in general agreement with previously reported empirical Hamiltonians and quantitatively reproduces experimental absorption and circular dichroism spectra of the FMO protein. The developed computational protocol is sufficiently simple and can be utilized for predictive modeling of other wild-type and mutated photosynthetic pigment-protein complexes.
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Affiliation(s)
- Yongbin Kim
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
| | - Dmitry Morozov
- Nanoscience Center and Department of Chemistry, University of Jyväskylä, P.O. Box 35, Jyväskylä 40014, Finland
| | - Valentyn Stadnytskyi
- Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
- Laboratory of Chemical Physics, National Institute of Diabetes, Digestion and Kidney Diseases, National Institutes of Health, 5 Memorial Drive, Bethesda, Maryland 20892, United States
| | - Sergei Savikhin
- Department of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | - Lyudmila V Slipchenko
- Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States
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7
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8
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Stadnytskyi V, Orf GS, Blankenship RE, Savikhin S. Near shot-noise limited time-resolved circular dichroism pump-probe spectrometer. Rev Sci Instrum 2018; 89:033104. [PMID: 29604771 DOI: 10.1063/1.5009468] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We describe an optical near shot-noise limited time-resolved circular dichroism (TRCD) pump-probe spectrometer capable of reliably measuring circular dichroism signals in the order of μdeg with nanosecond time resolution. Such sensitivity is achieved through a modification of existing TRCD designs and introduction of a new data processing protocol that eliminates approximations that have caused substantial nonlinearities in past measurements and allows the measurement of absorption and circular dichroism transients simultaneously with a single pump pulse. The exceptional signal-to-noise ratio of the described setup makes the TRCD technique applicable to a large range of non-biological and biological systems. The spectrometer was used to record, for the first time, weak TRCD kinetics associated with the triplet state energy transfer in the photosynthetic Fenna-Matthews-Olson antenna pigment-protein complex.
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Affiliation(s)
- Valentyn Stadnytskyi
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47906, USA
| | - Gregory S Orf
- Departments of Biology and Chemistry, Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, Missouri 63130, USA
| | - Robert E Blankenship
- Departments of Biology and Chemistry, Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, Missouri 63130, USA
| | - Sergei Savikhin
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47906, USA
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9
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Saer RG, Stadnytskyi V, Magdaong NC, Goodson C, Savikhin S, Blankenship RE. Probing the excitonic landscape of the Chlorobaculum tepidum Fenna-Matthews-Olson (FMO) complex: a mutagenesis approach. Biochim Biophys Acta Bioenerg 2017; 1858:288-296. [PMID: 28159567 DOI: 10.1016/j.bbabio.2017.01.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 01/27/2017] [Accepted: 01/30/2017] [Indexed: 12/17/2022]
Abstract
In this paper we report the steady-state optical properties of a series of site-directed mutants in the Fenna-Matthews-Olson (FMO) complex of Chlorobaculum tepidum, a photosynthetic green sulfur bacterium. The FMO antenna complex has historically been used as a model system for energy transfer due to the water-soluble nature of the protein, its stability at room temperature, as well as the availability of high-resolution structural data. Eight FMO mutants were constructed with changes in the environment of each of the bacteriochlorophyll a pigments found within each monomer of the homotrimeric FMO complex. Our results reveal multiple changes in low temperature absorption, as well as room temperature CD in each mutant compared to the wild-type FMO complex. These datasets were subsequently used to model the site energies of each pigment in the FMO complex by employing three different Hamiltonians from the literature. This enabled a basic approximation of the site energy shifts imparted on each pigment by the changed amino acid residue. These simulations suggest that, while the three Hamiltonians used in this work provide good fits to the wild-type FMO absorption spectrum, further efforts are required to obtain good fits to the mutant minus wild-type absorption difference spectra. This demonstrates that the use of FMO mutants can be a valuable tool to refine and iterate the current models of energy transfer in this system.
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Affiliation(s)
- Rafael G Saer
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, United States; Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130, United States
| | - Valentyn Stadnytskyi
- Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, United States
| | - Nikki C Magdaong
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, United States; Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130, United States; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, United States
| | - Carrie Goodson
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, United States
| | - Sergei Savikhin
- Department of Physics and Astronomy, Purdue University, West Lafayette, IN 47907, United States
| | - Robert E Blankenship
- Department of Biology, Washington University in St. Louis, St. Louis, MO 63130, United States; Photosynthetic Antenna Research Center, Washington University in St. Louis, St. Louis, MO 63130, United States; Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, United States.
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10
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Bhaduri S, Stadnytskyi V, Zakharov SD, Hasan SS, Bujnowicz Ł, Sarewicz M, Savikhin S, Osyczka A, Cramer WA. Pathways of Transmembrane Electron Transfer in Cytochrome bc Complexes: Dielectric Heterogeneity and Interheme Coulombic Interactions. J Phys Chem B 2017; 121:975-983. [DOI: 10.1021/acs.jpcb.6b11709] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
| | | | | | | | - Ł. Bujnowicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and
Biotechnology, Jagiellonian University, Kraków 31-007, Poland
| | - M. Sarewicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and
Biotechnology, Jagiellonian University, Kraków 31-007, Poland
| | | | - A. Osyczka
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics, and
Biotechnology, Jagiellonian University, Kraków 31-007, Poland
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11
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Kihara S, Hartzler DA, Orf GS, Blankenship RE, Savikhin S. The Fate of the Triplet Excitations in the Fenna–Matthews–Olson Complex. J Phys Chem B 2015; 119:5765-72. [DOI: 10.1021/jp512222c] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Shigeharu Kihara
- Department
of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | - Daniel A. Hartzler
- Department
of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | - Gregory S. Orf
- Photosynthetic
Antenna Research Center, Departments of Chemistry and Biology, Washington University in St. Louis, St. Louis, Missouri 63110, United States
| | - Robert E. Blankenship
- Photosynthetic
Antenna Research Center, Departments of Chemistry and Biology, Washington University in St. Louis, St. Louis, Missouri 63110, United States
| | - Sergei Savikhin
- Department
of Physics and Astronomy, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
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12
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Chauvet A, Jankowiak R, Kell A, Picorel R, Savikhin S. Does the singlet minus triplet spectrum with major photobleaching band near 680-682 nm represent an intact reaction center of Photosystem II? J Phys Chem B 2014; 119:448-55. [PMID: 25495638 DOI: 10.1021/jp510049k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
We use both frequency- and time-domain low-temperature (5-20 K) spectroscopies to further elucidate the shape and spectral position of singlet minus triplet (triplet-bottleneck) spectra in the reaction centers (RCs) of Photosystem II (PSII) isolated from wild-type Chlamydomonas reinhardtii and spinach. It is shown that the shape of the nonresonant transient hole-burned spectrum in destabilized RCs from C. reinhardtii is very similar to that typically observed for spinach. This suggests that the previously observed difference in transient spectra between RCs from C. reinhardtii and spinach is not due to the sample origin but most likely due to a partial destabilization of the D1 and D2 polypeptides. This supports our previous assignments that destabilized RCs (referred to as RC680) (Acharya, K. et al. J. Phys. Chem. B 2012, 116, 4860-4870), with a major photobleaching band near 680-682 nm and the absence of a photobleaching band near 673 nm, do not represent the intact RC residing within the PSII core complex. Time-resolved absorption difference spectra obtained for partially destabilized RCs of C. reinhardtii and for typical spinach RCs support the above conclusions. The absence of clear photobleaching bands near 673 and 684 nm (where the PD1 chlorophyll and the active pheophytin (PheoD1) contribute, respectively) in picosecond transient absorption spectra in both RCs studied in this work indicates that the cation can move from the primary electron donor (ChlD1) to PD1 (i.e., PD1ChlD1(+)PheoD1(-) → PD1(+)ChlD1PheoD1(-)). Therefore, we suggest that ChlD1 is the major electron donor in usually studied destabilized RCs (with a major photobleaching near 680-682 nm), although the PD1 path (where PD1 serves as the primary electron donor) is likely present in intact RCs, as discussed in Acharya, K. et al. J. Phys. Chem. B 2012, 116, 4860-4870.
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Affiliation(s)
- Adrien Chauvet
- Department of Physics and Astronomy, Purdue University , West Lafayette, Indiana 47907, United States
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13
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Hartzler DA, Niedzwiedzki DM, Bryant DA, Blankenship RE, Pushkar Y, Savikhin S. Triplet Excited State Energies and Phosphorescence Spectra of (Bacterio)Chlorophylls. J Phys Chem B 2014; 118:7221-32. [DOI: 10.1021/jp500539w] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Daniel A. Hartzler
- Department
of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | | | - Donald A. Bryant
- Department of Biochemistry & Molecular Biology, The Pennsylvania State University, 108 Althouse Laboratory, University Park, Pennsylvania 16802, United States
- Department
of Chemistry and Biochemistry, Montana State University, 103 Chemistry
and Biochemistry Building, P.O. Box 173400, Bozeman, Montana 59717, United States
| | | | - Yulia Pushkar
- Department
of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
| | - Sergei Savikhin
- Department
of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, United States
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14
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Hasan SS, Zakharov SD, Chauvet A, Stadnytskyi V, Savikhin S, Cramer WA. A map of dielectric heterogeneity in a membrane protein: the hetero-oligomeric cytochrome b6f complex. J Phys Chem B 2014; 118:6614-25. [PMID: 24867491 PMCID: PMC4067154 DOI: 10.1021/jp501165k] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
![]()
The
cytochrome b6f complex,
a member of the cytochrome bc family that
mediates energy transduction in photosynthetic and respiratory membranes,
is a hetero-oligomeric complex that utilizes two pairs of b-hemes in a symmetric dimer to accomplish trans-membrane
electron transfer, quinone oxidation–reduction, and generation
of a proton electrochemical potential. Analysis of electron storage
in this pathway, utilizing simultaneous measurement of heme reduction,
and of circular dichroism (CD) spectra, to assay heme–heme
interactions, implies a heterogeneous distribution of the dielectric
constants that mediate electrostatic interactions between the four
hemes in the complex. Crystallographic information was used to determine
the identity of the interacting hemes. The Soret band CD signal is
dominated by excitonic interaction between the intramonomer b-hemes, bn and bp, on the electrochemically negative and positive sides
of the complex. Kinetic data imply that the most probable pathway
for transfer of the two electrons needed for quinone oxidation–reduction
utilizes this intramonomer heme pair, contradicting the expectation
based on heme redox potentials and thermodynamics, that the two higher
potential hemes bn on different monomers
would be preferentially reduced. Energetically preferred intramonomer
electron storage of electrons on the intramonomer b-hemes is found to require heterogeneity of interheme dielectric
constants. Relative to the medium separating the two higher potential
hemes bn, a relatively large dielectric
constant must exist between the intramonomer b-hemes,
allowing a smaller electrostatic repulsion between the reduced hemes.
Heterogeneity of dielectric constants is an additional structure–function
parameter of membrane protein complexes.
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Affiliation(s)
- S Saif Hasan
- Department of Biological Sciences and ‡Department of Physics, Purdue University , West Lafayette, Indiana 47907, United States
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15
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Kihara S, Hartzler DA, Savikhin S. Oxygen concentration inside a functioning photosynthetic cell. Biophys J 2014; 106:1882-9. [PMID: 24806920 PMCID: PMC4017319 DOI: 10.1016/j.bpj.2014.03.031] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Revised: 02/13/2014] [Accepted: 03/12/2014] [Indexed: 11/23/2022] Open
Abstract
The excess oxygen concentration in the photosynthetic membranes of functioning oxygenic photosynthetic cells was estimated using classical diffusion theory combined with experimental data on oxygen production rates of cyanobacterial cells. The excess oxygen concentration within the plesiomorphic cyanobacterium Gloeobactor violaceus is only 0.025 μM, or four orders of magnitude lower than the oxygen concentration in air-saturated water. Such a low concentration suggests that the first oxygenic photosynthetic bacteria in solitary form could have evolved ∼2.8 billion years ago without special mechanisms to protect them against reactive oxygen species. These mechanisms instead could have been developed during the following ∼500 million years while the oxygen level in the Earth's atmosphere was slowly rising. Excess oxygen concentrations within individual cells of the apomorphic cyanobacteria Synechocystis and Synechococcus are 0.064 and 0.25 μM, respectively. These numbers suggest that intramembrane and intracellular proteins in isolated oxygenic photosynthetic cells are not subjected to excessively high oxygen levels. The situation is different for closely packed colonies of photosynthetic cells. Calculations show that the excess concentration within colonies that are ∼40 μm or larger in diameter can be comparable to the oxygen concentration in air-saturated water, suggesting that species forming colonies require protection against reactive oxygen species even in the absence of oxygen in the surrounding atmosphere.
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Affiliation(s)
- Shigeharu Kihara
- Department of Physics, Purdue University, West Lafayette, Indiana
| | | | - Sergei Savikhin
- Department of Physics, Purdue University, West Lafayette, Indiana.
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16
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Zakharov SD, Hasan SS, Chauvet A, Stadnytsky V, Savikhin S, Cramer WA. Dielectric Heterogeneity in the Cytochrome B6F Complex. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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17
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Eaton SW, Shoer LE, Karlen SD, Dyar SM, Margulies EA, Veldkamp BS, Ramanan C, Hartzler DA, Savikhin S, Marks TJ, Wasielewski MR. Singlet exciton fission in polycrystalline thin films of a slip-stacked perylenediimide. J Am Chem Soc 2013; 135:14701-12. [PMID: 24011336 DOI: 10.1021/ja4053174] [Citation(s) in RCA: 211] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The crystal structure of N,N-bis(n-octyl)-2,5,8,11-tetraphenylperylene-3,4:9,10-bis(dicarboximide), 1, obtained by X-ray diffraction reveals that 1 has a nearly planar perylene core and π-π stacks at a 3.5 Å interplanar distance in well-separated slip-stacked columns. Theory predicts that slip-stacked, π-π-stacked structures should enhance interchromophore electronic coupling and thus favor singlet exciton fission. Photoexcitation of vapor-deposited polycrystalline 188 nm thick films of 1 results in a 140 ± 20% yield of triplet excitons ((3*)1) in τ(SF) = 180 ± 10 ps. These results illustrate a design strategy for producing perylenediimide and related rylene derivatives that have the optimized interchromophore electronic interactions which promote high-yield singlet exciton fission for potentially enhancing organic solar cell performance and charge separation in systems for artificial photosynthesis.
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Affiliation(s)
- Samuel W Eaton
- Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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18
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Chauvet A, Sarrou J, Lin S, Romberger SP, Golbeck JH, Savikhin S, Redding KE. Temporal and spectral characterization of the photosynthetic reaction center from Heliobacterium modesticaldum. Photosynth Res 2013; 116:1-9. [PMID: 23812833 DOI: 10.1007/s11120-013-9871-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Accepted: 06/11/2013] [Indexed: 06/02/2023]
Abstract
A time-resolved spectroscopic study of the isolated photosynthetic reaction center (RC) from Heliobacterium modesticaldum reveals that thermal equilibration of light excitation among the antenna pigments followed by trapping of excitation and the formation of the charge-separated state P800 (+)A0 (-) occurs within ~25 ps. This time scale is similar to that reported for plant and cyanobacterial photosystem I (PS I) complexes. Subsequent electron transfer from the primary electron acceptor A0 occurs with a lifetime of ~600 ps, suggesting that the RC of H. modesticaldum is functionally similar to that of Heliobacillus mobilis and Heliobacterium chlorum. The (A0 (-) - A0) and (P800 (+) - P800) absorption difference spectra imply that an 8(1)-OH-Chl a F molecule serves as the primary electron acceptor and occupies the position analogous to ec3 (A0) in PS I, while a monomeric BChl g pigment occupies the position analogous to ec2 (accessory Chl). The presence of an intense photobleaching band at 790 nm in the (A0 (-) - A0) spectrum suggests that the excitonic coupling between the monomeric accessory BChl g and the 8(1)-OH-Chl a F in the heliobacterial RC is significantly stronger than the excitonic coupling between the equivalent pigments in PS I.
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Affiliation(s)
- Adrien Chauvet
- Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907, USA
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19
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Chauvet A, Dashdorj N, Golbeck JH, Johnson TW, Savikhin S. Spectral resolution of the primary electron acceptor A0 in Photosystem I. J Phys Chem B 2012; 116:3380-6. [PMID: 22332796 DOI: 10.1021/jp211246a] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The reduced state of the primary electron acceptor of Photosystem I, A(0), was resolved spectroscopically in its lowest energy Q(y) region for the first time without the addition of chemical reducing agents and without extensive data manipulation. To carry this out, we used the menB mutant of Synechocystis sp. PCC 6803 in which phylloquinone is replaced by plastoquinone-9 in the A(1) sites of Photosystem I. The presence of plastoquinone-9 slows electron transfer from A(0) to A(1), leading to a long-lived A(0)(-) state. This allows its spectral signature to be readily detected in a time-resolved optical pump-probe experiment. The maximum bleaching (A(0)(-) - A(0)) was found to occur at 684 nm with a corresponding extinction coefficient of 43 mM(-1) cm(-1). The data show evidence for an electrochromic shift of an accessory chlorophyll pigment, suggesting that the latter Q(y) absorption band is centered around 682 nm.
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Affiliation(s)
- Adrien Chauvet
- Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, Indiana 47907, USA
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20
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Savikhin S, Hartzler DA, Kihara S, Niklas J, Poluektov O, Li H, Tsukatani Y, Bryant DA. Efficient Intrinsic Photoprotection in Strongly Coupled (Bacterio) Chloropyll Complexes. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.905] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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21
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Ananyev GM, Savikhin S. Young research investigators honored at the 2011 Gordon research conference on photosynthesis: ambiance and a perspective. Photosynth Res 2011; 110:143-149. [PMID: 22068391 DOI: 10.1007/s11120-011-9706-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2011] [Accepted: 10/24/2011] [Indexed: 05/31/2023]
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22
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Xu W, Wang Y, Taylor E, Laujac A, Gao L, Savikhin S, Chitnis PR. Mutational analysis of photosystem I of Synechocystis sp. PCC 6803: the role of four conserved aromatic residues in the j-helix of PsaB. PLoS One 2011; 6:e24625. [PMID: 21931782 PMCID: PMC3171458 DOI: 10.1371/journal.pone.0024625] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 08/15/2011] [Indexed: 11/19/2022] Open
Abstract
Photosystem I is the light-driven plastocyanin-ferredoxin oxidoreductase in the photosynthetic electron transfer of cyanobacteria and plants. Two histidyl residues in the symmetric transmembrane helices A-j and B-j provide ligands for the P700 chlorophyll molecules of the reaction center of photosystem I. To determine the role of conserved aromatic residues adjacent to the histidyl molecule in the helix of B-j, we generated six site-directed mutants of the psaB gene in Synechocystis sp. PCC 6803. Three mutant strains with W645C, W643C/A644I and S641C/V642I substitutions could grow photoautotrophically and showed no obvious reduction in the photosystem I activity. Kinetics of P700 re-reduction by plastocyanin remained unaltered in these mutants. In contrast, the strains with H651C/L652M, F649C/G650I and F647C substitutions could not grow under photoautotrophic conditions because those mutants had low photosystem I activity, possibly due to low levels of proteins. A procedure to select spontaneous revertants from the mutants that are incapable to photoautotrophic growth resulted in three revertants that were used in this study. The molecular analysis of the spontaneous revertants suggested that an aromatic residue at F647 and a small residue at G650 may be necessary for maintaining the structural integrity of photosystem I. The (P700⁺-P700) steady-state absorption difference spectrum of the revertant F647Y has a ∼5 nm narrower peak than the recovered wild-type, suggesting that additional hydroxyl group of this revertant may participate in the interaction with the special pair while the photosystem I complexes of the F649C/G650T and H651Q mutants closely resemble the wild-type spectrum. The results presented here demonstrate that the highly conserved residues W645, W643 and F649 are not critical for maintaining the integrity and in mediating electron transport from plastocyanin to photosystem I. Our data suggest that an aromatic residue is required at position of 647 for structural integrity and/or function of photosystem I.
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Affiliation(s)
- Wu Xu
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, Louisiana, United States of America
| | - Yingchun Wang
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Science, Beijing, China
| | - Eric Taylor
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, Louisiana, United States of America
| | - Amelie Laujac
- Department of Chemistry, University of Louisiana at Lafayette, Lafayette, Louisiana, United States of America
| | - Liyan Gao
- Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Science, Beijing, China
| | - Sergei Savikhin
- Department of Physics, Purdue University, West Lafayette, Indiana, United States of America
| | - Parag R. Chitnis
- Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, United States of America
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23
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Chauvet A, Jagannathan B, Golbeck JH, Savikhin S. Type I reaction center from the green sulfur bacterium Chlorobium tepidum: is Chl a a primary electron acceptor? Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.2717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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24
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Yan J, Dashdorj N, Baniulis D, Yamashita E, Savikhin S, Cramer WA. On the Structural Role of the Aromatic Residue Environment of the Chlorophyll a in the Cytochrome b6f Complex. Biochemistry 2008; 47:3654-61. [PMID: 18302324 DOI: 10.1021/bi702299b] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [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)
- Jiusheng Yan
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Naranbaatar Dashdorj
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Danas Baniulis
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Eiki Yamashita
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - Sergei Savikhin
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
| | - William A. Cramer
- Departments of Biological Sciences and Physics, Purdue University, West Lafayette, Indiana 47907
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25
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Dashdorj N, Yamashita E, Schaibley J, Cramer WA, Savikhin S. Ultrafast Optical Pump−Probe Studies of the Cytochrome b6f Complex in Solution and Crystalline States. J Phys Chem B 2007; 111:14405-10. [PMID: 18047317 DOI: 10.1021/jp076536p] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [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)
- Naranbaatar Dashdorj
- Department of Physics and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Eiki Yamashita
- Department of Physics and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
| | - John Schaibley
- Department of Physics and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
| | - William A. Cramer
- Department of Physics and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Sergei Savikhin
- Department of Physics and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907
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26
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Abstract
Chlorosomes comprise thousands of bacteriochlorophylls (BChl c, d, or e) in a closely packed structure surrounded by a lipid-protein envelope and additionally contain considerable amounts of carotenoids, quinones, and BChl a. It has been suggested that carotenoids in chlorosomes provide photoprotection by rapidly quenching triplet excited states of BChl via a triplet-triplet energy transfer mechanism that prevents energy transfer to oxygen and the formation of harmful singlet oxygen. In this work we studied triplet energy transfer kinetics and photodegradation of chlorosomes isolated from wild-type Chlorobium tepidum and from genetically modified species with different types of carotenoids and from a carotenoid-free mutant. Supporting a photoprotective function of carotenoids, carotenoid-free chlorosomes photodegrade approximately 3 times faster than wild-type chlorosomes. However, a significant fraction of the BChls forms a long-lived, triplet-like state that does not interact with carotenoids or with oxygen. We propose that these states are triplet excitons that form due to triplet-triplet interaction between the closely packed BChls. Numerical exciton simulations predict that the energy of these triplet excitons may fall below that of singlet oxygen and triplet carotenoids; this would prevent energy transfer from triplet BChl. Thus, the formation of triplet excitons in chlorosomes serves as an alternative photoprotection mechanism.
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Affiliation(s)
- Hanyoup Kim
- Department of Physics, Purdue University, West Lafayette, Indiana, USA
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27
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Kim H, Kane MD, Kim S, Dominguez W, Applegate BM, Savikhin S. A molecular beacon DNA microarray system for rapid detection of E. coli O157:H7 that eliminates the risk of a false negative signal. Biosens Bioelectron 2007; 22:1041-7. [PMID: 16815005 DOI: 10.1016/j.bios.2006.04.032] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2006] [Revised: 04/20/2006] [Accepted: 04/27/2006] [Indexed: 11/29/2022]
Abstract
A DNA hybridization based optical detection platform for the detection of foodborne pathogens has been developed with virtually zero probability of the false negative signal. This portable, low-cost and real-time assaying detection platform utilizes the color changing molecular beacon as a probe for the optical detection of the target sequence. The computer-controlled detection platform exploits the target hybridization induced change of fluorescence color due to the Förster (fluorescence) resonance energy transfer (FRET) between a pair of spectrally shifted fluorophores conjugated to the opposite ends of a beacon (oligonucleotide probe). Unlike the traditional fluorophore-quencher beacon design, the presence of two fluorescence molecules allows to actively visualize both hybridized and unhybridized states of the beacon. This eliminates false negative signal detection characteristic for the fluorophore-quencher beacon where bleaching of the fluorophore or washout of a beacon is indistinguishable from the absence of the target DNA sequence. In perspective, the two-color design allows also to quantify the concentration of the target DNA in a sample down to < =1 ng/microl. The new design is suitable for simultaneous reliable detection of hundreds of DNA target sequences in one test run using a series of beacons immobilized on a single substrate in a spatial format.
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Affiliation(s)
- Hanyoup Kim
- Department of Physics, Purdue University, West Lafayette, IN 47907, USA
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28
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Kim H, Dashdorj N, Zhang H, Yan J, Cramer WA, Savikhin S. An anomalous distance dependence of intraprotein chlorophyll-carotenoid triplet energy transfer. Biophys J 2005; 89:L28-30. [PMID: 16055550 PMCID: PMC1366788 DOI: 10.1529/biophysj.105.069609] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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29
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Dashdorj N, Zhang H, Kim H, Yan J, Cramer WA, Savikhin S. The single chlorophyll a molecule in the cytochrome b6f complex: unusual optical properties protect the complex against singlet oxygen. Biophys J 2005; 88:4178-87. [PMID: 15778449 PMCID: PMC1305648 DOI: 10.1529/biophysj.104.058693] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2004] [Accepted: 03/16/2005] [Indexed: 11/18/2022] Open
Abstract
The cytochrome b(6)f complex of oxygenic photosynthesis mediates electron transfer between the reaction centers of photosystems I and II and facilitates coupled proton translocation across the membrane. High-resolution x-ray crystallographic structures (Kurisu et al., 2003; Stroebel et al., 2003) of the cytochrome b(6)f complex unambiguously show that a Chl a molecule is an intrinsic component of the cytochrome b(6)f complex. Although the functional role of this Chl a is presently unclear (Kuhlbrandt, 2003), an excited Chl a molecule is known to produce toxic singlet oxygen as the result of energy transfer from the excited triplet state of the Chl a to oxygen molecules. To prevent singlet oxygen formation in light-harvesting complexes, a carotenoid is typically positioned within approximately 4 A of the Chl a molecule, effectively quenching the triplet excited state of the Chl a. However, in the cytochrome b(6)f complex, the beta-carotene is too far (> or =14 Angstroms) from the Chl a for effective quenching of the Chl a triplet excited state. In this study, we propose that in this complex, the protection is at least partly realized through special arrangement of the local protein structure, which shortens the singlet excited state lifetime of the Chl a by a factor of 20-25 and thus significantly reduces the formation of the Chl a triplet state. Based on optical ultrafast absorption difference experiments and structure-based calculations, it is proposed that the Chl a singlet excited state lifetime is shortened due to electron exchange transfer with the nearby tyrosine residue. To our knowledge, this kind of protection mechanism against singlet oxygen has not yet been reported for any other chlorophyll-containing protein complex. It is also reported that the Chl a molecule in the cytochrome b(6)f complex does not change orientation in its excited state.
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30
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Dashdorj N, Xu W, Martinsson P, Chitnis PR, Savikhin S. Electrochromic shift of chlorophyll absorption in photosystem I from Synechocystis sp. PCC 6803: a probe of optical and dielectric properties around the secondary electron acceptor. Biophys J 2004; 86:3121-30. [PMID: 15111425 PMCID: PMC1304177 DOI: 10.1016/s0006-3495(04)74360-x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [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
Nanosecond absorption dynamics at approximately 685 nm after excitation of photosystem I (PS I) from Synechocystis sp. PCC 6803 is consistent with electrochromic shift of absorption bands of the Chl a pigments in the vicinity of the secondary electron acceptor A(1). Based on experimental optical data and structure-based simulations, the effective local dielectric constant has been estimated to be between 3 and 20, which suggests that electron transfer in PS I is accompanied by considerable protein relaxation. Similar effective dielectric constant values have been previously observed for the bacterial photosynthetic reaction center and indicate that protein reorganization leading to effective charge screening may be a necessary structural property of proteins that facilitate the charge transfer function. The data presented here also argue against attributing redmost absorption in PS I to closely spaced antenna chlorophylls (Chls) A38 and A39, and suggest that optical transitions of these Chls, along with that of connecting chlorophyll (A40) lie in the range 680-695 nm.
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31
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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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Savikhin S, Tao N, Song PS, Struve WS. Ultrafast pump-probe spectroscopy of the photoreceptor stentorins from the ciliate Stentor coeruleus. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100149a045] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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33
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Savikhin S, Zhu Y, Lin S, Blankenship RE, Struve WS. Femtosecond Spectroscopy of Chlorosome Antennas from the Green Photosynthetic Bacterium Chloroflexus aurantiacus. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j100091a056] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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34
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Savikhin S, Xu W, Martinsson P, Chitnis PR, Struve WS. Kinetics of charge separation and A0- --> A1 electron transfer in photosystem I reaction centers. Biochemistry 2001; 40:9282-90. [PMID: 11478895 DOI: 10.1021/bi0104165] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.4] [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: 11/29/2022]
Abstract
The charge separation P700*A(0) --> P700(+)A(0)(-) and the subsequent electron transfer from the primary to secondary electron acceptor have been studied by subtracting absorption difference profiles for cyanobacterial photosystem I (PS I) complexes with open and closed reaction centers. Samples were excited at 660 nm, which lies toward the blue edge of the core antenna absorption spectrum. The resulting PS I kinetics were analyzed in terms of the relevant P700, P700(+), A(0), and A(0)(-) absorption spectra. In our kinetic model, the radical pair P700(+)A(0)(-) forms with 1.3 ps rise kinetics after creation of electronically excited P700*. The formation of A(1)(-) via electron transfer from A(0)(-) requires approximately 13 ps. The kinetics of the latter step are appreciably faster than previously estimated by other groups (20--50 ps).
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Affiliation(s)
- S Savikhin
- Ames Laboratory-U.S. Department of Energy, Iowa State University, Ames, Iowa 50011, USA
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35
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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 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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38
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Savikhin S, Buck DR, Struve WS, Blankenship RE, Taisova AS, Novoderezhkin VI, Fetisova ZG. Excitation delocalization in the bacteriochlorophyll c antenna of the green bacterium Chloroflexus aurantiacus as revealed by ultrafast pump-probe spectroscopy. FEBS Lett 1998; 430:323-6. [PMID: 9688564 DOI: 10.1016/s0014-5793(98)00691-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Room temperature absorption difference spectra were measured on the femtosecond through picosecond time scales for chlorosomes isolated from the green bacterium Chloroflexus aurantiacus. Anomalously high values of photoinduced absorption changes were revealed in the BChl c Qy transition band. Photoinduced absorption changes at the bleaching peak in the BChl c band were found to be 7-8 times greater than those at the bleaching peak in the BChl a band of the chlorosome. This appears to be the first direct experimental proof of excitation delocalization over many BChl c antenna molecules in the chlorosome.
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Affiliation(s)
- S Savikhin
- Ames Laboratory-USDOE and Department of Chemistry, Iowa State University, 50011, USA
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39
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Affiliation(s)
- Sergei Savikhin
- Ames LaboratoryUSDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011
| | - Daniel R. Buck
- Ames LaboratoryUSDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011
| | - Walter S. Struve
- Ames LaboratoryUSDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011
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40
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Novoderezhkin VI, Taisova AS, Fetisova ZG, Blankenship RE, Savikhin S, Buck DR, Struve WS. Energy transfers in the B808-866 antenna from the green bacterium Chloroflexus aurantiacus. Biophys J 1998; 74:2069-75. [PMID: 9545065 PMCID: PMC1299547 DOI: 10.1016/s0006-3495(98)77913-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Energy transfers within the B808-866 BChl a antenna in chlorosome-membrane complexes from the green photosynthetic bacterium Chloroflexus aurantiacus were studied in two-color pump-probe experiments at room temperature. The steady-state spectroscopy and protein sequence of the B808-866 complex are reminiscent of well-studied LH2 antennas from purple bacteria. B808-->B866 energy transfers occur with approximately 2 ps kinetics; this is slower by a factor of approximately 2 than B800-->B850 energy transfers in LH2 complexes from Rhodopseudomonas acidophila or Rhodobacter sphaeroides. Anisotropy studies show no evidence for intra-B808 energy transfers before the B808-->B866 step; intra-B866 processes are reflected in 350-550 fs anisotropy decays. Two-color anisotropies under 808 nm excitation suggest the presence of a B808-->B866 channel arising either from direct laser excitation of upper B866 exciton components that overlap the B808 absorption band or from excitation of B866 vibronic bands in nontotally symmetric modes.
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Affiliation(s)
- V I Novoderezhkin
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia
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41
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Savikhin S, Buck DR, Struve WS. Oscillating anisotropies in a bacteriochlorophyll protein: Evidence for quantum beating between exciton levels. Chem Phys 1997. [DOI: 10.1016/s0301-0104(97)00223-1] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Affiliation(s)
- Daniel R. Buck
- Ames LaboratoryU.S. Department of Energy and Department of Chemistry, Iowa State University, Ames, Iowa 50011
| | - Sergei Savikhin
- Ames LaboratoryU.S. Department of Energy and Department of Chemistry, Iowa State University, Ames, Iowa 50011
| | - Walter S. Struve
- Ames LaboratoryU.S. Department of Energy and Department of Chemistry, Iowa State University, Ames, Iowa 50011
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Savikhin S, Buck DR, Struve WS. Pump-probe anisotropies of Fenna-Matthews-Olson protein trimers from Chlorobium tepidum: a diagnostic for exciton localization? Biophys J 1997; 73:2090-6. [PMID: 9336204 PMCID: PMC1181109 DOI: 10.1016/s0006-3495(97)78239-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [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: 02/05/2023] Open
Abstract
Exciton calculations on symmetric and asymmetric Fenna-Matthews-Olson (FMO) trimers, combined with absorption difference anisotropy measurements on FMO trimers from the green bacterium Chlorobium tepidum, suggest that real samples exhibit sufficient diagonal energy disorder so that their laser-excited exciton states are noticeably localized. Our observed anisotropies are clearly inconsistent with 21-pigment exciton simulations based on a threefold-symmetric FMO protein. They are more consistent with a 7-pigment model that assumes that the laser-prepared states are localized within a subunit of the trimer. Differential diagonal energy shifts of 50 cm(-1) between symmetry-related pigments in different subunits are large enough to cause sharp localization in the stationary states; these shifts are commensurate with the approximately 95 cm(-1) inhomogeneous linewidth of the lowest exciton levels. Experimental anisotropies (and by implication steady-state linear and circular dichroism) likely arise from statistical averaging over states with widely contrasting values of these observables, in consequence of their sensitivity to diagonal energy disorder.
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Affiliation(s)
- S Savikhin
- U.S. Department of Energy, and Department of Chemistry, Iowa State University, Ames 50011, USA
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44
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Abstract
We describe simulations of absorption difference spectra in strongly coupled photosynthetic antennas. In the presence of large resonance couplings, distinctive features arise from excited-state absorption transitions between one- and two-exciton levels. We first outline the theory for the heterodimer and for the general N-pigment system, and we demonstrate the transition between the strong and weak coupling regimes. The theory is applied to Fenna-Matthews-Olson (FMO) bacteriochlorophyll a protein trimers from the green photosynthetic bacterium Prosthecochloris aestuarii and then compared with experimental low-temperature absorption difference spectra of FMO trimers from the green bacterium Chlorobium tepidum.
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Affiliation(s)
- D R Buck
- Ames Laboratory-USDOE, Iowa, USA
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45
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Savikhin S, Struve WS. Temperature dependence of electronic energy transfers within B850 antennae of the NF57 mutant of the purple bacterium Rhodobacter sphaeroides. Chem Phys 1996. [DOI: 10.1016/0301-0104(96)00122-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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46
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Wu HM, Savikhin S, Reddy NRS, Jankowiak R, Cogdell RJ, Struve WS, Small GJ. Femtosecond and Hole-Burning Studies of B800's Excitation Energy Relaxation Dynamics in the LH2 Antenna Complex of Rhodopseudomonas acidophila (Strain 10050). ACTA ACUST UNITED AC 1996. [DOI: 10.1021/jp9608178] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.3] [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)
- H.-M. Wu
- Ames Laboratory−USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Botany, The University of Glasgow, G12 8QQ, U.K
| | - S. Savikhin
- Ames Laboratory−USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Botany, The University of Glasgow, G12 8QQ, U.K
| | - N. R. S. Reddy
- Ames Laboratory−USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Botany, The University of Glasgow, G12 8QQ, U.K
| | - R. Jankowiak
- Ames Laboratory−USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Botany, The University of Glasgow, G12 8QQ, U.K
| | - R. J. Cogdell
- Ames Laboratory−USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Botany, The University of Glasgow, G12 8QQ, U.K
| | - W. S. Struve
- Ames Laboratory−USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Botany, The University of Glasgow, G12 8QQ, U.K
| | - G. J. Small
- Ames Laboratory−USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011, and Department of Botany, The University of Glasgow, G12 8QQ, U.K
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Savikhin S, Struve WS. Low-temperature energy transfer in FMO trimers from the green photosynthetic bacterium Chlorobium tepidum. Photosynth Res 1996; 48:271-276. [PMID: 24271308 DOI: 10.1007/bf00041018] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/1995] [Accepted: 03/07/1996] [Indexed: 06/02/2023]
Abstract
The pump-probe kinetics of the slowest spectral equilibrations between inequivalent BChl a Qy states in FMO trimers from Chlorobium tepidum are decelerated by nearly two orders of magnitude when the temperature is lowered from 300 K to 19 K. The pump-probe anisotropy decays are also markedly slower at 19 K than at 300 K. Singlet-singlet annihilation in FMO trimers is negligible at the laser powers used here. However, reduced temperatures greatly accentuate the probability of singlet-triplet annihilation, due to accumulation of metastable BChl a states under high laser repetition rates.
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Affiliation(s)
- S Savikhin
- Ames Laboratory-USDOE, Iowa State University, 50011, Ames, IA, USA
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48
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Savikhin S, Zhu Y, Blankenship RE, Struve WS. Ultrafast energy transfer in chlorosomes from the green photosynthetic bacterium Chloroflexus aurantiacus. J Phys Chem 1996; 100:3320-2. [PMID: 11539413 DOI: 10.1021/jp953734k] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Energy transfers between the bacteriochlorophyll c and a antennae in light-harvesting chlorosomes from the green bacterium Chloroflexes aurantiacus have been studied in two-color pump-probe experiments with improved sensitivity and wavelength versatility. The BChl c --> BChl a energy transfers are well simulated with biexponential kinetics, with lifetimes of 2-3 and 11 ps. They do not exhibit an appreciable subpicosecond component. In the context of a kinetic model for chlorosomes, these lifetimes suggest that both internal BChl c processes and the BChl c --> BChl a energy-transfer step contribute materially to the empirical rod-to-baseplate energy-transfer kinetics.
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Affiliation(s)
- S Savikhin
- Ames Laboratory and Department of Chemistry, Iowa State University, Ames 50011, USA
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49
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Savikhin S, Zhu Y, Blankenship RE, Struve WS. Intraband Energy Transfers in the BChlcAntenna of Chlorosomes from the Green Photosynthetic BacteriumChloroflexus aurantiacus. ACTA ACUST UNITED AC 1996. [DOI: 10.1021/jp961752b] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Savikhin S, van Noort PI, Blankenship RE, Struve WS. Femtosecond probe of structural analogies between chlorosomes and bacteriochlorophyll c aggregates. Biophys J 1995; 69:1100-4. [PMID: 8519963 PMCID: PMC1236337 DOI: 10.1016/s0006-3495(95)79983-0] [Citation(s) in RCA: 18] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Bacteriochlorophyll c pigments extracted from light harvesting chlorosomes in green photosynthetic bacteria are known to self-assemble into aggregates whose electronic spectroscopy resembles that of intact chlorosomes. Femtosecond optical experiments reveal that the chlorosomes and their reconstituted aggregates exhibit closely analogous internal energy transfer kinetics and exciton state evolution. These comparisons furnish compelling new evidence that proteins do not exert a major local role in the BChl c antenna pigment organization of intact chlorosomes.
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Affiliation(s)
- S Savikhin
- Ames Laboratory, U.S. Department of Energy, Iowa, USA
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