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Kimura A, Kitoh-Nishioka H, Kondo T, Oh-Oka H, Itoh S, Azai C. Experimental and Theoretical Mutation of Exciton States on the Smallest Type-I Photosynthetic Reaction Center Complex of a Green Sulfur Bacterium Chlorobaclum tepidum. J Phys Chem B 2024; 128:731-743. [PMID: 38198639 DOI: 10.1021/acs.jpcb.3c07424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2024]
Abstract
The exciton states on the smallest type-I photosynthetic reaction center complex of a green sulfur bacterium Chlorobaculum tepidum (GsbRC) consisting of 26 bacteriochlorophylls a (BChl a) and four chlorophylls a (Chl a) located on the homodimer of two PscA reaction center polypeptides were investigated. This analysis involved the study of exciton states through a combination of theoretical modeling and the genetic removal of BChl a pigments at eight sites. (1) A theoretical model of the pigment assembly exciton state on GsbRC was constructed using Poisson TrESP (P-TrESP) and charge density coupling (CDC) methods based on structural information. The model reproduced the experimentally obtained absorption spectrum, circular dichroism spectrum, and excitation transfer dynamics, as well as explained the effects of mutation. (2) Eight BChl a molecules at different locations on the GsbRC were selectively removed by genetic exchange of the His residue, which ligates the central Mg atom of BChl a, with the Leu residue on either one or two PscAs in the RC. His locations are conserved among all type-I RC plant polypeptide, cyanobacteria, and bacteria amino acid sequences. (3) Purified mutant-GsbRCs demonstrated distinct absorption and fluorescence spectra at 77 K, which were different from each other, suggesting successful pigment removal. (4) The same mutations were applied to the constructed theoretical model to analyze the outcomes of these mutations. (5) The combination of theoretical predictions and experimental mutations based on structural information is a new tool for studying the function and evolution of photosynthetic reaction centers.
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Affiliation(s)
- Akihiro Kimura
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Hirotaka Kitoh-Nishioka
- Department of Energy and Materials, Faculty of Science and Engineering, Kindai University, Osaka 577-8502, Japan
| | - Toru Kondo
- School of Life Science and Technology, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan
| | - Hirozo Oh-Oka
- Department of Biological Sciences, Graduate School of Science, Osaka University, Osaka 560-0043, Japan
| | - Shigeru Itoh
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Chihiro Azai
- Department of Biological Sciences, Faculty of Science and Engineering, Chuo University, Tokyo 112-8551, Japan
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2
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Brütting M, Foerster JM, Kümmel S. Understanding Primary Charge Separation in the Heliobacterial Reaction Center. J Phys Chem Lett 2023; 14:3092-3102. [PMID: 36951395 DOI: 10.1021/acs.jpclett.3c00377] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The homodimeric reaction center of heliobacteria retains features of the ancestral reaction center and can thus provide insights into the evolution of photosynthesis. Primary charge separation is expected to proceed in a two-step mechanism along either of the two reaction center branches. We reveal the first charge-separation step from first-principles calculations based on time-dependent density functional theory with an optimally tuned range-separated hybrid and ab initio Born-Oppenheimer molecular dynamics: the electron is most likely localized on the electron transfer cofactor 3 (EC3, OH-chlorophyll a), and the hole on the adjacent EC2. Including substantial parts of the surrounding protein environment into the calculations shows that a distinct structural mechanism is decisive for the relative energetic positioning of the electronic excitations: specific charged amino acids in the vicinity of EC3 lower the energy of charge-transfer excitations and thus facilitate efficient charge separation. These results are discussed considering recent experimental insights.
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Reiter S, Kiss FL, Hauer J, de Vivie-Riedle R. Thermal site energy fluctuations in photosystem I: new insights from MD/QM/MM calculations. Chem Sci 2023; 14:3117-3131. [PMID: 36970098 PMCID: PMC10034153 DOI: 10.1039/d2sc06160k] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 02/03/2023] [Indexed: 02/09/2023] Open
Abstract
Cyanobacterial photosystem I (PSI) is one of the most efficient photosynthetic machineries found in nature. Due to the large scale and complexity of the system, the energy transfer mechanism from the antenna complex to the reaction center is still not fully understood. A central element is the accurate evaluation of the individual chlorophyll excitation energies (site energies). Such an evaluation must include a detailed treatment of site specific environmental influences on structural and electrostatic properties, but also their evolution in the temporal domain, because of the dynamic nature of the energy transfer process. In this work, we calculate the site energies of all 96 chlorophylls in a membrane-embedded model of PSI. The employed hybrid QM/MM approach using the multireference DFT/MRCI method in the QM region allows to obtain accurate site energies under explicit consideration of the natural environment. We identify energy traps and barriers in the antenna complex and discuss their implications for energy transfer to the reaction center. Going beyond previous studies, our model also accounts for the molecular dynamics of the full trimeric PSI complex. Via statistical analysis we show that the thermal fluctuations of single chlorophylls prevent the formation of a single prominent energy funnel within the antenna complex. These findings are also supported by a dipole exciton model. We conclude that energy transfer pathways may form only transiently at physiological temperatures, as thermal fluctuations overcome energy barriers. The set of site energies provided in this work sets the stage for theoretical and experimental studies on the highly efficient energy transfer mechanisms in PSI.
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Affiliation(s)
- Sebastian Reiter
- Department of Chemistry, Ludwig-Maximilians-Universität München Butenandtstr. 11 81377 Munich Germany
| | - Ferdinand L Kiss
- Department of Chemistry, Ludwig-Maximilians-Universität München Butenandtstr. 11 81377 Munich Germany
| | - Jürgen Hauer
- Department of Chemistry, Technical University of Munich Lichtenbergstr. 4, Garching 85747 Germany
| | - Regina de Vivie-Riedle
- Department of Chemistry, Ludwig-Maximilians-Universität München Butenandtstr. 11 81377 Munich Germany
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4
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Kimura A, Kitoh-Nishioka H, Aota T, Hamaguchi T, Yonekura K, Kawakami K, Shinzawa-Itoh K, Inoue-Kashino N, Ifuku K, Yamashita E, Kashino Y, Itoh S. Theoretical Model of the Far-Red-Light-Adapted Photosystem I Reaction Center of Cyanobacterium Acaryochloris marina Using Chlorophyll d and the Effect of Chlorophyll Exchange. J Phys Chem B 2022; 126:4009-4021. [PMID: 35617171 DOI: 10.1021/acs.jpcb.2c00869] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A theoretical model of the far-red-light-adapted photosystem I (PSI) reaction center (RC) complex of a cyanobacterium, Acaryochloris marina (AmPSI), was constructed based on the exciton theory and the recently identified molecular structure of AmPSI by Hamaguchi et al. (Nat. Commun., 2021, 12, 2333). A. marina performs photosynthesis under the visible to far-red light (400-750 nm), which is absorbed by chlorophyll d (Chl-d). It is in contrast to the situation of all the other oxygenic photosynthetic processes of cyanobacteria and plants, which contains chlorophyll a (Chl-a) that absorbs only 400-700 nm visible light. AmPSI contains 70 Chl-d, 1 Chl-d', 2 pheophytin a (Pheo-a), and 12 carotenoids in the currently available structure. A special pair of Chl-d/Chl-d' acts as the electron donor (P740) and two Pheo-a act as the primary electron acceptor A0 as the counterparts of P700 and Chl-a, respectively, of Chl-a-type PSIs. The exciton Hamiltonian of AmPSI was constructed considering the excitonic coupling strength and site energy shift of individual pigments using the Poisson-TrESP (P-TrESP) and charge density coupling (CDC) methods. The model was constructed to fit the experimentally measured spectra of absorption and circular dichroism (CD) spectra during downhill/uphill excitation energy transfer processes. The constructed theoretical model of AmPSI was further compared with the Chl-a-type PSI of Thermosynechococcus elongatus (TePSI), which contains only Chl-a and Chl-a'. The functional properties of AmPSI and TePSI were further examined by the in silico exchange of Chl-d by Chl-a in the models.
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Affiliation(s)
- Akihiro Kimura
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | | | - Toshimichi Aota
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Tasuku Hamaguchi
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, 776 Sayo, Hyogo 679-5148, Japan
| | - Koji Yonekura
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, 776 Sayo, Hyogo 679-5148, Japan
| | - Keisuke Kawakami
- Biostructural Mechanism Laboratory, RIKEN SPring-8 Center, 776 Sayo, Hyogo 679-5148, Japan
| | - Kyoko Shinzawa-Itoh
- Graduate School of Science, University of Hyogo, Ako-gun, Hyogo 678-1297, Japan
| | | | - Kentaro Ifuku
- Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
| | - Eiki Yamashita
- Laboratory of Supramolecular Crystallography, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Yasuhiro Kashino
- Graduate School of Science, University of Hyogo, Ako-gun, Hyogo 678-1297, Japan
| | - Shigeru Itoh
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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5
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Kondo T, Mutoh R, Arai S, kurisu G, Oh-oka H, Fujiyoshi S, Matsushita M. Energy transfer fluctuation observed by single-molecule spectroscopy of red-shifted bacteriochlorophyll in the homodimeric photosynthetic reaction center. J Chem Phys 2022; 156:105102. [DOI: 10.1063/5.0077290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Toru Kondo
- Department of Life Science and Technology, Tokyo Institute of Technology, Japan
| | | | - Shun Arai
- Tokyo Institute of Technology, Japan
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Orf GS, Gisriel CJ, Granstrom J, Baker PL, Redding KE. The PshX subunit of the photochemical reaction center from Heliobacterium modesticaldum acts as a low-energy antenna. PHOTOSYNTHESIS RESEARCH 2022; 151:11-30. [PMID: 34480322 DOI: 10.1007/s11120-021-00871-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2021] [Accepted: 08/09/2021] [Indexed: 06/13/2023]
Abstract
The anoxygenic phototrophic bacterium Heliobacterium modesticaldum contains a photochemical reaction center protein complex (called the HbRC) consisting of a homodimer of the PshA polypeptide and two copies of a newly discovered polypeptide called PshX, which is a single transmembrane helix that binds two bacteriochlorophyll g molecules. To assess the function of PshX, we produced a ∆pshX strain of Hbt. modesticaldum by leveraging the endogenous Hbt. modesticaldum Type I-A CRISPR-Cas system to aid in mutant selection. We optimized this system by separating the homologous recombination and CRISPR-based selection steps into two plasmid transformations, allowing for markerless gene replacement. Fluorescence and low-temperature absorbance of the purified HbRC from the wild-type and ∆pshX strains showed that the bacteriochlorophylls bound by PshX have the lowest site energies in the entire HbRC. This indicates that PshX acts as a low-energy antenna subunit, participating in entropy-assisted uphill energy transfer toward the P800 special bacteriochlorophyll g pair. We further discuss the role that PshX may play in stability of the HbRC, its conservation in other heliobacterial species, and the evolutionary pressure to produce and maintain single-TMH subunits in similar locations in other reaction centers.
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Affiliation(s)
- Gregory S Orf
- Center for Bioenergy and Photosynthesis, School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA
- Infectious Disease Research, Abbott Diagnostics Division, Abbott Park, IL, 60064, USA
| | - Christopher J Gisriel
- Center for Bioenergy and Photosynthesis, School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA
- Department of Chemistry, Yale University, New Haven, CT, 06520, USA
| | - Jesse Granstrom
- Center for Bioenergy and Photosynthesis, School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA
| | - Patricia L Baker
- Center for Bioenergy and Photosynthesis, School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA
| | - Kevin E Redding
- Center for Bioenergy and Photosynthesis, School of Molecular Sciences, Arizona State University, Tempe, AZ, 85287, USA.
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7
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Meech S. Virtual Issue on Ultrafast Spectroscopy. J Phys Chem B 2021; 125:6037-6039. [PMID: 34134490 DOI: 10.1021/acs.jpcb.1c04148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Steve Meech
- School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, U.K
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8
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Agostini A, Bortolus M, Ferlez B, Walters K, Golbeck JH, van der Est A, Carbonera D. Differential sensitivity to oxygen among the bacteriochlorophylls g in the type-I reaction centers of Heliobacterium modesticaldum. Photochem Photobiol Sci 2021; 20:747-759. [PMID: 34018156 DOI: 10.1007/s43630-021-00049-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Accepted: 04/28/2021] [Indexed: 11/27/2022]
Abstract
The type-I, homodimeric photosynthetic reaction center (RC) of Heliobacteria (HbRC) is the only known RC in which bacteriochlorophyll g (BChl g) is found. It is also simpler than other RCs, having the smallest number of protein subunits and bound chromophores of any type-I RC. In the presence of oxygen, BChl g isomerizes to 81-hydroxychlorophyll aF (Chl aF). This naturally occurring process provides a way of altering the chlorophylls and studying the effect of these changes on energy and electron transfer. Transient absorbance difference spectroscopy reveals that triplet-state formation occurs in the antenna chlorophylls of HbRCs but does not provide site-specific information. Here, we report on an extended optically detected magnetic resonance (ODMR) study of the antenna triplet states in HbRCs with differing levels of conversion of BChl g to Chl aF. The data reveal pools of BChl g molecules with different triplet zero-field splitting parameters and different susceptibilities to chemical oxidation. By relating the detailed spectroscopic characteristics derived from the ODMR data to the recently solved crystallographic structure, we have tentatively identified BChl g molecules in which the probability of triplet formation is high and sites at which BChl g conversion is more likely, providing useful information about the fate of the excitation in the complex.
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Affiliation(s)
- Alessandro Agostini
- Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131, Padua, Italy.,Biology Centre, Czech Academy of Sciences, Institute of Plant Molecular Biology, Branisovska 31, 37005, České Budějovice, Czechia
| | - Marco Bortolus
- Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131, Padua, Italy
| | - Bryan Ferlez
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA.,Department of Biochemistry and Molecular Biology and MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI, USA
| | - Karim Walters
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA
| | - John H Golbeck
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Art van der Est
- Department of Chemistry, Brock University, 1812 Sir Isaac Brock, Way, Saint Catharines, ON, L2S 3A1, Canada.
| | - Donatella Carbonera
- Department of Chemical Sciences, University of Padova, Via Marzolo, 1, 35131, Padua, Italy.
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9
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Excitonic structure and charge separation in the heliobacterial reaction center probed by multispectral multidimensional spectroscopy. Nat Commun 2021; 12:2801. [PMID: 33990569 PMCID: PMC8121816 DOI: 10.1038/s41467-021-23060-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Accepted: 04/09/2021] [Indexed: 12/29/2022] Open
Abstract
Photochemical reaction centers are the engines that drive photosynthesis. The reaction center from heliobacteria (HbRC) has been proposed to most closely resemble the common ancestor of photosynthetic reaction centers, motivating a detailed understanding of its structure-function relationship. The recent elucidation of the HbRC crystal structure motivates advanced spectroscopic studies of its excitonic structure and charge separation mechanism. We perform multispectral two-dimensional electronic spectroscopy of the HbRC and corresponding numerical simulations, resolving the electronic structure and testing and refining recent excitonic models. Through extensive examination of the kinetic data by lifetime density analysis and global target analysis, we reveal that charge separation proceeds via a single pathway in which the distinct A0 chlorophyll a pigment is the primary electron acceptor. In addition, we find strong delocalization of the charge separation intermediate. Our findings have general implications for the understanding of photosynthetic charge separation mechanisms, and how they might be tuned to achieve different functional goals. The primary energy conversion step in photosynthesis, charge separation, takes place in the reaction center. Here the authors investigate the heliobacterial reaction center using multispectral two-dimensional electronic spectroscopy, identifying the primary electron acceptor and revealing the charge separation mechanism.
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Brütting M, Foerster JM, Kümmel S. Investigating Primary Charge Separation in the Reaction Center of Heliobacterium modesticaldum. J Phys Chem B 2021; 125:3468-3475. [PMID: 33788561 DOI: 10.1021/acs.jpcb.0c10283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We compute the primary charge separation step in the homodimeric reaction center (RC) of Heliobacterium modesticaldum from first principles. Using time-dependent density functional theory with the optimally tuned range-separated hybrid functional ωPBE, we calculate the excitations of a system comprising the special pair, the adjacent accessory bacteriochlorophylls, and the most relevant parts of the surrounding protein environment. The structure of the excitation spectrum can be rationalized from coupling of the individual bacteriochlorophyll pigments similar to molecular J- and H-aggregates. We find excited states corresponding to forward-charge transfer along the individual branches of the RC of H. modesticaldum. In the spectrum, these are located at an energy between the coupled Qy and Qx transitions. With ab initio Born-Oppenheimer molecular dynamics simulations, we reveal the influence of thermal vibrations on the excited states. The results show that the energy gap between the coupled Qy and the forward-charge transfer excitations is ∼0.4 eV, which we consider to conflict with the concept of a direct transfer mechanism. Our calculations, however, reveal a certain spectral overlap of the forward-charge transfer and the coupled Qx excitations. The reliability and robustness of the results are demonstrated by several numerical tests.
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Kimura A, Kitoh-Nishioka H, Shigeta Y, Itoh S. Comparison between the Light-Harvesting Mechanisms of Type-I Photosynthetic Reaction Centers of Heliobacteria and Photosystem I: Pigment Site Energy Distribution and Exciton State. J Phys Chem B 2021; 125:3727-3738. [DOI: 10.1021/acs.jpcb.0c09400] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Akihiro Kimura
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Hirotaka Kitoh-Nishioka
- JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
- Graduate School of System Informatics, Kobe University, Kobe 657-8501, Japan
| | - Yasuteru Shigeta
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
| | - Shigeru Itoh
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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Wang Z, Suo B, Yin S, Zou W. Quantum Chemical Simulation of the Qy Absorption Spectrum of Zn Chlorin Aggregates for Artificial Photosynthesis. Molecules 2021; 26:1086. [PMID: 33669551 PMCID: PMC7922025 DOI: 10.3390/molecules26041086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Revised: 02/13/2021] [Accepted: 02/15/2021] [Indexed: 11/16/2022] Open
Abstract
Zn chlorin (Znchl) is easy to synthesize and has similar optical properties to those of bacteriochlorophyll c in the nature, which is expected to be used as a light-harvesting antenna system in artificial photosynthesis. In order to further explore the optical characteristics of Znchl, various sizes of a parallel layered Znchl-aggregate model and the THF-Znchl explicit solvent monomer model were constructed in this study, and their Qy excited state properties were simulated by using time-dependent density functional theory (TDDFT) and exciton theory. For the Znchl monomer, with a combination of the explicit solvent model and the implicit solvation model based on density (SMD), the calculated Qy excitation energy agreed very well with the experimental one. The Znchl aggregates may be simplified to a Zn36 model to reproduce the experimental Qy absorption spectrum by the Förster coupling theory. The proposed Znchl aggregate model provides a good foundation for the future exploration of other properties of Znchl and simulations of artificial light-harvesting antennas. The results also indicate that J-aggregrates along z-direction, due to intermolecular coordination bonds, are the dominant factor in extending the Qy band of Znchl into the near infrared region.
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Affiliation(s)
- Zhimo Wang
- Institute of Modern Physics, Northwest University, and Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi’an 710127, China;
| | - Bingbing Suo
- Institute of Modern Physics, Northwest University, and Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi’an 710127, China;
| | - Shiwei Yin
- Key Laboratory for Macromolecular Science of Shaanxi Province, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710062, China;
| | - Wenli Zou
- Institute of Modern Physics, Northwest University, and Shaanxi Key Laboratory for Theoretical Physics Frontiers, Xi’an 710127, China;
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Orf GS, Redding KE. Perturbation of the primary acceptor chlorophyll site in the heliobacterial reaction center by coordinating amino acid substitution. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2020; 1862:148324. [PMID: 33039349 DOI: 10.1016/j.bbabio.2020.148324] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 10/01/2020] [Accepted: 10/05/2020] [Indexed: 11/19/2022]
Abstract
All known Type I photochemical reaction center protein complexes contain a form of the pigment chlorophyll a in their primary electron acceptor site (termed ec3). In the reaction center from the primitive heliobacteria (HbRC), all of the pigment cofactors are bacteriochlorophyll g except in the ec3 sites, which contain 81-hydroxychlorophyll a. To explore the energetic flexibility of this site, we performed site-directed mutagenesis on two of the amino acids of the PshA core polypeptide responsible for coordinating the 81-hydroxychlorophyll a. These two amino acids are serine-545, which coordinates the central Mg(II) through an intermediary water molecule, and serine-553, which participates in a hydrogen bond with the 131-keto O atom. Mutagenesis of serine-545 to histidine (S545H) changes how the chlorophyll's central Mg(II) is coordinated, with the result of decreasing the chlorophyll's site energy. Mutagenesis of serine-545 to methionine (S545M), which was made to mimic the ec3 site of Photosystem I, abolishes chlorophyll binding and charge separation altogether. Mutagenesis of serine-553 to alanine (S553A) removes the aforementioned hydrogen bond, increasing the site energy of the chlorophyll. In the S545H and S553A mutants, the forward and reverse electron transfer rates from ec3 are both faster. This coincides with a decrease in both the quantum yield of initial charge separation and the overall photochemical quantum yield. Taken together, these data indicate that wild-type HbRC is optimized for overall photochemical efficiency, rather than just for maximizing the forward electron transfer rate. The necessity for a chlorophyll a derivative at the ec3 site is also discussed.
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Affiliation(s)
- Gregory S Orf
- Center for Bioenergy and Photosynthesis, School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - Kevin E Redding
- Center for Bioenergy and Photosynthesis, School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, USA.
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14
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Energy transfer and primary charge separation upon selective femtosecond excitation at 810 nm in the reaction center complex from Heliobacterium modesticaldum. J Photochem Photobiol A Chem 2020. [DOI: 10.1016/j.jphotochem.2020.112758] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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15
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Kitoh-Nishioka H, Shigeta Y, Itoh S, Kimura A. Excitonic Coupling on a Heliobacterial Symmetrical Type-I Reaction Center: Comparison with Photosystem I. J Phys Chem B 2019; 124:389-403. [DOI: 10.1021/acs.jpcb.9b11290] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Hirotaka Kitoh-Nishioka
- JST, PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
| | - Yasuteru Shigeta
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan
| | - Shigeru Itoh
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Akihiro Kimura
- Department of Physics, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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