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A special issue of International Journal of Molecular Sciences (ISSN 1422-0067). This special issue belongs to the section "Molecular Plant Sciences".

Deadline for manuscript submissions: 31 October 2024 | Viewed by 7470

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Dr. Stefano Santabarbara

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Guest Editor

Photosynthesis Research Unit, National Research Council of Italy (CNR-IBBA), Via Corti 12, 20133 Milan, Italy
Interests: biophysics; biochemistry; plant physiology; plant biology; plant biotechnology; plant environmental; stress physiology; fluorescence; abiotic stress tolerance; spectroscopy; absorption

Prof. Dr. Gary Hastings

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Guest Editor

Department of Physics and Astronomy, Georgia State University, Atlanta, GA, USA
Interests: photosynthesis; absorption; Raman spectroscopy; electronic structure; spectrometry

Special Issue Information

Dear Colleagues,

Photosystem I is a large protein-cofactor super-complex fundamental component of the electron transport chain of oxygen-evolving photosynthetic organisms, and it can operate either in series with Photosystem II in the linear electron transport chain, or independently from Photosystem II in a cyclic transport. Photosystem I is known to operate with a photochemical quantum conversion yield close to the unit, which makes it a attractive system for the development of biological-mimicking artificial molecules and devices. In Photosystem I, two structurally symmetric electron transfer chains operate in electron transfer through the so-called bidirectional mechanism, which distinguishes it from both PSII and its homologue, the purple bacteria reaction centre. However, despite intense research over several decades, some of the key mechanisms concerning the primary photochemical conversion reactions, the energy of successive electron transfer cascade, and the mechanisms controlling the functionality of the two active electron transfer branches remain to be fully elucidated. Furthermore, the partners and mechanism of cyclic electron transfer in the thylakoid membranes, and the physiological role of this transport mechanism, remain to be fully established.

This Special Issue for IJMS aims at gathering contributions aiming at improving the understanding of the molecular mechanism of light harvesting, photochemical energy conversion, electron transfer and electron transport reaction involving Photosystem I.

Dr. Stefano Santabarbara
Prof. Dr. Gary Hastings
Guest Editors

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Keywords

photosystem I
photochemisty
electron transfer
protein–cofactor interaction
reaction kinetics
reaction mechanism
redox tuning
light harvesting
low-energy (red) forms
bioenergetics
cyclic electron transfer

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Published Papers (9 papers)

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Research

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23 pages, 6028 KiB

Open AccessArticle

Dependence of Protein Immobilization and Photocurrent Generation in PSI–FTO Electrodes on the Electrodeposition Parameters

by Theresa Kehler, Sebastian Szewczyk and Krzysztof Gibasiewicz

Int. J. Mol. Sci. 2024, 25(18), 9772; https://doi.org/10.3390/ijms25189772 - 10 Sep 2024

Viewed by 283

Abstract

This study investigates the immobilization of cyanobacterial photosystem I (PSI) from Synechocystis sp. PCC 6803 onto fluorine-doped tin oxide (FTO) conducting glass plates to create photoelectrodes for biohybrid solar cells. The fabrication of these PSI–FTO photoelectrodes is based on two immobilization processes: rapid electrodeposition driven by an external electric field and slower adsorption during solvent evaporation, both influenced by gravitational sedimentation. Deposition and performance of photoelectrodes was investigated by UV–Vis absorption spectroscopy and photocurrent measurements. We investigated the efficiency of PSI immobilization under varying conditions, including solution pH, applied electric field intensity and duration, and electrode polarization, with the goals to control (1) the direction of migration and (2) the orientation of the PSI particles on the substrate surface. Variation in the pH value of the PSI solution alters the surface charge distribution, affecting the net charge and the electric dipole moment of these proteins. Results showed PSI migration to the positively charged electrode at pH 6, 7, and 8, and to the negatively charged electrode at pH 4.4 and 5, suggesting an isoelectric point of PSI between 5 and 6. At acidic pH, the electrophoretic migration was largely hindered by protein aggregation. Notably, photocurrent generation was consistently cathodic and correlated with PSI layer thickness, and no conclusions can be drawn on the orientation of the immobilized proteins. Overall, these findings suggest mediated electron transfer from FTO to PSI by the used electrolyte containing 10 mM sodium ascorbate and 200 μM dichlorophenolindophenol. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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19 pages, 7703 KiB

Open AccessArticle

A Simple Expression for the Screening of Excitonic Couplings between Chlorophylls as Inferred for Photosystem I Trimers

by Matthias Eder and Thomas Renger

Int. J. Mol. Sci. 2024, 25(16), 9006; https://doi.org/10.3390/ijms25169006 - 19 Aug 2024

Viewed by 435

Abstract

The Coulomb coupling between transition densities of the pigments in photosynthetic pigment-protein complexes, termed excitonic coupling, is a key factor for the description of optical spectra and energy transfer. A challenging question is the quantification of the screening of the excitonic coupling by the optical polarizability of the environment. We use the equivalence between the sophisticated quantum chemical polarizable continuum (PCM) model and the simple electrostatic Poisson-TrEsp approach to analyze the distance and orientation dependence of the dielectric screening between chlorophylls in photosystem I trimers. On the basis of these calculations we find that the vacuum couplings

V_{m n}^{(0)}

and the couplings in the dielectric medium

V_{m n} = f_{m n} V_{m n}^{(0)}

are related by the empirical screening factor

f_{m n} = 0.60 + 39.6 θ (| κ_{m n} | - 1.17) exp (- 0.56 R_{m n} / Å)

, where

κ_{m n}

is the usual orientational factor of the dipole-dipole coupling between the pigments,

R_{m n}

is the center-to-center distance, and the Heaviside-function

θ (| κ_{m n} | - 1.17)

ensures that the exponential distance dependence only contributes for in-line type dipole geometries. We are confident that the present expression can be applied also to other pigment-protein complexes with chlorophyll or related pigments of similar shape. The variance between the Poisson-TrEsp and the approximate coupling values is found to decrease by a factor of 8 and 3–4 using the present expression, instead of an exponential distance dependent or constant screening factor, respectively, assumed previously in the literature. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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15 pages, 1276 KiB

Open AccessArticle

Light-Induced Charge Separation in Photosystem I from Different Biological Species Characterized by Multifrequency Electron Paramagnetic Resonance Spectroscopy

by Jasleen K. Bindra, Tirupathi Malavath, Mandefro Y. Teferi, Moritz Kretzschmar, Jan Kern, Jens Niklas, Lisa M. Utschig and Oleg G. Poluektov

Int. J. Mol. Sci. 2024, 25(15), 8188; https://doi.org/10.3390/ijms25158188 - 26 Jul 2024

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Abstract

Photosystem I (PSI) serves as a model system for studying fundamental processes such as electron transfer (ET) and energy conversion, which are not only central to photosynthesis but also have broader implications for bioenergy production and biomimetic device design. In this study, we employed electron paramagnetic resonance (EPR) spectroscopy to investigate key light-induced charge separation steps in PSI isolated from several green algal and cyanobacterial species. Following photoexcitation, rapid sequential ET occurs through either of two quasi-symmetric branches of donor/acceptor cofactors embedded within the protein core, termed the A and B branches. Using high-frequency (130 GHz) time-resolved EPR (TR-EPR) and deuteration techniques to enhance spectral resolution, we observed that at low temperatures prokaryotic PSI exhibits reversible ET in the A branch and irreversible ET in the B branch, while PSI from eukaryotic counterparts displays either reversible ET in both branches or exclusively in the B branch. Furthermore, we observed a notable correlation between low-temperature charge separation to the terminal [4Fe-4S] clusters of PSI, termed F_A and F_B, as reflected in the measured F_A/F_B ratio. These findings enhance our understanding of the mechanistic diversity of PSI’s ET across different species and underscore the importance of experimental design in resolving these differences. Though further research is necessary to elucidate the underlying mechanisms and the evolutionary significance of these variations in PSI charge separation, this study sets the stage for future investigations into the complex interplay between protein structure, ET pathways, and the environmental adaptations of photosynthetic organisms. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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14 pages, 1808 KiB

Open AccessArticle

Is the A_-1 Pigment in Photosystem I Part of P700? A (P700⁺–P700) FTIR Difference Spectroscopy Study of A_-1 Mutants

by Julia S. Kirpich, Lujun Luo, Michael R. Nelson, Neva Agarwala, Wu Xu and Gary Hastings

Int. J. Mol. Sci. 2024, 25(9), 4839; https://doi.org/10.3390/ijms25094839 - 29 Apr 2024

Viewed by 1146

Abstract

The involvement of the second pair of chlorophylls, termed A_-1A and A_-1B, in light-induced electron transfer in photosystem I (PSI) is currently debated. Asparagines at PsaA600 and PsaB582 are involved in coordinating the A_-1B and A_-1A pigments, respectively. Here we have mutated these asparagine residues to methionine in two single mutants and a double mutant in PSI from Synechocystis sp. PCC 6803, which we term NA600M, NB582M, and NA600M/NB582M mutants. (P700⁺–P700) FTIR difference spectra (DS) at 293 K were obtained for the wild-type and the three mutant PSI samples. The wild-type and mutant FTIR DS differ considerably. This difference indicates that the observed changes in the (P700⁺–P700) FTIR DS cannot be due to only the P_A and P_B pigments of P700. Comparison of the wild-type and mutant FTIR DS allows the assignment of different features to both A_-1 pigments in the FTIR DS for wild-type PSI and assesses how these features shift upon cation formation and upon mutation. While the exact role the A_-1 pigments play in the species we call P700 is unclear, we demonstrate that the vibrational modes of the A_-1A and A_-1B pigments are modified upon P700⁺ formation. Previously, we showed that the A_-1 pigments contribute to P700 in green algae. In this manuscript, we demonstrate that this is also the case in cyanobacterial PSI. The nature of the mutation-induced changes in algal and cyanobacterial PSI is similar and can be considered within the same framework, suggesting a universality in the nature of P700 in different photosynthetic organisms. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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20 pages, 3421 KiB

Open AccessArticle

Impact of Peripheral Hydrogen Bond on Electronic Properties of the Primary Acceptor Chlorophyll in the Reaction Center of Photosystem I

by Lujun Luo, Antoine P. Martin, Elijah K. Tandoh, Andrei Chistoserdov, Lyudmila V. Slipchenko, Sergei Savikhin and Wu Xu

Int. J. Mol. Sci. 2024, 25(9), 4815; https://doi.org/10.3390/ijms25094815 - 28 Apr 2024

Viewed by 876

Abstract

Photosystem I (PS I) is a photosynthetic pigment–protein complex that absorbs light and uses the absorbed energy to initiate electron transfer. Electron transfer has been shown to occur concurrently along two (A- and B-) branches of reaction center (RC) cofactors. The electron transfer chain originates from a special pair of chlorophyll a molecules (P700), followed by two chlorophylls and one phylloquinone in each branch (denoted as A₋₁, A₀, A₁, respectively), converging in a single iron–sulfur complex F_x. While there is a consensus that the ultimate electron donor–acceptor pair is P700⁺A₀⁻, the involvement of A₋₁ in electron transfer, as well as the mechanism of the very first step in the charge separation sequence, has been under debate. To resolve this question, multiple groups have targeted electron transfer cofactors by site-directed mutations. In this work, the peripheral hydrogen bonds to keto groups of A₀ chlorophylls have been disrupted by mutagenesis. Four mutants were generated: PsaA-Y692F; PsaB-Y667F; PsaB-Y667A; and a double mutant PsaA-Y692F/PsaB-Y667F. Contrary to expectations, but in agreement with density functional theory modeling, the removal of the hydrogen bond by Tyr → Phe substitution was found to have a negligible effect on redox potentials and optical absorption spectra of respective chlorophylls. In contrast, Tyr → Ala substitution was shown to have a fatal effect on the PS I function. It is thus inferred that PsaA-Y692 and PsaB-Y667 residues have primarily structural significance, and their ability to coordinate respective chlorophylls in electron transfer via hydrogen bond plays a minor role. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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19 pages, 4195 KiB

Open AccessArticle

Energy Transfer and Radical-Pair Dynamics in Photosystem I with Different Red Chlorophyll a Pigments

by Ivo H. M. van Stokkum, Marc G. Müller and Alfred R. Holzwarth

Int. J. Mol. Sci. 2024, 25(7), 4125; https://doi.org/10.3390/ijms25074125 - 8 Apr 2024

Viewed by 1043

Abstract

We establish a general kinetic scheme for the energy transfer and radical-pair dynamics in photosystem I (PSI) of Chlamydomonas reinhardtii, Synechocystis PCC6803, Thermosynechococcus elongatus and Spirulina platensis grown under white-light conditions. With the help of simultaneous target analysis of transient-absorption data sets measured with two selective excitations, we resolved the spectral and kinetic properties of the different species present in PSI. WL-PSI can be described as a Bulk Chl a in equilibrium with a higher-energy Chl a, one or two Red Chl a and a reaction-center compartment (WL-RC). Three radical pairs (RPs) have been resolved with very similar properties in the four model organisms. The charge separation is virtually irreversible with a rate of ≈900 ns⁻¹. The second rate, of RP1 → RP2, ranges from 70–90 ns⁻¹ and the third rate, of RP2 → RP3, is ≈30 ns⁻¹. Since RP1 and the Red Chl a are simultaneously present, resolving the RP1 properties is challenging. In Chlamydomonas reinhardtii, the excited WL-RC and Bulk Chl a compartments equilibrate with a lifetime of ≈0.28 ps, whereas the Red and the Bulk Chl a compartments equilibrate with a lifetime of ≈2.65 ps. We present a description of the thermodynamic properties of the model organisms at room temperature. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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Review

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19 pages, 10150 KiB

Open AccessReview

Photosystem I: A Paradigm for Understanding Biological Environmental Adaptation Mechanisms in Cyanobacteria and Algae

by Li-Rong Tian and Jing-Hua Chen

Int. J. Mol. Sci. 2024, 25(16), 8767; https://doi.org/10.3390/ijms25168767 - 12 Aug 2024

Viewed by 726

Abstract

The process of oxygenic photosynthesis is primarily driven by two multiprotein complexes known as photosystem II (PSII) and photosystem I (PSI). PSII facilitates the light-induced reactions of water-splitting and plastoquinone reduction, while PSI functions as the light-driven plastocyanin-ferredoxin oxidoreductase. In contrast to the highly conserved structure of PSII among all oxygen-evolving photosynthetic organisms, the structures of PSI exhibit remarkable variations, especially for photosynthetic organisms that grow in special environments. In this review, we make a concise overview of the recent investigations of PSI from photosynthetic microorganisms including prokaryotic cyanobacteria and eukaryotic algae from the perspective of structural biology. All known PSI complexes contain a highly conserved heterodimeric core; however, their pigment compositions and peripheral light-harvesting proteins are substantially flexible. This structural plasticity of PSI reveals the dynamic adaptation to environmental changes for photosynthetic organisms. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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16 pages, 9570 KiB

Open AccessReview

Investigating the Balance between Structural Conservation and Functional Flexibility in Photosystem I

by Nathan Nelson

Int. J. Mol. Sci. 2024, 25(10), 5073; https://doi.org/10.3390/ijms25105073 - 7 May 2024

Cited by 1 | Viewed by 791

Abstract

Photosynthesis, as the primary source of energy for all life forms, plays a crucial role in maintaining the global balance of energy, entropy, and enthalpy in living organisms. Among its various building blocks, photosystem I (PSI) is responsible for light-driven electron transfer, crucial for generating cellular reducing power. PSI acts as a light-driven plastocyanin-ferredoxin oxidoreductase and is situated in the thylakoid membranes of cyanobacteria and the chloroplasts of eukaryotic photosynthetic organisms. Comprehending the structure and function of the photosynthetic machinery is essential for understanding its mode of action. New insights are offered into the structure and function of PSI and its associated light-harvesting proteins, with a specific focus on the remarkable structural conservation of the core complex and high plasticity of the peripheral light-harvesting complexes. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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45 pages, 8996 KiB

Open AccessReview

High-Resolution Frequency-Domain Spectroscopic and Modeling Studies of Photosystem I (PSI), PSI Mutants and PSI Supercomplexes

by Valter Zazubovich and Ryszard Jankowiak

Int. J. Mol. Sci. 2024, 25(7), 3850; https://doi.org/10.3390/ijms25073850 - 29 Mar 2024

Viewed by 866

Abstract

Photosystem I (PSI) is one of the two main pigment–protein complexes where the primary steps of oxygenic photosynthesis take place. This review describes low-temperature frequency-domain experiments (absorption, emission, circular dichroism, resonant and non-resonant hole-burned spectra) and modeling efforts reported for PSI in recent years. In particular, we focus on the spectral hole-burning studies, which are not as common in photosynthesis research as the time-domain spectroscopies. Experimental and modeling data obtained for trimeric cyanobacterial Photosystem I (PSI₃), PSI₃ mutants, and PSI₃–IsiA₁₈ supercomplexes are analyzed to provide a more comprehensive understanding of their excitonic structure and excitation energy transfer (EET) processes. Detailed information on the excitonic structure of photosynthetic complexes is essential to determine the structure–function relationship. We will focus on the so-called “red antenna states” of cyanobacterial PSI, as these states play an important role in photochemical processes and EET pathways. The high-resolution data and modeling studies presented here provide additional information on the energetics of the lowest energy states and their chlorophyll (Chl) compositions, as well as the EET pathways and how they are altered by mutations. We present evidence that the low-energy traps observed in PSI are excitonically coupled states with significant charge-transfer (CT) character. The analysis presented for various optical spectra of PSI₃ and PSI₃-IsiA₁₈ supercomplexes allowed us to make inferences about EET from the IsiA₁₈ ring to the PSI₃ core and demonstrate that the number of entry points varies between sample preparations studied by different groups. In our most recent samples, there most likely are three entry points for EET from the IsiA₁₈ ring per the PSI core monomer, with two of these entry points likely being located next to each other. Therefore, there are nine entry points from the IsiA₁₈ ring to the PSI₃ trimer. We anticipate that the data discussed below will stimulate further research in this area, providing even more insight into the structure-based models of these important cyanobacterial photosystems. Full article

(This article belongs to the Special Issue New Insights into Photosystem I)

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