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New Insights into Photosystem I

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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 July 2024 | Viewed by 2567

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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

Published Papers (5 papers)

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Research

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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

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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

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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

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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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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

Viewed by 165

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 467

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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