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Journal of the American Chemical Society Jun 2024Understanding how water ligands regulate the conformational changes and functionality of the oxygen-evolving complex (OEC) in photosystem II (PSII) throughout the...
Understanding how water ligands regulate the conformational changes and functionality of the oxygen-evolving complex (OEC) in photosystem II (PSII) throughout the catalytic cycle of oxygen evolution remains a highly intriguing and unresolved challenge. In this study, we investigate the effect of water insertion (WI) on the redox state of the OEC by using the molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) hybrid methods. We find that water binding significantly reduces the free energy change for proton-coupled electron transfer (PCET) from Mn to Y, underscoring the important regulatory role of water binding, which is essential for enabling the OEC redox-leveling mechanism along the catalytic cycle. We propose a water binding mechanism in which WI is thermodynamically favored by the closed-cubane form of the OEC, with water delivery mediated by Ca ligand exchange. Isomerization from the closed- to open-cubane conformation at three post-WI states highlights the importance of the location of the Mn center in the OEC and the orientation of its Jahn-Teller axis to conformational changes of the OEC, which might be critical for the formation of the O-O bond. These findings reveal a complex interplay between conformational changes in the OEC and the ligand environment during the activation of the OEC by Y. Analogous regulatory effects due to water ligand binding are expected to be important for a wide range of catalysts activated by redox state transitions in aqueous environments.
Topics: Photosystem II Protein Complex; Oxidation-Reduction; Water; Ligands; Oxygen; Molecular Dynamics Simulation; Thermodynamics; Quantum Theory
PubMed: 38833517
DOI: 10.1021/jacs.4c02926 -
Nature Chemical Biology Jul 2024Natural photosystems couple light harvesting to charge separation using a 'special pair' of chlorophyll molecules that accepts excitation energy from the antenna and...
Natural photosystems couple light harvesting to charge separation using a 'special pair' of chlorophyll molecules that accepts excitation energy from the antenna and initiates an electron-transfer cascade. To investigate the photophysics of special pairs independently of the complexities of native photosynthetic proteins, and as a first step toward creating synthetic photosystems for new energy conversion technologies, we designed C-symmetric proteins that hold two chlorophyll molecules in closely juxtaposed arrangements. X-ray crystallography confirmed that one designed protein binds two chlorophylls in the same orientation as native special pairs, whereas a second designed protein positions them in a previously unseen geometry. Spectroscopy revealed that the chlorophylls are excitonically coupled, and fluorescence lifetime imaging demonstrated energy transfer. The cryo-electron microscopy structure of a designed 24-chlorophyll octahedral nanocage with a special pair on each edge closely matched the design model. The results suggest that the de novo design of artificial photosynthetic systems is within reach of current computational methods.
Topics: Chlorophyll; Crystallography, X-Ray; Models, Molecular; Photosynthesis; Energy Transfer; Cryoelectron Microscopy; Protein Conformation; Light-Harvesting Protein Complexes
PubMed: 38831036
DOI: 10.1038/s41589-024-01626-0 -
Chem May 2024Natural light-harvesting systems spatially organize densely packed dyes in different configurations to either transport excitons or convert them into charge...
Natural light-harvesting systems spatially organize densely packed dyes in different configurations to either transport excitons or convert them into charge photoproducts, with high efficiency. In contrast, artificial photosystems like organic solar cells and light-emitting diodes lack this fine structural control, limiting their efficiency. Thus, biomimetic multi-dye systems are needed to organize dyes with the sub-nanometer spatial control required to sculpt resulting photoproducts. Here, we synthesize 11 distinct perylene diimide (PDI) dimers integrated into DNA origami nanostructures and identify dimer architectures that offer discrete control over exciton transport versus charge separation. The large structural-space and site-tunability of origami uniquely provides controlled PDI dimer packing to form distinct excimer photoproducts, which are sensitive to interdye configurations. In the future, this platform enables large-scale programmed assembly of dyes mimicking natural systems to sculpt distinct photophysical products needed for a broad range of optoelectronic devices, including solar energy converters and quantum information processors.
PubMed: 38827435
DOI: 10.1016/j.chempr.2024.03.007 -
Frontiers in Plant Science 2024Cyanobacteria respond to iron limitation by producing the pigment-protein complex IsiA, forming rings associated with photosystem I (PSI). Initially considered a...
Cyanobacteria respond to iron limitation by producing the pigment-protein complex IsiA, forming rings associated with photosystem I (PSI). Initially considered a chlorophyll-storage protein, IsiA is known to act as an auxiliary light-harvesting antenna of PSI, increasing its absorption cross-section and reducing the need for iron-rich PSI core complexes. Spectroscopic studies have demonstrated efficient energy transfer from IsiA to PSI. Here we investigate the room-temperature excitation dynamics in isolated PSI-IsiA, PSI, IsiA monomer complexes and IsiA aggregates using two-dimensional electronic spectroscopy. Cross analyses of the data from these three samples allow us to resolve components of energy transfer between IsiA and PSI with lifetimes of 2-3 ps and around 20 ps. Structure-based Förster theory calculations predict a single major timescale of IsiA-PSI equilibration, that depends on multiple energy transfer routes between different IsiA subunits in the ring. Despite the experimentally observed lifetime heterogeneity, which is attributed to structural heterogeneity of the supercomplexes, IsiA is found to be a unique, highly efficient, membrane antenna complex in cyanobacteria.
PubMed: 38817933
DOI: 10.3389/fpls.2024.1393886 -
Journal of Biosciences 2024ATP-uncoupling alternative oxidase (AOX) in the plant respiratory chain is often induced under stress conditions such as low temperature (LT). The importance of AOX in...
ATP-uncoupling alternative oxidase (AOX) in the plant respiratory chain is often induced under stress conditions such as low temperature (LT). The importance of AOX in photosynthesis has been examined, and leaves having larger amounts of AOX tended to show larger decrease in photosynthetic electron transport rate (ETR) by AOX inhibition. However, the details were not clarified. Here, we used three ecotypes of which differed in AOX amounts and their responses to LT, and examined whether AOX amount was related to the degree of decrease in ETR by AOX inhibition. In Tiv-0, which originates from a warmer site, grown at high temperature (HT), AOX inhibition decreased ETR, but not in the other ecotypes. LT treatment significantly increased ETR and AOX, especially in Bur-0, but AOX inhibition did not decrease ETR in LT plants of any ecotype. AOX inhibition significantly increased the non-regulated energy dissipation in photosystem II (PSII), Y(NO), and decreased the maximal quantum yield of PSII, F/F, especially in LT plants. Since AOX inhibition did not affect the parameters of PSI, AOX inhibition may directly affect the reaction center of PSII in LT plants.
Topics: Arabidopsis; Oxidoreductases; Mitochondrial Proteins; Electron Transport; Photosynthesis; Plant Leaves; Photosystem II Protein Complex; Plant Proteins; Cold Temperature; Mitochondria
PubMed: 38817160
DOI: No ID Found -
Structure of plant photosystem I in a native assembly state defines PsaF as a regulatory checkpoint.Nature Plants Jun 2024Plant photosystem I (PSI) consists of at least 13 nuclear-encoded and 4 chloroplast-encoded subunits that together act as a sunlight-driven oxidoreductase. Here we...
Plant photosystem I (PSI) consists of at least 13 nuclear-encoded and 4 chloroplast-encoded subunits that together act as a sunlight-driven oxidoreductase. Here we report the structure of a PSI assembly intermediate that we isolated from greening oat seedlings. The assembly intermediate shows an absence of at least eight subunits, including PsaF and LHCI, and lacks photoreduction activity. The data show that PsaF is a regulatory checkpoint that promotes the assembly of LHCI, effectively coupling biogenesis to function.
Topics: Photosystem I Protein Complex; Avena; Plant Proteins; Light-Harvesting Protein Complexes; Seedlings
PubMed: 38816499
DOI: 10.1038/s41477-024-01699-8 -
BMC Plant Biology May 2024Nutritional disorders of phosphorus (P), due to deficiency or toxicity, reduce the development of Eucalyptus spp. seedlings. Phosphorus deficiency often results in...
BACKGROUND
Nutritional disorders of phosphorus (P), due to deficiency or toxicity, reduce the development of Eucalyptus spp. seedlings. Phosphorus deficiency often results in stunted growth and reduced vigor, while phosphorus toxicity can lead to nutrient imbalances and decreased physiological function. These sensitivities highlight the need for precise management of P levels in cultivation practices. The use of the beneficial element silicon (Si) has shown promising results under nutritional stress; nevertheless, comprehensive studies on its effects on Eucalyptus spp. seedlings are still emerging. To further elucidate the role of Si under varying P conditions, an experiment was conducted with clonal seedlings of a hybrid Eucalyptus spp. (Eucalyptus grandis × Eucalyptus urophylla, A207) in a soilless cultivation system. Seedlings were propagated using the minicutting method in vermiculite-filled tubes, followed by treatment with a nutrient solution at three P concentrations: a deficient dose (0.1 mM), an adequate dose (1.0 mM) and an excessive dose (10 mM), with and without the addition of Si (2mM). This study assessed P and Si concentration, nutritional efficiency, oxidative metabolism, photosynthetic parameters, and dry matter production.
RESULTS
Si supply increased phenolic compounds production and reduced electrolyte leakage in seedlings provided with 0.1 mM of P. On the other hand, Si favored quantum efficiency of photosystem II as well as chlorophyll a content in seedlings supplemented with 10 mM of P. In general, Si attenuates P nutritional disorder by reducing the oxidative stress, favoring the non-enzymatic antioxidant system and photosynthetic parameters in seedlings of Eucalyptus grandis × Eucalyptus urophylla.
CONCLUSION
The results of this study indicate that Eucalyptus grandis × Eucalyptus urophylla seedlings are sensitive to P deficiency and toxicity and Si has shown a beneficial effect, attenuating P nutritional disorder by reducing the oxidative stress, favoring the non-enzymatic antioxidant system and photosynthetic parameters.
Topics: Eucalyptus; Seedlings; Silicon; Phosphorus; Photosynthesis; Antioxidants; Chlorophyll; Oxidative Stress
PubMed: 38811870
DOI: 10.1186/s12870-024-05147-9 -
Pest Management Science May 2024This study investigates factors contributing Amaranthus albus control failure in processing tomato fields in northern Israel. The study region is characterized by a...
Unraveling the reasons for failure to control Amaranthus albus: insights into herbicide application at different growth stages, temperature effect, and herbicide resistance on a regional scale.
BACKGROUND
This study investigates factors contributing Amaranthus albus control failure in processing tomato fields in northern Israel. The study region is characterized by a significant climate gradient from east to west, providing the opportunity to investigate the effect of critical elements of the agricultural environment, e.g., temperature. Eight populations were collected from commercial fields in this region. Post-emergence herbicide efficacy of metribuzin, a photosystem II inhibitor, and rimsulfuron, an acetolactate synthase (ALS) inhibitor, was assessed through dose-response analyses at various growth stages. Temperature effects on control efficacy and resistance mechanisms were also explored.
RESULTS
Standard metribuzin dose (X) was ineffective on A. albus plants with more than six true-leaves, whereas 2X dose proved effective. Rimsulfuron at 16X dose was ineffective on plants with more than four true-leaves. We report here the first case of target site resistance to ALS inhibitors in A. albus, due to point mutation in the ALS gene (Pro197 to Leu). Furthermore, our findings suggest potential involvement of CYT P450 enzymes in enhanced metabolizing of rimsulfuron. An overall decrease in dry weight was observed in response to both herbicides at 16/22 °C (P < 0.0001). Rimsulfuron was effective against only one population when applied at 28/34 °C. A possible fitness cost associated with target site-resistant biotypes was observed under low temperature conditions, leading to effective control.
CONCLUSION
This regional-scale study highlights the challenges faced by growers, emphasizes the need for adapting management practices to the local climatic conditions and lays the groundwork for implementing location-specific weed management strategies in commercial fields. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
PubMed: 38809094
DOI: 10.1002/ps.8192 -
Nature Communications May 2024Cryptophyte algae are an evolutionarily distinct and ecologically important group of photosynthetic unicellular eukaryotes. Photosystem II (PSII) of cryptophyte algae...
Cryptophyte algae are an evolutionarily distinct and ecologically important group of photosynthetic unicellular eukaryotes. Photosystem II (PSII) of cryptophyte algae associates with alloxanthin chlorophyll a/c-binding proteins (ACPs) to act as the peripheral light-harvesting system, whose supramolecular organization is unknown. Here, we purify the PSII-ACPII supercomplex from a cryptophyte alga Chroomonas placoidea (C. placoidea), and analyze its structure at a resolution of 2.47 Å using cryo-electron microscopy. This structure reveals a dimeric organization of PSII-ACPII containing two PSII core monomers flanked by six symmetrically arranged ACPII subunits. The PSII core is conserved whereas the organization of ACPII subunits exhibits a distinct pattern, different from those observed so far in PSII of other algae and higher plants. Furthermore, we find a Chl a-binding antenna subunit, CCPII-S, which mediates interaction of ACPII with the PSII core. These results provide a structural basis for the assembly of antennas within the supercomplex and possible excitation energy transfer pathways in cryptophyte algal PSII, shedding light on the diversity of supramolecular organization of photosynthetic machinery.
Topics: Photosystem II Protein Complex; Cryptophyta; Cryoelectron Microscopy; Chlorophyll; Chlorophyll Binding Proteins; Protein Multimerization; Chlorophyll A; Models, Molecular; Light-Harvesting Protein Complexes
PubMed: 38806516
DOI: 10.1038/s41467-024-48878-x -
The Journal of Physical Chemistry... Jun 2024Density functional theory calculated N hyperfine couplings are obtained for the Mn1 ligated π-N of residue His332 of the photosystem 2 water oxidizing complex. An open...
Density functional theory calculated N hyperfine couplings are obtained for the Mn1 ligated π-N of residue His332 of the photosystem 2 water oxidizing complex. An open cubane, O4H, model closely matches the experimental coupling obtained for the high spin = 5/2 form of the S state, supporting an open cubane structure for this state. We also investigate the unusual geometric features for the S state obtained by X-ray free electron laser structure determinations and rationalize it as an equilibrium occurring at room temperature between W1/O4 deprotonated and protonated forms of the open cubane structure.
PubMed: 38804862
DOI: 10.1021/acs.jpclett.4c00997