Two-dimensional HYSCORE spectroscopy reveals a histidine imidazole as the axial ligand to Chl3A in the M688HPsaA genetic variant of Photosystem I

Gorka, Michael; Gruszecki, Elijah; Charles, P. A.; Kalendra, Vidmantas; Lakshmi, K. V.; Golbeck, John H.

doi:10.1016/j.bbabio.2021.148424

Cited by 6 publications

(4 citation statements)

References 77 publications

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“…The removal of the A 1 cofactor by chemical treatment and/or interruption of phylloquinone biosynthesis could result in small perturbations of the protein environment. However, a recent study where forward ET was halted without altering the A 1 binding pocket also yielded identical hyperfine interactions in the A 0 $state and the spin density distribution of the A 0 $state in the current DFT calculations is not impacted by the presence or absence of the phylloquinone cofactor, A 1A (Gorka et al, 2021). Therefore, while there are inherent uncertainties associated with the chemical or genetic modification of PS I, it is clear that changes to the phylloquinone binding pocket do not impact the electronic properties of the A 0 $state.…”

Section: Discussionmentioning

confidence: 55%

A dimeric chlorophyll electron acceptor differentiates type I from type II photosynthetic reaction centers

et al. 2021

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This research addresses one of the most compelling issues in the field of photosynthesis, namely, the role of the accessory chlorophyll molecules in primary charge separation. Using a combination of empirical and computational methods, we demonstrate that the primary acceptor of photosystem (PS) I is a dimer of accessory and secondary chlorophyll molecules, Chl 2A and Chl 3A , with an asymmetric electron charge density distribution. The incorporation of highly coupled donors and acceptors in PS I allows for extensive delocalization that prolongs the lifetime of the charge-separated state, providing for high quantum efficiency. The discovery of this motif has widespread implications ranging from the evolution of naturally occurring reaction centers to the development of a new generation of highly efficient artificial photosynthetic systems.While the kinetics and thermodynamics of each ET step beyond A 0 are well characterized (

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Section: Discussionmentioning

confidence: 55%

A dimeric chlorophyll electron acceptor differentiates type I from type II photosynthetic reaction centers

et al. 2021

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“…•+ (Gorka et al, 2021b). The isotropic hyperfine couplings, A iso , range from 1.4-2.8 MHz, indicating that the electron spin is distributed on at least four nitrogen atoms.…”

Section: Continuous-wave and Pulsed Electron Paramagnetic Resonance Spectroscopy Measurementsmentioning

confidence: 99%

Shedding Light on Primary Donors in Photosynthetic Reaction Centers

et al. 2021

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Chlorophylls (Chl)s exist in a variety of flavors and are ubiquitous in both the energy and electron transfer processes of photosynthesis. The functions they perform often occur on the ultrafast (fs–ns) time scale and until recently, these have been difficult to measure in real time. Further, the complexity of the binding pockets and the resulting protein-matrix effects that alter the respective electronic properties have rendered theoretical modeling of these states difficult. Recent advances in experimental methodology, computational modeling, and emergence of new reaction center (RC) structures have renewed interest in these processes and allowed researchers to elucidate previously ambiguous functions of Chls and related pheophytins. This is complemented by a wealth of experimental data obtained from decades of prior research. Studying the electronic properties of Chl molecules has advanced our understanding of both the nature of the primary charge separation and subsequent electron transfer processes of RCs. In this review, we examine the structures of primary electron donors in Type I and Type II RCs in relation to the vast body of spectroscopic research that has been performed on them to date. Further, we present density functional theory calculations on each oxidized primary donor to study both their electronic properties and our ability to model experimental spectroscopic data. This allows us to directly compare the electronic properties of hetero- and homodimeric RCs.

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“…The A 0 ligand mutants of Met to Leu, Asn, and His of Synechocystis sp. PCC 6803 were generated and characterized [49,[55][56][57][58][59][60][61]. It was demonstrated that His could provide a ligand to A 0 in the Met → His substitutions [60].…”

Section: Introductionmentioning

confidence: 99%

“…PCC 6803 were generated and characterized [49,[55][56][57][58][59][60][61]. It was demonstrated that His could provide a ligand to A 0 in the Met → His substitutions [60]. The X-band spin-polarized transient EPR spectra of PS I trimers isolated from the A 0 Met → His mutants at 80 K showed that P700 + A 1A − radical pair of PsaA-M684H differed from the WT and PsaB-M659H, suggesting that PsaA-M684H provides an additional hydrogen bond to A 1A [49,60].…”

Section: Introductionmentioning

confidence: 99%

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

Luo,

Martin,

Tandoh

et al. 2024

IJMS

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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 Fx. 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.

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Two-dimensional HYSCORE spectroscopy reveals a histidine imidazole as the axial ligand to Chl3A in the M688HPsaA genetic variant of Photosystem I

Cited by 6 publications

References 77 publications

A dimeric chlorophyll electron acceptor differentiates type I from type II photosynthetic reaction centers

A dimeric chlorophyll electron acceptor differentiates type I from type II photosynthetic reaction centers

Shedding Light on Primary Donors in Photosynthetic Reaction Centers

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

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