Redox properties and regulatory mechanism of the iron-quinone electron acceptor in photosystem II as revealed by FTIR spectroelectrochemistry

Kato, Yuki; Noguchi, Takumi

doi:10.1007/s11120-021-00894-4

Cited by 13 publications

(12 citation statements)

References 91 publications

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“…PCC 6803. Light-induced FTIR difference spectroscopy is a powerful method to investigate the structures and reactions of cofactors in PSII. − For Chl molecules, the 13 1 -keto CO stretching vibrations, which have strong infrared intensities and are sensitive to hydrogen bond interactions, , have been used as useful markers to study the interactions in proteins. ,,,, We measured triplet-minus-singlet (T 1 /S 0 ) FTIR difference spectra with the PSII core complexes from the D1-V157H, D2-V156H, D2-H197A, and D1-H198A mutants, in which the hydrogen-bond interactions at the 13 1 -keto CO groups of P D1 , P D2 , Chl D1 , and Chl D2 , respectively, are expected to be perturbed, and compared with the spectrum of the wild-type (WT) PSII complexes. It was previously shown that the replacement of D1-V157 and D2-V156 with a His residue introduced weak and strong hydrogen bonds to the 13 1 -keto CO groups of P D1 and P D2 , respectively (Figure b), by detecting P680 + /P680, Y Z • /Y Z , and Y D • /Y D FTIR difference spectra .…”

Section: Introductionmentioning

confidence: 99%

Triplet Delocalization over the Reaction Center Chlorophylls in Photosystem II

et al. 2023

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The triplet state of chlorophyll formed by charge recombination in photosystem II (PSII) is a precursor of harmful singlet oxygen. Although main localization of the triplet state on the monomeric chlorophyll, ChlD1, at cryogenic temperatures has been suggested, how the triplet state is delocalized on other chlorophylls remains unclear. Here, we investigated the distribution of the triplet state of chlorophyll in PSII using light-induced Fourier transform infrared (FTIR) difference spectroscopy. Measurements of triplet-minus-singlet FTIR difference spectra with PSII core complexes from cyanobacterial mutants, D1-V157H, D2-V156H, D2-H197A, and D1-H198A, in which the interactions of the 131-keto CO groups of the reaction center chlorophylls, PD1, PD2, ChlD1, and ChlD2, respectively, were perturbed, identified the 131-keto CO bands of the individual chlorophylls and showed that the triplet state is delocalized over all of these chlorophylls. It is suggested that the triplet delocalization plays important roles in the photoprotection and photodamage mechanisms in PSII.

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Section: Introductionmentioning

confidence: 99%

Triplet Delocalization over the Reaction Center Chlorophylls in Photosystem II

et al. 2023

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“…The exact cause of this change in the E m (Q A − / Q A ) is unknown at present, but it can be speculated that the change in the hydrogen bond interaction of Q B is propagated to the Q A interaction. Indeed, it has been shown that different types of herbicide bound at the Q B site induced the change in E m (Q A − /Q A ), 22,44,45 accompanied with the change in the hydrogen bond interaction of Q A . 46 The previous theoretical study also showed the presence of such propagation of the interaction from the Q B to the Q A site.…”

Section: ■ Discussionmentioning

confidence: 99%

“…It has been shown that this Q B – relaxation is significantly accelerated at high pH, although the relaxation of Q A – is rather insensitive to pH. − This phenomenon indicates that the redox reaction of Q B is strongly coupled with the protonation/deprotonation reaction of a nearby titratable group. The p K a ’s of this group were estimated to be 6.2–6.7 and 7.5–8.1 in the neutral Q B and anionic Q B – states, respectively. ,, It has been suggested that this pH dependence of the Q B – relaxation is a feedback regulation of the electron flow in PSII, in which a pH increase at the stroma by excessive photoreactions downshifts the redox potential ( E m ) of the Q B – /Q B couple [ E m (Q B – /Q B )] to accelerate the relaxation of Q B – by shifting the redox equilibrium between Q A – and Q B – to the Q A – side. , …”

Section: Introductionmentioning

confidence: 99%

“…The pK a 's of this group were estimated to be 6.2−6.7 and 7.5−8.1 in the neutral Q B and anionic Q B − states, respectively. 3,18,21 It has been suggested that this pH dependence of the Q B − relaxation is a feedback regulation of the electron flow in PSII, in which a pH increase at the stroma by excessive photoreactions downshifts the redox potential (E m ) of the Q 21,22 The titratable group responsible for the pH dependence of the E m (Q B − /Q B ) is predicted to be an imidozole group of histidine from the observed pK a values of 6−8. D1-H252, which interacts with the distal oxygen of Q B through D1-S264, has been suggested as a primary candidate.…”

Section: ■ Introductionmentioning

confidence: 99%

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pH-Dependent Regulation of Electron Flow in Photosystem II by a Histidine Residue at the Stromal Surface

et al. 2022

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In photosystem II (PSII), the secondary plastoquinone electron acceptor QB functions as a substrate that converts into plastoquinol upon its double reduction by electrons abstracted from water. It has been suggested that a histidine residue, D1-H252, which is located at the stromal surface near QB, is involved in the pH-dependent regulation of electron flow and proton transfer to QB. However, definitive evidence for the involvement of D1-H252 in the QB reactions has not been obtained yet. Here, we studied the roles of D1-H252 in PSII using a cyanobacterial mutant, in which D1-H252 was replaced with Ala. Delayed luminescence (DL) measurement upon a single flash showed a faster QB – decay at higher pH in the thylakoids from the wild-type strain due to the downshift of the redox potential of QB [E m(QB –/QB)]. This pH dependence of the QB – decay was lost in the D1-H252A mutant. The experimental E m(QB –/QB) changes were well reproduced by the density functional theory calculations for models with different protonation states of D1-H252 and with Ala replaced for H252. It was further shown that the period-four oscillation of the DL intensity by successive flashes was significantly diminished in the D1-H252A mutant, suggesting the inhibition of plastoquinone exchange at the QB pocket in this mutant. It is thus concluded that D1-H252 is a key amino acid residue that regulates electron flow in PSII by sensing pH in the stroma and stabilizes the QB binding site to facilitate the quinone exchange reaction.

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“…The resulting Q A – then transfers its electron to a bound secondary plastoquinone (Q B ) to form the stable semiquinone anion. Upon absorption of a second photon the sequence repeats, and Q B undergoes protonation to form plastoquinol (PQH 2 ). − The reduced PQH 2 is released from the Q B -binding site, and a new plastoquinone (PQ) from a PQ pool replaces it to complete the full cycle. , The oxidized primary donor is reduced by electrons from the Mn 4 CaO 5 oxygen-evolving complex (OEC) with dioxygen formed by the oxidation of two water molecules following four successive turnovers of the reaction center. , …”

Section: Introductionmentioning

confidence: 99%

Tyr244 of the D2 Protein Is Required for Correct Assembly and Operation of the Quinone-Iron-Bicarbonate Acceptor Complex of Photosystem II

et al. 2022

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Two plastoquinone electron acceptors, QA and QB, are present in Photosystem II (PS II) with their binding sites formed by the D2 and D1 proteins, respectively. A hexacoordinate non-heme iron is bound between QA and QB by D2 and D1, each providing two histidine ligands, and a bicarbonate that is stabilized via hydrogen bonds with D2-Tyr244 and D1-Tyr246. Both tyrosines and bicarbonate are conserved in oxygenic photosynthetic organisms but absent from the corresponding quinone-iron electron acceptor complex of anoxygenic photosynthetic bacteria. We investigated the role of D2-Tyr244 by introducing mutations in the cyanobacterium Synechocystis sp. PCC 6803. Alanine, histidine, and phenylalanine substitutions were introduced creating the Y244A, Y244H, and Y244F mutants. Electron transfer between QA and QB was impaired, the back-reaction with the S2 state of the oxygen-evolving complex was modified, and PS II assembly was disrupted, with the Y244A strain being more affected than the Y244F and Y244H mutants. The strains were also highly susceptible to photodamage in the presence of PS II-specific electron acceptors. Thermoluminescence and chlorophyll a fluorescence decay measurements indicated that the redox potential of the QA/QA – couple became more positive in the Y244F and Y244H mutants, consistent with bicarbonate binding being impacted. The replacement of Tyr244 by alanine also led to an insertion of two amino acid repeats from Gln239 to Ala249 within the DE loop of D2, resulting in an inactive PS II complex that lacked PS II-specific variable fluorescence. The 66 bp insertion giving rise to the inserted amino acids therefore created an obligate photoheterotrophic mutant.

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Redox properties and regulatory mechanism of the iron-quinone electron acceptor in photosystem II as revealed by FTIR spectroelectrochemistry

Cited by 13 publications

References 91 publications

Triplet Delocalization over the Reaction Center Chlorophylls in Photosystem II

Triplet Delocalization over the Reaction Center Chlorophylls in Photosystem II

pH-Dependent Regulation of Electron Flow in Photosystem II by a Histidine Residue at the Stromal Surface

Tyr244 of the D2 Protein Is Required for Correct Assembly and Operation of the Quinone-Iron-Bicarbonate Acceptor Complex of Photosystem II

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