Kinetics of reformation of the S state capable of progressing to the S state after the O release by photosystem II.

The active site for water oxidation in photosystem II (PSII) comprises a MnCaO cluster adjacent to a redox-active tyrosine residue (Tyr). During the water-splitting process, the enzyme transitions through five sequential oxidation states (S to S), with O evolution occurring during the STyr· to STyr transition. Chloride also plays a role in this mechanism.

Absorption changes in Photosystem II in the Soret band region upon the formation of the chlorophyll cation radical [PP].

Flash-induced absorption changes in the Soret region arising from the [PP] state, the chlorophyll cation radical formed upon light excitation of Photosystem II (PSII), were measured in Mn-depleted PSII cores at pH 8.6. Under these conditions, Tyr is i) reduced before the first flash, and ii) oxidized before subsequent flashes.

Tuning of the Chl and Chl properties in photosystem II by site-directed mutagenesis of neighbouring amino acids.

Photosystem II is the water/plastoquinone photo-oxidoreductase of photosynthesis. The photochemistry and catalysis occur in a quasi-symmetrical heterodimer, D1D2, that evolved from a homodimeric ancestor. Here, we studied site-directed mutants in PSII from the thermophilic cyanobacterium Thermosynechoccocus elongatus, focusing on the primary electron donor chlorophyll a in D1, Chl, and on its symmetrical counterpart in D2, Chl, which does not play a direct photochemical role.

Energetics and proton release in photosystem II from Thermosynechococcus elongatus with a D1 protein encoded by either the psbA or psbA gene.

In the cyanobacterium Thermosynechococcus elongatus, there are three psbA genes coding for the Photosystem II (PSII) D1 subunit that interacts with most of the main cofactors involved in the electron transfers. Recently, the 3D crystal structures of both PsbA2-PSII and PsbA3-PSII have been solved [Nakajima et al., J.

Crystal structures of photosystem II from a cyanobacterium expressing psbA in comparison to psbA reveal differences in the D1 subunit.

Three psbA genes (psbA, psbA, and psbA) encoding the D1 subunit of photosystem II (PSII) are present in the thermophilic cyanobacterium Thermosynechococcus elongatus and are expressed differently in response to changes in the growth environment. To clarify the functional differences of the D1 protein expressed from these psbA genes, PSII dimers from two strains, each expressing only one psbA gene (psbA or psbA), were crystallized, and we analyzed their structures at resolutions comparable to previously studied PsbA1-PSII. Our results showed that the hydrogen bond between pheophytin/D1 (Pheo) and D1-130 became stronger in PsbA2- and PsbA3-PSII due to change of Gln to Glu, which partially explains the increase in the redox potential of Pheo observed in PsbA3.

Probing the proton release by Photosystem II in the S to S high-spin transition.

The stoichiometry and kinetics of the proton release were investigated during each transition of the S-state cycle in Photosystem II (PSII) from Thermosynechococcus elongatus containing either a MnCaO (PSII/Ca) or a MnSrO (PSII/Sr) cluster. The measurements were done at pH 6.0 and pH 7.

Properties of Photosystem II lacking the PsbJ subunit.

Photosystem II (PSII), the oxygen-evolving enzyme, consists of 17 trans-membrane and 3 extrinsic membrane proteins. Other subunits bind to PSII during assembly, like Psb27, Psb28, and Tsl0063. The presence of Psb27 has been proposed (Zabret et al.

Probing the role of arginine 323 of the D1 protein in photosystem II function.

The Mn CaO cluster of photosystem II (PSII) advances sequentially through five oxidation states (S to S ). Under the enzyme cycle, two water molecules are oxidized, O is generated and four protons are released into the lumen. Umena et al.

What can we still learn from the electrochromic band-shifts in Photosystem II?

Electrochromic band-shifts have been investigated in Photosystem II (PSII) from Thermosynechoccocus elongatus. Firstly, by using Mn-depleted PsbA1-PSII and PsbA3-PSII in which the Q absorption of Phe differs, a band-shift in the Q region of Phe centered at ~ 544 nm has been identified upon the oxidation, at pH 8.6, of Tyr.

Proton Release Process during the S-to-S Transition of Photosynthetic Water Oxidation As Revealed by the pH Dependence of Kinetics Monitored by Time-Resolved Infrared Spectroscopy.

Photosynthetic water oxidation takes place at the MnCaO cluster in photosystem II via a light-driven cycle of intermediates called S states (S-S). Clarifying how electron and proton transfer reactions are coupled with each other in the S → S transition, which occurs just before O-O bond formation, is crucial for understanding the water oxidation mechanism. Here, we investigated the pH dependence of the kinetics of the S → S transition using time-resolved infrared (TRIR) spectroscopy to identify the proton release phase in this transition.

An alternative plant-like cyanobacterial ferredoxin with unprecedented structural and functional properties.

Photosynthetic [2Fe-2S] plant-type ferredoxins have a central role in electron transfer between the photosynthetic chain and various metabolic pathways. Several genes are coding for [2Fe2S] ferredoxins in cyanobacteria, with four in the thermophilic cyanobacterium Thermosynechococcus elongatus. The structure and functional properties of the major ferredoxin Fd1 are well known but data on the other ferredoxins are scarce.

New insights on Chl function in Photosystem II from site-directed mutants of D1/T179 in Thermosynechococcus elongatus.

The monomeric chlorophyll, Chl, which is located between the PP chlorophyll pair and the pheophytin, Pheo is the longest wavelength chlorophyll in the heart of Photosystem II and is thought to be the primary electron donor. Its central Mg is liganded to a water molecule that is H-bonded to D1/T179. Here, two site-directed mutants, D1/T179H and D1/T179V, were made in the thermophilic cyanobacterium, Thermosynechococcus elongatus, and characterized by a range of biophysical techniques.

Probing the role of Valine 185 of the D1 protein in the Photosystem II oxygen evolution.

In Photosystem II (PSII), the MnCaO-cluster of the active site advances through five sequential oxidation states (S to S) before water is oxidized and O is generated. The V185 of the D1 protein has been shown to be an important amino acid in PSII function (Dilbeck et al. Biochemistry 52 (2013) 6824-6833).

Mechanism of Proton-Coupled Electron Transfer in the S-to-S Transition of Photosynthetic Water Oxidation As Revealed by Time-Resolved Infrared Spectroscopy.

Photosynthetic water oxidation takes place at the MnCaO cluster in photosystem II through a light-driven cycle of intermediates called S states (S-S). To unravel the mechanism of water oxidation, it is essential to understand the coupling of electron- and proton-transfer reactions during the S-state transitions. Here, we monitored the reaction process in the S → S transition using time-resolved infrared (TRIR) spectroscopy.

Consequences of structural modifications in cytochrome b on the electron acceptor side of Photosystem II.

Cytb in Photosystem II is a heterodimeric b-type cytochrome. The subunits, PsbE and PsbF, consist each in a membrane α-helix. Mutants were previously designed and studied in Thermosynechococcus elongatus (Sugiura et al.

Dimer-monomer equilibrium of human HSP27 is influenced by the in-cell macromolecular crowding environment and is controlled by fatty acids and heat.

Small heat shock protein 27 (HSP27) is an essential element of the proteostasis network in human cells. The HSP27 monomer coexists with the dimer, which can bind unfolded client proteins. Here, we evaluated the in-cell dimer-monomer equilibrium and its relevance to the binding of client proteins in a normal human vascular endothelial cell line.

The low spin - high spin equilibrium in the S-state of the water oxidizing enzyme.

In Photosystem II (PSII), the MnCaO-cluster of the active site advances through five sequential oxidation states (S to S) before water is oxidized and O is generated. Here, we have studied the transition between the low spin (LS) and high spin (HS) configurations of S using EPR spectroscopy, quantum chemical calculations using Density Functional Theory (DFT), and time-resolved UV-visible absorption spectroscopy. The EPR experiments show that the equilibrium between S and S is pH dependent, with a pK ≈ 8.

Crystal structure and redox properties of a novel cyanobacterial heme protein with a His/Cys heme axial ligation and a Per-Arnt-Sim (PAS)-like domain.

Photosystem II catalyzes light-induced water oxidation leading to the generation of dioxygen indispensable for sustaining aerobic life on Earth. The Photosystem II reaction center is composed of D1 and D2 proteins encoded by and genes, respectively. In cyanobacteria, different genes are present in the genome.

Corrigendum to "Influence of Histidine-198 of the D1 subunit on the properties of the primary electron donor, P, of photosystem II in Thermosynechococcus elongatus".

Two mutants, D1-H198Q and D1-H198A, have been previously constructed in Thermosynechococcus elongatus with the aim at modifying the redox potential of the P/P couple by changing the axial ligand of P, one the two chlorophylls of the Photosystem II primary electron donor [Sugiura et al., Biochim. Biophys.

Electron transfer pathways from the S2-states to the S3-states either after a Ca2+/Sr2+ or a Cl-/I- exchange in Photosystem II from Thermosynechococcus elongatus.

The site for water oxidation in Photosystem II (PSII) goes through five sequential oxidation states (S0 to S4) before O2 is evolved. It consists of a Mn4CaO5-cluster close to a redox-active tyrosine residue (YZ). Cl- is also required for enzyme activity.

Assembly of oxygen-evolving Photosystem II efficiently occurs with the apo-Cytb559 but the holo-Cytb559 accelerates the recovery of a functional enzyme upon photoinhibition.

Cytb559 in Photosystem II is a heterodimeric b-type cytochrome. The subunits, PsbE and PsbF, consist each in a membrane α-helix. Roles for Cytb559 remain elusive.

The D1-173 amino acid is a structural determinant of the critical interaction between D1-Tyr161 (TyrZ) and D1-His190 in Photosystem II.

The main cofactors of Photosystem II (PSII) are borne by the D1 and D2 subunits. In the thermophilic cyanobacterium Thermosynechococcus elongatus, three psbA genes encoding D1 are found in the genome. Among the 344 residues constituting the mature form of D1, there are 21 substitutions between PsbA1 and PsbA3, 31 between PsbA1 and PsbA2, and 27 between PsbA2 and PsbA3.

Some Photosystem II properties depending on the D1 protein variants in Thermosynechococcus elongatus.

Cyanobacteria have multiple psbA genes encoding PsbA, the D1 reaction center protein of the Photosystem II complex which bears together with PsbD, the D2 protein, most of the cofactors involved in electron transfer reactions. The thermophilic cyanobacterium Thermosynechococcus elongatus has three psbA genes differently expressed depending on the environmental conditions. Among the 344 residues constituting each of the 3 possible PsbA variants there are 21 substitutions between PsbA1 and PsbA3, 31 between PsbA1 and PsbA2 and 27 between PsbA2 and PsbA3.

Evidence for an unprecedented histidine hydroxyl modification on D2-His336 in Photosystem II of Thermosynechoccocus vulcanus and Thermosynechoccocus elongatus.

The electron density map of the 3D crystal of Photosystem II from Thermosynechococcus vulcanus with a 1.9 Å resolution (PDB: 3ARC ) exhibits, in the two monomers in the asymmetric unit cell, an, until now, unidentified and uninterpreted strong difference in electron density centered at a distance of around 1.5 Å from the nitrogen Nδ of the imidazole ring of D2-His336.