Phe265 of the D1 protein is required to stabilize plastoquinone binding in the Q-binding site of photosystem II in Synechocystis sp. PCC 6803.

In Photosystem II electrons from water splitting pass through a primary quinone electron acceptor (Q) to the secondary plastoquinone (Q). The D2 protein forms the Q-binding site and the D1 protein forms the Q-binding site. A non-heme iron sits between Q and Q resulting in a quinone-Fe-acceptor complex that must be activated before assembly of the oxygen-evolving complex can occur.

Enhancing Photosynthesis and Plant Productivity through Genetic Modification.

Enhancing crop photosynthesis through genetic engineering technologies offers numerous opportunities to increase plant productivity. Key approaches include optimizing light utilization, increasing cytochrome complex levels, and improving carbon fixation. Modifications to Rubisco and the photosynthetic electron transport chain are central to these strategies.

Arg24 and 26 of the D2 protein are important for photosystem II assembly and plastoquinol exchange in Synechocystis sp. PCC 6803.

Photosystem II (PS II) assembly is a stepwise process involving preassembly complexes or modules focused around four core PS II proteins. The current model of PS II assembly in cyanobacteria is derived from studies involving the deletion of one or more of these core subunits. Such deletions may destabilize other PS II assembly intermediates, making constructing a clear picture of the intermediate events difficult.

International conference on "Photosynthesis and Hydrogen Energy Research for Sustainability-2023": in honor of Robert Blankenship, Győző Garab, Michael Grätzel, Norman Hüner and Gunnar Öquist.

The 11th International Photosynthesis Conference on Hydrogen Energy Research and Sustainability 2023 was organized in honor of Robert Blankenship, Győző Garab, Michael Grätzel, Norman Hüner, and Gunnar Öquist, in Istanbul, Türkiye at Bahçeşehir University Future Campus from 03 to 09 July 2023. It was jointly supported by the International Society of Photosynthesis Research (ISPR) and the International Association for Hydrogen Energy (IAHE). In this article we provide brief details of the conference, its events, keynote speakers, and the scientific contribution of scientists honored at this conference.

Indirect interactions involving the PsbM or PsbT subunits and the PsbO, PsbU and PsbV proteins stabilize assembly and activity of Photosystem II in Synechocystis sp. PCC 6803.

The low-molecular-weight PsbM and PsbT proteins of Photosystem II (PS II) are both located at the monomer-monomer interface of the mature PS II dimer. Since the extrinsic proteins are associated with the final step of assembly of an active PS II monomer and, in the case of PsbO, are known to impact the stability of the PS II dimer, we have investigated the potential cooperativity between the PsbM and PsbT subunits and the PsbO, PsbU and PsbV extrinsic proteins. Blue-native polyacrylamide electrophoresis and western blotting detected stable PS II monomers in the ∆PsbM:∆PsbO and ∆PsbT:∆PsbO mutants that retained sufficient oxygen-evolving activity to support reduced photoautotrophic growth.

Mutagenesis of Ile184 in the cd-loop of the photosystem II D1 protein modifies acceptor-side function via spontaneous mutation of D1-His252 in Synechocystis sp. PCC 6803.

The Photosystem II water-plastoquinone oxidoreductase is a multi-subunit complex which catalyses the light-driven oxidation of water to molecular oxygen in oxygenic photosynthesis. The D1 reaction centre protein exists in multiple forms in cyanobacteria, including D1 which is expressed under far-red light. We investigated the role of Phe184 that is found in the lumenal cd-loop of D1 but is typically an isoleucine in other D1 isoforms.

Expression of the far-red D1 protein or introduction of conserved far-red D1 residues into Synechocystis sp. PCC 6803 impairs Photosystem II.

The wavelengths of light harvested in oxygenic photosynthesis are ~400-700 nm. Some cyanobacteria respond to far-red light exposure via a process called far-red light photoacclimation which enables absorption of light at wavelengths >700 nm and its use to support photosynthesis. Far-red-light-induced changes include up-regulation of alternative copies of multiple proteins of Photosystem II (PS II).

Lys264 of the D2 Protein Performs a Dual Role in Photosystem II Modifying Assembly and Electron Transfer through the Quinone-Iron Acceptor Complex.

Bicarbonate (HCO) binding regulates electron flow between the primary (Q) and secondary (Q) plastoquinone electron acceptors of Photosystem II (PS II). Lys264 of the D2 subunit of PS II contributes to a hydrogen-bond network that stabilizes HCO ligation to the non-heme iron in the Q-Fe-Q complex. Using the cyanobacterium sp.

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

Two plastoquinone electron acceptors, Q and Q, 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 Q and Q 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.

PsbX maintains efficient electron transport in Photosystem II and reduces susceptibility to high light in Synechocystis sp. PCC 6803.

PsbX is a 4.1 kDa intrinsic Photosystem II (PS II) protein, found together with the low-molecular-weight proteins, PsbY and PsbJ, in proximity to cytochrome b. The function of PsbX is not yet fully characterized but PsbX may play a role in the exchange of the secondary plastoquinone electron acceptor Q with the quinone pool in the thylakoid membrane.

The PsbJ protein is required for photosystem II activity in centers lacking the PsbO and PsbV lumenal subunits.

Photosystem II (PS II) of oxygenic photosynthesis is found in the thylakoid membranes of plastids and cyanobacteria. The mature PS II complex comprises a central core of four membrane proteins that bind the majority of the redox-active cofactors. In cyanobacteria the central core is surrounded by 13 low-molecular-weight (LMW) subunits which each consist of one or two transmembrane helices.

The hydrophobicity of mutations targeting D1:Val219 modifies formate and diuron binding in the quinone-Fe-acceptor complex of Photosystem II.

The D1:Val219 residue of Photosystem II in the cyanobacterium Synechocystis sp. PCC 6803 was mutated to alanine or isoleucine, creating the V219A and V219I mutants, respectively. Oxygen evolution was slowed in these mutants, while chlorophyll a fluorescence induction assays indicated slowed electron transfer.

The Interaction between PsbT and the DE Loop of D1 in Photosystem II Stabilizes the Quinone-Iron Electron Acceptor Complex.

The X-ray-derived Photosystem II (PS II) structure from the thermophilic cyanobacterium (Protein Data Bank entry 4UB6) indicates Phe239 of the DE loop of the D1 protein forms a hydrophobic interaction with Pro27 and Ile29 at the C-terminus of the 5 kDa PsbT protein found at the monomer-monomer interface of the PS II dimer. To investigate the importance of this interaction, we created the F239A and F239L mutants in sp. PCC 6803 through targeted mutagenesis of the D1:Phe239 residue into either an alanine or a leucine.

The D1:Ser268 residue of Photosystem II contributes to an alternative pathway for Q protonation in the absence of bound bicarbonate.

Photosystem II catalyses the splitting of water and the reduction in plastoquinone in thylakoid membranes of all oxygenic photosynthetic organisms. The final step in quinol formation is protonation of the reduced secondary quinone electron acceptor to give Q H . The proton for this step is hypothesized to be provided by a hydrogen-bond network incorporating amino acids from the Photosystem II D1 and D2 reaction center proteins, together with several bound waters and a bicarbonate ion ligated to a non-heme iron found between the primary plastoquinone electron acceptor Q and Q .

The diversity and distribution of D1 proteins in cyanobacteria.

The psbA gene family in cyanobacteria encodes different forms of the D1 protein that is part of the Photosystem II reaction centre. We have identified a phylogenetically distinct D1 group that is intermediate between previously identified G3-D1 and G4-D1 proteins (Cardona et al. Mol Biol Evol 32:1310-1328, 2015).

Stabilization of Photosystem II by the PsbT protein impacts photodamage, repair and biogenesis.

Photosystem II (PS II) catalyzes the light-driven process of water splitting in oxygenic photosynthesis. Four core membrane-spanning proteins, including D1 that binds the majority of the redox-active co-factors, are surrounded by 13 low-molecular-weight (LMW) proteins. We previously observed that deletion of the LMW PsbT protein in the cyanobacterium Synechocystis sp.

International conference on "Photosynthesis and Hydrogen Energy Research for Sustainability-2019": in honor of Tingyun Kuang, Anthony Larkum, Cesare Marchetti, and Kimiyuki Satoh.

The 10th International Conference on «Photosynthesis and Hydrogen Energy Research for Sustainability-2019» was held in honor of Tingyun Kuang (China), Anthony Larkum (Australia), Cesare Marchetti (Italy), and Kimiyuki Satoh (Japan), in St. Petersburg (Russia) during June 23-28, 2019. The official conference organizers from the Russian side were from the Institute of Basic Biological Problems of the Russian Academy of Sciences (IBBP RAS), Russian Society for Photobiology (RSP), and the Komarov Botanical Institute of the Russian Academy of Sciences ([K]BIN RAS).

D1:Glu244 and D1:Tyr246 of the bicarbonate-binding environment of Photosystem II moderate high light susceptibility and electron transfer through the quinone-Fe-acceptor complex.

In cyanobacteria, Glu-244 and Tyr-246 of the Photosystem II (PS II) D1 protein are hydrogen bonded to two water molecules that are part of a hydrogen-bond network between the bicarbonate ligand to a non-heme iron and the cytosol. Ala substitutions were introduced in Synechocystis sp. PCC 6803 to investigate the roles of these residues and the hydrogen-bond network on electron transfer between the primary plastoquinone acceptor, Q, and the secondary plastoquinone acceptor, Q, of the quinone-Fe-acceptor complex.

Environmental pH and a Glu364 to Gln mutation in the chlorophyll-binding CP47 protein affect redox-active TyrD and charge recombination in Photosystem II.

In Photosystem II, loop E of the chlorophyll-binding CP47 protein is located near a redox-active tyrosine, Y , forming a symmetrical analog to loop E in CP43, which provides a ligand to the oxygen-evolving complex (OEC). A Glu364 to Gln substitution in CP47, near Y , does not affect growth in the cyanobacterium Synechocystis sp. PCC 6803; however, deletion of the extrinsic protein PsbV in this mutant leads to a strain displaying a pH-sensitive phenotype.

Environmental pH and the Requirement for the Extrinsic Proteins of Photosystem II in the Function of Cyanobacterial Photosynthesis.

In one of the final stages of cyanobacterial Photosystem II (PS II) assembly, binding of up to four extrinsic proteins to PS II stabilizes the oxygen-evolving complex (OEC). Growth of cyanobacterial mutants deficient in certain combinations of these thylakoid-lumen-associated polypeptides is sensitive to changes in environmental pH, despite the physical separation of the membrane-embedded PS II complex from the external environment. In this perspective we discuss the effect of environmental pH on OEC function and photoautotrophic growth in cyanobacteria with reference to pH-sensitive PS II mutants lacking extrinsic proteins.

Mutation of Gly195 of the ChlH Subunit of Mg-chelatase Reduces Chlorophyll and Further Disrupts PS II Assembly in a Ycf48-Deficient Strain of Synechocystis sp. PCC 6803.

Biogenesis of the photosystems in oxygenic phototrophs requires co-translational insertion of chlorophyll a. The first committed step of chlorophyll a biosynthesis is the insertion of a Mg(2+) ion into the tetrapyrrole intermediate protoporphyrin IX, catalyzed by Mg-chelatase. We have identified a Synechocystis sp.

Comparison of D1´- and D1-containing PS II reaction centre complexes under different environmental conditions in Synechocystis sp. PCC 6803.

In oxygenic photosynthesis, the D1 protein of Photosystem II is the primary target of photodamage and environmental stress can accelerate this process. The cyanobacterial response to stress includes transcriptional regulation of genes encoding D1, including low-oxygen-induction of psbA1 encoding the D1´ protein in Synechocystis sp. PCC 6803.