Biology subjects

selles, j.

Publications and source records attributed to selles, j..

3 recordsLinked to original sources

bioRxiv2024

New insights into the involvement of residue D1-V185 in Photosystem II function in Synechocystis 6803 and Thermosynechococcus vestitus.

The effects of D1-V185T and D1-V185N mutations in Photosystem II (PSII) from Thermosynechococcus vestitus (formerly T. elongatus) and Synechocystis 6803, respectively, were studied using both EPR and optical kinetics. EPR spectroscopy reveals the presence of a mixture of a S2 state in a high spin configuration (S2HS) and in a low spin configuration (S2LS) in both mutants. In contrast to the S2HS in the wild type, the S2HS state in the D1-V185T mutant does not progress to the S3 state at 198 K. This inability is likely due to alterations in the protonation state and hydrogen-bonding network around the Mn4CaO5 cluster. Optical studies show that these mutations significantly affect proton release during the S3-to-S0 transition. While the initial fast proton release associated with TyrZ[bullet] formation remains unaffected within the resolution of our measurements, the second, and slower, proton release is delayed, suggesting that the mutations disrupt the hydrogen-bonding interactions necessary for efficient deprotonation of substrate water (O6). This disruption in proton transfer also correlates with slower water exchange in the S3 state, likely due to non-native hydrogen bonds introduced by the threonine or asparagine side chains at position 185. These findings point to a critical role of D1-V185 in regulating both proton transfer dynamics and water binding, underscoring a complex interplay between structural and functional changes in PSII.

biophysics↗

bioRxiv2023

Energetics and proton release in Photosystem II from Thermosynechococcus elongatus with a D1 protein encoded by either the psbA2 or psbA3 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. Biol. Chem. 298 (2022) 102668.]. It was proposed that the loss of one hydrogen bond of PheD1 due to the D1-Y147F exchange in PsbA2-PSII resulted in a more negative Em of PheD1 in PsbA2-PSII when compared to PsbA3-PSII. In addition, the loss of two water molecules in the Cl-1 channel was attributed to the D1-P173M substitution in PsbA2-PSII. This exchange, by narrowing the Cl-1 proton channel, could be at the origin of a slowing down of the proton release. Here, we have continued the characterization of PsbA2- PSII by measuring the thermoluminescence from the S2QA-/DCMU charge recombination and by measuring proton release kinetics using time-resolved absorption changes of the dye bromocresol purple. It was found that i) the Em of PheD1-*/PheD1 was decreased by [~] 30 mV in PsbA2-PSII when compared to PsbA3-PSII and ii) the kinetics of the proton release into the bulk was significantly slowed down in PsbA2-PSII in the S2TyrZ* to S3TyrZ and S3TyrZ* [->] (S3TyrZ*) transitions. This slowing down was partially reversed by the PsbA2/M173P mutation and induced by the PsbA3/P173M mutation thus confirming a role of the D1-173 residue in the egress of protons trough the Cl-1 channel.

plant biology↗

bioRxiv2021

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, Tsl0063. The presence of Psb27 has been proposed (Zabret et al. 2021; Huang et al. 2021; Xiao et al. 2021) to prevent the binding of PsbJ, a single transmembrane -helix close to the quinone QB binding site. Consequently, a PSII rid of Psb27, Psb28 and Tsl0034 prior to the binding of PsbJ would logically correspond to an assembly intermediate. The present work describes experiments aiming at further characterizing such a {Delta}PsbJ-PSII, purified from the thermophilic Thermosynechococcus elongatus, by means of MALDI-TOF spectroscopy, Thermoluminescence, EPR spectroscopy and UV-visible time-resolved spectroscopy. In the purified {Delta}PsbJ-PSII, an active Mn4CaO5 cluster is present in 60-70 % of the centers. In these centers, although the forward electron transfer seems not affected, the Em of the QB/QB- couple increases by [≥] 120 mV thus disfavoring the electron coming back on QA. The increase of the energy gap between QA/QA- and QB/QB- could contribute in a protection against the charge recombination between the donor side and QB-, identified at the origin of photoinhibition under low light (Keren et al. 1997), and possibly during the slow photoactivation process.

biophysics↗