A Protein Phosphorylation Threshold for Functional Stacking of Plant Photosynthetic Membranes

Phosphorylation of photosystem II (PSII) proteins affects macroscopic structure of thylakoid photosynthetic membranes in chloroplasts of the model plant Arabidopsis. In this study, light-scattering spectroscopy revealed that stacking of thylakoids isolated from wild type Arabidopsis and the mutant lacking STN7 protein kinase was highly influenced by cation (Mg++) concentrations. The stacking of thylakoids from the stn8 and stn7stn8 mutants, deficient in STN8 kinase and consequently in light-dependent phosphorylation of PSII, was increased even in the absence of Mg++. Additional PSII protein phosphorylation in wild type plants exposed to high light enhanced Mg++-dependence of thylakoid stacking. Protein phosphorylation in the plant leaves was analyzed during day, night and prolonged darkness using three independent techniques: immunoblotting with anti-phosphothreonine antibodies; Diamond ProQ phosphoprotein staining; and quantitative mass spectrometry of peptides released from the thylakoid membranes by trypsin. All assays revealed dark/night-induced increase in phosphorylation of the 43 kDa chlorophyll-binding protein CP43, which compensated for decrease in phosphorylation of the other PSII proteins in wild type and stn7, but not in the stn8 and stn7stn8 mutants. Quantitative mass spectrometry determined that every PSII in wild type and stn7 contained on average 2.5±0.1 or 1.4±0.1 phosphoryl groups during day or night, correspondingly, while less than every second PSII had a phosphoryl group in stn8 and stn7stn8. It is postulated that functional cation-dependent stacking of plant thylakoid membranes requires at least one phosphoryl group per PSII, and increased phosphorylation of PSII in plants exposed to high light enhances stacking dynamics of the photosynthetic membranes

High Light Induced Disassembly of Photosystem II Supercomplexes in Arabidopsis Requires STN7-Dependent Phosphorylation of CP29

Photosynthetic oxidation of water and production of oxygen by photosystem II (PSII) in thylakoid membranes of plant chloroplasts is highly affected by changes in light intensities. To minimize damage imposed by excessive sunlight and sustain the photosynthetic activity PSII, organized in supercomplexes with its light harvesting antenna, undergoes conformational changes, disassembly and repair via not clearly understood mechanisms. We characterized the phosphoproteome of the thylakoid membranes from Arabidopsis thaliana wild type, stn7, stn8 and stn7stn8 mutant plants exposed to high light. The high light treatment of the wild type and stn8 caused specific increase in phosphorylation of Lhcb4.1 and Lhcb4.2 isoforms of the PSII linker protein CP29 at five different threonine residues. Phosphorylation of CP29 at four of these residues was not found in stn7 and stn7stn8 plants lacking the STN7 protein kinase. Blue native gel electrophoresis followed by immunological and mass spectrometric analyses of the membrane protein complexes revealed that the high light treatment of the wild type caused redistribution of CP29 from PSII supercomplexes to PSII dimers and monomers. A similar high-light-induced disassembly of the PSII supercomplexes occurred in stn8, but not in stn7 and stn7stn8. Transfer of the high-light-treated wild type plants to normal light relocated CP29 back to PSII supercomplexes. We postulate that disassembly of PSII supercomplexes in plants exposed to high light involves STN7-kinase-dependent phosphorylation of the linker protein CP29. Disruption of this adaptive mechanism can explain dramatically retarded growth of the stn7 and stn7stn8 mutants under fluctuating normal/high light conditions, as previously reported

Advanced continuum approaches for treating time correlation functions. The role of solute shape and solvent structure

Time correlation functions describing the solvent relaxation around a molecule of coumarin-153 and a benzophenone anion in acetonitrile are calculated using dynamical continuum theories of solvation with an experimental dielectric function epsilon(omega) including the resonance absorption region of the solvent. Apart from the local model with a single molecular-shaped solute cavity of the solute studied previously, a new dynamic local model with a double molecular-shaped cavity and a dynamic nonlocal theory with a spherical cavity are presented, both of which introduce elements of solvent structure. It is shown that both local models, one- and two-cavity, exhibit experimentally unobserved oscillations in the shorter time region t < 1 ps, although the experimental asymptote for t > 1 ps for coumarin is obtained. The dynamics of the two-cavity model are not seen to differ from those of the one-cavity model. The nonlocal dynamic theory is shown to be able to suppress these oscillations, but the long-time asymptote differs markedly from that of the local theories. The nature of this asymptote is studied analytically

An advanced dielectric continuum approach for treating solvation effects: Time correlation functions. I. Local treatment

A local continuum solvation theory, exactly treating electrostatic matching conditions on the boundary of a cavity occupied by a solute particle, is extended to cover time-dependent solvation phenomena. The corresponding integral equation is solved with a complex-valued frequency-dependent dielectric function epsilon(omega), resulting in a complex-valued omega-dependent reaction field. The inverse Fourier transform then produces the real-valued solvation energy, presented in the form of a time correlation function (TCF). We applied this technique to describe the solvation TCF for a benzophenone anion in Debye (acetonitrile) and two-mode Debye (dimethylformamide) solvents. For the Debye solvent the TCF is described by two exponential components, for the two-mode Debye solvent, by three. The overall dynamics in each case is longer than that given by the simple continuum model. We also consider a steady-state kinetic regime and the corresponding rate constant for adiabatic electron-transfer reactions. Here the boundary effect introduced within a frequency-dependent theory generates only a small effect in comparison with calculations made within the static continuum model

High light acclimation in green microalgae in Non-Photochemical Quenching and Thermal Energy Dissipation In Plants, Algae and Cyanobacteria

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