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Your search keyword '"Milanovsky, Georgy E."' showing total 14 results
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14 results on '"Milanovsky, Georgy E."'

13. Molecular dynamics study of the primary charge separation reactions in Photosystem I: Effect of the replacement of the axial ligands to the electron acceptor A0.

Author

Milanovsky, Georgy E., Ptushenko, Vasily V., Golbeck, John H., Semenov, Alexey Yu., and Cherepanov, Dmitry A.

Subjects
*MOLECULAR dynamics, *PHOTOSYSTEMS, *LIGANDS (Biochemistry), *ELECTROPHILES, *THERMOSYNECHOCOCCUS elongatus, *CHARGE exchange, *QUANTUM chemistry, *CHLOROPHYLL
Abstract

Molecular dynamics (MD) calculations, a semi-continuum (SC) approach, and quantum chemistry (QC) calculations were employed together to investigate the molecular mechanics of ultrafast charge separation reactions in Photosystem I (PS I) of Thermosynechococcus elongatus. A molecular model of PS I was developed with the aim to relate the atomic structure with electron transfer events in the two branches of cofactors. A structural flexibility map of PS I was constructed based on MD simulations, which demonstrated its rigid hydrophobic core and more flexible peripheral regions. The MD model permitted the study of atomic movements (dielectric polarization) in response to primary and secondary charge separations, while QC calculations were used to estimate the direct chemical effect of the A0A/A0B ligands (Met or Asn in the 688/668 position) on the redox potential of chlorophylls A0A/A0B and phylloquinones A1A/A1B. A combination of MD and SC approaches was used to estimate reorganization energies λ of the primary (λ1) and secondary (λ2) charge separation reactions, which were found to be independent of the active branch of electron transfer; in PS I from the wild type, λ1 was estimated to be 390 ± 20 mV, while λ2 was estimated to be higher at 445 ± 15 mV. MD and QC approaches were used to describe the effect of substituting Met688PsaA/Met668PsaB by Asn688PsaA/Asn668PsaB on the energetics of electron transfer. Unlike Met, which has limited degrees of freedom in the site, Asn was found to switch between two relatively stable conformations depending on cofactor charge. The introduction of Asn and its conformation flexibility significantly affected the reorganization energy of charge separation and the redox potentials of chlorophylls A0A/A0B and phylloquinones A1A/A1B, which may explain the experimentally observed slowdown of secondary electron transfer in the M688NPsaA variant. This article is part of a Special Issue entitled: Photosynthesis research for sustainability: Keys to produce clean energy. [ABSTRACT FROM AUTHOR]

Published
2014
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14. Trehalose matrix effects on charge-recombination kinetics in Photosystem I of oxygenic photosynthesis at different dehydration levels

Author

Marco Malferrari, Mahir D. Mamedov, Giovanni Venturoli, Georgy E. Milanovsky, Anton Savitsky, Alexey Yu. Semenov, Klaus Möbius, Wolfgang Lubitz, Malferrari, Marco, Savitsky, Anton, Mamedov, Mahir D., Milanovsky, Georgy E., Lubitz, Wolfgang, Möbius, Klau, Semenov, Alexey Yu., and Venturoli, Giovanni

Subjects
0301 basic medicine, SP PCC 6803, Kinetics, Biophysics, ELECTRON-TRANSFER KINETICS, 010402 general chemistry, Photosystem I, Photochemistry, 01 natural sciences, Biochemistry, law.invention, 03 medical and health sciences, chemistry.chemical_compound, Electron transfer, law, HIGH-FIELD EPR, Photosynthesis, Electron paramagnetic resonance, P700, Photosystem I Protein Complex, Protein dynamics, CONFORMATIONAL DYNAMICS, Electron Spin Resonance Spectroscopy, Trehalose, Humidity, Cell Biology, PROTEIN DYNAMICS, MOLECULAR-DYNAMICS SIMULATION, 0104 chemical sciences, DIFFERENT HYDRATION LEVELS, Oxygen, Crystallography, ROOM-TEMPERATURE, 030104 developmental biology, Solvation shell, chemistry, BACTERIAL REACTION CENTERS, EXTERNAL MATRIX
Abstract

Matrix effects on long-range electron transfer were studied in cyanobacterial Photosystem I (PS I) complexes, embedded into trehalose glasses at different hydration levels. W-band EPR studies demonstrated, via nitroxide spin probes, structural homogeneity of the dry PS I-trehalose matrix and no alteration of cofactors' distance and relative orientation under temperature and matrix variation. In dry trehalose glasses at room temperature (RT), PS I was stable for months. Flash-induced charge recombination kinetics were examined by high-field time-resolved EPR and optical spectroscopies. The kinetics in hydrated PS I-trehalose glasses mostly reflected the reduction of the photooxidized primary donor P700•+ by the reduced terminal iron-sulfur clusters. Upon dehydration, the P700•+ decay accelerated and became more distributed. Continuous distributions of lifetimes τ were extracted from the kinetics by two numerical approaches: a maximum entropy method (MemExp program) and a constrained regularization method (CONTIN program). Both analyses revealed that upon dehydration the contribution of the two slowest components (lifetimes τ ~ 300 ms and ~ 60 ms), attributed to P700•+[FA/FB] − recombination, decreased in parallel with the increase of the fastest component (τ ~ 150 μs), and of additional distributed phases with intermediate lifetimes. Dehydration at RT mimicked the effects of freezing water-glycerol PS I systems, suggesting an impairment of PS I protein dynamics in the dry trehalose glass. Similar effects were observed previously in bacterial reaction centers. The work presented for PS I provides new insights into the crucial issue of protein-matrix interactions for protein functionality as controlled by hydrogen-bond networks of the hydration shell.

Published
2015

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