Russian Photobiological Society
Website: http://www.photobiology.ru/ E-mail: info@photobiology.ru,
Scientific Secretary Dr. Larissa Koppel
Program of International Conference of the Russian Photobiological Society
“Primary Electron Transfer in Photosynthetic Reaction Centers”, Hotel
Pleskov, township Pechki, Pskov region, 27 – 31 May 2015
The conference is partially sponsored by the International Society of Photosynthesis Research
27 May
Registration of participants
12.00. – 22.00
28 May
10.00. – 10.30. Opening remarks
Chair: Wolfgang Lubitz
10.30. – 11.30. Klaus Moebius "The magic of trehalose sugar matrix for protein dynamics and
function - as decoded by high-field EPR spectroscopy. Case study: The photosynthetic reaction
center"
11.30. – 12.30. Kev Salikhov “Potential of pulse EPR in studying spatial distribution of spins”
12.30. – 13.00. Coffee break
Chair: John Golbeck
13.00. – 14.00. Vladimir Shuvalov “Primary charge transfer in Photosystem II of green plants”
14.00. – 15.00 Wolfgang Lubitz “Light-induced charge separation and water oxidation in
photosystem II”
Break 15.00 – 16.00
16.00. – 18.00. Round table discussion “Trehalose matrix and water oxidation in PS II”.
Moderator: Kev Salikhov.
29 May
Chairs: Klaus Moebius, Kev Salikhov
10.00. – 11.00. Dmitry Cherepanov “Elastic vibrations in the photosynthetic bacterial reaction
center coupled to the primary charge separation: implications from molecular dynamics
simulations and stochastic Langevin approach”
11.00. – 11.30. Georgy Milanovsky “Molecular dynamics study of the primary reactions in
Photosystem I: effect of A0 axial ligand on charge separation kinetics"
11.30. – 12.00. Coffee break
Chairs: Victor Nadtochenko, Dmitry Cherepanov
12.00. – 13.00. John Golbeck "Key Amino Acid Residues for Charge Separation and
Stabilization in Photosystem I".
13.00. – 14.00. Alexey Semenov “Trehalose matrix effects on electron transfer in cyanobacterial
Photosystem I at different dehydration levels”
Break 14.00 – 16.00
16.00. – 18.00. Round table discussion “Protein dynamics and light-driven reactions of
Photosystem I”; Moderator: Victor Nadtochenko.
30 May
Chairs: Vladimir Shuvalov, Alexey Semenov
10.00. – 11.00. Victor Nadtochenko “Primary Stages of Electron and Energy Transfer in
Photosystem I: Effect of Excitation Pulse Wavelength”
11.00. – 12.00. Mahir Mamedov “Effect of trehalose on vectorial electron and proton transfer in
Photosystem II”
12.00. – 12.30. Coffee break
Chair: Mahir Mamedov
12.30. – 13.00. Vasily Kurashov “Contributions of D575PsaB and Q583PsaA to the Redox
Potentials of the A1A and A1B Phylloquinones in Photosystem I”
13.00. – 13.30. Anastasia Petrova. “Interaction of quinones in the A1-site of Photosystem I with
electron acceptors”
13.30 – 14.00. Arseny Aybush “Effect of quinone substitution on the primary electron transfer
in PS I from menB mutant of Synechocystis sp. PCC 6803”
14.00 – 14.30. Fedor Gostev. “Fast reactions in photosystems”
14.30 – 15.30 Break
15.30. – 17.30. Round table discussion “Primary reactions in photosystems and the role of
quinones”; Moderator: Alexey Semenov.
31 May
10.00. – 12.00. General discussion and closing remarks
ABSTRACTS
The magic of trehalose sugar matrix for protein dynamics and function
as decoded by high-field EPR spectroscopy.
Case study: The photosynthetic reaction center
Klaus Möbius 1,2
1
2
Department of Physics, Free University Berlin, Germany
Max Planck Institute for Chemical Energy Conversion, Mülheim (Ruhr), Germany
moebius@physik.fu-berlin.de
Some organisms in the kingdoms of plants, animals and micro-organisms can survive long
periods of complete dehydration and high temperatures; by adding some water they resume their
metabolism (e.g., "resurrection plants"). When dehydrated, they adapt to an "anhydrobiotic"
state, in which the intracellular medium contains large amounts of the non-reducing
disaccharides trehalose or sucrose. Trehalose is most effective in protecting isolated in vitro
biostructures [1] which to exploit is a common technique in food preservation. Remarkably,
much of what is known today about successful anhydrobiosis, and the degree of biostability in
the dry state, was already pre-determined in the time of the late 18th century. But until now, the
molecular mechanism of the anhydrobiotic biostability in disaccharide sugar matrices is largely
unknown.
To clarify the molecular mechanisms of disaccharide bioprotection, we studied the structure and
dynamics of photosynthetic reaction centers (RCs) in sucrose and trehalose matrices as well as
binary systems of nitroxide spin-label/sugar at different hydration levels by means of cw and
pulse high-field W-band EPR and FTIR [2,3]. From these experiments we conclude that the
anhydrobiosis state of the RC-trehalose system is NOT the result of matrix-induced changes of

the local structure of the charge-separated radical-pair cofactors, the primary donor P865
and
acceptor Q A . It is also NOT the result of changes of local dynamics and local hydrogen bonding
of QA in its binding pocket. Rather, the stability of the charge-separated radical-pair state
originates in the high rigidity of the dry trehalose glass matrix coating the RC protein surface
already at room temperature. This surface scaffolding by hydogen-bonding shifts the correlation
time of thermal conformational fluctuations into the non-biological time domain.
In the first part of the lecture, a short personal account of the discovery of oxygen will be given.
The second part will deal with the trehalose matrix effects in photosynthetic RCs.
This work has been done in collaboration with M. Malferrari, F. Francia and G. Venturoli from
the University of Bologna, Italy, with A. Savitsky, A. Nalepa and W. Lubitz from the Max
Planck Institute in Mülheim (Ruhr), Germany, and with A. Semenov from Moscow State
University, Russia.
[1] Clegg, J.S., Comp. Biochem. Physiol., B: Comp. Biochem., 2001, 128, 613-624
[2]
Savitsky,
A.,
Malferrari,
M.,
Francia,
F.,
Venturoli,
G.,
Möbius,
K.,
J. Phys. Chem. B, 2010, 114, 12729-12743
[3] Malferrari, M., Nalepa, A., Francia, F., Venturoli, G., Lubitz, W., Möbius, K., Savitsky, A.,
Phys. Chem. Chem. Phys. 2014, 16, 9831-9848
Potential of pulse EPR in studying spatial distribution of spins
Kev.M. Salikhov
Kazan physical-technical institute of RAS, Russia, Kazan, Sibirsky trakt 10/7
e-mail: salikhov@kfti.knc.ru
The spatial distribution of paramagnetic centers (PC) in solids is an important subject in
radiation chemistry, photochemistry, quantum electronics, quantum computing with electron
spins as qubits, etc. Site directed spin labeling of proteins offers a possibility to create spin
architectures. Detail information about the spatial configuration of these spins is important for
determining the structure of proteins.
Distances between PCs and their mutual positions determine the dipole-dipole (d-d) interaction
between PCs. By measuring the d-d interaction between PCs one can obtain useful information
about the spin architecture, the spatial distribution of spins.
EPR methods provide tools for measuring the energy of the d-d interaction. In many cases the dd interaction parameter is 2 orders of magnitude less than the inhomogeneous broadening of the
EPR spectra of PCs. Under these conditions it is extremely difficult to subtract the d-d
interaction from the continuous-wave EPR spectrum. Electron spin echo methods eliminate the
effect of the inhomogeneous broadening and allow one to measure distances between PCs in the
nanoscale region, namely in about 1-8 nm interval.
The state-of the-art of EPR methodology in measuring the distances between two spins in pairs,
in spin clusters, in studying spin architectures, and the spatial distribution of PCs is outlined.
Light-induced Charge Separation, Electron Transport and
Catalytic Water Oxidation in Oxygenic Photosynthesis
Wolfgang Lubitz
Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany
Light-induced charge separation and electron transport in the two photosystems (PSI and PSII)
of oxygenic photosynthesis has been a matter of intensive studies for many years, in particular
after the successful crystallization of these systems and the availability of x-ray crystallographic
structures. Since radical ions, radical pairs, and triplet states of the pigments (chlorophylls,
pheophytins and quinones), and even amino acid radicals are formed in the single-electron
transfer processes, EPR techniques have been instrumental for characterizing the intermediates
of these reactions [1]. Together with other techniques his has led to a deep insight into the
primary events in photosynthetic systems.
In this contribution an overview is given on charge separation and the subsequent catalytic water
oxidation reaction in photosystem II (PSII). Water oxidation is performed by an oxygen-bridged
tetranuclear manganese cluster (Mn4OxCa) located in the D1 protein subunit [2]. The cofactor´s
reaction cycle is comprised of 5 distinct redox intermediates Sn, where the subscript indicates the
number of stored oxidizing equivalents in the Mn cluster (n = 0 - 4) required to split 2 water
molecule and release O2. A redox-active tyrosine residue couples the fast photoinduced singleelectron charge separation to the slow catalytic four-electron water oxidation process. The Sstates are trapped by laser flash/freeze techniques and their electronic structure is studied by
advanced EPR techniques (ENDOR, ESEEM, ELDOR-detected NMR) [3,4]. These data are
corroborated by DFT calculations. The results give information on the spin and oxidation states
of the manganese ions, the spin coupling in the cluster [5], the function of the Ca2+ [6], the effect
of the amino acid surrounding, and the binding, location and reaction dynamics of the 2 substrate
water molecules, the O-O bond formation and the release of molecular oxygen. A robust model
for the water oxidation mechanism is derived [7]. This information can be used for the design of
bioinspired catalysts for water oxidation, which will also be discussed [7].
References
1. Lubitz W. EPR in Photosynthesis. In: Electron Paramagnetic Resonance. A Specialist Periodical Report. Gilbert
B, Davies M, Murphy D (eds), Royal Society of Chemistry, Cambridge (2004) 174-242; and refs. cited therein.
2. Umena Y, Kawakami K, Shen JR, Kamiya N. Crystal Structure of Oxygen-Evolving Photosystem II at a
Resolution of 1.9 Å. Nature, 473 (2011) 55-60.
3. Cox N, Pantazis DA, Neese F, Lubitz W. Biological Water Oxidation. Acc Chem Res, 46 (2013) 1588-1596.
4. Cox N, Retegan M, Neese F, Pantazis DA, Boussac A, Lubitz W. Electronic Stucture of the Oxygen-evolving
Complex in Photosystem II Prior to O-O Bond Formation. Science 345 (2014) 804-808.
5. Krewald V, Retegan M, Cox N, Messinger J, Lubitz W, DeBeer S, Neese F, Pantazis DA. Metal Oxidation States
in Biological Water Splitting. Chem Sci 6 (2015) 1676-1695.
6. a) Lohmiller T, Cox N, Su JH, Messinger J, Lubitz W. The Basic Properties of the Electronic Structure of the
Oxygen-evolving Complex of Photosystem II are not Perturbed by Ca 2+ Removal. J Biol Chem 287 (2012) 2472124733; b) Cox N, Rapatskiy L, Su JH, Pantazis DA, Sugiura M, Kulik LV, Rutherford AW, Neese F, Boussac A,
Lubitz W, Messinger J. Effect of Ca2+/Sr2+ Substitution on the Electronic Structure of the Oxygen-evolving Complex
of Photosystem II: A Combined Multifrequency EPR, 55Mn-ENDOR, and DFT Study of the S2 State. J. Am. Chem.
Soc. 133 (2011) 3635-3648.
7. Cox N, Pantazis DA, Neese F, Lubitz W. Artifical Photosynthesis: Understanding Water Splitting in Nature.
Interface Focus 5 (2015) 20150009 http://dx.doi.org/10.1098/rsfs.2015.0009.
PRIMARY CHARGE TRANSFER IN PHOTOSYSTEM II
OF GREEN PLANTS
V.A. SHUVALOV1,2,3, V.A. NADTOCHENKO3, A.Y. SEMENOV2,3
1
Institute of Basic Biological Problems RAS, Pushchino, Moscow region
2
Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119991
Moscow, Russia
3
Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, 119991 Moscow,
Russia
Measurements with femtosecond (~20 fs) time resolution have shown that primary charge separation in
core complexes of PSII occurs within special pair P680 with electron transfer to Chl D1 for 0.9 ps and to
PheoD1 for 14 ps. It was found that at low temperature two alternative electron donors P680 and ChlD1
might be active.
The work was supported by RSF 14-14-00789.
Conversion of a Homodimeric Reaction Center from Heliobacterium
modesticaldum into a Heterodimeric Reaction Center
Bryan Ferlez†,%, Weibing Dong†,%, Reza Siavashi§, Kevin Redding#, Harvey J. M. Hou‡*, Art
van der Est§,¶,* and John. H. Golbeck†,‡,*
†
Department of Biochemistry and Molecular Biology and ‡Department of Chemistry, The
Pennsylvania State University, University Park, PA 16802 USA
‡
Department of Physical Sciences, Alabama State University, Montgomery, AL 36104
§
Department of Physics and ¶Department of Chemistry, Brock University, 500 Glenridge Ave.,
St. Catharines, ON Canada L2S 3A1
#
Department of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287 USA
The heliobacteria are a family of strictly anaerobic, gram positive, photoheterotrophs in the
Firmicutes. They make use of a homodimeric Type I reaction center (RC) that contains ~20
antenna bacteriochlorophyll (BChl) g molecules, a special pair of BChl g molecules (P800), two
81-OH-Chl aF molecules (A0), a [4Fe-4S] iron-sulfur cluster (FX), and a carotenoid (4,4’
diaponeurosporene). It is known that in presence of light and oxygen BChl g is converted to a
species with an absorption spectrum identical to that of Chl a. Here, we show that main product
of the conversion is 81-OH-Chl aF. Smaller amounts of two other oxidized Chl aF species are
also produced. In the presence of light and oxygen, the kinetics of the conversion are
monophasic and temperature dependent, with an activation energy of 662 kJ mol–1. In the
presence of oxygen in the dark, the conversion occurs in two temperature-dependent kinetic
phases: a slow phase followed by a fast phase with an activation energy of 531 kJ mol–1. The
loss of BChl g′ occurs at the same rate as the loss of Bchl g, hence the special pair converts at the
same rate as the antenna Chls. However, the loss of P800 photooxidiation and flavodoxin
reduction are not linear with the loss of BChl g. In anaerobic RCs the charge recombination
between P800+ and FX– at 80 K is monophasic with a lifetime of 4.2 ms but after exposure to
oxygen an additional phase with a lifetime 0.3 ms is observed. Transient EPR data show that the
line-width of P800+ increases as BChl g is converted to Chl aF and the rate of electron transfer
from A0 to FX, as estimated from the net polarization generated by singlet-triplet mixing during
the lifetime of P800+A0–, is unchanged. The transient EPR data also show that conversion of the
BChl g results in increased formation of triplet states of both BChl g and Chl aF. The non-linear
loss of P800 photooxidiation and flavodoxin reduction, the biphasic backreaction kinetics and
increased EPR linewidth of P800+ are all consistent with a model in which the BChl g/BChl g
and the BChl g/Chl aF special pairs are functional, but the Chl aF/Chl aF special pair is not.
Elastic vibrations in the photosynthetic bacterial reaction center coupled to
the primary charge separation: implications from molecular dynamics
simulations and stochastic Langevin approach
Georgy E. Milanovsky1, Vladimir A. Shuvalov1,2, Alexey Yu. Semenov1,2 and Dmitry A.
Cherepanov*1,3
1
- A.N. Belozersky Institute of Physical–Chemical Biology, Moscow State University, Moscow,
Russia; 2 - N.N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow,
Russia; 3 - A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy
of Sciences, Moscow, Russia.
Primary electron transfer reactions in the bacterial reaction center (BRC) are difficult for
theoretical explication: the reaction kinetics, being almost unalterable over a wide range of
temperature and free energy changes, revealed oscillatory features observed initially by
Shuvalov at al.1. Here the reaction mechanism was studied by molecular dynamics (MD) and
analyzed within a phenomenological Langevin approach. The spectral function of polarization
around the bacteriochlorophyll special pair PL/PM and the dielectric response upon the formation
of PL+/PM− dipole within the special pair were calculated. The system response was approximated
by a set of Langevin oscillators, the respective frequencies, friction and energy coupling
coefficients were determined. The protein dynamics around PL and PM was determined to be
highly asymmetric. The polarization around PL was described vastly by a single Debye mode
with relaxation time of 80 fs and the amplitude of 130 mV; the protein response around PM could
be largely described by two oscillatory modes with frequencies of ~90 and ~150 cm-1 and the
total amplitude of 50 mV. The revealed polarization dynamics is in agreement with the
oscillatory kinetics observed by Shuvalov et al. and could rationalize the known properties of
BRC charge separation.
1
Streltsov, A. M.; Yakovlev, A. G.; Shkuropatov, A. Y.; Shuvalov, V. A. Femtosecond
Kinetics of Electron Transfer in the bacteriochlorophyll (M)-Modified Reaction Centers
from Rhodobacter sphaeroides (R-26). FEBS Lett. 1996, 383 (1-2), 129–132.
Trehalose matrix effects on charge recombination kinetics in cyanobacterial
Photosystem I at different dehydration levels
Marco Malferrari1, Anton Savitsky2, Klaus Moebius2,3*, Alexey Yu. Semenov*4, Giovanni
Venturoli1*
1
Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy; 2Max
Planck Institute for Chemical Energy Conversion, Mülheim (Ruhr), Germany; 3Department of
Physics, Free University Berlin, Germany, 4A.N. Belozersky Institute of Physical-Chemical
Biology, Moscow State University
Flash-induced charge recombination kinetics has been studied in Photosystem I (PS I) complexes
from Synechocystis sp. PCC 6803, embedded into trehalose matrices at different hydration
levels. W-band high-field 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 changes and matrix variation. In dry trehalose matrices at room
temperature (RT) PS I was stable for months. Charge-recombination kinetics in PS I-trehalose
matrices measured at comparable hydration by transient EPR and flash-spectrometry at 810 nm
were similar. The kinetics in hydrated PS I-trehalose glasses and in solution were comparable
and mostly reflected the reduction of the photooxidized primary donor P700 by the reduced
terminal iron-sulphur clusters. The optically detected P700+ decay accelerated and became more
distributed upon dehydration. The Maximum-Entropy type analysis of the recombination kinetics
revealed that upon dehydration the contribution of the slowest component with average lifetime
~200 ms decreased in parallel with the increase of the fastest component with 150 µs. At
relative humidity r<53%, two additional distributed components appear between 1–30 ms. The
effects of dehydration at RT mimic those observed upon freezing water-glycerol PS I systems,
suggesting an impairment of PS I protein dynamics in trehalose glass. The acceleration of the
kinetics reflects inhibition of the forward electron transfer to the iron-sulphur centers. At r=11%,
the main kinetic component is attributed to the back reaction from the phylloquinone acceptor
A1-. Similar effects were observed previously in bacterial reaction centers.
Primary Stages of Electron and Energy Transfer in Photosystem 1: Effect of Excitation
Pulse Wavelength
A. Semenov1*, I. Shelaev2, F. Gostev2, M. Mamedov1,V. Shuvalov1, V. A. Nadtochenko2,3*
1
A.N. Belozersky Institute of Physical-Chemical Biology, Lomonosov Moscow State University,
119991 Moscow, Russia;
2
Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, 119991
Moscow, Russia;
3
Institute of Chemical Physics Problems, Russian Academy of Sciences, pr. Akademika
Semenova 1, 142432 Chernogolovka, Moscow Region, Russia;
Time-resolved differential spectra of photosystem 1 complex were obtained by the “pump–
probe” technique with 25-fs pulses with maxima at 670, 700, 720, 740 and 760 nm. The ratio
between the number of excited chlorophyll molecules of the antenna and of the reaction center
was shown to depend on spectral characteristics of the pump pulses. The appearance of the
excitons and charge separated pairs in PS I at these different excitation conditions are considered
as excitations of antenna pigments, excitations of Chls in the reaction center, possible excitations
in the charge transfer band and two photon excitations. The findings help to explain possible
reasons for discrepancies of kinetics of primary stages of electron transfer recorded in different
laboratories.
This work was supported by the Russian Science Foundation, Grant # 14-14-00789.
EFFECT OF TREHALOSE ON VECTORIAL ELECTRON AND PROTON TRANSFER
IN PHOTOSYSTEM II
M.D. Mamedov
A.N. Belozersky Institute of Physical-Chemical Biology, Moscow State University
The light-induced functioning of pigment-protein complex of photosystem II (PS II) is directly
linked to the translocation of charges across the membrane, which results in the formation of
transmembrane electric potential difference (ΔΨ). Herein, we studied the effect of the
disaccharide trehalose, which is unique in its physicochemical properties, on electron and proton
transfer at the water oxidizing side of PS II using direct electrometrical technique under single
turnover of enzyme induced by a laser flash. It was found that trehalose significantly accelerates
the kinetics of the electrogenic reactions due to proton transport during S2→S3, and S4→S0
transitions of the water-splitting complex of PS II. In so doing, the transfer of an electron from
Mn to the redox-active tyrosine (YZ) radical (S1 -->S2 transition) is not affected. The data
obtained suggest that trehalose probably keeps the water-oxidizing complex in a more optimal
conformation for effective functioning.
Contributions of D575PsaB and Q583PsaA to the Redox Potentials
of the A1A and A1B Phylloquinones in Photosystem I
Vasily Kurashov1, Matthew Radle1 and John H. Golbeck1,2
1
Department of Biochemistry and Molecular Biology, The Pennsylvania State University,
University Park, PA, 16802, vuk14@psu.edu, 2Department of Chemistry, The Pennsylvania State
University, University Park, PA 16802, jhg5@psu.edu
The core of photosystem I (PSI) is a heterodimer of PsaA and PsaB subunits. These structurally
similar polypeptides, probably, were the result of a gene duplication event. The transition to a
heterodimer was accompanied by the divergence of several amino acids, including Q588 PsaA and
D575PsaB, which occupy the same relative positions in the X-ray crystal structure of PSI.
According to electrostatic calculations, the Em of A1B is–844 mV and the Em of A1A is–671 mV.
Because the Em of FX is –720, electron transfer from A1A to FX is slightly uphill, and electron
transfer from A1B to FX is downhill. Ishikita and Knapp have proposed that D575PsaB has a
greater propensity to become protonated when A1A is reduced than when A1B is reduced, and
given that D575PsaB is closer to A1A than to A1B, the Em of A1A is consequently more positive
than A1B. We are testing this hypothesis by generating the following variants in Synechocystis sp.
PCC 6803: D575PsaB/D588PsaA, Q575PsaB/Q588PsaA, and Q575PsaB/D588PsaA. Preliminary timeresolved measurements at 480 nm at 20°C showed that forward electron transfer from both A1A
and A1B to FX is present in all three mutants. However, in the case of Q575PsaB/Q588PsaA only fast
20 ns component was resolved. It might indicate that in this mutant only A1B to FX electron
transport is present. In Q575PsaB/D588PsaA mutant fast ~20 ns and slow ~200 ns components were
resolved indicating that both branches are active, however the ratio was ~2:1 instead of 1:2
observed in wild type. Also both mutants had additional s component which can indicate a
recombination between A1 and P700+. For D575PsaB/D588PsaA mutant decrease in the rate of both
fast and slow component was observed, but the ration was still ~1:2. The implications of these
new kinetic phases will be discussed in the context of altered reduction potentials of the
phylloquinones.
Molecular dynamics study of the primary charge separation reactions in
Photosystem I: effect of A0 axial ligand on charge separation kinetics
Georgy E. Milanovsky1, Alexey Yu. Semenov1 and Dmitry A. Cherepanov1,2
1
A.N. Belozersky Institute of Physical–Chemical Biology, Moscow State University, Moscow,
Russia; 2A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy
of Sciences, Moscow, Russia.
Molecular dynamics (MD) and quantum chemistry (QC) calculations allows direct investigation
of the molecular mechanics of ultrafast charge separation reactions in Photosystem I (PS I). 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. The MD model permits the study of atomic
movements (dielectric polarization) in response to primary and secondary charge separations,
while QC calculations allow us to estimate the direct chemical effect of individual amino acids in
the vicinity of the cofactors on the redox potential of these cofactors. QC were used to
investigate the A0A/A0B ligands (Met in the PS I from the wild type or Asn from mutated variants
in the 688/668 position) on the redox potential of chlorophylls A0A/A0B and phylloquinones
A1A/A1B. A combination of MD and semi-continual 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. MD and QC
approaches were used to describe the effect of substituting Met688(PsaA)/Met668(PsaB) by
Asn688(PsaA)/Asn668(PsaB) on the energetics of electron transfer. The conformation flexibility
of introduced Asn significantly affected the reorganization energy of charge separation and the
redox potentials of chlorophylls A0A/A0B and phylloquinones A1A/A1B, thereby slowing down the
electron transfer rate. The obtained data were used to develop a kinetic model of the first steps of
charge separation in PS I, which portray the possibility of electron redistribution between chains
A and B even after the primary charge separation.
Interaction of quinones in the A1-site of Photosystem I with electron acceptors
Anastasia A. Petrova1, Baina K. Boskhomdzhieva2, Mahir D. Mamedov1 and Alexey Yu.
Semenov1
1
A.N. Belozersky Institute of Physical–Chemical Biology, Moscow State University, Moscow,
Russia; 2 Faculty of Bioengineering and Bioinformatics, Moscow State University, Moscow,
Russia
Photosystem I (PS I) from the cyanobacterial menB mutant binds plastoquinone (PQ) instead of
phylloquinone (PhQ) into the A1-site. One of the most important features of the menB is the
weak binding of PQ to the A1-site, which can be easily replaced by the other soluble quinones.
Thus, menB is very interesting model for investigations of the electron transfer processes
involving PhQ. In this work we turned to the investigation of the electron transfer from quinone
to the iron-sulfur cluster FX, and an interaction of quinone acceptor with the oxygen and artificial
electron acceptor methylviologen (MV).
The kinetic of the forward electron transfer from quinone to the iron-sulfur clusters in PS I
complexes from Synechocystis sp. PCC 6803 menB mutant were investigated by the direct
electrometric technique. We obtained kinetics of the electron transfer in the PS I from menB
containing either PQ (menB-PQ) or 2,3-dichloro-1,4-naphtoquinone (menB-Cl2NQ) in the A1
site. In the case of menB-PQ we observed the phase of additional potential generation, which
corresponds to the forward electron transfer from PQ to the iron-sulfur clusters. Upon
replacement of PQ by Cl2NQ, the phase disappeared and the fast recombination of electron from
the quinone was observed, which we interpreted as an indication of the interruption of forward
electron transfer.
We also studied interaction of PS I, containing PQ and Cl2NQ in the A1 site, with MV by timeresolved spectroscopy in the near infrared region. In the case of menB-PQ, addition of MV led
to increase of the slowest kinetic component, which we attributed to the electron transfer from
exogenous acceptor. On the other hand, addition of MV in concentration up to 1 mM to menBCl2NQ did not affect the kinetics, while in the presence of 1 mM MV the slowest component
increased. This fact indicates that under high concentration of MV, an interaction of quinone
cofactor with MV becomes possible.
Effect of quinone substitution on the primary electron transfer in
Photosystem I from menB mutant of Synechocystis sp. PCC 6803
A. Aybush1, F. Gostev1, I. Shelaev1, W. Johnson2, A. Semenov1,3, V. Nadtochenko1,3,4
1
N.N. Semenov Institute of Chemical Physics RAS, Moscow, Russia;
Department of Chemistry, Susquehanna University, Selinsgrove, PA, USA;
3
A.N. Belozersky Institute of Physical-Chemical Biology Moscow State University, Moscow,
Russia;
4
Institute of Problems of Chemical Physics RAS, Chernogolovka, Russia
2
Time constants of the primary electron transfer from the primary chlorophyll acceptor A0 to the
secondary quinone acceptor A1 in Photosystem (PS) I from cyanobacterium Synechocystis sp.
PCC 6803 are known to proceed in the picosecond time range [1]. Mutant strains of
Synechocystis sp. PCC 6803 with substituted quinone acceptors A1 were studied in this work.
The substitution of the native phylloquinone in the A1-site by 2,3-dichloro-1,4-naphthoquinone,
plastoquinone, 1,5-anthraquinone and 1,2-anthraquinone results in the following change of the
free energy ΔG for the electron transfer in the reaction A0-→A1: -350 mV, -100 mV, +100 mV
and +150 mV (with respect to the wild-type). Transient absorption spectra in the range from 0.1
ps to 500 ps were measured for all substituted samples using femtosecond pump-probe laser
spectroscopy. The analysis of time constants allowed to draw a conclusion that the electron
transfer rates between A0 and A1 in PS I samples containing 2,3-dichloro-1,4-naphthoquinone
and plastoquinone are close to the inverted region of the Marcus curve.
This work was supported by the Russian Foundation for Basic Research (grant No. 13-0300936).
[1] Shelaev,I.V., F.E.Gostev, M.D.Mamedov, O.M.Sarkisov, V.A.Nadtochenko, V.A.Shuvalov,
and A.Y.Semenov. Femtosecond primary charge separation in Synechocystis sp PCC 6803
photosystem I. //Biochimica et Biophysica Acta-Bioenergetics -2010. –V.1797-P.1410-1420.