1Institute of Physical Biology, University of south Bohemia, Zámek 136,
373 33 Nové Hrady, Czech Republic
2Institute of Plant Molecular Biology, AS CR, Branišovská
31, 370 05 České Budějovice, Czech Republic
3Faculty of Mathematics and Physics, Charles University,
Ke Karlovu 3, 120 00 Prague, Czech Republic
4Institute of Landscape Ecology, AS CR, Zámek 136, 373 33
Nové Hrady, Czech Republic
Photosystem II (PSII) is a pigment-protein complex located in thylakoid
membrane of cyanobacteria, algae and higher plants. It performs series of light
driven reactions, which result in a separation of charge and subsequently in a
reduction of an electron-transport chain and water oxidation. Primary site of
the energy conversion is located in so-called reaction centre (RC).
Recently, structure of the PSII complex
isolated from cyanobacteria Synechococcus elongatus has been presented
at the resolution of 3.8A [1] and from Synechococcus vulkanus at 3.7 A
[2]. Also time constants of charge distribution and molecules involved in this
process are already known, although X-ray and also spectroscopy methods are
unfortunatelly not able to give us sufficient explanation of the
charge-separation processes. Theoretical molecular modelling study could be
such complementary method for a complex understanding of properties and
function of the PSII RC pigments during a charge-separation process.
In our last study [3,4] we have combined the structural homology modelling based model proposed by Svensson et al. [5] (1DOP model), and the experimental structure presented by Zouni et al. [1] and succesfully calculated absorption and circular dichroism spectra using point-dipole approximations [6] and compared them with the experimental results in order to locate accumulated chlorophyll cation during a light treatment of Photosystem II reaction centre in presence of artificial electron acceptor silicomolybdate. Along with the spectra calculations the charge distribution on the primary electron acceptor pheophytine of the combined model in a ground and reduced state and its influence on the surrounding protein environment is studied by using quantum chemistry methods on a semiempirical (ZINDO-1), density functional (B3LYP) and ab initio (HF) levels.
Acknowledgments: This
work is supported by grants MSMT LN00A141, MSM12310001, GACR 206/02/0942 and
GACR 206/02/D177.
References:
[1] Zouni, A., Witt, H.T., Kern, J., Fromme, P., Krauss, N., Saenger, W. and Orth, P. Nature 409 (2001) 739-743.
[2] Kamiya N. and Shen J.-R. Proc. Natl.
Acad. Sci. USA 100(2003) 98-103.
[3] Vácha F., Kutý M., Durchan M.,
Šiffel P. and Pšenčík J.: Localisation of accumulated chlorophyll cation in
reaction centre of photosystem II. Mat. Struct. 10 (2003) No.1, 21-25
[4] Vácha F., Kutý M. and Pšenčík J. Experimental and calculated optical spectra as a tool for chlorophyll cation localization in reaction centre of photosystem II. The 21st European Crystallographic Meeting, Durban, SA, 24-29 August 2003.
[5] Svensson, B., Etchebest, C., Tuffery,
P., van Kan, P., Smith, J. and Styring, S. Biochemistry 35 (1996)
14486-14502.
[6] Durrant, J.R., Klug, D.R., Kwa, S.L.S.,
van Grondelle, R., Porter, G. and Dekker, J.P. Proc. Natl. Acad. Sci.
USA 92 (1995) 4798-4802.