Photosystem II reaction center, QM study of charge distribution and transfer

Michal Kutý^1,2, Žofie Sovová², Ivana Kutá Smatanová^1,2 and David Řeha²

¹ University of South Bohemia in Ceske Budejovice, Faculty of Fisheries and Protection of Waters, South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses and School of complex systems, Zamek 136, 373 33 Nove Hrady

² Academy of Sciences of the Czech Republic, Inst. of Nanobiology and Structural Biology GCRC, Zamek 136, 373 33 Nove Hrady

Photosystem II (PSII) is a pigment-protein complex of thylakoid membrane in cyanobacteria, algae and higher plants. PSII performs series of light driven reactions resulting in charge separation and subsequently in a reduction of an electron-transport chain and water oxidation. Primary site of the light to chemical energy conversion is located in so-called reaction center (RC).

In our previous computational studies of the PSII RC we focused on the role of the reduced pheophytin a (PHO) inducing conformational changes of the RC protein environment and affecting the excitonic interaction of the RC chlorophylls. Nowadays we are developing QM/MM approach to study charge separation and transfer in the PSII RC pigments. The charge distribution is calculated using QM/MM method with novel polarized embedding. The quantum-classical approach is used for kinetic study of charge transfer in the PSII RC pigments. The method is using the stochastic time evolution of charge on PSII RC pigments based on the combination of classical MD simulation with QM calculation of charge transfer rates.

In a paralell direction we are developing model of thylakoid photosynthetical membrane (glycolipid membrane instead of our previous octane layer) to build complex model of PSII RC.

The authors gratefully acknowledge financial support by the ME CR (COST LD11011, ME09016, ME09062, CZ.1.05/2.1.00/01.0024), GACR (P207/12/0775, P207/11/0717) and by the AS CR (AV0Z60870520).