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Molecular dynamics simulations of Photosystem II in membrane environment: The role of the dynamic in the PSII complex

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Photosystem II (PSII) is a homodimeric protein-cofactor complex embedded in the photosynthetic thylakoid membrane where it acts as a water: plastoquinone oxidoreductase, thus catalyzing the water splitting process [1]. PSII can capture and convert the sunlight-derived energy into chemical energy by simultaneously reducing plastoquinone molecules and oxidizing water molecules with the subsequent generation of molecular oxygen and a proton gradient across the membrane. Investigation of the molecular basis behind the PSII function is mandatory in order to reproduce artificially the photosynthetic process and ultimately to be able to convert solar energy into chemical energy close to the thermodynamic efficiency. The (low-resolution) x-ray structures of PSII solved in the last decade [1,2] as well as several spectroscopy and computational studies performed on PSII [3-5] allowed to build reasonable models describing the PSII function. However, the molecular mechanism behind the water splitting process still remains largely elusive and matter of debate. The last x-ray structure solved in 2011 by Umena et al. at a resolution of 1.9 A revealed for the first time a detailed structure of the catalytic center of water splitting [6]. We study by MD simulations the dynamical properties of the full PSII complex in a membrane environment after developing the force-field of all cofactors and lipids present in the structure solved by Umena et. al. On the basis of this setup we also perform QM/MM molecular dynamics simulations of the manganese cluster to investigate the effect of the protein environment on its structural properties and on the surrounding protonation pattern.



[1] A. Guskov et al. Cyanobacterial photosystem II at 2.9-A resolution and the role of quinones, lipids, channels and chloride. Nat. Struct. Mol. Biol. 16: 334-342 (2009) 

[2] J. Kern & G. Renger. Photosystem II: Structure and mechanism of the water:plastoquinone oxidoreductase. Photosynth. Res. 94: 183-202 (2007)

[3] A. Haddy. EPR spectroscopy of the manganese cluster of photosystem II. Photosynth. Res. 92: 357-368 (2007)

[4] P. Gatt et al. Application of computational chemistry to understanding the structure and mechanism of the Mn catalytic site in photosystem II - A review. J. Photochem. Photobiol. B Biol. 104: 80-93 (2011)

[5] P.E.M. Siegbahn. Recent theoretical studies of water oxidation in photosystem II. J. Photochem. Photobiol. B Biol. 104: 94-99 (2011)

[6] Y. Umena et al. Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9 A. Nature 473: 55-61 (2011)



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