报告题目：Electron, proton and water transfer along the catalytic cycle of the Photosystem II

报 告 人：Daniele Narzi (Research fellow, Universityof L’Aquila)

报告时间： 2015年4月23日（周四）上午10:00--11:30

报告地点：嘉定园区学术活动中心307房间

报告人简介：

Biography

Dr. Daniele Narzi, Dr. Rer. Nat., now is a research fellow in the Department of of Physical and Chemical Sciences at University of L’Aquila (Italy) in the group of Computational Biophysics, Biochemistry and Chemistryof Prof. Leonardo Guidoni. He got his M Sc in Chemistry in 2004 at University of Rome “La Sapienza” (Italy). In 2005 he worked in the group of Prof. Alfredo Di Nola studying the protein folding mechanisms by molecular dynamics simulations. He got his PhD at University of Erlangen-Nürnberg (Germany)under the supervision of Prof.Rainer A. Böckmannin 2011 with a thesis on the dynamics and the protonation state characterization of Major Histocompatibility Complex molecules and thioredoxins. Currently Dr. Daniele Narziis involved in the study of photosynthetic proteins by means of classical and ab initiomolecular dynamics simulations.

Abstract

Water oxidation in photosynthetic organisms occurs through the five intermediate steps S0–S4 of theKok cycle in the oxygen evolving complex of Photosystem　II　(PSII).　Along　the　catalytic　cycle,　four　electrons　are　subsequently　removed　from　the　Mn4CaO5core　by　the　nearby　tyrosine　Tyr-Z, which is in turn oxidized by the chlorophyll special pair P680, the photo-induced primary donor in PSII. Recently, two Mn4CaO5 conformations, consistent with the S2state (namely, S2Aand S2Bmodels) were suggested to exist,perhaps playing a different role within the S2-to-S3transition. Here we report multiscale ab initiodensity functional theory plus U simulations revealing that upon such oxidation the relative thermodynamic stability of the two previously proposed geometries is reversed, the S2Bstate becoming the leading conformation. In this latter state a proton coupled electron transfer is spontaneously observed at ∼100 fsat room temperature dynamics. Upon oxidation, the Mn cluster, which is tightly electronically coupled along dynamics to the Tyr-Z tyrosyl group, releases aproton from the nearby W1 water molecule to the close Asp-61 on the femtosecond timescale, thus　undergoing　a conformational　transition　increasing　the　available space　for　the　subsequent　coordination　of　an　additional　water　molecule.　The results　can　help　to rationalize　previous　spectroscopic　experiments　and　confirm that　the　water-splitting　reaction　has to proceed　through　the　S2Bconformation.