Computer Simulation of Electron and Proton Transfer

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DESCRIPTION (provided by applicant): Electron transfer (ET) and proton translocations (PTR) play a crucial role in biology. The advances in structural studies of photosynthetic reaction centers (RCs) and systems that transfer and/or pump protons, present the exciting opportunity of gaining a detailed understanding of the molecular origin of biological ET and PTR processes. In past grant periods, we developed microscopic approaches for computer simulation of biological ET and applied them effectively in studies of RCs and related systems. In the last grant period we developed powerful approaches for simulating PTR and ion transfer in proteins and applied these in fundamental studies of key systems. Our progress coincided with the recent spectacular progress in structure elucidation of ion and proton channels, and increased interest in the microscopic nature of biological PTR and ion selectivity. Studies during the last grant period supported our early view that PTR in proteins is controlled by the electrostatic energy of the transferred proton. To establish the validity of the electrostatic idea, we moved from our early modified Marcus' model to a simplified EVB approach which was applied to key test systems (carbonic anhydrase, and gramicidin). We also started to chart the PTR landscape in several key biological systems. Thus we are ready now to exploit our advances in realistic simulation studies of PTR in biological systems for which we have sufficient structural information. The main proposed projects are: (i) Studies of the PTR in bacterial RCs and bacteriorhodopsin using the simplified EVB approach to explore the overall PTR process, as well as its relationship to mutations and conformational changes, (ii) Studies of the gating mechanism of COX by the modified Marcus' treatment and by the simplified EVB. (iii) Exploring the conversion of the proton gradient to ATP synthesis in ATPase. (iv) Continuing our studies of the bacterial RCs. (v) Continuing fundamental studies of electrostatic energies in proteins and, (vi) continue our studies of the selectivity of biological ion channels.