Quantum dynamical effects on proton transduction in biomolecular environments

Abstract

Proton transfer belongs to the most fundamental chemical reactions in biomolecular systems. In particular, vectorial proton transduction in proteins plays a crucial role in photosynthesis, enzymatic reactions, or in pH regulation of the cell. However, the small mass of the proton allows for quantum effects, such as zero point motion and tunnelling, which are well documented in view of huge isotope effects measured. Recent experiments as well as simulations indicate that such effects have a major impact on the dynamics of the so-called release proton of bacteriorhodopsin, which is a photon-driven proton pump embedded in cell membranes that transports protons to the extracellular side thus establishing a proton gradient and enabling bacterial photosynthesis. Crucial is the experimental finding that deuteration, i.e. the exchange of H by D, basically stops the pumping process. Our very recent progress in simulation techniques relying on an ab initio path integral treatment of the quantum protons in full dimensionality combined with a QM/MM treatment of the protein environment allows for an accurate description of reactive parts in complex protein environments as well as incorporating quantum dynamical effects in molecular simulation. The aim of this project is to understand in atomistic detail the workings of this proton pump related to proton translocation.