An accurate description of non-covalent interactions is an essence for modeling and understanding of structure and function of biological systems. The Effective Fragment Potential (EFP) is a quantum mechanical-based model that can be thought of as a non-empirical polarizable force field. In proteins where non-covalent interactions span a broad range from weak non-polar to strong polar and ionic forces, EFP is superior to classical force fields. In EFP-based QM/MM schemes (so called QM/EFP), the protein environment is described with explicit inclusion of polarization. In the present study, we utilize the EFP method to elucidate excitonic interactions and energy transfer in Fenna-Matthews-Olson (FMO) photosynthetic pigment-protein complex. In photosynthetic organisms, the FMO complex mediates the excitation energy transfer from light harvesting antenna to the reaction center with amazingly high efficiency. We find that internal geometries of <i>bacteriochlorophyll a </i>(<i>BChl a</i>) pigments are strongly coupled with several amino acids. Hence, we characterize effects of nearby amino acids as well as long-range electrostatic and polarization effects of the protein scaffold on the electronic properties of pigments. We demonstrate that QM/EFP produces qualitatively more accurate excitation site energies and absorption and circular dichroism spectra of the FMO complex as compared to non-polarizable QM/MM models.

Effective modeling of photobiology with the effective fragment potential method

2019 Fall National Meeting

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