title: Role of the Molecular Environment in Flavoprotein Color and Redox Tuning: QM Cluster versus QM/MM Modeling.
abstract: We investigate the origin of the excitation energy shifts induced by the apoprotein in the active site of the bacterial photoreceptor BLUF (Blue Light sensor Using Flavin adenine dinucleotide). In order to compute the vertical excitation energies of three low-lying electronic states, including two π-π* states of flavin (S1 and S2) and a π-π* tyrosine-flavin electron-transfer state (ET), with respect to the energy of the closed-shell ground state (S0), we prepared alternative quantum mechanical (QM) cluster and quantum mechanics/molecular mechanics (QM/MM) models. We found that the excitation energies computed with both types of models correlate with the magnitude of the charge transfer character of the excitation. Accordingly, we conclude that the small charge transfer character of the light absorbing S0-S1 transition and the substantial charge transfer character of the nonabsorbing but redox active S0-ET transition explain the small color changes but substantial redox tuning in BLUF and also in other flavoproteins. Further analysis showed that redox tuning is governed by the electrostatic interaction in the QM/MM model and transfer of charge between the active site and its environment in the QM cluster. Moreover, the wave function polarization of the QM subsystem by the MM subsystem influences the magnitude of the charge transfer, resulting in the QM/MM and QM excitation energies that are not entirely consistent.
authors.affiliation: Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research , Jahnstrasse 29, 69120 Heidelberg, Germany.
authors.forename: Anikó
authors.initials: A
authors.lastname: Udvarhelyi
authors.affiliation: Dipartimento di Biotecnologie, Chimica e Farmacia, via A. Moro 2, Universitá di Siena , I-53100 Siena, Italy.|Chemistry Department, Overman Hall, Bowling Green State University , Bowling Green, Ohio 67200, United States.|Institut de Physique et de Chimie des Materiaux de Strasbourg, Université de Strasbourg , Batiment 69, 23 Rue du Loess, 67200 Strasbourg, France.
authors.forename: Massimo
authors.initials: M
authors.lastname: Olivucci
authors.affiliation: Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research , Jahnstrasse 29, 69120 Heidelberg, Germany.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Domratcheva
mesh_terms: D020134:Catalytic Domain; D004579:Electron Transport; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry; D005420:Flavoproteins / Q000737:chemistry* / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D010084:Oxidation-Reduction; D011789:Quantum Theory; D055672:Static Electricity
chemical_list: D005420:Flavoproteins; D005182:Flavin-Adenine Dinucleotide