title: Electrostatic versus Resonance Interactions in Photoreceptor Proteins: The Case of Rhodopsin.
abstract: Light sensing in photoreceptor proteins is subtly modulated by the multiple interactions between the chromophoric unit and its binding pocket. Many theoretical and experimental studies have tried to uncover the fundamental origin of these interactions but reached contradictory conclusions as to whether electrostatics, polarization, or intrinsically quantum effects prevail. Here, we select rhodopsin as a prototypical photoreceptor system to reveal the molecular mechanism underlying these interactions and regulating the spectral tuning. Combining a multireference perturbation method and density functional theory with a classical but atomistic and polarizable embedding scheme, we show that accounting for electrostatics only leads to a qualitatively wrong picture, while a responsive environment can successfully capture both the classical and quantum dominant effects. Several residues are found to tune the excitation by both differentially stabilizing ground and excited states and through nonclassical "inductive resonance" interactions. The results obtained with such a quantum-in-classical model are validated against both experimental data and fully quantum calculations.
authors: MESA+ Institute for Nanotechnology, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors: Riccardo
authors: R
authors: Guareschi
authors: Department of Chemistry and Applied Bioscience, ETH Zurich and Facoltà di Informatica, Instituto di Scienze Computazionali, Università della Svizzera italiana , Via Giuseppe Buffi 13, CH-6900 Lugano, Switzerland.
authors: Omar
authors: O
authors: Valsson
authors: Departament de Fisicoquímica, Facultat de Farmàcia, Universitat de Barcelona , Av. Joan XXIII, s/n 08028 Barcelona, Spain.
authors: Carles
authors: C
authors: Curutchet
authors: Dipartimento di Chimica e Chimica Industriale, Università di Pisa , Via Giuseppe Moruzzi 13, 56124 Pisa, Italy.
authors: Benedetta
authors: B
authors: Mennucci
authors: MESA+ Institute for Nanotechnology, University of Twente , P.O. Box 217, 7500 AE Enschede, The Netherlands.
authors: Claudia
authors: C
authors: Filippi
mesh_terms: D008958:Models, Molecular; D010786:Photoreceptor Cells; D011487:Protein Conformation; D011506:Proteins; D011789:Quantum Theory; D012243:Rhodopsin / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D011506:Proteins; D012243:Rhodopsin