Electron density deformations provide new insights into the spectral shift of rhodopsins

Spectral shifts of rhodopsin, which are related to variations of the electron distribution in 11‐cis‐retinal, are investigated here using the method of deformed atoms in molecules. We found that systems carrying the M207R and S186W mutations display large perturbations of the π‐conjugated system with respect to wild‐type rhodopsins. These changes agree with the predicted behavior of the bond length alternation (BLA) and the blue shifts of vertical excitation energies of these systems. The effect of the planarity of the central and Schiff‐base regions of retinal chain on the electronic structure of the chromophore is also investigated. By establishing nonlinear polynomial relations between BLA, chain distortions, and vertical excitation energies, we are also able to provide a semiquantitative approach for the understanding of the mechanisms regulating spectral shifts in rhodopsin and its mutants. © 2013 Wiley Periodicals, Inc. The method of deformed atoms in molecules is used to study the electron distribution in 11‐cis‐retinal in bovine and human wild‐type rhodopsins and two mutations associated with retinitis pigmentosa disease: M207R and S186W. The apparition of an electron density gap in hM207R and hS186W rhodopsins is related to a loss of charge delocalization. This perturbation provides new insights into the spectral shift of rhodopsins. Changes in the electron density affect the behavior of the bond length alternation, the blue shifts of vertical excitation energies, and the effect of the planarity of Schiff‐base regions of the retinal chain in rhodopsins and mutants.