Rhodopsins, light-responsive seven-helix transmembrane proteins, play an important role in a number of biophysical processes such as vision, ion transport and phototaxis, and they are widely used in bionanotechnology and optogenetic applications. One of the goals of computational studies is to understand   the correlation between the composition/structure of these proteins and their optical properties. This knowledge is important because it facilitates not only the control of the optical properties of these photoreceptors but also the interpretation of a variety of experimental studies that utilize spectroscopic techniques. In the present study, we used an ab initio multireference Quantum Mechanics/Molecular Mechanics methodology to investigate the origin of the spectral shift   between the chloride-bound and anion-free forms of Halorhodopsin from Natronobacterium pharaonis. We demonstrate that the chloride ion tunes the spectral properties of phR via two distinct mechanisms: (i) electrostatic interaction with the chromophore, which results in a 95 nm difference between the absorption maxima of the two forms, and (ii) induction of a structural reorganization in the protein, which changes the positions of charged and polar residues and reduces this difference to 29 nm. In the presentation we will give a detailed description of these mechanisms and will discuss how this knowledge can be used to elucidate the molecular mechanisms that control the spectral properties of rhodopsins in general.Ryazantsev MN, Altun A, Morokuma K J. Am. Chem. Soc. 2012 (in print, DOI:  10.1021/ja3009117)

Mechanisms that control the spectral properties of rhodopsins: The origin of the spectral shift between the chloride-bound and anion-free forms of halorhodopsin

244th National Meeting (2012)

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