AB-INITIO MOLECULAR-DYNAMICS OF RHODOPSIN

We present a Car-Parrinello ab initio molecular dynamics study of the retinylidene chromophore of rhodopsin, the protein responsible for the first step in vision. The primary photochemical event involves an 11- cis to all-trans photoisomerization of a protonated Schiff base of ret inal. The ground-state structures of the two conformations of the chro mophore, before and after the photon absorption, have been determined by a simulated annealing procedure. We compute the electrostatic and t he torsional contributions to the energy storage in the primary photop roduct and study the role played by a counterion located in the vicini ty of the chromophore. We also analyse localization and dynamics of a positively charged soliton on the chromophore backbone. The non-planar ity of the chromophore results in a strong coupling of the soliton dyn amics to the out-of-plane hydrogen oscillations, which may be relevant for the photoinduced isomerization process.