A First-Principles Study of 11-Cis-Retinal: Modelling the Chromophore-Protein Interaction In Rhodopsin

The 11- cis -retinal protonated Schiff base is the chromophore of rhodopsin, the photoreceptor in the vertebrate eye. The photochemical isomerization from 11- cis to the all- trans form triggers a series of enzymatic reactions known as the visual cascade which eventually leads to a neural signal. Experiments such as resonance Raman, NMR etc., have shown that 11- cis -retinal is probably highly twisted in the protein pocket. Because detailed knowledge about the kind of interaction with the protein is missing, a theoretical description of the chromophore conformation is difficult. In the simulations the results of which will be presented here, we assume that the retinal chromophore, as a consequence of the steric fit into the protein binding pocket, undergoes a specific kind of conformational change.The structure we obtain is in good agreement with the experimentally observed highly twisted conformation of the chromophore backbone.