Protein assistance in the photoisomerization of rhodopsin and 9-cis-rhodopsin-insights from experiment and theory

The artificial isomeric 9-cis form of retinal has been investigated within the chromophore binding pocket of rhodopsin by x-ray crystallography and quantum-mechanics with particular emphasis on the geometry imposed on the chromophore by the protein. Comparison with the native 11-cis-rhodopsin structure reveals similarities and differences providing valuable insights into the photophysical properties of the visual pigment.