Modelling photoreactions in proteins by density functional theory

Photoactive proteins are an important class of biomolecules that, apart from their biological relevance, offer potential technological applications in the field of molecular electronics. In the first hundreds of femtoseconds of their photocycle, light absorption produces conformational changes that trigger a cascade of chemical reactions culminating in a specific biological signal. The extremely short time of the initial photoreaction makes an accurate experimental characterisation of these processes very difficult. Computer simulations could therefore complement the experimental information and help provide a microscopic picture of the initial events of protein photocycles. We present here some attempts to use a density functional theory based method to investigate photochemical reactions in proteins. Results for the photoisomerisation of the rhodopsin chromophore are discussed.