The chromophore of asFP595: a theoretical study

We investigate the electronic and structural properties of the chromophore of the asCP/asFP595, a newly discovered protein of the (green) fluorescent protein family. The use of theoretical methods with different degrees of accuracy and efficiency (DFT, TDDFT, CASSCF and perturbative corrections) allows us to compare the properties of a large number of hypothetic molecular models for the chromophore. The models are sorted on the basis of the relative stability and through a comparison with the experimental values of the excitation energy. Our study indicates that the most probable structure of the photoactive moiety in the protein and in water is the one resulting from the GFP-like rather than the "alternative" cyclization scheme.