Relationship between structure and optical properties in green fluorescent proteins: a quantum mechanical study of the chromophore environment

The present paper reports the first quantum mechanical modeling of a realistic chromophore environment of the green fluorescent proteins (GFPs). Based on density functional theory (DFT) and semiempirical calculation, we studied the effect of each amino acid in close contact with the chromophore and derived a quantitative and predictive relationship between structure and optical properties. On the basis of this relationship, the structural, optical and vibrational properties of the different states of wildtype GFP and of two mutants, EGFP (F64L/S65T) and E(2)GFP (F64L/S65T/T203Y), are then specifically studied. This approach can be applied to infer some structural features of spectroscopic states for which no structural data is available, such as the dark states involved in GFP photodynamics.