Аннотация:The green fluorescent protein (GFP) is one of the most important light-responsive biological systems. We describe applications of a particular QM/MM version based on the flexible effective fragment potential theory to characterize the properties of this protein including transformations between different forms of GFP. We also show how the chemical reactions of chromophore maturation in GFP and the photochemical reactions leading to GFP malfunction are characterized in QM/MM simulations.