Photoisomerization of green fluorescent protein and the dimensions of the chromophore cavity Original Research Article

Green fluorescent protein (GFP) has a fairly large central cavity, which contains the chromophore, however it does not have a shape that is complementary with a planar chromophore. The protein exerts some strain on the chromophore when it is planar and the only reason planar chromophores are found in GFP is due to their delocalized π-electrons. Our calculations show that the protein environment of GFP allows the chromophore some rotational freedom, especially by a hula-twist and in the ϕ dihedral angle. The excited state, responsible for fluorescence, may therefore be twisted relative to the ground state. However, cis–trans photoisomerization cannot occur by a 180° rotation of the τ dihedral angle.