Electric field effect on the ground state proton transfer in the H-bonded HBDI complex: an implication of the green fluorescent protein

Abstract

In this paper, first-principles calculations were performed regarding the electric field effect on the ground state proton transfer (GSPT) in the H-bonded p-hydroxybenzylideneimidazolidinone (HBDI) network that represents the active site of the green fluorescent protein (GFP). Potential energy surfaces (PESs) in the absence or presence of electric fields were obtained using DFT calculations with the functional CAM-B3LYP. Surprisingly, it was found that the magnitude of the equilibrium constant (K) under the electric fields can be closely fitted to a linear relationship. The concerted and asynchronous proton transfer mechanism in field free conditions can be altered by the electric field. Moreover, the electric field parallel to the x axis (F_x) has the strongest effect on the absorption energy of both the neutral and anionic HBDI complexes. Our results demonstrate that the electric field can be used for the rational design of GFP mutants with desirable properties.