Temperature Controlled Decay and Pendulum Dynamics of Green Fluorescent Protein (GFP) Chromophore

초록

The excited-state dynamics of the GFP chromophore, HBDI- (anionic p-hydroxybenzylidene-2,3-dimethylimidazolinone), were investigated through a combination of theoretical nonadiabatic molecular dynamics (NAMD) simulations and femtosecond transient absorption spectroscopy (fs-TA). The NAMD simulations revealed that the primary dynamics in excited states involve the formation of a P-twisted intermediate (S1min,P ), which undergoes pendulum-like oscillations with respect to phi = 90 degrees. This motion serves as a reservoir for the excited-state population and the primary source of fluorescence. Rather than a direct channel from the major S1min,P , a coordinated pathway of S1min,P -> S1min -> S1min,I -> S0 is responsible for the decay to the ground state, emphasizing the importance of planar intermediate (S1min ) formation. The experimental fs-TA spectra confirmed these dynamics, revealing three distinct time scales (340-470 fs, 1.4 ps, and 8.3 ps), corresponding to the formation of S1min,P and its decay governed by the coordinated pathway. At low temperatures, the coordinated decay pathway is suppressed, leading to prolonged fluorescence lifetimes, consistent with low-temperature experimental results. This study presents a new model for the excited-state dynamics of GFP chromophore, suggesting that pendulum motion and the coordinated decay pathway play a crucial role in regulating fluorescence intensity.

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