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Using Three-color Single-molecule FRET to Study the Correlation of Protein Interactions
Published on: January 30, 2018
A QM/MM calculation to identify a low frequency mode that causes anharmonic vibrational coupling in green fluorescent
Tomotsumi Fujisawa1, Masashi Unno1
1Department of Chemistry and Applied Chemistry, Faculty of Science and Engineering, Saga University, Saga 840-8502, Japan.
Abstract:
The bright fluorescence of green fluorescent protein (GFP) from Aequorea victoria arises from the excited state proton transfer (ESPT) of its p-hydroxybenzylidene imidazolinone chromophore in the binding pocket. Recent ultrafast Raman studies have observed vibrational coupling between a low frequency mode (∼100 cm-1) and the phenolic CH bend (∼1140 cm-1) of the chromophore in the ESPT, spurring a debate over the assignment of the low frequency mode, its importance in the reaction, and the vibrational coupling mechanism. We performed a hybrid quantum mechanics/molecular mechanics calculation to analyze the vibrational modes of GFP below 300 cm-1. We identified one low-frequency mode (128 cm-1) with a strong anharmonic coupling that can modulate the resonance Raman intensity of the phenolic CH bend. The low frequency mode corresponds to phenolic twisting, which is unlikely to promote ESPT directly.
