Ultrafast action chemistry in slow motion: atomistic description of the excitation and fluorescence processes in an archetypal fluorescent protein.

We report quantum mechanical/molecular mechanical non-adiabatic molecular dynamics simulations on the electronically excited state of green fluorescent protein mutant S65T/H148D. We examine the driving force of the ultrafast (τ < 50 fs) excited-state proton transfer unleashed by absorption in the A band at 415 nm and propose an atomistic description of the two dynamical regimes experimentally observed [Stoner Ma et al., J.

Chromophore interactions leading to different absorption spectra in mNeptune1 and mCardinal red fluorescent proteins.

Extensive MD simulations combined with QM/MM calculations have been performed on mNeptune1 and mCardinal red fluorescent proteins to establish the reasons behind the red shift of the excitation wavelength of mCardinal with respect to mNeptune1. In both cases, it is seen that Arg197 stabilizes the chromophore but cannot be described as stabilizing preferentially the excited state because of the anchor point of the interaction. The interactions of the linking bonds to the α-helix of both proteins to the chromophore have been analyzed.

Theoretical Computer-Aided Mutagenic Study on the Triple Green Fluorescent Protein Mutant S65T/H148D/Y145F.

Green fluorescent protein (GFP) mutant S65T/H148D has been proposed to host a photocycle that involves an excited-state proton transfer between the chromophore (Cro) and the Asp148 residue and takes place in less than 50 fs without a measurable kinetic isotope effect. It has been suggested that the interaction between the unsuspected Tyr145 residue and the chromophore is needed for the ultrafast sub-50 fs rise in fluorescence. To verify this, we have performed a computer-aided mutagenic study to introduce the additional mutation Y145F, which eliminates this interaction.

New insights into the structure-spectrum relationship in S65T/H148D and E222Q/H148D green fluorescent protein mutants: a theoretical assessment.

The green fluorescent protein (GFP) variant S65T/H148D recovers the A-band fluorescence lost in the single mutant S65T, and it has been established that Asp148 is the alternate proton acceptor for the excited state proton transfer (ESPT). This mutant has been widely studied and presents unique spectroscopic properties, such as an ultrafast rise in the fluorescence (<50 fs). Also it exhibits a red-shift of the A absorption band of 20 nm with respect to wt-GFP's.

Unveiling how an archetypal fluorescent protein operates: theoretical perspective on the ultrafast excited state dynamics of GFP variant S65T/H148D.

Green fluorescent protein variant S65T/H148D has been reported to host a photocycle involving the photoinduced proton transfer reaction between the chromophore and residue Asp148 under 50 fs and without a measurable kinetic isotope effect, and experimental evidence is suggestive of the existence of a highly delocalized proton between these residues. The blinding speed at which this biological system undergoes proton transfer has been ascribed to the extreme increase of acidity of the GFP chromophore in the electronic excited state where proton transfer takes place. This work strives to present a coherent, complete, and balanced description of the dynamics of this specific variant of GFP in which it will be shown that this increase of acidity is insufficient to explain the behavior observed.