Isomerization in Fluorescent Protein Chromophores Involves Addition/Elimination

We present quantum chemical calculations of the properties of the anionic form of the green fluorescent protein (GFP) chromophore that can be directly compared to the results of experimental measurements: the cis-trans isomerization energy profile in water. Calculations of the cis-trans chromophore isomerization pathway in the gas phase and in water reveal a problematic behavior of density functional theory and scaled opposite-spin-MP2 due to the multiconfigurational character of the wave function at twisted geometries. The solvent effects treated with the continuum solvation models, as well as with the water cluster model, are found to be important and can reduce the activation energy by more than 10 kcal/mol. Strong solvent effects are explained by the change in charge localization patterns along the isomerization coordinate. At the equilibrium, the negative charge is almost equally delocalized between the phenyl and imidazolin rings due to the interaction of two resonance structures, whereas at the transition state the charge is localized on the imidazolin moiety. Our best estimate of the barrier obtained in cluster calculations employing the effective fragment potential-based quantum mechanics/molecular mechanics method with the complete active space self-consistent field description of the chromophore augmented by perturbation theory correction and the TIP3P water model is 14.8 kcal/mol, which is in excellent agreement with the experimental value of 15.4 kcal/mol. This result helps to resolve previously reported disagreements between experimental measurements and theoretical estimates.

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“…12,13,17 Below we demonstrate that this discrepancy is resolved when solvent effects are taken into account.…”

Section: Cis-trans Isomerization Pathway In the Gasmentioning

confidence: 71%

Quantum Chemical Benchmark Studies of the Electronic Properties of the Green Fluorescent Protein Chromophore: 2. Cis−Trans Isomerization in Water

Polyakov

Epifanovsky

Grigorenko

et al. 2009

J. Chem. Theory Comput.

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“…We do note, however, that recent experimental evidence suggests this may occur for the ground-state isomerization, if it is catalyzed by the presence of a base. 93 When we do observe a breakdown of the SA-CASSCF solution space ͑as outlined above͒, there is usually no effect on the S 1 or S 0 states, but the character of the S 2 state changes. Also, breakdowns occur at values of acute torsion, which are not likely to be accessed that in the early photodynamics.…”

Section: Limits Of Applicabilitymentioning

confidence: 99%

A diabatic three-state representation of photoisomerization in the green fluorescent protein chromophore

Olsen

McKenzie

2009

The Journal of Chemical Physics

122

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We give a quantum chemical description of the photoisomerization reaction of green fluorescent protein (GFP) chromophores using a representation over three diabatic states. Photoisomerization leads to non-radiative decay, and competes with fluorescence in these systems. In the protein, this pathway is suppressed, leading to fluorescence. Understanding the electronic states relevant to photoisomerization is a prerequisite to understanding how the protein suppresses it, and preserves the emitting state of the chromophore. We present a solution to the state-averaged complete active space problem, which is spanned at convergence by three fragment-localized orbitals. We generate the diabatic-state representation by block diagonalization transformation of the Hamiltonian calculated for the anionic chromophore model HBDI with multi-reference, multi-state perturbation theory. The diabatic states are charge-localized and admit a natural valence-bond interpretation. At planar geometries, the diabatic picture of the optical excitation reduces to the canonical two-state charge transfer resonance of the anion. Extension to a three-state model is necessary to describe decay via two possible pathways associated with photoisomerization of the (methine) bridge. Parametric Hamiltonians based on the three-state ansatz can be fit directly to data generated using the underlying active space. We provide an illustrative example of such a parametric Hamiltonian.

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“…[6][7][8] Although GFP was discovered more than 20 years ago, the photophysics of p-HBI and of its mutants is still intensively investigated mainly because of the spectacular decrease of its fluorescence quantum yield, Φ fl , and lifetime, τ, taking place when going from the protein (Φ fl ) 0.79, 9 τ ) 3.3 ns) 8,10 to liquid solutions (Φ fl < 10 -3 , 11 τ < 1 ps). [12][13][14] In this respect, the photophysical properties of the synthetic dimethyl derivative of the GFP chromophore (p-HBDI) 13,[15][16][17][18][19][20][21][22][23][24][25][26] and other related model systems 24,25,[27][28][29][30][31][32] have been extensively investigated.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Excited-State Dynamics of GFP-Inspired Imidazolone Derivatives

et al. 2009

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The excited-state dynamics of five derivatives of the GFP-chromophore, which differ by the position and nature of their substituents, has been investigated in solvents of various viscosity and polarity and in rigid media using femtosecond-resolved spectroscopy. In polar solvents of low viscosity, like acetonitrile or methanol, the fluorescence decays of all compounds are multiexponential, with average lifetimes of the order of a few picoseconds, whereas in rigid matrices (polymer films and low temperature glasses), they are single exponential with lifetimes of the order of a few nanoseconds and fluorescence quantum yields close to unity. Global analysis of the fluorescence decays recorded at several wavelengths and of the transient absorption spectra reveals the presence of several excited-state populations with slightly different fluorescence and absorption spectra and with distinct lifetimes. These populations are attributed to the existence of multiple ground-state conformers. From the analysis of the dependence of the excited-state dynamics on the solvent and on the nature of the substituents, it follows that the nonradiative deactivation of all these excited chromophores involves an intramolecular coordinate with large amplitude motion. However, depending on the solvent and substituent, additional channels, namely, inter-and intramolecular hydrogen bond assisted nonradiative deactivation, are operative. This allows tuning of the excited-state lifetime of the chromophore. Finally, an ultrafast photoinduced intramolecular charge transfer is observed in polar solvents with one derivative bearing a dimethylaminophenyl substituent.

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Isomerization in Fluorescent Protein Chromophores Involves Addition/Elimination

Cited by 60 publications

References 28 publications

Quantum Chemical Benchmark Studies of the Electronic Properties of the Green Fluorescent Protein Chromophore: 2. Cis−Trans Isomerization in Water

Quantum Chemical Benchmark Studies of the Electronic Properties of the Green Fluorescent Protein Chromophore: 2. Cis−Trans Isomerization in Water

A diabatic three-state representation of photoisomerization in the green fluorescent protein chromophore

Tuning the Excited-State Dynamics of GFP-Inspired Imidazolone Derivatives

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