Photoacid Dynamics in the Green Fluorescent Protein

Abstract

The photoacid dynamics of fluorescent proteins include both electronic excited- and ground-state mechanisms of proton transfer. The associated characteristic timescales of these reactions range over many orders of magnitude, and the tunneling, barrier crossing, and relevant thermodynamics have in certain cases been linked to coherent nuclear motion. We review the literature and summarize the experiments and theory that demonstrate proton tunneling in the electronic ground state of the green fluorescent protein (GFP). We also discuss the excited-state proton-transfer reaction of GFP that takes place on the picosecond timescale. Although this reaction has been investigated using several vibrational spectroscopic methods, the interpretation remains unsettled. We discuss recent advances as well as remaining questions, in particular those related to the vibrational mode couplings that involve low-frequency modulations of chromophore vibrations on the timescale of proton transfer. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 74 is April 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Ultrafast fluorescence depolarisation in green fluorescence protein tandem dimers as hydrophobic environment sensitive probes

“…This peak is attributed to an increase of the neutral (protonated) chromophores states. 34,35 These results suggest that the dEGFP-TD has a higher proportion of neutral chromophore than the mEGFP. We speculate that the absorbance decrease of the neutral chromophore is caused by the change of solvent polarity as described for wild-type GFP in ref.…”

Nuclear Quantum Effects in Proton or Hydrogen Transfer

“…Regarding the latter, development of ultrafast IR and Raman techniques that can probe the dynamics and coupling of vibrational modes during the reaction is extremely promising. An example is provided by investigation of ground and excited proton transfer dynamics in green fluorescence protein (GFP), suggesting not only tunneling but also coherent nuclear motions . GFP has been proposed as an excellent model system for studying the fundamental reaction mechanisms.…”

“…An example is provided by investigation of ground and excited proton transfer dynamics in green fluorescence protein (GFP), suggesting not only tunneling but also coherent nuclear motions. 41 GFP has been proposed as an excellent model system for studying the fundamental reaction mechanisms. In our opinion, somewhat simpler systems, like the molecules presented in this work, seem more realistic (although “simpler” in these cases still looks quite complex!).…”

Quantum dynamics of excited state proton transfer in green fluorescent protein

“…8 Consequently, ESPT in GFP is less well understood than GSPT, which has been extensively characterized, both experimentally and theoretically. 2 Transient electronic absorption measurements reveal that ESPT occurs over two distinct timescales (2-3 and 10 ps for wt-GFP) and has a large kinetic isotope effect (timescales increase to 11-12 and 69 ps for deuterated GFP). 9 The shorter of the two timescales appears to be largely temperature independent, while the longer timescale increases further at lower temperatures.…”

“…Green fluorescent protein (GFP), which is the quintessential example of a fluorescent protein, 1 is also highly studied as a small, stable model system for the functioning of proton wires. 2 GFP has an 11-stranded beta-barrel structure with a single alpha helix hanging down the center of the barrel. 3 The GFP chromophore, phydroxybenzylideneimidazolidinone (HBDI), forms in situ halfway along the central helix via a cyclization reaction between exposed serine, tyrosine, and glycine residues.…”