Potential Energy Landscape of the Photoinduced Multiple Proton-Transfer Process in the Green Fluorescent Protein:  Classical Molecular Dynamics and Multiconfigurational Electronic Structure Calculations

Abstract

The green fluorescent protein proton wire operating upon photoexcitation of the internally caged chromophore is investigated by means of classical molecular dynamics and multiconfigurational electronic structure calculations. The structure of the proton wire is studied for the solvated protein, showing that the wire is likely to be found in a configuration ready to operate as soon as the chromophore is photoexcited, and leading to a total of three proton translocations in the vicinity of the chromophore. Multiconfigurational CASSCF and CASPT2 calculations provide a detailed overview of the energy landscape of the proton wire for the ground electronic state S0, the photoactive 1pi pi* state, and the charge-transfer 1pi sigma* state. The results allow discussion of the operation of the wire in terms of the sequence of proton-transfer events and the participation of each electronic state.

Study of the Photochemical Properties and Conical Intersections of [2,2′‐Bipyridyl]‐3‐amine‐3′‐ol

“…In contrast to the single ESIPT process present in HBX, SA, and other related systems, GFP-like systems may undergo two or more ESIPT processes. [17,18] This opens the door to several reaction paths so that the possibility of obtaining a stable structure upon photoexcitation at a given wavelength largely increases. In fact, a GFP-like fluorescent protein called Dronpa has recently been proposed as a very promising candidate for a molecular photomemory.…”

Photoswitching of the Fluorescent Protein asFP595: Mechanism, Proton Pathways, and Absorption Spectra

“…In GFP, an anionic and a neutral chromophore protonation state are interconverted through a proton-relay mechanism. [16][17][18][19][20] As protons are not observed in the X-ray crystal structures, their role and possible transfers during the kindling of asFP595 remain largely unclear.…”

“…This situation is similar to that in GFP, where the neutral protonation state is also favored for the cis chromophore. [16][17][18][19][20] GFP fluorescence originates from the anionic chromophore, which is formed through excited-state proton transfer (ESPT). Further studies are required to elucidate whether such ESPT processes play an important role in asFP595 as well.…”

Concerted Asynchronous Proton Transfer in H-Bonding Relay Model: An Implication of Green Fluorescent Protein

“…15 All the three protons were placed at 1.0 Å from either the donor or the acceptor O atoms and the heavy atoms in the proton chain were restricted during calculations. A reasonable argument was reported that why complete relaxation of heavy atom may not be meaningful on the ESPT time scale.…”

“…However, in their simulation the first proton transfer from chromophore to water was enforced excluding a fully concerted mechanism (The H1 was shifted to chromophore and the back transfer was forbidden, then simulation was started). Vendrell et al 15 reported that it is a rough concerted process by the treatment of freezing heavy atoms in the proton wires. As well, it was pointed out that the starting point of the ESPT process is the Ser25 proton transfer to Glu222, rather than the phenolic proton of chromophore, and the GSPT should take place via the same order.…”