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Transition in the Temperature-Dependence of GFP Fluorescence: From Proton Wires to Proton Exit

Summary: Transition in the Temperature-Dependence of GFP Fluorescence:
From Proton Wires to Proton Exit
Pavel Leiderman,* Dan Huppert,* and Noam Agmony
*Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel-Aviv University, Tel-Aviv, Israel; and
Department of Physical Chemistry and the Fritz Haber Research Center, The Hebrew University, Jerusalem, Israel
ABSTRACT In green fluorescent protein, photo-excitation leads to excited-state proton transfer from its chromophore, leaving
behind a strongly fluorescing anion, while the proton is commonly thought to migrate internally to Glu-222. X-ray data show that the
protein contains more extended hydrogen-bonded networks that can support proton migration (i.e., proton wires). Here we study
the temperature-dependence of the transient fluorescence from both the acid and anionic forms up to 15 ns. At low temperatures,
we find that the (lifetime-corrected) fluorescence of the acidic form decays asymptotically as t1/2
, following quantitatively the
solution of a one-dimensional diffusion equation for reversible geminate recombination with quenching. This indicates proton
migration along the internal proton wires. A small degree of geminate proton quenching is attributed to the formation of the
zwitterion by proton migration on a side-branch of the proton wire. Above 230 K, the fluorescence kinetics undergo a transition,
exhibiting an asymptotic t3/2
decay, and the quenching effect disappears. We interpret these findings as evidence for
a conformational change enabling the rotation of Thr-203, which eventually allows the proton to escape to the exterior solution.
The green fluorescent protein (GFP) of the jellyfish Aequorea


Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry