1emb
From Proteopedia
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GREEN FLUORESCENT PROTEIN (GFP) FROM AEQUOREA VICTORIA, GLN 80 REPLACED WITH ARG
Overview
The 2.1-A resolution crystal structure of wild-type green fluorescent, protein and comparison of it with the recently determined structure of the, Ser-65 --> Thr (S65T) mutant explains the dual wavelength absorption and, photoisomerization properties of the wild-type protein. The two absorption, maxima are caused by a change in the ionization state of the chromophore., The equilibrium between these states appears to be governed by a hydrogen, bond network that permits proton transfer between the chromophore and, neighboring side chains. The predominant neutral form of the fluorophore, maximally absorbs at 395 nm. It is maintained by the carboxylate of, Glu-222 through electrostatic repulsion and hydrogen bonding via a bound, water molecule and Ser-205. The ionized form of the fluorophore, absorbing, at 475 nm, is present in a minor fraction of the native protein. Glu-222, donates its charge to the fluorophore by proton abstraction through a, hydrogen bond network, involving Ser-205 and bound water. Further, stabilization of the ionized state of the fluorophore occurs through a, rearrangement of the side chains of Thr-203 and His-148. UV irradiation, shifts the ratio of the two absorption maxima by pumping a proton relay, from the neutral chromophore's excited state to Glu-222. Loss of the, Ser-205-Glu-222 hydrogen bond and isomerization of neutral Glu-222, explains the slow return to the equilibrium dark-adapted state of the, chromophore. In the S65T structure, steric hindrance by the extra methyl, group stabilizes a hydrogen bonding network, which prevents ionization of, Glu-222. Therefore the fluorophore is permanently ionized, causing only a, 489-nm excitation peak. This new understanding of proton redistribution in, green fluorescent protein should enable engineering of environmentally, sensitive fluorescent indicators and UV-triggered fluorescent markers of, protein diffusion and trafficking in living cells.
About this Structure
1EMB is a Single protein structure of sequence from Aequorea victoria. Full crystallographic information is available from OCA.
Reference
Structural basis for dual excitation and photoisomerization of the Aequorea victoria green fluorescent protein., Brejc K, Sixma TK, Kitts PA, Kain SR, Tsien RY, Ormo M, Remington SJ, Proc Natl Acad Sci U S A. 1997 Mar 18;94(6):2306-11. PMID:9122190
Page seeded by OCA on Tue Nov 20 14:07:30 2007
