Structure
GFP has a typical beta barrel structure, consisting of eleven β-sheets with six alpha helix(s) containing the covalently bonded chromophore 4-(p-hydroxybenzylidene)imidazolidin-5-one (HBI) running through the center. HBI is nonfluorescent in the absence of the properly folded GFP scaffold and exists mainly in the unionized phenol form in wtGFP. Inward-facing sidechains of the barrel induce specific cyclization reactions in the tripeptide Ser65–Tyr66–Gly67 that induce ionization of HBI to the phenolate form and chromophore formation. This process of post-translational modification is referred to as maturation. The hydrogen-bonding network and electron-stacking interactions with these sidechains influence the color, intensity and photostability of GFP and its numerous derivatives. The tightly packed nature of the barrel excludes solvent molecules, protecting the chromophore fluorescence from quenching by water.
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Read more about this topic: Green Fluorescent Protein
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