The jellyfish Aequorea victoria possesses in the margin of its umbrella a green f luorescent protein (GFP, 27 kDa) that serves as the ultimate light emitter in the bioluminescence reaction of the animal. The protein is made up of 238 amino acid residues in a single polypeptide chain and produces a greenish f luorescence ( max ‫؍‬ 508 nm) when irradiated with long ultraviolet light. The f luorescence is due to the presence of a chromophore consisting of an imidazolone ring, formed by a post-translational modification of the tripeptide -Ser 65 -Tyr 66 -Gly 67 -. GFP has been used extensively as a reporter protein for monitoring gene expression in eukaryotic and prokaryotic cells, but relatively little is known about the chemical mechanism by which f luorescence is produced. To obtain a better understanding of this problem, we studied a peptide fragment of GFP bearing the chromophore and a synthetic model compound of the chromophore. The results indicate that the GFP chromophore consists of an imidazolone ring structure and that the light emitter is the singlet excited state of the phenolate anion of the chromophore. Further, the light emission is highly dependent on the microenvironment around the chromophore and that inhibition of isomerization of the exo-methylene double bond of the chromophore accounts for its efficient light emission.

The luminescent jellyfish Aequorea contains a photoprotein, aequorin, which emits light by an intramolecular reaction in the presence of a trace amount of Ca2+. A cDNA library of Aequorea was constructed and clones carrying the cDNA for the Ca2+-dependent photoprotein were isolated by the method of colony hybridization using synthetic oligonucleotide probes. The primary structure of the protein deduced from the nucleotide sequence showed that the protein is composed of 189 amino acid residues and has three F-F hand structures that are characteristic for Ca2+-binding sites. The sequence also suggested that the protein has hydrophobic regions at which the protein may interact with its functional chromophore, coelenterazine.

The localization, trafficking, and fluorescence ofAequorea green fluorescent protein (GFP)