Aequorea Aequorin, Coelenterazine

A cDNA encoding apoobelin was obtained from O. longissima and sequenced (Illarionov et al., 1995). The deduced amino acid sequence of the apoobelin consists of 195 amino acid residues, with a calculated molecular mass of about 22.2 kDa, closely matching the apoproteins of other Ca2+-sensitive photoproteins such as aequorin from the jellyfish Aequorea (Inouye et al., 1985 Prasher et al., 1985) and clytin from the jellyfish Phialidium gregarium (Inouye and Tsuji, 1993). To obtain recombinant apoobelin, the cDNA encoding apoobelin was expressed in E. coli (Illarionov et al., 2000). The recombinant apoobelin produced was purified and converted into obelin by incubation with coelenterazine in the presence of molecular oxygen and 2-mercaptoethanol or dithioerythritol, as in the case of aequorin. 

A Ca +-binding protein isolated from jellyfish Aequorea sp.) that is frequently used as a chemiluminescent calcium indicator.Aequorin contains a hydrophobic prosthetic group, coelenterazine. Investigators have been able to express the transfected gene recombinantly in a number of cells, and upon addition of the cofactor, one can measure intracellular calcium concentration. See Fura-2... 

In most BRET applications, the fused donor is RewHaluciferase (Rluc) rather than aequorin, to avoid any intrinsic affinity for Aequorea-derived GFP mutant the acceptor is the YFP, to increase the spectral distinction between the two emissions. When the donor and acceptor are in close proximity, the energy resulting from catalytic degradation of the coelenterazine derivative substrate is transferred from the luciferase to the YFP, which will then emit fluorescence at its characteristic wavelength (Xu etal. 1999). 

Aequorin is a Ca -sensitive, bioluminescent protein complex that was originally isolated from the jellyfish Aequorea victoria [166]. The protein complex is assembled in the presence of molecular oxygen from the protein apoaequorin and its cofactor, the luminophore coelenterazine [167] (see Fig. 18). The binding of Ca ions induces a conformational change in the complex, resulting in the oxidation of coelenterazine and a subsequent emission of blue light in the wavelength... 

Coelenterazine. C26H21N3O3, Mr 423.47. Prosthetic group with the imidazopyrazine structure of the photoprotein aequorin from bioluminescent jelly fish species of the genus Aequorea. A blue luminescence is observed in the presence of traces of Ca ions. Natural aequorin does not need oxygen for bioluminescence, thus it is assumed to exist in the form of a per-... 

---