Accepted name: Renilla-type luciferase
Reaction: coelenterazine h + O2 = excited coelenteramide h monoanion + CO2 (over-all reaction)
(1a) coelenterazine h + O2 = coelenterazine h dioxetanone
(1b) coelenterazine h dioxetanone = excited coelenteramide h monoanion + CO2
Glossary: coelenterazine h = Renilla luciferin = 2,8-dibenzyl-6-(4-hydroxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one
coelenteramide h = Renilla oxyluciferin = N-[3-benzyl-5-(4-hydroxyphenyl)pyrazin-2-yl]-2-phenylacetamide
Other name(s): Renilla-luciferin 2-monooxygenase; luciferase (Renilla luciferin); Renilla-luciferin:oxygen 2-oxidoreductase (decarboxylating)
Systematic name: coelenterazine h:oxygen 2-oxidoreductase (decarboxylating)
Comments: This enzyme has been studied from the soft coral Renilla reniformis. Before the reaction occurs the substrate is sequestered by a coelenterazine-binding protein. Elevation in the concentration of calcium ions releases the substrate, which then interacts with the luciferase. Upon binding the substrate, the enzyme catalyses an oxygenation, producing a very short-lived hydroperoxide that cyclizes into a dioxetanone structure, which collapses, releasing a CO2 molecule. The spontaneous breakdown of the dioxetanone releases the energy (about 50 kcal/mole) that is necessary to generate the excited state of the coelenteramide product, which is the singlet form of the monoanion. In vivo the product undergoes the process of nonradiative energy transfer to an accessory protein, a green fluorescent protein (GFP), which results in green bioluminescence. In vitro, in the absence of GFP, the product emits blue light.
1.  Cormier, M.J., Hori, K. and Anderson, J.M. Bioluminescence in coelenterates. Biochim. Biophys. Acta 346 (1974) 137–164. [PMID: 4154104]
2.  Hori, K., Anderson, J.M., Ward, W.W. and Cormier, M.J. Renilla luciferin as the substrate for calcium induced photoprotein bioluminescence. Assignment of luciferin tautomers in aequorin and mnemiopsin. Biochemistry 14 (1975) 2371–2376. [PMID: 237531]
3.  Anderson, J.M., Charbonneau, H. and Cormier, M.J. Mechanism of calcium induction of Renilla bioluminescence. Involvement of a calcium-triggered luciferin binding protein. Biochemistry 13 (1974) 1195–1200. [PMID: 4149963]
4.  Shimomura, O. and Johnson, F.H. Chemical nature of bioluminescence systems in coelenterates. Proc. Natl. Acad. Sci. USA 72 (1975) 1546–1549. [PMID: 236561]
5.  Charbonneau, H. and Cormier, M.J. Ca2+-induced bioluminescence in Renilla reniformis. Purification and characterization of a calcium-triggered luciferin-binding protein. J. Biol. Chem. 254 (1979) 769–780. [PMID: 33174]
6.  Lorenz, W.W., McCann, R.O., Longiaru, M. and Cormier, M.J. Isolation and expression of a cDNA encoding Renilla reniformis luciferase. Proc. Natl. Acad. Sci. USA 88 (1991) 4438–4442. [PMID: 1674607]
7.  Loening, A.M., Fenn, T.D. and Gambhir, S.S. Crystal structures of the luciferase and green fluorescent protein from Renilla reniformis. J. Mol. Biol. 374 (2007) 1017–1028. [PMID: 17980388]
[EC created 1976, modified 1981, modified 1982, modified 2004, modified 2017]
Accepted name: calcium-regulated photoprotein
Reaction: [apoaequorin] + coelenterazine + O2 + 3 Ca2+ = [excited state blue fluorescent protein] + CO2 (overall reaction)
(1a) [apoaequorin] + coelenterazine = [apoaequorin containing coelenterazine]
(1b) [apoaequorin containing coelenterazine] + O2 = [aequorin]
(1c) [aequorin] + 3 Ca2+ = [aequorin] 1,2-dioxetan-3-one
(1d) [aequorin] 1,2-dioxetan-3-one = [excited state blue fluorescent protein] + CO2
Glossary: coelenterazine = 8-benzyl-2-(4-hydroxybenzyl)-6-(4-hydroxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one
coelenteramide = N-[3-benzyl-5-(4-hydroxyphenyl)pyrazin-2-yl]-2-(4-hydroxyphenyl)acetamide
aequorin = the non-covalent complex formed by apoaequorin polypeptide and coelenterazine-2-hydroperoxide.
blue fluorescent protein = the non-covalent complex formed by Ca2+-bound apoaequorin polypeptide and coelenteramide
Other name(s): Ca2+-regulated photoprotein; calcium-activated photoprotein; aequorin; obelin; halistaurin; mitrocomin; phialidin; clytin; mnemiopsin; berovin
Systematic name: coelenterazine:oxygen 2-oxidoreductase (decarboxylating, calcium-dependent)
Comments: Ca2+-regulated photoproteins are found in a variety of bioluminescent marine organisms, mostly coelenterates, and are responsible for their light emission. The best studied enzyme is from the jellyfish Aequorea victoria. The enzyme tightly binds the imidazolopyrazinone derivative coelenterazine, which is then peroxidized by oxygen. The hydroperoxide is stably bound until three Ca2+ ions bind to the protein, inducing a structural change that results in the formation of a 1,2-dioxetan-3-one ring, followed by decarboxylation and generation of a protein-bound coelenteramide in an excited state. The calcium-bound protein-product complex is known as a blue fluorescent protein. In vivo the energy is transferred to a green fluorescent protein (GFP) by Förster resonance energy transfer. In vitro, in the absence of GFP, coelenteramide emits a photon of blue light while returning to its ground state.
1.  Shimomura, O., Johnson, F. H., and Saiga, Y. Purification and properties of aequorin, a bio-(chemi-) luminescent protein from the jellyfish, Aequorea aequorea. Fed. Proc. 21 (1962) 401.
2.  Morise, H., Shimomura, O., Johnson, F.H. and Winant, J. Intermolecular energy transfer in the bioluminescent system of Aequorea. Biochemistry 13 (1974) 2656–2662. [PMID: 4151620]
3.  Inouye, S., Noguchi, M., Sakaki, Y., Takagi, Y., Miyata, T., Iwanaga, S., Miyata, T. and Tsuji, F.I. Cloning and sequence analysis of cDNA for the luminescent protein aequorin. Proc. Natl. Acad. Sci. USA 82 (1985) 3154–3158. [PMID: 3858813]
4.  Head, J.F., Inouye, S., Teranishi, K. and Shimomura, O. The crystal structure of the photoprotein aequorin at 2.3 Å resolution. Nature 405 (2000) 372–376. [PMID: 10830969]
5.  Deng, L., Vysotski, E.S., Markova, S.V., Liu, Z.J., Lee, J., Rose, J. and Wang, B.C. All three Ca2+-binding loops of photoproteins bind calcium ions: the crystal structures of calcium-loaded apo-aequorin and apo-obelin. Protein Sci. 14 (2005) 663–675. [PMID: 15689515]
[EC created 2018]