KEGG   ENZYME: 1.13.12.24Help
Entry
EC 1.13.12.24               Enzyme                                 

Name
calcium-regulated photoprotein;
Ca2+-regulated photoprotein;
calcium-activated photoprotein;
aequorin;
obelin;
halistaurin;
mitrocomin;
phialidin;
clytin;
mnemiopsin;
berovin
Class
Oxidoreductases;
Acting on single donors with incorporation of molecular oxygen (oxygenases);
With incorporation of one atom of oxygen (internal monooxygenases or internal mixed-function oxidases)
BRITE hierarchy
Sysname
coelenterazine:oxygen 2-oxidoreductase (decarboxylating, calcium-dependent)
Reaction(IUBMB)
[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
Substrate
apoaequorin;
coelenterazine [CPD:C15037];
O2 [CPD:C00007];
Ca2+ [CPD:C00076];
apoaequorin containing coelenterazine;
aequorin;
[aequorin] 1,2-dioxetan-3-one
Product
excited state blue fluorescent protein;
CO2 [CPD:C00011];
apoaequorin containing coelenterazine;
aequorin;
[aequorin] 1,2-dioxetan-3-one
Comment
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 Forster resonance energy transfer. In vitro, in the absence of GFP, coelenteramide emits a photon of blue light while returning to its ground state.
History
EC 1.13.12.24 created 2018
Orthology
K22619  calcium-regulated photoprotein
Reference
1
  Authors
Shimomura, O., Johnson, F. H., and Saiga, Y.
  Title
Purification and properties of aequorin, a bio-(chemi-) luminescent protein from the jellyfish, Aequorea aequorea.
  Journal
Fed Proc 21:401 (1962)
Reference
2  [PMID:4151620]
  Authors
Morise H, Shimomura O, Johnson FH, Winant J
  Title
Intermolecular energy transfer in the bioluminescent system of Aequorea.
  Journal
Biochemistry 13:2656-62 (1974)
Reference
3  [PMID:3858813]
  Authors
Inouye S, Noguchi M, Sakaki Y, Takagi Y, Miyata T, Iwanaga S, Miyata T, Tsuji FI
  Title
Cloning and sequence analysis of cDNA for the luminescent protein aequorin.
  Journal
Proc Natl Acad Sci U S A 82:3154-8 (1985)
DOI:10.1073/pnas.82.10.3154
  Sequence
Reference
4  [PMID:10830969]
  Authors
Head JF, Inouye S, Teranishi K, Shimomura O
  Title
The crystal structure of the photoprotein aequorin at 2.3 A resolution.
  Journal
Nature 405:372-6 (2000)
DOI:10.1038/35012659
  Sequence
Reference
5  [PMID:15689515]
  Authors
Deng L, Vysotski ES, Markova SV, Liu ZJ, Lee J, Rose J, Wang BC
  Title
All three Ca2+-binding loops of photoproteins bind calcium ions: the crystal structures of calcium-loaded apo-aequorin and apo-obelin.
  Journal
Protein Sci 14:663-75 (2005)
DOI:10.1110/ps.041142905
  Sequence
Other DBs
ExplorEnz - The Enzyme Database: 1.13.12.24
IUBMB Enzyme Nomenclature: 1.13.12.24
ExPASy - ENZYME nomenclature database: 1.13.12.24
BRENDA, the Enzyme Database: 1.13.12.24

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