Molecular mechanism of Symplectoteuthis bioluminescence—Part 4: Chromophore exchange and oxidation of the cysteine residue

Genomic and Transcriptomic Analyses of Bioluminescence Genes in the Enope Squid Watasenia scintillans

“…The latter four candidates derived from genome assembly and arm tip RNA transcriptome had very similar sequences to S. oualaniensis symplectin. S. oualaniensis has been known to have another type of squid autofluorescence, which gives off shiny blue light (Tsuji and Leisman 1981 ; Chou et al 2014 ). Fujii et al ( 2002 ) singled out the agent of S. oualaniensis light and found symplectin as a new luciferase.…”

“…P. pyralis luciferase emits greenish light. S. oualaniensis luciferase symplectin with coelenterazine was measured to emit light with wide spectral range (Chou et al 2014 ), but Tsuji and Leisman ( 1981 ) measured the light spectrum of S. oualaniensis as a whole and found blue light emission around the wavelength of 455 nm. These pieces of evidence made us speculate that the two different types of luciferase are employed to emit different wavelength light.…”

Coelenterazine-dependent luciferases

“…Binding of Ca 2+ causes small conformational changes in a substrate binding cavity of the protein, which disturb the hydrogen bond network that stabilizes 2 hydroperoxycoelenterazine, thereby triggering the reaction of oxidative decarboxylation leading to the formation of the product in the excited state [31]. Unlike Ca 2+ regulated photoproteins, the photoproteins of squid Symplectoteuthis oualaniensis [15] and mollusc Pholas dactylus [16], simplectin and pholasin, are a complex of a protein with a covalently bound coelenterazine, which is formed upon binding of dehydrocoelenterazine with the apoprotein. The bioluminescent reaction of the photopro teins of squid and mollusc is initiated by O 2 and K + [15] and the reactive oxygen species [16], respectively.…”

“…Unlike Ca 2+ regulated photoproteins, the photoproteins of squid Symplectoteuthis oualaniensis [15] and mollusc Pholas dactylus [16], simplectin and pholasin, are a complex of a protein with a covalently bound coelenterazine, which is formed upon binding of dehydrocoelenterazine with the apoprotein. The bioluminescent reaction of the photopro teins of squid and mollusc is initiated by O 2 and K + [15] and the reactive oxygen species [16], respectively. Since a substrate whose oxidation is necessary for light emission is already bound in photoproteins, these, unlike luciferases, can react only once, i.e.…”

“…The hydromedusan and ctenophore Ca 2+ regulated pho toproteins contain a 2 hydroperoxy derivative of coelen terazine [3]. The squids Watasenia and Symplectoteuthis, as well as the mollusc Pholas dactylus, use coelenterazine derivatives as the substrates of bioluminescent reactionscoelenterazine disulfate in the case of Watasenia [14], and dehydrocoelenterazine in the cases of Symplectoteuthis [15] and Pholas dactylus [16]. Cypridina (Vargula) luciferin is a substrate of luciferases of ostracods [17], as well as of fish Porichthys notatus, Apogon, and Parapriacanthus [18].…”