Some properties of luciferase from the bioluminescent crustacean, Cypridina hilgendorfii

Selection, drift, and constraint in cypridinid luciferases and the diversification of bioluminescent signals in sea fireflies

Understanding the genetic causes of evolutionary diversification is challenging because differences across species are complex, often involving many genes. However, cases where single or few genetic loci affect a trait that varies dramatically across a radiation of species provide tractable opportunities to understand the genetics of diversification. Here, we begin to explore how diversification of bioluminescent signals across species of cypridinid ostracods ("sea fireflies") was influenced by evolution of a single gene, cypridinid-luciferase. In addition to emission spectra ("colour") of bioluminescence from 21 cypridinid species, we report 13 new c-luciferase genes from de novo transcriptomes, including in vitro assays to confirm function of four of those genes. Our comparative analyses suggest some amino acid sites in c-luciferase evolved under episodic diversifying selection and may be associated with changes in both enzyme kinetics and colour, two enzymatic functions that directly impact the phenotype of bioluminescent signals. The analyses also suggest multiple other amino acid positions in c-luciferase evolved neutrally or under purifying selection, and may have impacted the variation of colour of bioluminescent signals across genera. Previous mutagenesis studies at candidate sites show epistatic interactions, which could constrain the evolution of c-luciferase function. This work provides important steps toward understanding the genetic basis of diversification of behavioural signals across multiple species, suggesting different evolutionary processes act at different times during a radiation of species. These results set the stage for additional mutagenesis studies that could explicitly link selection, drift, and constraint to the evolution of phenotypic diversification.

Enzymatic Conversion of Cypridina Luciferyl Sulfate to Cypridina Luciferin with Coenzyme A as a Sulfate Acceptor in Cypridina (Vargula) hilgendorfii

In the luminous ostracod Cypridina (presently Vargula) hilgendorfii, Cypridina luciferyl sulfate (3-enol sulfate of Cypridina luciferin) is converted to Cypridina luciferin by a sulfotransferase with 3'-phosphoadenosine-5'-phosphate (PAP) as a sulfate acceptor. The resultant Cypridina luciferin is used for the luciferase-luciferin reaction of Cypridina to emit blue light. The luminescence stimulation with major organic cofactors was examined using the crude extracts of Cypridina specimens, and we found that the addition of coenzyme A (CoA) to the crude extracts significantly stimulated luminescence intensity. Further, the light-emitting source in the crude extracts stimulated with CoA was identified as Cypridina luciferyl sulfate, and we demonstrated that CoA could act as a sulfate acceptor from Cypridina luciferyl sulfate. In addition, the sulfate group of Cypridina luciferyl sulfate was also transferred to adenosine 5'-monophosphate (5'-AMP) and adenosine 3'-monophosphate (3'-AMP) by a sulfotransferase. The sulfated products corresponding to CoA, 5'-AMP and 3'-AMP were identified using mass spectrometry. This is the first report that CoA can act as a sulfate acceptor in a sulfotransferase reaction.

Phenotypic evolution shaped by current enzyme function in the bioluminescent courtship signals of sea fireflies

Mating behaviours are diverse and noteworthy, especially within species radiations where they may contribute to speciation. Studying how differences in mating behaviours arise between species can help us understand how diversity is generated at multiple biological levels. The bioluminescent courtship displays of cypridinid ostracods (or sea fireflies) are an excellent system for this because amazing variety evolves while using a conserved biochemical mechanism. We find that the evolution of one aspect in this behavioural phenotype-the duration of bioluminescent courtship pulses-is shaped by biochemical function. First, by measuring light production from induced bioluminescence in 38 species, we discovered differences between species in their biochemical reactions. Then, for 16 species for which biochemical, phylogenetic and behavioural data are all available, we used phylogenetic comparative models to show that differences in biochemical reaction are nonlinearly correlated with the duration of courtship pulses. This relationship indicates that changes to both enzyme (c-luciferase) function and usage have shaped the evolution of courtship displays, but that they differentially contribute to these phenotypic changes. This nonlinear dynamic may have consequences for the disparity of signalling phenotypes observed across species, and demonstrates how unappreciated diversity at the biochemical level can lead to inferences about behavioural evolution.

Continuous measurement of targeted promoter activity by a secreted bioluminescence reporter, Vargula hilgendorfii luciferase

The promoter activity of growth hormone (GH) was continuously monitored in rat pituitary adenoma cells (GH3) by a secreted bioluminescence reporter, Vargula hilgendorfii (Vh) luciferase. The sensitivity of the reporter was approximately 60-times higher than that of the firefly luciferase. GH3 cells were transfected with a plasmid containing a DNA sequence of the GH promoter (1.8 kb) and a full length of the Vh luciferase cDNA. Using the stable transformants, the Vh luciferase activity was monitored in the plate culture through the bioluminescence of Vh luciferase secreted into the culture medium. The reporter activity was well correlated with GH mRNA as well as GH when the GH promoter activity was activated by thyroid hormone. To develop a continuous monitoring system of the promoter, the reporter activity was sequentially measured in the perfusion system. When the promoter activity of the stable transformants was suppressed by a transcription inhibitor, the reporter activity and GH in the perfusate were simultaneously decreased. The Vh luciferase reporter is a sensitive and convenient tool for continuous and prolonged measurement of promoter activity in living cell culture systems.

Engineering of functional chimeric protein G-Vargula luciferase

Luciferase of Vargula hilgendorfli is infinitely stable at room temperature in dried state, and its light-emitting reaction is very simple. These unique characteristics of Vargula luciferase have prompted us to engineer chimeric protein, the other moiety chosen for conjugation being streptococcal protein G. A single domain of protein G which binds to IgG of a wide range of species was fused at the N-terminal region of Vargula luciferase. Unexpectedly, we found that the chimeric protein expressed in mammalian COS-1 cells had no IgG-binding ability, probably due to some sort of interaction between the two moieties or some conformational preferences of the IgG-binding domain of protein G when fused to Vargula luciferase. Here we report how we regained the IgG binding of protein G, by the intervention of three alpha-helices of protein A between protein G and luciferase. To our knowledge, the new chimeric protein provides the first reported model of this kind.

Imaging of luciferase secretion from transformed Chinese hamster ovary cells

The blue luminescence characteristic of the marine ostracod crustacean Vargula hilgendorfii is from a simple, but highly specific, enzyme-substrate reaction. Light is emitted by the oxidation of Vargula luciferin (substrate) by molecular oxygen, a reaction catalyzed by luciferase. Stable transformants of Chinese hamster ovary cells carrying the Vargula luciferase gene secreted luciferase from discrete sites on the cell surface, and this secretion could be monitored in real time by the bioluminescence produced by the secreted luciferase in the presence of Vargula luciferin by using an image-intensifying technique. Addition of anti-Vargula luciferase IgG to the luminescing cells almost completely extinguished the luminescence, confirming that Vargula luciferase caused the luminescence.

Cloning and expression of cDNA for the luciferase from the marine ostracod Vargula hilgendorfii

The marine ostracod Vargula hilgendorfii ejects luciferin and luciferase into seawater to produce a bright luminous cloud. The light is due to the oxidation of luciferin, an imidazopyrazine compound, by molecular oxygen, catalyzed by luciferase. The mechanism of the reaction has been studied extensively and the 60 kcal/mol required for the blue emission have been shown to be derived from the oxidation of luciferin via a dioxetanone intermediate, in which the excited state oxyluciferin bound to luciferase is the emitter. However, only limited information is available regarding the properties of the enzyme. This paper reports the cloning and sequence analysis of the cDNA for Vargula luciferase and the expression of the cDNA in a mammalian cell system. The primary structure, deduced from the nucleotide sequence, consists of 555 amino acid residues in a single polypeptide chain with a molecular weight of 62,171. Two regions of the enzyme show significant amino acid sequence homology with an N-terminal segment of the photoprotein aequorin. The Vargula luciferase gene, which contains a signal sequence for secretion, should be well suited as a reporter in studies of gene expression.