Characterization of luciferases and its paralogue in the Panamanian luminous click beetle Pyrophorus angustus: a click beetle luciferase lacks the fatty acyl-CoA synthetic activity

Similar enzymatic functions in distinct bioluminescence systems: Evolutionary recruitment of sulfotransferases in ostracod light organs

Genes from ancient families are sometimes involved in the convergent evolutionary origins of similar traits, even across vast phylogenetic distances. Sulfotransferases are an ancient family of enzymes that transfer sulfate from a donor to a wide variety of substrates, including probable roles in some bioluminescence systems. Here we demonstrate multiple sulfotransferases, highly expressed in light organs of the bioluminescent ostracod Vargula tsujii , transfer sulfate in vivo to the luciferin substrate, vargulin. We find luciferin sulfotransferases of ostracods are not orthologous to known luciferin sulfotransferases of fireflies or sea pansies; animals with distinct and convergently evolved bioluminescence systems compared to ostracods. Therefore, distantly related sulfotransferases were independently recruited at least three times, leading to parallel evolution of luciferin metabolism in three highly diverged organisms. Re-use of homologous genes is surprising in these bioluminescence systems because the other components, including luciferins and luciferases, are completely distinct. Whether convergently evolved traits incorporate ancient genes with similar functions or instead use distinct, often newer, genes may be constrained by how many genetic solutions exist for a particular function. When fewer solutions exist, as in genetic sulfation of small molecules, evolution may be more constrained to use the same genes time and again.

Resurrecting the ancient glow of the fireflies

The color of firefly bioluminescence is determined by the structure of luciferase. Firefly luciferase genes have been isolated from more than 30 species, producing light ranging in color from green to orange-yellow. Here, we reconstructed seven ancestral firefly luciferase genes, characterized the enzymatic properties of the recombinant proteins, and determined the crystal structures of the gene from ancestral Lampyridae. Results showed that the synthetic luciferase for the last common firefly ancestor exhibited green light caused by a spatial constraint on the luciferin molecule in enzyme, while fatty acyl-CoA synthetic activity, an original function of firefly luciferase, was diminished in exchange. All known firefly species are bioluminescent in the larvae, with a common ancestor arising approximately 100 million years ago. Combined, our findings propose that, within the mid-Cretaceous forest, the common ancestor of fireflies evolved green light luciferase via trade-off of the original function, which was likely aposematic warning display against nocturnal predation.

Enzymatic promiscuity and the evolution of bioluminescence

Bioluminescence occurs when an enzyme, known as a luciferase, oxidizes a small-molecule substrate, known as a luciferin. Nature has evolved multiple distinct luciferases and luciferins independently, all of which accomplish the impressive feat of light emission. One of the best-known examples of bioluminescence is exhibited by fireflies, a class of beetles that use d-luciferin as their substrate. The evolution of bioluminescence in beetles is thought to have emerged from ancestral fatty acyl-CoA synthetase (ACS) enzymes present in all insects. This theory is supported by multiple lines of evidence: Beetle luciferases share high sequence identity with these enzymes, often retain ACS activity, and some ACS enzymes from nonluminous insects can catalyze bioluminescence from synthetic d-luciferin analogues. Recent sequencing of firefly genomes and transcriptomes further illuminates how the duplication of ACS enzymes and subsequent diversification drove the evolution of bioluminescence. These genetic analyses have also uncovered candidate enzymes that may participate in luciferin metabolism. With the publication of the genomes and transcriptomes of fireflies and related insects, we are now better positioned to dissect and learn from the evolution of bioluminescence in beetles.

Firefly genomes illuminate parallel origins of bioluminescence in beetles

Fireflies and their luminous courtships have inspired centuries of scientific study. Today firefly luciferase is widely used in biotechnology, but the evolutionary origin of bioluminescence within beetles remains unclear. To shed light on this long-standing question, we sequenced the genomes of two firefly species that diverged over 100 million-years-ago: the North American Photinus pyralis and Japanese Aquatica lateralis. To compare bioluminescent origins, we also sequenced the genome of a related click beetle, the Caribbean Ignelater luminosus, with bioluminescent biochemistry near-identical to fireflies, but anatomically unique light organs, suggesting the intriguing hypothesis of parallel gains of bioluminescence. Our analyses support independent gains of bioluminescence in fireflies and click beetles, and provide new insights into the genes, chemical defenses, and symbionts that evolved alongside their luminous lifestyle.

1001 lights: luciferins, luciferases, their mechanisms of action and applications in chemical analysis, biology and medicine

Bioluminescence (BL) is a spectacular phenomenon involving light emission by live organisms. It is caused by the oxidation of a small organic molecule, luciferin, with molecular oxygen, which is catalysed by the enzyme luciferase. In nature, there are approximately 30 different BL systems, of which only 9 have been studied to various degrees in terms of their reaction mechanisms. A vast range of in vitro and in vivo analytical techniques have been developed based on BL, including tests for different analytes, immunoassays, gene expression assays, drug screening, bioimaging of live organisms, cancer studies, the investigation of infectious diseases and environmental monitoring. This review aims to cover the major existing applications for bioluminescence in the context of the diversity of luciferases and their substrates, luciferins. Particularly, the properties and applications of d-luciferin, coelenterazine, bacterial, Cypridina and dinoflagellate luciferins and their analogues along with their corresponding luciferases are described. Finally, four other rarely studied bioluminescent systems (those of limpet Latia, earthworms Diplocardia and Fridericia and higher fungi), which are promising for future use, are also discussed.

Orfelia-type luciferin and its associated storage protein in the non-luminescent cave worm Neoditomyia sp. (Diptera: Keroplatidae) from the Atlantic rainforest: biological and evolutionary implications

Bioluminescence in Diptera is found in the family Keroplatidae, in the glowworms of the genera Arachnocampa, Orfelia and Keroplatus.

Luciferase Activity of Insect Fatty Acyl-CoA Synthetases with Synthetic Luciferins

Long-chain fatty acyl-CoA synthetases (ACSLs) are homologues of firefly luciferase but are incapable of emitting light with firefly luciferin. Recently, we found that an ACSL from the fruit fly Drosophila melanogaster is a latent luciferase that will emit light with the synthetic luciferin CycLuc2. Here, we have profiled a panel of three insect ACSLs with a palette of >20 luciferin analogues. An ACSL from the nonluminescent beetle Agrypnus binodulus (AbLL) was found to be a second latent luciferase with distinct substrate specificity. Several rigid luciferins emit light with both ACSLs, but styryl luciferin analogues are light-emitting substrates only for AbLL. On the other hand, an ACSL from the luminescent beetle Pyrophorus angustus lacks luciferase activity with all tested analogues, despite its higher homology to beetle luciferases. Further study of ACSLs is expected to shed light on the features necessary for bioluminescence and substrate selectivity.

A new orange emitting luciferase from the Southern-Amazon Pyrophorus angustus (Coleoptera: Elateridae) click-beetle: structure and bioluminescence color relationship, evolutional and ecological considerations

Bioluminescent click-beetles display a wide variation of bioluminescence colors ranging from green to orange, including an unusual intra-specific color variation in the Jamaican Pyrophorus plagiophthalamus. Recently, we collected individuals of the Pyrophorus angustus species from the Southern Amazon forest, in Brazil, which displays an orange light emitting abdominal lantern. This species was also previously described from Central America, but displaying a bioluminescence spectrum from 536 nm (dorsal) to 578 nm (ventral). The biogeographic variation of the bioluminescence color in this species could be an adaptation to environmental reflectance and inter/intraspecific sexual competition. Here, we cloned, sequenced, characterized and performed site-direct mutagenesis of this new orange emitting luciferase. The in vitro luciferase spectrum displayed a peak at 594 nm, KM values for ATP and d-luciferin of 160 μM and 17 μM, respectively, and an optimum pH of approximately 8.5. Comparative multialignment and site-directed mutagenesis using different color emitting click-beetle luciferases from P. angustus, Fulgeochlizus bruchi and Pyrearinus termitilluminans luciferases cloned by our group showed an integral role of residue 247 in bioluminescence color modulation.

Cloning and characterization of luciferase from a Fijian luminous click beetle

Luminous click beetle is distributed almost exclusively in Central and South America with a single genus in Melanesia. Among these click beetles, the description of Melanesian species has been fragmentary, and its luciferase gene and phylogenetic relation to other click beetles still remain uncertain. We collected a living luminous click beetle, Photophorus jansonii in Fiji. It emits green-yellow light from two spots on the pronotum and has no ventral luminous organ. Here, we cloned a luciferase gene from this insect by RT-PCR. The deduced amino acid sequence showed high identity of ~85% to the luciferases derived from other click beetle species. The luciferase of the Fijian click beetle was produced as a recombinant protein to characterize its biochemical properties. The Km for D-luciferin and ATP were 173 and 270 μm, respectively. The luciferase was pH-insensitive and the spectrum measured at pH 8.0 showed a peak at 559 nm, which was in the range of green-yellow light as seen in the luminous spot of the living Fijian click beetle. The Fijian click beetle luciferase was assigned to the Elateridae clade by a phylogenetic analysis, but it made a clearly different branch from Pyrophorus group examined in this study.

Luciferase from Fulgeochlizus bruchi (Coleoptera:Elateridae), a Brazilian click-beetle with a single abdominal lantern: molecular evolution, biological function and comparison with other click-beetle luciferases

Bioluminescent click-beetles emit a wide range of bioluminescence colors (λ(Max) = 534-594 nm) from thoracic and abdominal lanterns, which are used for courtship. Only the luciferases from Pyrophorus and Pyrearinus species were cloned and sequenced. The Brazilian Fulgeochlizus bruchi click-beetle, which inhabits the Central-west Cerrado (Savannas), is noteworthy because, differently from other click-beetles, the adult stage displays only a functional abdominal lantern, which produces a bright green bioluminescence for sexual attraction purposes, and lacks functional thoracic lanterns. We cloned the cDNA for the abdominal lantern luciferase of this species. Notably, the primary sequence of this luciferase showed slightly higher identity with the green emitting dorsal lantern luciferases of the Pyrophorus genus instead of the abdominal lanterns luciferases. This luciferase displays a blue-shifted spectrum (λ(Max) = 540 nm), which is pH-insensitive from pH 7.5 to 9.5 and undergoes a slight red shift and broadening above this pH; the lowest K(M) for luciferin among studied click-beetle luciferases, and the highest optimum pH (9.0) ever reported for a beetle luciferase. At pH 9.0, the K(M) for luciferin increases, showing a decrease of affinity for this substrate, despite the higher activity. The slow luminescence decay rate of F. bruchi luciferase in vitro reaction could be an adaptation of this luciferase for the long and sustained in vivo luminescence display of the click-beetle during the courtship, and could be useful for in vivo intracellular imaging.

Firefly luciferase genes from the subfamilies Psilocladinae and Ototretinae (Lampyridae, Coleoptera)

Firefly luciferase genes have been isolated from approximately 20 species of Lampyrinae, Luciolinae, and Photurinae. These are mostly nocturnal luminescent species that use light signals for sexual communication. In this study, we isolated three cDNAs for firefly luciferase from Psilocladinae (Cyphonocerus ruficollis) and Ototretinae (Drilaster axillaris and Stenocladius azumai), which are diurnal non-luminescent or weakly luminescent species that may use pheromones for communication. The amino acid sequences deduced from the three cDNAs showed 81-89% identities to each other and 60-81% identities with known firefly luciferases. The three purified recombinant proteins showed luminescence and fatty acyl-CoA synthetic activities, as observed in other firefly luciferases. The emission maxima by the three firefly luciferases (λmax, 545-546nm) were shorter than those by known luciferases from the nocturnal fireflies (λmax, 550-568nm). These results suggest that the primary structures and enzymatic properties of luciferases are conserved in Lampyridae, but the luminescence colors were red-shifted in nocturnal species compared to diurnal species.

Identification and characterization of a luciferase isotype in the Japanese firefly, Luciola cruciata, involving in the dim glow of firefly eggs

We isolated the cDNA of a luciferase isotype (LcLuc2) from the Japanese firefly, Luciola cruciata (Lampyridae, Coleoptera). The gene product of LcLuc2 (LcLuc2) showed 59% amino acid identity with firefly luciferase LcLuc1, which was previously identified in L. cruciata. The recombinant LcLuc2 showed both luminescence activity and fatty acyl-CoA synthetic activity comparable to those of LcLuc1. The spectral maxima of the luminescence by LcLuc1 and LcLuc2 were 554 and 543 nm, respectively. Reverse transcription-PCR analysis showed that the transcripts of LcLuc1 were abundant in the lanterns of larva, adult male, and adult female, whereas both LcLuc1 and LcLuc2 were expressed in eggs. The luminescence spectra of the lantern extracts from larva, adult male, and adult female were in good agreement with that of recombinant LcLuc1. On the other hand, the emission maximum of the extract from eggs was between those of LcLuc1 and LcLuc2. These results suggest that L. cruciata possesses two luciferases: LcLuc1 is responsible for the major luminescence in larva and adult, whereas LcLuc1 and LcLuc2 are responsible for the dim glow in firefly eggs.

Identification of a functional luciferase gene in the non-luminous diurnal firefly, Lucidina biplagiata

We isolated a luciferase gene (LbLuc) from the non-luminous diurnal firefly, Lucidina biplagiata, with high similarity to that from the nocturnal firefly, Photinus pyralis. The recombinant LbLuc showed luminescence activity comparable to that of the luciferases from P. pyralis and Luciola cruciata. To understand the non-luminosity of L. biplagiata, we determined the amount of luciferase in the adult specimen using the luciferin-luciferase reaction and found that the content of luciferase in L. biplagiata was estimated to be only 0.1% of that in L. cruciata. As previously reported, the content of luciferin in L. biplagiata was less than 0.1% of that in L. cruciata. Thus, the non-luminosity of L. biplagiata might be explained by low levels of both luciferase and luciferin.