Structure and evolution of the luciferin-regenerating enzyme (LRE) gene from the firefly Photinus pyralis

Genomics investigation of the potentially invasive firefly Photinus signaticollis Blanchard 1845: Complete mitochondrial genome, multigene phylogenies and obtention of the luciferase and luciferin-regenerating genes

A genomic investigation of the potentially invasive firefly Photinus signaticollis Blanchard1845 has been performed and led to the obtention of its complete 16,411 bp long mitochondrial genome. The mitogenome encodes 13 protein-coding genes, 22 tRNA genes and 2 rRNA genes. With other species of the Photinus complex it shares several premature terminations of some protein-coding genes and also an overlap between cox1 and tRNA-Tyr. By data-mining, the complete luciferase and luciferin-regenerating genes were also identified from the contigs file and compared with existing data, in addition to WG and CAD, two genes used in pioneering phylogenetic studies on fireflies. Three maximum likelihood phylogenies were derived from all these data. The multigene phylogeny based on all mitochondrial protein-coding genes strongly associates P. signaticollis with Photinus pyralis Linnaeus, 1758 and the lantern-less daily "winter firefly", Photinus corruscus Linnaeus, 1767. A second phylogeny based on concatenated sequences of the cox1, WG and CAD genes positions P. signaticollis as a sister clade to a large cluster of species containing the 7 sub-groups previously evidenced among the North American species of the Photinus complex. A third phylogeny based on the amino-acid sequence of the luciferase protein associates P. signaticollis to Photinus scintillans. The analysis presented here will most certainly help to come to a better understanding of the very complex inter-relationships in the very large Photinus genus.

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.

Luciferin Regeneration in Firefly Bioluminescence via Proton-Transfer-Facilitated Hydrolysis, Condensation and Chiral Inversion

Firefly bioluminescence is produced via luciferin enzymatic reactions in luciferase. Luciferin has to be unceasingly replenished to maintain bioluminescence. How is the luciferin reproduced after it has been exhausted? In the early 1970s, Okada proposed the hypothesis that the oxyluciferin produced by the previous bioluminescent reaction could be converted into new luciferin for the next bioluminescent reaction. To some extent, this hypothesis was evidenced by several detected intermediates. However, the detailed process and mechanism of luciferin regeneration remained largely unknown. For the first time, we investigated the entire process of luciferin regeneration in firefly bioluminescence by density functional theory calculations. This theoretical study suggests that luciferin regeneration consists of three sequential steps: the oxyluciferin produced from the last bioluminescent reaction generates 2-cyano-6-hydroxybenzothiazole (CHBT) in the luciferin regenerating enzyme (LRE) via a hydrolysis reaction; CHBT combines with L-cysteine in vivo to form L-luciferin via a condensation reaction; and L-luciferin inverts into D-luciferin in luciferase and thioesterase. The presently proposed mechanism not only supports the sporadic evidence from previous experiments but also clearly describes the complete process of luciferin regeneration. This work is of great significance for understanding the long-term flashing of fireflies without an in vitro energy supply.

Biosynthetic bifunctional enzyme complex with high-efficiency luciferin-recycling to enhance the bioluminescence imaging

Firefly luciferase is a prominent reporter on molecular imaging with the advantage of longer wavelength on light emission and the ATP linear correlation, which makes it useful in most of current bioluminescence imaging model. However, the utility of this biomaterial was limited by the signal intensity and stability which are respectively affected by enzyme activity and substrate consumption. This study demonstrated a series of novel synthetic bifunctional enzyme complex of Firefly luciferase (Fluc) and Luciferin-regenerating enzyme (LRE). A peptide linker library was constructed for the fusion strategy on biosynthesis. The findings of both experimental data and structural simulation demonstrated that the intervention of fused LRE remarkably improve the stability of in vitro bioluminescence signal through luciferin recycling; and revealed the competitive relationship of Fluc and LRE on luciferin binding: Fluc performed higher activity with one copy number of rigid linker (EAAAK) at the C terminal while LRE acted more efficiently with two copy numbers of flexible linker (GGGGS) at the N terminal. With the advantage of signal intensity and stability, this fused bifunctional enzyme complex may expand the application of firefly luciferase to in vitro bioluminescence imaging.

Fusion expression of bifunctional enzyme complex for luciferin-recycling to enhance the luminescence imaging

Firefly luciferase (Fluc) has been widely used as a bioluminescent monitor. The ATP linear correlation and exogenous luciferin requirement make it useful in most of current imaging systems. However, the utility of this reporter was still limited by the intensity and decay of the luminescent signal, and the active site and structure of enzyme including the relevant substrate channeling region. This study demonstrated a novel construction of bifunctional enzyme system to improve the luminescence generation of firefly luciferase, by bringing in a luciferin-regenerating enzyme (LRE) fusion expressed to the C terminal of luciferase, between which were connected with peptide linker. The fusion protein constructed with typical type of linker, rigid linker (EAAAK) and flexible linker (GGGGS), were analyzed comparing with the unlinked free enzyme. In vivo and in vitro assessment of the bioluminescence intensity and decaying rate to the series of Fluc-LRE enzyme complex were assayed. The fInding demonstrated that the presence of LRE remarkably enhance the generation of luminescence and remained significant stronger signal than that of the control, and the peptide-linked dual enzyme present more stability and continuation on the signal generation and lower decaying rate on signal recession, especially at low dose of Fluc injection. With the advantage of luminescence intensity and reaction period, the peptide mediated fusion expressed LRE may expand the application of Firefly luciferase on bioluminescence imaging.

Luciferin-Regenerating Enzyme Crystal Structure Is Solved but its Function Is Still Unclear

Contribution of luciferin-regenerating enzyme (LRE) for in vitro recycling of D-luciferin has been reported. According to crystal structure of LRE, it is a beta-propeller protein which is a type of all β-protein architecture. In this overview, reinvestigation of the luciferase-based LRE assays and its function is reported. Until now, sequence of LRE genes from four different species of firefly has been reported. In spite of previous reports, T-LRE (from Lampyris turkestanicus) was cloned and expressed in Escherichia coli as well as Pichia pastoris in a nonsoluble form as inclusion body. According to recent investigations, bioluminescent signal of soluble T-LRE-luciferase-coupled assay increased and then reached an equilibrium state in the presence of D-cysteine. In addition, the results revealed that both D- and L-cysteine in the absence of T-LRE caused a significant increase in bioluminescence intensity of luciferase over a long time. Based on activity measurements and spectroscopic results, D-cysteine increased the activity of luciferase due to its redox potential and induction of conformational changes in structure and kinetics properties. In conclusion, in spite of previous reports on the effect of LRE (at least T-LRE) on luciferase activity, most of the increase in luciferase activity is caused by direct effect of D-cysteine on structure and activity of firefly luciferase. Moreover, bioinformatics analysis cannot support the presence of LRE in peroxisome of photocytes in firefly lanterns.

Senescence Marker Protein 30: Functional and Structural Insights to its Unknown Physiological Function

Senescence marker protein 30 (SMP30) is a multifunctional protein involved in cellular Ca(2+) homeostasis and the biosynthesis of ascorbate in non-primate mammals. The primary structure of the protein is highly conserved among vertebrates, suggesting the existence of a significant physiological function common to all mammals, including primates. Enzymatic activities of SMP30 include aldonolactone and organophosphate hydrolysis. Protective effects against apoptosis and oxidative stress have been reported. X-ray crystallography revealed that SMP30 is a six-bladed β-propeller with structural similarity to paraoxonase 1, another protein with lactonase and organophosphate hydrolase activities. SMP30 has recently been tied to several physiological conditions including osteoporosis, liver fibrosis, diabetes, and cancer. This review aims to describe the recent advances made toward understanding the connection between molecular structure, enzymatic activity and physiological function of this highly conserved, multifaceted protein.