Synthesis of dehydroluciferin by firefly luciferase: effect of dehydroluciferin, coenzyme A and nucleoside triphosphates on the luminescent reaction

Solid-Phase Synthesis of Caged Luminescent Peptides via Side Chain Anchoring

The synthesis of caged luminescent peptide substrates remains challenging, especially when libraries of the substrates are required. Most currently available synthetic methods rely on a solution-phase approach, which is less suited for parallel synthesis purposes. We herein present a solid-phase peptide synthesis (SPPS) method for the synthesis of caged aminoluciferin peptides via side chain anchoring of the P1 residue. After the synthesis of a preliminary test library consisting of 40 compounds, the synthetic method was validated and optimized for up to >100 g of resin. Subsequently, two separate larger peptide libraries were synthesized either having a P1 = lysine or arginine residue containing in total 719 novel peptide substrates. The use of a more stable caged nitrile precursor instead of caged aminoluciferin rendered our parallel synthetic approach completely suitable for SPPS and serine protease profiling was demonstrated using late-stage aminoluciferin generation.

Improving the Stability of Protein-Protein Interaction Assay FlimPIA Using a Thermostabilized Firefly Luciferase

The protein–protein interaction assay is a key technology in various fields, being applicable in drug screening as well as in diagnosis and inspection, wherein the stability of assays is important. In a previous study, we developed a unique protein–protein interaction assay “FlimPIA” based on the functional complementation of mutant firefly luciferases (Fluc). The catalytic step of Fluc was divided into two half steps: D-luciferin was adenylated in the first step, while adenylated luciferin was oxidized in the second step. We constructed two mutants of Fluc from Photinus pyralis (Ppy); one mutant named Donor is defective in the second half reaction, while the other mutant named Acceptor exhibited low activity in the first half reaction. To date, Ppy has been used in the system; however, its thermostability is low. In this study, to improve the stability of the system, we applied Fluc from thermostabilized Luciola lateralis to FlimPIA. We screened suitable mutants as probes for FlimPIA and obtained Acceptor and Donor candidates. We detected the interaction of FKBP12-FRB with FlimPIA using these candidates. Furthermore, after the incubation of the probes at 37°C for 1 h, the luminescence signal of the new system was 2.4-fold higher than that of the previous system, showing significant improvement in the stability of the assay.

Visualization of activity-regulated BDNF expression in the living mouse brain using non-invasive near-infrared bioluminescence imaging

Altered levels of brain-derived neurotrophic factor (BDNF) have been reported in neurologically diseased human brains. Therefore, it is important to understand how the expression of BDNF is controlled under pathophysiological as well as physiological conditions. Here, we report a method to visualize changes in BDNF expression in the living mouse brain using bioluminescence imaging (BLI). We previously generated a novel transgenic mouse strain, Bdnf-Luciferase (Luc), to monitor changes in Bdnf expression; however, it was difficult to detect brain-derived signals in the strain using BLI with d-luciferin, probably because of incomplete substrate distribution and light penetration. We demonstrate that TokeOni, which uniformly distributes throughout the whole mouse body after systematic injection and produces a near-infrared bioluminescence light, was suitable for detecting signals from the brain of the Bdnf-Luc mouse. We clearly detected brain-derived bioluminescence signals that crossed the skin and skull after intraperitoneal injection of TokeOni. However, repeated BLI using TokeOni should be limited, because repeated injection of TokeOni on the same day reduced the bioluminescence signal, presumably by product inhibition. We successfully visualized kainic acid-induced Bdnf expression in the hippocampus and sensory stimulation-induced Bdnf expression in the visual cortex. Taken together, non-invasive near-infrared BLI using Bdnf-Luc mice with TokeOni allowed us to evaluate alterations in BDNF levels in the living mouse brain. This will enable better understanding of the involvement of BDNF expression in the pathogenesis and pathophysiology of neurological diseases.

Characterisation of utrophin modulator SMT C1100 as a non-competitive inhibitor of firefly luciferase

Firefly luciferase (FLuc) is a powerful tool for molecular and cellular biology, and popular in high-throughput screening and drug discovery. However, FLuc assays have been plagued with positive and negative artefacts due to stabilisation and inhibition by small molecules from a range of chemical classes. Here we disclose Phase II clinical compound SMT C1100 for the treatment of Duchenne muscular dystrophy as an FLuc inhibitor (K_D of 0.40 ± 0.15 µM). Enzyme kinetic studies using SMT C1100 and other non-competitive inhibitors including resveratrol and NFκBAI4 identified previously undescribed modes of inhibition with respect to FLuc's luciferyl adenylate intermediate. Employing a photoaffinity strategy to identify SMT C1100's binding site, a photolabelled SMT C1100 probe instead underwent FLuc-dependent photooxidation. Our findings support novel binding sites on FLuc for non-competitive inhibitors.

Optimized bioluminescence analysis of adenosine triphosphate (ATP) released by platelets and its application in the high throughput screening of platelet inhibitors

Activated platelets release adenosine trisphosphate (ATP) and bioluminescence analysis of ATP release is usually used to monitor activation of platelets induced by various stimulants. However, bioluminescence analysis of ATP possesses poor linearity, the signal is quickly attenuated, and the accuracy of ATP release from platelets is hard to determine accurately enough to be used in a high throughput screening of platelet inhibitors. The present study was designed to optimize bioluminescence analysis of ATP released by platelets and expand its application in high throughput screening of platelet inhibitors. The results showed that accuracy of ATP analysis was significantly improved by adding coenzyme A (CoA) and signal attenuation of ATP analysis was greatly postponed by adding bovine serum albumin (BSA) both in Hank’s balanced salt solution (HBSS) and Tyrode’s buffer. Furthermore, ATP release of activated platelets and inhibitory effects of Ly294002 and Staurosporine on platelet activation were accurately determined by our optimized bioluminescence analysis of ATP. Thus, we have successfully constructed an optimized bioluminescence analysis of ATP which can be used in high throughput screening of platelet inhibitors.

High-Throughput Firefly Luciferase Reporter Assays

Firefly luciferase reporter gene assays find wide application in high-throughput screens to identify molecular components of biological networks or to identify chemical compounds capable of interfering with cellular signaling. Here, we present methods to prepare affordable firefly luciferase assay reagents and procedures to use these reagents in reporter gene high-throughput screening with large batches of 96-well cell culture plates.

Convergent synthesis and optical properties of near-infrared emitting bioluminescent infra-luciferins

Infra-luciferin, an alkene linked analogue of luciferin, gives bioluminescence emission >700 nm and has the potential to be used for multiparametric in vivo imaging. We report here a high yielding, scalable and convergent synthesis of infra-luciferin which will allow the synthesis of other conjugated luciferins for investigation in near-infrared bioluminescence imaging. We demonstrated this potential by using the new route to synthesise a diene linked analogue of luciferin, the fluorescent and bioluminescent properties of which were compared to those of d-luciferin and infra-luciferin. We found that extension of conjugation to a diene linker resulted in the specific bioluminescence activity being reduced by 3-4 orders of magnitude compared to d-luciferin. Analogous to its fluorescence emission spectrum, the diene linked analogue exhibited two peaks in its bioluminescence spectrum, the major one being slightly blue-shifted compared to natural d-luciferin, and a minor peak at ca. 800 nm. The fluorescence quantum yield and pH dependence of fluorescence were also determined.

A luciferin analogue generating near-infrared bioluminescence achieves highly sensitive deep-tissue imaging

In preclinical cancer research, bioluminescence imaging with firefly luciferase and D-luciferin has become a standard to monitor biological processes both in vitro and in vivo. However, the emission maximum (λ_max) of bioluminescence produced by D-luciferin is 562 nm where light is not highly penetrable in biological tissues. This emphasizes a need for developing a red-shifted bioluminescence imaging system to improve detection sensitivity of targets in deep tissue. Here we characterize the bioluminescent properties of the newly synthesized luciferin analogue, AkaLumine-HCl. The bioluminescence produced by AkaLumine-HCl in reactions with native firefly luciferase is in the near-infrared wavelength ranges (λ_max=677 nm), and yields significantly increased target-detection sensitivity from deep tissues with maximal signals attained at very low concentrations, as compared with D-luciferin and emerging synthetic luciferin CycLuc1. These characteristics offer a more sensitive and accurate method for non-invasive bioluminescence imaging with native firefly luciferase in various animal models.

D-luciferin is the standard bioluminescent substrate for in vitro and in vivo imaging. Here the authors introduce AkaLumine-HCl, a soluble luciferin analogue with a near-infrared emission maximum, which allows deep tissue imaging at lower concentrations than D-luciferin.

Identification of novel genes that regulate androgen receptor signaling and growth of androgen-deprived prostate cancer cells

Prostate cancer progression to castration refractory disease is associated with anomalous transcriptional activity of the androgen receptor (AR) in an androgen-depleted milieu. To identify novel gene products whose downregulation transactivates AR in prostate cancer cells, we performed a screen of enzymatically-generated shRNA lenti-libraries selecting for transduced LNCaP cells with elevated expression of a fluorescent reporter gene under the control of an AR-responsive promoter. The shRNAs present in selected populations were analyzed using high-throughput sequencing to identify target genes. Highly enriched gene targets were then validated with siRNAs against selected genes, testing first for increased expression of luciferase from an AR-responsive promoter and then for altered expression of endogenous androgen-regulated genes in LNCaP cells. We identified 20 human genes whose silencing affected the expression of exogenous and endogenous androgen-responsive genes in prostate cancer cells grown in androgen-depleted medium. Knockdown of four of these genes upregulated the expression of endogenous AR targets and siRNAs targeting two of these genes (IGSF8 and RTN1) enabled androgen-independent proliferation of androgen-dependent cells. The effects of IGSF8 appear to be mediated through its interaction with a tetraspanin protein, CD9, previously implicated in prostate cancer progression. Remarkably, homozygous deletions of IGSF8 are found almost exclusively in prostate cancers but not in other cancer types. Our study shows that androgen independence can be achieved through the inhibition of specific genes and reveals a novel set of genes that regulate AR signaling in prostate cancers.

Ultra sensitive firefly luciferase-based protein-protein interaction assay (FlimPIA) attained by hinge region engineering and optimized reaction conditions

Detecting and assaying protein-protein interactions are significant research procedures in biology and biotechnology. We recently reported a novel assay to detect protein-protein interaction, i.e. firefly luminescent intermediate-based protein-protein interaction assay (FlimPIA) using two mutant firefly luciferases (Flucs), which complement each other's deficient half reaction. This assay detects neighboring of two mutant Flucs, namely, a "Donor" that catalyzes the adenylation of firefly luciferin to produce a luciferyl-adenylate intermediate, and an "Acceptor" that catalyzes the subsequent light emitting reaction. However, its rather high background signal, derived from the remaining adenylation activity of the Acceptor, has limited its usefulness. To reduce this background signal, we introduced a mutation (R437K) into the hinge region of the Acceptor, while maintaining the oxidative activity. Interestingly, the signal/background (S/B) ratio of the assay was markedly improved by the addition of coenzyme A and reduction of the ATP concentration, probably due to reduced inhibition by dehydroluciferyl-adenylate formed during the catalysis and an increased ATP-based Km value of the Acceptor, respectively. As a result, a significantly improved maximal S/B ratio from 2.5 to ∼40 was attained, which promises wider use of the assay in in vitro diagnostics, drug discovery, and expanding our knowledge of various biological phenomena.

Luciferin-Regenerating Enzyme Mediates Firefly Luciferase Activation Through Direct Effects of D-Cysteine on Luciferase Structure and Activity

Luciferin-regenerating enzyme (LRE) contributes to in vitro recycling of D-luciferin. In this study, reinvestigation of the luciferase-based LRE assay is reported. Here, using quick change site-directed mutagenesis seven T-LRE (Lampyris turkestanicusLRE) mutants were constructed and the most functional mutant of T-LRE (T(69)R) was selected for this research and the effects of D- and L-cysteine on T(69)R T-LRE-luciferase-coupled assay are examined. Our results demonstrate that bioluminescent signal of T(69)R T-LRE-luciferase-coupled assay increases and then reach equilibrium state in the presence of 5 mm D-cysteine. In addition, results reveal that 5 mm D- and L-cysteine in the absence of T(69)R T-LRE cause a significant increase in bioluminescence intensity of luciferase over a long time as well as decrease in decay rate. Based on activity measurements, far-UV CD analysis, ANS fluorescence and DLS (Dynamic light scattering) results, D-cysteine increases the activity of luciferase due to weak redox potential, antiaggregatory effects, induction of changes in conformational structure and kinetics properties. In conclusion, in spite of previous reports on the effect of LRE on luciferase bioluminescent intensity, the majority of increase in luciferase light output and time-course originate from the direct effects of D-cysteine on structure and activity of firefly luciferase.

Reporter cell activity within hydrogel constructs quantified from oxygen-independent bioluminescence

By providing a three-dimensional (3D) support to cells, hydrogels offer a more relevant in vivo tissue-like environment as compared to two-dimensional cell cultures. Hydrogels can be applied as screening platforms to investigate in 3D the role of biochemical and biophysical cues on cell behaviour using bioluminescent reporter cells. Gradients in oxygen concentration that result from the interplay between molecular transport and cell metabolism can however cause substantial variability in the observed bioluminescent reporter cell activity. To assess the influence of these oxygen gradients on the emitted bioluminescence for various hydrogel geometries, a combined experimental and modelling approach was implemented. We show that the applied model is able to predict oxygen gradient independent bioluminescent intensities which correlate better to the experimentally determined viable cell numbers, as compared to the experimentally measured bioluminescent intensities. By analysis of the bioluminescence reaction dynamics we obtained a quantitative description of cellular oxygen metabolism within the hydrogel, which was validated by direct measurements of oxygen concentration within the hydrogel. Bioluminescence peak intensities can therefore be used as a quantitative measurement of reporter cell activity within a hydrogel, but an unambiguous interpretation of these intensities requires a compensation for the influence of cell-induced oxygen gradients on the luciferase activity.

Affordable luciferase reporter assay for cell-based high-throughput screening

The firefly luciferase gene is commonly used in cell-based reporter assays. Convenient luciferase assay reagents for use in high-throughput screening (HTS) are commercially available. However, the high cost of these reagents is not within the means of some academic laboratories. Therefore, we set out to develop an affordable luciferase assay reagent applicable in an HTS format using simple liquid-handling steps. The reagent was homemade from individual chemical components and optimized for luminescence intensity and stability. We determined the minimal concentrations of the most expensive components, dithiothreitol (DTT) and D-luciferin, resulting in a total assay reagent cost of less than 1 cent per sample. Signal stability was maximized by omission of coenzyme A and reduction of DTT concentration. The assay was validated in a high-throughput setting using two cancer cell lines carrying a p53-dependent luciferase reporter construct and siRNAs modulating p53 transcriptional activity. Induction of p53 activity by silencing PPM1D or SYVN1 and reduction of p53 activity by silencing p53 remained constant over a 2-h measurement period, with good assay quality (Z' factors mostly above 0.5). Hence, the luciferase assay described herein can be used for affordable reporter readout in cell-based HTS.

A selenium analogue of firefly D-luciferin with red-shifted bioluminescence emission

A selenium analogue of amino-D-luciferin, aminoseleno-D-luciferin, is synthesized and shown to be a competent substrate for the firefly luciferase enzyme. It has a red-shifted bioluminescence emission maximum at 600 nm and is suitable for bioluminescence imaging studies in living subjects.

Enzymatic synthesis of mono and dinucleoside polyphosphates

BACKGROUND

Mono and dinucleoside polyphosphates (p(n)Ns and Np(n)Ns) exist in living organisms and induce diverse biological effects through interaction with intracellular and cytoplasmic membrane proteins. The source of these compounds is associated with secondary activities of a diverse group of enzymes.

SCOPE OF REVIEW

Here we discuss the mechanisms that can promote their synthesis at a molecular level. Although all the enzymes described in this review are able to catalyse the in vitro synthesis of Np(n)Ns (and/or p(n)N), it is not clear which ones are responsible for their in vivo accumulation.

MAJOR CONCLUSIONS

Despite the large amount of knowledge already available, important questions remain to be answered and a more complete understanding of p(n)Ns and Np(n)Ns synthesis mechanisms is required. With the possible exception of (GTP:GTP guanylyltransferase of Artemia), all enzymes able to catalyse the synthesis of p(n)Ns and Np(n)Ns are unspecific and the factors that can promote their synthesis relative to the canonical enzyme activities are unclear.

GENERAL SIGNIFICANCE

The fact that p(n)Ns and Np(n)Ns syntheses are promiscuous activities of housekeeping enzymes does not reduce its physiological or pathological importance. Here we resume the current knowledge regarding their enzymatic synthesis and point the open questions on the field.

Kinetics of inhibition of firefly luciferase by dehydroluciferyl-coenzyme A, dehydroluciferin and L-luciferin

The inhibition mechanisms of the firefly luciferase (Luc) by three of the most important inhibitors of the reactions catalysed by Luc, dehydroluciferyl-coenzyme A (L-CoA), dehydroluciferin (L) and L-luciferin (L-LH(2)) were investigated. Light production in the presence and absence of these inhibitors (0.5 to 2 μM) has been measured in 50 mM Hepes buffer (pH = 7.5), 10 nM Luc, 250 μM ATP and D-luciferin (D-LH(2), from 3.75 up to 120 μM). Nonlinear regression analysis with the appropriate kinetic models (Henri-Michaelis-Menten and William-Morrison equations) reveals that L-CoA is a non-competitive inhibitor of Luc (K(i) = 0.88 ± 0.03 μM), L is a tight-binding uncompetitive inhibitor (K(i) = 0.00490 ± 0.00009 μM) and L-LH(2) acts as a mixed-type non-competitive-uncompetitive inhibitor (K(i) = 0.68 ± 0.14 μM and αK(i) = 0.34 ± 0.16 μM). The K(m) values obtained for L-CoA, L and L-LH(2) were 16.1 ± 1.0, 16.6 ± 2.3 and 14.4 ± 0.96 μM, respectively. L and L-LH(2) are strong inhibitors of Luc, which may indicate an important role for these compounds in Luc characteristic flash profile. L-CoA K(i) supports the conclusion that CoA can stimulate the light emission reaction by provoking the formation of a weaker inhibitor.

Illuminating insights into firefly luciferase and other bioluminescent reporters used in chemical biology

Understanding luciferase enzymology and the structure of compounds that modulate luciferase activity can be used to improve the design of luminescence-based assays. This review provides an overview of these popular reporters with an emphasis on the commonly used firefly luciferase from Photinus pyralis (FLuc). Large-scale chemical profile studies have identified a variety of scaffolds that inhibit FLuc. In some cell-based assays, these inhibitors can act in a counterintuitive way, leading to a gain in luminescent signal. Although formerly attributed to transcriptional activation, intracellular stabilization of FLuc is the primary mechanism underlying this observation. FLuc inhibition and stabilization can be complex, as illustrated by the compound PTC124, which is converted by FLuc in the presence of ATP to a high affinity multisubstrate adduct inhibitor, PTC124-AMP. The potential influence these findings can have on drug discovery efforts is provided here.

Enhanced beetle luciferase for high-resolution bioluminescence imaging

We developed an enhanced green-emitting luciferase (ELuc) to be used as a bioluminescence imaging (BLI) probe. ELuc exhibits a light signal in mammalian cells that is over 10-fold stronger than that of the firefly luciferase (FLuc), which is the most widely used luciferase reporter gene. We showed that ELuc produces a strong light signal in primary cells and tissues and that it enables the visualization of gene expression with high temporal resolution at the single-cell level. Moreover, we successfully imaged the nucleocytoplasmic shuttling of importin alpha by fusing ELuc at the intracellular level. These results demonstrate that the use of ELuc allows a BLI spatiotemporal resolution far greater than that provided by FLuc.

Practical application of bioluminescence enzyme immunoassay using enhancer for firefly luciferin-luciferase bioluminescence

Firefly luciferin-luciferase bioluminescence is known for its high quantum yield (41.0 ± 7.4%). Given this high quantum yield, application of this bioluminescence is expected to be useful in the field of clinical diagnostics. The kinetic profile of this bioluminescence exhibits an instant rise (<1 s) and a rapid decay in light emission (decreased to 42% after 5 s). In this study, we applied four enhancers including coenzyme A, inosine5'-triphosphate sodium salt, sodium tripolyphosphate and potassium pyrophosphate to prolong light emission. When these enhancers were used, luminescence was only decreased to 89, 83, 87 and 82% after 5 s, respectively. These materials modified the kinetic profile of bioluminescence so that the luminescence is more suitable for clinical application. It becomes more suitable because they enable highly sensitive integration and simplification of a device by separating luminescence measurements from dispensing of reagents. Using these enhancers, we then developed a bioluminescent enzyme immunoassay (BLEIA) for hepatitis B virus surface antigen (HBsAg) that employed firefly luciferase as a labeling enzyme. We compared the results obtained from the HBsAg BLEIA method with the conventional chemiluminescent enzyme immunoassay method, and found a satisfactory correlation (r=0.984, n=118).

Firefly bioluminescence: a mechanistic approach of luciferase catalyzed reactions

Luciferase is a general term for enzymes catalyzing visible light emission by living organisms (bioluminescence). The studies carried out with Photinus pyralis (firefly) luciferase allowed the discovery of the reaction leading to light production. It can be regarded as a two-step process: the first corresponds to the reaction of luciferase's substrate, luciferin (LH(2)), with ATP-Mg(2+) generating inorganic pyrophosphate and an intermediate luciferyl-adenylate (LH(2)-AMP); the second is the oxidation and decarboxylation of LH(2)-AMP to oxyluciferin, the light emitter, producing CO(2), AMP, and photons of yellow-green light (550- 570 nm). In a dark reaction LH(2)-AMP is oxidized to dehydroluciferyl-adenylate (L-AMP). Luciferase also shows acyl-coenzyme A synthetase activity, which leads to the formation of dehydroluciferyl-coenzyme A (L-CoA), luciferyl-coenzyme A (LH(2)-CoA), and fatty acyl-CoAs. Moreover luciferase catalyzes the synthesis of dinucleoside polyphosphates from nucleosides with at least a 3'-phosphate chain plus an intact terminal pyrophosphate moiety. The LH(2) stereospecificity is a particular feature of the bioluminescent reaction where each isomer, D-LH(2) or L-LH(2), has a specific function. Practical applications of the luciferase system, either in its native form or with engineered proteins, encloses the analytical assay of metabolites like ATP and molecular biology studies with luc as a reporter gene, including the most recent and increasing field of bioimaging.

Kinetics of inhibition of firefly luciferase by oxyluciferin and dehydroluciferyl-adenylate

The inhibition mechanisms of the firefly luciferase (Luc) by the two major products of the reactions catalysed by Luc, oxyluciferin and dehydroluciferyl-adenylate (L-AMP), were investigated. Light production in the presence and absence of these inhibitors (0.5 to 2 microM oxyluciferin; 0.0025 to 1.25 microM L-AMP) has been measured in 50 mM Hepes buffer (pH=7.5), 10 nM Luc, 250 microM ATP and D-Luciferin (from 3.75 up to 120 microM). Nonlinear regression analysis with the appropriate kinetic models (Henri-Michaelis-Menten and William-Morrison equations) reveals that oxyluciferin is a competitive inhibitor of luciferase (Ki=0.50+/-0.03 microM) while L-AMP act as a tight-binding competitive inhibitor (Ki=3.8+/-0.7 nM). The Km values obtained both for oxyluciferin and L-AMP were 14.7+/-0.7 and 14.9+/-0.2 microM, respectively. L-AMP is a stronger inhibitor of Luc than oxyluciferin and the major responsible for the characteristic flash profile of in vitro Luc bioluminescence.

An optimized luciferase bioluminescent assay for coenzyme A

A new bioluminescent method for coenzyme A (CoA) quantification is described. It is based on the enzymatic conversion of dehydroluciferyl-adenylate (L-AMP) into dehydroluciferyl-coenzyme A (L-CoA) by firefly luciferase (E.C. 1.13.12.7) (LUC), which causes a flash of light that can be measured in a luminometer. The method was subjected to optimization using experimental design methodologies to obtain optimum values for the concentrations of L-AMP ([L-AMP]), luciferase ([LUC]), ATP ([ATP]) and luciferin ([LH(2)]). This method has a linear response over the range of 0.25-4 microM of CoA, with a limit of detection (LOD) of 0.24 microM and a limit of quantification (LOQ) of 0.80 microM. The assay has a relative standard deviation of about 7%. By coupling this optimized procedure to bioluminescent detection, a sensible and robust method can be obtained for the analysis of CoA.

Pyrophosphate and tripolyphosphate affect firefly luciferase luminescence because they act as substrates and not as allosteric effectors

The activating and stabilizing effects of inorganic pyrophosphate, tripolyphosphate and nucleoside triphosphates on firefly luciferase bioluminescence were studied. The results obtained show that those effects are a consequence of the luciferase-catalyzed splitting of dehydroluciferyl-adenylate, a powerful inhibitor formed as a side product in the course of the bioluminescence reaction. Inorganic pyrophosphate, tripolyphosphate, CTP and UTP antagonize the inhibitory effect of dehydroluciferyl-adenylate because they react with it giving rise to products that are, at least, less powerful inhibitors. Moreover, we demonstrate that the antagonizing effects depended on the rate of the splitting reactions being higher in the cases of inorganic pyrophosphate and tripolyphosphate and lower in the cases of CTP and UTP. In the case of inorganic pyrophosphate, the correlation between the rate of dehydroluciferyl-adenylate pyrophosphorolysis and the activating effect on bioluminescence only occurs for low concentrations because inorganic pyrophosphate is, simultaneously, an inhibitor of the bioluminescence reaction. Our results demonstrate that previous reports concerning the activating effects of several nucleotides (including some that do not react with dehydroluciferyl-adenylate) on bioluminescence were caused by the presence of inorganic pyrophosphate contamination in the preparations used.

Firefly luminescence: a historical perspective and recent developments

Significant advances have occurred regarding our knowledge of firefly luciferase mechanisms. Although most of this progress was an outcome of molecular biology and structural studies, important achievements have also occurred on its fundamental chemistry. Those developments are here summarized and presented in a historical perspective.

Firefly luciferase produces hydrogen peroxide as a coproduct in dehydroluciferyl adenylate formation

Firefly luciferase catalyzes the synthesis of H2O2 from the same substrates as the bioluminescence reaction: ATP and luciferin (D-LH2). About 80% of the enzyme-bound intermediate D-luciferyl adenylate (D-LH2-AMP) is oxidized into oxyluciferin, and a photon is emitted during this reaction. The enzyme pathway responsible for the generation of H2O2 is a side reaction in which D-LH2-AMP is oxidized into dehydroluciferyl adenylate (L-AMP). Like the bioluminescence reaction, the luciferase-catalyzed synthesis of H2O2 and L-AMP is a stereospecific process, involving only the natural D enantiomer. However, the intramolecular electron transfer postulated as essential to the light emission process is not involved in this side reaction.

Stereoisomeric bio-inversion key to biosynthesis of fireflyd-luciferin

The chirality of the luciferin substrate is critical to the luciferin-luciferase reaction producing bioluminescence. In firefly, the biosynthetic pathway of D-luciferin is still unclear, although it can be synthesized in vitro from D-cysteine. Here, we show that the firefly produces both D- and L-luciferin, and that the amount of active D-luciferin increases gradually with maturation stage. Studies of firefly body extracts indicate the possible conversion of L-cysteine via L-luciferin into D-luciferin, suggesting that the biosynthesis is enzymatically regulated by stereoisomeric bio-inversion of L-luciferin. We conclude that the selection of chirality in living organisms is not as rigid as previously thought.

Optical imaging of luminescence for in vivo quantification of gene electrotransfer in mouse muscle and knee

BACKGROUND

Optical imaging is an attractive non-invasive way to evaluate the expression of a transferred DNA, mainly thanks to its lower cost and ease of realization. In this study optical imaging was evaluated for monitoring and quantification of the mouse knee joint and tibial cranial muscle electrotransfer of a luciferase encoding plasmid. Optical imaging was applied to study the kinetics of luciferase expression in both tissues.

RESULTS

The substrate of luciferase (luciferin) was injected either intraperitonealy (i.p.) or in situ into the muscle or the knee joint. Luminescence resulting from the luciferase-luciferin reaction was measured in vivo with a cooled CCD camera and/or in vitro on tissue lysate. Maximal luminescence of the knee joint and muscle after i.p. (2.5 mg) or local injection of luciferin (50 microg in the knee joint, 100 microg in the muscle) were highly correlated. With the local injection procedure adopted, in vivo and in vitro luminescences measured on the same muscles significantly correlated. Luminescence measurements were reproducible and the signal level was proportional to the amount of plasmid injected. In vivo luciferase activity in the electrotransfered knee joint was detected for two weeks. Intramuscular electrotransfer of 0.3 or 3 microg of plasmid led to stable luciferase expression for 62 days, whereas injecting 30 microg of plasmid resulted in a drop of luminescence three weeks after electrotransfer. These decreases were partially associated with the development of an immune response.

CONCLUSION

A particular advantage of the i.p. injection of substrate is a widespread distribution at luciferase production sites. We have also highlighted advantages of local injection as a more sensitive detection method with reduced substrate consumption. Besides, this route of injection is relatively free of uncontrolled parameters, such as diffusion to the target organ, crossing of biological barriers and evidencing variations in local enzymatic kinetics, probably related to the reaction medium in the targeted organ. Optical imaging was shown to be a sensitive and relevant technique to quantify variations of luciferase activity in vivo. Further evaluation of the effective amount of luciferase in a given tissue by in vivo optical imaging relies on conditions of the enzymatic reaction and light absorption and presently requires in vitro calibration for each targeted organ.

Coenzyme A affects firefly luciferase luminescence because it acts as a substrate and not as an allosteric effector

The effect of CoA on the characteristic light decay of the firefly luciferase catalysed bioluminescence reaction was studied. At least part of the light decay is due to the luciferase catalysed formation of dehydroluciferyl-adenylate (L-AMP), a by-product that results from oxidation of luciferyl-adenylate (LH2-AMP), and is a powerful inhibitor of the bioluminescence reaction (IC50 = 6 nm). We have shown that the CoA induced stabilization of light emission does not result from an allosteric effect but is due to the thiolytic reaction between CoA and L-AMP, which gives rise to dehydroluciferyl-CoA (L-CoA), a much less powerful inhibitor (IC50 = 5 microm). Moreover, the V(max) for L-CoA formation was determined as 160 min(-1), which is one order of magnitude higher than the V(max) of the bioluminescence reaction. Results obtained with CoA analogues also support the thiolytic reaction mechanism: CoA analogues without the thiol group (dethio-CoA and acetyl-CoA) do not react with L-AMP and do not antagonize its inhibitor effect; CoA and dephospho-CoA have free thiol groups, both react with L-AMP and both antagonize its effect. In the case of dephospho-CoA, it was shown that it reacts with L-AMP forming dehydroluciferyl-dephospho-CoA. Its slower reactivity towards L-AMP explains its lower potency as antagonist of the inhibitory effect of L-AMP on the light reaction. Moreover, our results support the conjecture that, in the bioluminescence reaction, the fraction of LH2-AMP that is oxidized into L-AMP, relative to other inhibitory products or intermediates, increases when the concentrations of the substrates ATP and luciferin increases.

PET imaging and optical imaging with D-luciferin [11C]methyl ester and D-luciferin [11C]methyl ether of luciferase gene expression in tumor xenografts of living mice

New carbon-11 labeled D-luciferin analogs D-luciferin [(11)C]methyl ester ([(11)C]LMEster, [(11)C]1) and D-luciferin [(11)C]methyl ether ([(11)C]LMEther, [(11)C]2) were synthesized in 25-55% radiochemical yield. PET studies with [(11)C]LMEster and [(11)C]LMEther demonstrate a lower retention of the C-11 label at 45 min post-injection in luciferase expression tumor. Optical imaging with unlabeled substrate D-luciferin and radiotracers [(11)C]LMEster and [(11)C]LMEther gave tumor luciferase images within a few minutes of photon counting.

Identification of luciferyl adenylate and luciferyl coenzyme a synthesized by firefly luciferase

The firefly luciferase reaction intermediate luciferyl adenylate was detected by RP-HPLC analysis when the luciferase reaction was performed under a nitrogen atmosphere. Although this compound is always specified as an intermediate in the light-production reaction, this is the first report of its identification by HPLC in a luciferase assay medium. Under a low-oxygen atmosphere, luciferase can catalyze the synthesis of luciferyl coenzyme A from luciferin, ATP, and coenzyme A, but in air dehydroluciferyl coenzyme A was produced. The luciferase-catalyzed synthesis of these coenzyme A derivatives may be a consequence of the postulated recent evolutionary origin of firefly luciferases from an ancestral acyl-coenzyme A synthetase.

pH opposite effects on synthesis of dinucleoside polyphosphates and on oxidation reactions catalyzed by firefly luciferase

Previous results have shown that an oxidizing product of firefly luciferin, dehydroluciferyl-adenylate, is the main intermediate in the process of synthesis of dinucleoside polyphosphates catalyzed by firefly luciferase (EC 1.13.12.7). However, we have found that the pH effects on the luciferase oxidizing processes and on the synthesis of dinucleoside polyphosphate are opposite: acidic assay media enhance the synthesis of dinucleoside polyphosphate and inhibit the oxidizing processes. The reason for this apparent contradiction lies on the activation effect of low pH on the adenylate transfer reaction from dehydroluciferyl-adenylate to the acceptor nucleotide.

Synthesis of dinucleoside polyphosphates catalyzed by firefly luciferase and several ligases

The findings presented here originally arose from the suggestion that the synthesis of dinucleoside polyphosphates (Np(n)N) may be a general process involving enzyme ligases catalyzing the transfer of a nucleotidyl moiety via nucleotidyl-containing intermediates, with release of pyrophosphate. Within this context, the characteristics of the following enzymes are presented. Firefly luciferase (EC 1.12. 13.7), an oxidoreductase with characteristics of a ligase, synthesizes a variety of (di)nucleoside polyphosphates with four or more inner phosphates. The discrepancy between the kinetics of light production and that of Np(n)N synthesis led to the finding that E*L-AMP (L = dehydroluciferin), formed from the E*LH(2)-AMP complex (LH(2) = luciferin) shortly after the onset of the reaction, was the main intermediate in the synthesis of (di)nucleoside polyphosphates. Acetyl-CoA synthetase (EC 6.2.1.1) and acyl-CoA synthetase (EC 6.2.1. 8) are ligases that synthesize p(4)A from ATP and P(3) and, to a lesser extent, Np(n)N. T4 DNA ligase (EC 6.5.1.1) and T4 RNA ligase (EC 6.5.1.3) catalyze the synthesis of Np(n)N through the formation of an E-AMP complex with liberation of pyrophosphate. DNA is an inhibitor of the synthesis of Np(n)N and conversely, P(3) or nucleoside triphosphates inhibit the ligation of a single-strand break in duplex DNA catalyzed by T4 DNA ligase, which could have therapeutic implications. The synthesis of Np(n)N catalyzed by T4 RNA ligase is inhibited by nucleoside 3'(2'),5'-bisphosphates. Reverse transcriptase (EC 2.7.7.49), although not a ligase, catalyzes, as reported by others, the synthesis of Np(n)ddN in the process of removing a chain termination residue at the 3'-OH end of a growing DNA chain.

The emitting species dissociated from the enzyme can emit the light in Photinus pyralis luciferase system

By fluorescent results, it has been proposed that the product (excited oxyluciferin) bounded in the firefly luciferase emits the light. Also it is generally accepted that two forms (keto and enol) of the oxyluciferin emit red and yellow-green light, respectively. In order to demonstrate the existence of free emitting species using His-tagged luciferase (His-luc), N-terminal 6x His-tagged luciferase (Photinus pyralis) was prepared and expressed in E. coli. After immobilization of His-luc on the membrane by IDA-Ni(2+)-His complex, His-luc clearly showed spectral changes of the emission toward red light. The luciferase-free product obtained from enzymatic reaction mixture in the presence of ATP and dATP emits the light with maximal wavelengths of 575 and 620 nm, respectively. Based on these results, we suppose that two different emitting species or two different energy levels of the emitting species are responsible for two different color lights.

Firefly luciferase has two nucleotide binding sites: effect of nucleoside monophosphate and CoA on the light-emission spectra

A laboratory-made spectroluminometer was used to analyse the light emitted by firefly (Photinus pyralis) luciferase reacting with several nucleotide derivatives. The analysis of the light emission in the presence of ATP or dATP provides some evidence that the enzyme has two nucleotide binding sites, each one leading to the formation of a complex emitting mainly at 575 nm (ATP) or 610 nm (dATP). AMP is able to displace dATP from the second site (610 nm) to the first one. Photoaffinity labelling of the second site by 8-azido-AMP gives similar results. The amplification effect of CoA and acetyl-CoA is also reconsidered according to this model.

Dehydroluciferyl-AMP is the main intermediate in the luciferin dependent synthesis of Ap4A catalyzed by firefly luciferase

It was previously assumed that E x LH2-AMP was the intermediate complex in the synthesis of Ap4A catalyzed by firefly luciferase (EC 1.13.12.7), when luciferin (LH2) was used as cofactor. However, here we show that LH2 is partly transformed, shortly after the onset of the luciferase reaction, to dehydroluciferin (L) with formation of an E x L-AMP complex which is the main intermediate for the synthesis of Ap4A. Formation of three more derivatives of LH2 were also observed, related to the production of light by the enzyme. CoA, a known stimulator of light production, inhibits the synthesis of Ap4A by reacting with the E x L-AMP complex and yielding L-CoA.

Acyl coenzyme A synthetase from Pseudomonas fragi catalyzes the synthesis of adenosine 5'-polyphosphates and dinucleoside polyphosphates

Acyl coenzyme A (CoA) synthetase (EC 6.2.1.8) from Pseudomonas fragi catalyzes the synthesis of adenosine 5'-tetraphosphate (p4A) and adenosine 5'-pentaphosphate (p5A) from ATP and tri- or tetrapolyphosphate, respectively. dATP, adenosine-5'-O-[gamma-thiotriphosphate] (ATP gamma S), adenosine(5')tetraphospho(5')adenosine (Ap4A), and adenosine(5')pentaphospho(5')adenosine (Ap5A) are also substrates of the reaction yielding p4(d)A in the presence of tripolyphosphate (P3). UTP, CTP, and AMP are not substrates of the reaction. The K(m) values for ATP and P3 are 0.015 and 1.3 mM, respectively. Maximum velocity was obtained in the presence of MgCl2 or CoCl2 equimolecular with the sum of ATP and P3. The relative rates of synthesis of p4A with divalent cations were Mg = Co > Mn = Zn >> Ca. In the pH range used, maximum and minimum activities were measured at pH values of 5.5 and 8.2, respectively; the opposite was observed for the synthesis of palmitoyl-CoA, with maximum activity in the alkaline range. The relative rates of synthesis of palmitoyl-CoA and p4A are around 10 (at pH 5.5) and around 200 (at pH 8.2). The synthesis of p4A is inhibited by CoA, and the inhibitory effect of CoA can be counteracted by fatty acids. To a lesser extent, the enzyme catalyzes the synthesis also of Ap4A (from ATP), Ap5A (from p4A), and adenosine(5')tetraphospho(5')nucleoside (Ap4N) from adequate adenylyl donors (ATP, ATP gamma S, or octanoyl-AMP) and adequate adenylyl acceptors (nucleoside triphosphates).