Bovine serum albumin interacts with bacterial luciferase

Bovine serum albumin (BSA) affects the amount of light obtained from bacterial luciferase by competing with luciferase for one of the luciferase substrates, the aldehyde. At low aldehyde concentrations BSA behaves as an inhibitor, but at high aldehyde concentrations BSA relieves substrate inhibition. BSA reversibly binds decanal with a K_si = 3.36 μmol/l, approximately half the affinity of luciferase for decanal (K_M = 1.5 μmol/l). BSA also increased the rate of intermediate II dark decay. The data suggest that this involves a direct protein-protein (BSA-luciferase) interaction.     

Chemistry,clones, and circadian control of the dinoflagellate bioluminescent system. The Marlene DeLuca memorial lecture

Bioluminescence in the dinoflagellate Gonyaulax polyedra occurs as brief bright flashes, originating from many (～400) small (～0.5 μm) cytoplasmic organelles which protrude into the acidic vacuole, and are thus surrounded by the tonoplast. Biochemically, the substrate is unusual; it is an open chain tetrapyrrole, highly unstable to air but protected in the cell at pH? 8 by virtue of a luciferin binding protein (LBP). This molecule is a dimer of 72 kDa subunits which, upon a decrease in pH, releases luciferin to react with oxygen in the luciferase (～140 kDa) catalysed luminescent reaction. cDNAs for both luciferase and LBP have been isolated and cloned, and the identity of LBP was confirmed by hybrid selection and in vitro translation of the message. The tenfold circadian (day to night) change in the amount of LBP, which parallels the in vivo rhythm of luminescence, is due to de novo synthesis and subsequent degradation of the protein each day. The LBP mRNA levels, as determined by in vitro translations and by Northern hybridizations, do not vary over the daily cycle, indicating that circadian control of bioluminescence in this species is mediated at the level of translation.     

THE ANALYSIS OF BIOLUMINESCENCES OF SHORT DURATION,RECORDED WITH PHOTOELECTRIC CELL AND STRING GALVANOMETER

1. The rapid decay of luminescence in extracts of the ostracod crustacean Cypridina hilgendorfii, has been studied by means of a photoelectric-amplifier-string galvanometer recording system. 2. For rapid flashes of luminescence, the decay is logarithmic if ratio of luciferin to luciferase is small; logarithmic plus an initial flash, if ratio of luciferin to luciferase is greater than five. The logarithmic plot of luminescence intensity against time is concave to time axis if ratio of luciferin to luciferase is very large. 3. The velocity constant of rapid flashes of luminescence is approximately proportional to enzyme concentration, is independent of luciferin concentration, and varies approximately inversely as the square root of the total luciferin (luciferin + oxyluciferin) concentration. For large total luciferin concentrations, the velocity constant is almost independent of the total luciferin. 4. The variation of velocity constant with total luciferin concentration (luciferin + oxyluciferin) and its independence of luciferin concentration is explained by assuming that light intensity is a measure of the luciferin molecules which become activated to oxidize (accompanied with luminescence) by adsorption on luciferase. The adsorption equilibrium is the same for luciferin and oxyluciferin and determines the velocity constant.     

Substrate and substrate analogue binding properties of Renilla luciferase.

Luciferase from the anthozoan coelenterate Renilla reniformis catalyzes the oxidative decarboxylation of luciferin consuming 1 mol of O2 per mol of luciferin oxidized and producing 1 mol of CO2, 1 mol of oxyluciferin, and light (lambdaB, 480 nm) with a 5.5% quantum yield. In this work we have examined the binding characteristics of luciferin, luciferin analogues, and competitive inhibitors of the luciferin-luciferase reaction. The results show that luciferin binding and orientation in the single luciferin binding site of luciferase are highly specific for and dependent upon the three group substituents of the luciferin molecule while the imidazolone-pyrazine nucleus of luciferin is not directly involved in binding. Anaerobic luciferin binding promotes a rapid concentration-dependent aggregation of luciferase which results in irreversible inactivation of the enzyme. This aggregation phenomenon is not observed upon binding of oxyluciferin, luciferyl sulfate, or luciferin analogues in which the substituent at the 2 position of the imidazolone-pyrazine ring has been substantially altered.     

Colocalization of luciferin binding protein and luciferase to the scintillons ofGonyaulax polyedra revealed by double immunolabeling after fast-freeze fixation

Summary Two proteins,Gonyaulax luciferase and the luciferin binding protein, are involved in the bioluminescent reaction of the unicellular marine algaGonyaulax polyedra. Using antibodies raised separately against the purified proteins, their ultrastructural localizations were visualized by double immunogold labeling on sections after fast-freeze fixation, freeze-substitution and embedding in Epon or in LR White. Gold particles of two sizes attached to the secondary antibodies allowed the two primary antibodies to be distinguished. The two colocalized to cytoplasmic densifications (scintillons), which occurred in close association with the vacuolar membrane near the periphery of the cell. They also occurred in the cytoplasm of the Golgi area, either over densifications without associated membranes (prescintillons), or as very small colocalizations not associated with any evident cytoplasmic differentiation. No other site of colocalization was observed, thus unambiguously establishing the ultrastructural identity of the bioluminescent organelles.Abbreviations FFF fast-freeze fixation - FS freeze-substitution - IGS immunogold staining - LBP luciferin binding protein - PBS phosphate buffered saline - TBS tris-buffered saline Dedicated to the memory of Professor Beatrice Marcy Sweeney     

Using fluorescence lifetime microscopy to study the subcellular localization of anthocyanins

Anthocyanins are flavonoid pigments that accumulate in most seed plants. They are synthesized in the cytoplasm but accumulate inside the vacuoles. Anthocyanins are pigmented at the lower vacuolar pH, but in the cytoplasm they can be visualized based on their fluorescence properties. Thus, anthocyanins provide an ideal system for the development of new methods to investigate cytoplasmic pools and association with other molecular components. We have analyzed the fluorescence decay of anthocyanins by fluorescence lifetime imaging microscopy (FLIM), in both in vitro and in vivo conditions, using wild‐type and mutant Arabidopsis thaliana seedlings. Within plant cells, the amplitude‐weighted mean fluorescence lifetime (τ_m) correlated with distinct subcellular localizations of anthocyanins. The vacuolar pool of anthocyanins exhibited shorter τ_m than the cytoplasmic pool. Consistently, lowering the pH of anthocyanins in solution shortened their fluorescence decay. We propose that FLIM is a useful tool for understanding the trafficking of anthocyanins and, potentially, for estimating vacuolar pH inside intact plant cells.     

Development of near-infrared firefly luciferin analogue reacted with wild-type and mutant luciferases

Interestingly, only the D-form of firefly luciferin produces light by luciferin–luciferase (L–L) reaction. Certain firefly luciferin analogues with modified structures maintain bioluminescence (BL) activity; however, all L-form luciferin analogues show no BL activity. To this date, our group has developed luciferin analogues with moderate BL activity that produce light of various wavelengths. For in vivo bioluminescence imaging, one of the important factors for detection sensitivity is tissue permeability of the number of photons emitted by L–L reaction, and the wavelengths of light in the near-infrared (NIR) range (700–900 nm) are most appropriate for the purpose. Some NIR luciferin analogues by us had performance for in vivo experiments to make it possible to detect photons from deep target tissues in mice with high sensitivity, whereas only a few of them can produce NIR light by the L–L reactions with wild-type luciferase and/or mutant luciferase. Based on the structure–activity relationships, we designed and synthesized here a luciferin analogue with the 5-allyl-6-dimethylamino-2-naphthylethenyl moiety. This analogue exhibited NIR BL emissions with wild-type luciferase (λ_max = 705 nm) and mutant luciferase AlaLuc (λ_max = 655 nm).     

Function of leaf hamamelitol as a compatible solute during water stress treatment of Hedera helix L.

Hamamelitol is an unusual branched-chain sugar alcohol previously suggested to function as a leaf compatible solute. In this study, we have examined the leaf metabolism and intracelluiar compartmentalization of hamamelitol and other soluble sugars during long-term water stress treatment of Hedera helix (English ivy). Total leaf hamamelitol content was relatively low in greenhouse control plants, but increased 2-fold during water stress treatment to levels approaching those observed in field-grown plants (6–7 μmol g^?1 fresh weight). Using density gradient fractionation with non-aqueous solvents, we showed that hamamelitol occurs primarily in the cytoplasm and vacuoles of leaf mesophyll cells. During water stress treatment most of the increase in leaf hamamelitol occurred in the mesophyll cytoplasm, compensating osmotically for a decrease in cytoplasmic sucrose concentration. The maximum concentration of cytoplasmic hamamelitol was 155 mol m^?3 and occurred in field-grown plants. Labelling experiments showed that hamamelitol is slowly synthesized from ¹⁴CO₂ in leaves of H. helix, but is very long-lived (estimated t_1/2 of 4 years). Together, these data indicate that hamamelitol probably functions during long-term stress conditions as an osmotically active, compatible solute in plant leaves. We suggest that the signal for enhanced accumulation of hamamelitol during the water stress treatment was initiated by decreased plant growth and increased leaf sucrose hydrolysis.     

Imaging of luciferase and GFP‐transfected human tumours in nude mice

Studies were performed to compare green ?uorescent protein (GFP)‐transfected and ?re?y luciferase (Luc)‐transfected MCF‐7 human breast tumour cells both in vitro and in vivo. For in vitro studies, cells were serially diluted in 96‐well microplates and analysed using a NightOwl LB 981 Molecular Light Imager and a Victor multilabel reader. For in vivo studies, nude mice were injected either intraperitoneally, intravenously or subcutaneously with transfected cells and then imaged using the NightOwl Imager after intraperitoneal injection of d ‐luciferin for Luc tumours, or excitation at 470 nm for GFP tumours. In vitro imaging studies revealed that both GFP and Luc transfectants were quanti?able. However, the Luc‐transfected cells were detectable at a signi?cantly lower concentration compared to GFP transfectants. In vivo studies demonstrated that GFP‐transfected tumours were detectable as subcutaneous and intraperitoneal tumours but not as deep tissue lesions, whereas Luc‐transfected tumours were detectable as subcutaneous and intraperitoneal tumours and as deep tissue lesions resulting from intraperitoneal or intravenous inoculation. These ?ndings demonstrate that GFP‐transfected cells may be useful for imaging studies of super?cial tumours where both excitation and emission wavelengths are able to penetrate tissues, whereas luciferase‐transfected cells appear superior for imaging studies of primary and metastatic tumours in distant sites and deep tissues. Copyright © 2003 John Wiley & Sons, Ltd.     

A Review Comparing Deoxyribonucleoside Triphosphate (dNTP) Concentrations in the Mitochondrial and Cytoplasmic Compartments of Normal and Transformed Cells

The deoxyribonucleoside triphosphate (dNTP) pools that support the replication of mitochondrial DNA are physically separated from the rest of the cell by the double membrane of the mitochondria. Perturbed homeostasis of mitochondrial dNTP pools is associated with a set of severe diseases collectively termed mitochondrial DNA depletion syndromes. The degree of interaction of the mitochondrial dNTP pools with the corresponding dNTP pools in the cytoplasm is currently not clear. We reviewed the literature on previously reported simultaneous measurements of mitochondrial and cytoplasmic deoxyribonucleoside triphosphate pools to investigate and quantify the extent of the influence of the cytoplasmic nucleotide metabolism on mitochondrial dNTP pools. We converted the reported measurements to concentrations creating a catalog of paired mitochondrial and cytoplasmic dNTP concentration measurements. Over experiments from multiple laboratories, dNTP concentrations in the mitochondria are highly correlated with dNTP concentrations in the cytoplasm in normal cells in culture (Pearson R = 0.79, p = 3 × 10^?7) but not in transformed cells. For dTTP and dATP there was a strong linear relationship between the cytoplasmic and mitochondrial concentrations in normal cells. From this linear model we hypothesize that the salvage pathway within the mitochondrion is only capable of forming a concentration of approximately 2 μM of dTTP and dATP, and that higher concentrations require transport of deoxyribonucleotides from the cytoplasm.     

Mathematical Model of the Firefly Luciferase Complementation Assay Reveals a Non-Linear Relationship between the Detected Luminescence and the Affinity of the Protein Pair Being Analyzed

The firefly luciferase complementation assay is widely used as a bioluminescent reporter technology to detect protein-protein interactions in vitro, in cellulo, and in vivo. Upon the interaction of a protein pair, complemented firefly luciferase emits light through the adenylation and oxidation of its substrate, luciferin. Although it has been suggested that kinetics of light production in the firefly luciferase complementation assay is different from that in full length luciferase, the mechanism behind this is still not understood. To quantitatively understand the different kinetics and how changes in affinity of a protein pair affect the light emission in the assay, a mathematical model of the in vitro firefly luciferase complementation assay was constructed. Analysis of the model finds that the change in kinetics is caused by rapid dissociation of the protein pair, low adenylation rate of luciferin, and increased affinity of adenylated luciferin to the enzyme. The model suggests that the affinity of the protein pair has an exponential relationship with the light detected in the assay. This relationship causes the change of affinity in a protein pair to be underestimated. This study underlines the importance of understanding the molecular mechanism of the firefly luciferase complementation assay in order to analyze protein pair affinities quantitatively.     

Enhanced luciferin entry causes rapid wound-induced light emission in plants expressing high levels of luciferase

In-vivo imaging of transgenic tobacco plants (Nicotiana tobacum L.) expressing firefly luciferase under the control of the Arabidopsis phenylalanine ammonia-lyase 1 (PAL1)-promoter showed that luciferase-catalyzed light emission began immediately after the substrate luciferin was sprayed onto the leaves and reached a plateau phase after approximately 60 min. This luminescence could easily be detected for up to 24 h after luciferin application although the light intensity declined continuously during this period. A strong and rapid increase in light emission was observed within the first minutes after wounding of luciferin-sprayed leaves. However, these data did not correlate with luciferase activity analysed by an in-vitro enzyme assay. In addition, Arabidopsis plants expressing luciferase under the control of the constitutive 35S-promoter showed similar wound-induced light emission. In experiments in which only parts of the leaves were sprayed with luciferin solutions, it was shown that increased uptake of luciferin at the wound site and its transport through vascular tissue were the main reasons for the rapid burst of light produced by preformed luciferase activity. These data demonstrate that there are barriers that restrict luciferin entry into adult plants, and that luciferin availability can be a limiting factor in non-invasive luciferase assays. Received: 11 March 2000 / Accepted: 16 May 2000     

Rapid obtention of stable,bioluminescent tumor cell lines using a tCD2-luciferase chimeric construct

Background  

Bioluminescent tumor cell lines are experimental tools of major importance for cancer investigation, especially imaging of tumors in xenografted animals. Stable expression of exogenous luciferase in tumor cells combined to systemic injection of luciferin provides an excellent signal/background ratio for external optical imaging. Therefore, there is a need to rationalize and speed up the production of luciferase-positive tumor cell lines representative of multiple tumor phenotypes. For this aim we have designed a fusion gene linking the luciferase 2 protein to the c-terminus of a truncated form of the rat CD2 protein (tCD2-luc2). To allow simultaneous assessment of the wild-type luciferase 2 in a context of tCD2 co-expression, we have made a bicistronic construct for concomitant but separate expression of these two proteins (luc2-IRES-tCD2). Both the mono- and bi-cistronic constructs were transduced in lymphoid and epithelial cells using lentiviral vectors.     

Extended‐release PEG–luciferin allows for long‐term imaging of firefly luciferase activity in vivo

Bioluminescence has gained favour in the last decade as an approach for observing tumours in vivo in a non‐destructive manner. This very sensitive technique is based on light emission by the reaction of luciferin with the enzyme luciferase, as measured by a photodetector. Ever since the development of recombinant tumour cell lines that have been engineered to produce luciferase, a vast number of experiments have been carried out examining tumour growth, tumour metastasis and the effect of therapeutic regimens in such cases. A primary stumbling block, however, is the relatively short circulatory half‐life of luciferin. In this paper, we propose the PEGylation of 6‐amino‐d ‐luciferin to extend its in vivo circulatory half‐life, thus making the possibility of long‐term observations in animals possible. The covalent attachment was through a carbamate linker that is known to hydrolyse in vivo, releasing the parent compound. Based on our studies, longer emission of the PEGylated luciferin was observed, as compared to free luciferin in mice bearing PC3 prostate tumours expressing luciferase. This result suggests that this reagent can be used in applications requiring extended monitoring of luciferase activation in vivo. Copyright © 2008 John Wiley & Sons, Ltd.     

The use of the luciferase reporter system forin planta gene expression studies

The properties of the firefly luciferase (LUC) make it a very good nondestructive reporter to quantify and image transgene promoter activity in plants. The short half-life of the LUC mRNA and protein, and the very limited regeneration of the LUC protein after reacting with luciferin, enables monitoring of changes in gene activity with a high time resolution. However, the ease at which luciferase activity is measuredin planta, using a light sensitive camera system (2D-luminometer), contrasts sharply with the complications that arise from interpreting the results. A variegated pattern of luciferase activity, that is often observed inin planta measurements, might either be caused by differences in influx, availability of the substrates (luciferin, oxygen, ATP) or by local differences in reporter gene activity. Here we tested the possible contribution of differences in the availability of each substrate to the variegatedin planta luciferase activity, and we show whenin planta luciferase activity is measured under substrate equilibrium conditions and can be related to the promoter activity of the reporter gene. Furthermore, we demonstrate the effects of protein stability, apparent half-life of luciferase activity, regeneration of luciferase and pH on thein vivo andin vitro luciferase measurements. The combined results give the prerequisites for the correct utilisation of the luciferase reporter system, especially forin vivo gene expression studies in plant research.     

Stability of d‐luciferin for bioluminescence to detect gene expression in freely moving mice for long durations

Circadian disturbance of clock gene expression is a risk factor for diseases such as obesity, cancer, and sleep disorders. To study these diseases, it is necessary to monitor and analyze the expression rhythm of clock genes in the whole body for a long duration. The bioluminescent reporter enzyme firefly luciferase and its substrate d ‐luciferin have been used to generate optical signals from tissues in vivo with high sensitivity. However, little information is known about the stability of d ‐luciferin to detect gene expression in living animals for a long duration. In the present study, we examined the stability of a luciferin solution over 21 days. l ‐Luciferin, which is synthesized using racemization of d ‐luciferin, was at high concentrations after 21 days. In addition, we showed that bioluminescence of Period1 (Per1) expression in the liver was significantly decreased compared with the day 1 solution, although locomotor activity rhythm was not affected. These results showed that d ‐luciferin should be applied to the mouse within, at most, 7 days to detect bioluminescence of Per1 gene expression rhythm in vivo.     

Optimized luciferase assay for cell-penetrating peptide-mediated delivery of short oligonucleotides

An improved assay for screening for the intracellular delivery efficacy of short oligonucleotides using cell-penetrating peptides is suggested. This assay is an improvement over previous assays that use luciferase reporters for cell-penetrating peptides because it has been scaled up from a 24-well format to a 96-well format and no longer relies on a luciferin reagent that has been commercially sourced. In addition, the homemade luciferin reagent is useful in multiple cell lines and in different assays that rely on altering the expression of luciferase. To establish a new protocol, the composition of the luciferin reagent was optimized for both signal strength and longevity by multiple two-factorial experiments varying the concentrations of adenosine triphosphate, luciferin, coenzyme A, and dithiothreitol. In addition, the optimal conditions with respect to cell number and time of transfection for both short interfering RNA (siRNA) and splice-correcting oligonucleotides (SCOs) are established. Optimal transfection of siRNA and SCOs was achieved using the reverse transfection method where the oligonucleotide complexes are already present in the wells before the cells are plated. Z′ scores were 0.73 for the siRNA assay and 0.71 for the SCO assay, indicating that both assays are suitable for high-throughput screening.     

Thein vivo pattern of firefly luciferase expression in transgenic plants

Expression of the firefly luciferase gene in transgenic plants produces light emission patterns when the plants are supplied with luciferin. We explored whether inin vivo pattern of light emission truly reveals the pattern of luciferase gene expression or whether it reflects other parameters such as the availability of the substrate, luciferin, or the tissue-specific distribution of organelles in which luciferase was localized. The tissue-specific distribution of luciferase activity and thein vivo pattern of light were examined when the luciferase gene was driven by different promoters and when luciferase was redirected from the peroxisome, where it is normally targeted, to the chloroplast compartment. It was found that the distribution of luciferase activity closely correlated with the tissue-specific pattern of luciferase mRNA. However, thein vivo light pattern appeared to reflect not only tissue-specific distribution of luciferase activity, but also the pattern of luciferin uptake.     

Development of a Cell-Based Bioassay for Phospholipase A2-Triggered Liposomal Drug Release

The feasibility of exploiting secretory phospholipase A₂ (sPLA₂) enzymes, which are overexpressed in tumors, to activate drug release from liposomes precisely at the tumor site has been demonstrated before. Although the efficacy of the developed formulations was evaluated using in vitro and in vivo models, the pattern of sPLA₂-assisted drug release is unknown due to the lack of a suitable bio-relevant model. We report here on the development of a novel bioluminescence living-cell-based luciferase assay for the monitoring of sPLA₂-triggered release of luciferin from liposomes. To this end, we engineered breast cancer cells to produce both luciferase and sPLA₂ enzymes, where the latter is secreted to the extracellular medium. We report on setting up a robust and reproducible bioassay for testing sPLA₂-sensitive, luciferin remote-loaded liposomal formulations, using 1,2-distearoyl-sn-glycero-3-phosphatidylcholine/1,2-distearoyl-sn-glycero-3-phosphatidylglycerol (DSPC/DSPG) 7:3 and DSPC/DSPG/cholesterol 4:3:3 as initial test systems. Upon their addition to the cells, the liposomes were degraded almost instantaneously by sPLA₂ releasing the encapsulated luciferin, which provided readout from the luciferase-expressing cells. Cholesterol enhanced the integrity of the formulation without affecting its susceptibility to sPLA₂. PEGylation of the liposomes only moderately broadened the release profile of luciferin. The provided bioassay represents a useful tool for monitoring active drug release in situ in real time as well as for testing and optimizing of sPLA₂-sensitive lipid formulations. In addition, the bioassay will pave the way for future in-depth in vitro and in vivo studies.     

THE OXIDATION-REDUCTION POTENTIAL OF THE LUCIFERIN-OXYLUCIFERIN SYSTEM

The oxidation-reduction potential of the Cypridina luciferin-oxyluciferin system determined by a method of "bracketing" lies somewhere between that of anthraquinone 2-6-di Na sulfonate (E_o ^'' at pH of 7.7 = –.22) which reduces luciferin, and quinhydrone (E_o ^'' at pH of 7.7 = +.24), which oxidizes luciferin. Systems having an E_o ^'' value between –.22 and +.24 volt neither reduce oxyluciferin nor oxidize luciferin. If the luciferin-oxyluciferin system were truly reversible considerable reduction and oxidation should occur between –.22 and +.24. The system appears to be an irreversible one, with both "apparent oxidation" and "apparent reduction potentials" in Conant''s sense. Hydrosulfites, sulfides, CrCl₂, TiCl₃, and nascent hydrogen reduce oxyluciferin readily in absence of oxygen but without luminescence. Luminescence only appears in water solution if luciferin is oxidized by dissolved oxygen in presence of luciferase. Rapid oxidation of luciferin by oxygen without luciferase or oxidation by K₃Fe(CN)₆ in presence of luciferase but without oxygen never gives luminescence.