Mechanical Stability of a Small, Highly-Luminescent Engineered Protein NanoLuc

NanoLuc is a bioluminescent protein recently engineered for applications in molecular imaging and cellular reporter assays. Compared to other bioluminescent proteins used for these applications, like Firefly Luciferase and Renilla Luciferase, it is ~150 times brighter, more thermally stable, and smaller. Yet, no information is known with regards to its mechanical properties, which could introduce a new set of applications for this unique protein, such as a novel biomaterial or as a substrate for protein activity/refolding assays. Here, we generated a synthetic NanoLuc derivative protein that consists of three connected NanoLuc proteins flanked by two human titin I91 domains on each side and present our mechanical studies at the single molecule level by performing Single Molecule Force Spectroscopy (SMFS) measurements. Our results show each NanoLuc repeat in the derivative behaves as a single domain protein, with a single unfolding event occurring on average when approximately 72 pN is applied to the protein. Additionally, we performed cyclic measurements, where the forces applied to a single protein were cyclically raised then lowered to allow the protein the opportunity to refold: we observed the protein was able to refold to its correct structure after mechanical denaturation only 16.9% of the time, while another 26.9% of the time there was evidence of protein misfolding to a potentially non-functional conformation. These results show that NanoLuc is a mechanically moderately weak protein that is unable to robustly refold itself correctly when stretch-denatured, which makes it an attractive model for future protein folding and misfolding studies.

A new brilliantly blue-emitting luciferin-luciferase system from Orfelia fultoni and Keroplatinae (Diptera)

Larvae of O. fultoni (Keroplatidae: Keroplatinae), which occur along river banks in the Appalachian Mountains in Eastern United States, produce the bluest bioluminescence among insects from translucent areas associated to black bodies, which are  located mainly in the anterior and posterior parts of the body. Although closely related to Arachnocampa spp (Keroplatidae: Arachnocampininae), O.fultoni has a morphologically and biochemically distinct bioluminescent system which evolved independently, requiring a luciferase enzyme, a luciferin, a substrate binding fraction (SBF) that releases luciferin in the presence of mild reducing agents, molecular oxygen, and no additional cofactors. Similarly, the closely related Neoceroplatus spp, shares the same kind of luciferin-luciferase system of Orfelia fultoni. However, the molecular properties, identities and functions of luciferases, SBF and luciferin of Orfelia fultoni and other  luminescent members of the Keroplatinae subfamily still remain to be fully elucidated. Using O. fultoni as a source of luciferase, and the recently discovered non-luminescent cave worm Neoditomiya sp as the main source of luciferin and SBF, we isolated and initially characterized these compounds. The luciferase of O. fultoni is a stable enzyme active as an apparent trimer (220 kDa) composed of ~70 kDa monomers, with an optimum pH of 7.8. The SBF, which is found in the black bodies in Orfelia fultoni and in smaller dark granules in Neoditomiya sp, consists of a high molecular weight complex of luciferin and proteins, apparently associated to mitochondria. The luciferin, partially purified from hot extracts by a combination of anion exchange chromatography and TLC, is a very polar and weakly fluorescent compound, whereas its oxidized product displays blue fluorescence with an emission spectrum matching the bioluminescence spectrum (~460 nm), indicating that it is oxyluciferin. The widespread occurrence of luciferin and SBF in both luminescent and non-luminescent Keroplatinae larvae indicate an additional important biological function for the substrate, and therefore the name keroplatin.

Optimized application of the secreted Nano-luciferase reporter system using an affinity purification strategy

Secreted Nano-luciferase (secNluc) is a newly engineered secreted luciferase that possesses advantages of high structural stability, long half-life, and glow-type kinetics together with high light emission intensity, and thus would become one of the most valuable tools for bioluminescence assays. However, like other secreted luciferases, secNluc has to mix with the components in the conditioned medium surrounding test cells, or in the biological samples such as blood or urine after being secreted. These components may interfere with secNluc-catalyzed bioluminescence reactions and thus limit the application of the secNluc reporter system. In this study, we first examined the effects of three factors, pH, serum and residual reagents, on secNluc-catalyzed bioluminescence reactions, finding that these factors could interfere with bioluminescence reactions and result in background signal. To resolve these problems, we applied a simple affinity purification strategy in which secNluc was fused with a FLAG-tag, and anti-FLAG magnetic beads were used to catch and transfer the fusion protein to PBST, an optimal buffer for secNluc-catalyzed bioluminescence reactions that was identified in this study. The results indicated that this strategy could not only negate the interferences from serum or residual reagents and enhance the stability of light emission but also greatly increase signal intensity through enzyme enrichment. This strategy may contribute to biomedical studies that utilize secNluc and other secreted luciferases, especially those requiring superior sensitivity, low background noise and high reproducibility.

Coupling genetics and proteomics to identify aphid proteins associated with vector-specific transmission of polerovirus (luteoviridae)

Cereal yellow dwarf virus-RPV (CYDV-RPV) is transmitted specifically by the aphids Rhopalosiphum padi and Schizaphis graminum in a circulative nonpropagative manner. The high level of vector specificity results from the vector aphids having the functional components of the receptor-mediated endocytotic pathways to allow virus to transverse the gut and salivary tissues. Studies of F(2) progeny from crosses of vector and nonvector genotypes of S. graminum showed that virus transmission efficiency is a heritable trait regulated by multiple genes acting in an additive fashion and that gut- and salivary gland-associated factors are not genetically linked. Utilizing two-dimensional difference gel electrophoresis to compare the proteomes of vector and nonvector parental and F(2) genotypes, four aphid proteins (S4, S8, S29, and S405) were specifically associated with the ability of S. graminum to transmit CYDV-RPV. The four proteins were coimmunoprecipitated with purified RPV, indicating that the aphid proteins are capable of binding to virus. Analysis by mass spectrometry identified S4 as a luciferase and S29 as a cyclophilin, both of which have been implicated in macromolecular transport. Proteins S8 and S405 were not identified from available databases. Study of this unique genetic system coupled with proteomic analysis indicated that these four virus-binding aphid proteins were specifically inherited and conserved in different generations of vector genotypes and suggests that they play a major role in regulating polerovirus transmission.

Coupling genetics and proteomics to identify aphid proteins associated with vector-specific transmission of polerovirus (luteoviridae)

Cereal yellow dwarf virus-RPV (CYDV-RPV) is transmitted specifically by the aphids Rhopalosiphum padi and Schizaphis graminum in a circulative nonpropagative manner. The high level of vector specificity results from the vector aphids having the functional components of the receptor-mediated endocytotic pathways to allow virus to transverse the gut and salivary tissues. Studies of F(2) progeny from crosses of vector and nonvector genotypes of S. graminum showed that virus transmission efficiency is a heritable trait regulated by multiple genes acting in an additive fashion and that gut- and salivary gland-associated factors are not genetically linked. Utilizing two-dimensional difference gel electrophoresis to compare the proteomes of vector and nonvector parental and F(2) genotypes, four aphid proteins (S4, S8, S29, and S405) were specifically associated with the ability of S. graminum to transmit CYDV-RPV. The four proteins were coimmunoprecipitated with purified RPV, indicating that the aphid proteins are capable of binding to virus. Analysis by mass spectrometry identified S4 as a luciferase and S29 as a cyclophilin, both of which have been implicated in macromolecular transport. Proteins S8 and S405 were not identified from available databases. Study of this unique genetic system coupled with proteomic analysis indicated that these four virus-binding aphid proteins were specifically inherited and conserved in different generations of vector genotypes and suggests that they play a major role in regulating polerovirus transmission.

Preparation of Biotinylated Cypridina Luciferase and Its Use in Bioluminescent Enzyme Immunoassay

Cypridina luciferase, a well-known secretory enzyme involved in the bioluminescence of marine ostracod, is used to monitor gene expression in mammalian cells. Here we report the preparation of biotinylated Cypridina luciferase and its use in bioluminescent enzyme immunoassay (BLEIA). Recombinant Cypridina luciferase was expressed in yeast and successfully purified to near homogeneity. The luciferase was biotinylated with conventional biotinylation reagents, and the biotinylated lysine sites were determined by liquid chromatography-tandem mass spectrometry. The biotinylated luciferase was stable when stored at 4 degrees C. The stability of synthetic S-Cypridina luciferin was significantly improved by adding antioxidants to Tris-HCl buffer. The biotinylated luciferase and S-Cypridina luciferin were used in a model study of the immunoassay for interferon-alpha. The linearity of this immunoassay extended from 7.8 to 500 pg/mL interferon-alpha. Our results show that Cypridina luciferase is a very sensitive and versatile bioluminescent reporter.

cDNA cloning, expression and homology modeling of a luciferase from the firefly Lampyroidea maculata

The cDNA of a firefly luciferase from lantern mRNA of Lampyroidea maculata has been cloned, sequenced and functionally expressed. The cDNA has an open reading frame of 1647 bp and codes for a 548-residue-long polypeptide. Noteworthy, sequence comparison as well as homology modeling showed the highest degree of similarity with H. unmunsana and L. mingrelica luciferases, suggesting a close phylogenetic relationship despite the geographical distance separation. The deduced amino acid sequence of the luciferase gene of firefly L. maculata showed 93% identity to H. unmunsana. Superposition of the three-dimensional model of L. maculata luciferase (generated by homology modeling) and three dimensional structure of Photinus pyralis luciferase revealed that the spatial arrangements of Luciferin and ATP-binding residues are very similar. Putative signature of AMPbinding domain among the various firefly species and Lampyroidea maculata was compared and a striking similarity was found. Different motifs and sites have been identified in Lampyroidea maculata by sequence analysis. Expression and purification of luciferase from Lampyroidea maculata was carried out using Ni-NTA Sepharose. Bioluminescence emission spectrum was similar to Photinus pyralis luciferase.

Active-site properties of Phrixotrix railroad worm green and red bioluminescence-eliciting luciferases

The luciferases of the railroad worm Phrixotrix (Coleoptera: Phengodidae) are the only beetle luciferases that naturally produce true red bioluminescence. Previously, we cloned the green- (PxGR) and red-emitting (PxRE) luciferases of railroad worms Phrixotrix viviani and P. hirtus[OLE1]. These luciferases were expressed and purified, and their active-site properties were determined. The red-emitting PxRE luciferase displays flash-like kinetics, whereas PxGR luciferase displays slow-type kinetics. The substrate affinities and catalytic efficiency of PxRE luciferase are also higher than those of PxGR luciferase. Fluorescence studies with 8-anilino-1-naphthalene sulfonic acid and 6-p-toluidino-2-naphthalene sulfonic acid showed that the PxRE luciferase luciferin-binding site is more polar than that of PxGR luciferase, and it is sensitive to guanidine. Mutagenesis and modelling studies suggest that several invariant residues in the putative luciferin-binding site of PxRE luciferase cannot interact with excited oxyluciferin. These results suggest that one portion of the luciferin-binding site of the red-emitting luciferase is tighter than that of PxGR luciferase, whereas the other portion could be more open and polar.

Kinetic characterization and in vitro toxicity evaluation of a luciferase less susceptible to HPV chemical inhibition

Enzyme-based in vitro toxicity assays are often susceptible to inhibition by test compounds. A mutant luciferase selected to be less susceptible to inhibition by chloroform (CNBLuc03-06) and other high production volume (HPV) chemicals, consisting of three point mutations was created and characterized. The mutant luciferase was less inhibited by chloroform, other HPV chemicals and common surfactant release reagents (Triton-X and SDS) compared to the wild-type. Inhibition was shown to be competitive. CNBLuc03-06 was a factor of 1.5-3.2 more active than wild type and exhibited a much higher affinity for ATP. CNBLuc03-06 was more thermostable than wild-type and also more active at pH values higher than 10. Both luciferases exhibited a significant tradeoff between activation and susceptibility to chemical inhibition in the presences of the reducing agent DTT. Inhibition to HPV chemicals was eliminated using an "optimum" formulation of DTT and co-solvent ethanol. The performance of CNBLuc03-06 in cell-based in vitro toxicity assays was shown to be superior to the current commercial formulation.

An alternative mechanism of bioluminescence color determination in firefly luciferase

Beetle luciferases (including those of the firefly) use the same luciferin substrate to naturally display light ranging in color from green (lambda(max) approximately 530 nm) to red (lambda(max) approximately 635 nm). In a recent communication, we reported (Branchini, B. R., Murtiashaw, M. H., Magyar, R. A., Portier, N. C., Ruggiero, M. C., and Stroh, J. G. (2002) J. Am. Chem. Soc. 124, 2112-2113) that the synthetic adenylate of firefly luciferin analogue D-5,5-dimethylluciferin was transformed into the emitter 5,5-dimethyloxyluciferin in bioluminescence reactions catalyzed by luciferases from Photinus pyralis and the click beetle Pyrophorus plagiophthalamus. 5,5-Dimethyloxyluciferin is constrained to exist in the keto form and fluoresces mainly in the red. However, bioluminescence spectra revealed that green light emission was produced by the firefly enzyme, and red light was observed with the click beetle protein. These results, augmented with steady-state kinetic studies, were taken as experimental support for mechanisms of firefly bioluminescence color that require only a single keto form of oxyluciferin. We report here the results of mutagenesis studies designed to determine the basis of the observed differences in bioluminescence color with the analogue adenylate. Mutants of P. pyralis luciferase putative active site residues Gly246 and Phe250, as well as corresponding click beetle residues Ala243 and Ser247 were constructed and characterized using bioluminescence emission spectroscopy and steady state kinetics with adenylate substrates. Based on an analysis of these and recently reported (Branchini, B. R., Southworth, T. L., Murtiashaw, M. H., Boije, H., and Fleet, S. E. (2003) Biochemistry 42, 10429-10436) data, we have developed an alternative mechanism of bioluminescence color. The basis of the mechanism is that luciferase modulates emission color by controlling the resonance-based charge delocalization of the anionic keto form of the oxyluciferin excited state.

Effects of Iodide on the Fluorescence and Activity of the Hydroperoxyflavin Intermediate of Vibrio harveyi Luciferase

The 4a-hydroperoxy-4a,5-dihydroFMN intermediate (II or HFOOH) of Vibrio harveyi luciferase is known to transform from a low quantum yield IIx to a high quantum yield (lambdamax 485 nm, uncorrected) IIy fluorescent species on exposure to excitation light. Similar results were observed with II prepared from the alphaH44A luciferase mutant, which is very weak in bioluminescence activity. Because of the rapid decay of the alphaH44A II, its true fluorescence was obscured by the more intense 520 nm fluorescence (uncorrected) from its decay product oxidized flavin mononucleotide (FMN). Potassium iodide (KI) at 0.2 M was effective in quenching the FMN fluorescence, leaving the 485 nm fluorescence of II from both the wild-type (WT) and alphaH44A luciferase readily detectable. For both II species, the luciferase-bound peroxyflavin was well shielded from KI quenching. KI also enhanced the decay rates of both the WT and alphaH44A II. For alphaH44A, the transformation of IIx to IIy can be induced by KI in the dark, and it is proposed to be a consequence of a luciferase conformational change. The WT II formed a bioluminescence-inactive complex with KI, resulting in two distinct decay time courses based on absorption changes and decreases of bioluminescence activity of II.

Recombinant Gaussia luciferase. Overexpression, purification, and analytical application of a bioluminescent reporter for DNA hybridization

The cDNA for Gaussia luciferase (GLuc), the enzyme responsible for the bioluminescent reaction of the marine copepod Gaussia princeps, has been cloned recently. GLuc (MW = 19 900) catalyzes the oxidative decarboxylation of coelenterazine to produce coelenteramide and light. We report the first quantitative anaytical study of GLuc and examine its potential as a new reporter for DNA hybridization. A plasmid encoding both a biotin acceptor peptide-GLuc fusion protein as well as the enzyme biotin protein ligase (BPL) is engineered by using GLuc cDNA as a starting template. BPL catalyzes the covalent attachment of a single biotin to the fusion protein in vivo. Purification of GLuc is then accomplished by affinity chromatography using immobilized monomeric avidin. Moreover, the in vivo biotinylation enables subsequent complexation of GLuc with streptavidin (SA), thereby avoiding chemical conjugation reactions that are known to inactivate luciferases. Purified GLuc can be detected down to 1 amol with a signal-to-background ratio of 2 and a linear range extending over 5 orders of magnitude. The background luminescence of coelenterazine is the main limiting factor for even higher detectability of GLuc. Furthermore, the GLuc-SA complex is used as a detection reagent in a microtiter well-based DNA hybridization assay. The analytical range extends from 1.6 to 800 pmol/L of target DNA. Biotinylated GLuc produced from 1 L of bacterial culture is sufficient for 150,000 hybridization assays.

Effects of removal of the N-terminal amino acid residues on the activity and conformation of firefly luciferase

A series of deletion mutants were constructed using polymerase chain reaction (PCR) to investigate the roles of luciferase N-terminal residues. The coding sequences of the first 0 (Luc0), 6 (Luc6), 7 (Luc7), 8 (Luc8), 9 (Luc9), 10 (Luc10) and 20 (Luc20) amino acids of the N-terminus were deleted and inserted into the prokaryotic expression vector pBV220. The results showed that the enzymes were completely inactivated when the first eight or more N-terminal amino acids were removed. The recombinant Luc0 and mutants Luc6 and Luc7 were purified to homogeneity by ammonium sulfate precipitation and liquid chromatography for determination of their activity and conformational changes. The activity assay showed that removal of the first six amino acids resulted in 29% loss of enzymatic activity while removal of the first seven amino acids resulted in nearly complete inactivation (with remaining activity <0.5% of the original activity). Circular dichroism spectra showed no significant secondary structure changes. But the fluorescence emission maximum red-shift indicated some conformational changes. Luc6 and Luc7 were more sensitive to guanidine unfolding than Luc0. The present result indicated the significant role of Ile7 to the luciferase stability.

Preparation of luciferase-bacterial magnetic particle complex by artificial integration of MagA-luciferase fusion protein into the bacterial magnetic particle membrane

MagA is an iron-translocating protein found in the membranes of magnetic bacterium. Luciferase-bacterial magnetic particle (BMP) complexes were prepared by artificially inserting MagA-luciferase fusion proteins into the membranes of BMPs from Magnetospirillum magneticum strain AMB-1. Fusion proteins were from recombinant Escherichia coli membranes. MagA-Luc fusion proteins were integrated by sonication in vitro. Successful integration of fusion proteins was confirmed by luciferase luminescence on BMPs. Maximum luminescence was obtained after sonication for 3 min with a solution containing 300 mM NaCl, and is 18 times higher compared with recombinant Luc-BMPs generated using previously reported gene fusion techniques.

[Characteristics and utilities of luminescent bacteria from the Black sea]

Luminescent bacteria, isolated from summer specimens of water of the Black sea, have been identified as strains of Photobacterium phosphoreum and Vibrio fischeri (two of each). Morphological, physiological, and biochemical properties of the four strains have been characterized, and the kinetic behavior of luciferases isolated therefrom has been studied. The sensitivity of the luminescence of the strains to certain toxic agents has been compared to that of the test strain Ph. phosphoreum (Cohn) Ford. The results obtained indicate that the new strains show promise as bioindicators.

Cloning and characterization of an active fragment of luciferase from a luminescent marine alga, Pyrocystis lunula

Two marine dinoflagellates, Lingulodinium polyedrum and Pyrocystis lunula, emit light in a reaction involving the enzymatic oxidation of its tetrapyrrole luciferin by molecular oxygen. The characteristic properties of P. lunula luciferase have not been clarified, whereas L. polyedrum luciferase, which has three active domains, has been characterized. A cloned partial cDNA of the P. lunula luciferase encodes an active fragment corresponding to part of domain 2 and all of domain 3 of L. polyedrum luciferase. The homology of the amino acid sequence between the two luciferases in domain 3 is about 84.3%. A recombinant His-tagged luciferase fragment containing domain 3 (Mr = 46 kDa) catalyzed the light-emitting oxidation of luciferin (lambdamax = 474 nm). This protein was purified by a single affinity-chromatography procedure. The pH-activity profile and the bioluminescence spectrum of the recombinant enzyme having a third domain are almost identical to those of an extract from P. lunula cultured in vitro. The recombinant enzyme is active at pH 8.0, although the recombinant enzyme derived from the second domain of L. polyedrum luciferase is inactive at pH 8.0. Substitution of Glu-201 by histidine in the third domain of P. lunula luciferase showed a decrease of activity above pH 7.0, suggesting that histidine residues could be responsible for pH-sensitivity in dinoflagellate luciferase.

Isolation and properties of the luciferase stored in the ovary of the scyphozoan medusa Periphylla periphylla

Bioluminescence of the medusa Periphylla is based on the oxidation of coelenterazine catalyzed by luciferase. Periphylla has two types of luciferase: the soluble form luciferase L, which causes the exumbrellar bioluminescence display of the medusa, and the insoluble aggregated form, which is stored as particulate material in the ovary, in an amount over 100 times that of luciferase L. The eggs are especially rich in the insoluble luciferase, which drastically decreases upon fertilization. The insoluble form could be solubilized by 2-mercaptoethanol, yielding a mixture of luciferase oligomers with molecular masses in multiples of approximately 20 kDa. Those having the molecular masses of 20 kDa, 40 kDa, and 80 kDa were isolated and designated, respectively, as luciferase A, luciferase B, and luciferase C. The luminescence activities of Periphylla luciferases A, B, and C were 1.2 approximately 4.1 x 10(16) photon/mg. s, significantly higher than any coelenterazine luciferase known, and the quantum yields of coelenterazine catalyzed by these luciferases (about 0.30 at 24 degrees C) are comparable to that catalyzed by Oplophorus luciferase (0.34 at 22 degrees C), which has been considered the most efficient coelenterazine luciferase until now. Luciferase L (32 kDa) could also be split by 2-mercaptoethanol into luciferase A and an accessory protein (approx. 12 kDa), as yet uncharacterized. Luciferases A, B, and C are highly resistant to inactivation: their luminescence activities are only slightly diminished at pH 1 and pH 11 and are enhanced in the presence of 1 approximately 2 M guanidine hydrochloride; but they are less stable to heating than luciferase L, which is practically unaffected by boiling.

The role of active site residue arginine 218 in firefly luciferase bioluminescence

Firefly luciferase catalyzes the highly efficient emission of yellow-green light from substrate firefly luciferin by a sequence of reactions that require Mg-ATP and molecular oxygen. We had previously developed a working model of the luciferase active site based on the X-ray structure of the enzyme without bound substrates. In our model, the side chain guanidinium group of Arg218 appears to be located in close proximity to the substrate's hydroxyl group at the bottom of the luciferin binding pocket. A similar role for Arg337 also has been proposed. We report here the construction, purification, and characterization of mutant luciferases R218A, R218Q, R218K, R337Q, and R337K. Alteration of the Arg218 side chain produced enzymes with 15-20-fold increases in the Km values for luciferin. The contrasting near-normal Km values for luciferin determined with the Arg337 enzymes support our proposal that Arg218 (and not Arg337) is an essential luciferin binding site residue. Bioluminescence emission studies indicated that in the absence of a positively charged group at position 218, red bioluminescence was produced. Based on this result and those of additional fluorescence experiments, we speculate that Arg218 maintains the polarity and rigidity of the emitter binding site necessary for the normal yellow-green emission of P. pyralis luciferase. The findings reported here are interpreted in the context of the firefly luciferase X-ray structures and computational-based models of the active site.

Expression and purification of polyhistidine-tagged firefly luciferase in insect cells--a potential alternative for process scale-up

The coleopteran firefly, Photinus pyralis, luciferase was produced in lepidopteran Trichoplusia ni insect cells using a baculovirus expression vector. The recombinant protein was equipped with a polyhistidine affinity tag at the carboxyl terminus and purified by immobilized metal-ion affinity chromatography in combination with an expanded bed adsorption system. This approach enabled an efficient, one-step purification protocol of a genetically modified luciferase with properties similar to those of the authentic counterpart. According to light emission measurements, the final yield of highly purified protein was 23 mg l(-1) of cell culture. In addition, no specific interaction of interfering substances, such as, ATP, adenylate kinase, nucleoside diphosphokinase, as well as, creatine kinase of the final preparation were identified. Together, the results presented here clearly show that the baculovirus expression system in combination with immobilized metal-ion affinity chromatography is a potential strategy for process scale-up of polyhistidine tagged insect luciferase.

Secretional luciferase of the luminous shrimp Oplophorus gracilirostris: cDNA cloning of a novel imidazopyrazinone luciferase(1)

The deep-sea shrimp Oplophorus gracilirostris secretes a luciferase that catalyzes the oxidation of coelenterazine to emit blue light. The luciferase (M(r) approx. 106000) was found to be a complex composed of 35 kDa and 19 kDa proteins, and the cDNAs encoding these two proteins were cloned. The expression of the cDNAs in bacterial and mammalian cells indicated that the 19 kDa protein, not the 35 kDa protein, is capable of catalyzing the luminescent oxidation of coelenterazine. The primary sequence of the 35 kDa protein revealed a typical leucine-rich repeat sequence, whereas the catalytic 19 kDa protein shared no homology with any known luciferases including various imidazopyrazinone luciferases.

Site-directed mutagenesis of firefly luciferase active site amino acids: a proposed model for bioluminescence color

Under physiological conditions firefly luciferase catalyzes the highly efficient emission of yellow-green light from the substrates luciferin, Mg-ATP, and oxygen. In nature, bioluminescence emission by beetle luciferases is observed in colors ranging from green (approximately 530 nm) to red (approximately 635 nm), yet all known luciferases use the same luciferin substrate. In an earlier report [Branchini, B. R., Magyar, R. M., Murtiashaw, M. H., Anderson, S. M., and Zimmer, M. (1998) Biochemistry 37, 15311-15319], we described the effects of mutations at His245 on luciferase activity. In the context of molecular modeling results, we proposed that His245 is located at the luciferase active site. We noted too that the H245 mutants displayed red-shifted bioluminescent emission spectra. We report here the construction and purification of additional His245 mutants, as well as mutants at residues Lys529 and Thr343, all of which are stringently conserved in the beetle luciferase sequences. Analysis of specific activity and steady-state kinetic constants suggested that these residues are involved in luciferase catalysis and the productive binding of substrates. Bioluminescence emission spectroscopy studies indicated that point mutations at His245 and Thr343 produced luciferases that emitted light over the color range from green to red. The results of mutational and biochemical studies with luciferase reported here have enabled us to propose speculative mechanisms for color determination in firefly bioluminescence. An essential role for Thr343, the participation of His245 and Arg218, and the involvement of bound AMP are indicated.

Occurrence of P-flavin binding protein in Vibrio fischeri and properties of the protein

In previous studies involving Photobacterium species we proposed that (i) P-flavin is the product of luciferase, (ii) the physiological function of the lux operon is not to produce light but to produce FP(390) (luxF protein), including its prosthetic group, P-flavin, and (iii) FP(390) reactivates oxidatively inactivated cobalamin-dependent methionine synthase similar to flavodoxin but at relatively high ionic strength. It seems difficult to extend this idea to all luminous bacteria because the luxF gene is not present in the lux operon in Vibrio or Xenorhabdus. But we predicted that a luciferase fragment which binds P-flavin should function like FP(390) in these species. In this study, we isolated P-flavin binding protein from Vibrio fischeri ATCC 7744. The obtained protein was a modified luciferase as expected, in which the beta-subunit was intact but about 25 amino acid residues at the C-terminus of the alpha-subunit were deleted and the prosthetic group was the fully reduced P-flavin. These results strongly support that the physiological function of the lux operon is as described above even in luminous bacteria other than Photobacterium species. We propose that chromophore B reported by Tu and Hastings [Tu, S.-C. and Hastings, J.W. (1975) Biochemistry 14, 1975-1980] is the reduced P-flavin.

[FMN-reductase from Escherichia coli and its effect on the activity of luciferase from marine bacterium Vibrio fischeri]

Interactions of luciferases isolated from Vibrio fischeri 6 and Escherichia coli JM109(pF3) (bearing cloned V. fischeri luxAB genes) with FMN reductase isolated from E. coli JM109 were studied. FMN reductase formed a stable complex with luciferase, suggesting similar properties of the FMN reductases in the taxonomically close families Vibrionaceae and Enterobacteriaceae.

Cyclin E-induced S phase without activation of the pRb/E2F pathway

In cells of higher eukaryotes, cyclin D-dependent kinases Cdk4 and Cdk6 and, possibly, cyclin E-dependent Cdk2 positively regulate the G1- to S-phase transition, by phosphorylating the retinoblastoma protein (pRb), thereby releasing E2F transcription factors that control S-phase genes. Here we performed microinjection and transfection experiments using rat R12 fibroblasts, their derivatives conditionally overexpressing cyclins D1 or E, and human U-2-OS cells, to explore the action of G1 cyclins and the relationship of E2F and cyclin E in S-phase induction. We demonstrate that ectopic expression of cyclin E, but not cyclin D1, can override G1 arrest imposed by either the p16INK4a Cdk inhibitor specific for Cdk4 and Cdk6 or a novel phosphorylation-deficient mutant pRb. Several complementary approaches to assess E2F activation, including quantitative reporter assays in live cells, showed that the cyclin E-induced S phase and completion of the cell division cycle can occur in the absence of E2F-mediated transactivation. Together with the ability of cyclin E to overcome a G1 block induced by expression of dominant-negative mutant DP-1, a heterodimeric partner of E2Fs, these results provide evidence for a cyclin E-controlled S phase-promoting event in somatic cells downstream of or parallel to phosphorylation of pRb and independent of E2F activation. They furthermore indicate that a lack of E2F-mediated transactivation can be compensated by hyperactivation of this cyclin E-controlled event.

[Action of lovastatin--an inhibitor of cholesterol biosynthesis on bacterial bioluminescence]

The action of lovastatin, a competing inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase, on bacterial bioluminescence was studied. The lovastatin lactone form and sodium salt of mevinolinic acid inhibited bacterial luciferase in vitro but did not affect bioluminescence of the intact cells of the luminous bacteria. The inhibition was found to be of a competing character in regard to aliphatic aldehyde, the bacterial luciferase substrate. Conditions under which the bioluminescence inhibition was proportional to the lovastatin concentration in the incubation mixture and a bioluminescence method for quantitative determination of the inhibitor were developed.

The roles of the two highly unstable components F and P involved in the bioluminescence of euphausiid shrimps

Bioluminescence of euphausiids takes place when a fluorescent tetrapyrrole F and a highly unstable protein P react in the presence of oxygen. A previous study on the euphausiid Meganyctiphanes norvegica indicated that F acts as a catalyst and P is consumed in the luminescence reaction, differing from the luminescence system of dinoflagellates in which a tetrapyrrole luciferin, nearly identical to F, is enzymatically oxidized in the presence of dinoflagellate luciferase. In the present study, P was extracted from Euphausia pacifica as well as from M. norvegica, then purified separately by affinity chromatography on a column of biliverdin-Sepharose 4B, completing the whole process in less than 5 h. The samples of P obtained from both species had a molecular weight of 600,000, a purity of about 80%, and a specific activity 50-100 times greater than that previously found. The activity of P rapidly decreased in solutions, even at 0 degrees C, and the inactivation of P derived from M. norvegica was more than four times faster than that derived from E. pacifica. The kinetics of the luminescence reaction was investigated with F and P whose concentrations were systematically varied. The reaction was characteristically slow and involved two different reaction rates; the turnover number at 0 degrees C was 30/h for the initial 20 min and 20/h after the initial 1 h. The total light emitted in a 50-h period indicated that the bioluminescence quantum yield of F was about 0.6 at 0 degrees C, and P recycled many times in the luminescence reaction. Thus, the present results conclusively show that F is a luciferin and P is a luciferase of an unusually slow-working type, contrary to early report.

The ATP hydrolysis-dependent reaction cycle of the Escherichia coli Hsp70 system DnaK, DnaJ, and GrpE

Molecular chaperones of the Hsp70 class bind unfolded polypeptide chains and are thought to be involved in the cellular folding pathway of many proteins. DnaK, the Hsp70 protein of Escherichia coli, is regulated by the chaperone protein DnaJ and the cofactor GrpE. To gain a biologically relevant understanding of the mechanism of Hsp70 action, we have analyzed a model reaction in which DnaK, DnaJ, and GrpE mediate the folding of denatured firefly luciferase. The binding and release of substrate protein for folding involves the following ATP hydrolysis-dependent cycle: (i) unfolded luciferase binds initially to DnaJ; (ii) upon interaction with luciferase-DnaJ, DnaK hydrolyzes its bound ATP, resulting in the formation of a stable luciferase-DnaK-DnaJ complex; (iii) GrpE releases ADP from DnaK; and (iv) ATP binding to DnaK triggers the release of substrate protein, thus completing the reaction cycle. A single cycle of binding and release leads to folding of only a fraction of luciferase molecules. Several rounds of ATP-dependent interaction with DnaK and DnaJ are required for fully efficient folding.

Mechanism of aldehyde inhibition of Vibrio harveyi luciferase. Identification of two aldehyde sites and relationship between aldehyde and flavin binding

Vibrio harveyi luciferase is sensitive to aldehyde substrate inhibition, and two kinetic schemes have been previously postulated to account for such an inhibition. One scheme depicts a sequential binding of 2 aldehyde molecules, yielding an active enzyme-aldehyde binary complex and subsequently an inactive enzyme-(aldehyde)2 ternary complex (Holzman, T. F., and Baldwin, T. O. (1983) Biochemistry 22, 2838-2846). This two-aldehyde model was later withdrawn, and recently, a different scheme was proposed, following which the prior binding of one aldehyde to the native luciferase forms an inactive dead-end complex (Abu-Soud, H. M., Clark, A. C., Francisco, W. A., Baldwin, T. O., and Raushel, F. M. (1993) J. Biol. Chem. 268, 7699-7706). In this work, kinetic and equilibrium studies were carried out to elucidate further the mechanism of aldehyde inhibition. Two, presumably independent, aldehyde-binding sites were detected, with a higher affinity site for the aldehyde substrate and a weaker affinity site for the aldehyde inhibitor. Binding to and dissociation from the inhibitor site by decanal were revealed by chemical relaxation analysis to be slow processes. Furthermore, whereas the binding of the decanal substrate enhances the affinity of the reduced riboflavin 5'-phosphate (FMNH2) site, the binding of decanal to the inhibitor site competes against FMNH2 binding, thus resulting in inhibition of luciferase activity. These findings are not compatible with either of the two earlier schemes mentioned above. A new kinetic model is formulated for the mechanism of aldehyde inhibition. Theoretical kinetic behaviors predicted on the basis of this model are in excellent agreement with experimental observations. A particularly reactive cysteine (residue 106) on the alpha subunit has been previously demonstrated to be at or near an aldehyde site (Fried, A., and Tu, S.-C. (1984) J. Biol. Chem. 259, 10754-10759). Evidence is presented to indicate that this residue is at or near the aldehyde inhibitor site. Relative locations of this residue and binding sites for FMNH2, the aldehyde substrate, and the aldehyde inhibitor are proposed.

The Vibrio fischeri luminescence gene activator LuxR is a membrane-associated protein

The Vibrio fischeri luminescence (lux) genes are activated at sufficiently high culture densities by the transcriptional activator LuxR in combination with a diffusible signal compound termed autoinducer. We have used antibodies directed against LuxR in immunoprecipitation experiments to study the subcellular location of this transcription factor. The LuxR polypeptide was detected in membranes and not in the soluble pool of cytoplasmic proteins from V. fischeri. LuxR was not released from the membranes by 0.6 M KCl or by the nonionic detergents Nonidet P-40, N-octyl-beta-D-glucopyranoside, and Triton X-100. LuxR and a number of other V. fischeri proteins were released from the membranes by EDTA. The autoinducer had no detectable influence on the subcellular location of LuxR. In spheroplasts, neither the abundance nor the molecular mass of the LuxR antigen was influenced by treatment with proteinase K. Together with other information, these results indicate that LuxR is an amphipathic protein that is associated with the cytoplasmic membrane of V. fischeri.

Subunit interactions and the role of the luxA polypeptide in controlling thermal stability and catalytic properties in recombinant luciferase hybrids

Bacterial luciferases with over 70% sequence identity from the terrestrial species, Xenorhabdus luminescens, and the marine species, Vibrio harveyi, exhibit large differences in thermal stability (Szittner and Meighen, 1990, J. Biol. Chem. 265, 16581-16587). The origin of these differences was investigated with genetically constructed hybrids containing one subunit from X. luminescens and the other from V. harveyi. While no activity was detected with the single (alpha and beta) subunits both in vitro and in vivo, the recombinant hybrid luciferases (alpha Xl beta Vh and alpha Vh beta Xh) were highly active and could be purified to homogeneity. The kinetic properties of the hybrid enzymes including aldehyde specificity, flavin binding and luminescence decay rates, were found to be nearly identical to those of the native luciferases (alpha Xl beta Xl or alpha Vh beta Vh) containing the same alpha subunit. In addition, the rate of thermal inactivation and temperature dependent quenching of the intrinsic fluorescence by flavin were found to be independent of the nature of the beta subunit, quite opposite to previous reports that the thermal stability is controlled by the beta subunit. Thus, the alpha subunit appears primarily responsible for controlling both the catalytic and structural properties of luciferase.

Luciferase from the east European firefly Luciola mingrelica: cloning and nucleotide sequence of the cDNA, overexpression in Escherichia coli and purification of the enzyme

We have cloned cDNA encoding luciferase in Luciola mingrelica, fireflies living near the Black Sea in southern Russia, and obtained high level expression of the cloned sequences in Escherichia coli. The nucleotide sequences of two isolated clones were determined; five single base differences were observed, but none resulted in a change in the encoded amino acid residue. The cDNA encoded a protein of 548 amino acid residues. The overall amino acid sequence identity with the luciferase from Photinus pyralis, the North American firefly, was 67%, while comparison of the L. mingrelica luciferase with L. cruciata and L. lateralis, both indigenous to Japan, showed about 80% of the residues were strictly conserved. A novel overexpression system which employs the regulatory genes of the luminous bacterium Vibrio fischeri allowed growth of cultures to high cell density and high luciferase content, facilitating purification of the enzyme. Luciferase was purified to homogeneity in good yield from lysates of recombinant E. coli by ammonium sulfate fractionation and chromatography on columns of DEAE Sephadex and Blue Sepharose. The physicochemical properties of the luciferases from the available recombinant sources are significantly different and should allow detailed investigations into the mechanism of the bioluminescence reaction and the physical basis of the differences in the color of light emitted from the various enzymes.

Refolding of luciferase subunits from urea and assembly of the active heterodimer. Evidence for folding intermediates that precede and follow the dimerization step on the pathway to the active form of the enzyme

Conditions have been established that allow reversible refolding of luciferase from 5 M urea. The kinetics of formation of the active enzyme showed a concentration-independent lag, suggesting the existence of intermediate structures on the pathway of refolding. The rate of approach to the final level of activity was strongly concentration-dependent at protein concentrations below 10 micrograms/ml, but at concentrations above about 20 micrograms/ml, the rate of approach to the final activity value did not change with concentration. The concentration dependence presumably reflects the second-order step yielding the heterodimeric structure. The finding that at concentrations above 20 micrograms/ml, the rate becomes insensitive to concentration suggests that under these conditions, some step subsequent to dimerization become rate-limiting. When the refolding reaction was initiated by dilution out of 5 M urea at 50 micrograms/ml followed at various times by a secondary dilution to a final concentration of 5 micrograms/ml, it was found that the increase in activity continued at the rate characteristic of the higher protein concentration for a period of about 1-2 min following the dilution before slowing to the rate expected for the lower protein concentration. These observations indicate that there are inactive heterodimeric species that form from assembly of the individual subunits and that these species must undergo further folding to yield the active heterodimeric species. At protein concentrations of 5-50 micrograms/ml, the final yield of active enzyme was about 65-85%, decreasing at higher and lower concentrations. At higher concentrations, aggregation probably accounts for the limit in recovery, whereas at lower concentrations, it appears that the reduced yield of activity is due to the competing process of the folding of one or both individual subunits into some form incompetent to interact with each other. These experiments demonstrate the existence of slow steps in the refolding of luciferase subunits from urea and the formation of the active heterodimeric structure, both preceding and following the dimerization. Furthermore, the failure of protein at low concentrations to efficiently reassemble into the active heterodimer is consistent with the prior finding that luciferase subunits produced independently in Escherichia coli fold into conformations that cannot interact to form the active heterodimer upin mixing (Waddle, J. J., Johnston, T. C., and Baldwin, T. O. (1987) Biochemistry 26, 4917-4921).

Contribution of folding steps involving the individual subunits of bacterial luciferase to the assembly of the active heterodimeric enzyme

Bacterial luciferase is an alpha beta heterodimer with a single active center in which the reaction of reduced FMN, O2, and an aliphatic aldehyde yields a photon of blue-green light. We have shown that refolding of the luciferase subunits from 5 M urea occurs via the intermediacy of several species, one of which is an inactive heterodimeric structure, resulting from the dimerization of alpha and beta, which isomerizes to the active alpha beta structure in a first-order reaction (Ziegler, M. M., Goldberg, M. E., Chaffotte, A. F., and Baldwin, T. O. (1993) J. Biol. Chem. 268, 10760-10765). We have also demonstrated the existence of an inactive heterodimeric species that is well populated at equilibrium in the presence of 1.6-2.8 M urea (Clark, A. C., Sinclair, J. F., and Baldwin, T. O. (1993) J. Biol. Chem. 268, 10773-10779). We have separated the alpha and beta subunits by ion exchange chromatography and investigated the effects on reformation of active luciferase of allowing the individual subunits to refold separately prior to mixing. These investigations show that the lag in formation of active luciferase is due to slow steps in folding of the individual subunits. The beta subunit appears to fold faster than the alpha subunit, but folding of the beta subunit also shows a distinct lag. When the alpha and beta subunits were allowed to refold from urea for periods of several hours or more prior to mixing, the yield of active heterodimeric luciferase was compromised, which is consistent with the finding that individual subunits produced in vivo fold into structures incompetent to interact with each other to form the active heterodimer (Waddle, J. J., Johnston, T. C., and Baldwin, T. O. (1987) Biochemistry 26, 4917-4921). It appeared that the rate with which the beta subunit assumed the heterodimerization-incompetent structure was faster than the rate with which the alpha subunit became heterodimerization-incompetent. These observations support a model for folding and assembly of the subunits of luciferase in which the two subunits fold into assembly-competent structures that associate to form the heterodimer. In a slow competing process, the subunits undergo a conformational rearrangement to form stable structures incompetent to form heterodimers. It appears that the association of the luciferase subunits might constitute an example of one polypeptide modifying the folding pathway of another, a model that is consistent with the suggestion that the formation of the heterodimeric structure of luciferase is a kinetic trap on the folding pathway of the individual subunits (Sugihara, J., and Baldwin, T. O. (1988) Biochemistry 27, 2872-2880).

Identification of a trans-acting activity from liver that stimulates hepatitis A virus translation in vitro

Hepatitis A virus (HAV), a picornavirus, is the causative agent of infectious hepatitis, generally a self-limiting disease of the liver. Recently, sequences within the 5' noncoding region that affect the translation of the viral genome have been identified using in vitro systems. In this report we demonstrate that extracts prepared from mouse liver cytoplasm specifically stimulate HAV RNA translation in a rabbit reticulocyte lysate in vitro. This activity appears to act specifically on HAV sequences and is not found in other mouse tissue and several cell lines of tissue culture origin.

The polypeptide components of scintillons, the bioluminescence organelles of the dinoflagellate Gonyaulax polyedra

Scintillons, the bioluminescence organelles of Gonyaulax polyedra, were purified by isopycnic density gradient centrifugation until only low levels of contaminating chloroplasts and mitochondria were detected by fluorescence and electron microscopy. Purified scintillons catalyzed the luminescent reaction with kinetics identical to those observed during the bioluminescence flash in vivo. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicated that the organelles appeared to contain only two proteins. These proteins were identified as luciferase (135 kilodaltons) and luciferin-binding protein (75 kilodaltons) based on their size and their known functions in the bioluminescence reaction in vitro. The staining of luciferin-binding protein by Coomassie blue was 2.4 +/- 0.3 (n = 19) times greater than the luciferase, suggesting that there are four binding protein monomers for every luciferase monomer. A model is proposed for the close packing of the two proteins inside the scintillons.

Synthesis and use of the n-bromododecane-1,12-diols as conformational probes for general anesthetic target sites

The n-bromododecane-1,12-diols with bromine on carbons 2, 3, 5, and 6, respectively, were synthesized and found to be potent general anesthetics. They were also found to be potent inhibitors of firefly luciferase, a protein model for the primary target sites underlying general anesthesia. However, their effects on lipid bilayers were small, lowering the chain-melting phase transition temperature by less than 1 degree C at their EC50 concentrations for general anesthesia. A large dependence upon the position of the bromine atom was found for both n-hexadecane/water partition coefficients and inhibition constants for firefly luciferase; a much smaller positional dependence was found for induction of general anesthesia and for disrupting lipids. These results are consistent with the bulky bromine atom inhibiting the conformational flexibility of the diol hydrocarbon chain, making these bromo diols useful probes for ascertaining the shapes of apolar binding sites. In particular, our measurements suggest that these novel anesthetics produce general anesthesia by binding to long and relatively narrow apolar target sites in the central nervous system.

Translational enhancement of the poliovirus 5' noncoding region mediated by virus-encoded polypeptide 2A

Genetic and biochemical studies have revealed that the 5' noncoding region of poliovirus mediates translation of the viral mRNA by an unusual mechanism involving entry of ribosomes in internal sequences of mRNA molecules. We have found that mRNAs bearing the 5' noncoding region of poliovirus were translated at an enhanced rate in poliovirus-infected mammalian cells at a time when translation of cellular mRNAs was not yet inhibited. This translational enhancement of the polioviral 5' noncoding region was mediated by the expression of virus-encoded polypeptide 2A. This indicates that 2A is a multifunctional protein involved directly or indirectly in the activation of viral mRNA translation, in addition to its known roles in viral polyprotein processing and in inhibition of cellular protein synthesis. Thus, 2A represents an activator of translation of a viral mRNA that is translated by an internal ribosome binding mechanism. A likely consequence of this role of 2A is the efficient translation of viral mRNAs early in the infectious cycle, when host cell mRNAs can still compete with viral mRNAs for the host cell translation apparatus.

Identification of a cis-acting element that enhances the pigment cell-specific expression of the human tyrosinase gene

To identify the cis-acting element that is responsible for the pigment cell-specific expression of the human tyrosinase gene, we analyzed the promoter activity of its 5'-flanking region by transient expression assays. The fusion genes were constructed by inserting the 5'-flanking region of the human tyrosinase gene upstream from the firefly luciferase gene and were introduced into human melanoma cells and HeLa cells. We thus found the element, located between 2.7 and 1.8 kilobase pairs upstream from the transcription initiation site, that enhances the transient expression of the luciferase reporter gene in melanoma cells, but not in HeLa cells, the tyrosinase gene expression of which is not detectable. Using the fusion genes containing putative enhancer elements under the control of the heterologous simian virus 40 promoter, we identified the pigment cell-specific enhancer of approximately 200 base pairs (bp) between -2.0 and -1.8 kilobase pairs and localized the core sequence to a 39-bp region. This 39-bp core element was then confirmed to direct the melanoma cell-specific expression of the reporter gene under the tyrosinase gene promoter. We thus propose that this core element is responsible for the pigment cell-specific expression of the human tyrosinase gene.

Stabilization of luciferase intermediates by fatty amines, amides, and nitriles

Long-chain aliphatic amides, mono- and diamines, mono- and dialcohols, and nitriles were found to inhibit the bacterial luciferase reaction by binding with an enzyme intermediate (II, the luciferase-bound 4 alpha-flavin hydroperoxide). Inhibition was determined by measuring the decay rates of the inhibitor-intermediate II complex at different inhibitor concentrations. The data fit a model which was used to estimate the KI. At high concentrations, a plot of the decay rate (k) vs 1/[I] produced a straight line; extrapolation of this to 1/[I] = 0 yields an estimate of the decay rate at infinite inhibitor concentration which we defined as the inhibitor-enzyme-substrate stabilization constant, kESI.

Purification and characterization of luciferases from fireflies, Luciola cruciata and Luciola lateralis

Luciferases of Luciola cruciata and Luciola lateralis, LcL and LlL, were purified to homogeneity by ammonium sulfate precipitation, gel-filtration column chromatography, and hydroxyapatite HPLC. The molecular masses of the enzymes determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were both 62 kDa, almost identical to that of Photinus pyralis (PpL). LcL was found to be similar to PpL in thermal stability, pH stability, and the wavelength of maximum light intensity. LlL was superior to LcL and PpL in thermal and pH stability, and the reaction catalyzed by LlL emits green light with a peak intensity at 552 nm, which is 10 nm shorter in wavelength than those of PpL and LcL.

Functional consequences of site-directed mutation of conserved histidyl residues of the bacterial luciferase alpha subunit

The available sequences for the different bacterial luciferases reveal five conserved histidyl residues at positions 44, 45, 82, 224, and 285 of the alpha subunit. Ten variants of Vibrio harveyi luciferase were obtained by selective site-directed mutations of these five histidines. The essentiality of alpha His44 and alpha His45 was indicated by 4-7 orders of magnitude of bioluminescence activity reductions resulting from the substitution of either histidine by alanine (alpha H44A or alpha H45A), aspartate (alpha H44D or alpha H45D), or lysine (alpha H45K). Moreover, alpha H44A and alpha H45A were distinct from the native luciferase in thermal stabilities. Mutations at the other three positions also resulted in activity reductions ranging from a fewfold to 3 orders of magnitude. Despite these widely different bioluminescence light outputs, mutated luciferases exhibited, in nonturnover in vitro assays, light emission decay rates mostly similar to that of the native luciferase using octanal, decanal, or dodecanal as a substrate. This is attributed to a similarity in the catalytic rate constants of the light-emitting pathway for the native and mutated luciferases, but various mutated luciferases suffer in different degrees from competing dark reaction(s). In accord with this interpretation, the bioluminescence activities of mutated luciferases showed a general parallel with the relative stabilities of their 4a-hydroperoxyflavin intermediate species. Furthermore, the drastically reduced bioluminescence activities for luciferases with the alpha His44 or alpha His45 substituted by aspartate, alanine, or lysine were accompanied by little or no activities for consuming the aldehyde substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Mapping the polarity profiles of general anesthetic target sites using n-alkane-(alpha, omega)-diols

The effects of the homologous series of n-alkane-(alpha, omega)-diols have been studied on the inhibition of the purified firefly luciferase enzyme from Photinus pyralis, the inhibition of the purified bacterial luciferase enzyme from Vibrio harveyi, and the induction of general anesthesia in Xenopus laevis tadpoles. All but one of the diols tested were found to be reversible general anesthetics. The diols inhibited firefly luciferase by competing with its normal substrate firefly luciferin, and they inhibited bacterial luciferase by competing with the substrate n-decanal. For all but the smallest agent (1,4-butanediol), only a single diol molecule was found to be involved in the inhibition of the enzymes. Inhibition constants Ki were determined for the enzymes, and general anesthetic EC50 concentrations were determined for tadpoles. These data were then used in conjunction with previously determined n-alkane and n-alcohol data to calculate, as a function of chain length, the incremental standard Gibbs free energies delta (delta G0) for adding apolar -CH2- groups and for converting apolar terminal -CH3 groups to polar -CH2OH groups. The resulting plots of delta (delta G0) versus chain length gave a consistent mapping of the polarity profiles of the anesthetic-binding pockets. They clearly reveal the existence of two substantial and distinct polar regions in the anesthetic-binding pocket of firefly luciferase but only one such region for bacterial luciferase and for the unknown target sites underlying general anesthesia. The polarities and geometric properties of these different binding sites for straight-chain anesthetics are discussed in terms of simple models.

Amplified luminometric assays of alkaline phosphatase using riboflavin phosphates

An assay for alkaline phosphatase is described which is based on the hydrolysis of riboflavin phosphates (5'FMN or 4'FMN) to produce riboflavin. This is converted to 5'FMN using riboflavin kinase, and then assayed using the bacterial bioluminescent system from Vibrio harveyi or V. fischeri. The most sensitive assay is obtained using 4'FMN, which can measure less than 20 amol after a 1-hour incubation.

A rapid microscale procedure for the simultaneous preparation of cytoplasmic RNA, nuclear DNA binding proteins and enzymatically active luciferase extracts

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