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Cloning and sequencing of a cDNA for firefly luciferase from Photuris pennsylvanica.

The first cDNA from the Photurinae subfamily of the Lampyridae encoding a firefly luciferase from lantern mRNA of Photuris pennsylvanica has been cloned, sequenced, the amino-acid sequence predicted and the sequence reported to GenBank. The cDNA was about 1.8 kb in length with the largest open reading frame coding for a 545-residue protein. The 5' noncoding region is 61 bp long and the 3' noncoding region is 135 bp in length. There is a 24-nucleotide poly(A) tail. When the amino-acid residues are aligned, P. pennsylvanica contains 154 (about 28% of the total residues) that are conserved in all 16 of the deduced luciferase sequences that are presently available. In this P. pennsylvanica luciferase, the amino acids at 276 of the positions are the same at corresponding positions of at least one of the other enzymes. There are two amino-acid differences between this luciferase and the unpublished sequence obtained by Dr. Keith Wood for a putative larval Photuris firefly luciferase cloned from a Maryland firefly. Signature amino-acid sequences and domains found in the deduced sequence are for adenylate kinase, the putative AMP-binding domain, luciferin 4-monooxygenase, 4-coumarate CoA ligase, long-chain fatty acid CoA ligase, 2-acylglycerophosphoethanolamine acyltransferase, the microbody-directing sequence, peptide-synthesizing complexes, and acyladenylate-synthesizing enzymes.

Amino Acid Sequence↗

Secretion of functional Renilla reniformis luciferase by mammalian cells.

The soft coral Renilla reniformis luciferase enzyme is a monomeric soluble intracellular protein that is used increasingly as a marker of gene expression. Here the Renilla luciferase gene was engineered to encode a protein product secreted by mammalian cells. The 5' end of the Renilla luciferase gene was fused in frame with the 3' end of a short DNA sequence encoding the signal peptide from human interleukin-2 (IL-2) protein. This construct was cloned under transcriptional control of the cytomegalovirus (CMV) promoter in a mammalian expression vector. Simian COS-7 cells were transiently transfected with the construct, and light emission was measured from cell lysates and from cell culture media. The results of these experiments indicated that Renilla luciferase was secreted as a functional enzyme by mammalian cells. The advantages and disadvantages of secreted Renilla luciferase as a marker of gene expression in comparison to other secreted protein markers are discussed.

Amino Acid Sequence↗

Crystal structure of firefly luciferase throws light on a superfamily of adenylate-forming enzymes.

BACKGROUND: Firefly luciferase is a 62 kDa protein that catalyzes the production of light. In the presence of MgATP and molecular oxygen, the enzyme oxidizes its substrate, firefly luciferin, emitting yellow-green light. The reaction proceeds through activation of the substrate to form an adenylate intermediate. Firefly luciferase shows extensive sequence homology with a number of enzymes that utilize ATP in adenylation reactions. RESULTS: We have determined the crystal structure of firefly luciferase at 2.0 A resolution. The protein is folded into two compact domains. The large N-terminal domain consists of a beta-barrel and two beta-sheets. The sheets are flanked by alpha-helices to form an alphabetaalphabetaalpha five-layered structure. The C-terminal portion of the molecule forms a distinct domain, which is separated from the N-terminal domain by a wide cleft. CONCLUSIONS: Firefly luciferase is the first member of a superfamily of homologous enzymes, which includes acyl-coenzyme A ligases and peptide synthetases, to have its structure characterized. The residues conserved within the superfamily are located on the surfaces of the two domains on either side of the cleft, but are too far apart to interact simultaneously with the substrates. This suggests that the two domains will close in the course of the reaction. Firefly luciferase has a novel structural framework for catalyzing adenylate-forming reactions.

Adenosine↗

Expression of luciferase in selected organs following delivery of naked and formulated DNA to rainbow trout (Oncorhynchus mykiss) by different routes of administration.

In the present work, the expression of luciferase in selected organs following administration of DNA delivered as naked, liposome-formulated or chitosan-formulated by different routes of administration (intramuscular, intraperitoneal and intravenous injection, immersion and anal intubation) was studied in rainbow trout (Oncorhynchus mykiss). The different formulations and routes of administration both influenced in which organs luciferase was expressed and the magnitude of expression. The highest expression levels of luciferase in the head kidney and liver were found after an intraperitoneal injection of lipoplex 2. In the spleen, the highest levels were detected after injection of naked DNA (intraperitonal or intramuscular) and lipoplex 2 (intraperitoneal). Following intravenous injection, naked DNA gave higher expression levels in the organs than the formulated plasmids and immersion and anal intubation were not effective routes of delivery as no expression of luciferase could be detected in any of the organs tested. Additionally, PCR using a primer specific for a 600 bp region of the luciferase gene pcDNA3-luc was used to assess the distribution of the plasmid itself after intramuscular and intraperitoneal injection. Positive amplification was obtained in spleen, head kidney, liver and muscle at the injection site following injection of formulated plasmids, while only muscle tissue from the injection site was positive when naked DNA was used.

Adjuvants, Pharmaceutic↗

Circadian and light-induced expression of luciferase in Neurospora crassa.

We have constructed a plasmid vector for expressing firefly luciferase in Neurospora crassa under control of the light- and clock-regulated ccg-2 (eas) promoter. The sequence of the luciferase gene in the vector has been modified to reflect the N. crassa codon bias. Both light-induced activity and circadian activity are demonstrated. Expression of luciferase in strains carrying mutant frequency alleles shows appropriate period length alterations. These data demonstrate that luciferase is a sensitive reporter of gene expression in N. crassa. Our results also show that the modified luciferase is expressed in Aspergillus nidulans.

Aspergillus nidulans↗

Split luciferase as an optical probe for detecting protein-protein interactions in mammalian cells based on protein splicing.

We describe a new method for detecting protein-protein interactions in intact mammalian cells; the approach is based on protein splicing-induced complementation of rationally designed fragments of firefly luciferase. The protein splicing is a posttranslational protein modification through which inteins (internal proteins) are excised out from a precursor fusion protein, ligating the flanking exteins (external proteins) into a contiguous polypeptide. As the intein, naturally split DnaE from Synechocystis sp. PCC6803 was used: The N- and C-terminal DnaE, each fused respectively to N- and C-terminal fragments of split luciferase, were connected to proteins of interest. In this approach, protein-protein interactions trigger the folding of DnaE intein, wherein the protein splicing occurs and thereby the extein of ligated luciferase recovers its enzymatic activity. To test the applicability of this split luciferase complementation, we used insulin-induced interaction between known binding partners, phosphorylated insulin receptor substrate 1 (IRS-1) and its target N-terminal SH2 domain of PI 3-kinase. Enzymatic luciferase activity triggered by insulin served to monitor the interaction between IRS-1 and the SH2 domain in an insulin dose-dependent manner, of which amount was assessed by the luminescent intensity. This provides a convenient method to study phosphorylation of any protein or interactions of integral membrane proteins, a class of molecules that has been difficult to study by existing biochemical or genetic methods. High-throughput drug screening and quantitative analysis for a specific pathway in tyrosine phosphorylation of IRS-1 in insulin signaling are also made possible in this system.

Animals↗

Properties of recombinant fluorescent proteins from Photobacterium leiognathi and their interaction with luciferase intermediates.

Ligand binding and luciferase interaction properties of the recombinant protein corresponding to the lumazine protein gene (EMBL X56534) of Photobacterium leiognathi have been determined by fluorescence dynamics, circular dichroism, gel filtration, and SDS-PAGE. Scatchard analysis of a fluorescence titration shows that the apoprotein possess one binding site, and at 30 degrees C the KdS (microM) are as follows: 6,7-dimethyl-8-ribityllumazine, 0.26; riboflavin, 0.53; and much more weakly bound FMN, 30. All holoproteins are highly fluorescent and have absorption spectra distinct from each other and from the free ligands. The longest wavelength absorption maxima are, respectively (nm, 2 degrees C), 420, 463, and 458. Ligand binding produces no change in the far-UV circular dichroism; all have mean residual ellipticity at 210 nm of -6500 deg cm2 dmol-1, the same as the native protein. However, in the bioluminescence reaction only the lumazine holoprotein shows a bioluminescence effect. Fluorescence emission anisotropy decay was used to establish that none of these holoproteins complexed with native luciferase and that the lumazine protein alone formed a 1:1 complex with the luciferase hydroxyflavin fluorescent transient and the luciferase peroxyflavin intermediates, revealed by a dominant channel of anisotropy loss, with rotational correlation time of 2.5 ns, and attributed to excitation transfer from the luciferase flavin donor to the acceptor, the lumazine ligand. The complex stability was sufficient to allow its isolation by FPLC gel filtration and verification by SDS-PAGE. These methods also confirmed the absence of interaction of the holoflavoproteins.

Bacterial Proteins↗

Stopped-flow kinetic analysis of the bacterial luciferase reaction.

The kinetics of the reaction catalyzed by bacterial luciferase have been measured by stopped-flow spectrophotometry at pH 7 and 25 degrees C. Luciferase catalyzes the formation of visible light, FMN, and a carboxylic acid from FMNH2, O2, and the corresponding aldehyde. The time courses for the formation and decay of the various intermediates have been followed by monitoring the absorbance changes at 380 and 445 nm along with the emission of visible light using n-decanal as the alkyl aldehyde. The synthesis of the 4a-hydroperoxyflavin intermediate (FMNOOH) was monitored at 380 nm after various concentrations of luciferase, O2, and FMNH2 were mixed. The second-order rate constant for the formation of FMNOOH from the luciferase-FMNH2 complex was found to be 2.4 x 10(6) M-1 s-1. In the absence of n-decanal, this complex decays to FMN and H2O2 with a rate constant of 0.10 s-1. The enzyme-FMNH2 complex was found to isomerize prior to reaction with oxygen. The production of visible light reaches a maximum intensity within 1 s and then decays exponentially over the next 10 s. The formation of FMN from the intermediate pseudobase (FMNOH) was monitored at 445 nm. This step of the reaction mechanism was inhibited by high levels of n-decanal which indicated that a dead-end luciferase-FMNOH-decanal could form. The time courses for these optical changes have been incorporated into a comprehensive kinetic model. Estimates for 15 individual rate constants have been obtained for this model by numeric simulations of the various time courses.

Aldehydes↗

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.

Amino Acid Sequence↗

Random and site-directed mutagenesis of bacterial luciferase: investigation of the aldehyde binding site.

Numerous luciferase structural gene mutants of Vibrio harveyi have been generated by random mutagenesis and phenotypically characterized [Cline, T.W., & Hastings, J.W. (1972) Biochemistry 11, 3359-3370]. All mutants selected by Cline and Hastings for altered kinetics in the bioluminescence reaction had lesions in the alpha subunit. One of these mutants, AK-20, has normal or slightly enhanced thermal stability and enhanced FMNH2 binding affinity but a much-reduced quantum yield of bioluminescence and dramatically altered stability of the aldehyde-C4a-peroxydihydroflavin-luciferase intermediate (IIA), with a different aldehyde chain length dependence from that of the wild-type luciferase. To better understand the structural aspects of the aldehyde binding site in bacterial luciferase, we have cloned the luxAB genes from the V. harveyi mutant AK-20, determined the nucleotide sequence of the entire luxA gene, and determined the mutation to be TCT----TTT, resulting in a change of serine----phenylalanine at position 227 of the alpha subunit. To confirm that this alteration caused the altered kinetic properties of AK-20, we reverted the AK-20 luxA gene by oligonucleotide-directed site-specific mutagenesis to the wild-type sequence and found that the resulting enzyme is indistinguishable from the wild-type luciferase with respect to quantum yield, FMNH2 binding affinity, and intermediate IIA decay rates with 1-octanal, 1-decanal, and 1-dodecanal. To investigate the cause of the AK-20 phenotype, i.e., whether the phenotype is due to loss of the seryl residue or to the properties of the phenylalanyl residue, we have constructed mutants with alanine, tyrosine, and tryptophan at alpha 227.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldehydes↗

Isolation and properties of bacterial luciferase-oxygenated flavin intermediate complexed with long-chain alcohols.

Nonsubstrate long-chain aliphatic alcohols, carboxylic acids, and their methyl esters were found to complex reversibly with and stabilize an oxygenated flavin-luciferase intermediate, with alcohols being more effective in stabilizing the intermediate. Dissociation constants for the binding of alcohols to luciferase intermediate are in the order of K8 greater than K10 greater than K12 congruent to K14 where the subscripts represent the numbers of carbon atoms of various alcohols. Thermodynamic activation parameters for the decay of oxygenated flavin-luciferase intermediate complexed with alcohols or aldehydes were determined, and similarities were noted between alcohol and aldehyde complexes. Luciferase intermediate complexes formed with 1-decanol and 1-tetradecanol were isolated at 0 degrees C in neutral phosphate buffer, and both showed absorption properties characteristic of 4a-substituted dihydroflavins. The 1-tetradecanol-intermediate species contained one favin per luciferase molecule. Initially this complex was weakly fluorescent, but upon exposure to 370-nm light it was transformed to a highly fluorescent species. The latter shows a fluorescence excitation peak at 370 nm, and its fluorescence emission (lambda max 505 nm) and quantum yield (0.17) closely correspond to that of bioluminescence in vitro. Both the weakly and the highly fluorescent species exhibit full bioluminescence activities when reacted with decanal.

Alcohols↗

Chemical modification of bacterial luciferase with ethoxyformic anhydride: evidence for an essential histidyl residue.

Bacterial luciferase is a heteropolymeric protein (alphabeta) that catalyses the conversion of chemical energy to light by oxidation of a reduced flavin mononucleotide and a long chain aliphatic aldehyde. Elucidation of the specific amino acid residues involved in the enzymatic reaction is essential for understanding the mechanisms of the bioluminescent reaction. Luciferase has been found to be inactivated by ethoxyformic anhydride with a second-order rate constant of 146 M-1 min-1 at pH 6.1 and 0 degrees C with a concomitant increase in absorbance at 240 nm due to formation of ethoxyformylhistidyl derivatives. Activity could be restored by hydroxylamine and the pH curve of inactivation indicated the involvement of a residue having a pKa of 6.8. Both substrates, FMNH2 and aldehyde, protected the enzyme against inactivation, suggesting that the modification occurred at or near the active site. Incorporation of [14C]ethoxyformyl groups in luciferase indicated that inactivation resulted from the modification of about three histidyl residues, one histidine being found on the alpha subunit and two on the beta subunit. Hybridization experiments, in which ethoxyformylluciferase, alphambetam, was complemented with native subunits, alpha or beta, showed that the hybrid alphambetam, has the same activity as alphambetam whereas the activity of the hybrid alphabetam, was close to that of the reconstituted luciferase alphabeta. The results indicate that modification of only one histidyl residue on the alpha subunit inactivates luciferase and suggest that this histidyl residue plays an essential role in the mechanism of the bacterial bioluminescent reaction.

Aldehydes↗

Active site hydrophobicity is critical to the bioluminescence activity of Vibrio harveyi luciferase.

Vibrio harveyi luciferase is an alphabeta heterodimer containing a single active site, proposed earlier to be at a cleft in the alpha subunit. In this work, six conserved phenylalanine residues at this proposed active site were subjected to site-directed mutations to investigate their possible functional roles and to delineate the makeup of luciferase active site. After initial screening of Phe --> Ala mutants, alphaF46, alphaF49, alphaF114, and alphaF117 were chosen for additional mutations to Asp, Ser, and Tyr. Comparisons of the general kinetic properties of wild-type and mutated luciferases indicated that the hydrophobic nature of alphaF46, alphaF49, alphaF114, and alphaF117 was important to luciferase V(max) and V(max)/K(m), which were reduced by 3-5 orders of magnitude for the Phe --> Asp mutants. Both alphaF46 and alphaF117 also appeared to be involved in the binding of reduced flavin substrate. Additional studies on the stability and yield of the 4a-hydroperoxyflavin intermediate II and measurements of decanal substrate oxidation by alphaF46D, alphaF49D, alphaF114D, and alphaF117D revealed that their marked reductions in the overall quantum yield (phi( degrees )) were a consequence of diminished yields of luciferase intermediates and, with the exception of alphaF114D, emission quantum yield of the excited emitter due to the replacement of the hydrophobic Phe by the anionic Asp. The locations of these four critical Phe residues in relation to other essential and/or hydrophobic residues are depicted in a refined map of the active site. Functional implications of these residues are discussed.

Binding Sites↗

Opiate analgesics' dual role in firefly luciferase activity.

The effects of three opiate analgesics, isolated from opium, on the firefly luciferase enzyme have been studied. Morphine (MN), 6-acetylmorphine (MAM), and diacetylmorphine (DAM) inhibited the enzyme activity at different levels. At lower concentrations, MN and MAM enhanced enzyme activity, effecting inhibition at higher concentrations. However, DAM inhibited the enzyme activity at all concentrations investigated. The stimulating activity of MN and MAM is attributed to the hydrophilic interaction of the proton donor-acceptor type with the polar regions of the luciferase located outside the binding pocket of the active site. The inhibition at higher concentrations of MN and MAM and at all concentrations of DAM is found to be competitive in nature, with the analgesics competing for the binding of the enzyme's natural substrate luciferin. The binding site of the luciferase could accommodate only one analgesic molecule. Binding constants determined from bioluminescence studies showed that the inhibitor binding site is hydrophobic in nature. The inhibition constants of analgesics are in the order MN > MAM > DAM. The greater binding of DAM to luciferase is attributed to its ability to form a ground state complex with ATP and greater hydrophobicity. At higher concentrations of ATP, the binding constants increased. The results obtained are explained assuming that the firefly luciferase acts as a subtype mu-opioid receptor model.

Adenosine Triphosphate↗

Effects of mutations of the alpha His45 residue of Vibrio harveyi luciferase on the yield and reactivity of the flavin peroxide intermediate.

This work was undertaken to investigate the functional consequences of mutations of the essential alpha His45 residue of Vibrio harveyi luciferase, especially with respect to the yield and reactivity of the flavin 4a-hydroperoxide intermediate II. A total of 14 luciferase variants, each with a different single-residue replacement for the alpha His45, were examined. These variants showed changes, mostly slight, in their light decay rates of the nonturnover luminescence reaction and in their Km values for decanal and reduced riboflavin 5'-phosphate (FMNH2). All alpha His45 mutants, however, showed markedly reduced bioluminescence activities, the magnitude of the reduction ranging from about 300-fold to 6 orders of magnitude. Remarkably, a good correlation was obtained for the wild-type luciferase, 12 alpha His45-mutated luciferases, and six additional variants with mutations of other alpha-subunit histidine residues between the degrees of luminescence activity reduction and the dark decay rates of intermediate II. Such a correlation further indicates that the activation of the O-O bond fission is an important function of the flavin 4a-hydroperoxide intermediate II. Both alpha H45G and alpha H45W were found to bind near-stoichiometric amounts of FMNH2. Moreover, each variant catalyzed the oxidation of bound FMNH2 by two mechanisms, with a minor pathway leading to the formation of a luminescence-active intermediate II and a major dark pathway not involving any detectable flavin 4a-hydroperoxide species. This latter pathway mimics that in the normal catalysis by flavooxidases, and its elicitation in luciferase was demonstrated for the first time by single-residue mutations.

Aldehydes↗

The role of lysine 529, a conserved residue of the acyl-adenylate-forming enzyme superfamily, in firefly luciferase.

Firefly luciferase catalyzes the highly efficient emission of yellow-green light from the substrates luciferin, Mg-ATP, and oxygen in a two-step process. The enzyme first catalyzes the adenylation of the carboxylate substrate luciferin with Mg-ATP followed by the oxidation of the acyl-adenylate to the light-emitting oxyluciferin product. The beetle luciferases are members of a large family of nonbioluminescent proteins that catalyze reactions of ATP with carboxylate substrates to form acyl-adenylates. Formation of the luciferase-luciferyl-AMP complex is a specific example of the chemistry common to this enzyme family. Site-directed mutants at positions Lys529, Thr343, and His245 were studied to determine the effects of the amino acid changes at these positions on the individual luciferase-catalyzed adenylation and oxidation reactions. The results suggest that Lys529 is a critical residue for effective substrate orientation and that it provides favorable polar interactions important for transition state stabilization leading to efficient adenylate production. These findings as well as those with the Thr343 and His245 mutants are interpreted in the context of the firefly luciferase X-ray structures and computational-based models of the active site.

Adenosine Monophosphate↗

Fluorescent properties of firefly luciferases and their complexes with luciferin.

Fluorescence of luciferases from Luciola mingrelica (single tryptophan residue, Trp-419) and Photinus pyralis (two tryptophan residues, Trp-417, Trp-426) was studied. Analysis of quenching of tryptophan fluorescence showed that the tryptophan residue conserved in all luciferases is not accessible for charged quenchers, which is explained by the presence of positively and negatively charged amino acid residues in the close vicinity to it. An effective energy transfer from tryptophan to luciferin was observed during quenching of tryptophan fluorescence of both luciferases with luciferin. From the data on the energy transfer, the distance between the luciferin molecule and Trp-417 (419) in the luciferin luciferase complex was calculated: 11-15 A for P. pyralis and 12-17 A for L. mingrelica luciferases. The role of the conserved Trp residue in the catalysis is discussed.

Amino Acids↗

A single-use luciferase-based mercury biosensor using Escherichia coli HB101 immobilized in a latex copolymer film.

A single-use Hg(II) patch biosensor has been developed consisting of 1.25-cm diameter patches of two acrylic vinyl acetate copolymer layers coated on polyester. The top layer copolymer was 47 microm thick whereas the bottom layer of copolymer plus E. coli cells was 30 microm thick. The immobilized E. coli HB101 cells harbored a mer-lux plasmid construct and produced a detectable light signal when exposed to Hg(II). The immobilized-cell Hg(II) biosensor had a sensitivity similar to that of suspended cells but a significantly larger detection range. The levels of mercury detected by the patches ranged from 0.1 nM to 10 000 nM HgCl2 in pyruvate buffer, and luciferase induction as a function of Hg(II) concentration was sigmoidal. Luciferase activity was detected in immobilized cells for more than 78 h after exposure of the cells to HgCl2. Addition of 1 mM D-cysteine to the pyruvate buffer increased luciferase induction more than 100-fold in the immobilized cell patches and 3.5-fold in a comparable suspension culture. The copolymer patches with immobilized cells were stable at -20 degrees C for at least 3 months, and the Hg(II)-induced luciferase activity after storage was similar to that of samples assayed immediately after coating. Patches stored desiccated at room temperature for 2 weeks showed lower mercury-induced luciferase activity when compared to freshly prepared patches, but they still had a considerable detection range of 1 to 10 000 nM HgCl2.

Biosensing Techniques↗