Construction of biotinylated firefly luciferases using biotin acceptor peptides

Diagnostic Accuracy of a Novel Stool Antigen Test for Helicobacter pylori Infection in a Medical Checkup Setting: A Prospective Cohort Study

Objective Of the highly accurate tests for current Helicobacter pylori infection, the urea breath test (UBT) and stool antigen test (SAT) are noninvasive and do not require endoscopy. We conducted a prospective study to evaluate the accuracy of the newly developed SAT in a medical checkup setting. Methods The accuracy of the proposed SAT was examined by determining H. pylori infection status based on a history of eradication therapy, endoscopic H. pylori infection diagnosis, and blood tests (serum H. pylori antibody, serum PG II) in individuals undergoing esophagogastroduodenoscopy (EGD) during a health checkup. Results The new SAT showed 97.3% (108/111) sensitivity for those "currently infected," as well as 99.3% (530/534), 98.0% (402/410), and 98.7% (932/944) specificity for those "never infected," those "previously infected," and those "never/previously infected", respectively. Conclusion The newly developed H. pylori SAT may be useful for diagnosing H. pylori infection. Patients should be suspected of being infected even after H. pylori eradication if they have a high cutoff index in this test.

Luciola mingrelica firefly luciferase as a marker in bioluminescent immunoassays

Chemical modification of the enzymes with biospecific macromolecules is used in various fields of biotechnology to impart new functions or improve their properties and is a fast and convenient way to get the final products. The preparation of highly active, stable, and functionally active conjugates of the thermostable luciferase through the NH2-groups or free SH-groups of the enzyme with target molecules of different molecular weight (albumin, avidin from chicken eggs, antibodies, and progesterone) is described. The obtained conjugates were successfully tested as a reporter in bioluminescent immunoassay for the detection of the molecules and pathogens. Thus, the luc-albumin (Luc-Alb) and luc-insulin (Luc-Ins) conjugates were used in competitive ELISA for the detection of an analyte (albumin or insulin) in the samples. Luc-progesterone (Luc-Pg) was used in the rapid homogeneous immunoassay of progesterone by the BRET technique with the detection limit of 0.5 ng/ml. Luciferase conjugates with avidin (Luc-Avi) and secondary and primary antibodies (Luc-RAM and Luc-Sal) were used for enzyme immunoassay detection of Salmonella paratyphi A cells with the cell detection limit of 5 × 104 CFU/ml. To reduce the detection limit of Salmonella cells, we developed a pseudo-homogeneous bioluminescent enzyme immunoassay of cells using a new matrix for the analyte capture-polystyrene microparticles coated with Pluronic F108, covalently labeled with Sal antibodies. This allowed to achieve efficient trapping of cells from solution, significantly reduced nonspecific sorption and decreased the cell detection limit to 2.7 × 103 CFU/ml without prior concentration of the sample. The methodology that was developed in this study can be applied for the development of novel bioanalytical systems based on firefly luciferases.

Clinical Evaluation of a Novel Stool Antigen Test Using Bioluminescent Enzyme Immunoassay for Detecting Helicobacter pylori

BACKGROUND

BLEIA ™ "EIKEN" Helicobacter pylori antigen (B[EIA]) is based on the bioluminescent enzyme immunoassay (BLEIA) method that was newly developed with high sensitivity in detecting Helicobacter pylori (H. pylori) antigen in feces.

METHODS

In the project for H. pylori screening and treatment in Saga Prefecture in 2019, 141 students received the stool H. pylori antigen test as a secondary test. For 141 students, a comparative test was conducted between B (EIA) and extracorporeal diagnostic agents that were marketed in Japan as of 2019. The detection performance of H. pylori ATCC43504 standard strain and H. pylori antigen in commercial human fecal specimens were conducted.

RESULTS

The comparison of B (EIA) with Quick Chaser ^TM H. pylori (Q [IC]) revealed positive and negative concordance ratios of B (EIA) to Q (IC) of 100.0% (110/110) and 71.0% (22/31), respectively. A comparative test was conducted between B (EIA) and extracorporeal diagnostic agents that were marketed in Japan as of 2019, and B (EIA) was most sensitive on "detecting H. pylori antigen of ATCC43504 standard strain" and "detecting H. pylori antigen in commercial human fecal specimens," compared with other kits. Nine dissociated specimens that were negative for Q (IC) and positive for B (EIA) were confirmed. The measured value of B (EIA) in the dissociation samples were 1.3-87.4 cutoff index in the range that can be evaluated as negative by other fecal H. pylori antigen test kits, all the dissociation samples were H. pylori antigen-positive cases, and finally the cause of result divergence was presumed as false negative due to insufficient sensitivity of Q (IC).

CONCLUSION

B (EIA) that is based on the BLEIA method, which applies firefly luciferase luminescence, is more sensitive than stool antigen test kits that are currently marketed in Japan and is very useful in diagnosing H. pylori infection, especially in situations where noninvasive tests are preferred, such as in children.

Screening of biotin-binding FV-antibodies from autodisplayed FV-library on E. coli outer membrane

This study aimed to isolate F_V-antibodies with biotin-binding activity from a F_V-antibody library that was successfully screened on the outer membrane of E. coli. The aims were achieved by (1) preparing a library of F_V-antibodies on the outer membrane of E. coli using autodisplay technology, (2) screening the F_V-antibodies with biotin-binding activity from the F_V-antibody library, and (3) synthesizing peptides (molecular weight of several kDa) from the biotin-binding amino acid sequence of F_V-antibodies. An F_V-antibody library with a diversity of 1.7 × 10⁵ clones was prepared on the outer membrane of E. coli, using a surface display method called autodisplay technology. For the screening of biotin-binding F_V-antibodies, the fluorescence-labeled biotin was introduced into the library, and the target E. coli with biotin-binding activity were screened using flow cytometry. For the screened E. coli clones, the binding affinity (K_D) of Fv-antibodies against biotin was calculated and the binding properties of the screened F_V-antibody were analyzed through competition assay with a synthetic peptide having the biotin-like activity. From the FRET experiment with the synthetic peptide corresponding to the CDR3 region of the screened Fv-antibody, the biotin-binding activity of the screened F_V-antibody was proved to be originated from the CDR3. Finally, the applicability of the biotin-binding domain was demonstrated through the co-expression with a protein called Z-domain with antibody binding activity.

Evaluation of protein-ligand interactions using the luminescent interaction assay FlimPIA with streptavidin-biotin linkage

Post-translational modifications, such as phosphorylation, are crucial in the regulation of protein-protein interactions and protein function in cell signaling. Here, we studied the interaction between the transactivation domain peptide of cancer suppressor protein p53 and its negative regulator Mdm2 using a novel protein-protein interaction assay, based on the modified FlimPIA using the streptavidin-biotin interaction to link the p53 peptide and the probe enzyme. We succeeded in detecting an attenuation in the affinity of p53 towards Mdm2 caused by the phosphorylation at Thr18. It showed that the targets, which are not easy to fuse with the FlimPIA probes, such as phosphorylated peptides can be used in this system. Also, the use of streptavidin nanobeads was found effective to get clearer signal, probably due to concentration of the detection system onto the bead surface. The system was further applied to the detection of FKBP-FRB interaction using biotinylated FKBP domain, which suggested another potential merit of this system that allows to avoid misfolding and steric hindrance often observed for the fusion protein approach.

Variants of the 5'-terminal region of p53 mRNA influence the ribosomal scanning and translation efficiency

The p53 protein is one of the major cell cycle regulators. The protein is expressed as at least twelve protein isoforms resulting from the use of alternative promoters, alternative splicing or downstream initiation codons. Importantly, there is growing evidence that translation initiation of p53 mRNA may be regulated by the structure and length of the naturally occurring variants of the 5′-terminal region of p53 mRNA transcripts. Here, several mRNA constructs were synthesized with variable length of the p53 5′-terminal regions and encoding luciferase reporter protein, and their translation was monitored continuously in situ in a rabbit reticulocyte lysate system. Moreover, four additional mRNA constructs were prepared. In two constructs, the structural context of AUG1 initiation codon was altered while in the other two constructs, characteristic hairpin motifs present in the p53 5′-terminal region were changed. Translation of the last two constructs was also performed in the presence of the cap analogue to test the function of the 5′-terminal region in cap-independent translation initiation. Superposition of several structural factors connected with the length of the 5′-terminal region, stable elements of the secondary structure, structural environment of the initiation codon and IRES elements greatly influenced the ribosomal scanning and translation efficiency.

1001 lights: luciferins, luciferases, their mechanisms of action and applications in chemical analysis, biology and medicine

Bioluminescence (BL) is a spectacular phenomenon involving light emission by live organisms. It is caused by the oxidation of a small organic molecule, luciferin, with molecular oxygen, which is catalysed by the enzyme luciferase. In nature, there are approximately 30 different BL systems, of which only 9 have been studied to various degrees in terms of their reaction mechanisms. A vast range of in vitro and in vivo analytical techniques have been developed based on BL, including tests for different analytes, immunoassays, gene expression assays, drug screening, bioimaging of live organisms, cancer studies, the investigation of infectious diseases and environmental monitoring. This review aims to cover the major existing applications for bioluminescence in the context of the diversity of luciferases and their substrates, luciferins. Particularly, the properties and applications of d-luciferin, coelenterazine, bacterial, Cypridina and dinoflagellate luciferins and their analogues along with their corresponding luciferases are described. Finally, four other rarely studied bioluminescent systems (those of limpet Latia, earthworms Diplocardia and Fridericia and higher fungi), which are promising for future use, are also discussed.

A Novel Streptavidin-luciferase Fusion Protein: Preparation, Properties and Application in Hybridization Analysis of DNA

A streptavidin-luciferase fusion protein comprising the thermostable mutant form of firefly luciferase Luciola mingrelica and minimal core streptavidin was constructed. The streptavidin-luciferase fusion was mainly produced in a tetrameric form with high luciferase and biotin-binding activities. It was shown that fusion has the same K_m values for ATP and luciferin and the bioluminescence spectra as initial luciferase. The linear dependence of the bioluminescence signal on the content of the fusion was observed within the range of 10^-18 -10^-13 mol per well. Successful application of obtained fusion in a biospecific bioluminescence assay based on biotin-streptavidin interactions was demonstrated by the example of a specific DNA hybridization analysis. A DNA hybridization analysis for Escherichia coli cells identification was developed using unique for these cells gadB fragment encoding glutamate decarboxylase. The amplified biotinylated GadB fragments were hybridized with the immobilized oligonucleotide probes; then, the biotin in the DNA duplexes was detected using the streptavidin-luciferase fusion protein. To reach the high sensitivity of the assay, we optimized the conditions of the assay. It was shown that the use of Pluronic for plate modification resulted in a significant reduction in the DNA detection limit which finally was 0.4 ng per well.

Firefly Luciferase-based Fusion Proteins and their Applications in Bioanalysis

Firefly luciferase is widely used in molecular biology and bioanalytical systems as a reporter molecule due to the high quantum yield of the bioluminescence, availability of stable mutant forms of the enzyme with prescribed spectral characteristics and abundance of bacterial expression systems suitable for production of recombinant proteins in limitless quantities. In this review, we described fusion proteins of luciferase with biotin-binding domain and streptavidin, with proteins A and G, antibodies, with DNA- and RNA-binding proteins, as well as fusion proteins designed for BRET systems. The firefly luciferase-based fusion proteins are represented as an effective tool for the development of different bioanalytical systems such as (1) systems in which luciferase is attached to the surface of the target and the bioluminescence signal is detected from the specific complexes formed; (2) BRET-based systems, in which the specific interaction induces changes in the bioluminescence spectrum; and (3) systems that use modified or split luciferases, in which the luciferase activity changes under the action of the analyte. All these systems have wide application in biochemical analysis of physiologically important compounds, for the detection of pathogenic bacteria and viruses, for evaluation of protein-protein interactions, assaying of metabolites involved in cell communication and cell signaling.

Application of enzyme bioluminescence for medical diagnostics

Nowadays luciferases are effectively used as analytical instruments in a great variety of research fields. Of special interest are the studies dealing with elaboration of novel analytical systems for the purposes of medical diagnostics. The ever-expanding spectrum of clinically important analytes accounts for the increasing demand for new techniques for their detection. In this chapter we have made an attempt to summarize the results on applications of luciferases as reporters in binding assays including immunoassay, nucleic acid hybridization assay, and so on. The data over the last 15 years have been analyzed and clearly show that luciferase-based assays, due to extremely high sensitivity, low cost, and the lack of need for skilled personnel, hold much promise for clinical diagnostics.

Real-time luminescence imaging of cellular ATP release

Extracellular ATP and other purines are ubiquitous mediators of local intercellular signaling within the body. While the last two decades have witnessed enormous progress in uncovering and characterizing purinergic receptors and extracellular enzymes controlling purinergic signals, our understanding of the initiating step in this cascade, i.e., ATP release, is still obscure. Imaging of extracellular ATP by luciferin-luciferase bioluminescence offers the advantage of studying ATP release and distribution dynamics in real time. However, low-light signal generated by bioluminescence reactions remains the major obstacle to imaging such rapid processes, imposing substantial constraints on its spatial and temporal resolution. We have developed an improved microscopy system for real-time ATP imaging, which detects ATP-dependent luciferin-luciferase luminescence at ∼10 frames/s, sufficient to follow rapid ATP release with sensitivity of ∼10 nM and dynamic range up to 100 μM. In addition, simultaneous differential interference contrast cell images are acquired with infra-red optics. Our imaging method: (1) identifies ATP-releasing cells or sites, (2) determines absolute ATP concentration and its spreading manner at release sites, and (3) permits analysis of ATP release kinetics from single cells. We provide instrumental details of our approach and give several examples of ATP-release imaging at cellular and tissue levels, to illustrate its potential utility.

Thermostable luciferase from Luciola cruciate for imaging of carbon nanotubes and carbon nanotubes carrying doxorubicin using in vivo imaging system

In the present study, we introduce a novel method for in vivo imaging of the biodistribution of single wall carbon nanotubes (SWNTs) labeled with recombinant thermo-stable Luciola cruciata luciferase (LcL). In addition, we highlight a new application for green fluorescent proteins in which they are utilized as imaging moieties for SWNTs. Carbon nanotubes show great positive potential compared to other drug nanocarriers with respect to loading capacity, cell internalization, and biodegradability. We have also studied the effect of binding mode (chemical conjugation and physical adsorption) on the chemiluminescence activity, decay rate, and half-life. We have shown that through proper chemical conjugation of LcL to CNTs, LcL remained biologically active for the catalysis of d-luciferin in the presence of ATP to release detectable amounts of photons for in vivo imaging. Chemiluminescence of LcL allows imaging of CNTs and their cargo in nonsuperficial locations at an organ resolution with no need of an excitation source. Loading LcL-CNTs with the antitumor antibiotic doxorubicin did not alter their biological activity for imaging. In vivo imaging of LcL-CNTs has been carried out using "IVIS spectrum" showing the uptake of LcL-CNTs by different organs in mice. We believe that the LcL-CNT system is an advanced powerful tool for in vivo imaging and therefore a step toward the advancement of the nanomedicine field.

Cellular heterogeneity and live cell arrays

In the past decade, the tendency to move from a global, one-size-fits-all treatment philosophy to personalized medicine is based, in part, on the nuanced differences and sub-classifications of disease states. Our knowledge of these varied states stems from not only the ability to diagnose, classify, and perform experiments on cell populations as a whole, but also from new technologies that allow interrogation of cell populations at the individual cell level. Such departures from conventional thinking are driven by the recognition that clonal cell populations have numerous activities that manifest as significant levels of non-genetic heterogeneity. Clonal populations by definition originate from a single genetic origin so are regarded as having a high level of homogeneity as compared to genetically distinct cell populations. However, analysis at the single cell level has revealed a different phenomenon; cells and organisms require an inherent level of non-genetic heterogeneity to function properly, and in some cases, to survive. The growing understanding of this occurrence has lead to the development of methods to monitor, analyze, and better characterize the heterogeneity in cell populations. Following the trend of DNA- and protein microarrays, platforms capable of simultaneously monitoring each cell in a population have been developed. These cellular microarray platforms and other related formats allow for continuous monitoring of single live cells and simultaneously generate individual cell and average population data that are more descriptive and information-rich than traditional bulk methods. These technological advances have helped develop a better understanding of the intricacies associated with biological processes and afforded greater insight into complex biological systems. The associated instruments, techniques, and reagents now allow for highly multiplexed analyses, which enable multiple cellular activities, processes, or pathways to be monitored simultaneously. This critical review will discuss the paradigm shift associated with cellular heterogeneity, speak to the key developments that have lead to our better understanding of systems biology, and detail the future directions of the discipline (281 references).

Development of ultra-high sensitivity bioluminescent enzyme immunoassay for hepatitis B virus surface antigen using firefly luciferase

Hepatitis B virus (HBV) infection continues to be a global public health concern. Efficient diagnosis of HBV surface antigen (HBsAg) is useful for identification of infection, treatment and prevention of transfusion-transmitted viral infections. Seronegative window reduction afforded by a highly sensitive measurement methodology is necessary as a small quantity of virus with infection risk exists for the period characterized by undetectable HBsAg following HBV infection. In this study, a bioluminescent enzyme immunoassay (BLEIA) for HBsAg was developed employing firefly luciferase as a labeling enzyme and a two-step sandwich immunoassay method. The cut-off value (10 mIU/mL) was 50-fold more sensitive relative to conventional chemiluminescent enzyme immunoassay based on luminol luminescence involving peroxidase as the labeling enzyme and the identical antibodies. Preliminary clinical data for this BLEIA revealed that the HBV seroconversion panel derived sequentially from HBV-infected human blood was detected 11 days following window closure from the first bleed, whereas detection occurred 14-25 days following window closure with the three conventional commercial kits.

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

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

Oriented immobilization of bacteriophages for biosensor applications

A method was developed for oriented immobilization of bacteriophage T4 through introduction of specific binding ligands into the phage head using a phage display technique. Fusion of the biotin carboxyl carrier protein gene (bccp) or the cellulose binding module gene (cbm) with the small outer capsid protein gene (soc) of T4 resulted in expression of the respective ligand on the phage head. Recombinant bacteriophages were characterized in terms of infectivity. It was shown that both recombinant phages retain their lytic activity and host range. However, phage head modification resulted in a decreased burst size and an increased latent period. The efficiency of bacteriophage immobilization with streptavidin-coated magnetic beads and cellulose-based materials was investigated. It was shown that recombinant bacteriophages form specific and strong bonds with their respective solid support and are able to specifically capture and infect the host bacterium. Thus, the use of immobilized BCCP-T4 bacteriophage for an Escherichia coli B assay using a phage multiplication approach and real-time PCR allowed detection of as few as 800 cells within 2 h.

Oriented immobilization of bacteriophages for biosensor applications

A method was developed for oriented immobilization of bacteriophage T4 through introduction of specific binding ligands into the phage head using a phage display technique. Fusion of the biotin carboxyl carrier protein gene (bccp) or the cellulose binding module gene (cbm) with the small outer capsid protein gene (soc) of T4 resulted in expression of the respective ligand on the phage head. Recombinant bacteriophages were characterized in terms of infectivity. It was shown that both recombinant phages retain their lytic activity and host range. However, phage head modification resulted in a decreased burst size and an increased latent period. The efficiency of bacteriophage immobilization with streptavidin-coated magnetic beads and cellulose-based materials was investigated. It was shown that recombinant bacteriophages form specific and strong bonds with their respective solid support and are able to specifically capture and infect the host bacterium. Thus, the use of immobilized BCCP-T4 bacteriophage for an Escherichia coli B assay using a phage multiplication approach and real-time PCR allowed detection of as few as 800 cells within 2 h.

Imaging localized astrocyte ATP release with firefly luciferase beads attached to the cell surface

Extracellular adenosine triphosphate (ATP) functions as a signaling molecule in many cell regulation processes. The traditional firefly luciferase assays measure the ATP release as a signal increase with time using a luminometer. Recently, advanced cell imaging techniques using charge-coupled device (CCD) cameras have enabled two-dimensional (2D) high-resolution detection providing both spatial and temporal information. Real-time imaging of ATP release from astrocyte cells has been reported. However, the observed chemiluminescence propagation wave reflects both ATP release and diffusion in the extracellular bulk solution. The dynamic ATP efflux at the cell surface could not be accurately measured. Hence, we constructed biotinylated fused firefly luciferase proteins, immobilized the proteins on 1 microm beads, and attached the beads to the cell surface to detect ATP release from mechanically stimulated astrocyte cells. This novel detection method enables us to monitor the actual ATP concentration at the surface of single live cells. The localized ATP release was found to be prominent but lasted only <20 s, which is very different from the results obtained by free firefly luciferase detection.

Metabolic biotinylation of recombinant antibody by biotin ligase retained in the endoplasmic reticulum

Due to its strength and specificity, the interaction between avidin and biotin has been used in a variety of scientific and medical applications ranging from immunohistochemistry to drug targeting. The present study describes two methods for biotinylation of proteins secreted from eukaryotic cells using the Escherichia coli biotin protein ligase. In one system the biotin ligase was co-secreted from the cells along with substrate protein enabling extracellular biotinylation of the tagged protein. In the other system, biotin ligase was engineered to be retained in the endoplasmic reticulum (ER) and metabolically biotinylates the secretory protein as it passes through the ER. An engineered antibody fragment, a diabody with specificity for carcinoembryonic antigen (CEA) was fused to the biotin acceptor domain (123 amino acid) of Propionibacterium shermanii. Coexpression of the fusion protein with ER retained biotin ligase showed higher biotinylation efficiency than biotinylation by co-secreted ligase. Biotinylation of the anti-CEA diabody tagged with a short (15 amino acid, Biotin Avitag) biotin acceptor peptide was also successful. Utilization of ER retained biotin ligase for biotinylation of protein is an attractive alternative for efficiently producing uniformly biotinylated recombinant proteins for a variety of avidin-biotin technologies.

Separation of tricomponent protein mixtures with triblock nanorods

Two-component triblock magnetic nanorods with gold end blocks and nickel interior blocks have been synthesized and used as affinity templates for the simultaneous and efficient separation of a three-component protein mixture. The gold blocks were selectively functionalized with 11-amino-1-undecanethiol, and then glutaraldehyde was used to covalently attach nitrostreptavidin to them. His-tagged proteins bind to the nickel block and biotin-tagged proteins bind to the functionalized gold ends, allowing one to separate a mixture of three proteins with a single material. Each surface-bound protein can be released selectively using imidazole for the His-tagged protein and biotin for the biotinylated protein.

Highly sensitive and rapid tandem bioluminescent immunoassay using aequorin labeled Fab fragment and biotinylated firefly luciferase

We established a simultaneous bioluminescent assay utilizing aequorin (Aq) and biotinylated firefly luciferase (b-Luc); furthermore, we developed a highly sensitive and rapid tandem bioluminescent immunoassay (BLIA) involving the Aq-labeled Fab fragment and b-Luc-streptavidin complex. Minimum detection limits of Aq and b-Luc were 9.4x10(-21) mol assay(-1) (blank + 3 S.D.) and 3.6x10(-19) mol assay(-1) (blank + 3 S.D.), respectively. Measurements of two luminescent proteins were completed in 4 s with a single assay medium. In this study, prostatic acid phosphatase (PAP) and prostate specific antigen (PSA), which served as analytes, were measured in the tandem BLIA. PAP and PSA were detected by the Aq-labeled anti-Dig Fab fragment and b-Luc-streptavidin complex, respectively. The measurable ranges of PAP and PSA were 0.04-100 and 0.2-200 ng mL(-1), respectively. This technique was also applied to the simultaneous measurement of PSA and alpha-fetoprotein (AFP). Measurable ranges of PSA and AFP were 0.2-200 and 1.95-1000 ng mL(-1), respectively. Levels of PAP and PSA or PSA and AFP in human serum could be accurately determined with the proposed BLIA. Satisfactory correlations were observed between results obtained from the proposed BLIA and those derived from commercial kits.

Cell-surface-localized ATP detection with immobilized firefly luciferase

We demonstrate the application of an assay technique for the detection of ATP efflux from the cell surface. Until recently, the firefly luciferase assay has conventionally been used to detect ATP release because of its high sensitivity and wide detection ability. However, since this technique can be used only to infer the amount of diffused ATP in bulk solutions, it does not accurately reflect the dynamic ATP flux at the cell membrane. We therefore constructed luciferase fusion proteins that could be immobilized onto the cell surface. However, the low activities and limited application ranges of these proteins prompted us to use biotinylated luciferase given its attributes of strong and stable localization. Furthermore, luciferase can be immobilized strongly onto the biotinylated cell surface via streptavidin-biotin binding and can thus be used to determine the dynamic release of ATP near the cell surface.

A novel multi-affinity tag system to produce high levels of soluble and biotinylated proteins in Escherichia coli

We describe here a novel multi-affinity tag vector that can be used to produce high levels of soluble, in vivo biotinylated proteins in Escherichia coli. This system combines the solubility-enhancing ability of maltose-binding protein (MBP), the versatility of the hexahistidine tag (His(6)), and the site-specific in vivo biotinylation of a 15-amino acid tag (AviTag). We used this multi-tag system in an attempt to improve expression levels of two prokaryotic proteins-elongation factor Tu (TufB) and DNA gyrase subunit A (GyrA)-as well as two eukaryotic nuclear receptors-glucocorticoid receptor (GR) and small heterodimer partner (SHP). The multi-tag system not only vastly improved the expression of the two prokaryotic proteins tested, but also yielded complete, site-specific, in vivo biotinylation of these proteins. The results obtained from the TufB expression and purification are presented and discussed in detail. The nuclear receptors, though soluble as fusion partners, failed to remain soluble once the MBP tag was cleaved. Despite this limitation of the system, the multi-affinity tag approach is a useful system that can improve expression of some otherwise insoluble or poorly expressing proteins, to obtain homogeneous, purified, fully biotinylated protein for downstream applications.

Evaluation of a 24-hour bioluminescent enzyme immunoassay for the rapid detection of Salmonella in chicken carcass rinses

A bioluminescent enzyme immunoassay (BEIA), using Salmonella-specific monoclonal antibody M183 for capture and biotinylated monoclonal antibody M183 for detection, was developed with InteLite AB streptavidin-biotinylated firefly luciferase complex as a reporter. Salmonella cultures were preenriched in buffered peptone water with shaking for 6 h at 37 degrees C and then selectively enriched in Muller-Kauffmann tetrathionate (MKTT) broth and modified semisolid Rappaport-Vassiliadis (MSRV) medium for 16 h at 42 degrees C. After enrichment, the total test time for the BEIA was 1.5 h. The analytical sensitivity of the BEIA ranged from 6.0 x 10(2) CFU/ml to 1.2 x 10(5) CFU/ml in MKTT and from 1.4 x 10(5) to 2.3 x 10(6) CFU/ml in MSRV using six Salmonella serovars prevalent in Canada. With enrichment cultures, the BEIA detected 1 CFU of Salmonella Typhimurium and Salmonella Enteritidis in 25 ml of chicken rinses. Representative strains of 10 Salmonella serovars were detected, and cross-reactivity was not observed with 25 non-Salmonella foodborne bacteria. The BEIA performance was assessed by testing 420 poultry samples, which were analyzed in parallel with the standard MSRV culture method. The BEIA detected 117 (27.88%) Salmonella-positive samples, whereas the standard MSRV culture method detected 124 (29.5%). The BEIA had a sensitivity of 64.5% and a specificity of 87.5% compared to the standard MSRV culture method. However, similar specificities and sensitivities were obtained when the standard MSRV culture method was compared to the BEIA (sensitivity = 68.4% and specificity = 85.5%). Neither method detected 100% of the Salmonella found in the samples tested, and statistical analyses indicated no significant difference between the two methods. In summary, the BEIA offers another alternative for the detection of Salmonella, with the additional advantage of providing a 24-h test for detecting Salmonella in chicken carcass rinses. The results obtained in this research indicate that tests are still needed for the isolation and detection of Salmonella that will establish the true prevalence of Salmonella in chicken samples.

Efficient biotinylation and single-step purification of tagged transcription factors in mammalian cells and transgenic mice

Proteomic approaches require simple and efficient protein purification methodologies that are amenable to high throughput. Biotinylation is an attractive approach for protein complex purification due to the very high affinity of avidin/streptavidin for biotinylated templates. Here, we describe an approach for the single-step purification of transcription factor complex(es) based on specific in vivo biotinylation. We expressed the bacterial BirA biotin ligase in mammalian cells and demonstrated very efficient biotinylation of a hematopoietic transcription factor bearing a small (23-aa) artificial peptide tag. Biotinylation of the tagged transcription factor altered neither the factor's protein interactions or DNA binding properties in vivo nor its subnuclear distribution. Using this approach, we isolated the biotin-tagged transcription factor and at least one other known interacting protein from crude nuclear extracts by direct binding to streptavidin beads. Finally, this method works efficiently in transgenic mice, thus raising the prospect of using biotinylation tagging in protein complex purification directly from animal tissues. Therefore, BirA-mediated biotinylation of tagged proteins provides the basis for the single-step purification of proteins from mammalian cells.

New label enzymes for bioluminescent enzyme immunoassay

Firefly luciferase catalyzes the oxidation of luciferin in the presence of ATP, magnesium ion and molecular oxygen with a high quantum yield. Due to its high sensitivity and specificity for ATP, luciferase has been used for bioluminescent detection of ATP in various biological samples. But it is not known well to apply the detection of immunoassay. In this article, the use of various enzymes as labels in the design and development of immunoassays for biomolecules has been reviewed.

A rapid bioluminescent enzyme immunoassay (BLEIA) for the detection of Shiga toxin types 1 and 2

In recent years, Escherichia coli O157: H7 has emerged as a global public health concern. Among the more important virulence characteristics of this strain is its ability to produce one or more Shiga toxins (Stx). Traditional culture-based methods for assay of enteric toxins in foods and clinical samples are relatively slow and results can be ambiguous. In this work, we established a toxin-detection system based on bioluminescent enzyme immunoassay (BLEIA) using a simple and inexpensive device. The system could detect both Shiga toxin types 1 and 2 individually within 150 min with a detection limit for each toxin at 5 pg/ml. In our study of previously characterized Shigatoxigenic and all non-Shigatoxigenic E. coli and other bacterial species, we found all Shigatoxigenic strains to be positive and non-Shigatoxigenic E. coli and other bacterial species to be negative. This assay was also used to detect Stxs in milk and supernatant fluids from minced chicken and beef. For clinical stool samples we noted a tendency for the system to give unexpectedly high background level. Our results suggest the feasibility of using BLEIA methodology for the simple, rapid and sensitive detection of toxins from culture supernatant, various foods and clinical samples.

Generation of recombinant human C3dg tetramers for the analysis of CD21 binding and function

CD21 (complement receptor 2, CR2) binds the terminal proteolytic fragments of the third component of complement (C3) that have been covalently attached to immune complexes or other targets during the activation of complement. We used the technique of in vivo biotinylation to create a recombinant multivalent ligand for CD21. A sequence coding for a biotinylation signal peptide was added to the 3' end of the human C3dg cDNA. The modified C3dg was expressed in Escherichia coli and biotinylated intracellularly by the bacterial biotin holoenzyme synthetase (BirA) enzyme. Monomeric C3dg was unable to bind to CD21 as determined by flow cytometry, while biotinylated recombinant C3dg (rC3dg) complexed with fluorochrome-conjugated streptavidin bound tightly. Binding was observed using CD21 positive B cells but not seen on pre-B cells that do not express this complement receptor. Two assays were used to assess the functional capacity of the recombinant C3dg. First, multimeric C3dg caused the phosphorylation of the mitogen-activated kinase, p38, in mature B lymphoma cells. Second, C3dg greatly enhanced the activation of primary B cells in combination with a sub-stimulatory concentration of anti-IgM monoclonal antibody. These results illustrate the utility of the technique of in vivo biotinylation to generate ligands for cell surface receptors that require multimerization for high avidity binding and function.

Oxyluciferin, a luminescence product of firefly luciferase, is enzymatically regenerated into luciferin

The activity regenerating luciferin from the luminescent product oxyluciferin was found in the protein fraction of a lantern extract from Photinus pyralis. The protein, luciferin-regenerating enzyme (LRE), was purified to homogeneity by ammonium sulfate precipitation followed by successive column chromatography on Ultrogel AcA34, S-Sepharose FF, Q-Sepharose FF, TSKgel super Q 5pw and TSKgel G3000 SW(XL). This enzyme was a single polypeptide with a molecular mass of 38 kDa. LRE converted oxyluciferin to 2-cyano-6-hydroxybenzothiazole and thioglycolic acid. In the presence of d-cysteine, 2-cyano-6-hydroxybenzothiazole was turned over into luciferin. The same activities were detected in the extracts from two Japanese fireflies, Luciola cruciata and Luciola lateralis. We have cloned a cDNA encoding LRE from poly(A)+ RNA of the lantern of P. pyralis using reverse transcription-polymerase chain reaction, 5'-RACE (rapid amplification of cDNA ends) and 3'-RACE. The primary structure of LRE from P. pyralis deduced from the nucleotide sequence was shown to consist of 308 amino acids with a molecular weight of 33,619. The cDNA was successfully expressed under the control of the tac promoter in Escherichia coli.

Development of ultra-high sensitivity bioluminescent enzyme immunoassay for prostate-specific antigen (PSA) using firefly luciferase

A bioluminescent enzyme immunoassay (BLEIA) for prostate-specific antigen (PSA) using biotinylated firefly luciferase-labelled antibody was developed. PSA is an important marker for the diagnosis and management of prostate cancer. Our BLEIA for PSA, based on the two-step sandwich method, had ultra-high sensitivity and a very wide measurable range. The detection limit (mean of nine replicates of the zero standard +2 SD) for PSA was 0.25 pg/mL and the measurable range for PSA was 0.25 pg/mL-100 ng/mL. Generally, PSA in the serum exists on two forms, called free PSA (f-PSA) and complex PSA (c-PSA), which is formed with alpha-antichymotripsin. Thus, the response of the PSA assay to these two forms has to be equimolar in the construction of the assay system. Our BLEIA for PSA also had an equimolar response to them.

Properties of firefly luciferase immobilized through a biotin carboxyl carrier protein domain

A fusion protein, consisting of biotin carboxyl carrier protein (BCCP) domain from Escherichia coli and firefly luciferase (FL) from Photinus pyralis, was immobilized through the biotin-avidin interaction on 6% cross-linked agarose beads. Several properties of the immobilized BCCP-FL were studied. Immobilized and free enzymes showed no significant difference in thermal stability; both retained at least 91% activity after incubation at 4 degrees C and 25 degrees C for 22 h. Incubation at 37 degrees C for 22 h caused significant activity loss. K(M) and k(cat) values were determined for both free and immobilized enzymes. K(M) values were similar between free and immobilized enzymes; however, k(cat) of immobilized BCCP-FL was one-third of the k(cat) of the free enzyme. 294 micromol/L Co-enzyme A (CoA) and 44 mmol/L dithiothreitol (DTT) enhanced the total bioluminescence output. Triton X-100, Tween 20, PEG 8,000, PVP 40,000 and PVP 360,000 did not enhance the bioluminescence reaction of immobilized BCCP-FL.

Rapid detection of Staphylococcus aureus using bioluminescent enzyme immunoassay

A bioluminescent enzyme immunoassay (BLEIA) method for detecting protein A-bearing Staphylococcus aureus was developed using biotinylated firefly luciferase. The BLEIA was able to detect protein A at one pg ml-1 and 103 cfu ml-1 level of Staph. aureus. The BLEIA showed significant signals with overnight cultures of all 24 Staph. aureus strains, and the BLEIA did not show any significant signals with overnight cultures of all 44 strains of coagulase-negative staphylococci and the other genus bacteria. After 5 h cultivation beginning at approximately 50 cfu ml-1, the BLEIA was able to detect all 35 Staph. aureus strains isolated from healthy humans.

Development of a rapid positive/absent test for coliforms using sensitive bioluminescence assay

We have developed a sensitive bioluminescence assay for beta-galactosidase using a luminescent substrate, D-luciferin-O-beta-galactopyranoside (LuGal). The detection limit for beta-galactosidase was 3 x 10-20 mol per assay, which was approximately 50-fold more sensitive than the test using a fluorescent substrate. This assay was applied to a positive/absent (P/A) test for coliforms. Observations made after 7 h of culture followed by a 10-min enzyme assay using LuGal were comparable to those made after a 22-24-h culture by the current method. Therefore, the LuGal method allows a rapid P/A test for coliforms.

Detection of luciferase having two kinds of luminescent colour based on optical filter procedure: application to an enzyme immunoassay

This paper reports on our study using several optical filters known to be efficient in separating compounds having various levels of maximum luminescence, to separate information from three kinds of Luciola lateralis luciferase with a maximum luminescence of 559 nm, 604 nm and 607 nm. Simultaneous luminescence of Luciola lateralis luciferase was determined by measuring the luminescence through a band pass filter or sharp cut filter (BPB50, 53, 58, No.58, SC58, 60, 62, 64). It was possible to determine luciferase with a maximum luminescence lambda(max) of 559 nm (yellow-green) utilizing the band pass filter (BPB 50), described here. Meanwhile, luciferase with a lambda(max) of 607 nm (red) could be determined by calculations based on the bioluminescent intensity through the band pass filter and sharp cut filter (SC58). In addition, we also applied a simultaneous bioluminescent enzyme immunoassay of pepsinogen I (PGI) and pepsinogen II (PGII) in which two kinds of biotinylated luciferase (Luciola lateralis) labelled as an enzyme producing yellow-green light (lambda(max) = 559 nm) and red light (lambda(max) = 607 nm) were used. In the proposed method, PGI and PGII in serum were simultaneously captured in a sandwich-type immune reaction between anti-PGI and anti-PGII monoclonal antibody-coated magnetic particles, and streptavidin-biotinylated luciferase biotinylated anti-PGI and anti-PGII monoclonal antibodies triplexes, respectively. The result was a calibration range for PGI of 2-200 ng/mL, and for PGII of 1-100 ng/mL. In conclusion, the correlation of PG values in serum between the proposed method (simultaneous assay) and an individual specific bioluminescent immunoassay (specific assay) were satisfactory.

In vivo enzymatic protein biotinylation

Biotin is biologically active only when protein-bound and is covalently attached to a class of important metabolic enzymes, the biotin carboxylases and decarboxylases. Biotinylation is a relatively rare modification, with between one and five biotinylated protein species found in different organisms. We discuss the mechanism and structures involved in this extraordinarily specific protein modification and its exploitation in tagging recombinant proteins.

Two-Site Expression Immunoassay Using a Firefly Luciferase-coding DNA Label

Background: We report the first two-site, “sandwich type” expression immunoassay using as a label an expressible DNA fragment encoding firefly luciferase.

Methods: The DNA label consisted of a T7 RNA polymerase promoter, a firefly luciferase-coding sequence, and a poly(dA/dT) tail. The 3′ end of the DNA label was biotinylated and complexed with streptavidin. A sandwich immunoassay for prostate-specific antigen (PSA) was developed in which the antigen was first bound to an immobilized monoclonal antibody and then reacted with a biotinylated polyclonal antibody. The streptavidin-luciferase-coding DNA complex was then bound to the immunocomplex. The DNA label was subsequently expressed in vitro by coupled transcription and translation. The generated luciferase was measured by its characteristic bioluminescent reaction.

Results: The bioluminescence was linearly related to the concentration of PSA in the sample. As low as 30 ng/L PSA was measured (12.5-μL sample) with a signal-to-background ratio of 2.3, and the linear range extended to 3 μg/L. The results obtained from the proposed assay agreed well to those determined by IMx immunoassay (y = 0.98x + 0.74 μg/L; r = 0.971; n = 44).

Conclusions: The use of the newly developed DNA label in a two-site immunoassay was demonstrated for the first time. The assay was applied successfully to the measurement of serum PSA.

A minimal peptide substrate in biotin holoenzyme synthetase-catalyzed biotinylation

The Escherichia coli biotin holoenzyme synthetase, BirA, catalyzes transfer of biotin to the epsilon amino group of a specific lysine residue of the biotin carboxyl carrier protein (BCCP) subunit of acetyl-CoA carboxylase. Sequences of naturally biotinylated substrates are highly conserved across evolutionary boundaries, and cross-species biotinylation has been demonstrated in several systems. To define the minimal substrate requirements in BirA-catalyzed biotinylation, we have measured the kinetics of modification of a 23-residue peptide previously identified by combinatorial methods. Although the sequence of the peptide bears little resemblance to the biotinylated sequence in BCCP, it is enzymatically biotinylated in vivo. Rates of biotin transfer to the 23-residue peptide are similar to those determined for BCCP. To further elucidate the sequence requirements for biotinylation, transient kinetic measurements were performed on a series of amino- and carboxy-terminal truncations of the 23-mer. The results, determined by stopped-flow fluorescence, allowed identification of a 14-residue peptide as the minimum required sequence. Additional support was obtained using matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometric analysis of peptides that had been incubated with an excess of biotinyl-5'-adenylate intermediate and catalytic amounts of BirA. Results of these measurements indicate that while kinetically inactive truncations showed no significant shift in molecular mass to the values expected for biotinylated species, kinetically active truncations exhibited 100% biotinylation. The specificity constant (k(cat)/Km) governing BirA-catalyzed biotinylation of the 14-mer minimal substrate is similar to that determined for the natural substrate, BCCP. We conclude that the 14-mer peptide efficiently mimics the biotin acceptor function of the much larger protein domain normally recognized by BirA.