This work was funded by Luminex Corporation.

<ol>
	<li>Fulton, J. R., McDade, R. L., Smith, P. L., Kienker, L. J., Kettman, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advanced+multiplexed+analysis+with+the+FlowMetrix+system.">Advanced multiplexed analysis with the FlowMetrix system.</a> Clinical Chemistry. 43, 1749-1756 (1997).</li><li>Carson, R. T., Vignali, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+quantation+of+15+cytokines+using+a+multiplexed+flow+cytometric+assay.">Simultaneous quantation of 15 cytokines using a multiplexed flow cytometric assay.</a> J. Immunol. Methods. 227, 41-52 (1999).</li><li>Peck, D., Crawford, E. D., Ross, K. N., Stegmaier, K., Golub, T. R., Lamb, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+for+high-throughput+gene+expression+signature+analysis.">A method for high-throughput gene expression signature analysis.</a> Genome Biol. 7, 61 (2006).</li><li>VanDerMeid, K. R., Su, S. P., Krenzer, K. L., Ward, K. W., Zhang, J. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+method+to+extract+cytokines+and+matrix+metalloproteinases+from+Schirmer+strips+and+analyze+using+Luminex.">A method to extract cytokines and matrix metalloproteinases from Schirmer strips and analyze using Luminex.</a> Mol Vis. 17, 1056-1063 (2011).</li><li>Liu, J., Kibiki, G., Maro, V., Maro, A., Kumburu, H., Swai, N., Taniuchi, M., Gratz, J., Toney, D., Kang, G., Houpt, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiplex+reverse+transcription+PCR+Luminex+assay+for+detection+and+quantitation+of+viral+agents+of+gastroenteritis.">Multiplex reverse transcription PCR Luminex assay for detection and quantitation of viral agents of gastroenteritis.</a> J. Clin. Virol. 50, 308-313 (2011).</li><li>de Jager, W., Prakken, B. J., Bijlsma, J., WJ Kuis, W., Rijkers, G. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+multiplex+immunoassay+performance+in+human+plasma+and+synovial+fluid+following+removal+of+interfering+heterophilic+antibodies.">Improved multiplex immunoassay performance in human plasma and synovial fluid following removal of interfering heterophilic antibodies.</a> J. Immunol. Methods. 300, 124-135 (2005).</li><li>Codorean, E., Nichita, C., Albulescu, L., Raducan, E., Popescu, I. D., Lonita, A. C., Albulescu, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlation+of+xMAP+and+ELISA+cytokine+profiles;+development+and+validation+for+immunotoxicological+studies+in+vitro.">Correlation of xMAP and ELISA cytokine profiles; development and validation for immunotoxicological studies in vitro.</a> Roum. Arch. Microbiol. Immunol. 69, 3-19 (2010).</li><li>de Jager, W., te Velthuis, H., Prakken, B. J., Kuis, W., Rijkers, G. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+detection+of+15+human+cytokines+in+a+single+sample+of+stimulated+peripheral+blood+mononuclear+cells.">Simultaneous detection of 15 human cytokines in a single sample of stimulated peripheral blood mononuclear cells.</a> Clin. Diagn. Lab. Immunol. 10, 133-139 (2003).</li><li>DuPont, N. C., Wang, K. H., Wadhwa, P. D., Culhane, J. F., Nelson, E. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validation+and+comparison+of+Luminex+multiplex+cytokine+analysis+kits+with+ELISA:+Determinations+of+a+panel+of+nine+cytokines+in+clinical+sample+culture+supernatants.">Validation and comparison of Luminex multiplex cytokine analysis kits with ELISA: Determinations of a panel of nine cytokines in clinical sample culture supernatants.</a> J. Reprod. Immunol. 66, 175-191 (2005).</li><li>Richens, J. L., Urbanowicz, R. A., Metcalf, R., Corne, J., O'Shea, P., Fairclough, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+validation+and+comparison+of+multiplex+cytokine+kits.">Quantitative validation and comparison of multiplex cytokine kits.</a> Journal of Biomolecular Screening. 15, 562-568 (2010).</li><li>Rizzi, G., Zhang, Y. J., Latek, R., Weiner, R., Rhyne, P. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+and+development+of+a+Luminex-based+assay+for+the+detection+of+human+IL-23.">Characterization and development of a Luminex-based assay for the detection of human IL-23.</a> Bioanalysis. 2, 1561-1572 (2010).</li></ol>

This work was done at Luminex Corporation with equipment manufactured at Luminex Corporation.
R&amp;D Systems &amp; EMD Millipore are strategic partners of Luminex Corporation; licensed to develop and commercialize multiplex xMAP based assays.

The conversion of an ELISA assay to the Luminex xMAP platform can be as simple as substituting streptavidin horseradish peroxidase (SA-HRP) in a typical ELISA kit with streptavidin phycoerythrin (SA-PE), and optimizing for performance. For those who want to create an xMAP immunoassay from the ground up, this can be accomplished with a straightforward protocol that also enables the fast, multiplex evaluation of the antibody pairs. The reagents for the xMAP assay were easily prepared using the xMAP Antibody Coupling kit to couple the designated capture antibodies to MagPlex low concentration microspheres. The use of low concentration microspheres reduces the cost of assay development while providing the same assay performance of higher concentration microspheres. The amount of time required to prepare coupled MagPlex microspheres is approximately 3 hours, which is much faster than the 22 - 24 hours required to coat the well of an ELISA plate, followed by treatment of the coated wells. The performance of the xMAP assay is also superior to the ELISA in terms of limit of detection (&lt;4 pg/mL vs. &gt;31 pg/mL) and dynamic range (&lt;4 pg/mL to &gt;8000 pg/mL vs. 16 pg/mL to 1000 pg/mL). Plate readers have a limited OD range which is either 3 or 4 OD, restricting the upper limit of the dynamic range for an assay.
Undoubtedly, not all antibodies will work in an ELISA format and not all antibodies that work well in an ELISA are readily transferable to the xMAP assay format. However, since xMAP assays can be multiplexed (i.e., run simultaneously), it is possible to evaluate several capture and detection antibody combinations concurrently to identify the best pair to use for an assay. This process saves significant time and reagents compared to the ELISA development procedure, which is limited to the evaluation of one pair at a time. Should two or more antibody pairs perform equivalently; other parameters of the assay can be considered to determine suitability of the pair (e.g., availability, cost, etc.).
In addition to improved assay performance and flexibility with the xMAP assay, there are also significant cost savings. The recommended quantity of antibody required to coat a single well of an ELISA plate is 400ng, whereas the quantity required for the beads used in one well of an xMAP assay is approximately 7.5 ng. Thus, the amount of antibody required for one ELISA well will provide more than 50 test results, if used in an xMAP assay. For applications involving precious samples, xMAP also has a significant advantage. The volume of sample recommended for the ELISA is 100 &mu;L whereas the volume required for the xMAP assay can be half of that, or less.
In summary, conversion of an ELISA assay to the Luminex xMAP platform is uncomplicated, efficient and cost-saving, while producing an assay with superior dynamic range and sensitivity.

<table border="1">
 <tbody>
 <tr>
 <td>Description</td>
 <td>Vendor</td>
 <td>Catalogue Number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Human TNF-&alpha;/TNFSF1A DuoSet ELISA kit</td>
 <td>R &amp; D Systems</td>
 <td>DY210</td>
 <td>Includes monoclonal and biotin coupled polyclonal antibodies and recombinant TNF-&alpha; protein standard</td>
 </tr>
 <tr>
 <td>Monoclonal Antibody to TNF-&alpha;</td>
 <td>Abcam</td>
 <td>Ab18696</td>
 <td>Capture Antibody, clone CH8820</td>
 </tr>
 <tr>
 <td>Monoclonal Antibody to TNF-&alpha;</td>
 <td>Abcam</td>
 <td>Ab16166</td>
 <td>Biotin coupled Detection Antibody, clone AS1</td>
 </tr>
 <tr>
 <td>TNF alpha protein</td>
 <td>Abcam</td>
 <td>Ab9642</td>
 <td>Recombinant TNF-&alpha; protein standard</td>
 </tr>
 <tr>
 <td>Monoclonal Antibody to TNF-&alpha;</td>
 <td>Novus</td>
 <td>NBP1-50115</td>
 <td>Capture Antibody, clone 4H31</td>
 </tr>
 <tr>
 <td>Monoclonal Antibody to TNF-&alpha;</td>
 <td>Novus</td>
 <td>NB100-78162</td>
 <td>Biotin coupled Detection Antibody, clone MAb11</td>
 </tr>
 <tr>
 <td>TNF alpha protein</td>
 <td>Novus</td>
 <td>NBC1-18460</td>
 <td>Recombinant TNF-&alpha; protein standard</td>
 </tr>
 <tr>
 <td>Monoclonal Antibody to TNF-&alpha;</td>
 <td>EMD Millipore</td>
 <td>MAB1141</td>
 <td>Capture Antibody, clone 3C7.2</td>
 </tr>
 <tr>
 <td>Polyclonal Antibody to TNF-&alpha;</td>
 <td>EMD Millipore</td>
 <td>654250</td>
 <td>Rabbit polyclonal Detection Antibody</td>
 </tr>
 <tr>
 <td>Streptavidin-Phycoerythrin</td>
 <td>Moss</td>
 <td>SAPE-001</td>
 <td>Fluorescent reporter reagent for Luminex xMAP Assay</td>
 </tr>
 <tr>
 <td>MAGPIX w/ xPONENT Software</td>
 <td>Luminex Corporation</td>
 <td>MAGPIX-XPONENT</td>
 <td>Luminex Instrument</td>
 </tr>
 <tr>
 <td>xMAP Antibody Coupling (AbC) Kit </td>
 <td>Luminex Corporation</td>
 <td>40-50016</td>
 <td>Includes EDC reagent, Sulfo-NHS reagent, activation buffer, wash buffer, 1.5 mL reaction tubes, and disposable pipettes</td>
 </tr>
 <tr>
 <td>MagPlex Microspheres, Low Concentration</td>
 <td>Luminex Corporation</td>
 <td>MC10012-ID, MC10013-ID, MC10014-ID, MC10015-ID</td>
 <td>Low concentration beads
 (@ 2.5 x 106 bead/mL)</td>
 </tr>
 <tr>
 <td>EZ-Link Sulfo-NHS-LC-Biotin</td>
 <td>Thermo Fisher</td>
 <td>PI-21335</td>
 <td>Biotinylation kit for unmodified detection antibody</td>
 </tr>
 <tr>
 <td>Tecan Infinite F200 Reader</td>
 <td>Tecan</td>
 <td>&nbsp;</td>
 <td>ELISA plate reader</td>
 </tr>
 <tr>
 <td>Phosphate Buffered Saline</td>
 <td>Sigma-Aldrich</td>
 <td>P-3688</td>
 <td>1% PBS-BSA, Assay Buffer</td>
 </tr>
 <tr>
 <td>One-Pint Compact Ultrasonic Cleaner, 115 VAC</td>
 <td>Cole-Parmer</td>
 <td>WU-08849-00</td>
 <td>Produce an effective operating frequency of 55 kHz</td>
 </tr>
 <tr>
 <td>Magnetic Tube Separator</td>
 <td>Luminex Corporation</td>
 <td>CN-0288-01</td>
 <td>For single 1.5mL tube magnetic separation in coupling wash steps</td>
 </tr>
 <tr>
 <td>Magnetic Plate Separator</td>
 <td>Luminex Corporation</td>
 <td>CN-0269-01</td>
 <td>For 96-well plate magnetic separation in assay wash steps</td>
 </tr>
 </tbody>
</table>

conversion of a capture elisa to a luminex xmap assay using a multiplex antibody screening method

The enzyme-linked immunosorbent assay (ELISA) has long been the primary tool for detection of analytes of interest in biological samples for both life science research and clinical diagnostics. However, ELISA has limitations. It is typically performed in a 96-well microplate, and the wells are coated with capture antibody, requiring a relatively large amount of sample to capture an antigen of interest . The large surface area of the wells and the hydrophobic binding of capture antibody can also lead to non-specific binding and increased background. Additionally, most ELISAs rely upon enzyme-mediated amplification of signal in order to achieve reasonable sensitivity. Such amplification is not always linear and can thus skew results.
In the past 15 years, a new technology has emerged that offers the benefits of the ELISA, but also enables higher throughput, increased flexibility, reduced sample volume, and lower cost, with a similar workflow 1, 2. Luminex xMAP Technology is a microsphere (bead) array platform enabling both monoplex and multiplex assays that can be applied to both protein and nucleic acid applications 3-5. The beads have the capture antibody covalently immobilized on a smaller surface area, requiring less capture antibody and smaller sample volumes, compared to ELISA, and non-specific binding is significantly reduced. Smaller sample volumes are important when working with limiting samples such as cerebrospinal fluid, synovial fluid, etc. 6. Multiplexing the assay further reduces sample volume requirements, enabling multiple results from a single sample.
Recent improvements by Luminex include: the new MAGPIX system, a smaller, less expensive, easier-to-use analyzer; Low-Concentration Magnetic MagPlex Microspheres which eliminate the need for expensive filter plates and come in a working concentration better suited for assay development and low-throughput applications; and the xMAP Antibody Coupling (AbC) Kit, which includes a protocol, reagents, and consumables necessary for coupling beads to the capture antibody of interest. (See Materials section for a detailed list of kit contents.)
In this experiment, we convert a pre-optimized ELISA assay for TNF-alpha cytokine to the xMAP platform and compare the performance of the two methods 7-11. TNF-alpha is a biomarker used in the measurement of inflammatory responses in patients with autoimmune disorders.
We begin by coupling four candidate capture antibodies to four different microsphere sets or regions. When mixed together, these four sets allow for the simultaneous testing of all four candidates with four separate detection antibodies to determine the best antibody pair, saving reagents, sample and time. Two xMAP assays are then constructed with the two most optimal antibody pairs and their performance is compared to that of the original ELISA assay in regards to signal strength, dynamic range, and sensitivity.

Watch this Scientific Journal Video about Conversion of a Capture ELISA to a Luminex xMAP Assay using a Multiplex Antibody Screening Method at JoVE.com

Conversion of a Capture ELISA to a Luminex xMAP Assay using a Multiplex Antibody Screening Method

An ELISA can be easily converted to a Luminex xMAP assay and, through the benefits of multiplexing, several antibodies can be screened simultaneously to identify an optimum antibody pair, resulting in increased sensitivity and dynamic range, while reducing assay cost.

The enzyme-linked immunosorbent assay (ELISA) has long been the primary tool for detection of analytes of interest in biological samples for both life ...

conversion-capture-elisa-to-luminex-xmap-assay-using-multiplex

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JoVE Journal

Biology

43.5K Views.  Luminex Corporation. An ELISA can be easily converted to a Luminex xMAP assay and, through the benefits of multiplexing, several antibodies can be screened simultaneously to identify an optimum antibody pair, resulting in increased sensitivity and dynamic range, while reducing assay cost.

Video: Conversion of a Capture ELISA to a Luminex xMAP Assay using a Multiplex Antibody Screening Method

Laser Capture Microdissection of Mammalian Tissue

Laser capture microscopy, also known as laser microdissection (LMD), enables the user to isolate small numbers of cells or tissues from frozen or formalin-fixed, paraffin-embedded tissue sections. LMD techniques rely on a thermo labile membrane placed either on top of, or underneath, the tissue section. In one method, focused laser energy is used to melt the membrane onto the underlying cells, which can then be lifted out of the tissue section. In the other, the laser energy vaporizes the foil along a path "drawn" on the tissue, allowing the selected cells to fall into a collection device. Each technique allows the selection of cells with a minimum resolution of several microns. DNA, RNA, protein, and lipid samples may be isolated and analyzed from micro-dissected samples. In this video, we demonstrate the use of the Leica AS-LMD laser microdissection instrument in seven segments, including an introduction to the principles of LMD, initializing the instrument for use, general considerations for sample preparation, mounting the specimen and setting up capture tubes, aligning the microscope, adjusting the capture controls, and capturing tissue specimens. Laser-capture micro-dissection enables the investigator to isolate samples of pure cell populations as small as a few cell-equivalents. This allows the analysis of cells of interest that are free of neighboring contaminants, which may confound experimental results.

Laser capture microscopy, also known as laser microdissection (LMD), enables the user to isolate small numbers of cells or tissues from frozen or ...

Cell Capture Using a Microfluidic Device

Generation of Stable Transgenic C. elegans Using Microinjection

Transgenic Caenorhabditis elegans can be readily created via microinjection of a DNA plasmid solution into the gonad 1. The plasmid DNA rearranges to form extrachromosomal concatamers that are stably inherited, though not with the same efficiency as actual chromosomes 2. A gene of interest is co-injected with an obvious phenotypic marker, such as rol-6 or GFP, to allow selection of transgenic animals under a dissecting microscope. The exogenous gene may be expressed from its native promoter for cellular localization studies. Alternatively, the transgene can be driven by a different tissue-specific promoter to assess the role of the gene product in that particular cell or tissue. This technique efficiently drives gene expression in all tissues of C. elegans except for the germline or early embryo 3. Creation of transgenic animals is widely utilized for a range of experimental paradigms. This video demonstrates the microinjection procedure to generate transgenic worms. Furthermore, selection and maintenance of stable transgenic C. elegans lines is described.

This video demonstrates the technique of microinjection into the gonad of C. elegans to create transgenic animals.

Transgenic Caenorhabditis elegans can be readily created via microinjection of a DNA plasmid solution into the gonad 1.  The plasmid DNA rearranges to ...

Method for Whole Mount Antibody Staining in Chick

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ideal tool for studying antibody expression in developing brain, neural tube and somite. This video demonstrates the different steps in whole-mount antibody staining using HRP conjugated secondary antibodies; First, the embryo is dissected from the egg and fixed in paraformaldehyde. Second, endogenous peroxidase is inactivated; The embryo is then exposed to primary antibody. After several washes, the embryo is incubated with secondary antibody conjugated to HRP. Peroxidase activity is revealed using reaction with diaminobenzidine substrate. Finally, the embryo is fixed and processed for photography and sectioning. The advantage of this method over the use of fluorescent antibodies is that embryos can be processed for wax sectioning, thus enabling the study of antigen sites in cross section. This method was originally introduced by Jane Dodd and Tom Jessell 1.

This video demonstrates whole mount immunohistochemistry, a method by which the spatial and temporal expression pattern of an antigen can be visualized in young chick embryos. This method was originally introduced by Jane Dodd and Tom Jessell.

The chick embryo is a valuable tool in the study of early embryonic development. Its transparency, accessibility and ease of manipulation, make it an ...

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated tools and resources for studies in this system are facilitating continued discovery of genes with more subtle phenotypes or roles. 
Here we present a generalized protocol we adapted for identifying C. elegans genes with postembryonic phenotypes of interest using RNAi2. This procedure is easily modified to assay the phenotype of choice, whether by light or fluorescence optics on a dissecting or compound microscope. This screening protocol capitalizes on the physical assets of the organism and molecular tools the C. elegans research community has produced. As an example, we demonstrate the use of an integrated transgene that expresses a fluorescent product in an RNAi screen to identify genes required for the normal localization of this product in late stage larvae and adults. First, we used a commercially available genomic RNAi library with full-length cDNA inserts. This library facilitates the rapid identification of multiple candidates by RNAi reduction of the candidate gene product. Second, we generated an integrated transgene that expresses our fluorecently tagged protein of interest in an RNAi-sensitive background. Third, by exposing hatched animals to RNAi, this screen permits identification of gene products that have a vital embryonic role that would otherwise mask a post-embryonic role in regulating the protein of interest. Lastly, this screen uses a compound microscope equipped for single cell resolution.

RNAi Screening to Identify Postembryonic Phenotypes in C. elegans

We describe a sensitized method to identify postembryonic regulators of protein expression and localization in C. elegans using an RNAi-based genomic screen and an integrated transgene that expresses a functional, fluorescently tagged protein.

C. elegans has proven to be a valuable model system for the discovery and functional characterization of many genes and gene pathways1. More sophisticated ...

A Fluorescent Screening Assay for Identifying Modulators of GIRK Channels

G protein-gated inward rectifier K+ (GIRK) channels function as cellular mediators of a wide range of hormones and neurotransmitters and are expressed in the brain, heart, skeletal muscle and endocrine tissue1,2. GIRK channels become activated following the binding of ligands (neurotransmitters, hormones, drugs, etc.) to their plasma membrane-bound, G protein-coupled receptors (GPCRs). This binding causes the stimulation of G proteins (Gi and Go) which subsequently bind to and activate the GIRK channel. Once opened the GIRK channel allows the movement of K+ out of the cell causing the resting membrane potential to become more negative. As a consequence, GIRK channel activation in neurons decreases spontaneous action potential formation and inhibits the release of excitatory neurotransmitters. In the heart, activation of the GIRK channel inhibits pacemaker activity thereby slowing the heart rate.
GIRK channels represent novel targets for the development of new therapeutic agents for the treatment neuropathic pain, drug addiction, cardiac arrhythmias and other disorders3. However, the pharmacology of these channels remains largely unexplored. Although a number of drugs including anti-arrhythmic agents, antipsychotic drugs and antidepressants block the GIRK channel, this inhibition is not selective and occurs at relatively high drug concentrations3.
Here, we describe a real-time screening assay for identifying new modulators of GIRK channels. In this assay, neuronal AtT20 cells, expressing GIRK channels, are loaded with membrane potential-sensitive fluorescent dyes such as bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC4(3)] or HLB 021-152 (Figure 1). The dye molecules become strongly fluorescent following uptake into the cells (Figure 1). Treatment of the cells with GPCR ligands stimulates the GIRK channels to open. The resulting K+ efflux out of the cell causes the membrane potential to become more negative and the fluorescent signal to decrease (Figure 1). Thus, drugs that modulate K+ efflux through the GIRK channel can be assayed using a fluorescent plate reader. Unlike other ion channel screening assays, such atomic absorption spectrometry4 or radiotracer analysis5, the GIRK channel fluorescent assay provides a fast, real-time and inexpensive screening procedure.

A real-time screening procedure for identifying drugs that interact with G protein-gated inward rectifier K+ (GIRK) channels is described. The assay utilizes membrane potential-sensitive fluorescent dyes to measure GIRK channel activity. This technique is adaptable for use on a number of cell lines.

G protein-gated inward rectifier K+ (GIRK) channels function as cellular mediators of a wide range of hormones and neurotransmitters and are expressed in ...

A Liquid Phase Affinity Capture Assay Using Magnetic Beads to Study Protein-Protein Interaction: The Poliovirus-Nanobody Example

In this article, a simple, quantitative, liquid phase affinity capture assay is presented. Provided that one protein can be tagged and another protein labeled, this method can be implemented for the investigation of protein-protein interactions. It is based on one hand on the recognition of the tagged protein by cobalt coated magnetic beads and on the other hand on the interaction between the tagged protein and a second specific protein that is labeled. First, the labeled and tagged proteins are mixed and incubated at room temperature. The magnetic beads, that recognize the tag, are added and the bound fraction of labeled protein is separated from the unbound fraction using magnets. The amount of labeled protein that is captured can be determined in an indirect way by measuring the signal of the labeled protein remained in the unbound fraction. The described liquid phase affinity assay is extremely useful when conformational conversion sensitive proteins are assayed. The development and application of the assay is demonstrated for the interaction between poliovirus and poliovirus recognizing nanobodies1. Since poliovirus is sensitive to conformational conversion2 when attached to a solid surface (unpublished results), the use of ELISA is limited and a liquid phase based system should therefore be preferred. An example of a liquid phase based system often used in polioresearch3,4 is the micro protein A-immunoprecipitation test5. Even though this test has proven its applicability, it requires an Fc-structure, which is absent in the nanobodies6,7. However, as another opportunity, these interesting and stable single-domain antibodies8 can be easily engineered with different tags. The widely used (His)6-tag shows affinity for bivalent ions such as nickel or cobalt, which can on their turn be easily coated on magnetic beads. We therefore developed this simple quantitative affinity capture assay based on cobalt coated magnetic beads. Poliovirus was labeled with 35S to enable unhindered interaction with the nanobodies and to make a quantitative detection feasible. The method is easy to perform and can be established with a low cost, which is further supported by the possibility of effectively regenerating the magnetic beads.

In this article, a simple, quantitative, liquid phase affinity capture assay is presented. It is a reliable technique based on the interaction between magnetic beads and tagged proteins (e.g. nanobodies) on one hand and the affinity between the tagged protein and a second, labeled protein (e.g. poliovirus) on the other.

In this article, a simple, quantitative, liquid phase affinity capture assay is presented. Provided that one protein can be tagged and another protein ...

High-throughput Functional Screening using a Homemade Dual-glow Luciferase Assay

We present a rapid and inexpensive high-throughput screening protocol to identify transcriptional regulators of alpha-synuclein, a gene associated with Parkinson&#39;s disease. 293T cells are transiently transfected with plasmids from an arrayed ORF expression library, together with luciferase reporter plasmids, in a one-gene-per-well microplate format. Firefly luciferase activity is assayed after 48 hr to determine the effects of each library gene upon alpha-synuclein transcription, normalized to expression from an internal control construct (a hCMV promoter directing Renilla luciferase). This protocol is facilitated by a bench-top robot enclosed in a biosafety cabinet, which performs aseptic liquid handling in 96-well format. Our automated transfection protocol is readily adaptable to high-throughput lentiviral library production or other functional screening protocols requiring triple-transfections of large numbers of unique library plasmids in conjunction with a common set of helper plasmids. We also present an inexpensive and validated alternative to commercially-available, dual luciferase reagents which employs PTC124, EDTA, and pyrophosphate to suppress firefly luciferase activity prior to measurement of Renilla luciferase. Using these methods, we screened 7,670 human genes and identified 68 regulators of alpha-synuclein. This protocol is easily modifiable to target other genes of interest.

We present a rapid and inexpensive screening method for identifying transcriptional regulators using high-throughput robotic transfections and a homemade dual-glow luciferase assay. This protocol rapidly generates direct side-by-side functional data for thousands of genes and is easily modifiable to target any gene of interest.

We present a rapid and inexpensive high-throughput screening protocol to identify transcriptional regulators of alpha-synuclein, a gene associated with ...

Anti-Nuclear Antibody Screening Using HEp-2 Cells

The American College of Rheumatology position statement on ANA testing stipulates the use of IIF as the gold standard method for ANA screening1. Although IIF is an excellent screening test in expert hands, the technical difficulties of processing and reading IIF slides &#8211; such as the labor intensive slide processing, manual reading, the need for experienced, trained technologists and the use of dark room &#8211; make the IIF method difficult to fit in the workflow of modern, automated laboratories.
The first and crucial step towards high quality ANA screening is careful slide processing. This procedure is labor intensive, and requires full understanding of the process, as well as attention to details and experience.
Slide reading is performed by fluorescent microscopy in dark rooms, and is done by trained technologists who are familiar with the various patterns, in the context of cell cycle and the morphology of interphase and dividing cells. Provided that IIF is the first line screening tool for SARD, understanding the steps to correctly perform this technique is critical.
Recently, digital imaging systems have been developed for the automated reading of IIF slides. These systems, such as the NOVA View Automated Fluorescent Microscope, are designed to streamline the routine IIF workflow. NOVA View acquires and stores high resolution digital images of the wells, thereby separating image acquisition from interpretation; images are viewed an interpreted on high resolution computer monitors. It stores images for future reference and supports the operator&#8217;s interpretation by providing fluorescent light intensity data on the images. It also preliminarily categorizes results as positive or negative, and provides pattern recognition for positive samples. In summary, it eliminates the need for darkroom, and automates and streamlines the IIF reading/interpretation workflow. Most importantly, it increases consistency between readers and readings. Moreover, with the use of barcoded slides, transcription errors are eliminated by providing sample traceability and positive patient identification. This results in increased patient data integrity and safety.
The overall goal of this video is to demonstrate the IIF procedure, including slide processing, identification of common IIF patterns, and the introduction of new advancements to simplify and harmonize this technique.

Indirect immunofluorescent (IIF) assays have traditionally been used for the detection of antinuclear antibodies (ANA) in human serum. The presence of these antibodies can aid in the diagnosis of systemic autoimmune rheumatic diseases (SARD). This protocol demonstrates how to effectively perform the IIF technique to accurately detect these autoantibodies.

The American College of Rheumatology position statement on ANA testing stipulates the use of IIF as the gold standard method for ANA screening1. Although ...

A Method for Selecting Structure-switching Aptamers Applied to a Colorimetric Gold Nanoparticle Assay

Small molecules provide rich targets for biosensing applications due to their physiological implications as biomarkers of various aspects of human health and performance. Nucleic acid aptamers have been increasingly applied as recognition elements on biosensor platforms, but selecting aptamers toward small molecule targets requires special design considerations. This work describes modification and critical steps of a method designed to select structure-switching aptamers to small molecule targets. Binding sequences from a DNA library hybridized to complementary DNA capture probes on magnetic beads are separated from nonbinders via a target-induced change in conformation. This method is advantageous because sequences binding the support matrix (beads) will not be further amplified, and it does not require immobilization of the target molecule. However, the melting temperature of the capture probe and library is kept at or slightly above RT, such that sequences that dehybridize based on thermodynamics will also be present in the supernatant solution. This effectively limits the partitioning efficiency (ability to separate target binding sequences from nonbinders), and therefore many selection rounds will be required to remove background sequences. The reported method differs from previous structure-switching aptamer selections due to implementation of negative selection steps, simplified enrichment monitoring, and extension of the length of the capture probe following selection enrichment to provide enhanced stringency. The selected structure-switching aptamers are advantageous in a gold nanoparticle assay platform that reports the presence of a target molecule by the conformational change of the aptamer. The gold nanoparticle assay was applied because it provides a simple, rapid colorimetric readout that is beneficial in a clinical or deployed environment. Design and optimization considerations are presented for the assay as proof-of-principle work in buffer to provide a foundation for further extension of the work toward small molecule biosensing in physiological fluids.

A protocol is provided to select structure-switching aptamers for small molecule targets based on a tunable stringency magnetic bead selection method. Aptamers selected with structure-switching properties are beneficial for assays that require a conformational change to signal the presence of a target, such as the described gold nanoparticle assay.

Small molecules provide rich targets for biosensing applications due to their physiological implications as biomarkers of various aspects of human health ...