Name: an optimized protocol for electrophoretic mobility shift assay using infrared fluorescent dye-labeled oligonucleotides
Uploaded: 2016-11-29T13:00:00
Description: Watch this Scientific Journal Video about An Optimized Protocol for Electrophoretic Mobility Shift Assay Using Infrared Fluorescent Dye-labeled Oligonucleotides at JoVE.com

This work was supported by an Alfred P. Sloan Research Fellowship (to C.-F.C.) and an NIH R01 grant (5R01GM098026-05 to C.-F.C.). We thank David Crowe for access to the advanced infrared imaging system.

NOTE: EMSAs using fluorescently labeled DNA probes or other forms of labeled DNA share the same protocols for protein or cell extract preparation, protein-DNA binding reaction, and PAGE gel preparation and running (Figure 1A). The key differences are DNA labeling procedures, post-run gel processing steps, and detection methods.
1. Gel Preparation
<ol>
	<li>Prepare 5% native polyacrylamide gel containing 0.5x&#160;TBE (45 mM Tris-Borate, 1 mM EDTA) and 2.5% glycerol, using a mini protein gel syst...

<ol>
	<li>Hellman, L. M., Fried, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophoretic+mobility+shift+assay+(EMSA)+for+detecting+protein-nucleic+acid+interactions.">Electrophoretic mobility shift assay (EMSA) for detecting protein-nucleic acid interactions.</a> Nat Protoc. 2, 1849-1861 (2007).</li><li>Ludwig, L. B., Hughes, B. J., Schwartz, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biotinylated+probes+in+the+electrophoretic+mobility+shift+assay+to+examine+specific+dsDNA,+ssDNA+or+RNA-protein+interactions.">Biotinylated probes in the electrophoretic mobility shift assay to examine specific dsDNA, ssDNA or RNA-protein interactions.</a> Nucleic Acids Res. 23, 3792-3793 (1995).</li><li>Engler-Blum, G., Meier, M., Frank, J., Muller, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduction+of+background+problems+in+nonradioactive+northern+and+Southern+blot+analyses+enables+higher+sensitivity+than+32P-based+hybridizations.">Reduction of background problems in nonradioactive northern and Southern blot analyses enables higher sensitivity than 32P-based hybridizations.</a> Anal Biochem. 210, 235-244 (1993).</li><li>Jing, D., Agnew, J., Patton, W. F., Hendrickson, J., Beechem, J. 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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=LUEGO:+a+cost+and+time+saving+gel+shift+procedure.">LUEGO: a cost and time saving gel shift procedure.</a> Biotechniques. 51, 267-269 (2011).</li><li>Poulin-Laprade, D., Burrus, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrophoretic+Mobility+Shift+Assay+Using+Radiolabeled+DNA+Probes.">Electrophoretic Mobility Shift Assay Using Radiolabeled DNA Probes.</a> Methods Mol Biol. 1334, 1-15 (2015).</li><li>Ruscher, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+fluorescence+based+non-radioactive+electrophoretic+mobility+shift+assay.">A fluorescence based non-radioactive electrophoretic mobility shift assay.</a> J Biotechnol. 78, 163-170 (2000).</li><li>Pagano, J. M., Clingman, C. C., Ryder, S. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+approaches+to+monitor+protein-nucleic+acid+interactions+using+fluorescent+probes.">Quantitative approaches to monitor protein-nucleic acid interactions using fluorescent probes.</a> RNA. 17, 14-20 (2011).</li><li>Alqadah, A., Hsieh, Y. W., Chuang, C. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sox2+goes+beyond+stem+cell+biology.">Sox2 goes beyond stem cell biology.</a> Cell cycle. , (2016).</li><li>Larouche, K., Bergeron, M. J., Leclerc, S., Guerin, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimization+of+competitor+poly(dI-dC).poly(dI-dC)+levels+is+advised+in+DNA-protein+interaction+studies+involving+enriched+nuclear+proteins.">Optimization of competitor poly(dI-dC).poly(dI-dC) levels is advised in DNA-protein interaction studies involving enriched nuclear proteins.</a> Biotechniques. 20, 439-444 (1996).</li><li>Sorenson, A. E., Schaeffer, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In-gel+detection+of+biotin-protein+conjugates+with+a+green+fluorescent+streptavidin+probe.">In-gel detection of biotin-protein conjugates with a green fluorescent streptavidin probe.</a> Anal. 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fEMSAs are an efficient tool to investigate protein-DNA interactions, and are an alternative to radioactive labeling of DNA. Fluorescent dyes such as infrared dyes are commercially available, and provide a safer and more environmentally friendly method compared to radioactive DNA labeling. EMSAs using infrared fluorescent dye-labeled oligonucleotides do not require postrun gel processing steps, and therefore save time and cost compared to other DNA labeling techniques. The time to detect bands using radioactive EMSAs can...

EMSAs are used to analyze interactions between DNA and proteins by using native PolyAcrylamide Gel Electrophoresis (PAGE) to resolve a mixture of a protein of interest and a labeled DNA probe containing potential target sites of the protein1. A DNA probe bound with protein will migrate slower compared with a free DNA probe, and is therefore retarded in its migration through a polyacrylamide matrix. Radiolabeling of DNA by 32P has been the predominant method for detection in EMSAs. Although the application of radiolabeling in biochemical research has been beneficial, methods of alternative DNA labeling with comparable sensitivity are being employed due to the health and safety risks associated with handling radioactivity. These alternative methods include conjugation of DNA with biotin2 or digoxigenin (DIG)3 (both of which are then detected by chemiluminescent systems), SYBR green staining of the PAGE gels4, or direct detection of DNA-fluorescent dye conjugates by scanning the gel5,6.
The resolved gels of EMSAs using radioactively labeled DNA probes require postrun processing through autoradiography films or a phosphorimager system to detect radioactive signals1,7. Gels of EMSAs using biotin-2 or DIG-conjugated3 DNA probes must also be processed and transferred onto a suitable membrane and then detected by chemiluminescence6. SYBR green staining of the gel requires postrun gel staining and a fluorescent scanner4. Since postrun gel processing steps are required for EMSAs using these DNA labeling techniques, the resolved gel can be assayed only once. In contrast, DNA probes labeled with fluorophores can be directly detected in the gel inside the glass plates by a scanner. Therefore, the DNA-protein interactions can be monitored and assayed several times at different time points during the run, which significantly reduces time and cost. The DNA-fluorescent dye conjugates that have been used for EMSAs include Cy36,8, Cy56,8, fluorescein9, and infrared fluorescent dyes4-6.
Transcriptional regulation requires protein-DNA interactions of transcription factors and their target genes. Coordination of these interactions generates diverse cell types from a common progenitor during animal development. An unbiased forward genetic screen identified a missense mutation, G73E, in the highly conserved HMG DNA-binding domain of the Caenorhabditis elegans transcription factor SOX-2. The mutation results in a cell identity transformation of AWB olfactory neurons into AWC olfactory neurons at molecular, morphological, and functional levels5,10. SOX-2 differentially regulates the terminal differentiation of AWB and AWC neurons by interacting with context-dependent partner transcription factors and respective DNA target sites5,10. SOX-2 partners with LIM-4 (LHX) in terminal AWB neuronal differentiation, while SOX-2 partners with CEH-36 (OTX/OTD) in terminal AWC neuronal differentiation. Luciferase reporter assays show that SOX-2 and mutant SOX-2G73E proteins have cooperative interactions with transcriptional cofactors LIM-4 and CEH-36 to activate a promoter expressed in AWB and AWC neurons. However, SOX-2 and mutant SOX-2G73E displayed differential activation properties of the promoter. To investigate the molecular basis of differential DNA binding activities of SOX-2 and SOX-2G73E, fEMSAs were performed with these proteins and their potential target sites.
First, a bioinformatics approach was taken to identify the biologically relevant DNA binding sequences within the 1 kb promoter region used in the luciferase assay. Since multiple potential SOX-2 binding sites were present throughout the promoter, we focused on predicted SOX-2 binding sites adjacent to putative CEH-36 or LIM-4 binding sites and evolutionarily conserved between various nematode species. These sequences were deleted or mutated, and subsequently tested in vivo for their activity to express GFP reporter transgenes in AWB or AWC neurons. Through this approach, we identified potential LIM-4/SOX-2 and CEH-36/SOX-2 adjacent target sites that are specifically required for the expression of GFP in AWB and AWC neurons, respectively5. We investigated the potential differences in the DNA binding of SOX-2 and SOX-2G73E using fEMSA with the identified LIM-4/SOX-2 and CEH-36/SOX-2 adjacent target sites. Our EMSA analysis showed that SOX-2G73E did not bind the DNA probe containing the LIM-4/SOX-2 adjacent target sites (required for gene expression in AWB) as efficiently as WT SOX-2 did. However, SOX-2 and SOX-2G73E had no difference in binding the DNA probe containing the CEH-36/SOX-2 adjacent target site (required for gene expression in AWC)5,10. Our fEMSA analyses provide mechanistic insight into the nature of the SOX-2G73E mutation in affecting specific DNA binding activity for the AWB-to-AWC cell identity transformation phenotype. Here, we describe an optimized protocol of fEMSA using purified 6xHis-SOX-2 or 6xHis-SOX-2G73E together with infrared fluorescent dye-labeled DNA probes containing the LIM-4/SOX-2 adjacent target sites as a case study to tackle an important biological question.

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			<td height="21" style="height:21px;width:332px;">30% Acrylamide/Bis Solution, 37.5:1&#160;</td>
			<td style="width:199px;">Bio-Rad</td>
			<td style="width:207px;">1610158</td>
			<td style="width:281px;">Acrylamide is harmful and toxic.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:332px;">6x-His Epitope Tag Antibody (HIS.H8)</td>
			<td style="width:199px;">ThermoFisher</td>
			<td style="width:207px;">MA1-21315</td>
			<td style="width:281px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:332px;">Anti Flag M2 antibody&#160;</td>
			<td style="width:199px;">Sigma-Aldrich</td>
			<td style="width:207px;">F3165-.2MG</td>
			<td style="width:281px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:332px;">Bovine Serum Albumin molecular-biology-grade</td>
			<td style="width:199px;">New England Biolabs</td>
			<td style="width:207px;">B9000S</td>
			<td style="width:281px;"></td>
		</tr>
		<tr height="126">
			<td height="126" style="height:126px;width:332px;">5&#39;IRDye700-labeled DNA Oligos</td>
			<td style="width:199px;">Integrated DNA Technologies</td>
			<td style="width:207px;">Custom DNA oligo</td>
			<td style="width:281px;">These are referred as 5&#39;Dye-labeled or infrared fluorescent dye-labeled DNA oligos in the manuscript. The company will custom synthesize 5&#39; IRDye labeled DNA oligonucleotides.&#160; Requires minimum 100&#956;M scale synthesis and HPLC purification.</td>
		</tr>
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			<td height="21" style="height:21px;width:332px;">Klenow Fragment (3&#39;--&#62;5&#39; exo-)</td>
			<td style="width:199px;">New England Biolabs</td>
			<td style="width:207px;">M0212S</td>
			<td style="width:281px;"></td>
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			<td height="21" style="height:21px;width:332px;">LightShif Poly (dI-dC)</td>
			<td style="width:199px;">ThermoFisher</td>
			<td style="width:207px;">20148E</td>
			<td style="width:281px;"></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:332px;">Mini-PROTEAN&#160;Vertical Electrophoresis Cell&#160;</td>
			<td style="width:199px;">Bio-Rad</td>
			<td style="width:207px;">1658000FC&#160;</td>
			<td style="width:281px;">This is referred as a mini protein gel system in the manuscript. Any electrophoretic system can be used as long as they are clear glass plates of less than 25cm x 25cm in size.</td>
		</tr>
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			<td height="42" style="height:42px;width:332px;">Odyssey CLx Infrared Imaging System</td>
			<td style="width:199px;">LI-COR Biotechnology</td>
			<td style="width:207px;">Odyssey CLx Infrared Imagng System</td>
			<td style="width:281px;">This is referred as an advanced infrared imaging system in the mansucript.</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;">Odyssey Fc Imaging System&#160;</td>
			<td style="width:199px;">LI-COR Biotechnology</td>
			<td style="width:207px;">Odyssey Fc Dual-Mode Imaging System</td>
			<td style="width:281px;">This is referred as a near-infrared fluorescent imaging system primarily for Western blots in the mansucript.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:332px;">Image Studio software (version 4.0)</td>
			<td style="width:199px;">LI-COR Biotechnology</td>
			<td style="width:207px;">Image Studio software&#160;</td>
			<td style="width:281px;">This is referred as a particular imaging software in the mansucript.&#160;</td>
		</tr>
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			<td height="21" style="height:21px;width:332px;">Orange G</td>
			<td style="width:199px;">Sigma-Aldrich</td>
			<td style="width:207px;">O3756-25G</td>
			<td style="width:281px;"></td>
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			<td height="21" style="height:21px;width:332px;">6x Orange loading dye</td>
			<td style="width:199px;"></td>
			<td style="width:207px;"></td>
			<td>0.25% Orange G; 30% Glycerol</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.5x TBE</td>
			<td style="width:199px;"></td>
			<td style="width:207px;"></td>
			<td>45 mM Tris-Borate; 1 mM EDTA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:332px;">1x TE</td>
			<td style="width:199px;"></td>
			<td style="width:207px;"></td>
			<td>10 mM Tris-HCl; 1 mM EDTA, pH8.0</td>
		</tr>
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			<td height="42" style="height:42px;width:332px;">1x STE</td>
			<td style="width:199px;"></td>
			<td style="width:207px;"></td>
			<td style="width:281px;">100 mM NaCl; 10 mM Tris-HCl, pH8.0; 1 mM EDTA</td>
		</tr>
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			<td height="63" style="height:63px;">5x Binding Buffer</td>
			<td style="width:199px;"></td>
			<td style="width:207px;"></td>
			<td style="width:281px;">50 mM Tris-HCl, pH7.5; 50 mM NaCl; 200 mM KCl; 5 mM MgCl2; 5 mM EDTA, pH8.0; 5 mM DTT; 250 ug/ml BSA</td>
		</tr>
	</tbody>
</table>

an optimized protocol for electrophoretic mobility shift assay using infrared fluorescent dye-labeled oligonucleotides

Electrophoretic Mobility Shift Assays (EMSA) are an instrumental tool to characterize the interactions between proteins and their target DNA sequences. Radioactivity has been the predominant method of DNA labeling in EMSAs. However, recent advances in fluorescent dyes and scanning methods have prompted the use of fluorescent tagging of DNA as an alternative to radioactivity for the advantages of easy handling, saving time, reducing cost, and improving safety. We have recently used fluorescent EMSA (fEMSA) to successfully address an important biological question. Our fEMSA analysis provides mechanistic insight into the effect of a missense mutation, G73E, in the highly conserved HMG transcription factor SOX-2 on olfactory neuron type diversification. We found that mutant SOX-2G73E protein alters specific DNA binding activity, thereby causing olfactory neuron identity transformation. Here, we present an optimized and cost-effective step-by-step protocol for fEMSA using infrared fluorescent dye-labeled oligonucleotides containing the LIM-4/SOX-2 adjacent target sites and purified SOX-2 proteins (WT and mutant SOX-2G73E proteins) as a biological example.

Orange G loading dye (6x: 0.12 g Orange G in 100 mL&#160;30% Glycerol) can be added to the binding reaction prior to loading to visualize the progress of the electrophoresis. Other loading dyes including bromophenol blue will be detected during scanning and therefore interfere with image analysis (Figure 1B).
In some instances of EMSAs, especially if nuclear extract preparation is used, poly deoxyinosinic-deoxyc...

Watch this Scientific Journal Video about An Optimized Protocol for Electrophoretic Mobility Shift Assay Using Infrared Fluorescent Dye-labeled Oligonucleotides at JoVE.com

An Optimized Protocol for Electrophoretic Mobility Shift Assay Using Infrared Fluorescent Dye-labeled Oligonucleotides

We describe here an optimized protocol of fluorescent Electrophoretic Mobility Shift Assays (fEMSA) using purified SOX-2 proteins together with infrared fluorescent dye-labeled DNA probes as a case study to tackle an important biological question.

Electrophoretic Mobility Shift Assays (EMSA) are an instrumental tool to characterize the interactions between proteins and their target DNA sequences. ...

The overall goal of this assay is to detect protein-DNA interactions using non-radioactive probes. This method can help answer key questions in the molecular biology and biochemistry fields, such as determining DNA target sequence of proteins. The main advantage of this technique is that it is an easy, safe, and time saving alternative to using radioactive probes.To begin this procedure, prepare a five percent native polyacrylamide gel containing 0.5x tris borate EDTA or TBE, and 2.5%glycerol using a mini protein gel system. To prepare 30 milliliters of gel solution for four gels, mix distilled water, TBE, ammonium persulfate, TEMED, acrylamide bis, and glycerol. Pass the gel solution immediately.After polymerization, wrap the gels in clear plastic wrap pre-wetted with 0.5x TBE and store them at four degrees Celsius. Next, design a long oligonucleotide for approximately 51 mers. Design complementary short oligonucleotides for approximately 14 mers with infrared fluorescent dye modification at the five prime terminus.Once the oligonucleotides have been prepared, resuspend them in 1x Tris-EDTA buffer to a final concentration of 100 micromolar. For annealing, mix 0.6 microliters of five prime dye short oligonucleotide, 1.2 microliters of long oligonucleotide, and 28.2 microliters of sodium chloride Tris-EDTA buffer in a 1.5 milliliter tube. Place the tube in boiling water for five minutes, then turn off the heat source and allow the water with the annealed oligonucleotides to cool overnight in the dark.To make double-stranded DNA probes, mix 30 microliters of the annealed oligonucleotides with DNTPs, Klenow buffer, Klenow five prime dye tag, and double distilled water in a 0.2 milliliter PCR tube. Incubate the mixture for 60 minutes at 37 degrees Celsius in a PCR machine. Then, add 3.4 microliters of 0.5 molar EDTA to stop the reaction, and heat inactivate at 75 degrees Celsius for 20 minutes in the PCR machine.Following this, dilute the filled in probes with sodium chloride Tris-EDTA buffer to a final concentration of 0.1 micromolar. Store the oligonucleotides at minus 20 degrees Celsius in the dark until ready to use. To prepare unlabeled probes, mix 20 microliters of long oligonucleotide, 20 microliters of Long R oligonucleotide, and 60 microliters of sodium chloride Tris-EDTA buffer in a 1.5 milliliter tube.Place the tube in boiling water for five minutes, then turn off the heat source and allow the water with the annealed oligos to cool overnight. Prepare one milliliter of 5x binding buffer by mixing Tris HCl, Sodium Chloride, Potassium Chloride, Magnesium Chloride, EDTA, DTT, BSA, and double-distilled water. Prior to setting up the binding reactions, pre-run the 5%native polyacrylamide gel in 0.5x TBE and 2.5%glycerol to remove all traces of ammonium persulfate at 80 volts for 30 minutes to one hour, or until the current no longer varies with time.Next, mix four microliters of 5x binding buffer, 80 to 200 nanograms of purified protein A, one microliter of 0.1 micromolar dye conjugated probe, and double-distilled water. Incubate the mixture at room temperature in the dark for 15 minutes. Following incubation, load all of the binding reaction onto the gel and run the gel at 10 volts per centimeter to the desired distance.Cover the gel apparatus with aluminum to keep the gel in the dark as much as possible. Clean the scanner bed of an infrared imaging system with distilled water. Wipe dry the glass plates containing the gel and place them on the scanner bed.Open the infrared imaging software and click on the Acquire tab. For thicker plates, use the settings of 700 for channel, auto for intensity, 84 micrometers for resolution, medium for quality, and 3.5 millimeters for focus offset. Select the area that the gel occupies on the scanner.Finally, click Start to begin the scan. The progress of electrophoresis can be visualized with Orange G loading dye, whereas Bromophenol blue is detected during scanning and therefore interferes with image analysis. Addition of dI-dC to the binding reaction abolished the binding of purified 6xHis-SOX-2 with the five prime dye DNA probes.The LIM-4 mutant and SOX-2 cold probe mutated in the LIM-4 binding site is as efficient as the wild type cold probe in competing with the infrared fluorescent dye labeled probe for binding to 6xHis-SOX-2. However, the competition efficiency of the LIM-4 and SOX-2 mutant cold probe mutated in the SOX-2 binding site is much lower than the wild type cold probe for binding to 6xHis-SOX-2. Supershift assays of the SOX-2 DNA complex using 6xHis and flag epitopes resulted in a supershifted SOX-2 DNA band.Once mastered, this technique can be done in two to four hours if it is performed properly. While attempting this procedure, it is important to remember to keep the infrared probes in the dark. Following this procedure, other methods like CRISPR cas9 genome editing can be performed in order to answer additional questions like the importance of a particular DNA binding sequence.After its development, this technique paved the way for researchers in the field of biochemistry to explore protein-DNA interactions in various model organisms. After watching this video, you should have a good understanding of how to determine protein-DNA interactions using non-radioactive DNA labels. Don't forget that working with acrylamide can be extremely hazardous and precautions such as personal protective equipment should always be taken while performing this procedure.

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JoVE Journal

Biochemistry

Optimized Protocol for the Extraction of Proteins from the Human Mitral Valve

Analysis of the cellular proteome can help to elucidate the molecular mechanisms underlying diseases due to the development of technologies that permit the large-scale identification and quantification of the proteins present in complex biological systems.The knowledge gained from a proteomic approach can potentially lead to a better understanding of the pathogenic mechanisms underlying diseases, allowing for the identification of novel diagnostic and prognostic disease markers, and, hopefully, of therapeutic targets. However, the cardiac mitral valve represents a very challenging sample for proteomic analysis because of the low cellularity in proteoglycan and collagen-enriched extracellular matrix. This makes it challenging to extract proteins for a global proteomic analysis. This work describes a protocol that is compatible with subsequent protein analysis, such as quantitative proteomics and immunoblotting. This can allow for the correlation of data concerning protein expression with data on quantitative mRNA expression and non-quantitative immunohistochemical analysis. Indeed, these approaches, when performed together, will lead to a more comprehensive understanding of the molecular mechanisms underlying diseases, from mRNA to post-translational protein modification. Thus, this method can be relevant to researchers interested in the study of cardiac valve physiopathology.

The protein composition of the human mitral valve is still partially unknown, because its analysis is complicated by low cellularity and therefore by low protein biosynthesis. This work provides a protocol to efficiently extract protein for the analysis of the mitral valve proteome.

Analysis of the cellular proteome can help to elucidate the molecular mechanisms underlying diseases due to the development of technologies that permit ...

DNA Polymerase Activity Assay Using Near-infrared Fluorescent Labeled DNA Visualized by Acrylamide Gel Electrophoresis

For any enzyme, robust, quantitative methods are required for characterization of both native and engineered enzymes. For DNA polymerases, DNA synthesis can be characterized using an in vitro DNA synthesis assay followed by polyacrylamide gel electrophoresis. The goal of this assay is to quantify synthesis of both natural DNA and modified DNA (M-DNA). These approaches are particularly useful for resolving oligonucleotides with single nucleotide resolution, enabling observation of individual steps during enzymatic oligonucleotide synthesis. These methods have been applied to the evaluation of an array of biochemical and biophysical properties such as the measurement of steady-state rate constants of individual steps of DNA synthesis, the error rate of DNA synthesis, and DNA binding affinity. By using modified components including, but not limited to, modified nucleoside triphosphates (NTP), M-DNA, and/or mutant DNA polymerases, the relative utility of substrate-DNA polymerase pairs can be effectively evaluated. Here, we detail the assay itself, including the changes that must be made to accommodate nontraditional primer DNA labeling strategies such as near-infrared fluorescently labeled DNA. Additionally, we have detailed crucial technical steps for acrylamide gel pouring and running, which can often be technically challenging.

This protocol describes the characterization of DNA polymerase synthesis of modified DNA through observation of changes to near-infrared fluorescently labeled DNA using gel electrophoresis and gel imaging. Acrylamide gels are used for high resolution imaging of the separation of short nucleic acids, which migrate at different rates depending on size.

For any enzyme, robust, quantitative methods are required for characterization of both native and engineered enzymes. For DNA polymerases, DNA synthesis ...

Detection of Heterodimerization of Protein Isoforms Using an in Situ Proximity Ligation Assay

Regulated protein-protein interactions are a guiding principle for many signaling events, and the detection of such events is an important element in understanding how such pathways are organized and how they function. There are many methods to detect protein-protein interactions in cells, but relatively few can be used to detect interactions between endogenous proteins. One such method, the proximity ligation assay (PLA), has several advantages to recommend its use. Compared to other common methods of protein-protein interaction analysis, PLA has relatively high sensitivity and specificity, can be performed with minimal cell manipulation, and, in the protocol described herein, requires only two target-specific antibodies derived from different species (e.g., from mouse and rabbit) and one specialized reagent: a set of secondary antibodies that are covalently linked to specific oligonucleotides that, when brought in close proximity of one another, create an amplifiable platform for in situ PCR or rolling circle amplification. In this presentation, we show how to apply the PLA technique to visualize changes in MST1 and MST2 proximity in fixed cells. The technique described in this manuscript is particularly applicable for the analysis of cell signaling studies.

Detection of Heterodimerization of Protein Isoforms Using an in Situ Proximity Ligation Assay

Here, we show how to use a Proximity Ligation Assay (PLA) to visualize MST1/MST2 heterodimerization in fixed cells with high sensitivity.

Regulated protein-protein interactions are a guiding principle for many signaling events, and the detection of such events is an important element in ...

Acyl-PEGyl Exchange Gel Shift Assay for Quantitative Determination of Palmitoylation of Brain Membrane Proteins

Activity-dependent alterations in the levels of synaptic AMPA receptors (AMPARs) within the postsynaptic density (PSD) is thought to represent a cellular mechanism for learning and memory. Palmitoylation regulates localization and function of many synaptic proteins including AMPA-Rs, auxiliary factors and synaptic scaffolds in an activity-dependent manner. We identified the synapse differentiation induced gene (SynDIG) family of four genes (SynDIG1-4) encoding brain-specific transmembrane proteins that associate with AMPARs and regulate synapse strength. SynDIG1 is palmitoylated at two cysteine residues located at positions 191 and 192 in the juxta-transmembrane region important for activity-dependent excitatory synapse development. Here, we describe an innovative biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay, to investigate the palmitoylation state of any protein of interest and demonstrate its utility with the SynDIG family of proteins in mouse brain lysates.

Palmitoylation entails the incorporation of a 16-carbon palmitate moiety to cysteine residues of target proteins in a reversible manner. Here, we describe a biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay, to investigate the palmitoylation state of any protein of interest in mouse brain lysates.

Activity-dependent alterations in the levels of synaptic AMPA receptors (AMPARs) within the postsynaptic density (PSD) is thought to represent a cellular ...

An Electrochemiluminescence-Based Assay for MeCP2 Protein Variants

The ECLIA is a versatile method which is able to quantify endogenous and recombinant protein amounts in a 96-well format. To demonstrate ECLIA efficiency, this assay was used to analyze intrinsic levels of MeCP2 in mouse brain tissue and the uptake of TAT-MeCP2 in human dermal fibroblasts. The MeCP2-ECLIA produces highly accurate and reproducible measurements with low intra- and inter-assay error. In summary, we developed a quantitative method for the evaluation of MeCP2 protein variants that can be utilized in high-throughput screens.

The electrochemiluminescence immunoassay (ECLIA) is a novel approach for quantitative detection of endogenous and exogenously applied MeCP2 protein variants, which produces highly quantitative, accurate and reproducible measurements with low intra- and inter-assay error over a wide working range. Here, the protocol for the MeCP2-ECLIA in a 96-well format is described.

The ECLIA is a versatile method which is able to quantify endogenous and recombinant protein amounts in a 96-well format. To demonstrate ECLIA efficiency, ...

Assessment of Cellular Oxidation using a Subcellular Compartment-Specific Redox-Sensitive Green Fluorescent Protein

Measuring the intracellular oxidation/reduction balance provides an overview of the physiological and/or pathophysiological redox status of an organism. Thiols are especially important for illuminating the redox status of cells via their reduced dithiol and oxidized disulfide ratios. Engineered cysteine-containing fluorescent proteins open a new era for redox-sensitive biosensors. One of them, redox-sensitive green fluorescent protein (roGFP), can easily be introduced into cells with adenoviral transduction, allowing the redox status of subcellular compartments to be evaluated without disrupting cellular processes. Reduced cysteines and oxidized cystines of roGFP have excitation maxima at 488 nm and 405 nm, respectively, with emission at 525 nm. Assessing the ratios of these reduced and oxidized forms allows the convenient calculation of redox balance within the cell. In this method article, immortalized human triple-negative breast cancer cells (MDA-MB-231) were used to assess redox status within the living cell. The protocol steps include MDA-MB-231 cell line transduction with adenovirus to express cytosolic roGFP, treatment with H2O2, and assessment of cysteine and cystine ratio with both flow cytometry and fluorescence microscopy.

This protocol describes the assessment of subcellular compartment-specific redox status within the cell. A redox-sensitive fluorescent probe allows convenient ratiometric analysis in intact cells.

Measuring the intracellular oxidation/reduction balance provides an overview of the physiological and/or pathophysiological redox status of an organism. ...

Optimized Incorporation of Alkynyl Fatty Acid Analogs for the Detection of Fatty Acylated Proteins using Click Chemistry

Fatty acylation, the covalent addition of saturated fatty acids to protein substrates, is important in regulating a myriad of cellular functions in addition to its implications in cancer and neurodegenerative diseases. Recent developments in fatty acylation detection methods have enabled efficient and non-hazardous detection of fatty acylated proteins, particularly through the use of click chemistry with bio-orthogonal labeling. However, click chemistry detection can be limited by the poor solubility and potential toxic effects of adding long chain fatty acids to cell culture. Described here is a labeling approach with optimized delivery using saponified fatty acids in combination with fatty-acid free BSA, as well as delipidated media, which can improve detection of hard to detect fatty acylated proteins. This effect was most pronounced with the alkynyl-stearate analog, 17-ODYA, which has been the most commonly used fatty acid analog in click chemistry detection of acylated proteins. This modification will improve cellular incorporation and increase sensitivity to acylated protein detection. In addition, this approach can be applied in a variety of cell types and combined with other assays such as pulse-chase analysis, stable isotope labeling with amino acids in cell culture, and mass spectrometry for quantitative profiling of fatty acylated proteins.

The study of fatty acylation has important implications in cellular protein interactions and diseases. Presented here is a modified protocol to improve click chemistry detection of fatty acylated proteins, which can be applied in various cell types and combined with other assays, including pulse-chase and mass spectrometry.

Fatty acylation, the covalent addition of saturated fatty acids to protein substrates, is important in regulating a myriad of cellular functions in ...

Deciphering Molecular Mechanism of Histone Assembly by DNA Curtain Technique

Chromatin is a higher-order structure that packages eukaryotic DNA. Chromatin undergoes dynamic alterations according to the cell cycle phase and in response to environmental stimuli. These changes are essential for genomic integrity, epigenetic regulation, and DNA metabolic reactions such as replication, transcription, and repair. Chromatin assembly is crucial for chromatin dynamics and is catalyzed by histone chaperones. Despite extensive studies, the mechanisms by which histone chaperones enable chromatin assembly remains elusive. Moreover, the global features of nucleosomes organized by histone chaperones are poorly understood. To address these problems, this work describes a unique single-molecule imaging technique named DNA curtain, which facilitates the investigation of the molecular details of nucleosome assembly by histone chaperones. DNA curtain is a hybrid technique that combines lipid fluidity, microfluidics, and total internal reflection fluorescence microscopy (TIRFM) to provide a universal platform for real-time imaging of diverse protein-DNA interactions.Using DNA curtain, the histone chaperone function of Abo1, the Schizosaccharomyces pombe bromodomain-containing AAA+ ATPase, is investigated, and the molecular mechanism underlying histone assembly of Abo1 is revealed. DNA curtain provides a unique approach for studying chromatin dynamics.

DNA curtain, a high-throughput single-molecule imaging technique, provides a platform for real-time visualization of diverse protein-DNA interactions. The present protocol utilizes the DNA curtain technique to investigate the biological role and molecular mechanism of Abo1, a Schizosaccharomyces pombe bromodomain-containing AAA+ ATPase.

Chromatin is a higher-order structure that packages eukaryotic DNA. Chromatin undergoes dynamic alterations according to the cell cycle phase and in ...

An Optimized Single-Molecule Pull-Down Assay for Quantification of Protein Phosphorylation

Phosphorylation is a necessary posttranslational modification that regulates protein function and directs cell signaling outcomes. Current methods to measure protein phosphorylation cannot preserve the heterogeneity in phosphorylation across individual proteins. The single-molecule pull-down (SiMPull) assay was developed to investigate the composition of macromolecular complexes via immunoprecipitation of proteins on a glass coverslip followed by single-molecule imaging. The current technique is an adaptation of SiMPull that provides robust quantification of the phosphorylation state of full-length membrane receptors at the single-molecule level. Imaging thousands of individual receptors in this way allows for quantifying protein phosphorylation patterns. The present protocol details the optimized SiMPull procedure, from sample preparation to imaging. Optimization of glass preparation and antibody fixation protocols further enhances data quality. The current protocol provides code for the single-molecule data analysis that calculates the fraction of receptors phosphorylated within a sample. While this work focuses on phosphorylation of the epidermal growth factor receptor (EGFR), the protocol can be generalized to other membrane receptors and cytosolic signaling molecules.

The present protocol describes sample preparation and data analysis to quantify protein phosphorylation using an improved single-molecule pull-down (SiMPull) assay.

Phosphorylation is a necessary posttranslational modification that regulates protein function and directs cell signaling outcomes. Current methods to ...

An Optimized Quantitative Pull-Down Analysis of RNA-Binding Proteins Using Short Biotinylated RNA

Protein-RNA interactions regulate gene expression and cellular functions at transcriptional and post-transcriptional levels. For this reason, identifying the binding partners of an RNA of interest remains of high importance to unveil the mechanisms behind many cellular processes. However, RNA molecules might interact transiently and dynamically with some RNA-binding proteins (RBPs), especially with non-canonical ones. Hence, improved methods to isolate and identify such RBPs are greatly needed.
To identify the protein partners of a known RNA sequence efficiently and quantitatively, we developed a method based on the pull-down and characterization of all interacting proteins, starting from cellular total protein extract. We optimized the protein pull-down using biotinylated RNA pre-loaded on streptavidin-coated beads. As a proof of concept, we employed a short RNA sequence known to bind the neurodegeneration-associated protein TDP-43 and a negative control of a different nucleotide composition but the same length. After blocking the beads with yeast tRNA, we loaded the biotinylated RNA sequences on the streptavidin beads and incubated them with the total protein extract from HEK 293T cells. After incubation and several washing steps to remove nonspecific binders, we eluted the interacting proteins with a high-salt solution, compatible with the most commonly used protein quantification reagents and with sample preparation for mass spectrometry. We quantified the enrichment of TDP-43 in the pull-down performed with the known RNA binder compared to the negative control by mass spectrometry. We used the same technique to verify the selective interactions of other proteins computationally predicted to be unique binders of our RNA of interest or of the control. Finally, we validated the protocol by western blot via the detection of TDP-43 with an appropriate antibody. 
This protocol will allow the study of the protein partners of an RNA of interest in near-to-physiological conditions, helping uncover unique and unpredicted protein-RNA interactions.

Here, we present an optimized in vitro method to uncover, quantify, and validate protein interactors of specific RNA sequences, using total protein extract from human cells, streptavidin beads coated with biotinylated RNA, and mass spectrometry analysis.

Protein-RNA interactions regulate gene expression and cellular functions at transcriptional and post-transcriptional levels. For this reason, identifying ...