Name: protein-trna agarose gel retardation assays for the analysis of the n6-threonylcarbamoyladenosine tcda function
Uploaded: 2017-06-21T12:30:00
Description: Watch this Scientific Journal Video about Protein-tRNA Agarose Gel Retardation Assays for the Analysis of the N6-threonylcarbamoyladenosine TcdA Function at JoVE.com

MCV is member of the CIB Intramural Program &#8220;Molecular Machines for Better Life&#8221; (MACBET). The research leading to these results has received funding from the Spanish Instituto de Salud Carlos III (PI12/01667 to MCV), the Spanish Ministerio de Econom&#237;a y Competitividad (CTQ2015-66206-C2-2-R and SAF2015-72961-EXP to MCV), the Regional Government of Madrid (S2010/BD-2316 to MCV), and the European Commission (Framework Programme 7 (FP7)) project ComplexINC (Contract No. 279039 to MCV). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Caution: Consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in this protocol are toxic and corrosive. Use appropriate practices when performing the extraction of tRNA using phenol, including the use of a fume hood and personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes, etc.). This protocol uses a non-toxic nucleic acid stain. The use of alternative stains may require additional precautions and specialized disposal of...

<ol>
	<li>Scott, V., Clark, A. R., Docherty, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+gel+retardation+assay.">The gel retardation assay.</a> Methods Mol Biol. 31, 339-347 (1994).</li><li>L&#243;pez-Estepa, M., 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=The+crystal+structure+and+small-angle+X-ray+analysis+of+CsdL/TcdA+reveal+a+new+tRNA+binding+motif+in+the+MoeB/E1+superfamily.">The crystal structure and small-angle X-ray analysis of CsdL/TcdA reveal a new tRNA binding motif in the MoeB/E1 superfamily.</a> Plos One. 10 (4), e0118606 (2015).</li><li>Miyauchi, K., Kimura, S., Suzuki, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+cyclic+form+of+N6-threonylcarbamoyladenosine+as+a+widely+distributed+tRNA+hypermodification.">A cyclic form of N6-threonylcarbamoyladenosine as a widely distributed tRNA hypermodification.</a> Nat Chem Biol. 9 (2), 105-111 (2013).</li><li>Bolstad, H. M., Botelho, D. J., Wood, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proteomic+analysis+of+protein-protein+interactions+within+the+Cysteine+Sulfinate+Desulfinase+Fe-S+cluster+biogenesis+system.">Proteomic analysis of protein-protein interactions within the Cysteine Sulfinate Desulfinase Fe-S cluster biogenesis system.</a> J Proteome Res. 9 (10), 5358-5369 (2010).</li><li>Loiseau, L., Ollagnier-de Choudens, S., Lascoux, D., Forest, E., Fontecave, M., Barras, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+the+heteromeric+CsdA-CsdE+cysteine+desulfurase,+assisting+Fe-S+cluster+biogenesis+in+Escherichia+coli.">Analysis of the heteromeric CsdA-CsdE cysteine desulfurase, assisting Fe-S cluster biogenesis in Escherichia coli.</a> J Biol Chem. 280 (29), 26760-26769 (2005).</li><li>Fried, M. G., Crothers, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Equilibrium+studies+of+the+cyclic+AMP+receptor+protein-DNA+interaction.">Equilibrium studies of the cyclic AMP receptor protein-DNA interaction.</a> J Mol Biol. 172 (3), 241-262 (1984).</li><li>Garner, M. M., Revzin, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+gel+electrophoresis+method+for+quantifying+the+binding+of+proteins+to+specific+DNA+regions:+application+to+components+of+the+Escherichia+coli+lactose+operon+regulatory+system.">A gel electrophoresis method for quantifying the binding of proteins to specific DNA regions: application to components of the Escherichia coli lactose operon regulatory system.</a> Nucleic Acids Res. 9 (13), 3047-3060 (1981).</li><li>Rio, D. C. <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+assays+for+RNA-protein+complexes.">Electrophoretic mobility shift assays for RNA-protein complexes.</a> Cold Spring Harb Protoc. 2014 (4), 435-440 (2014).</li><li>Ryder, S. P., Recht, M. I., Williamson, 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=Quantitative+analysis+of+protein-RNA+interactions+by+gel+mobility+shift.">Quantitative analysis of protein-RNA interactions by gel mobility shift.</a> Methods Mol Biol. 488, 99-115 (2008).</li><li>Yakhnin, A. V., Yakhnin, H., Babitzke, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gel+mobility+shift+assays+to+detect+protein-RNA+interactions.">Gel mobility shift assays to detect protein-RNA interactions.</a> Methods Mol Biol. 905, 201-211 (2012).</li><li>Ream, J. A., Lewis, L. K., Lewis, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+agarose+gel+electrophoretic+mobility+shift+assay+for+quantitating+protein:+RNA+interactions.">Rapid agarose gel electrophoretic mobility shift assay for quantitating protein: RNA interactions.</a> Anal Biochem. 511, 36-41 (2016).</li><li>Hagel, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gel-filtration+chromatography.">Gel-filtration chromatography.</a> Curr Protoc Mol Biol. , (2001).</li></ol>

The protein-tRNA agarose gel retardation assay described herein can be modified in a number of ways. First, the percentage of agarose in the gel can be reduced to allow the separation and visualization of protein-tRNA complexes significantly larger than the one analyzed here (120 kDa). Second, if the target protein is thermolabile, extra precautions must be taken to ensure that the temperature is kept below the maximum acceptable temperature by moving the electrophoresis apparatus to a cold room or by using ice packs ins...

The gel retardation assay1 (also known as electrophoretic mobility shift assay, EMSA) is an electrophoretic method designed to study and characterize protein-nucleic acid interactions. It allows the analysis of protein-DNA as well as protein-RNA interactions and in particular, interactions between tRNA and tRNA-binding proteins, using either purified components or complex mixtures of proteins (e.g., cell lysates) or nucleic acids (e.g., tRNA pools). We have applied gel retardation assays to the study of the interaction between purified tRNA(UUU) and TcdA, an N6-threonylcarbamoyladenosine (t6A) dehydratase, which cyclizes the threonylcarbamoyl side chain attached to A37 in the anticodon stem loop (ASL) of tRNAs to cyclic t6 (ct6A)2,3. TcdA is also known as CsdL3,4. The tcdA/csdL gene forms a cluster with the csdA and csdE genes5, which encode the cysteine desulfurase and the sulfur acceptor of the cysteine sulfinase desulfinate (CSD) system and is required to sustain TcdA function in vivo3.
The rationale behind the gel retardation assays is that, while free nucleic acid molecules migrate rapidly to the front of acrylamide or agarose gels by virtue of their large negative charge, the electrophoretic mobility of protein complexes of the same nucleic acids is dramatically reduced. The reduction in mobility is visualized as a &#34;shift&#34; in the nucleic acid-protein complexes, which resolve as discrete bands. Positively charged and larger nucleic acid-protein complex show a greater shift or reduction in mobility on a gel.
Since charge neutralization of the complex is a universal phenomenon for protein-nucleic acid complexes, the gel retardation assay can be applied to a wide range of complexes and nucleic acid types. The method is simple, inexpensive, and can be conducted in laboratories with minimum equipment. It requires only small amounts of proteins and tRNA. This is an advantage over alternative biophysical techniques, which usually consume larger quantities of sample.
The gel retardation assay has been widely used for the study of transcription factors. The assay has been used to analyze binding kinetics, strength, and specificity of transcription factors for many different DNA sequences. It was indeed in this field that the EMSA was first developed6,7. Gel retardation assays with RNA8,9,10,11 and tRNA molecules have also been used in ribosome research and to analyze, as we do here, the enzymes that modify tRNA nucleosides post-transcriptionally.
Many different parameters affect the result of a gel retardation assay such as temperature, quality of the protein and tRNA sample, and the strength of the binding. Careful planning and execution of the experiment is crucial for the interpretation of the results of the free nucleic acid and protein-bound species. Here, we used the synthetic gene encoding tRNA(UUU) cloned into an expression vector whose promoter lacks the Shine-Dalgarno ribosome binding site, leading to the synthesis of large amounts of the tRNA2. This detailed protocol is intended to provide a clear guide for performing tRNA gel retardation experiments while avoiding common mistakes.

<table border="0" cellpadding="0" cellspacing="0" width="1054">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:433px;">E. coli BL21(DE3)</td>
			<td style="width:135px;">Novagen</td>
			<td style="width:119px;">70235</td>
			<td style="width:367px;">DE3 lysogen contains T7 polymerase upon IPTG induction.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">pET23d</td>
			<td style="width:135px;">Novagen</td>
			<td style="width:119px;">69748-3</td>
			<td style="width:367px;">pET23d confers resistance to ampicillin; T7 promoter.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">LB Broth, Low Salt (Lennox L Broth), Granulated</td>
			<td style="width:135px;">Melford</td>
			<td style="width:119px;">GL1703</td>
			<td style="width:367px;">Conventional LB Broth, High Salt, can also be used.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Ampicillin</td>
			<td style="width:135px;">Sigma-Aldrich</td>
			<td style="width:119px;">10419313</td>
			<td style="width:367px;"></td>
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			<td height="42" style="height:42px;width:433px;">Incubator Shaker (Thermostated)</td>
			<td style="width:135px;">NBS</td>
			<td style="width:119px;">Excella E24&#160;</td>
			<td style="width:367px;">Any shaker incubator with temperature control can be used.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Isopropyl-beta-D-thiogalactopyranoside (IPTG), &#62;=99%</td>
			<td style="width:135px;">Acros Organics</td>
			<td style="width:119px;">BP1755</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Sodium acetate, anhydrous, &#62;99%</td>
			<td style="width:135px;">Melford</td>
			<td style="width:119px;">B4017</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Ethylenediaminetetraacetic acid (EDTA), Disodium salt, &#62;99%</td>
			<td style="width:135px;">Acros Organics</td>
			<td style="width:119px;">AC327205000</td>
			<td style="width:367px;">Harmful if inhaled.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Centrifuge (refrigerated)</td>
			<td style="width:135px;">Eppendorf</td>
			<td style="width:119px;">5430</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Centrifuge (refrigerated) rotor</td>
			<td style="width:135px;">Eppendorf</td>
			<td style="width:119px;">5430/5430P</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Centrifuge</td>
			<td style="width:135px;">Sorvall</td>
			<td style="width:119px;">RC5C</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Centrifuge rotor</td>
			<td style="width:135px;">Sorvall</td>
			<td style="width:119px;">SLA-3000</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:433px;">Phenol solution, Saturated with 0.1 M citrate buffer, pH 4.3 &#177; 0.2</td>
			<td style="width:135px;">Sigma-Aldrich</td>
			<td style="width:119px;">P4682</td>
			<td style="width:367px;">Acute toxicity (oral, dermal, inhalation), corrosive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Ethanol absolute for analysis, 100% v/v</td>
			<td style="width:135px;">Merck Millipore</td>
			<td style="width:119px;">100983</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Sodium phosphate dibasic dihydrate, Na2HPO4, &#62;=99%</td>
			<td style="width:135px;">Sigma-Aldrich</td>
			<td style="width:119px;">71643</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Potassium dihydrogen phosphate, KH2PO4</td>
			<td style="width:135px;">Merck</td>
			<td style="width:119px;">48,730,250</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">HiLoad 16/60 Superdex 75&#160;</td>
			<td style="width:135px;">GE Healthcare</td>
			<td style="width:119px;">28989333</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Agarose</td>
			<td style="width:135px;">Melford</td>
			<td style="width:119px;">MB1200</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Tris [Tris(hydroxymethyl) aminomethane HCl]</td>
			<td style="width:135px;">Melford</td>
			<td style="width:119px;">T1513</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Boric Acid</td>
			<td style="width:135px;">Melford</td>
			<td style="width:119px;">B0503</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Microwave</td>
			<td style="width:135px;">Haier</td>
			<td style="width:119px;">HDA-2070M</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">TCEP [Tris(2-carboxyethyl)phosphine hydrochloride]</td>
			<td style="width:135px;">Sigma-Aldrich</td>
			<td style="width:119px;">C4706</td>
			<td style="width:367px;">Corrosive to metals and skin.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:433px;">ATP [Adenosine 5&#8242;-triphosphate disodium salt hydrate], Grade I, &#62;=99%</td>
			<td style="width:135px;">Sigma-Aldrich</td>
			<td style="width:119px;">A2383</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:433px;">Magnesium chloride (MgCl2), anhydrous, &#62;=98%</td>
			<td style="width:135px;">Sigma-Aldrich</td>
			<td style="width:119px;">M8266</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Sodium chloride (NaCl), &#62;99%</td>
			<td style="width:135px;">Fisher Bioreagents</td>
			<td style="width:119px;">BP358</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Potassium chloride (KCl), &#62;99%</td>
			<td style="width:135px;">Melford</td>
			<td style="width:119px;">P0515</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">NZYDNA Ladder VI</td>
			<td style="width:135px;">NZYtech</td>
			<td style="width:119px;">MB8901</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Power supply</td>
			<td style="width:135px;">Consort</td>
			<td style="width:119px;">EV261</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Electrophoresis unit</td>
			<td style="width:135px;">Real Laboratory</td>
			<td style="width:119px;">RELSMINI10</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Real Safe nucleic acid staining</td>
			<td style="width:135px;">Real Laboratory</td>
			<td style="width:119px;">RBMSAFE</td>
			<td style="width:367px;">20,000X stock</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">UV Transilluminator (G:Box/EF)</td>
			<td style="width:135px;">Syngene</td>
			<td style="width:119px;">2216498</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Coomassie Brilliant Blue G</td>
			<td style="width:135px;">Sigma-Aldrich</td>
			<td style="width:119px;">B0770</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Rocker (Gyro-Rocker)</td>
			<td style="width:135px;">Stuart</td>
			<td style="width:119px;">SSL3</td>
			<td style="width:367px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Mixer Vortex&#160;</td>
			<td style="width:135px;">Fisher brand</td>
			<td style="width:119px;">13214789</td>
			<td style="width:367px;"></td>
		</tr>
	</tbody>
</table>

protein-trna agarose gel retardation assays for the analysis of the n6-threonylcarbamoyladenosine tcda function

We demonstrate methods for the expression and purification of tRNA(UUU) in Escherichia coli and the analysis by gel retardation assays of the binding of tRNA(UUU) to TcdA, an N6-threonylcarbamoyladenosine (t6A) dehydratase, which cyclizes the threonylcarbamoyl side chain attached to A37 in the anticodon stem loop (ASL) of tRNAs to cyclic t6A (ct6A). Transcription of the synthetic gene encoding tRNA(UUU) is induced in E. coli with 1 mM isopropyl &#946;-D-1-thiogalactopyranoside (IPTG) and the cells containing tRNA are harvested 24 h post-induction. The RNA fraction is purified using the acid phenol extraction method. Pure tRNA is obtained by a gel filtration chromatography that efficiently separates the small-sized tRNA molecules from larger intact or fragmented nucleic acids. To analyze TcdA binding to tRNA(UUU), TcdA is mixed with tRNA(UUU) and separated on a native agarose gel at 4 &#176;C. The free tRNA(UUU) migrates faster, while the TcdA-tRNA(UUU) complexes undergo a mobility retardation that can be observed upon staining of the gel. We demonstrate that TcdA is a tRNA(UUU)-binding enzyme. This gel retardation assay can be used to study TcdA mutants and the effects of additives and other proteins on binding.

Large amounts of tRNA(UUU) can be obtained by expressing the tRNA gene in E. coli under the control of a strong inducible T7 promoter. The expressed tRNA(UUU) accumulates in the cytoplasm and is enriched over the pool of naturally abundant tRNAs. A two-step purification process consisting of a capture/extraction step and a gel filtration/polishing step was utilized to obtain EMSA-grade tRNA. The capture/extraction step uses pH 4.3 phenol to achieve the simultaneous precipitation ...

Watch this Scientific Journal Video about Protein-tRNA Agarose Gel Retardation Assays for the Analysis of the N6-threonylcarbamoyladenosine TcdA Function at JoVE.com

Protein-tRNA Agarose Gel Retardation Assays for the Analysis of the N6-threonylcarbamoyladenosine TcdA Function

A protocol is presented for the production of tRNA(UUU) and the analysis of tRNA(UUU) in complex with the enzyme TcdA by agarose gel retardation assays.

Protein-tRNA Agarose Gel Retardation Assays for the Analysis of the N6-threonylcarbamoyladenosine TcdA Function

We demonstrate methods for the expression and purification of tRNA(UUU) in Escherichia coli and the analysis by gel retardation assays of the binding of ...

The overall goal of this procedure is to demonstrate an RNA gel retardation assay designed for the discovery and characterization of RNA-binding proteins. Application of this assay is used to investigate the interaction between TcdA and transfer RNA. The agarose gel retardation method can provide answers to key questions in the field of RNA biology.For example, whether a certain protein interacts with RNA, whether the interaction is sequences-specific, and the strength of the interaction. The main advantages of this technique are that it uses various small amounts of protein and RNA samples, and yields very informative results about the protein-RNA interactions quite quickly. Though this method can provide insight into protein-tRNA complexes, it can also be applied to many other systems such as ribosomal RNA, messenger RNA, and any other kinds of RNA molecule.In the morning, retrieve a vial of frozen E coli BL21 DE3 transformed with the expression vector pET-23D EC triple-U. Streak a low salt luria broth or LB plate supplemented with 100 micrograms per milliliter ampicillin. Invert the plate and place it into a 37 degrees Celsius incubator until colonies appear in the late afternoon.Inoculate one well-grown single colony in five milliliters of LB plus 100 micrograms per milliliter of ampicillin and grow overnight. The next morning, pellet the cells. Following centrifugation, replace the medium with five milliliters of fresh LB plus 100 micrograms per milliliter of ampicillin and re-suspend.Use this suspension to inoculate 200 milliliter of LB plus 100 micrograms per milliliter of ampicillin. Grow the cells for five hours at 220 RPM and 37 degrees Celsius. When the optical density of the culture at 590 nanometers has reached 0.6 to 0.8, atdd1 millimolar IPTG to the culture to trigger the expression of the tRNA triple-U gene.After incubating the cells at 37 degrees Celsius for three hours, harvest the cells by centrifuging the culture at 6500 times g for 10 minutes at four degrees Celsius. To perform lysis, first re-suspend the cell pellet in five milliliters of lysis buffer. Add one volume of acid phenol to the re-suspended cell pellet in the fume hood and mix for one minute by inversion to lyse the cells.Then, centrifuge at 10 thousand times g for 10 minutes at 4 degrees Celsius. Collect the upper aqueous phase containing the soluble tRNA triple-U using a pipette. Take care not to aspirate the organic bottom phase.Precipitate the tRNA by thoroughly mixing the soluble phase with 2.5 volumes of 100%volume per volume ethanol by inversion for one hour at four degrees Celsius. Then, centrifuge at 15 thousand times g for 30 minutes at four degrees Celsius. Decant the supernatant carefully, then resuspend the tRNA-rich pellet in four milliliters of gel filtration buffer.Following standard chromatographic practice, load the re-suspended tRNA triple-U onto a high-resolution preparative gel filtration column previously equilibrated in gel filtration buffer. Set the flow rate to 1 milliliter per minute to elute the samples. To begin sample preparation, pipette the corresponding amount of TcdA as indicated in the text protocol into properly labeled 1.5 milliliter centrifuge tubes.Add a final concentration of 1.6 millimolar TCEP and gently mix using a pipette. Close the lid and incubate the mixture at room temperature for five minutes. Following incubation, add adenosine triphosphate and magnesium chloride.Mix with a pipette before incubating the mixture for five minutes at room temperature. Next, add purified tRNA triple-U according to the text protocol and mix the sample with a pipette. After incubating the sample at room temperature for five minutes, add phosphate buffered saline up to a 100 microliter final volume.Mix properly and add glycerol to a final concentration of 10%Vortex the sample before briefly spinning down the contents of the tube. Prepare the agarose gel as described in the text protocol. Place the electrophoresis unit into a tray filled with crushed ice to maintain the chamber at four degrees Celsius during the electrophoresis run.Carefully pipette five microliters of each sample into the corresponding well. Also add a suitable DNA size marker. Then, plug the electrodes into the corresponding slots of the power supply unit.After turning on the power supply unit, set the voltage to 100 volts and run the gel for 90 minutes. Next, prepare the staining solution by mixing 50 milliliters of TBE with 1X of a suitable DNA stain. After 90 minutes of electrophoresis, carefully remove the gel from the tray and place it in a container with staining solution.Place the container on a rocker at low rocking speed and rock at room temperature for 30 minutes. Remove the agarose gel from the staining container and tap it carefully on a piece of cellulose paper to remove excess liquid. Then, place the gel directly on a transilluminator.Switch on the UV light to visualize bands containing tRNA. Finally, take a photograph of the gel. Shown here are representative results of tRNA purification for gel retardation assays.In the chromatogram the absorbance of the elution fractions at 254 nanometers is recorded. The tRNA pool, enriched in over-expressed tRNA triple-U elutes at the highest peak. The quality and quantity of the tRNA pool is examined by agarose gel electrophoresis.The RNA gel retardation assay reveals that TcdA forms a stable complex with tRNA triple-U in tRNA concentration-dependent manner, which results in a protein-tRNA band that migrates more slowly than the free tRNA at the front of the gel. Once mastered, this technique can be done in less than two hours. While attempting this protocol, it's important to remember to follow strict laboratory techniques to ensure the chemical stability of tRNA.After watching this video, you should have a good understanding how to use agarose gel retardation assay to investigate the interaction of your protein of choice with tRNA, as in the case of TcdA or with any other type of RNA.

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Research

JoVE Journal

Biochemistry

Method for Identifying Small Molecule Inhibitors of the Protein-protein Interaction Between HCN1 and TRIP8b

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the excitability of neurons. The subcellular distribution of these channels in pyramidal neurons of hippocampal area CA1 is regulated by tetratricopeptide repeat-containing Rab8b interacting protein (TRIP8b), an auxiliary subunit. Genetic knockout of HCN pore forming subunits or TRIP8b, both lead to an increase in antidepressant-like behavior, suggesting that limiting the function of HCN channels may be useful as a treatment for Major Depressive Disorder (MDD). Despite significant therapeutic interest, HCN channels are also expressed in the heart, where they regulate rhythmicity. To circumvent off-target issues associated with blocking cardiac HCN channels, our lab has recently proposed targeting the protein-protein interaction between HCN and TRIP8b in order to specifically disrupt HCN channel function in the brain. TRIP8b binds to HCN pore forming subunits at two distinct interaction sites, although here the focus is on the interaction between the tetratricopeptide repeat (TPR) domains of TRIP8b and the C terminal tail of HCN1. In this protocol, an expanded description of a method for purifying TRIP8b and executing a high throughput screen to identify small molecule inhibitors of the interaction between HCN and TRIP8b, is described. The method for high throughput screening utilizes a Fluorescence Polarization (FP) -based assay to monitor the binding of a large TRIP8b fragment to a fluorophore-tagged eleven amino acid peptide corresponding to the HCN1 C terminal tail. This method allows &#39;hit&#39; compounds to be identified based on the change in the polarization of emitted light. Validation assays are then performed to ensure that &#39;hit&#39; compounds are not artifactual.

The interaction between HCN channels and their auxiliary subunit has been identified as a therapeutic target in Major Depressive Disorder. Here, a fluorescence polarization-based method for identifying small molecule inhibitors of this protein-protein interaction, is presented.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the ...

Automated Acoustic Dispensing for the Serial Dilution of Peptide Agonists in Potency Determination Assays

As with small molecule drug discovery, screening for peptide agonists requires the serial dilution of peptides to produce concentration-response curves. Screening peptides affords an additional layer of complexity as conventional tip-based sample handling methods expose peptides to a large surface area of plasticware, providing an increased opportunity for peptide loss via adsorption. Preventing excessive exposure to plasticware reduces peptide loss via adherence to plastics and thus minimizes inaccuracies in potency prediction, and we have previously described the benefits of non-contact acoustic dispensing for in vitro high-throughput screening of peptide agonists1. Here we discuss a fully integrated automation solution for non-contact acoustic preparation of peptide serial dilutions in microtiter plates utilizing the example of screening for peptide agonists at the mouse glucagon-like peptide-1 receptor (GLP-1R). Our methods allow for high-throughput cell-based assays to screen for agonists and are easily scalable to support increased sample throughput, or to allow for increased numbers of assay plate copies (e.g., for a panel of more target cell lines).

Peptide adsorption to plasticware during traditional tip-based serial dilutions can significantly impact potency determination and confound the understanding of structure-activity relationships used for lead identification and lead optimization phases of drug discovery. Here methods for automated acoustic non-contact serial dilution of peptide samples are described.

As with small molecule drug discovery, screening for peptide agonists requires the serial dilution of peptides to produce concentration-response curves. ...

Analyzing Supercomplexes of the Mitochondrial Electron Transport Chain with Native Electrophoresis, In-gel Assays, and Electroelution

The mitochondrial electron transport chain (ETC) transduces the energy derived from the breakdown of various fuels into the bioenergetic currency of the cell, ATP. The ETC is composed of 5 massive protein complexes, which also assemble into supercomplexes called respirasomes (C-I, C-III, and C-IV) and synthasomes (C-V) that increase the efficiency of electron transport and ATP production. Various methods have been used for over 50 years to measure ETC function, but these protocols do not provide information on the assembly of individual complexes and supercomplexes. This protocol describes the technique of native gel polyacrylamide gel electrophoresis (PAGE), a method that was modified more than 20 years ago to study ETC complex structure. Native electrophoresis permits the separation of ETC complexes into their active forms, and these complexes can then be studied using immunoblotting, in-gel assays (IGA), and purification by electroelution. By combining the results of native gel PAGE with those of other mitochondrial assays, it is possible to obtain a completer picture of ETC activity, its dynamic assembly and disassembly, and how this regulates mitochondrial structure and function. This work will also discuss limitations of these techniques. In summary, the technique of native PAGE, followed by immunoblotting, IGA, and electroelution, presented below, is a powerful way to investigate the functionality and composition of mitochondrial ETC supercomplexes.

This protocol describes the separation of functional mitochondrial electron transport chain complexes (Cx) I-V and supercomplexes thereof using native electrophoresis to reveal information about their assembly and structure. The native gel can be subjected to immunoblotting, in-gel assays, and purification by electroelution to further characterize individual complexes.

The mitochondrial electron transport chain (ETC) transduces the energy derived from the breakdown of various fuels into the bioenergetic currency of the ...

Use of Two Dimensional Semi-denaturing Detergent Agarose Gel Electrophoresis to Confirm Size Heterogeneity of Amyloid or Amyloid-like Fibers

Amyloid or amyloid-like fibers have been associated with many human diseases, and are now being discovered to be important for many signaling pathways. The ability to readily detect the formation of these fibers under various experimental conditions is essential for understanding their potential function. Many methods have been used to detect the fibers, but not without some drawbacks. For example, electron microscopy (EM), or staining with Congo Red or Thioflavin T often requires purification of the fibers. On the other hand, semi-denaturing detergent agarose gel electrophoresis (SDD-AGE) allows detection of the SDS-resistant amyloid-like fibers in the cell extracts without purification. In addition, it allows the comparison of the size difference of the fibers. More importantly, it can be used to identify specific proteins within the fibers by Western blotting. It is less time consuming and more easily accessible to a wider number of labs. SDD-AGE results often show variable degree of heterogeneity. It raises the question whether part of the heterogeneity results from the dissociation of the protein complex during the electrophoresis in the presence of SDS. For this reason, we have employed a second dimension of SDD-AGE to determine if the size heterogeneity seen in SDD-AGE is truly a result of fiber heterogeneity in vivo and not a result of either degradation or dissociation of some of the proteins during electrophoresis. This method allows fast, qualitative confirmation that the amyloid or amyloid-like fibers are not partially dissociating during the SDD-AGE process.

Here we use two-dimensional semi-denaturing agarose gel electrophoresis to confirm the presence of amyloid-like fibers of heterogeneous size and exclude the possibility that the size heterogeneity is due to dissociation of the amyloid fibers during the gel running process.

Amyloid or amyloid-like fibers have been associated with many human diseases, and are now being discovered to be important for many signaling pathways. ...

Toeprinting Analysis of Translation Initiation Complex Formation on Mammalian mRNAs

Translation initiation is the rate-limiting step of protein synthesis and represents a key point at which cells regulate their protein output. Regulation of protein synthesis is the key to cellular stress-response, and dysregulation is central to many disease states, such as cancer. For instance, although cellular stress leads to the inhibition of global translation by attenuating cap-dependent initiation, certain stress-response proteins are selectively translated in a cap-independent manner. Discreet RNA regulatory elements, such as cellular internal ribosome entry sites (IRESes), allow for the translation of these specific mRNAs. Identification of such mRNAs, and the characterization of their regulatory mechanisms, have been a key area in molecular biology. Toeprinting is a method for the study of RNA structure and function as it pertains to translation initiation. The goal of toeprinting is to assess the ability of in vitro transcribed RNA to form stable complexes with ribosomes under a variety of conditions, in order to determine which sequences, structural elements, or accessory factors are involved in ribosome binding&#8212;a pre-cursor for efficient translation initiation. Alongside other techniques, such as western analysis and polysome profiling, toeprinting allows for a robust characterization of mechanisms for the regulation of translation initiation.

Toeprinting aims to measure the ability of in vitro transcribed RNA to form translation initiation complexes with ribosomes under a variety of conditions. This protocol describes a method for toeprinting mammalian RNA and can be used to study both cap-dependent and IRES-driven translation.

Translation initiation is the rate-limiting step of protein synthesis and represents a key point at which cells regulate their protein output. Regulation ...

Analysis of Thylakoid Membrane Protein Complexes by Blue Native Gel Electrophoresis

Photosynthetic electron transfer chain (ETC) converts solar energy to chemical energy in the form of NADPH and ATP. Four large protein complexes embedded in the thylakoid membrane harvest solar energy to drive electrons from water to NADP+ via two photosystems, and use the created proton gradient for production of ATP. Photosystem PSII, PSI, cytochrome b6f (Cyt b6f) and ATPase are all multiprotein complexes with distinct orientation and dynamics in the thylakoid membrane. Valuable information about the composition and interactions of the protein complexes in the thylakoid membrane can be obtained by solubilizing the complexes from the membrane integrity by mild detergents followed by native gel electrophoretic separation of the complexes. Blue native polyacrylamide gel electrophoresis (BN-PAGE) is an analytical method used for the separation of protein complexes in their native and functional form. The method can be used for protein complex purification for more detailed structural analysis, but it also provides a tool to dissect the dynamic interactions between the protein complexes. The method was developed for the analysis of mitochondrial respiratory protein complexes, but has since been optimized and improved for the dissection of the thylakoid protein complexes. Here, we provide a detailed up-to-date protocol for analysis of labile photosynthetic protein complexes and their interactions in Arabidopsis thaliana.

A protocol for the elucidation of plant thylakoid protein complex organization and composition with blue native polyacrylamide gel electrophoresis (BN-PAGE) and 2D-SDS-PAGE is described. The protocol is optimized for Arabidopsis thaliana, but can be used for other plant species with minor modifications.

Photosynthetic electron transfer chain (ETC) converts solar energy to chemical energy in the form of NADPH and ATP. Four large protein complexes embedded ...

Activated Cross-linked Agarose for the Rapid Development of Affinity Chromatography Resins - Antibody Capture as a Case Study

The purification of monoclonal antibodies (mAbs) is commonly achieved by Protein A affinity chromatography, which can account for up to 25% of the overall process costs. Alternative, cost-effective capture steps are therefore valuable for industrial-scale manufacturing, where large quantities of a single mAb are produced. Here we present a method for the immobilization of a DsRed-based epitope ligand to a cross-linked agarose resin allowing the selective capture of the HIV-neutralizing antibody 2F5 from crude plant extracts without using Protein A. The linear epitope ELDKWA was first genetically fused to the fluorescent protein DsRed and the fusion protein was expressed in transgenic tobacco (Nicotiana tabacum) plants before purification by immobilized metal-ion affinity chromatography. Furthermore, a method based on activated cross-linked agarose was optimized for high ligand density, efficient coupling and low costs. The pH and buffer composition and the soluble ligand concentration were the most important parameters during the coupling procedure, which was improved using a design-of-experiments approach. The resulting affinity resin was tested for its ability to selectively bind the target mAb in a crude plant extract and the elution buffer was optimized for high mAb recovery, product activity and affinity resin stability. The method can easily be adapted to other antibodies with linear epitopes. The new resins allow gentler elution conditions than Protein A and could also reduce the costs of an initial capture step for mAb production.

In this procedure, a DsRed-based epitope ligand is immobilized to produce a highly selective affinity resin for the capture of monoclonal antibodies from crude plant extracts or cell culture supernatants, as an alternative to Protein A.

The purification of monoclonal antibodies (mAbs) is commonly achieved by Protein A affinity chromatography, which can account for up to 25% of the overall ...

The Extraction of Liver Glycogen Molecules for Glycogen Structure Determination

Liver glycogen is a hyperbranched glucose polymer that is involved in the maintenance of blood sugar levels in animals. The properties of glycogen are influenced by its structure. Hence, a suitable extraction method that isolates representative samples of glycogen is crucial to the study of this macromolecule. Compared to other extraction methods, a method that employs a sucrose density gradient centrifugation step can minimize molecular damage. Based on this method, a recent publication describes how the density of the sucrose solution used during centrifugation was varied (30%, 50%, 72.5%) to find the most suitable concentration to extract glycogen particles of a wide variety of sizes, limiting the loss of smaller particles. A 10 min boiling step was introduced to test its ability to denature glycogen degrading enzymes, thus preserving glycogen. The lowest sucrose concentration (30%) and the addition of the boiling step were shown to extract the most representative samples of glycogen.

An optimal sucrose concentration was determined for the extraction of liver glycogen using sucrose density gradient centrifugation. The addition of a 10 min boiling step to inhibit glycogen-degrading enzymes proved beneficial.

Liver glycogen is a hyperbranched glucose polymer that is involved in the maintenance of blood sugar levels in animals. The properties of glycogen are ...

Stable Isotope Tracing &amp; LC-MS Analysis to Measure DHODH and SDH Activities

Oxygen-Independent Assays to Measure Mitochondrial Function in Mammals

The flow of electrons in the mitochondrial electron transport chain (ETC) supports multifaceted biosynthetic, bioenergetic, and signaling functions in mammalian cells. As oxygen (O2) is the most ubiquitous terminal electron acceptor for the mammalian ETC, the O2 consumption rate is frequently used as a proxy for mitochondrial function. However, emerging research demonstrates that this parameter is not always indicative of mitochondrial function, as fumarate can be employed as an alternative electron acceptor to sustain mitochondrial functions in hypoxia. This article compiles a series of protocols that allow researchers to measure mitochondrial function independently of the O2 consumption rate. These assays are particularly useful when studying mitochondrial function in hypoxic environments. Specifically, we describe methods to measure mitochondrial ATP production, de novo pyrimidine biosynthesis, NADH oxidation by complex I, and superoxide production. In combination with classical respirometry experiments, these orthogonal and economical assays will provide researchers with a more comprehensive assessment of mitochondrial function in their system of interest.

Author Spotlight: Oxygen-Independent Assays to Measure Mitochondrial Function in Mammals  

Here, we present a compilation of assays to directly measure mitochondrial function in mammalian cells independently of their ability to consume molecular oxygen.

The flow of electrons in the mitochondrial electron transport chain (ETC) supports multifaceted biosynthetic, bioenergetic, and signaling functions in ...

Characterization of Ternary Complex Formation in PROTACs Using Biophysical Assays

The Development and Application of Biophysical Assays for Evaluating Ternary Complex Formation Induced by Proteolysis Targeting Chimeras (PROTACS)

E3 ligases and proteins targeted for degradation can be induced to form complexes by heterobifunctional molecules in a multi-step process. The kinetics and thermodynamics of the interactions involved contribute to efficiency of ubiquitination and resulting degradation of the protein. Biophysical techniques such as surface plasmon resonance (SPR), biolayer interferometry (BLI), and isothermal titration calorimetry (ITC) provide valuable information that can be used in the optimization of those interactions. Using two model systems, a biophysical assay tool kit for understanding the cooperativity of ternary complex formation and the impact of the &#39;hook effect&#39; on binding kinetics was established. In one case, a proteolysis targeting chimera (PROTAC) molecule that induced ternary complex formation between Brd4BD2 and VHL was evaluated. The heterobifunctional molecule, MZ1, has nM affinities for both the Brd4BD2 protein (SPR KD = 1 nM, ITC KD = 4 nM) and the VHL complex (SPR KD = 29 nM, ITC KD = 66 nM). For this system, robust SPR, BLI, and ITC assays were developed that reproduced published results demonstrating the cooperativity of ternary complex formation. In the other case, a molecule that induced ternary complexes between a 46.0 kDa protein, PPM1D, and cereblon [CRBN (319-442)] was studied. The heterobifunctional molecule, BRD-5110, has an SPR KD = 1 nM for PPM1D but much weaker binding against the truncated CRBN (319-442) complex (SPR KD= ~ 3 &#181;M). In that case, the binding for CRBN in SPR was not saturable, resulting in a &#34;hook-effect&#34;. Throughput and reagent requirements for SPR, BLI, and ITC were evaluated, and general recommendations for their application to PROTAC projects were provided.

Author Spotlight: Evaluating Biophysical Assays for Characterizing PROTACS Ternary Complexes 

Here we describe protocols for the biophysical characterization of ternary complex formation induced by proteolysis targeting chimeras (PROTACS) that involve the ubiquitin ligases Von Hippel-Lindau E3 ligase (VHL) and Cereblon (CRBN). Biophysical methods illustrated herein include surface plasmon resonance (SPR), biolayer interferometry (BLI), and isothermal titration calorimetry (ITC).

E3 ligases and proteins targeted for degradation can be induced to form complexes by heterobifunctional molecules in a multi-step process. The kinetics ...