Name: detection of protein s-acylation using acyl-resin assisted capture
Uploaded: 2020-04-10T15:00:00
Description: Watch this Scientific Journal Video about Detection of Protein S-Acylation using Acyl-Resin Assisted Capture at JoVE.com

This work was supported by the National Institutes of Health grants 5R01GM115446 and 1R01GM130840.

Mice used in this protocol were euthanized according to NIH guidelines. The Animal Welfare Committee at University of Texas Health Science Center in Houston approved all animal work.
1. Preparation of cell lysates
<ol>
	<li>Prepare lysis buffer as described in Table 1. To 10 mL of PBS, add 0.1 g of n-dodecyl &#946;-D-maltoside detergent (DDM) and rotate to dissolve. Add 100 &#181;L of phosphatase inhibitor cocktail 2, ML211 (10 &#181;M), PMSF (10 mM) and protease inhibitor c...

<ol>
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T., 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=Site-specific+analysis+of+protein+S+-acylation+by+resin-assisted+capture.">Site-specific analysis of protein S -acylation by resin-assisted capture.</a> Journal of Lipid Research. 52 (2), 393-398 (2011).</li><li>Guo, J., 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=Proteomic+Profiling+of+Cysteine-Based+Reversible+Modifications.">Proteomic Profiling of Cysteine-Based Reversible Modifications.</a> Nature Protocols. 9 (1), 64-75 (2014).</li><li>Zaballa, M. E., van der Goot, F. 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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+activation+of+murine+lymphocytes.">Isolation and activation of murine lymphocytes.</a> Journal of Visualized Experiments. (116), 1-8 (2016).</li><li>Schneider, U., Schwenk, H., Bornkamm, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+EBV-genome+negative+"null"+and+"T"+cell+lines+derived+from+children+with+acute+lymphoblastic+leukemia+and+leukemic+transformed+non-Hodgkin+lymphoma.">Characterization of EBV-genome negative "null" and "T" cell lines derived from children with acute lymphoblastic leukemia and leukemic transformed non-Hodgkin lymphoma.</a> International Journal of Cancer. 19, 621-626 (1977).</li><li>Bijlmakers, M. 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Here, we successfully utilized the acyl-RAC assay to detect S-acylation of selected proteins in both cultured human cells and primary cells derived from mouse tissue. This method is simple, sensitive, and can be easily performed with minimal equipment requirements using standard biochemistry techniques. This method has been shown to successfully identify novel S-acylated proteins such as the &#946;-subunit of the protein translocating system (Sec61b), ribosomal protein S11 (Rps11), and microsomal glutathione-S-t...

S-acylation is a reversible post-translational modification involving addition of a fatty acyl chain to an internal cysteine residue on a target protein via a labile thioester bond1. It was first reported as a modification of proteins with palmitate, a saturated 16-carbon fatty acid2, and therefore this modification is often referred to as S-palmitoylation. In addition to palmitate, proteins can be reversibly modified by a variety of longer and shorter saturated (myristate and stearate), monounsaturated (oleate) and polyunsaturated (arachidonate and eicosapentanoate) fatty acids3,4,5,6,7. In eukaryotic cells, S-acylation is catalyzed by a family of enzymes known as DHHC protein acyltransferases and the reverse reaction of cysteine deacylation is catalyzed by protein thioesterases, most of which still remain enigmatic8.
The lability of the thioester bond makes this lipid modification reversible, allowing it to dynamically regulate protein clustering, plasma membrane localization, intracellular trafficking, protein-protein interactions and protein stability9,10. Consequently, S-acylation has been linked to several disorders including Huntington&#8217;s disease, Alzheimer&#8217;s disease and several types of cancer (prostate, gastric, bladder, lung, colorectal), which necessitates development of reliable methods to detect this post-translational protein modification11.
Metabolic labeling with radioactive ([3H], [14C] or&#160;[125I]) palmitate was one of the first approaches developed to assay protein S-acylation12,13,14. However, radiolabeling-based methods present health concerns, are not very sensitive, time consuming, and only detect lipidation of highly abundant proteins15. A faster and nonradioactive alternative to radiolabeling is metabolic labeling with bioorthogonal fatty acid probes, which is used routinely to assay dynamics of protein S-acylation16. In this method, a fatty acid with a chemical reporter (alkyne or azide group) is incorporated into the S-acylated protein by a protein acyltransferase. Azide-alkyne Huisgen cycloaddition reaction (click chemistry)&#160;can then be used to attach a functionalized group, such as a fluorophore or biotin, to the integrated fatty acid allowing for detection of the S-acylated protein17,18,19.
Acyl-biotin exchange (ABE) is one of the extensively used biochemical methods for capture and identification of S-acylated proteins that bypasses some of the shortcomings of metabolic labeling such as unsuitability for tissue samples15. This method can be applied for analysis of S-acylation in a diverse range of biological samples, including tissues and frozen cell samples20,21. This method is based on selective cleavage of the thioester bond between the acyl group and the cysteine residue by neutral hydroxylamine. The liberated thiol groups are then captured with a thiol-reactive biotin derivative. The generated biotinylated proteins are then affinity-purified using streptavidin agarose and analyzed by immunoblotting.
An alternative approach termed acyl-resin assisted capture (Acyl-RAC) was later introduced to replace the biotinylation step with direct conjugation of free cysteines by a thiol-reactive resin22,23. This method has fewer steps compared to ABE and similarly can be used to detect protein S-acylation in a wide range of samples1.
Acyl-RAC consists of 4 main steps (Figure 1), 
1. Blocking of free thiol groups; 
2. Selective cleavage of the cysteine-acyl thioester bond with neutral hydroxylamine (HAM) to expose cysteine thiol groups; 
3. Capturing of the lipidated cysteines with a thiol-reactive resin; 
4. Selective enrichment of the S-acylated proteins after elution with reducing buffer.
The captured proteins can then be analyzed by immunoblotting or subjected to mass spectrometry (MS) based proteomics to assess the S-acylated proteome in a varied range of species and tissues22,24,25. Individual S-acylation sites can also be identified by trypsin digestion of the captured proteins and analysis of the resulting peptides by LC-MS/MS22. Here, we demonstrate how acyl-RAC can be used for simultaneous detection of S-acylation of multiple proteins in both a cell line and a tissue sample.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">cOmplete Protease Inhibitor Cocktail tablets</td>
			<td style="width:244px;">Sigma</td>
			<td align="right" style="width:119px;">11836170001</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Eppendorf Centrifuge 5424</td>
			<td>Eppendorf</td>
			<td align="right" style="width:119px;">22620444</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hydroxylamine (HAM)</td>
			<td>Sigma</td>
			<td align="right" style="width:119px;">159417</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Methyl methanethiosulfonate (MMTS)</td>
			<td>Sigma</td>
			<td align="right" style="width:119px;">64306</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mini tube rotator</td>
			<td>LabForce</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ML211</td>
			<td>Cayman</td>
			<td align="right" style="width:119px;">17630</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Multi-Therm Cool-Heat-Shake</td>
			<td>Benchmark Scientific</td>
			<td style="width:119px;">H5000-HC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">n-Dodecyl &#946;-D-maltoside (DDM)</td>
			<td>Sigma</td>
			<td style="width:119px;">D641</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Phosphatase Inhibitor Cocktail 2</td>
			<td>Sigma</td>
			<td style="width:119px;">P5726</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thiopropyl-Sepharose 6B (TS)</td>
			<td>Sigma</td>
			<td style="width:119px;">T8387</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ultrasonics Quantrex Sonicator</td>
			<td>L &#38; R</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

detection of protein s-acylation using acyl-resin assisted capture

Protein S-acylation, also referred to as S-palmitoylation, is a reversible post-translational modification of cysteine residues with long-chain fatty acids via a labile thioester bond. S-acylation, which is emerging as a widespread regulatory mechanism, can modulate almost all aspects of the biological activity of proteins, from complex formation to protein trafficking and protein stability. The recent progress in understanding of the biological function of protein S-acylation was achieved largely due to the development of novel biochemical tools allowing robust and sensitive detection of protein S-acylation in a variety of biological samples. Here, we describe acyl resin-assisted capture (Acyl-RAC), a recently developed method based on selective capture of endogenously S-acylated proteins by thiol-reactive Sepharose beads. Compared to existing approaches, Acyl-RAC requires fewer steps and can yield more reliable results when coupled with mass spectrometry for identification of novel S-acylation targets. A major limitation in this technique is the lack of ability to discriminate between fatty acid species attached to cysteines via the same thioester bond.

Following the protocol described above, we first used acyl-RAC to simultaneously detect S-acylation of several proteins in Jurkat cells, an immortalized T cell line originally derived from the peripheral blood of a T cell leukemia patient27. Regulatory T cell proteins previously identified as S-acylated9,28,29 were chosen to demonstrate the utility of this method. As shown in Figure 2...

Watch this Scientific Journal Video about Detection of Protein S-Acylation using Acyl-Resin Assisted Capture at JoVE.com

Detection of Protein S-Acylation using Acyl-Resin Assisted Capture

Acyl-RAC (Acyl-Resin Assisted Capture) is a highly sensitive, reliable and easy to perform method to detect reversible lipid modification of cysteine residues (S-acylation) in a variety of biological samples.

Protein S-acylation, also referred to as S-palmitoylation, is a reversible post-translational modification of cysteine residues with long-chain fatty ...

Acyl-resin assisted capture or Acyl-RAC is a sensitive and reliable method that can be used to detect protein S-acylation in a variety of biological samples. This protocol bypasses some of the limitations of metabolic labeling and radio labeling, and allows the simultaneous detection of S-acylation of multiple proteins. Not only live cells but also primary tissues and frozen samples.S-acylation can regulate a variety of cellular processes such as protein trafficking, plasma membrane targeting, signal transduction, iron transport, and protein-protein interactions. It is important to use freshly prepared hydroxylamine solution with carefully adjusted pH for each experiment to ensure an efficient and specific cleavage of the thioester bond. With a demonstration of this method it's critical for steps like chloroform, methanol precipitation.The pancake shape pellet obtained during this step should be handle very carefully. It can be fragile and partial loss of the sample during the step can lead to uneven sample recovery. Demonstrating the procedure will be Savannah West, a graduate student from our laboratory.To obtain cell lysates, collect the cells of interest into a conical centrifuge tube. And remove any cell debris by centrifugation. Wash the pellet in 5 milliliters of PBS.And immediately resuspend the cells in 600 microliters of freshly prepared lysis buffer. Agitate the sample at 1, 500 revolutions per minute in a thermo shaker for 30 minutes at four degree Celsius. Before clearing the lysates, pellet detergent and soluble material by centrifugation.At the end of centrifugation, collect the cleared lysate in a pre-cooled 1.5 milliliter microcentrifuge tube on ice. And perform a Bradford or bicinchoninic acid assay to estimate the protein concentration according to standard protocols. Add methanol and chloroform to lysate at a 2:1 ratio.Shake rigorously to create a homogenous suspension and centrifuge the sample to collect a protein pellet at the interface between the aqueous and organic phases. Tilting the tube, use a needle or a gel loading tip to aspirate as much solvent as possible. Air dry the protein pellet for a few minutes.Before gently mixing the tube contents with 600 microliters of methanol, taking care not to break up the pellet. After carefully removing the methanol wash, dry the protein pellet on a bench top for approximately five minutes. Next, resuspend the protein pellet in 200 microliters of 2SHB buffer.And vortex at 42 degree Celsius and 1, 500 revolutions per minute in a thermo shaker. When the pellet is dissolved, add 200 microliters of 0.2%MMTS in 2SHB to the sample. And incubate the protein for 15 minutes at 42 degree Celsius and 1, 500 revolutions per minute in a thermo shaker.At the end of the incubation, perform 3:4 chloroform-methanol precipitations as demonstrated. To remove the MMTS, dissolve the pellet in 100 microliters of fresh 2SHB buffer with vortexing. And dilute the sample with 300 microliters of buffer A after each precipitation.After the final precipitation, dissolve the samples in 200 microliters of 2SHB buffer and dilute with 240 microliters of buffer A.Measure the protein concentration again and set aside a 40 microliters from each sample as input controls. Split samples into two equal volumes of 200 microliters. And mark the tubes as plus hydroxylamine and minus hydroxylamine.Add 50 microliters of freshly prepared neutral two molar hydroxylamine to a final concentration of 400 millimolar to the plus hydroxylamine tube. And 50 microliters of neutral two molar sodium chloride to the negative control, a minus hydroxylamine tube. Then add 30 microliters of TS bead slurry to each tube.And rotate the tubes for one to two hours at room temperature. At the end of the incubation wash the beads four times with 1%SDS in buffer A to remove any residual hydroxylamine. After the last wash, wash all of the bead samples with three gentle one minute microcentrifugations.Carefully aspirating the supernatants and resuspending the beads in 500 microliters of 1%SDS in buffer A at each wash. After the last wash, gently spin down the beads as demonstrated. And aspirate as much supernatant as possible without disturbing the beads.To recover the proteins from the beads, add 50 microliters of 4%SDS sample buffer to each tube and incubate the samples at 80 degree Celsius and 1, 500 revolutions per minute for 15 minutes in a thermo shaker. At the end of the incubation, let the samples cool before centrifuging to completely pellet the beads. Then use a gel loading tip to transfer the eluted proteins into new 1.5 milliliter tubes.And run the samples on an SDS-PAGE gel to analyze the S-acylation of the proteins of interest by Western blotting. Tyrosine kinase Lck can be detected in lysates treated with neutral two molar hydroxylamine. to cleave the thioester bond between cysteine residues and the fatty acid moiety.Stripping and reprobing with antibodies against proteins Fyn and LAT demonstrate that acyl-resin assisted capture assay can be used to analyze S-acylation of multiple proteins at the same time. In addition, S-acylation of Lck, Fyn, and LAT can be readily detected in primary mouse splenocytes. Indicating that this modification is conserved between two species.In addition to the identification of novel S-acylated proteins, this method can also be used to assess changes in protein S-acylation under different biological conditions. The number of newly identified S-acylated proteins has increased tremendously after the double up meant a fast, and reliable technique such as Acyl-RAC. In addition to the identification of novel S-acylated proteins, this method can also be used to assess changes in protein S-acylation under different biological conditions.

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JoVE Journal

Biochemistry

Protein Complex Affinity Capture from Cryomilled Mammalian Cells

Affinity capture is an effective technique for isolating endogenous protein complexes for further study. When used in conjunction with an antibody, this technique is also frequently referred to as immunoprecipitation. Affinity capture can be applied in a bench-scale and in a high-throughput context. When coupled with protein mass spectrometry, affinity capture has proven to be a workhorse of interactome analysis. Although there are potentially many ways to execute the numerous steps involved, the following protocols implement our favored methods. Two features are distinctive: the use of cryomilled cell powder to produce cell extracts, and antibody-coupled paramagnetic beads as the affinity medium. In many cases, we have obtained superior results to those obtained with more conventional affinity capture practices. Cryomilling avoids numerous problems associated with other forms of cell breakage. It provides efficient breakage of the material, while avoiding denaturation issues associated with heating or foaming. It retains the native protein concentration up to the point of extraction, mitigating macromolecular dissociation. It reduces the time extracted proteins spend in solution, limiting deleterious enzymatic activities, and it may reduce the non-specific adsorption of proteins by the affinity medium. Micron-scale magnetic affinity media have become more commonplace over the last several years, increasingly replacing the traditional agarose- and Sepharose-based media. Primary benefits of magnetic media include typically lower non-specific protein adsorption; no size exclusion limit because protein complex binding occurs on the bead surface rather than within pores; and ease of manipulation and handling using magnets.

Here we describe protocols to disrupt mammalian cells by solid-state milling at a cryogenic temperature, produce a cell extract from the resulting cell powder, and isolate protein complexes of interest by affinity capture upon antibody-coupled micron-scale paramagnetic beads.

Affinity capture is an effective technique for isolating endogenous protein complexes for further study. When used in conjunction with an antibody, this ...

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating these studies, reincorporation of detergent-solubilized membrane proteins into liposomes is a stochastic process where protein topology is impossible to enforce. This paper offers an alternative method to these challenging techniques that utilizes a liposome-based scaffold. Protein solubility is enhanced by deletion of the transmembrane domain, and these amino acids are replaced with a tethering moiety, such as a His-tag. This tether interacts with an anchoring group (Ni2+ coordinated by nitrilotriacetic acid (NTA(Ni2+)) for His-tagged proteins), which enforces a uniform protein topology at the surface of the liposome. An example is presented wherein the interaction between Dynamin-related protein 1 (Drp1) with an integral membrane protein, Mitochondrial Fission Factor (Mff), was investigated using this scaffold liposome method. In this work, we have demonstrated the ability of Mff to efficiently recruit soluble Drp1 to the surface of liposomes, which stimulated its GTPase activity. Moreover, Drp1 was able to tubulate the Mff-decorated lipid template in the presence of specific lipids. This example demonstrates the effectiveness of scaffold liposomes using structural and functional assays and highlights the role of Mff in regulating Drp1 activity.

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

This paper describes a method for assessing the interactions and assemblies of integral membrane proteins in vitro with various partner factors in a lipid-proximal environment.

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating ...

Detection and Visualization of DNA Damage-induced Protein Complexes in Suspension Cell Cultures Using the Proximity Ligation Assay

The DNA damage response orchestrates the repair of DNA lesions that occur spontaneously, are caused by genotoxic stress, or appear in the context of programmed DNA breaks in lymphocytes. The Ataxia-Telangiectasia Mutated kinase (ATM), ATM- and Rad3-Related kinase (ATR) and the catalytic subunit of DNA-dependent Protein Kinase (DNA-PKcs) are among the first that are activated upon induction of DNA damage, and are central regulators of a network that controls DNA repair, apoptosis and cell survival. As part of a tumor-suppressive pathway, ATM and ATR activate p53 through phosphorylation, thereby regulating the transcriptional activity of p53. DNA damage also results in the formation of so-called ionizing radiation-induced foci (IRIF) that represent complexes of DNA damage sensor and repair proteins that accumulate at the sites of DNA damage, which are visualized by fluorescence microscopy. Co-localization of proteins in IRIFs, however, does not necessarily imply direct protein-protein interactions, as the resolution of fluorescence microscopy is limited. 
In situ Proximity Ligation Assay (PLA) is a novel technique that allows the direct visualization of protein-protein interactions in cells and tissues with unprecedented specificity and sensitivity. This technique is based on the spatial proximity of specific antibodies binding to the proteins of interest. When the interrogated proteins are within ~40 nm an amplification reaction is triggered by oligonucleotides that are conjugated to the antibodies, and the amplification product is visualized by fluorescent labeling, yielding a signal that corresponds to the subcellular location of the interacting proteins. Using the established functional interaction between ATM and p53 as an example, it is demonstrated here how PLA can be used in suspension cell cultures to study the direct interactions between proteins that are integral parts of the DNA damage response.

Here, it is demonstrated how the in situ Proximity Ligation Assay (PLA) can be used to detect and visualize the direct protein-protein interactions between ATM and p53 in suspension cell cultures exposed to genotoxic stress.

The DNA damage response orchestrates the repair of DNA lesions that occur spontaneously, are caused by genotoxic stress, or appear in the context of ...

mRNA Interactome Capture from Plant Protoplasts

RNA-binding proteins (RBPs) determine the fates of RNAs. They participate in all RNA biogenesis pathways and especially contribute to post-transcriptional gene regulation (PTGR) of messenger RNAs (mRNAs). In the past few years, a number of mRNA-bound proteomes from yeast and mammalian cell lines have been successfully isolated through the use of a novel method called &#34;mRNA interactome capture,&#34; which allows for the identification of mRNA-binding proteins (mRBPs) directly from a physiological environment. The method is composed of in vivo ultraviolet (UV) crosslinking, pull-down and purification of messenger ribonucleoprotein complexes (mRNPs) by oligo(dT) beads, and the subsequent identification of the crosslinked proteins by mass spectrometry (MS). Very recently, by applying the same method, several plant mRNA-bound proteomes have been reported simultaneously from different Arabidopsis tissue sources: etiolated seedlings, leaf tissue, leaf mesophyll protoplasts, and cultured root cells. Here, we present the optimized mRNA interactome capture method for Arabidopsis thaliana leaf mesophyll protoplasts, a cell type that serves as a versatile tool for experiments that include various cellular assays. The conditions for optimal protein yield include the amount of starting tissue and the duration of UV irradiation. In the mRNA-bound proteome obtained from a medium-scale experiment (107 cells), RBPs noted to have RNA-binding capacity were found to be overrepresented, and many novel RBPs were identified. The experiment can be scaled up (109 cells), and the optimized method can be applied to other plant cell types and species to broadly isolate, catalog, and compare mRNA-bound proteomes in plants.

Here, we present an interactome capture protocol applied to Arabidopsis thaliana leaf mesophyll protoplasts. This method critically relies on in vivo UV crosslinking and allows for the isolation and identification of plant mRNA-binding proteins from a physiological environment.

RNA-binding proteins (RBPs) determine the fates of RNAs. They participate in all RNA biogenesis pathways and especially contribute to post-transcriptional ...

Horizontal Gel Electrophoresis for Enhanced Detection of Protein-RNA Complexes

Native polyacrylamide gel electrophoresis is a fundamental tool of molecular biology that has been used extensively for the biochemical analysis of RNA-protein interactions. These interactions have been traditionally analyzed with polyacrylamide gels generated between two glass plates and samples electrophoresed vertically. However, polyacrylamide gels cast in trays and electrophoresed horizontally offers several advantages. For example, horizontal gels used to analyze complexes between fluorescent RNA substrates and specific proteins can be imaged multiple times as electrophoresis progresses. This provides the unique opportunity to monitor RNA-protein complexes at several points during the experiment. In addition, horizontal gel electrophoresis makes it possible to analyze many samples in parallel. This can greatly facilitate time course experiments as well as analyzing multiple reactions simultaneously to compare different components and conditions. Here we provide a detailed protocol for generating and using horizontal native gel electrophoresis for analyzing RNA-Protein interactions.

Native polyacrylamide gel electrophoresis is a fundamental tool for analyzing RNA-protein interactions. Traditionally most experiments have used vertical gels. However, horizontal gels provide several advantages, such as the opportunity to monitor complexes during electrophoresis. We provide a detailed protocol for generating and using horizontal native gel electrophoresis.

Native polyacrylamide gel electrophoresis is a fundamental tool of molecular biology that has been used extensively for the biochemical analysis of ...

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 ...

Studying Protein Import into Chloroplasts Using Protoplasts

The chloroplast is an essential organelle that is responsible for various cellular processes in plants, such as photosynthesis and the production of many secondary metabolites and lipids. Chloroplasts require a large number of proteins for these various physiological processes. Over 95% of chloroplast proteins are nucleus-encoded and imported into chloroplasts from the cytosol after translation on cytosolic ribosomes. Thus, the proper import or targeting of these nucleus-encoded chloroplast proteins to chloroplasts is essential for the proper functioning of chloroplasts as well as the plant cell. Nucleus-encoded chloroplast proteins contain signal sequences for specific targeting to chloroplasts. Molecular machinery localized to the chloroplast or cytosol recognize these signals and carry out the import process. To investigate the mechanisms of protein import or targeting to chloroplasts in vivo, we developed a rapid, efficient protoplast-based method to analyze protein import into chloroplasts of Arabidopsis. In this method, we use protoplasts isolated from leaf tissues of Arabidopsis. Here, we provide a detailed protocol for using protoplasts to investigate the mechanism by which proteins are imported into chloroplasts.

Here we describe a protocol to express proteins into protoplasts by using PEG-mediated transformation method. The method provides easy expression of proteins of interest, and efficient investigation of protein localization and the import process for various experimental conditions in vivo.

The chloroplast is an essential organelle that is responsible for various cellular processes in plants, such as photosynthesis and the production of many ...

Extracellular Protein Microarray Technology for High Throughput Detection of Low Affinity Receptor-Ligand Interactions

Secreted factors, membrane-tethered receptors, and their interacting partners are main regulators of cellular communication and initiation of signaling cascades during homeostasis and disease, and as such represent prime therapeutic targets. Despite their relevance, these interaction networks remain significantly underrepresented in current databases; therefore, most extracellular proteins have no documented binding partner. This discrepancy is primarily due to the challenges associated with the study of the extracellular proteins, including expression of functional proteins, and the weak, low affinity, protein interactions often established between cell surface receptors. The purpose of this method is to describe the printing of a library of extracellular proteins in a microarray format for screening of protein-protein interactions. To enable detection of weak interactions, a method based on multimerization of the query protein under study is described. Coupled to this microbead-based multimerization approach for increased multivalency, the protein microarray allows robust detection of transient protein-protein interactions in high throughput. This method offers a rapid and low sample consuming-approach for identification of new interactions applicable to any extracellular protein. Protein microarray printing and screening protocol are described. This technology will be useful for investigators seeking a robust method for discovery of protein interactions in the extracellular space.

Here, we present a protocol to screen extracellular protein microarrays for identification of novel receptor-ligand interactions in high throughput. We also describe a method to enhance detection of transient protein-protein interactions by using protein-microbead complexes.

Secreted factors, membrane-tethered receptors, and their interacting partners are main regulators of cellular communication and initiation of signaling ...

Capture and Identification of RNA-binding Proteins by Using Click Chemistry-assisted RNA-interactome Capture (CARIC) Strategy

A comprehensive identification of RNA-binding proteins (RBPs) is key to understanding the posttranscriptional regulatory network in cells. A widely used strategy for RBP capture exploits the polyadenylation [poly(A)] of target RNAs, which mostly occurs on eukaryotic mature mRNAs, leaving most binding proteins of non-poly(A) RNAs unidentified. Here we describe the detailed procedures of a recently reported method termed click chemistry-assisted RNA-interactome capture (CARIC), which enables the transcriptome-wide capture of both poly(A) and non-poly(A) RBPs by combining the metabolic labeling of RNAs, in vivo UV cross-linking, and bioorthogonal tagging.

Capture and Identification of RNA-binding Proteins by Using Click Chemistry-assisted RNA-interactome Capture CARIC Strategy

A detailed protocol for applying the click chemistry-assisted RNA-interactome capture (CARIC) strategy to identify proteins binding to both coding and noncoding RNAs is presented.

A comprehensive identification of RNA-binding proteins (RBPs) is key to understanding the posttranscriptional regulatory network in cells. A widely used ...

High Sensitivity Measurement of Transcription Factor-DNA Binding Affinities by Competitive Titration Using Fluorescence Microscopy

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing approaches suffer from significant limitations, we have developed a new method for determining TF-DNA binding affinities with high sensitivity on a large scale. The assay relies on the established fluorescence anisotropy (FA) principle but introduces important technical improvements. First, we measure a full FA competitive titration curve in a single well by incorporating TF and a fluorescently labeled reference DNA in a porous agarose gel matrix. Unlabeled DNA oligomer is loaded on the top as a competitor and, through diffusion, forms a spatio-temporal gradient. The resulting FA gradient is then read out using a customized epifluorescence microscope setup. This improved setup greatly increases the sensitivity of FA signal detection, allowing both weak and strong binding to be reliably quantified, even for molecules of similar molecular weights. In this fashion, we can measure one titration curve per well of a multi-well plate, and through a fitting procedure, we can extract both the absolute dissociation constant (KD) and active protein concentration. By testing all single-point mutation variants of a given consensus binding sequence, we can survey the entire binding specificity landscape of a TF, typically on a single plate. The resulting position weight matrices (PWMs) outperform those derived from other methods in predicting in vivo TF occupancy. Here, we present a detailed guide for implementing HiP-FA on a conventional automated fluorescent microscope and the data analysis pipeline.

Here we present a novel method for determining binding affinities at equilibrium and in solution with high sensitivity on a large scale. This improves the quantitative analysis of transcription factor-DNA binding. The method is based on automated fluorescence anisotropy measurements in a controlled delivery system.

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing ...