Name: synthesis of 1,2-azaborines and the preparation of their protein complexes with t4 lysozyme mutants
Uploaded: 2017-03-25T13:00:00
Description: Watch this Scientific Journal Video about Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants at JoVE.com

This research was supported by the National Institutes of Health NIGMS (R01-GM094541) and Boston College.

NOTE: All oxygen- and moisture-sensitive manipulations were carried out under an inert atmosphere (N2) using either standard air-free techniques or a glove box. THF (tetrahydrofuran), Et2O (diethyl ether), CH2Cl2 (dichloromethane), toluene, and pentane were purified by passing through a neutral alumina column under argon. Acetonitrile was dried over CaH2 (calcium hydride) and distilled under nitrogen atmosphere prior to use. Pd/C (palladium on carbon) was heated unde...

<ol>
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In the first part of this protocol, we described a modified synthesis of 1,2-azaborines based on previously reported methods12, 13. Triallylborane22 was used as a substitute for the routes using allyltriphenyl tin or potassium allyltrifluoroborate to prepare N-allyl-N-TBS-B-allyl chloride adduct (1). This method allows for a more atom-economical and environmentally friendly approach. For the synt...

Boron-nitrogen containing heterocycles (i.e. 1,2-azaborines) have recently drawn significant attention as isosteres of arenes. This isosterism can lead to diversification of existing structural motifs to expand the chemical space2,3,4. Azaborines have potential utility for application in biomedical research5,6,7,8, especially in the area of medicinal chemistry in which chemists carry out synthesis of libraries of structurally and functionally relevant molecules. Significantly, however, while there are numerous well-developed synthetic routes to available arene-containing molecules, only a limited number of methods for the synthesis of azaborines have been reported9,10,11,12,13. This is mainly due to a limited number of options for the boron source and the air- and moisture- sensitive nature of the molecule in the early stage of synthetic sequence.
In the first part of this article, we will describe a multi-gram scale synthesis of N-TBS-B-Cl-1,2-azaborine (3) using standard air-free techniques. This compound serves as a versatile intermediate that can be further functionalized to structurally more complex molecules14,15. Starting from 3, the synthesis and purification of N-H-B-ethyl-1,2-azaborine (5) for use in protein binding studies will be described. Due to the volatility of 5, its efficient isolation requires precise control of reaction temperature, time, and distillation conditions.
In the second part, protocols for protein expression and isolation of T4 lysozyme mutants (L99A and L99A/M102Q)17,18,19,20 will be presented, followed by protein crystallization and preparation of protein-ligand crystal complexes. T4 lysozyme mutants L99A and L99A/M102Q were chosen as biological model systems to examine the hydrogen bonding capability of N-H containing azaborine molecules17. Using a standard molecular biology protocol, the protein is expressed in Escherichia coli RR1 strain and induced with isopropyl-&#946;-D-1-thiogalactopyranoside (IPTG). Protein purification is carried out using ion-exchange column chromatography. Protein crystallization is performed with highly concentrated purified protein solution (&#62;95% purity by gel electrophoresis) using the hanging drop vapor diffusion method. Because of the sensitivity of this study&#39;s ligands to oxygen, the protein-ligand complexes are prepared under air-free conditions.

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	<tbody>
		<tr>
			<td>Tetrahydrofuran (THF), inhibitor-free, for HPLC, &#8805;99.9%</td>
			<td>Sigma Aldrich</td>
			<td>34865</td>
			<td></td>
		</tr>
		<tr>
			<td>Diethyl ether (Et2O), for HPLC, &#8805;99.9%, inhibitor-free</td>
			<td>Sigma Aldrich</td>
			<td>309966</td>
			<td></td>
		</tr>
		<tr>
			<td>Methylene chloride&#160; (CH2Cl2), (Stabilized/Certified ACS)</td>
			<td>Fisher</td>
			<td>D37-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Toluene</td>
			<td>Fisher</td>
			<td>T290-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Pentane, HPLC</td>
			<td>Fisher</td>
			<td>P399-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetonitrile</td>
			<td>Fisher</td>
			<td>A21-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium hydride (CaH2), reagent grade, 95%</td>
			<td>Sigma Aldrich</td>
			<td>208027</td>
			<td>Pyrophoric</td>
		</tr>
		<tr>
			<td>Palladium on activated carbon (Pd/C), 10 wt% Pd</td>
			<td>Strem</td>
			<td>46-1900</td>
			<td></td>
		</tr>
		<tr>
			<td>1.0 M Boron trichloride solution in hexane</td>
			<td>Sigma Aldrich</td>
			<td>211249</td>
			<td>Highly toxic/ Pyrophoric</td>
		</tr>
		<tr>
			<td>Triethylamine, &#8805;99.5%</td>
			<td>Sigma Aldrich</td>
			<td>471283</td>
			<td></td>
		</tr>
		<tr>
			<td>Grubbs 1st generation catalyst&#160;</td>
			<td>materia</td>
			<td>C823</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetamide</td>
			<td>Sigma Aldrich</td>
			<td>A0500</td>
			<td></td>
		</tr>
		<tr>
			<td>n-Butanol, anhydrous, 99.8%</td>
			<td>Sigma Aldrich</td>
			<td>281549</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyllithium solution, 0.5 M in benzene/cyclohexane</td>
			<td>Sigma Aldrich</td>
			<td>561452</td>
			<td>Highly toxic/ Pyrophoric</td>
		</tr>
		<tr>
			<td>HCl solution, 2.0 M in Et2O</td>
			<td>Sigma Aldrich</td>
			<td>455180</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Methylbutane, anhydrous, &#8805;99%</td>
			<td>Sigma Aldrich</td>
			<td>277258</td>
			<td></td>
		</tr>
		<tr>
			<td>Escherichia coli, (Migula) Castellani and Chalmers (ATCC&#174; 31343&#8482;)</td>
			<td>ATCC</td>
			<td>31343</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 lysozyme WT* (L99A)</td>
			<td>Addgene</td>
			<td>18476</td>
			<td></td>
		</tr>
		<tr>
			<td>T4 lysozyme mutant (S38D L99A M102Q N144D)</td>
			<td>Addgene</td>
			<td>18477</td>
			<td></td>
		</tr>
		<tr>
			<td>Ampicillin sodium salt</td>
			<td>Sigma Aldrich</td>
			<td>A0166</td>
			<td></td>
		</tr>
		<tr>
			<td>isopropyl-&#946;-D-1-thiogalactopyranoside (IPTG)&#160;</td>
			<td>Invitrogen</td>
			<td>AM9464</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate monobasic&#160; anhydrous</td>
			<td>Fisher</td>
			<td>BP329</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Phosphate dibasic anhydrous</td>
			<td>Fisher</td>
			<td>BP332</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Fisher</td>
			<td>S642212&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylenediaminetetraacetic acid</td>
			<td>Fisher</td>
			<td>BP118</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride</td>
			<td>Sigma Aldrich</td>
			<td>M4880</td>
			<td>Corrosive</td>
		</tr>
		<tr>
			<td>Thermo scientific pierce DNaseI</td>
			<td>Fisher</td>
			<td>PI-90083</td>
			<td></td>
		</tr>
		<tr>
			<td>GE Healthcare&#160;Sepharose Fast Flow Cation Exchange Media</td>
			<td>Fisher</td>
			<td>45-002-931</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-base</td>
			<td>Fisher</td>
			<td>BP152-500&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>TCI</td>
			<td>S0489</td>
			<td>Highly toxic</td>
		</tr>
		<tr>
			<td>2-Mercaptoethanol</td>
			<td>Fisher</td>
			<td>ICN806443&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Sartorius&#160;Vivaspin 20 Centrifugal Concentrators</td>
			<td>Fisher</td>
			<td>14-558-501</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic</td>
			<td>Sigma Aldrich</td>
			<td>P5379</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Hydroxyethyl disulfide</td>
			<td>Sigma Aldrich</td>
			<td>380474</td>
			<td></td>
		</tr>
		<tr>
			<td>N-paratone&#160;</td>
			<td>Hampton Research</td>
			<td>HR2-643</td>
			<td></td>
		</tr>
		<tr>
			<td>4 RC Dialysis Membrane Tubing 12,000 to 14,000 Dalton MWCO&#160;</td>
			<td>Fisher</td>
			<td>08-667E</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;CryoLoop</td>
			<td>Hampton Research</td>
			<td></td>
			<td>cryogenic tubing shaped into a loop</td>
		</tr>
		<tr>
			<td>CryoTong</td>
			<td>Thermo Fisher</td>
			<td></td>
			<td>cryogenic tong</td>
		</tr>
		<tr>
			<td>Coot</td>
			<td></td>
			<td></td>
			<td>Electron density images are generated from the software</td>
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synthesis of 1,2-azaborines and the preparation of their protein complexes with t4 lysozyme mutants

We describe a general synthesis of 1,2-azaborines using standard air-free techniques and protein complex preparation with T4 lysozyme mutants by vapor diffusion. Oxygen- and moisture-sensitive compounds are prepared and isolated under an inert atmosphere (N2) using either a vacuum gas manifold or a glove box. As an example of azaborine synthesis, we demonstrate the synthesis and purification of the volatile N-H-B-ethyl-1,2-azaborine by a five-step sequence involving distillation and column chromatography for the isolation of products. T4 lysozyme mutants L99A and L99A/M102Q are expressed with Escherichia coli RR1 strain. Standard protocols for chemical cell lysis followed by purification using carboxymethyl ion exchange column affords protein of sufficiently high purity for crystallization. Protein crystallization is performed in various concentrations of precipitant at different pH ranges using the hanging drop vapor diffusion method. Complex preparation with the small molecules is carried out by vapor diffusion method under an inert atmosphere. X-ray diffraction analysis of the crystal complex provides unambiguous structural evidence of binding interactions between the protein binding site and 1,2-azaborines.

The schematic synthetic route for 1,2-azaborines is shown in Figure 1. This protocol applies to the synthesis of five different boron-nitrogen containing molecules. Figure 2 represents 11B NMR spectra measured during the course of step 1.3 to monitor the formation of the desired product (3). Protein purification was performed by using low-pressure chromatography system and a representative chromatogram is shown in Figur...

Watch this Scientific Journal Video about Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants at JoVE.com

Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants

A protocol for the synthesis of 1,2-azaborines and the preparation of their protein complexes with T4 lysozyme mutants is presented.

We describe a general synthesis of 1,2-azaborines using standard air-free techniques and protein complex preparation with T4 lysozyme mutants by vapor ...

The overall goal of this protocol is to describe a general method to synthesize 1, 2-Azaborines, and its potential application in biomedical research. The main advantage of this technique is that is shows a sure synthesis of 1, 2-azaborine compounds, which are a merging boron containing isosteres of the ubiquitous benzene motif. The precursor that is described can be further functionalized into potentially more complex molecules.The preparation of protein complexes with 1, 2-azaborine will give some insight into future application in biomedical research. To begin this procedure, prepare the ring-closed product as outlined in the text protocol. Add 14 grams of palladium on carbon to this prepared product in toluene.Then, remove the flask from the box. Fit the flask with an oven-dried 24/40 reflux condenser that has been purged with nitrogen and equipped with chilled water. Place the flask in an oil bath, and heat the reaction to a vigorous reflux at 135 degrees celsius while stirring.Maintain the reaction at reflux for 16 hours. After this, remove the flask from the oil bath to cool the reaction to room temperature. Once it's cooled, replace the reflux condenser with the septum on the reaction flask.Using a syringe equipped with an oven-dried Luer Lock needle, withdraw a 5 milliliter aliquot. Transfer the aliquot to a screw-top NMR tube. Analyze the sample via Boron-11 NMR.If the reaction is incomplete, transfer the reaction flask into a glove box. Then, add an additional three grams of palladium on carbon. Next, remove the flask from the glove box.Fit the flask with a 24/40 reflux condenser that has been purged with nitrogen and equipped with chilled water. Using an oil bath, heat the reaction to a vigorous reflux at 135 degrees celsius while stirring for 24 hours. Using Boron-11 NMR, analyze another aliquot to ensure the reaction is complete.After this, transfer the reaction flask back to the glove box. Pass the reaction mixture through a flash chromatography column packed with paper wipes. Then, collect the filtrate into a one liter round-bottom flask equipped with a stir bar.Wash the column with 50 milliliters of toluene. Remove the vessel of filtrate from the glove box and connect it to a vacuum gas manifold equipped with a nitrogen line. Place a water bath underneath the flask, and a dewar containing liquid nitrogen to trap solvent.Open the high vacuum valve to begin the removal of all volatiles from the filtrate. Then, return the reaction mixture to the glove box. Transfer the mixture into an oven-dried 24/40 250 milliliter round-bottom flask with a stir bar.Rinse the residual reaction mixture with dichloromethane, and transfer it into the flask. Cap the flask with a septum. Transfer the flask from the glove box to the vacuum manifold, and connect it.Open the high vacuum valve to remove the residual solvent. Next, quickly remove the septum and add calcium hydride using a scoopula. Connect the round-bottom flask to the distillation apparatus detailed in the text protocol, and set the oil bath temperature to 100 degrees Celsius.After distillation is complete, remove the heat source and cool the apparatus to room temperature. Re-pressurize the cooled apparatus with nitrogen, and tightly close the plug valve on the air-free storage flask. After transferring the isolated product from the flask to a vial in a glove box, store the vial in the glove box freezer.After purifying the protein, transfer the purified solution to dialysis membrane tubing. Place the dialysis tubing into a bin containing a four-liter solution of 100 millimolar sodium phosphate, 550 millimolar sodium chloride, and 02%sodium azide. Stir overnight at four degrees celsius.The next day, add 2-mercaptoethanol to the dialyzed sample, such that the final concentration is five millimolar. Then, use a centrifugal concentrator to concentrate the solution to 40 milligrams per milliliter. Spin the sample at 5, 000 RPM and six degrees celsius, and remove any precipitate after concentration.Next, in a 24-well plate, set up various conditions with the reservoir solution, as outlined in the text protocol. Use grease for tight sealing by applying it onto the edge of each well. Mix five microliters of the concentrated protein solution with five microliters of reservoir solution on a siliconized glass cover slide.Place the cover slide upside-down over the wells containing reservoir solution. Store the plate at 4 degrees celsius for crystal growth. Using a loop of cryogenic tubing, pick the grown crystals and place them in a 6 milliliter microcentrifuge tube.Add 50 microliters of mother liquor. Then, transfer the tube to a glove box. Transfer five microliters of the prepared azaborine ligand to the inside of the tube's snap cap.Cap the tube, and store in a refrigerator inside the glove box for two to seven days for equilibration by vapor diffusion. After this, deposit a droplet of N Paratone onto a glass slide. Using a micro pipette, transfer a crystal to the slide.Next, use a loop of cryogenic tubing to pick up the crystal and transfer it from the aqueous solution into the N Paratone. Plunge the crystal protected with N Paratone into a dewar containing liquid nitrogen. Using cryogenic tongs, mount the flash-frozen crystal on the loop.Then, analyze the collected crystal data as outlined in the text protocol. In this study, a modified synthesis of 1, 2-azaborines is presented based on previously reported methods. Tri-allele borine is used to prepare N-allele NTBSB-allele chloride adduct.A one pop two step sequence is employed for the synthesis of NTBS BCl 1, 2-azaborine, which results in higher isolated yield than previous methods. The synthesis of N-H-B-ethyl-1, 2-azaborine is accomplished in two steps, using ethyllithium in place of chromium complex used in previously reported methods. The protein is purified using a low-pressure chromatography system.A chromatogram run at 280 nanometers shows a peak consistent with the T4 Lysozyme mutant, L99am102q. Protein is then crystallized and complexed with ligands. While attempting this procedure, it's important to remember that the azaborine synthesis requires uses of air-free conditions, such as a glove box and a vacuum gas manifold, to prevent decomposition of compounds.After its development, this technique paved the way to explore the unique chemical and physical properties of azaborines compared to carbonaceous aromatics in classic biological areal reclamation pockets.

synthesis-12-azaborines-preparation-their-protein-complexes-with-t4

Research

JoVE Journal

Biochemistry

Preparation and Delivery of Protein Microcrystals in Lipidic Cubic Phase for Serial Femtosecond Crystallography

Membrane proteins (MPs) are essential components of cellular membranes and primary drug targets. Rational drug design relies on precise structural information, typically obtained by crystallography; however MPs are difficult to crystallize. Recent progress in MP structural determination has benefited greatly from the development of lipidic cubic phase (LCP) crystallization methods, which typically yield well-diffracting, but often small crystals that suffer from radiation damage during traditional crystallographic data collection at synchrotron sources. The development of new-generation X-ray free-electron laser (XFEL) sources that produce extremely bright femtosecond pulses has enabled room temperature data collection from microcrystals with no or negligible radiation damage. Our recent efforts in combining LCP technology with serial femtosecond crystallography (LCP-SFX) have resulted in high-resolution structures of several human G protein-coupled receptors, which represent a notoriously difficult target for structure determination. In the LCP-SFX technique, LCP is recruited as a matrix for both growth and delivery of MP microcrystals to the intersection of the injector stream with an XFEL beam for crystallographic data collection. It has been demonstrated that LCP-SFX can substantially improve the diffraction resolution when only sub-10 &#181;m crystals are available, or when the use of smaller crystals at room temperature can overcome various problems associated with larger cryocooled crystals, such as accumulation of defects, high mosaicity and cryocooling artifacts. Future advancements in X-ray sources and detector technologies should make serial crystallography highly attractive and practicable for implementation not only at XFELs, but also at more accessible synchrotron beamlines. Here we present detailed visual protocols for the preparation, characterization and delivery of microcrystals in LCP for serial crystallography experiments. These protocols include methods for conducting crystallization experiments in syringes, detecting and characterizing the crystal samples, optimizing crystal density, loading microcrystal laden LCP into the injector device and delivering the sample to the beam for data collection.

We describe procedures for the preparation and delivery of membrane protein microcrystals in lipidic cubic phase for serial crystallography at X-ray free-electron lasers and synchrotron sources. These protocols can also be applied for incorporation and delivery of soluble protein microcrystals, leading to substantially reduced sample consumption compared to liquid injection.

Membrane proteins (MPs) are essential components of cellular membranes and primary drug targets. Rational drug design relies on precise structural ...

An Efficient Method for the Synthesis of Peptoids with Mixed Lysine-type/Arginine-type Monomers and Evaluation of Their Anti-leishmanial Activity

This protocol describes the manual solid-phase synthesis of linear peptoids that contain two differently functionalized cationic monomers. In this procedure amino functionalized 'lysine' and guanido functionalized 'arginine' peptoid monomers can be included within the same peptoid sequence. This procedure uses on-resin (N-(1-(4,4-dimethyl-2,6-dioxocyclohexylidene)ethyl) or Dde protection, orthogonal conditions to the Boc protection of lysine monomers. Subsequent deprotection allows an efficient on-resin guanidinylation reaction to form the arginine residues. The procedure is compatible with the commonly used submonomer method of peptoid synthesis, allowing simple peptoids to be made using common laboratory equipment and commercially available reagents. The representative synthesis, purification and characterization of two mixed peptoids is described. The evaluation of these compounds as potential anti-infectives in screening assays against Leishmania mexicana is also described. The protozoan parasite L. mexicana is a causative agent of cutaneous leishmaniasis, a neglected tropical disease that affects up to 12 million people worldwide.

A protocol to synthesize peptoids with mixed cationic functionality in the same sequence is presented (lysine- and arginine-type monomers). Subsequent testing of these compounds against Leishmania mexicana, the protozoan parasites that cause cutaneous leishmaniasis, is also described.

This protocol describes the manual solid-phase synthesis of linear peptoids that contain two differently functionalized cationic monomers. In this ...

Tandem Affinity Purification of Protein Complexes from Eukaryotic Cells

The purification of active protein-protein and protein-nucleic acid complexes is crucial for the characterization of enzymatic activities and de novo identification of novel subunits and post-translational modifications. Bacterial systems allow for the expression and purification of a wide variety of single polypeptides and protein complexes. However, this system does not enable the purification of protein subunits that contain post-translational modifications (e.g., phosphorylation and acetylation), and the identification of novel regulatory subunits that are only present/expressed in the eukaryotic system. Here, we provide a detailed description of a novel, robust, and efficient tandem affinity purification (TAP) method using STREP- and FLAG-tagged proteins that facilitates the purification of protein complexes with transiently or stably expressed epitope-tagged proteins from eukaryotic cells. This protocol can be applied to characterize protein complex functionality, to discover post-translational modifications on complex subunits, and to identify novel regulatory complex components by mass spectrometry. Notably, this TAP method can be applied to study protein complexes formed by eukaryotic or pathogenic (viral and bacterial) components, thus yielding a wide array of downstream experimental opportunities. We propose that researchers working with protein complexes could utilize this approach in many different ways.

We describe here a novel, robust, and efficient tandem affinity purification (TAP) method for the expression, isolation, and characterization of protein complexes from eukaryotic cells. This protocol could be utilized for the biochemical characterization of discrete complexes as well as the identification of novel interactors and post-translational modifications that regulate their function.

The purification of active protein-protein and protein-nucleic acid complexes is crucial for the characterization of enzymatic activities and de novo ...

Resolving Affinity Purified Protein Complexes by Blue Native PAGE and Protein Correlation Profiling

Most proteins act in association with others; hence, it is crucial to characterize these functional units in order to fully understand biological processes. Affinity purification coupled to mass spectrometry (AP-MS) has become the method of choice for identifying protein-protein interactions. However, conventional AP-MS studies provide information on protein interactions, but the organizational information is lost. To address this issue, we developed a strategy to unravel the distinct functional assemblies a protein might be involved in, by resolving affinity-purified protein complexes prior to their characterization by mass spectrometry. Protein complexes isolated through affinity purification of a bait protein using an epitope tag and competitive elution are separated through blue native electrophoresis. Comparison of protein migration profiles through correlation profiling using quantitative mass spectrometry allows assignment of interacting proteins to distinct molecular entities. This method is able to resolve protein complexes of close molecular weights that might not be resolved by traditional chromatographic techniques such as gel filtration. With little more work than conventional AP-geLC-MS/MS, we demonstrate this strategy may in many cases be adequate for obtaining protein complex topological information concomitantly to identifying protein interactions.

Here we present protocols for affinity purification of protein complexes and their separation by blue native PAGE, followed by protein correlation profiling using label free quantitative mass spectrometry. This method is useful to resolve interactomes into distinct protein complexes.

Most proteins act in association with others; hence, it is crucial to characterize these functional units in order to fully understand biological ...

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 ...

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 ...

Split-BioID &#8212; Proteomic Analysis of Context-specific Protein Complexes in Their Native Cellular Environment

To complement existing affinity purification (AP) approaches for the identification of protein-protein interactions (PPI), enzymes have been introduced that allow the proximity-dependent labeling of proteins in living cells. One such enzyme, BirA* (used in the BioID approach), mediates the biotinylation of proteins within a range of approximately 10 nm. Hence, when fused to a protein of interest and expressed in cells, it allows the labeling of proximal proteins in their native environment. As opposed to AP that relies on the purification of assembled protein complexes, BioID detects proteins that have been marked within cells no matter whether they are still interacting with the protein of interest when they are isolated. Since it biotinylates proximal proteins, one can moreover capitalize on the exceptional affinity of streptavidin for biotin to very efficiently isolate them. While BioID performs better than AP for identifying transient or weak interactions, both AP- and BioID-mass spectrometry approaches provide an overview of all possible interactions a given protein may have. However, they do not provide information on the context of each identified PPI. Indeed, most proteins are typically part of several complexes, corresponding to distinct maturation steps or different functional units. To address this common limitation of both methods, we have engineered a protein-fragments complementation assay based on the BirA* enzyme. In this assay, two inactive fragments of BirA* can reassemble into an active enzyme when brought in close proximity by two interacting proteins to which they are fused. The resulting split-BioID assay thus allows the labeling of proteins that assemble around a pair of interacting proteins. Provided these two only interact in a given context, split-BioID then allows the analysis of specific context-dependent functional units in their native cellular environment. Here, we provide a step-by-step protocol to test and apply split-BioID to a pair of interacting proteins.

Split-BioID &amp;#8212; Proteomic Analysis of Context-specific Protein Complexes in Their Native Cellular Environment

We provide a step-by-step protocol for split-BioID, a protein fragments-complementation assay based on the proximity-labeling technique BioID. Activated on the interaction of two given proteins, it allows the proteomics analysis of context-dependent protein complexes in their native cellular environment. The method is simple, cost-effective and only requires standard laboratory equipment.

To complement existing affinity purification (AP) approaches for the identification of protein-protein interactions (PPI), enzymes have been introduced ...

2 in 1: One-step Affinity Purification for the Parallel Analysis of Protein-Protein and Protein-Metabolite Complexes

Cellular processes are regulated by interactions between biological molecules such as proteins, metabolites, and nucleic acids. While the investigation of protein-protein interactions (PPI) is no novelty, experimental approaches aiming to characterize endogenous protein-metabolite interactions (PMI) constitute a rather recent development. Herein, we present a protocol that allows simultaneous characterization of the PPI and PMI of a protein of choice, referred to as bait. Our protocol was optimized for Arabidopsis cell cultures and combines affinity purification (AP) with mass spectrometry (MS)-based protein and metabolite detection. In short, transgenic Arabidopsis lines, expressing bait protein fused to an affinity tag, are first lysed to obtain a native cellular extract. Anti-tag antibodies are used to pull down protein and metabolite partners of the bait protein. The affinity-purified complexes are extracted using a one-step methyl tert-butyl ether (MTBE)/methanol/water method. Whilst metabolites separate into either the polar or the hydrophobic phase, proteins can be found in the pellet. Both metabolites and proteins are then analyzed by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS or UPLC-MS/MS). Empty-vector (EV) control lines are used to exclude false positives. The major advantage of our protocol is that it enables identification of protein and metabolite partners of a target protein in parallel in near-physiological conditions (cellular lysate). The presented method is straightforward, fast, and can be easily adapted to biological systems other than plant cell cultures.

Protein-protein and protein-metabolite interactions are crucial for all cellular functions. Herein, we describe a protocol that allows parallel analysis of these interactions with a protein of choice. Our protocol was optimized for plant cell cultures and combines affinity purification with mass spectrometry-based protein and metabolite detection.

Cellular processes are regulated by interactions between biological molecules such as proteins, metabolites, and nucleic acids. While the investigation of ...

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 ...

Affinity Purification of Chloroplast Translocon Protein Complexes Using the TAP Tag

Chloroplast biogenesis requires the import of thousands of nucleus-encoded proteins into the plastid. The import of these proteins depends on the translocon at the outer (TOC) and inner (TIC) chloroplast membranes. The TOC and TIC complexes are multimeric and probably contain yet unknown components. One of the main goals in the field is to establish the complete inventory of TOC and TIC components. For the isolation of TOC-TIC complexes and the identification of new components, the preprotein receptor TOC159 has been modified N-terminally by the addition of the tandem affinity purification (TAP) tag resulting in TAP-TOC159. The TAP-tag is designed for two sequential affinity purification steps (hence "tandem affinity"). The TAP-tag used in these studies consists of a N-terminal IgG-binding domain derived from Staphylococcus aureus Protein A (ProtA) followed by a calmodulin-binding peptide (CBP). Between these two affinity tags, a tobacco etch virus (TEV) protease cleavage site has been included. Therefore, TEV protease can be used for gentle elution of TOC159-containing complexes after binding to IgG beads. In the protocol presented here, the second Calmodulin-affinity purification step was omitted. The purification protocol starts with the preparation and solubilization of total cellular membranes. After the detergent-treatment, the solubilized membrane proteins are incubated with IgG beads for the immunoisolation of TAP-TOC159-containing complexes. Upon binding and extensive washing, TAP-TOC159 containing complexes are cleaved and released from the IgG beads using the TEV protease whereby the S. aureus IgG-binding domain is removed. Western blotting of the isolated TOC159-containing complexes can be used to confirm the presence of known or suspected TOC and TIC proteins. More importantly, the TOC159-containing complexes have been used successfully to identify new components of the TOC and TIC complexes by mass spectrometry. The protocol that we present potentially allows the efficient isolation of any membrane-bound protein complex to be used for the identification of yet unknown components by mass spectrometry.

We here present a proven and tested protocol for the purification of chloroplast protein import complexes (TOC-TIC complex) using the TAP-tag. The one-step affinity-isolation protocol can potentially be applied to any protein and be used to identify new interaction partners by mass spectrometry.