We acknowledge the Wilhelm Sander-Foundation (2017.008.02), the Center of Dynamic Systems (CDS), funded by the EU-program ERDF (European Regional Development Fund) and the DFG (LA 2386) for supporting our work. We thank Karina Guttek for supporting our experiments. We acknowledge Prof. Dirk Reinhold (OvGU, Magdeburg) for providing us primary T cells.

&#8203;T cell experiments were performed according to the ethical agreement 42502-2-1273 Uni MD.
1. Preparing cells for the experiment
NOTE: The average number of cells for this immunoprecipitation is 1 &#215; 107. Adherent cells have to be seeded one day before the experiment so that there are 1 &#215; 107 cells&#160;on the day of the experiment.
<ol>
	<li>Preparing adherent cells for the experiment
	<ol>
		<li>Seed 5-8 &#215; 106 adherent cells in 20 mL of medium (see the Table of Materials for the composition) for each condition in 14.5 cm dishes one day before the experiment starts.</li>
		<li>On the day of the experiment, ensure that the cells are 80-90% confluent and adherent to the dish. Discard the medium and add fresh medium to the adherent cells.</li>
	</ol>
	</li>
	<li>Preparing suspension cells for the experiment
	<ol>
		<li>Carefully place 1 &#215; 107 suspension cells in 10 mL of culture medium (see the Table of Materials for the composition) per condition in 14.5 cm dishes immediately before the experiment starts.</li>
		<li>If using primary cells, isolate primary T cells according to the previously described procedure21. Treat primary T cells with 1 &#181;g/mL phytohemagglutinin for 24 h, followed by 25 U/mL IL2 treatment for 6 days.</li>
		<li>Carefully place 1 &#215; 108 primary T cells in 10 mL of culture medium (see the Table of Materials for the composition) per condition in 14.5 cm dishes immediately before the experiment starts. 
		&#8203;NOTE: This higher number of primary T cells is recommended, as these cells are smaller.</li>
	</ol>
	</li>
</ol>
2. CD95L stimulation
<ol>
	<li>Stimulate the cells with CD95L (produced as described previously20 or commercially available (see the Table of Materials)). 
	&#8203;NOTE: The concentration of the CD95L and the time of stimulation are cell-type dependent13,15,22,23,24,25. Prepare one stimulation condition twice to generate a &#39;bead control&#39; sample in parallel.
	<ol>
		<li>Stimulate adherent cells with the selected concentration of CD95L. Hold the plate at an angle and pipet the ligand into the medium without touching the adherent cells.</li>
		<li>Stimulate suspension cells with CD95L by pipetting the ligand solution into the cell suspension.</li>
	</ol>
	</li>
</ol>
3. Cell harvest and lysis
<ol>
	<li>Place the cell dishes on ice. 
	NOTE: Do not discard the medium. Dying cells float in the medium and are important for the analysis.</li>
	<li>Add 10 mL of cold phosphate-buffered saline (PBS) to the cell suspension and scrape the attached cells off the plate. Collect the cell suspension in a 50 mL tube.</li>
	<li>Wash the cell dish with 10 mL of cold PBS twice and place the wash solution into the same 50 mL tube. Centrifuge the cell suspension at 500 &#215; g for 5 min, 4 &#176;C.</li>
	<li>Discard the supernatant and resuspend the cell pellet with 1 mL of cold PBS. Transfer the cell suspension into a 1.5 mL tube.</li>
	<li>Centrifuge the cell suspension at 500 &#215; g for 5 min, 4 &#176;C. Discard the supernatant and resuspend the cell pellet with 1 mL of cold PBS.</li>
	<li>Centrifuge the cell suspension at 500 &#215; g for 5 min, 4 &#176;C. Discard the supernatant and resuspend the cell pellet with 1 mL of lysis buffer (containing 4% protease inhibitor cocktail). Incubate it for 30 min on ice.</li>
	<li>Centrifuge the lysate at maximal speed (~17,000 &#215; g) for 15 min, 4 &#176;C.</li>
	<li>Transfer the supernatant (lysate) to a clean tube. Discard the pellet. Take 50 &#181;L of the lysate in another tube. Analyze the protein concentration by Bradford assay and take the amount of lysate corresponding to 25 &#181;g of protein in a vial. Add loading buffer (see the Table of Materials for the composition) to the vial. Store it at -20 &#176;C as lysate control.</li>
</ol>
4. Immunoprecipitation (IP)
<ol>
	<li>Add 2 &#181;L of anti-APO-1 antibodies and 10 &#181;L of protein A sepharose beads (prepared as recommended by the manufacturer) to the lysate. Add only 10 &#181;L of the beads to a separate tube containing lysate (stimulated sample) to generate a &#39;bead control.&#39; 
	NOTE: Use pipet tips with wide orifices either by cutting the tips or buying special tips for IP while handling the protein A sepharose beads.</li>
	<li>Incubate the mixture of lysate with antibodies/protein A sepharose beads with gentle mixing overnight at 4 &#176;C. Centrifuge the lysates with antibodies/protein A sepharose beads at 500 &#215; g for 4 min, 4 &#176;C. Discard the supernatant, add 1 mL of cold PBS to the beads, and repeat this step at least three times.</li>
	<li>Discard the supernatant. Aspirate the beads preferably with a 50 &#181;L Hamilton syringe.</li>
</ol>
5. Western blot
<ol>
	<li>Add 20 &#181;L of 4x loading buffer (see the Table of Materials for the composition) to the beads and heat at 95 &#176;C for 10 min. Heat the lysate controls at 95 &#176;C for 5 min.</li>
	<li>Load the lysates, IPs, and a protein standard onto a 12.5% sodium dodecyl sulfate (SDS) gel (see the Table of Materials for the gel preparation) and run with a constant voltage of 80 V.</li>
	<li>Transfer the proteins from the SDS gel to a nitrocellulose membrane. 
	NOTE: Here, the semi-dry technique, optimized for the proteins of interest, was used for the transfer over 12 min (25 V; 2.5 A= constant). Soak the nitrocellulose membrane and two mini-size transfer stacks in electrophoresis buffer (see the Table of Materials for the composition, prepare according to the manufacturer&#39;s instructions) for a few minutes before western blotting.</li>
	<li>Place the blotted membrane in a box and block it for 1 h in blocking solution (0.1% Tween-20 in PBS (PBST) + 5% milk). Incubate the membrane with the blocking solution under gentle agitation.</li>
	<li>Wash the membrane three times with PBST for 5 min each wash.</li>
</ol>
6. Western blot detection
<ol>
	<li>Add the first primary antibody at the indicated dilution (see the Table of Materials) to the membrane and incubate it overnight at 4 &#176;C with gentle agitation.</li>
	<li>Wash the membrane three times with PBST for 5 min each wash.</li>
	<li>Incubate the membrane with 20 mL of secondary antibody (diluted 1:10,000 in PBST + 5% milk) with gentle shaking for 1 h at room temperature.</li>
	<li>Wash the membrane three times with PBST for 5 min each wash.</li>
	<li>Discard PBST and add approximately 1 mL of horseradish peroxidase substrate to the membrane.</li>
	<li>Detect the chemoluminescent signal (see the Table of Materials). 
	NOTE: The exposure time and the number of captured images depend on the amount of protein in the cell and the specificity of the antibodies used. It must be established empirically for each antibody used for the detection.</li>
</ol>

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D., Shi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanism+of+procaspase-8+activation+by+c-FLIPL.">Mechanism of procaspase-8 activation by c-FLIPL.</a> Proceedings of the National Academy of Sciences of the United States of America. 106 (20), 8169-8174 (2009).</li><li>Micheau, O., 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+long+form+of+FLIP+is+an+activator+of+caspase-8+at+the+Fas+death-inducing+signaling+complex.">The long form of FLIP is an activator of caspase-8 at the Fas death-inducing signaling complex.</a> Journal of Biological Chemistry. 277 (47), 45162-45171 (2002).</li><li>Chang, D. W., 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=C-FLIPL+is+a+dual+function+regulator+for+caspase-8+activation+and+CD95-mediated+apoptosis.">C-FLIPL is a dual function regulator for caspase-8 activation and CD95-mediated apoptosis.</a> EMBO Journal. 21 (14), 3704-3714 (2002).</li><li>Hillert, L. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dissecting+DISC+regulation+via+pharmacological+targeting+of+caspase-8/c-FLIPL+heterodimer.">Dissecting DISC regulation via pharmacological targeting of caspase-8/c-FLIPL heterodimer.</a> Cell Death and Differentiation. 27 (7), 2117-2130 (2020).</li><li>Fricker, N., 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=Model-based+dissection+of+CD95+signaling+dynamics+reveals+both+a+pro-+and+antiapoptotic+role+of+c-FLIPL.">Model-based dissection of CD95 signaling dynamics reveals both a pro- and antiapoptotic role of c-FLIPL.</a> Journal of Cell Biology. 190 (3), 377-389 (2010).</li><li>Arndt, B., 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=Analysis+of+TCR+activation+kinetics+in+primary+human+T+cells+upon+focal+or+soluble+stimulation.">Analysis of TCR activation kinetics in primary human T cells upon focal or soluble stimulation.</a> Journal of Immunological Methods. 387 (1-2), 276-283 (2013).</li><li>Pietkiewicz, S., Eils, R., Krammer, P. 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N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combinatorial+treatment+of+CD95L+and+gemcitabine+in+pancreatic+cancer+cells+induces+apoptotic+and+RIP1-mediated+necroptotic+cell+death+network.">Combinatorial treatment of CD95L and gemcitabine in pancreatic cancer cells induces apoptotic and RIP1-mediated necroptotic cell death network.</a> Experimental Cell Research. 339 (1), 1-9 (2015).</li><li>Schleich, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+architecture+of+the+DED+chains+at+the+DISC:+regulation+of+procaspase-8+activation+by+short+DED+proteins+c-FLIP+and+procaspase-8+prodomain.">Molecular architecture of the DED chains at the DISC: regulation of procaspase-8 activation by short DED proteins c-FLIP and procaspase-8 prodomain.</a> Cell Death and Differentiation. 23 (4), 681-694 (2016).</li><li>Lavrik, I. N., 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=Analysis+of+CD95+threshold+signaling:+Triggering+of+CD95+(FAS/APO-1)+at+low+concentrations+primarily+results+in+survival+signaling.">Analysis of CD95 threshold signaling: Triggering of CD95 (FAS/APO-1) at low concentrations primarily results in survival signaling.</a> Journal of Biological Chemistry. 282 (18), 13664-13671 (2007).</li><li>Sprick, M. R., 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=Caspase-10+is+recruited+to+and+activated+at+the+native+TRAIL+and+CD95+death-inducing+signalling+complexes+in+a+FADD-dependent+manner+but+can+not+functionally+substitute+caspase-8.">Caspase-10 is recruited to and activated at the native TRAIL and CD95 death-inducing signalling complexes in a FADD-dependent manner but can not functionally substitute caspase-8.</a> EMBO Journal. 21 (17), 4520-4530 (2002).</li><li>Neumann, L., 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=Dynamics+within+the+CD95+death-inducing+signaling+complex+decide+life+and+death+of+cells.">Dynamics within the CD95 death-inducing signaling complex decide life and death of cells.</a> Molecular Systems Biology. 6 (1), 352 (2010).</li><li>Kischkel, F. C., 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=Cytotoxicity-dependent+APO-1+(Fas/CD95)-associated+proteins+form+a+death-inducing+signaling+complex+(DISC)+with+the+receptor.">Cytotoxicity-dependent APO-1 (Fas/CD95)-associated proteins form a death-inducing signaling complex (DISC) with the receptor.</a> EMBO Journal. 14 (22), 5579-5588 (1995).</li><li>Seyrek, K., Richter, M., Lavrik, I. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Decoding+the+sweet+regulation+of+apoptosis:+the+role+of+glycosylation+and+galectins+in+apoptotic+signaling+pathways.">Decoding the sweet regulation of apoptosis: the role of glycosylation and galectins in apoptotic signaling pathways.</a> Cell Death and Differentiation. 26 (6), 981-993 (2019).</li><li>Kallenberger, S. 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The authors have no conflicts of interest to disclose.

This approach was first described by Kischkel et al.27 and has successfully been developed since then by several groups. Several important issues have to be considered for efficient DISC-immunoprecipitation and monitoring caspase-8 processing in this complex.
First, it is essential to follow all washing steps during immunoprecipitation. Especially important are the final washing steps of the sepharose beads and the drying of the sepharose beads. This must be done correc...

One of the best-studied death receptors (DRs) is CD95 (Fas, APO-1). The extrinsic apoptotic pathway starts with the interaction of the DR with its cognate ligand, i.e., CD95L interacts with CD95 or TRAIL binds to TRAIL-Rs. This results in the formation of the DISC at the corresponding DR. DISC consists of CD95, FADD, procaspase-8/-10, and c-FLIP proteins1,2. Furthermore, the DISC is assembled by interactions between death domain (DD)-containing proteins, such as CD95 and FADD, and DED-containing proteins such as FADD, procaspase-8/-10, and c-FLIP (Figure 1). Procaspase-8 undergoes oligomerization via association of its DEDs, resulting in the formation of DED filaments, followed by procaspase-8 activation and processing. This triggers a caspase cascade, which leads to cell death (Figure 1)3,4. Thus, procaspase-8 is a central initiator caspase of the extrinsic apoptosis pathway mediated by CD95 or the TRAIL-Rs, activated at the corresponding macromolecular platform, DISC.
Two isoforms of procaspase-8, namely procaspase-8a (p55) and -8b (p53), are known to be recruited to the DISC5. Both isoforms comprise two DEDs. DED1 and DED2 are located at the N-terminal part of procaspase-8a/b followed by the catalytic p18 and p10 domains. Detailed cryo-electron microscopy (cryo-EM) analysis of procaspase-8 DEDs revealed the assembly of procaspase-8 proteins into filamentous structures called DED filaments4,6. Remarkably, the linear procaspase-8 chains were initially suggested to be engaged in the dimerization followed by procaspase-8 activation at the DISC. Now, it is known that those chains are only a substructure of the procaspase-8 DED filament, the latter comprising three chains assembled into a triple helix3,4,6,7.
Upon dimerization at the DED filament, conformational changes in procaspase-8a/b lead to the formation of the active center of procaspase-8 and its activation3,8. This is followed by procaspase-8 processing, which is mediated via two pathways: the first one goes via the generation of a p43/p41 cleavage product and the second one via the initial generation of a p30 cleavage product. The p43/p41 pathway is initiated by the cleavage of procaspase-8a/b at Asp374, resulting in p43/p41 and p12 cleavage products (Figure 2). Further, these fragments are auto-catalytically cleaved at Asp384 and Asp210/216, giving rise to the formation of the active caspase-8 heterotetramer, p102/p1829,10,11. In addition, it was shown that in parallel to the p43/p41 pathway of processing, procaspase-8a/b is also cleaved at Asp216, which leads to the formation of the C-terminal cleavage product p30, followed by its proteolysis to p10 and p1810 (Figure 2).
Procaspase-8a/b activation at the DED filament is strictly regulated by proteins named c-FLIPs12. The c-FLIP proteins occur in three isoforms: c-FLIPLong (c-FLIPL), c-FLIPShort (c-FLIPS), and c-FLIPRaji (c-FLIPR). All three isoforms contain two DEDs in their N-terminal region. c-FLIPL also has a C-terminal catalytically inactive caspase-like domain12,13. Both short isoforms of c-FLIP-c-FLIPS and c-FLIPR-act in an anti-apoptotic manner by disrupting DED filament formation at the DISC6,14,15. In addition, c-FLIPL can regulate caspase-8 activation in a concentration-dependent manner. This can result in both pro- and anti-apoptotic effects16,17,18. By forming the catalytically active procaspase-8/c-FLIPL heterodimer, c-FLIPL leads to the stabilization of the active center of procaspase-8 and its activation. The pro- or anti-apoptotic function of c-FLIPL is directly dependent on its amount at the DED filaments and the subsequent amount of assembled procaspase-8/c-FLIPL heterodimers19. Low or intermediate concentrations of c-FLIPL at the DISC result in sufficient amounts of procaspase-8/c-FLIPL heterodimers at the DED filament, which supports the activation of caspase-8. In contrast, increased amounts of c-FLIPL directly lead to its anti-apoptotic effects at the DISC20.
Taken together, the activation and processing of procaspase-8a/b at the DISC is a highly regulated process involving several steps. This paper discusses the measurement of procaspase-8 processing directly at the DISC as well as the analysis of the composition of this complex. This will be presented using CD95 DISC as the exemplary DR complex.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>12.5% SDS gel</td>
			<td>self made</td>
			<td></td>
			<td>for two separating gels: 
			3.28 mL distilled H2O 
			2.5 mL Tris; pH 8.8; 1.5 M 
			4.06 mL acrylamide 
			100 &#181;L 10% SDS 
			100 &#181;L 10% APS 
			7.5 &#181;L TEMED 
			 
			for two collecting gels: 
			3.1 mL distilled H2O 
			1.25 mL Tris; pH 6.8; 1.5 M 
			0.5 mL acrylamide 
			50 &#181;L 10% SDS 
			25 &#181;L 10% APS 
			7.5 &#181;L TEMED</td>
		</tr>
		<tr>
			<td>14.5 cm cell dishes</td>
			<td>Greiner</td>
			<td>639160</td>
			<td></td>
		</tr>
		<tr>
			<td>acrylamide</td>
			<td>Carl Roth</td>
			<td>A124.1</td>
			<td></td>
		</tr>
		<tr>
			<td>anti-actin Ab</td>
			<td>Sigma Aldrich</td>
			<td>A2103</td>
			<td>dilution: 1:4000 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>anti-APO-1 Ab</td>
			<td>provided in these experiments by Prof. P. Krammer or can be purchased by Enzo</td>
			<td>ALX-805-038-C100</td>
			<td>used only for immunoprecipitation</td>
		</tr>
		<tr>
			<td>anti-caspase-10 Ab</td>
			<td>Biozol</td>
			<td>MBL-M059-3</td>
			<td>dilution: 1:1000 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>anti-caspase-3 Ab</td>
			<td>cell signaling</td>
			<td>9662 S</td>
			<td>dilution: 1:2000 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>anti-caspase-8 Ab C15</td>
			<td>provided in these experiments by Prof. P. Krammer or can be purchased by ENZO</td>
			<td>ALX-804-242-C100</td>
			<td>dilution: 1:20 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>anti-CD95 Ab</td>
			<td>Santa Cruz</td>
			<td>sc-715</td>
			<td>dilution: 1:2000 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>anti-c-FLIP NF6 Ab</td>
			<td>provided in these experiments by Prof. P. Krammer or can be purchased by ENZO</td>
			<td>ALX-804-961-0100</td>
			<td>dilution: 1:10 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>anti-FADD 1C4 Ab</td>
			<td>provided in these experiments by Prof. P. Krammer or can be purchased by ENZO</td>
			<td>ADI-AAM-212-E</td>
			<td>dilution: 1:10 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>anti-PARP Ab</td>
			<td>cell signaling</td>
			<td>9542</td>
			<td>dilution: 1:1000 in PBST + 1:100 NaN3</td>
		</tr>
		<tr>
			<td>APS</td>
			<td>Carl Roth</td>
			<td>9592.3</td>
			<td></td>
		</tr>
		<tr>
			<td>&#946;-mercaptoethanol</td>
			<td>Carl Roth</td>
			<td>4227.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Bradford solution 
			Protein Assay Dye Reagent Concentrate 450ml</td>
			<td>Bio Rad</td>
			<td>500-0006</td>
			<td>used according to manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>CD95L</td>
			<td>provided in these experiments by Prof. P. Krammer or can be purchased by ENZO</td>
			<td>ALX-522-020-C005</td>
			<td></td>
		</tr>
		<tr>
			<td>chemoluminescence detector 
			Chem Doc XRS+</td>
			<td>Bio Rad</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>cOmplete Protese Inhibitor Cocktail (PIC)</td>
			<td>Sigma Aldrich</td>
			<td>11 836 145 001</td>
			<td>prepared according to manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>DPBS (10x) w/o Ca, Mg</td>
			<td>PAN Biotech</td>
			<td>P04-53500</td>
			<td>dilution 1:10 with H2O, storage in the fridge</td>
		</tr>
		<tr>
			<td>eletrophoresis buffer</td>
			<td>self made</td>
			<td></td>
			<td>10x electrophoresis buffer: 
			60.6 g Tris 
			288 g glycine 
			20 g SDS 
			ad 2 L H2O 
			1:10 dilution before usage</td>
		</tr>
		<tr>
			<td>glycine</td>
			<td>Carl Roth</td>
			<td>3908.3</td>
			<td></td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgG1 HRP</td>
			<td>SouthernBiotech</td>
			<td>1070-05</td>
			<td>dilution 1:10.000 in PBST + 5% milk</td>
		</tr>
		<tr>
			<td>Goat Anti-Mouse IgG2b</td>
			<td>SouthernBiotech</td>
			<td>1090-05</td>
			<td>dilution 1:10.000 in PBST + 5% milk</td>
		</tr>
		<tr>
			<td>Goat Anti-Rabbit IgG-HRP</td>
			<td>SouthernBiotech</td>
			<td>4030-05</td>
			<td>dilution 1:10.000 in PBST + 5% milk</td>
		</tr>
		<tr>
			<td>Interleukin-2 Human(hIL-2)</td>
			<td>Merckgroup/ Roche</td>
			<td>11011456001</td>
			<td>for activation of T cells</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Carl Roth</td>
			<td>6781.2</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Carl Roth</td>
			<td>3904.1</td>
			<td></td>
		</tr>
		<tr>
			<td>loading buffer 
			4x Laemmli Sample Buffer,10 mL</td>
			<td>Bio Rad</td>
			<td>161-0747</td>
			<td>prepared according to manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>Luminata Forte Western HRP substrate</td>
			<td>Millipore</td>
			<td>WBLUFO500</td>
			<td></td>
		</tr>
		<tr>
			<td>lysis buffer</td>
			<td>self made</td>
			<td></td>
			<td>13.3 mL Tris-HCl; pH 7.4; 1.5 M 
			27.5 mL NaCl; 5 M 
			10 mL EDTA; 2 mM 
			100 mL Triton X-100 
			add 960 mL H2O</td>
		</tr>
		<tr>
			<td>medium for adhaerent cells DMEM F12 (1:1) w stable Glutamine,&#160; 2,438 g/L</td>
			<td>PAN Biotech</td>
			<td>P04-41154</td>
			<td>adding 10% FCS, 1% Penicillin-Streptomycin and 0.0001% Puromycin to the medium</td>
		</tr>
		<tr>
			<td>medium for primary T cells</td>
			<td>gibco by Life Technologie</td>
			<td>21875034</td>
			<td>adding 10% FCS and 1% Penicillin-Streptomycin to the medium</td>
		</tr>
		<tr>
			<td>milk powder</td>
			<td>Carl Roth</td>
			<td>T145.4</td>
			<td></td>
		</tr>
		<tr>
			<td>Na2HPO4</td>
			<td>Carl Roth</td>
			<td>P030.3</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Carl Roth</td>
			<td>3957.2</td>
			<td></td>
		</tr>
		<tr>
			<td>PBST</td>
			<td>self made</td>
			<td></td>
			<td>20x PBST: 
			230 g NaCl 
			8 g KCl 
			56.8 g Na2HPO4 
			8 g KH2PO4 
			20 mL Tween-20 
			ad 2 L H2O 
			dilution 1:20 before usage</td>
		</tr>
		<tr>
			<td>PBST + 5% milk</td>
			<td>self made</td>
			<td></td>
			<td>50 g milk powder + 1 L PBST</td>
		</tr>
		<tr>
			<td>PHA</td>
			<td>Thermo Fisher Scientific</td>
			<td>R30852801</td>
			<td>for actavation of T ells</td>
		</tr>
		<tr>
			<td>Power Pac HC</td>
			<td>Bio Rad</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Precision Plus Protein Standard All Blue</td>
			<td>Bio Rad</td>
			<td>161-0373</td>
			<td>use between 3-5 &#181;L</td>
		</tr>
		<tr>
			<td>Protein A Sepharose CL-4B beads</td>
			<td>Novodirect/ Th.Geyer</td>
			<td>GE 17-0780-01</td>
			<td>affinity resin beads prepared according to manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>scraper</td>
			<td>VWR</td>
			<td>734-2602</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS</td>
			<td>Carl Roth</td>
			<td>4360.2</td>
			<td></td>
		</tr>
		<tr>
			<td>shaker</td>
			<td>Heidolph</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sodium azide</td>
			<td>Carl Roth</td>
			<td>K305.1</td>
			<td></td>
		</tr>
		<tr>
			<td>TEMED</td>
			<td>Carl Roth</td>
			<td>2367.3</td>
			<td></td>
		</tr>
		<tr>
			<td>Trans Blot Turbo mini-size transfer stacks</td>
			<td>Bio Rad</td>
			<td>170-4270</td>
			<td>used according to manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>TransBlot Turbo 5x Transfer Buffer</td>
			<td>Bio Rad</td>
			<td>10026938</td>
			<td>prepared according to manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>TransBlot Turbo Mini-size nictrocellulose membrane</td>
			<td>Bio Rad</td>
			<td>170-4270</td>
			<td>used according to manufacturer&#39;s instructions</td>
		</tr>
		<tr>
			<td>Trans-Blot-Turbo</td>
			<td>Bio Rad</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Chem Solute</td>
			<td>8,08,51,000</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Carl Roth</td>
			<td>3051.4</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween-20</td>
			<td>Pan Reac Appli Chem</td>
			<td>A4974,1000</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring composition of cd95 death-inducing signaling complex and processing of procaspase-8 in this complex

Extrinsic apoptosis is mediated by the activation of death receptors (DRs) such as CD95/Fas/APO-1 or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-receptor 1/receptor 2 (TRAIL-R1/R2). Stimulation of these receptors with their cognate ligands leads to the assembly of the death-inducing signaling complex (DISC). DISC comprises DR, the adaptor protein Fas-associated protein with death domain (FADD), procaspases-8/-10, and cellular FADD-like interleukin (IL)-1&#946;-converting enzyme-inhibitory proteins (c-FLIPs). The DISC serves as a platform for procaspase-8 processing and activation. The latter occurs via its dimerization/oligomerization in the death effector domain (DED) filaments assembled at the DISC. 
Activation of procaspase-8 is followed by its processing, which occurs in several steps. In this work, an established experimental workflow is described that allows the measurement of DISC formation and the processing of procaspase-8 in this complex. The workflow is based on immunoprecipitation techniques supported by western blot analysis. This workflow allows careful monitoring of different steps of procaspase-8 recruitment to the DISC and its processing and is highly relevant for investigating molecular mechanisms of extrinsic apoptosis.

To analyze caspase-8 recruitment to the DISC and its processing at the CD95 DISC, this paper describes a classical workflow, which combines IP of the CD95 DISC with western blot analysis. This allows the detection of several key features of caspase-8 activation at the DISC: the assembly of the caspase-8-activating macromolecular platform, recruitment of procaspase-8 to the DISC, and the processing of this initiator caspase (Figure 1 and Figure 2). This workflow ...

Watch this Scientific Journal Video about Measuring Composition of CD95 Death-Inducing Signaling Complex and Processing of Procaspase-8 in this Complex at JoVE.com

Measuring Composition of CD95 Death-Inducing Signaling Complex and Processing of Procaspase-8 in this Complex

Here, an experimental workflow is presented that enables the detection of caspase-8 processing directly at the death-inducing signaling complex (DISC) and determines the composition of this complex. This methodology has broad applications, from unraveling the molecular mechanisms of cell death pathways to the dynamic modeling of apoptosis networks.

Extrinsic apoptosis is mediated by the activation of death receptors (DRs) such as CD95/Fas/APO-1 or tumor necrosis factor-related apoptosis-inducing ...

measuring-composition-cd95-death-inducing-signaling-complex

Research

JoVE Journal

Biochemistry

2.4K Views.  Otto von Guericke University Magdeburg. Here, an experimental workflow is presented that enables the detection of caspase-8 processing directly at the death-inducing signaling complex (DISC) and determines the composition of this complex. This methodology has broad applications, from unraveling the molecular mechanisms of cell death pathways to the dynamic modeling of apoptosis networks.

Video: Measuring Composition of CD95 Death-Inducing Signaling Complex and Processing of Procaspase-8 in this Complex

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 ...

A Method for Measuring Metabolism in Sorted Subpopulations of Complex Cell Communities Using Stable Isotope Tracing

Mammalian cell types exhibit specialized metabolism, and there is ample evidence that various co-existing cell types engage in metabolic cooperation. Moreover, even cultures of a single cell type may contain cells in distinct metabolic states, such as resting or cycling cells. Methods for measuring metabolic activities of such subpopulations are valuable tools for understanding cellular metabolism. Complex cell populations are most commonly separated using a cell sorter, and subpopulations isolated by this method can be analyzed by metabolomics methods. However, a problem with this approach is that the cell sorting procedure subjects cells to stresses that may distort their metabolism.
To overcome these issues, we reasoned that the mass isotopomer distributions (MIDs) of metabolites from cells cultured with stable isotope-labeled nutrients are likely to be more stable than absolute metabolite concentrations, because MIDs are formed over longer time scales and should be less affected by short-term exposure to cell sorting conditions. Here, we describe a method based on this principle, combining cell sorting with liquid chromatography-high resolution mass spectrometry (LC-HRMS). The procedure involves analyzing three types of samples: (1) metabolite extracts obtained directly from the complex population; (2) extracts of "mock sorted" cells passed through the cell sorter instrument without gating any specific population; and (3) extracts of the actual sorted populations. The mock sorted cells are compared against direct extraction to verify that MIDs are indeed not altered by the cell sorting procedure itself, prior to analyzing the actual sorted populations. We show example results from HeLa cells sorted according to cell cycle phase, revealing changes in nucleotide metabolism.

This article describes a method for studying cellular metabolism in complex communities of multiple cell types, using a combination of stable isotope tracing, cell sorting to isolate specific cell types, and mass spectrometry.

Mammalian cell types exhibit specialized metabolism, and there is ample evidence that various co-existing cell types engage in metabolic cooperation. ...

Preparation of Giant Vesicles Encapsulating Microspheres by Centrifugation of a Water-in-oil Emulsion

The constructive biology and the synthetic biology approach to creating artificial life involve the bottom-up assembly of biological or nonbiological materials. Such approaches have received considerable attention in research on the boundary between living and nonliving matter and have been used to construct artificial cells over the past two decades. In particular, Giant Vesicles (GVs) have often been used as artificial cell membranes. In this paper, we describe the preparation of GVs encapsulating highly packed microspheres as a model of cells containing highly condensed biomolecules. The GVs were prepared by means of a simple water-in-oil emulsion centrifugation method. Specifically, a homogenizer was used to emulsify an aqueous solution containing the materials to be encapsulated and an oil containing dissolved phospholipids, and the resulting emulsion was layered carefully on the surface of another aqueous solution. The layered system was then centrifuged to generate the GVs. This powerful method was used to encapsulate materials ranging from small molecules to microspheres.

Giant vesicles containing highly packed micrometer-sized components are useful cell models. The water-in-oil emulsion centrifugation method is a simple, powerful tool for the preparation of giant vesicles with encapsulated materials.

The constructive biology and the synthetic biology approach to creating artificial life involve the bottom-up assembly of biological or nonbiological ...

Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding

G-Protein-Coupled Receptors (GPCRs) are a large family of transmembrane receptors that play critical roles in normal cellular physiology and constitute a major pharmacological target for multiple indications, including analgesia, blood pressure regulation, and the treatment of psychiatric disease. Upon ligand binding, GPCRs catalyze the activation of intracellular G-proteins by stimulating the incorporation of guanosine triphosphate (GTP). Activated G-proteins then stimulate signaling pathways that elicit cellular responses. GPCR signaling can be monitored by measuring the incorporation of a radiolabeled and non-hydrolyzable form of GTP, [35S]guanosine-5&#39;-O-(3-thio)triphosphate ([35S]GTP&#947;S), into G-proteins. Unlike other methods that assess more downstream signaling processes, [35S]GTP&#947;S binding measures a proximal event in GPCR signaling and, importantly, can distinguish agonists, antagonists, and inverse agonists. The present protocol outlines a sensitive and specific method for studying GPCR signaling using crude membrane preparations of an archetypal GPCR, the &#181;-opioid receptor (MOR1). Although alternative approaches to fractionate cells and tissues exist, many are cost-prohibitive, tedious, and/or require non-standard laboratory equipment. The present method provides a simple procedure that enriches functional crude membranes. After isolating MOR1, various pharmacological properties of its agonist, [D-Ala, N-MePhe, Gly-ol]-enkephalin (DAMGO), and antagonist, naloxone, were determined.

Guanosine triphosphate (GTP) binding is one of the earliest events in G-Protein-Coupled Receptor (GPCR) activation. This protocol describes how to pharmacologically characterize specific GPCR-ligand interactions by monitoring the binding of the radio-labeled GTP analog, [35S]guanosine-5&#39;-O-(3-thio)triphosphate ([35S]GTP&#947;S), in response to a ligand of interest.

G-Protein-Coupled Receptors (GPCRs) are a large family of transmembrane receptors that play critical roles in normal cellular physiology and constitute a ...

A Modified Yeast-one Hybrid System for Heteromeric Protein Complex-DNA Interaction Studies

Over the years, the yeast one-hybrid assay has proven to be an important technique for the identification and validation of physical interactions between proteins such as transcription factors (TFs) and their DNA target. The method presented here utilizes the underlying concept of the Y1H but is modified further to study and validate protein complexes binding to their target DNA. Hence, it is referred to as the modified yeast one-hybrid (Y1.5H) assay. This assay is cost effective and can be easily performed in a regular laboratory setting. Albeit using a heterologous system, the described method could be a valuable tool to test and validate the heteromeric protein complex binding to their DNA target(s) for functional genomics in any system of study, especially plant genomics.

The modified yeast one-hybrid assay described here is an extension of the classical yeast one-hybrid (Y1H) assay to study and validate the heteromeric protein complex-DNA interaction in a heterologous system for any functional genomics study.

Over the years, the yeast one-hybrid assay has proven to be an important technique for the identification and validation of physical interactions between ...

Biochemical and Structural Characterization of the Carbohydrate Transport Substrate-binding-protein SP0092

Development of new antimicrobials and vaccines for Streptococcus pneumoniae (pneumococcus) are necessary to halt the rapid rise in multiple resistant strains. Carbohydrate substrate binding proteins (SBPs) represent viable targets for the development of protein-based vaccines and new antimicrobials because of their extracellular localization and the centrality of carbohydrate import for pneumococcal metabolism, respectively. Described here is a rationalized integrated protocol to carry out a comprehensive characterization of SP0092, which can be extended to other carbohydrate SBPs from the pneumococcus and other bacteria. This procedure can aid the structure-based design of inhibitors for this class of proteins. Presented in the first part of this manuscript are protocols for biochemical analysis by thermal shift assay, multi angle light scattering (MALS), and size exclusion chromatography (SEC), which optimize the stability and homogeneity of the sample directed to crystallization trials and so enhance the probability of success. The second part of this procedure describes the characterization of the SBP crystals using a tunable wavelength anomalous diffraction synchrotron beamline, and data collection protocols for measuring data that can be used to resolve the crystallized protein structure.

A streamlined protocol for performing an extensive biochemical and structural characterization of a carbohydrate substrate binding protein from Streptococcus pneumoniae is presented.

Development of new antimicrobials and vaccines for Streptococcus pneumoniae (pneumococcus) are necessary to halt the rapid rise in multiple resistant ...

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 ...

Strategic Screening and Characterization of the Visual GPCR-mini-G Protein Signaling Complex for Successful Crystallization

The key to determining crystal structures of membrane protein complexes is the quality of the sample prior to crystallization. In particular, the choice of detergent is critical, because it affects both the stability and monodispersity of the complex. We recently determined the crystal structure of an active state of bovine rhodopsin coupled to an engineered G protein, mini-Go, at 3.1 &#197; resolution. Here, we detail the procedure for optimizing the preparation of the rhodopsin&#8211;mini-Go complex. Dark-state rhodopsin was prepared in classical and neopentyl glycol (NPG) detergents, followed by complex formation with mini-Go under light exposure. The stability of the rhodopsin was assessed by ultraviolet-visible (UV-VIS) spectroscopy, which monitors the reconstitution into rhodopsin of the light-sensitive ligand, 9-cis retinal. Automated size-exclusion chromatography (SEC) was used to characterize the monodispersity of rhodopsin and the rhodopsin&#8211;mini-Go complex. SDS-polyacrylamide electrophoresis (SDS-PAGE) confirmed the formation of the complex by identifying a 1:1 molar ratio between rhodopsin and mini-Go after staining the gel with Coomassie blue. After cross-validating all this analytical data, we eliminated unsuitable detergents and continued with the best candidate detergent for large-scale preparation and crystallization. An additional problem arose from the heterogeneity of N-glycosylation. Heterologously-expressed rhodopsin was observed on SDS-PAGE to have two different N-glycosylated populations, which would probably have hindered crystallogenesis. Therefore, different deglycosylation enzymes were tested, and endoglycosidase F1 (EndoF1) produced rhodopsin with a single species of N-glycosylation. With this strategic pipeline for characterizing protein quality, preparation of the rhodopsin&#8211;mini-Go complex was optimized to deliver the crystal structure. This was only the third crystal structure of a GPCR&#8211;G protein signaling complex. This approach can also be generalized for other membrane proteins and their complexes to facilitate sample preparation and structure determination.

This report describes screening of different detergents for preparing the visual GPCR, rhodopsin, and its complex with mini-Go. Biochemical methods characterizing the quality of the complex at different stages during purification are demonstrated. This protocol can be generalized to other membrane protein complexes for their future structural studies.

The key to determining crystal structures of membrane protein complexes is the quality of the sample prior to crystallization. In particular, the choice ...

Crystallization and Structural Determination of an Enzyme:Substrate Complex by Serial Crystallography in a Versatile Microfluidic Chip

The preparation of well diffracting crystals and their handling before their X-ray analysis are two critical steps of biocrystallographic studies. We describe a versatile microfluidic chip that enables the production of crystals by the efficient method of counter-diffusion. The convection-free environment provided by the microfluidic channels is ideal for crystal growth and useful to diffuse a substrate into the active site of the crystalline enzyme. Here we applied this approach to the CCA-adding enzyme of the psychrophilic bacterium Planococcus halocryophilus in the presented example. After crystallization and substrate diffusion/soaking, the crystal structure of the enzyme:substrate complex was determined at room temperature by serial crystallography and the analysis of multiple crystals directly inside the chip. The whole procedure preserves the genuine diffraction properties of the samples because it requires no crystal handling.

A versatile microfluidic device is described that enables the crystallization of an enzyme using the counter-diffusion method, the introduction of a substrate in the crystals by soaking, and the 3D structure determination of the enzyme:substrate complex by a serial analysis of crystals inside the chip at room temperature.

The preparation of well diffracting crystals and their handling before their X-ray analysis are two critical steps of biocrystallographic studies. We ...

Complementation of Splicing Activity by a Galectin-3 - U1 snRNP Complex on Beads

Classic depletion-reconstitution experiments indicate that galectin-3 is a required splicing factor in nuclear extracts. The mechanism of incorporation of galectin-3 into the splicing pathway is addressed in this paper. Sedimentation of HeLa cell nuclear extracts on 12%-32% glycerol gradients yields fractions enriched in an endogenous ~10S particle that contains galectin-3 and U1 snRNP. We now describe a protocol to deplete nuclear extracts of U1 snRNP with concomitant loss of splicing activity. Splicing activity in the U1-depleted extract can be reconstituted by the galectin-3 - U1 snRNP particle trapped on agarose beads covalently coupled with anti-galectin-3 antibodies. The results indicate that the galectin-3 - U1 snRNP - pre-mRNA ternary complex is a functional E complex leading to intermediates and products of the splicing reaction and that galectin-3 enters the splicing pathway through its association with U1 snRNP. The scheme of using complexes affinity- or immuno-selected on beads to reconstitute splicing activity in extracts depleted of a specific splicing factor may be generally applicable to other systems.

This article describes the experimental procedures for (a) depletion of U1 snRNP from nuclear extracts, with concomitant loss of splicing activity; and (b) reconstitution of splicing activity in the U1-depleted extract by galectin-3 - U1 snRNP particles bound to beads covalently coupled with anti-galectin-3 antibodies.

Classic depletion-reconstitution experiments indicate that galectin-3 is a required splicing factor in nuclear extracts. The mechanism of incorporation of ...