The ubiquitin variant technology was devised in the laboratory of Dr. Sachdev Sidhu (University of Toronto). WZ is currently a CIFAR Azrieli Global Scholar in the Humans &#38; The Microbiome Program. This research was funded by NSERC Discovery Grants awarded to WZ (RGPIN-2019-05721).

1. Reagent preparation
<ol>
	<li>PBS (phosphate buffered saline): Mix 50 mL of 10x PBS solution with 450 mL of ultrapure H2O. Sterilize by filtration and store at 4 &#176;C or room temperature (~20-25 &#176;C).</li>
	<li>10% BSA (bovine serum albumin): Slowly add 1 g of BSA to 7 mL of ultrapure H2O and mix until fully dissolved (no clumps). Top up with ultrapure H2O until the final volume is 10 mL. Sterilize by filtration and store at 4 &#176;C.</li>
	<li>PB buffer (PBS supplemented wit...

<ol>
	<li>Karlsson, O. A., 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=Design+of+a+PDZbody,+a+bivalent+binder+of+the+E6+protein+from+human+papillomavirus.">Design of a PDZbody, a bivalent binder of the E6 protein from human papillomavirus.</a> Scientific Reports. 5 (1), 9382 (2015).</li><li>Veggiani, G., 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=Engineered+SH2+domains+with+tailored+specificities+and+enhanced+affinities+for+phosphoproteome+analysis.">Engineered SH2 domains with tailored specificities and enhanced affinities for phosphoproteome analysis.</a> Protein Science. 28 (2), 403-413 (2019).</li><li>Kaneko, 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=Superbinder+SH2+domains+act+as+antagonists+of+cell+signaling.">Superbinder SH2 domains act as antagonists of cell signaling.</a> Science Signaling. 5 (243), (2012).</li><li>Wiechmann, S., 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+inhibition+of+the+small+ubiquitin-like+modifier+(SUMO)-conjugating+enzyme+Ubc9+selectively+impairs+SUMO+chain+formation.">Site-specific inhibition of the small ubiquitin-like modifier (SUMO)-conjugating enzyme Ubc9 selectively impairs SUMO chain formation.</a> Journal of Biological Chemistry. 292 (37), 15340-15351 (2017).</li><li>Ernst, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+strategy+for+modulation+of+enzymes+in+the+ubiquitin+system.">A strategy for modulation of enzymes in the ubiquitin system.</a> Science. 339 (6119), 590-595 (2013).</li><li>Zhang, 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=Potent+and+selective+inhibition+of+pathogenic+viruses+by+engineered+ubiquitin+variants.">Potent and selective inhibition of pathogenic viruses by engineered ubiquitin variants.</a> PLOS Pathogens. 13 (5), 1006372 (2017).</li><li>Zhang, 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=System-wide+modulation+of+HECT+E3+ligases+with+selective+ubiquitin+variant+probes.">System-wide modulation of HECT E3 ligases with selective ubiquitin variant probes.</a> Molecular Cell. 62 (1), 121-136 (2016).</li><li>Gabrielsen, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+general+strategy+for+discovery+of+inhibitors+and+activators+of+RING+and+U-box+E3+ligases+with+ubiquitin+variants.">A general strategy for discovery of inhibitors and activators of RING and U-box E3 ligases with ubiquitin variants.</a> Molecular Cell. 68 (2), 456-470 (2017).</li><li>Brown, N. G., 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=Dual+RING+E3+architectures+regulate+multiubiquitination+and+ubiquitin+chain+elongation+by+APC/C.">Dual RING E3 architectures regulate multiubiquitination and ubiquitin chain elongation by APC/C.</a> Cell. 165 (6), 1440-1453 (2016).</li><li>Gorelik, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+SCF+ubiquitin+ligases+by+engineered+ubiquitin+variants+that+target+the+Cul1+binding+site+on+the+Skp1-F-box+interface.">Inhibition of SCF ubiquitin ligases by engineered ubiquitin variants that target the Cul1 binding site on the Skp1-F-box interface.</a> Proceedings of the National Academy of Sciences. 113 (13), 3527-3532 (2016).</li><li>Goldring, J. P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+quantification+methods+to+determine+protein+concentration+prior+to+electrophoresis.">Protein quantification methods to determine protein concentration prior to electrophoresis.</a> Protein Electrophoresis. 869, 29-35 (2012).</li><li>Zhang, W., Sidhu, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generating+intracellular+modulators+of+E3+ligases+and+deubiquitinases+from+phage-displayed+ubiquitin+variant+libraries.">Generating intracellular modulators of E3 ligases and deubiquitinases from phage-displayed ubiquitin variant libraries.</a> The Ubiquitin Proteasome System: Methods and Protocols. 1844, 101-119 (2018).</li><li>Sheehan, J., Marasco, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phage+and+yeast+display.">Phage and yeast display.</a> Microbiology Spectrum. 3 (1), 1-17 (2015).</li><li>Lowman, H. B., Wells, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monovalent+phage+display:+A+method+for+selecting+variant+proteins+from+random+libraries.">Monovalent phage display: A method for selecting variant proteins from random libraries.</a> Methods. 3 (3), 205-216 (1991).</li><li>Lowman, H. B., Bass, S. H., Simpson, N., Wells, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selecting+high-affinity+binding+proteins+by+monovalent+phage+display.">Selecting high-affinity binding proteins by monovalent phage display.</a> Biochemistry. 30 (45), 1-7 (1991).</li><li>Beaber, J. W., Tam, E. M., Lao, L. S., Rondon, I. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+helper+phage+for+improved+monovalent+display+of+Fab+molecules.">A new helper phage for improved monovalent display of Fab molecules.</a> Journal of Immunological Methods. 376 (1-2), 46-54 (2012).</li><li>Gal&#225;n, A., 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=Library-based+display+technologies:+where+do+we+stand.">Library-based display technologies: where do we stand.</a> Molecular BioSystems. 12 (8), 2342-2358 (2016).</li><li>Huang, S., 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=Ribosome+display+and+selection+of+single-chain+variable+fragments+effectively+inhibit+growth+and+progression+of+microspheres+in+vitro+and+in+vivo.">Ribosome display and selection of single-chain variable fragments effectively inhibit growth and progression of microspheres in vitro and in vivo.</a> Cancer Science. 109 (5), 1503-1512 (2018).</li><li>Yamaguchi, 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=cDNA+display:+a+novel+screening+method+for+functional+disulfide-rich+peptides+by+solid-phase+synthesis+and+stabilization+of+mRNA-protein+fusions.">cDNA display: a novel screening method for functional disulfide-rich peptides by solid-phase synthesis and stabilization of mRNA-protein fusions.</a> Nucleic Acids Research. 37 (16), 1-13 (2009).</li><li>Mochizuki, Y., Kumachi, S., Nishigaki, K., Nemoto, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increasing+the+library+size+in+cDNA+display+by+optimizing+purification+procedures.">Increasing the library size in cDNA display by optimizing purification procedures.</a> Biological Procedures Online. 15 (1), 1-5 (2013).</li><li>Odegrip, 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=CIS+display:+In+vitro+selection+of+peptides+from+libraries+of+protein-DNA+complexes.">CIS display: In vitro selection of peptides from libraries of protein-DNA complexes.</a> Proceedings of the National Academy of Sciences. 101 (9), 2806-2810 (2004).</li><li>Reiersen, H., 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=Covalent+antibody+display--an+in+vitro+antibody-DNA+library+selection+system.">Covalent antibody display--an in vitro antibody-DNA library selection system.</a> Nucleic Acids Research. 33 (1), 1-9 (2005).</li><li>Houlihan, G., Gatti-Lafranconi, P., Lowe, D., Hollfelder, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directed+evolution+of+anti-HER2+DARPins+by+SNAP+display+reveals+stability/function+trade-offs+in+the+selection+process.">Directed evolution of anti-HER2 DARPins by SNAP display reveals stability/function trade-offs in the selection process.</a> Protein Engineering Design and Selection. 28 (9), 269-279 (2015).</li><li>Zhang, 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=Generation+and+validation+of+intracellular+ubiquitin+variant+inhibitors+for+USP7+and+USP10.">Generation and validation of intracellular ubiquitin variant inhibitors for USP7 and USP10.</a> Journal of Molecular Biology. 429 (22), 3546-3560 (2017).</li><li>Teyra, 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=Structural+and+functional+characterization+of+ubiquitin+variant+inhibitors+of+USP15.">Structural and functional characterization of ubiquitin variant inhibitors of USP15.</a> Structure. 27 (4), 590-605 (2019).</li></ol>

As mentioned in step 2.1 (protein preparation), a variety of methods can be used to assess the protein concentration, and each will have unique benefits and drawbacks based on the specific target protein used for phage display. A source of detailed descriptions and protocols for popular methods has been provided previously11.
Using the phage retained by a previous round of phage display as the input for a subsequent round enriches the good binders by gradually removing ...

Understanding the molecular details of protein-protein interactions is critical for delineating the signal transduction mechanisms of biological processes, particularly those that contribute to clinically important diseases. In recent years, phage display has been utilized as a practical and accessible method to isolate proteins/peptides with much improved binding to a desired target protein1,2,3,4, which in turn can be used as intracellular probes of protein-protein interactions.
Ubiquitination is a cascade of enzymatic activities (E1 activating enzyme &#8594; E2 conjugating enzyme &#8594; E3 ligases) that covalently conjugate ubiquitin (Ub) to protein substrates to target them for degradation or to mediate cell signaling changes. In addition, deubiquitinases catalyze the removal of ubiquitin from proteins. Therefore, in cells, there are thousands of Ub-dependent protein-protein interactions, the vast majority of which recognize a common surface with low affinity but high specificity to allow weak interactions through large and diverse surfaces.
Ernst et al. introduced mutations into known binding regions of Ub in order to see if they could enhance binding affinity for a protein of interest while still maintaining high selectivity5. A combinatorial library of over 10 billion (7.5 x 1010) Ub variants (UbVs) with mutations at positions across the Ub surface that mediate the known Ub-protein interactions was developed. This library consisted of phagemids that express the M13 bacteriophage pIII coat protein fused to diversified UbVs. Therefore, individual UbVs can be displayed on the phage surface via the coat protein upon expression. During the selection process, phage that display UbVs with considerable binding interactions with the target protein will be retained and enriched in subsequent rounds of phage display, whereas phage displaying UbVs that bind poorly to the target protein are washed away and removed from the phage pool. The retained phage particles contain the phagemid corresponding to their displayed UbV, allowing them to be sequenced and further characterized once isolated.
Using this protein engineering strategy, UbV inhibitors were developed for human deubiquitinases5 and viral proteases6. Importantly, we have generated inhibitory UbVs for human HECT-family E3 ligases through hijacking the E2-binding site and activating UbVs that occupy a Ub-binding exosite on the HECT domain7. We can also inhibit monomeric RING-family E3s by targeting the E2 binding site and induce UbV dimerization to activate homodimeric RING E3s8. For multi-subunit RING E3s, UbVs can achieve inhibition by targeting the RING subunit (e.g., for APC/C complex9) or disrupting complex formation (e.g., for SCF E3s10). Collectively, UbVs can be leveraged to systematically interrogate protein-protein interactions in the Ub-proteasome system (UPS) so that we can better decipher biochemical mechanisms of UPS enzymes and to identify and validate functional sites for therapeutic intervention.
The following protocol describes how to employ a previously generated phage displayed UbV library to target a protein of interest and how to enrich the UbV binders that interact with the target protein through successive rounds of phage display.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Axygen Mini Tube System (0.65 mL, sterile, 96/Rack, 10 Racks/pack)</td>
			<td>Fisher Scientific</td>
			<td>14-222-198</td>
			<td>Culturing phage outputs after phage display.</td>
		</tr>
		<tr>
			<td>BD Difco Dehydrated Culture Media: LB Broth, Miller (Luria-Bertani)</td>
			<td>Fisher Scientific</td>
			<td>DF0446-17-3</td>
			<td>Preparing plates for titering.</td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA), Fraction V</td>
			<td>BioShop Canada</td>
			<td>ALB001</td>
			<td>Buffer component.</td>
		</tr>
		<tr>
			<td>Carbenicillin disodium salt 89.0-100.5% anhydrous</td>
			<td>Millipore-Sigma</td>
			<td>C1389-5G</td>
			<td>Culturing phagemid-infected cells.</td>
		</tr>
		<tr>
			<td>Compact Digital Microplate Shaker</td>
			<td>Fisher Scientific</td>
			<td>11-676-337</td>
			<td>Shaking plates during incubation with the phage library.</td>
		</tr>
		<tr>
			<td>Corning Microplate Aluminum Sealing Tape</td>
			<td>Fisher Scientific</td>
			<td>07-200-684</td>
			<td>Sealing phage glycerol stocks.</td>
		</tr>
		<tr>
			<td>Dehydrated Agar</td>
			<td>Fisher Scientific</td>
			<td>DF0140-01-0</td>
			<td>Preparing plates for titering.</td>
		</tr>
		<tr>
			<td>DS-11 Spectrophotometer/Fluorometer</td>
			<td>DeNovix</td>
			<td>DS-11 FX+</td>
			<td>Protein concentration measurement.</td>
		</tr>
		<tr>
			<td>Greiner Bio-One CellStar 96-Well, Non-Treated, U-Shaped-Bottom Microplate</td>
			<td>Fisher Scientific</td>
			<td>7000133</td>
			<td>Storing phage glycerol stocks.</td>
		</tr>
		<tr>
			<td>Hydrochloric Acid</td>
			<td>Fisher Scientific</td>
			<td>A144-500</td>
			<td>Phage elution.</td>
		</tr>
		<tr>
			<td>Invitrogen One Shot OmniMAX 2 T1R Chemically Competent E. coli</td>
			<td>Fisher Scientific</td>
			<td>C854003</td>
			<td>Bacterial strain for phage infection.</td>
		</tr>
		<tr>
			<td>Kanamycin Sulfate</td>
			<td>Fisher Scientific</td>
			<td>AAJ1792406</td>
			<td>Culturing M13K07 helper phage-infected cells.</td>
		</tr>
		<tr>
			<td>M13KO7 Helper Phage</td>
			<td>New England Biolabs</td>
			<td>&#160;N0315S</td>
			<td>Permit phagemid packing and secretion.</td>
		</tr>
		<tr>
			<td>MaxQ 4000 Benchtop Orbital Shaker</td>
			<td>Fisher Scientific</td>
			<td>11-676-076</td>
			<td>Bacterial cell culture.</td>
		</tr>
		<tr>
			<td>Nunc MaxiSorp 96 well microplate, flat bottom</td>
			<td>Life Technologies</td>
			<td>44-2404-21</td>
			<td>Immobilizing proteins.</td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (PBS) 10X Solution</td>
			<td>Fisher Scientific</td>
			<td>BP3994</td>
			<td>Buffer component/phage resuspension medium.</td>
		</tr>
		<tr>
			<td>Polyester Films for ELISA and Incubation</td>
			<td>VWR</td>
			<td>60941-120</td>
			<td>Covering the microplates during incubation.</td>
		</tr>
		<tr>
			<td>Polyethylene Glycol 8000 (PEG)</td>
			<td>Fisher Scientific</td>
			<td>BP233-1</td>
			<td>Phage precipitation.</td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Millipore-Sigma</td>
			<td>S3014</td>
			<td>Phage precipitation.</td>
		</tr>
		<tr>
			<td>Sterile Plastic Culture Tubes: Translucent Polypropylene</td>
			<td>Fisher Scientific</td>
			<td>14-956-1D</td>
			<td>Culturing phage inputs.</td>
		</tr>
		<tr>
			<td>Tetracycline Hydrochloride</td>
			<td>Fisher Scientific</td>
			<td>BP912-100</td>
			<td>Culturing E. coli OmniMax cells.</td>
		</tr>
		<tr>
			<td>Tris Base</td>
			<td>Fisher Scientific</td>
			<td>BP1525</td>
			<td>Neutralizing eluted phage solution.</td>
		</tr>
		<tr>
			<td>Tryptone Powder</td>
			<td>Fisher Scientific</td>
			<td>BP1421-2</td>
			<td>Cell growth media component.</td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Fisher Scientific</td>
			<td>BP337500</td>
			<td>Buffer component.</td>
		</tr>
		<tr>
			<td>Yeast Extract</td>
			<td>Fisher Scientific</td>
			<td>BP1422-2</td>
			<td>Cell growth media component.</td>
		</tr>
	</tbody>
</table>

using phage display to develop ubiquitin variant modulators for e3 ligases

Ubiquitin is a small 8.6 kDa protein that is a core component of the ubiquitin-proteasome system. Consequently, it can bind to a diverse array of proteins with high specificity but low affinity. Through phage display, ubiquitin variants (UbVs) can be engineered such that they exhibit improved affinity over wildtype ubiquitin and maintain binding specificity to target proteins. Phage display utilizes a phagemid library, whereby the pIII coat protein of a filamentous M13 bacteriophage (chosen because it is displayed externally on the phage surface) is fused with UbVs. Specific residues of human wildtype ubiquitin are soft and randomized (i.e., there is a bias towards to native wildtype sequence) to generate UbVs so that deleterious changes in protein conformation are avoided while introducing the diversity necessary for promoting novel interactions with the target protein. During the phage display process, these UbVs are expressed and displayed on phage coat proteins and panned against a protein of interest. UbVs that exhibit favorable binding interactions with the target protein are retained, whereas poor binders are washed away and removed from the library pool. The retained UbVs, which are attached to the phage particle containing the UbV's corresponding phagemid, are eluted, amplified, and concentrated so that they can be panned against the same target protein in another round of phage display. Typically, up to five rounds of phage display are performed, during which a strong selection pressure is imposed against UbVs that bind weakly and/or promiscuously so that those with higher affinities are concentrated and enriched. Ultimately, UbVs that demonstrate higher specificity and/or affinity for the target protein than their wildtype counterparts are isolated and can be characterized through further experiments.

Binders produced from phage display can be verified and analyzed in many ways. It is recommended to first proceed with sequencing the phage with primers that flank the diversified insert in the phagemid library. An ideal phage display experiment will show a clear bias towards several sequences (Figure 1). Other sequences will also be present but with a lower count, appearing more as background noise. In the example provided, where phage display was performed between ubiquitin variants (UbVs)...

Watch this Scientific Journal Video about Using Phage Display to Develop Ubiquitin Variant Modulators for E3 Ligases at JoVE.com

Using Phage Display to Develop Ubiquitin Variant Modulators for E3 Ligases

Ubiquitination is a critical protein post-translational modification, dysregulation of which has been implicated in numerous human diseases. This protocol details how phage display can be utilized to isolate novel ubiquitin variants that can bind and modulate the activity of E3 ligases that control the specificity, efficiency, and patterns of ubiquitination.

Ubiquitin is a small 8.6 kDa protein that is a core component of the ubiquitin-proteasome system. Consequently, it can bind to a diverse array of proteins ...

Phage display not only helps us investigate the binding characteristics of clinically important enzymes, but also develop modulators for those enzymes and the corresponding diseases. Phage display can be used to develop novel binders for a wide array of target proteins and is also easier to perform than other conventional display methods. This procedure involved a lot of repetitive action, so the key is to not autopilot and to remain focused throughout.Begin by inoculating 30 milliliters of 2YT tetracycline broth with 200 microliters of the seed culture. Incubate it for approximately three hours at 37 degrees Celsius with 200 RPM orbital shaking until the bacteria are in the mid-log phase. Discard the coating solution from the plate into a sink.Dry it gently with paper towels. Then add 200 microliters of PB buffer to each coated well. Discard the PB buffer from the plate and dry it on paper towels.Add another 200 microliters of PB buffer to each coated well of the plate. Incubate it at room temperature for an hour with 300 RPM orbital shaking. Thaw the phage library on ice, then dilute it to 100X the library diversity in PBS.Add the polyethylene glycol sodium chloride solution at one-fifth of the diluted library volume and incubate the solution on ice for 30 minutes. Next, centrifuge the solution at 11, 000 times G for 30 minutes at four degrees Celsius. Discard the supernatant and centrifuge it for another two minutes to pull down the remaining supernatant and concentrate the phage pellet.Gently resuspend the phage pellet in one milliliter of PBT buffer per target protein to be analyzed, typically four in total. Add 100 microliters of phage library to each coated well in the control plate. Incubate it at room temperature for an hour with 300 RPM orbital shaking.Discard the PB buffer from the target plate into the sink and dry the plate on paper towels. Transfer all 100 microliters of the phage library in the control plate to each coated well of the target plate. Incubate it at room temperature for an hour with 300 RPM orbital shaking.Next, remove the phage library from the plate and wash the coated wells four times with PT buffer. Invert the plate and tap on a paper towel to remove the last drops of buffer. Add 100 microliters of 0.1 molar hydrochloric acid to each coated well to elute the phage.Incubate the plate at room temperature for five minutes with 300 RPM orbital shaking. After that, neutralize the pH by adding 12.5 microliters of pH 11 one molar tris hydrochloride to each coated well. Transfer the eluted phage from all eight wells into a single 1.5 milliliter microcentrifuge tube.Pipette up and down during the transfer to make solutions homogenous and aspirate all liquid from the wells. Add 10%BSA to the eluted phage to make the final concentration 1%Store the microcentrifuge tube at four degrees Celsius. This is the round one output.Prepare a seed culture for culturing the phage input for the next round of selection by inoculating five milliliters of 2YT tetracycline seed culture with an isolated E.coli colony from an agar plate. Incubate it overnight at 37 degrees Celsius with 200 RPM orbital shaking. Dilute the target protein in the rounds two and three tube with an appropriate amount of PBS.Take half of the contents of rounds two and three tube and coat four wells per target protein in a 96-well binding plate for the next round. Next, use half of the round one output to inoculate three milliliters of mid-log phase cells. Incubate it at 37 degree Celsius for 30 minutes with 200 RPM orbital shaking.Add M13KO7 helper phage to a final concentration of 10 billion PFU per milliliter. Incubate it again at 37 degrees Celsius for an hour with 200 RPM orbital shaking. After an hour, transfer the entire three milliliters of culture to 30 milliliters of 2YT carbenicillin kanamycin solution.Grow overnight at 37 degrees Celsius with 200 RPM orbital shaking. The representative results for a ubiquitin variant selection against UBE4B are shown here. UBVs were ordered from the highest to lowest frequency.Sequences represent the diversified ubiquitin region in the UBV with all the randomized residues. The relative binding affinity of the binders to the wild type target protein, mutated target protein, as well as off-target proteins is measured by enzyme-linked immunosorbent assays or ELISA. All ELISA absorbances were normalized against 96 averaged BSA ELISA scores and 96 averaged GST ELISA scores.Darker green represents the stronger relative binding. GST was included as a control for nonspecific binding because the target protein is GST tagged. The ELISA results are graphically presented here.The x-axis represents the UBVs and the y-axis represents the corresponding normalized absorbance. When attempting this procedure, it's important that you don't discard the solution in the plate after you add the hydrochloric acid. The phages are now suspended in solution and you want to keep these so that you can perform subsequent enrichment final analyses or both.Following this procedure, sequencing should be done to determine UBV frequencies. ELISAs and IC50 assays can be done to determine binding efficacies and inhibitory efficacies respectively and also to help determine which UBVs to further characterize.

using-phage-display-to-develop-ubiquitin-variant-modulators-for-e3

Research

JoVE Journal

Biochemistry

2.9K ビュー.  University of Guelph. ファージディスプレイは、臨床的に重要な酵素の結合特性を調べるだけでなく、それらの酵素および対応する疾患のモジュレーターを開発するのに役立ちます。ファージディスプレイは、幅広い標的タンパク質の新規結合剤を開発するために使用することができ、また他の従来の表示方法よりも容易に実行できます。この手順には多くの繰り返しアクションが含まれる?...

ビデオ: Using Phage Display to Develop Ubiquitin Variant Modulators for E3 Ligases

Ubiquitination is a critical protein post-translational modification, dysregulation of which has been implicated in numerous human diseases. This protocol details how phage display can be utilized to isolate novel ubiquitin variants that can bind and modulate the activity of E3 ligases that control the specificity, efficiency, and patterns of...

using phage display to select proteins with high affinity to a target protein

In this video, we demonstrate the phage display technique to isolate pre-engineered phages expressing proteins with high affinity to the target...

Using Phage Display to Select Proteins with High Affinity to a Target Protein

functional characterization of ring-type e3 ubiquitin ligases in vitro and in planta

Functional Characterization of RING-Type E3 Ubiquitin Ligases In Vitro and In Planta

The goal of this manuscript is to present an outline for the comprehensive biochemical and functional studies of the RING-type E3 ubiquitin ligases. This multistep pipeline, with detailed protocols, validates an enzymatic activity of the tested protein and demonstrates how to link the activity to...

in vitro analysis of e3 ubiquitin ligase function

In Vitro Analysis of E3 Ubiquitin Ligase Function

The present study provides detailed in vitro ubiquitylation assay protocols for the analysis of E3 ubiquitin ligase catalytic activity. Recombinant proteins were expressed using prokaryotic systems such as Escherichia coli...

In Vitro Analysis of E3 Ubiquitin Ligase Function

Gently re-suspend the phage pellet in one milliliter of PBT buffer per target protein to be analyzed, typically, four in total. Add 100 microliters of phage library to each coated well in the control plate. Incubate it at room temperature for an hour with 300 RPM orbital...

a protocol for phage display and affinity selection using recombinant protein baits

A Protocol for Phage Display and Affinity Selection Using Recombinant Protein Baits

Phage display is a powerful technique to capture proteins or protein moieties that interact with an immobilized molecule of interest. Once a decision of the type of phage cDNA library to create and screen has been made, the protocol described here permits efficient affinity selection leading to identification of...

evaluation of substrate ubiquitylation by e3 ubiquitin-ligase in mammalian cell lysates

Evaluation of Substrate Ubiquitylation by E3 Ubiquitin-ligase in Mammalian Cell Lysates

We provide a detailed protocol for a ubiquitylation assay of a specific substrate and an E3 ubiquitin-ligase in mammalian cells. HEK293T cell lines were used for protein overexpression, the polyubiquitylated substrate was purified from cell lysates by immunoprecipitation, and resolved in SDS-PAGE. Immunoblotting was used to visualize this post-translational modification.

chemical inactivation of the e3 ubiquitin ligase cereblon by pomalidomide-based homo-protacs

Chemical Inactivation of the E3 Ubiquitin Ligase Cereblon by Pomalidomide-based Homo-PROTACs

This work describes the synthesis and characterization of a pomalidomide-based, bifunctional homo-PROTAC as a novel approach to induce ubiquitination and degradation of the E3 ubiquitin ligase cereblon (CRBN), the target of thalidomide...

comprehensive workflow for the genome-wide identification and expression meta-analysis of the atl e3 ubiquitin ligase gene family in grapevine

Comprehensive Workflow for the Genome-wide Identification and Expression Meta-analysis of the ATL E3 Ubiquitin Ligase Gene Family in Grapevine

This article describes the procedure for the identification and characterization of a gene family in grapevine applied to the family of Arabidopsis T&#243;xicos in Levadura (ATL) E3 ubiquitin...

screening and identification of small peptides targeting fibroblast growth factor receptor2 using a phage display peptide library

Screening and Identification of Small Peptides Targeting Fibroblast Growth Factor Receptor2 using a Phage Display Peptide Library

Herein, we present a detailed protocol for screening small peptides that bind to FGFR2 using a phage display peptide library. We further analyze the affinity of the selected peptides toward FGFR2 in vitro and its ability to suppress cell...

interactome-seq: a protocol for domainome library construction, validation and selection by phage display and next generation sequencing

Interactome-Seq: A Protocol for Domainome Library Construction, Validation and Selection by Phage Display and Next Generation Sequencing

The protocols described allow the construction, characterization and selection (against the target of choice) of a &#34;domainome&#34; library made from any DNA source. This is achieved by a research pipeline that combines different technologies: phage display, a folding reporter and next generation sequencing with a web tool for data...

in vitro sumoylation assay to study sumo e3 ligase activity

In Vitro SUMOylation Assay to Study SUMO E3 Ligase Activity

Unlike ubiquitin ligases, few E3 SUMO ligases have been identified. This modified in vitro SUMOylation protocol is able to identify novel SUMO E3 ligases by an in vitro reconstitution...

In Vitro SUMOylation Assay to Study SUMO E3 Ligase Activity

characterization of anisotropic leaky mode modulators for holovideo

Characterization of Anisotropic Leaky Mode Modulators for Holovideo

This work describes fabrication and characterization of anisotropic leaky mode modulators for holographic...

sirna screening to identify ubiquitin and ubiquitin-like system regulators of biological pathways in cultured mammalian cells

siRNA Screening to Identify Ubiquitin and Ubiquitin-like System Regulators of Biological Pathways in Cultured Mammalian Cells

Here, we describe a methodology to perform a targeted siRNA &#8220;ubiquitome&#8221; screen to identify novel ubiquitin and ubiquitin-like regulators of the HIF1A-mediated cellular response to hypoxia.&#160; This can be adapted to any biological pathway where a robust read out of reporter activity is...

peptides from phage display library modulate gene expression in mesenchymal cells and potentiate osteogenesis in unicortical bone defects

Peptides from Phage Display Library Modulate Gene Expression in Mesenchymal Cells and Potentiate Osteogenesis in Unicortical Bone Defects

A phage display library was used to identify peptide sequences that target bone. The objective was to investigate the effect of these peptides on mesenchymal cell differentiation and to determine their effect on bone...

genetic variant detection in the calr gene using high resolution melting analysis

Genetic Variant Detection in the CALR gene using High Resolution Melting Analysis

High resolution melting analysis (HRM) is a sensitive and rapid solution for genetic variant detection. It depends on sequence differences that result in heteroduplexes changing the shape of the melting curve. By combing HRM and agarose gel electrophoresis, different types of genetic variants such as indels can be...

Genetic Variant Detection in the CALR gene using High Resolution Melting Analysis

bacterial peptide display for the selection of novel biotinylating enzymes

Bacterial Peptide Display for the Selection of Novel Biotinylating Enzymes

Here we present a method to select for novel variants of the E. coli biotin-protein ligase BirA that biotinylates a specific target peptide. The protocol describes the construction of a plasmid for the bacterial display of the target peptide, generation of a BirA library, selection and characterization of BirA...

protein engineering by yeast surface display

Author Spotlight: Next-Generation Cellular Therapies Through Specialized Protein Engineering Techniques

This protocol describes the essential steps for conducting yeast surface display selection campaigns to enrich protein variants binding to an antigen of...

Optimizing Protein Functions Through Yeast Surface Display Techniques

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using micro-electro-mechanical systems (mems) to develop diagnostic tools

Using Micro-Electro-Mechanical Systems MEMS to Develop Diagnostic Tools

Using Micro-Electro-Mechanical Systems (MEMS) to Develop Diagnostic Tools

a screenable in vivo assay for mitochondrial modulators using transgenic bioluminescent caenorhabditis elegans

A Screenable In Vivo Assay for Mitochondrial Modulators Using Transgenic Bioluminescent Caenorhabditis elegans

A protocol is described for in vivo detection of effects of mitochondrial inhibitors in the model organism Caenorhabditis elegans and for identification of potential enhancing compounds. This protocol can be used to screen drug libraries for compounds modulating mitochondrial function.

A Screenable In Vivo Assay for Mitochondrial Modulators Using Transgenic Bioluminescent Caenorhabditis elegans

Bacterial Inner-membrane Display for Screening a Library of Antibody Fragments

Antibodies engineered for intracellular function must not only have affinity for their target antigen, but must also be soluble and correctly folded in the cytoplasm. Commonly used methods for the display and screening of recombinant antibody libraries do not incorporate intracellular protein folding quality control, and, thus, the antigen-binding capability and cytoplasmic folding and solubility of antibodies engineered using these methods often must be engineered separately. Here, we describe a protocol to screen a recombinant library of single-chain variable fragment (scFv) antibodies for antigen-binding and proper cytoplasmic folding simultaneously. The method harnesses the intrinsic intracellular folding quality control mechanism of the Escherichia coli twin-arginine translocation (Tat) pathway to display an scFv library on the E. coli inner membrane. The Tat pathway ensures that only soluble, well-folded proteins are transported out of the cytoplasm and displayed on the inner membrane, thereby eliminating poorly folded scFvs prior to interrogation for antigen-binding. Following removal of the outer membrane, the scFvs displayed on the inner membrane are panned against a target antigen immobilized on magnetic beads to isolate scFvs that bind to the target antigen. An enzyme-linked immunosorbent assay (ELISA)-based secondary screen is used to identify the most promising scFvs for additional characterization. Antigen-binding and cytoplasmic solubility can be improved with subsequent rounds of mutagenesis and screening to engineer antibodies with high affinity and high cytoplasmic solubility for intracellular applications.

We provide a method to simultaneously screen a library of antibody fragments for binding affinity and cytoplasmic solubility by using the Escherichia coli twin-arginine translocation pathway, which has an inherent quality control mechanism for intracellular protein folding, to display the antibody fragments on the inner membrane.

Antibodies engineered for intracellular function must not only have affinity for their target antigen, but must also be soluble and correctly folded in ...

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 ...

Semi-automated Biopanning of Bacterial Display Libraries for Peptide Affinity Reagent Discovery and Analysis of Resulting Isolates

Biopanning bacterial display libraries is a proven technique for peptide affinity reagent discovery for recognition of both biotic and abiotic targets. Peptide affinity reagents can be used for similar applications to antibodies, including sensing and therapeutics, but are more robust and able to perform in more extreme environments. Specific enrichment of peptide capture agents to a protein target of interest is enhanced using semi-automated sorting methods which improve binding and wash steps and therefore decrease the occurrence of false positive binders. A semi-automated sorting method is described herein for use with a commercial automated magnetic-activated cell sorting device with an unconstrained bacterial display sorting library expressing random 15-mer peptides. With slight modifications, these methods are extendable to other automated devices, other sorting libraries, and other organisms. A primary goal of this work is to provide a comprehensive methodology and expound the thought process applied in analyzing and minimizing the resulting pool of candidates. These techniques include analysis of on-cell binding using fluorescence-activated cell sorting (FACS), to assess affinity and specificity during sorting and in comparing individual candidates, and the analysis of peptide sequences to identify trends and consensus sequences for understanding and potentially improving the affinity to and specificity for the target of interest.

Biopanning bacterial display libraries is a proven technique for discovery of peptide affinity reagents, a robust alternative to antibodies. The semi-automated sorting method herein has streamlined biopanning to decrease the occurrence of false positives. Here we illustrate the thought process and techniques applied in evaluating candidates and minimizing downstream analysis.

Biopanning bacterial display libraries is a proven technique for peptide affinity reagent discovery for recognition of both biotic and abiotic targets. ...

Using High Content Imaging to Quantify Target Engagement in Adherent Cells

Quantitating the interaction of small molecules with their intended protein target is critical for drug development, target validation and chemical probe validation. Methods that measure this phenomenon without modification of the protein target or small molecule are particularly valuable though technically challenging. The cellular thermal shift assay (CETSA) is one technique to monitor target engagement in living cells. Here, we describe an adaptation of the original CETSA protocol, which allows for high throughput measurements while retaining subcellular localization at the single cell level. We believe this protocol offers important advances to the application of CETSA for in-depth characterization of compound-target interaction, especially in heterogeneous populations of cells.

Measurements of drug target engagement are central to effective drug development and chemical probe validation. Here, we detail a protocol for measuring drug-target engagement using high content imaging in a microplate-compatible adaption of the cellular thermal shift assay (CETSA).

Quantitating the interaction of small molecules with their intended protein target is critical for drug development, target validation and chemical probe ...

Profiling Ubiquitin and Ubiquitin-like Dependent Post-translational Modifications and Identification of Significant Alterations

Ubiquitin (ub) and ubiquitin-like (ubl) dependent post-translational modifications of proteins play fundamental biological regulatory roles within the cell by controlling protein stability, activity, interactions, and intracellular localization. They enable the cell to respond to signals and to adapt to changes in its environment. Alterations within these mechanisms can lead to severe pathological situations such as neurodegenerative diseases and cancers. The aim of the technique described here is to establish ub/ubls dependent PTMs profiles, rapidly and accurately, from cultured cell lines. The comparison of different profiles obtained from different conditions allows the identification of specific alterations, such as those induced by a treatment for example. Lentiviral mediated cell transduction is performed to create stable cell lines expressing a two-tags (6His and Flag) version of the modifier (ubiquitin or a ubl such as SUMO1 or Nedd8). These tags permit the purification of ubiquitin and therefore of ubiquitinated proteins from the cells. This is done through a two-step purification process: The first one is performed in denaturing conditions using the 6His tag, and the second one in native conditions using the Flag tag. This leads to a highly specific and pure isolation of modified proteins which are subsequently identified and semi-quantified by liquid chromatography followed by tandem mass spectrometry (LC-MS/MS) technology. Easy informatics analysis of MS data using Excel software enables the establishment of PTM profiles by eliminating background signals. These profiles are compared between each condition in order to identify specific alterations which will then be studied more specifically, starting with their validation by standard biochemistry techniques.

This protocol aims at establishing ubiquitin (Ub) and ubiquitin-likes (Ubls) specific proteomes in order to identify alterations of these kind of post-translational modifications (PTMs), associated with a specific condition such as a treatment or a phenotype.

Ubiquitin (ub) and ubiquitin-like (ubl) dependent post-translational modifications of proteins play fundamental biological regulatory roles within the ...

Ubiquitination, as a posttranslational modification of proteins, plays an important regulatory role in homeostasis of eukaryotic cells. The covalent attachment of 76 amino acid ubiquitin modifiers to a target protein, depending on the length and topology of the polyubiquitin chain, can result in different outcomes ranging from protein degradation to changes in the localization and/or activity of modified protein. Three enzymes sequentially catalyze the ubiquitination process: E1 ubiquitin-activating enzyme, E2 ubiquitin-conjugating enzyme, and E3 ubiquitin ligase. E3 ubiquitin ligase determines substrate specificity and, therefore, represents a very interesting study subject. Here we present a comprehensive approach to study the relationship between the enzymatic activity and function of the RING-type E3 ubiquitin ligase. This four-step protocol describes 1) how to generate an E3 ligase deficient mutant through site-directed mutagenesis targeted at the conserved RING domain; 2&#8211;3) how to examine the ubiquitination activity both in vitro and in planta; 4) how to link those biochemical analysis to the biological significance of the tested protein. Generation of an E3 ligase-deficient mutant that still interacts with its substrate but no longer ubiquitinates it for degradation facilitates the testing of enzyme-substrate interactions in vivo. Furthermore, the mutation in the conserved RING domain often confers a dominant negative phenotype that can be utilized in functional knockout studies as an alternative approach to an RNA-interference approach. Our methods were optimized to investigate the biological role of the plant parasitic nematode effector RHA1B, which hijacks the host ubiquitination system in plant cells to promote parasitism. With slight modification of the in vivo expression system, this protocol can be applied to the analysis of any RING-type E3 ligase regardless of its origins.

The goal of this manuscript is to present an outline for the comprehensive biochemical and functional studies of the RING-type E3 ubiquitin ligases. This multistep pipeline, with detailed protocols, validates an enzymatic activity of the tested protein and demonstrates how to link the activity to function.

Ubiquitination, as a posttranslational modification of proteins, plays an important regulatory role in homeostasis of eukaryotic cells. The covalent ...

Ubiquitin Chain Analysis by Parallel Reaction Monitoring

Assessment of the global profile of ubiquitin chain topologies within a proteome is of interest to answer a wide range of biological questions. The protocol outlined here takes advantage of the di-glycine (-GG) modification left after the tryptic digestion of ubiquitin incorporated in a chain. By quantifying these topology-characteristic peptides the relative abundance of each ubiquitin chain topology can be determined. The steps required to quantify these peptides by a parallel reaction monitoring experiment are reported taking into consideration the stabilization of ubiquitin chains. Preparation of heavy controls, cell lysis, and digestion are described along with the appropriate mass spectrometer setup and data analysis workflow. An example data set with perturbations in ubiquitin topology is presented, accompanied by examples of how optimization of the protocol can affect results. By following the steps outlined, a user will be able to perform a global assessment of the ubiquitin topology landscape within their biological context.

This method describes the assessment of global changes in ubiquitin chain topology. The assessment is performed by the application of a mass spectrometry-based targeted proteomics approach.

Assessment of the global profile of ubiquitin chain topologies within a proteome is of interest to answer a wide range of biological questions. The ...

Creating Highly Specific Chemically Induced Protein Dimerization Systems by Stepwise Phage Selection of a Combinatorial Single-Domain Antibody Library

Protein dimerization events that occur only in the presence of a small-molecule ligand enable the development of small-molecule biosensors for the dissection and manipulation of biological pathways. Currently, only a limited number of chemically induced dimerization (CID) systems exist and engineering new ones with desired sensitivity and selectivity for specific small-molecule ligands remains a challenge in the field of protein engineering. We here describe a high throughput screening method, combinatorial binders-enabled selection of CID (COMBINES-CID), for the de novo engineering of CID systems applicable to a large variety of ligands. This method uses the two-step selection of a phage-displayed combinatorial nanobody library to obtain 1) &#34;anchor binders&#34; that first bind to a ligand of interest and then 2) &#34;dimerization binders&#34; that only bind to anchor binder-ligand complexes. To select anchor binders, a combinatorial library of over 109 complementarity-determining region (CDR)-randomized nanobodies is screened with a biotinylated ligand and hits are validated with the unlabeled ligand by bio-layer interferometry (BLI). To obtain dimerization binders, the nanobody library is screened with anchor binder-ligand complexes as targets for positive screening and the unbound anchor binders for negative screening. COMBINES-CID is broadly applicable to select CID binders with other immunoglobulin, non-immunoglobulin, or computationally designed scaffolds to create biosensors for in vitro and in vivo detection of drugs, metabolites, signaling molecules, etc.

Creating chemically induced protein dimerization systems with desired affinity and specificity for any given small molecule ligand would have many biological sensing and actuation applications. Here, we describe an efficient, generalizable method for de novo engineering of chemically induced dimerization systems via the stepwise selection of a phage-displayed combinatorial single-domain antibody library.

Protein dimerization events that occur only in the presence of a small-molecule ligand enable the development of small-molecule biosensors for the ...

Ubiquitylation is a post-translational modification which occurs in eukaryotic cells that is critical for several biological pathways' regulation, including cell survival, proliferation, and differentiation. It is a reversible process that consists of a covalent attachment of ubiquitin to the substrate through a cascade reaction of at least three different enzymes, composed of E1 (Ubiquitin-activation enzyme), E2 (Ubiquitin-conjugating enzyme), and E3 (Ubiquitin-ligase enzyme). The E3 complex plays an important role in substrate recognition and ubiquitylation. Here, a protocol is described to evaluate substrate ubiquitylation in mammalian cells using transient co-transfection of a plasmid encoding the selected substrate, an E3 ubiquitin ligase, and a tagged ubiquitin. Before lysis, the transfected cells are treated with the proteasome inhibitor MG132 (carbobenzoxy-leu-leu-leucinal) to avoid substrate proteasomal degradation. Furthermore, the cell extract is submitted to small-scale immunoprecipitation (IP) to purify the polyubiquitylated substrate for subsequent detection by western blotting (WB) using specific antibodies for ubiquitin tag. Hence, a consistent and uncomplicated protocol for ubiquitylation assay in mammalian cells is described to assist scientists in addressing ubiquitylation of specific substrates and E3 ubiquitin ligases.

We provide a detailed protocol for a ubiquitylation assay of a specific substrate and an E3 ubiquitin-ligase in mammalian cells. HEK293T cell lines were used for protein overexpression, the polyubiquitylated substrate was purified from cell lysates by immunoprecipitation, and resolved in SDS-PAGE. Immunoblotting was used to visualize this post-translational modification.

Ubiquitylation is a post-translational modification which occurs in eukaryotic cells that is critical for several biological pathways' regulation, ...

A Fibrinolytic Enzyme-Based Method to Study Cerebral Thrombus Cell Components

A Comprehensive Approach to Analyze the Cell Components of Cerebral Blood Clots

Cerebral thrombosis, a blood clot in a cerebral artery or vein, is the most common type of cerebral infarction. The study of the cell components of cerebral blood clots is important for diagnosis, treatment, and prognosis. However, the current approaches to studying the cell components of the clots are mainly based on in situ staining, which is unsuitable for the comprehensive study of the cell components because cells are tightly wrapped in the clots. Previous studies have successfully isolated a fibrinolytic enzyme (sFE) from Sipunculus nudus, which can degrade the cross-linked fibrin directly, releasing the cell components. This study established a comprehensive method based on the sFE to study the cell components of cerebral thrombus. This protocol includes clot dissolving, cell releasing, cell staining, and routine blood examination. According to this method, the cell components could be studied quantitatively and qualitatively. The representative results of experiments using this method are shown.

Author Spotlight: A Novel Method for Comprehensive Cell Component Analysis of Cerebral Blood Clots 

This study describes a fast and effective method for the cell component analysis of cerebral blood clots through clot dissolving, cell staining, and routine blood examination.

Cerebral thrombosis, a blood clot in a cerebral artery or vein, is the most common type of cerebral infarction. The study of the cell components of ...