This work was supported by a grant from the NIH. The assays shown in Figure 1 was performed by Dr. Joseph Fasolo. We thank Dr. Rui Chen for helpful comments.

1. Probe Preparation
<ol>
	<li>Culture and purify the V5-fusion kinase probes used to examine interactions with other proteins as follows:
	<ol>
		<li>Use freshly streaked yeast strain Y258 (MATa pep4-3, his4-580, ura3-53, leu2-3,112) containing V5-fusion protein (expressed from GATEWAY vector pYES-DEST52). Use the isolated protein as probe on the microarrays. Plate the yeast on synthetic complete-uracil (Sc-Ura)/2% Dextrose/Agar and grow at 30&#160;&#176;C&#160;for 3 days from frozen culture (-80 &#176;C glycerol stock).</li>
		<li>Inoculate starter cultures (5&#8211;20 ml) from a single colony and grow overnight in Sc-Ura/2% Dextrose on shaking platform (220-250 rpm) or wheel at 30&#160;&#176;C.</li>
		<li>The following morning, inoculate 400 ml&#160;of the Sc-Ura/2% raffinose culture with sufficient starter culture to a final OD600 of 0.1.</li>
		<li>Grow the inoculums to OD600 of 0.6 followed by galactose induction of the V5-kinase fusion construct expression by adding a solution of 3x&#160;Yeast Extract/Peptone (YEP) supplemented with 6% Galactose, by adding enough to dilute the induction media by a factor of 3 so that final concentration of galactose is 2%.</li>
		<li>Induce cells at 30 &#176;C for 6 hr&#160;on a shaking platform. Use a 2 L&#160;Erlenmeyer flask to ensure appropriate aeration.</li>
		<li>Harvest cells using a JA-10 (or comparable) rotor by spinning 400 ml&#160;of cell suspension at 1,000 x g for 5 min at 4 &#176;C.</li>
		<li>Wash the cells once with 50 ml&#160;of ice cold PBS buffer&#160;and transfer to a 50 ml&#160;conical tube. Wash the pellet again in ice cold PBS buffer (without detergents or other additives) used for lysis and transfer to 2 ml&#160;snap-cap tubes for lysis.</li>
		<li>Spin the cells at 20,000 x g for 1 min at 4 &#176;C to a pellet and pipette away the buffer.</li>
		<li>Place tubes on ice and proceed with lysis step.</li>
		<li>Lyse the cells (250-350 &#181;l pellet) with 0.5 mm zirconia beads in a 1:1:1 volume of cell pellet, beads, and Phosphate-buffered saline ( PBS) lysis buffer and vortex the mixture using a agitation platform 3 times at 2 min intervals at 4 &#176;C.</li>
		<li>Centrifuge the lysate at 20,000 x g in a tabletop microfuge for 10 min at 4 &#176;C.</li>
		<li>Pipette supernatant into polycarbonate high speed centrifuge tube and clarify by ulracentrufugation for 30 min at 150,000 x g at 4 &#176;C.</li>
		<li>Transfer the clarified lysate to a tube containing prewashed Ni2+ affinity resin (~100 &#181;l) and incubate on a nutator for 2 hr&#160;at 4 &#176;C to capture Histidine(His)6X tagged V5-fusion protein.</li>
		<li>Wash the resin three times for 10 min&#160;at 4 &#176;C with Wash Buffer. Pellet the resin using a table top centrifuge for 5 min at 1,000 x g at 4 &#176;C and aspirate the supernatant. Add fresh wash buffer for each wash and return the tube the nutator for agitation during the wash.</li>
		<li>After the wash steps are complete, apply the washed resin to a fresh G-25 column for elution.</li>
		<li>Apply 25 &#181;l of elution buffer in a step-wise manner beginning with 100 mM Imidazole to 500 mM imidazole in 50 mM increments for a total of 9 fractions.</li>
		<li>Assay the collected fractions using sodium dodecyl sulfate polyacrylamide gel (SDS-PAGE) and coomassie staining to identify the most highly enriched fraction(s) for use in the assay and add glycerol to 30% and store at -80&#160;&#176;C&#160;until used in the assay.</li>
	</ol>
	</li>
</ol>
2. Probing the Arrays
NOTE: Please see step 2.6 of this section to prepare the antibody solution before beginning the assay.
<ol>
	<li>To detect interactions, dilute the V5-fluorophore conjugated antibody (i.e. AlexaFluor 647 ) to 260 ng/ml&#160;in probe buffer and mix thoroughly by shaking. 
	NOTE: Prepare this antibody solution 30 min&#160;prior to use and place the tube on a nutator or wheel to ensure complete mixing and a homogenous suspension of antibody.</li>
	<li>Dilute the V5-fusion protein probe over a concentration range of 5&#8211;500 &#956;g/ml. 
	NOTE: Optimized for each protein&#8211;protein interaction assay, using probe buffer. Optimization involves adding more probes to probe buffer. Typically 10 &#181;g/ml is used as starting point and adjusted accordingly based on the signal strength.</li>
	<li>Remove the protein microarrays from the freezer (&#8722;20 &#176;C) and bring to 4 &#176;C in the refrigerator just prior to use.</li>
	<li>Add blocking buffer directly to the slide holder containing the protein micorarrays and cover the top with parafilm to prevent leakage. Block the arrays in blocking buffer for 1 hr&#160;by shaking at 50 rpm on a stage at 4 &#176;C.</li>
	<li>After blocking, transfer the arrays to a humidified chamber chilled to 4&#160;&#176;C, and add 90 &#956;l&#160;of diluted probe directly to the array surface. Overlay the arrays with a raised lifter slip and incubate static (no shaking) in the humidified chamber at 4&#160;&#176;C&#160;for 1.5 hr.</li>
	<li>Wash the arrays 3 times for 1 min each in probe buffer in three 50 ml&#160;conical tubes. Add the slide to conical tubes containing enough pre-chilled probe buffer to completely envelope the slide. Allow the lifter slip to gently slide off of the protein microarray (do not force it off as this could result in damage to the array surface).</li>
	<li>Apply the antibody solution directly to array immediately after completing the wash (step 2.5) and overlay with a raised lifter slip as before. Incubate the arrays for 30 min at 4 &#176;C in the humidified chamber.</li>
	<li>Perform the same wash step as before (3 times 1 min in probe buffer), and spin in a 50 ml&#160;conical tube at 800 x g in a tabletop centrifuge for 5 min at room temperature. Air-dry the arrays in a slide holder in the dark for 30 min prior to scanning the array at 647 nm.</li>
</ol>

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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=Functional+organization+of+the+yeast+proteome+by+systematic+analysis+of+protein+complexes.">Functional organization of the yeast proteome by systematic analysis of protein complexes.</a> Nature. 415, 141-147 (2002).</li><li>Jeong, J. 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=Rapid+identification+of+monospecific+monoclonal+antibodies+using+a+human+proteome+microarray.">Rapid identification of monospecific monoclonal antibodies using a human proteome microarray.</a> Mol Cell Proteomics. 11 (6), (2012).</li><li>Krogan, N. 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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=Differential+binding+of+calmodulin-related+proteins+to+their+targets+revealed+through+high-density+Arabidopsis+protein+microarrays.">Differential binding of calmodulin-related proteins to their targets revealed through high-density Arabidopsis protein microarrays.</a> Proceedings of the National Academy of Sciences of the United States of America. 104, 4730-4735 (2007).</li><li>Zhu, 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=Global+analysis+of+protein+activities+using+proteome+chips.">Global analysis of protein activities using proteome chips.</a> Science. 293, 2101-2105 (2001).</li><li>Ptacek, 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=Global+analysis+of+protein+phosphorylation+in+yeast.">Global analysis of protein phosphorylation in yeast.</a> Nature. 438, 679-684 (2005).</li><li>Haab, B. 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The authors declare that they have no competing financial interests.

The protocol presented was originally performed using 85 unique yeast protein kinase-V5 fusion proteins to compare binding activity across distinct and related families of yeast protein kinases resulting in the identification of new kinase interaction networks in vivo1. As an emerging proteomic profiling technology, the development of High Throughput (HTP) screening of proteomes using protein microarrays relied on peptide libraries, and eukaryotic and prokaryotic model organisms8,17; later,...

The need to perform global analyses of protein biochemistry and binding activity in vivo has resulted in the development of new methods for profiling protein-protein interactions (PPIs) and the post-translational modifications of whole proteomes1,3-8. Protein microarrays are manufactured as functional protein microarrays using full-length functional proteins4-6,8,9, or analytical protein microarrays containing antibodies10,11. They are engineered to contain a high-density of proteins arrayed onto microscope slides with a variety of surface chemistries to facilitate a variety of experimental conditions required for conducting wide-ranging biochemical analyses12. Nitrocellulose and aldehyde surface chemistries for chemical attachment through lysine or affinity attachment methods such as nickel- chelated slides for attaching His-tagged proteins and glutathione for affinity attachment among others13.
The use of functional protein microarrays to detect protein-protein interactions requires access to a high-quality functional protein library14. S. cerevisiae is amenable to producing such a library through the pairing of high-copy affinity tagged protein constructs with high-throughput chromatographic purification techniques. The vast majority of the yeast genome has been sequenced and nearly the entire proteome can be expressed from a high-copy plasmid for purification and biochemical analyses12. Once the proteins are obtained and arrayed in 384-well format, they are printed onto a microscope slide allowing for rapid parallel multi-parametric biochemical analysis and bioinformatic interrogation8,14-16. Protein microarrays have been used for enzymatic assays and interactions with proteins, lipids, small molecules, and nucleic acids among many other applications. The accessibility of proteins on the surface of proteome arrays make them amenable to different types of analytical detection including, immune-affinity, Surface Plasmon Resonance, fluorescence and many other techniques. Moreover, it allows for fine control of the experimental condition where it might be hard to do in vivo.
The aim of this protocol is to demonstrate the appropriate use of functional protein microarrays to detect protein-protein interactions. This application enables the high-throughput parallel biochemical analysis of protein binding activities using a highly purified analyte (protein) of interest. A C-terminal(carboxy-terminal) tagged V5-fusion bait protein of interest is produced from a high-copy plasmid in a yeast strain optimized for protein purification. C-terminal tagging ensures that the full-length protein has been translated. The protein used in this study is Tda1-V5 fusion protein kinase, which is purified using nickel affinity resin via a His6X tag. The Tda1-V5 fusion construct is purified through serial elution using an imidazole gradient to elute the most highly enriched fraction for use in the assay.

<table border="0" cellpadding="0" cellspacing="0" width="855">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Name of Material/ Equipment</td>
			<td style="width:180px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:291px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Petri Dishes</td>
			<td style="width:180px;">VWR</td>
			<td>NC-10747</td>
			<td>or comparable</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto yeast extract</td>
			<td style="width:180px;">Difco</td>
			<td>0217-17</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto peptone</td>
			<td style="width:180px;">Difco</td>
			<td>0118-17</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bacto agar</td>
			<td style="width:180px;">Difco</td>
			<td>0140-01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Dextrose</td>
			<td style="width:180px;">Sigma</td>
			<td>D9434</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Raffinose</td>
			<td style="width:180px;">Sigma</td>
			<td>R0514</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Galactose</td>
			<td style="width:180px;">Sigma</td>
			<td>G0750</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Sc-Ura drop out media</td>
			<td style="width:180px;">MP Bio</td>
			<td>114410622</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Small Culture tubes</td>
			<td style="width:180px;">VWR/Fisher</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Large Erlenmeyer Flask</td>
			<td style="width:180px;">VWR/Fisher</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Centrifuge JA-10 rotor</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Centrifuge tubes (500 mL)</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Falcon tube (50 mL)</td>
			<td style="width:180px;">VWR/Fisher</td>
			<td>21008-951</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">PBS Tablets</td>
			<td style="width:180px;">Sigma</td>
			<td>P4417</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">FastPrep Tubes(2ml screw cap tube)</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">FastPrep Machine</td>
			<td style="width:180px;">MP Biomedicals</td>
			<td align="right" style="width:119px;">116004500</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Zircon Beads</td>
			<td style="width:180px;">BioSpec</td>
			<td align="right" style="width:119px;">11079105</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Triton X100</td>
			<td style="width:180px;">Sigma</td>
			<td>P4417</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">DTT</td>
			<td style="width:180px;">Sigma</td>
			<td>D9779</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:267px;">MgCl2</td>
			<td style="width:180px;">Sigma</td>
			<td>M8266&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">NaCl</td>
			<td style="width:180px;">Sigma</td>
			<td>S3014&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Imidazole (pH = 7.4)</td>
			<td style="width:180px;">Sigma</td>
			<td>I5513&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">PMSF</td>
			<td style="width:180px;">Sigma</td>
			<td>93482</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Complete Inhibitor Cocktail (EDTA Free)</td>
			<td style="width:180px;">Roche</td>
			<td style="width:119px;">11873580001</td>
			<td style="width:291px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Phosphatase inhibitor cocktail 1</td>
			<td style="width:180px;">sigma</td>
			<td>P2850</td>
			<td style="width:291px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">BSA</td>
			<td style="width:180px;">Sigma</td>
			<td>A2153&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Tween-20</td>
			<td style="width:180px;">Sigma</td>
			<td>P1379&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">ATP</td>
			<td style="width:180px;">Sigma</td>
			<td>A1852&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Shaking Incubator (30 &#176;C)</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Nickel Affinity Resin</td>
			<td style="width:180px;">Life Technologies</td>
			<td>R901-01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">G25 column</td>
			<td style="width:180px;">GE life sciences</td>
			<td>27-5325-01&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Nutator</td>
			<td style="width:180px;">VWR/Fisher</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">SDS-PAGE Gel (NuPage)</td>
			<td style="width:180px;">Life Technologies</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Coomassie Blue Stain</td>
			<td style="width:180px;">Life Technologies</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Monoclonal V5 Antibody</td>
			<td style="width:180px;">Life Technologies</td>
			<td>R960-25</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:267px;">Alexa647 Tagged monoclonal V5 Antibody</td>
			<td style="width:180px;">Life Technologies</td>
			<td>451098</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Protein Microarrays Kit</td>
			<td style="width:180px;">Life Technologies</td>
			<td>PAH0525013</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:267px;">Genepix Scanner</td>
			<td style="width:180px;">Molecular Devices</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="62">
			<td height="62" style="height:63px;width:267px;">Lifter Slips</td>
			<td style="width:180px;">Thomas Scientific</td>
			<td style="width:119px;"></td>
			<td style="width:291px;">http://www.thomassci.com/Supplies/Microscope-Cover-Glass/_/LIFTER-SLIPS/</td>
		</tr>
		<tr height="124">
			<td height="124" style="height:124px;width:267px;">Lysis Buffer: 0.1% Triton X-100, 0.5 mM DTT, 
			2 mM MgCl2, 500 mM NaCl, 50 mM imidazole (pH 7.4), Complete protease inhibitor cocktail &#8211; EDTA-free, Phosphatase inhibitor Cocktail 1, 1 mM PMSF&#160; (add just prior to use)</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td style="width:291px;">Add the reagents to 1 X PBS (0.01 M phosphate buffer, 0.0027 M potassium chloride, 0.137 M sodium chloride; pH 7.4) to obtain the desired volume of lysis solution</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:267px;">Blocking Buffer: 1% bovine serum albumin (BSA), 0.1% Tween-20</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td style="width:291px;">Add the reagents to 1 X PBS to obtain the desired volume of blocking buffer</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:267px;">Probe Buffer: 2 mM MgCl2, 0.5 mM DTT, 0.05% Triton X-100, 50 mM NaCl,500 &#956;M ATP (for kinases), 1% BSA</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td style="width:291px;">Add the reagent to 1 X PBS to obtain desired volume of probe buffer</td>
		</tr>
		<tr height="67">
			<td height="67" style="height:67px;width:267px;">Wash Buffer: 0.1% Triton X-100, 500 mM NaCl, 0.5 mM DTT, 50 mM imidazole (pH 7.4),2 mM MgCl2</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td style="width:291px;">Add the reagent to 1 X PBS to obtain desired volume of probe buffer</td>
		</tr>
		<tr height="168">
			<td height="168" style="height:168px;width:267px;">Elution Buffer: 0.1% Triton X-100, 0.5 mM DTT, 2 mM MgCl2, 500 mM NaCl, 50 &#8211; 500 mM imidazole (pH 7.4), Complete protease inhibitor cocktail &#8211; EDTA-free, Phosphatase inhibitor Cocktail 1, 1 mM PMSF (add just prior to use)</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td style="width:291px;">Before you begin, it is important to note the concentration gradient of imidazole (50 &#8211; 500 mM) and to create separate tubes for each concentration (it is advisable to create the interval using 50 mM increments). Add the reagent to 1 X PBS to obtain desired volume of probe buffer</td>
		</tr>
		<tr height="105">
			<td height="105" style="height:105px;width:267px;">3x YEP +6% galactose: Dissolve 30 g of yeast extract and&#160; 60 g of peptone in 700 ml of H2O, and autoclave. Add 300 ml of filter sterilized 20% galactose (wt/vol)</td>
			<td style="width:180px;"></td>
			<td style="width:119px;"></td>
			<td>&#160;galactose should not be autoclaved</td>
		</tr>
	</tbody>
</table>

probing high-density functional protein microarrays to detect protein-protein interactions

High-density functional protein microarrays containing ~4,200 recombinant yeast proteins are examined for kinase protein-protein interactions using an affinity purified yeast kinase fusion protein containing a V5-epitope tag for read-out. Purified kinase is obtained through culture of a yeast strain optimized for high copy protein production harboring a plasmid containing a Kinase-V5 fusion construct under a GAL inducible promoter. The yeast is grown in restrictive media with a neutral carbon source for 6 hr followed by induction with 2% galactose. Next, the culture is harvested and kinase is purified using standard affinity chromatographic techniques to obtain a highly purified protein kinase for use in the assay. The purified kinase is diluted with kinase buffer to an appropriate range for the assay and the protein microarrays are blocked prior to hybridization with the protein microarray. After the hybridization, the arrays are probed with monoclonal V5 antibody to identify proteins bound by the kinase-V5 protein. Finally, the arrays are scanned using a standard microarray scanner, and data is extracted for downstream informatics analysis1,2 to determine a high confidence set of protein interactions for downstream validation in vivo.

The protein-protein interaction activity was observed using a standard chip reader to evaluate the Tda1-V5 protein kinase fusion construct as a bait protein against a yeast functional protein microarray containing approximately 4,200 unique S. cerevisiae GST-fusion proteins. Further interrogation with the Genepix software revealed a multitude of binding events of varying intensities. The affinity was gauged from the graded intensity of the signal derived from a monoclonal V5-Fluorophore conjugated antibody bound...

Watch this Scientific Journal Video about Probing High-density Functional Protein Microarrays to Detect Protein-protein Interactions at JoVE.com

Probing High-density Functional Protein Microarrays to Detect Protein-protein Interactions

Using protein microarrays containing nearly the entire S. cerevisiae proteome is probed for rapid unbiased interrogation of thousands of protein-protein interactions in parallel. This method can be utilized for protein-small molecule, posttranslational modification, and other assays in high-throughput.

High-density functional protein microarrays containing ~4,200 recombinant yeast proteins are examined for kinase protein-protein interactions using an ...

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7.9K Views.  Stanford University. Using protein microarrays containing nearly the entire S. cerevisiae proteome is probed for rapid unbiased interrogation of thousands of protein-protein interactions in parallel. This method can be utilized for protein-small molecule, posttranslational modification, and other assays in high-throughput.

Video: Probing High-density Functional Protein Microarrays to Detect Protein-protein Interactions

Split-Ubiquitin Based Membrane Yeast Two-Hybrid (MYTH) System: A Powerful Tool For Identifying Protein-Protein Interactions

The fundamental biological and clinical importance of integral membrane proteins prompted the development of a yeast-based system for the high-throughput identification of protein-protein interactions (PPI) for full-length transmembrane proteins. To this end, our lab developed the split-ubiquitin based Membrane Yeast Two-Hybrid (MYTH) system. This technology allows for the sensitive detection of transient and stable protein interactions using Saccharomyces cerevisiae as a host organism. MYTH takes advantage of the observation that ubiquitin can be separated into two stable moieties: the C-terminal half of yeast ubiquitin (Cub) and the N-terminal half of the ubiquitin moiety (Nub). In MYTH, this principle is adapted for use as a 'sensor' of protein-protein interactions. Briefly, the integral membrane bait protein is fused to Cub which is linked to an artificial transcription factor. Prey proteins, either in individual or library format, are fused to the Nub moiety. Protein interaction between the bait and prey leads to reconstitution of the ubiquitin moieties, forming a full-length 'pseudo-ubiquitin' molecule. This molecule is in turn recognized by cytosolic deubiquitinating enzymes, resulting in cleavage of the transcription factor, and subsequent induction of reporter gene expression. The system is highly adaptable, and is particularly well-suited to high-throughput screening. It has been successfully employed to investigate interactions using integral membrane proteins from both yeast and other organisms.

Split-Ubiquitin Based Membrane Yeast Two-Hybrid MYTH System: A Powerful Tool For Identifying Protein-Protein Interactions

MYTH allows the sensitive detection of transient and stable interactions between proteins that are expressed in the model organism Saccharomyces cerevisiae. It has been successfully applied to study exogenous and yeast integral membrane proteins in order to identify their interacting partners in a high throughput manner.

The fundamental biological and clinical importance of integral membrane proteins prompted the development of a yeast-based system for the high-throughput ...

In-vivo Detection of Protein-protein Interactions on Micro-patterned Surfaces

Unraveling the interaction network of molecules in-vivo is key to understanding the mechanisms that regulate cell function and metabolism. A multitude of methodological options for addressing molecular interactions in cells have been developed, but most of these methods suffer from being rather indirect and therefore hardly quantitative. On the contrary, a few high-end quantitative approaches were introduced, which however are difficult to extend to high throughput. To combine high throughput capabilities with the possibility to extract quantitative information, we recently developed a new concept for identifying protein-protein interactions (Schwarzenbacher et al., 2008). Here, we describe a detailed protocol for the design and the construction of this system which allows for analyzing interactions between a fluorophore-labeled protein ("prey") and a membrane protein ("bait") in-vivo. Cells are plated on micropatterned surfaces functionalized with antibodies against the bait exoplasmic domain. Bait-prey interactions are assayed via the redistribution of the fluorescent prey. The method is characterized by high sensitivity down to the level of single molecules, the capability to detect weak interactions, and high throughput capability, making it applicable as screening tool.

In-vivo Detection of Protein-protein Interactions on Micro-patterned Surfaces

This video shows experiments with subsequent analysis of protein-protein interactions by the use of micro-patterned surfaces. The approach offers the possibility to detect protein interactions in living cells and combines high throughput capabilities with the possibility to extract quantitative information.

Unraveling the interaction network of molecules in-vivo is key to understanding the mechanisms that regulate cell function and metabolism. A multitude of ...

Imaging Protein-protein Interactions in vivo

Protein-protein interactions are a hallmark of all essential cellular processes. However, many of these interactions are transient, or energetically weak, preventing their identification and analysis through traditional biochemical methods such as co-immunoprecipitation. In this regard, the genetically encodable fluorescent proteins (GFP, RFP, etc.) and their associated overlapping fluorescence spectrum have revolutionized our ability to monitor weak interactions in vivo using F&ouml;rster resonance energy transfer (FRET)1-3. Here, we detail our use of a FRET-based proximity assay for monitoring receptor-receptor interactions on the endothelial cell surface.

Imaging Protein-protein Interactions in vivo

This protocol describes how to image protein-protein interactions using a FRET-based proximity assay.

Protein-protein interactions are a hallmark of all essential cellular processes. However, many of these interactions are transient, or energetically weak, ...

A Protocol for the Identification of Protein-protein Interactions Based on 15N Metabolic Labeling, Immunoprecipitation, Quantitative Mass Spectrometry and Affinity Modulation

Protein-protein interactions are fundamental for many biological processes in the cell. Therefore, their characterization plays an important role in current research and a plethora of methods for their investigation is available1. Protein-protein interactions often are highly dynamic and may depend on subcellular localization, post-translational modifications and the local protein environment2. Therefore, they should be investigated in their natural environment, for which co-immunoprecipitation approaches are the method of choice3. Co-precipitated interaction partners are identified either by immunoblotting in a targeted approach, or by mass spectrometry (LC-MS/MS) in an untargeted way. The latter strategy often is adversely affected by a large number of false positive discoveries, mainly derived from the high sensitivity of modern mass spectrometers that confidently detect traces of unspecifically precipitating proteins. A recent approach to overcome this problem is based on the idea that reduced amounts of specific interaction partners will co-precipitate with a given target protein whose cellular concentration is reduced by RNAi, while the amounts of unspecifically precipitating proteins should be unaffected. This approach, termed QUICK for QUantitative Immunoprecipitation Combined with Knockdown4, employs Stable Isotope Labeling of Amino acids in Cell culture (SILAC)5 and MS to quantify the amounts of proteins immunoprecipitated from wild-type and knock-down strains. Proteins found in a 1:1 ratio can be considered as contaminants, those enriched in precipitates from the wild type as specific interaction partners of the target protein. Although innovative, QUICK bears some limitations: first, SILAC is cost-intensive and limited to organisms that ideally are auxotrophic for arginine and/or lysine. Moreover, when heavy arginine is fed, arginine-to-proline interconversion results in additional mass shifts for each proline in a peptide and slightly dilutes heavy with light arginine, which makes quantification more tedious and less accurate5,6. Second, QUICK requires that antibodies are titrated such that they do not become saturated with target protein in extracts from knock-down mutants.
Here we introduce a modified QUICK protocol which overcomes the abovementioned limitations of QUICK by replacing SILAC for 15N metabolic labeling and by replacing RNAi-mediated knock-down for affinity modulation of protein-protein interactions. We demonstrate the applicability of this protocol using the unicellular green alga Chlamydomonas reinhardtii as model organism and the chloroplast HSP70B chaperone as target protein7 (Figure 1). HSP70s are known to interact with specific co-chaperones and substrates only in the ADP state8. We exploit this property as a means to verify the specific interaction of HSP70B with its nucleotide exchange factor CGE19.

A Protocol for the Identification of Protein-protein Interactions Based on 15N Metabolic Labeling, Immunoprecipitation, Quantitative Mass Spectrometry and Affinity Modulation

We present a variation of the QUICK (QUantitative Immunoprecipitation Combined with Knockdown) approach that was introduced previously to distinguish between true and false protein-protein interactions. Our approach is based on 15N metabolic labeling, the modulation of affinities of protein-protein interactions by the presence/absence of ATP, immunoprecipitation, and quantitative mass spectrometry.

Protein-protein interactions are fundamental for many biological processes in the cell. Therefore, their characterization plays an important role in ...

Flow Cytometric Analysis of Bimolecular Fluorescence Complementation: A High Throughput Quantitative Method to Study Protein-protein Interaction

Among methods to study protein-protein interaction inside cells, Bimolecular Fluorescence Complementation (BiFC) is relatively simple and sensitive. BiFC is based on the production of fluorescence using two non-fluorescent fragments of a fluorescent protein (Venus, a Yellow Fluorescent Protein variant, is used here). Non-fluorescent Venus fragments (VN and VC) are fused to two interacting proteins (in this case, AKAP-Lbc and PDE4D3), yielding fluorescence due to VN-AKAP-Lbc-VC-PDE4D3 interaction and the formation of a functional fluorescent protein inside cells.
BiFC provides information on the subcellular localization of protein complexes and the strength of protein interactions based on fluorescence intensity. However, BiFC analysis using microscopy to quantify the strength of protein-protein interaction is time-consuming and somewhat subjective due to heterogeneity in protein expression and interaction. By coupling flow cytometric analysis with BiFC methodology, the fluorescent BiFC protein-protein interaction signal can be accurately measured for a large quantity of cells in a short time. Here, we demonstrate an application of this methodology to map regions in PDE4D3 that are required for the interaction with AKAP-Lbc. This high throughput methodology can be applied to screening factors that regulate protein-protein interaction.

Flow cytometric analysis of Bimolecular Fluorescence Complementation provides a high throughput quantitative method to study protein-protein interaction. This methodology can be applied to mapping protein binding sites and for screening factors that regulate protein-protein interaction.

Among methods to study protein-protein interaction inside cells, Bimolecular Fluorescence Complementation (BiFC) is relatively simple and sensitive. BiFC ...

Using Coculture to Detect Chemically Mediated Interspecies Interactions

In nature, bacteria rarely exist in isolation; they are instead surrounded by a diverse array of other microorganisms that alter the local environment by secreting metabolites. These metabolites have the potential to modulate the physiology and differentiation of their microbial neighbors and are likely important factors in the establishment and maintenance of complex microbial communities. We have developed a fluorescence-based coculture screen to identify such chemically mediated microbial interactions. The screen involves combining a fluorescent transcriptional reporter strain with environmental microbes on solid media and allowing the colonies to grow in coculture. The fluorescent transcriptional reporter is designed so that the chosen bacterial strain fluoresces when it is expressing a particular phenotype of interest (i.e. biofilm formation, sporulation, virulence factor production, etc.) Screening is performed under growth conditions where this phenotype is not expressed (and therefore the reporter strain is typically nonfluorescent). When an environmental microbe secretes a metabolite that activates this phenotype, it diffuses through the agar and activates the fluorescent reporter construct. This allows the inducing-metabolite-producing microbe to be detected: they are the nonfluorescent colonies most proximal to the fluorescent colonies. Thus, this screen allows the identification of environmental microbes that produce diffusible metabolites that activate a particular physiological response in a reporter strain. This publication discusses how to: a) select appropriate coculture screening conditions, b) prepare the reporter and environmental microbes for screening, c) perform the coculture screen, d) isolate putative inducing organisms, and e) confirm their activity in a secondary screen. We developed this method to screen for soil organisms that activate biofilm matrix-production in Bacillus subtilis; however, we also discuss considerations for applying this approach to other genetically tractable bacteria.

Bacteria produce secreted compounds that have the potential to affect the physiology of their microbial neighbors. Here we describe a coculture screen that allows detection of such chemically mediated interspecies interactions by mixing soil microbes with fluorescent transcriptional reporter strains of Bacillus subtilis on solid media.

In nature, bacteria rarely exist in isolation; they are instead surrounded by a diverse array of other microorganisms that alter the local environment by ...

Protein-protein Interactions Visualized by Bimolecular Fluorescence Complementation in Tobacco Protoplasts and Leaves

Many proteins interact transiently with other proteins or are integrated into multi-protein complexes to perform their biological function. Bimolecular fluorescence complementation (BiFC) is an in vivo method to monitor such interactions in plant cells. In the presented protocol the investigated candidate proteins are fused to complementary halves of fluorescent proteins and the respective constructs are introduced into plant cells via agrobacterium-mediated transformation. Subsequently, the proteins are transiently expressed in tobacco leaves and the restored fluorescent signals can be detected with a confocal laser scanning microscope in the intact cells. This allows not only visualization of the interaction itself, but also the subcellular localization of the protein complexes can be determined. For this purpose, marker genes containing a fluorescent tag can be coexpressed along with the BiFC constructs, thus visualizing cellular structures such as the endoplasmic reticulum, mitochondria, the Golgi apparatus or the plasma membrane. The fluorescent signal can be monitored either directly in epidermal leaf cells or in single protoplasts, which can be easily isolated from the transformed tobacco leaves. BiFC is ideally suited to study protein-protein interactions in their natural surroundings within the living cell. However, it has to be considered that the expression has to be driven by strong promoters and that the interaction partners are modified due to fusion of the relatively large fluorescence tags, which might interfere with the interaction mechanism. Nevertheless, BiFC is an excellent complementary approach to other commonly applied methods investigating protein-protein interactions, such as coimmunoprecipitation, in vitro pull-down assays or yeast-two-hybrid experiments.

Formation of protein complexes in vivo can be visualized by bimolecular fluorescence complementation. Interaction partners are fused to complementary parts of fluorescent tags and transiently expressed in tobacco leaves, resulting in a reconstituted fluorescent signal upon close proximity of the two proteins.

Many proteins interact transiently with other proteins or are integrated into multi-protein complexes to perform their biological function. Bimolecular ...

Investigating Protein-protein Interactions in Live Cells Using Bioluminescence Resonance Energy Transfer

Assays based on Bioluminescence Resonance Energy Transfer (BRET) provide a sensitive and reliable means to monitor protein-protein interactions in live cells. BRET is the non-radiative transfer of energy from a 'donor' luciferase enzyme to an 'acceptor' fluorescent protein. In the most common configuration of this assay, the donor is Renilla reniformis luciferase and the acceptor is Yellow Fluorescent Protein (YFP). Because the efficiency of energy transfer is strongly distance-dependent, observation of the BRET phenomenon requires that the donor and acceptor be in close proximity. To test for an interaction between two proteins of interest in cultured mammalian cells, one protein is expressed as a fusion with luciferase and the second as a fusion with YFP. An interaction between the two proteins of interest may bring the donor and acceptor sufficiently close for energy transfer to occur. Compared to other techniques for investigating protein-protein interactions, the BRET assay is sensitive, requires little hands-on time and few reagents, and is able to detect interactions which are weak, transient, or dependent on the biochemical environment found within a live cell. It is therefore an ideal approach for confirming putative interactions suggested by yeast two-hybrid or mass spectrometry proteomics studies, and in addition it is well-suited for mapping interacting regions, assessing the effect of post-translational modifications on protein-protein interactions, and evaluating the impact of mutations identified in patient DNA.

Interactions between proteins are fundamental to all cellular processes. Using Bioluminescence Resonance Energy Transfer, the interaction between a pair of proteins can be monitored in live cells and in real time. Furthermore, the effects of potentially pathogenic mutations can be assessed.

Assays based on Bioluminescence Resonance Energy Transfer (BRET) provide a sensitive and reliable means to monitor protein-protein interactions in live ...

Identifying Protein-protein Interaction Sites Using Peptide Arrays

Protein-protein interactions mediate most of the processes in the living cell and control homeostasis of the organism. Impaired protein interactions may result in disease, making protein interactions important drug targets. It is thus highly important to understand these interactions at the molecular level. Protein interactions are studied using a variety of techniques ranging from cellular and biochemical assays to quantitative biophysical assays, and these may be performed either with full-length proteins, with protein domains or with peptides. Peptides serve as excellent tools to study protein interactions since peptides can be easily synthesized and allow the focusing on specific interaction sites. Peptide arrays enable the identification of the interaction sites between two proteins as well as screening for peptides that bind the target protein for therapeutic purposes. They also allow high throughput SAR studies. For identification of binding sites, a typical peptide array usually contains partly overlapping 10-20 residues peptides derived from the full sequences of one or more partner proteins of the desired target protein. Screening the array for binding the target protein reveals the binding peptides, corresponding to the binding sites in the partner proteins, in an easy and fast method using only small amount of protein.
In this article we describe a protocol for screening peptide arrays for mapping the interaction sites between a target protein and its partners. The peptide array is designed based on the sequences of the partner proteins taking into account their secondary structures. The arrays used in this protocol were Celluspots arrays prepared by INTAVIS Bioanalytical Instruments. The array is blocked to prevent unspecific binding and then incubated with the studied protein. Detection using an antibody reveals the binding peptides corresponding to the specific interaction sites between the proteins.

Peptide array screening is a high throughput assay for identifying protein-protein interaction sites. This allows mapping multiple interactions of a target protein and can serve as a method for identifying sites for inhibitors that target a protein. Here we describe a protocol for screening and analyzing peptide arrays.

Protein-protein interactions mediate most of the processes in the living cell and control homeostasis of the organism. Impaired protein interactions may ...

Development of Inhibitors of Protein-protein Interactions through REPLACE: Application to the Design and Development Non-ATP Competitive CDK Inhibitors

REPLACE is a unique strategy developed to more effectively target protein-protein interactions (PPIs). It aims to expand available drug target space by providing improved methodology for the identification of inhibitors for such binding sites and which represent the majority of potential drug targets. The main goal of this paper is to provide a methodological overview of the use and application of the REPLACE strategy which involves computational and synthetic chemistry approaches. REPLACE is exemplified through its application to the development of non-ATP competitive cyclin dependent kinases (CDK) inhibitors as anti-tumor therapeutics. CDKs are frequently deregulated in cancer and hence are considered as important targets for drug development. Inhibition of CDK2/cyclin A in S phase has been reported to promote selective apoptosis of cancer cells in a p53 independent manner through the E2F1 pathway. Targeting the protein-protein interaction at the cyclin binding groove (CBG) is an approach which will allow the specific inhibition of cell cycle over transcriptional CDKs. The CBG is recognized by a consensus sequence derived from CDK substrates and tumor suppressor proteins termed the cyclin binding motif (CBM). The CBM has previously been optimized to an octapeptide from p21Waf (HAKRRIF) and then further truncated to a pentapeptide retaining sufficient activity (RRLIF). Peptides in general are not cell permeable, are metabolically unstable and therefore the REPLACE (REplacement with Partial Ligand Alternatives through Computational Enrichment) strategy has been applied in order to generate more drug-like inhibitors. The strategy begins with the design of Fragment ligated inhibitory peptides (FLIPs) that selectively inhibit cell cycle CDK/cyclin complexes. FLIPs were generated by iteratively replacing residues of HAKRRLIF/RRLIF with fragment like small molecules (capping groups), starting from the N-terminus (Ncaps), followed by replacement on the C-terminus. These compounds are starting points for the generation of non-ATP competitive CDK inhibitors as anti-tumor therapeutics.

We describe implementation of the REPLACE strategy for targeting protein-protein interactions. REPLACE is an iterative strategy involving synthetic and computational approaches for the conversion of optimized peptidic inhibitors into drug like molecules.

REPLACE is a unique strategy developed to more effectively target protein-protein interactions (PPIs). It aims to expand available drug target space by ...