Name: high-throughput screening for protein-based inheritance in s. cerevisiae
Uploaded: 2017-08-08T14:00:00
Description: Watch this Scientific Journal Video about High-throughput Screening for Protein-based Inheritance in S. cerevisiae at JoVE.com

We thank Sohini Chakrabortee, Sandra Jones, David Garcia, Bhupinder Bhullar, Amelia Chang, Richard She, and Susan Lindquist for their assistance in developing the assays used in this paper, as well as the reviewers for their thoughtful comments.

1. Initial Overexpression
<ol>
	<li>Transform the yeast cells (in this case, BY4741 MAT a haploids) previously grown in YPD liquid (10 g of yeast extract, 20 g of peptone, and 20 g of glucose per 1 L) with the desired candidate constructs from the FLEXGene ORFeome library (yeast ORFs under the control of a galactose-inducible promoter in the URA3-marked centromericplasmid backbone, pBY01129).</li>
	<li>Use autoclaved toothpicks to pick four separate colonies from these...

<ol>
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Y., 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=Prion-inducing+domain+2-114+of+yeast+Sup35+protein+transforms+in+vitro+into+amyloid-like+filaments.">Prion-inducing domain 2-114 of yeast Sup35 protein transforms in vitro into amyloid-like filaments.</a> Proc Natl Acad Sci U S A. 94 (13), 6618-6622 (1997).</li><li>Shorter, J., Lindquist, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hsp104+catalyzes+formation+and+elimination+of+self-replicating+Sup35+prion+conformers.">Hsp104 catalyzes formation and elimination of self-replicating Sup35 prion conformers.</a> Science. 304 (5678), 1793-1797 (2004).</li><li>Ferreira, P. C., Ness, F., Edwards, S. R., Cox, B. S., Tuite, M. 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The first yeast prions were identified by their unusual phenotypes and perplexing patterns of inheritance. The characteristics of these prions were then used to build algorithms and computational tools to screen for additional prion proteins. The method described here, in contrast, is experimental and relies on transient overexpression to create a lasting change-a stable state-encoded in protein conformation. However, if the efficiency of &#34;seeding&#34; prion assembly by overexpression for any given protein is very lo...

Biological systems frequently experience transient fluctuations in protein abundance. Whether these have a lasting impact in shaping the phenotype of an organism or of future generations remains unclear. The best-known instances of this biology involve a rare class of proteins, prions, which drive the emergence of heritable traits without genome modification. Instead, these proteinaceous and infectious particles transmit phenotypes via self-perpetuating changes to protein conformation1,2. This type of inheritance was discovered as the cause of the unusual inheritance patterns of a devastating neurodegenerative disease. However, studies in organisms ranging from fungi to mammals3,4,5,6,7,8,9,10 have since revealed that prion-like elements can confer adaptive value. Nonetheless, prions have been viewed as a fascinating but rare biological oddity.
This prevailing wisdom is in part held because the characterization of protein-based inheritance has long been restricted by a small set of examples. Recent systematic screening efforts have widened this picture significantly by identifying several new bona fide prions11 and almost two dozen protein domains12 with the capacity to fuel prion-like conformational conversion. However, because these approaches have generally focused on strong amino acid sequence biases, the prions that have been discovered share the biochemical properties of the founding yeast prions [PSI+]13,14, [URE3]15, and [RNQ+]11,16. These include: 1) modular domains that are rich in long polymeric stretches of asparagine (N) and glutamine (Q), 2) assembly into an amyloid [PRION+] conformation17,18,19, and 3) complete reliance on disaggregase Hsp104 function for faithful propagation from mother to daughter13,20,21. Indeed, many bona fide prions, including [GAR+], [Het-s], and even the original prion (PrPSc), would be missed under such stringent criteria. Perhaps more importantly, they would be unable to capture any novel mechanisms of protein-based inheritance22. Thus, the true biological breadth of such phenomena may be far more common in nature than previously assumed.
To investigate this question, a high-throughput, proteome-wide strategy was employed. A hallmark of all prions, including PrPSc, [GAR+], and [Het-s], is that the transient overexpression of the causal proteins strongly increases the rate of prion acquisition15,23,24,25,26. We took advantage of this feature to systematically ask, across the entire yeast ORFeome, if stable protein-based, epigenetic states could be initiated by transiently inducing the overexpression of individual proteins. It is well known that protein overexpression can alter phenotypes27. However, prion proteins are unusual because their temporary overproduction produces a change in phenotype that is heritable for many hundreds of generations after the initial overexpression. We previously took advantage of this feature, as well as the unusual inheritance patterns of protein-based genetic elements, to identify dozens of proteins that are capable of heritably re-wiring phenotypic landscapes without altering the genome28. Although some identified proteins were previously known as prions, most were not, underscoring the power of this approach to uncover new forms of protein-based inheritance.

<table width="958">
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		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="width:356px;height:21px;">Guanidine hydrochloride</td>
			<td style="width:299px;">Sigma</td>
			<td style="width:125px;">Cat#G3272-25G</td>
			<td style="width:179px;">Chemical</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Manganese chloride</td>
			<td>Sigma</td>
			<td>Cat#M8054-100G</td>
			<td>Chemical</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ethidium bromide</td>
			<td>Sigma</td>
			<td>E1510</td>
			<td>Chemical</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">5-Fluoroorotic Acid</td>
			<td>Sigma</td>
			<td>Cat#F5013-50MG</td>
			<td>Chemical</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">BY4741 MATa (his3&#916;1 leu2&#916;0 LYS2 met15&#916;0 ura3&#916;0)</td>
			<td>Winston et al., 1995; Brachmann et al., 1998</td>
			<td>N/A</td>
			<td>Yeast strain</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">BY4741 MAT&#945; (his3&#916;1 leu2&#916;0 lys2&#916;0 MET15 ura3&#916;0)</td>
			<td>Winston et al., 1995; Brachmann et al., 1998</td>
			<td>N/A</td>
			<td>Yeast strain</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hsp70 (K69M)&#160;</td>
			<td>Jarosz et al., 2014b</td>
			<td>N/A</td>
			<td>Plasmid</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">FLEXGene library</td>
			<td>Hu et al., 2007</td>
			<td>N/A</td>
			<td>Plasmid library</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dextrose (glucose)</td>
			<td>Fisher Scientific</td>
			<td>D16-3</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Raffinose</td>
			<td>Sigma</td>
			<td>R0250-25G</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Galactose</td>
			<td>Fisher Scientific</td>
			<td>BP656-500</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CSM</td>
			<td>Sunrise Science</td>
			<td>1001-100</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CSM-URA</td>
			<td>Sunrise Science</td>
			<td>1004-100</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CSM-LYS</td>
			<td>Sunrise Science</td>
			<td>1032-100</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CSM-MET</td>
			<td>Sunrise Science</td>
			<td>1019-100</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CSM-LYS-MET</td>
			<td>Sunrise Science</td>
			<td>1035-100</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">yeast extract</td>
			<td>Fisher Scientific</td>
			<td>BP1422-2</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">peptone</td>
			<td>Research Products International</td>
			<td>P20240-5000</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">bacto-peptone</td>
			<td>BD</td>
			<td align="right">211677</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">glycerol</td>
			<td>EMD Millipore</td>
			<td>GX0185-2</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">yeast nitrogen base w/o amino acids</td>
			<td>BD</td>
			<td align="right">291920</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">agar</td>
			<td>IBI Scientific</td>
			<td>IB49172</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Adenine sulfate</td>
			<td>Sigma</td>
			<td>A3159-25G</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Potassium acetate</td>
			<td>Sigma</td>
			<td>P1190-500G</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Uracil</td>
			<td>Sigma</td>
			<td>U0750-100G</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Histidine</td>
			<td>Sigma</td>
			<td>H8000-100G</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Leucine</td>
			<td>Sigma</td>
			<td>L8000-25G</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lysine</td>
			<td>Sigma</td>
			<td>L5501-25G</td>
			<td>Media component</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">RNase I&#160;</td>
			<td>Thermo Fisher Scientific</td>
			<td>EN0601</td>
			<td>Enzyme</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">biotinylated DNase</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM1906</td>
			<td>Enzyme</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">zymolyase 100T (yeast lytic enzyme)</td>
			<td>Sunrise Science</td>
			<td>N0766555</td>
			<td>Enzyme</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microplate reader</td>
			<td>BioTek</td>
			<td>Synergy H1</td>
			<td>Equipment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Microplate stacker</td>
			<td>BioTek</td>
			<td>BioStack3</td>
			<td>Equipment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Plate filler</td>
			<td>BiotTek</td>
			<td>EL406</td>
			<td>Equipment</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Liquid handling robot</td>
			<td>Beckman Coulter</td>
			<td>Biomek FX</td>
			<td>Equipment</td>
		</tr>
	</tbody>
</table>

high-throughput screening for protein-based inheritance in s. cerevisiae

The encoding of biological information that is accessible to future generations is generally achieved via changes to the DNA sequence. Long-lived inheritance encoded in protein conformation (rather than sequence) has long been viewed as paradigm-shifting but rare. The best characterized examples of such epigenetic elements are prions, which possess a self-assembling behavior that can drive the heritable manifestation of new phenotypes. Many archetypal prions display a striking N/Q-rich sequence bias and assemble into an amyloid fold. These unusual features have informed most screening efforts to identify new prion proteins. However, at least three known prions (including the founding prion, PrPSc) do not harbor these biochemical characteristics. We therefore developed an alternative method to probe the scope of protein-based inheritance based on a property of mass action: the transient overexpression of prion proteins increases the frequency at which they acquire a self-templating conformation. This paper describes a method for analyzing the capacity of the yeast ORFeome to elicit protein-based inheritance. Using this strategy, we previously found that &gt;1% of yeast proteins could fuel the emergence of biological traits that were long-lived, stable, and arose more frequently than genetic mutation. This approach can be employed in high throughput across entire ORFeomes or as a targeted screening paradigm for specific genetic networks or environmental stimuli. Just as forward genetic screens define numerous developmental and signaling pathways, these techniques provide a methodology to investigate the influence of protein-based inheritance in biological processes.

Protein overexpression is known to dramatically alter cellular phenotypes27. Indeed, with an initial screening approach, hundreds of new phenotypes were reproducibly recovered from the overexpression of clones from the yeast ORFeome using just ten stressors. However, the assays described above allow for the assessment of whether cells retain any long-term stable phenotypes following this overexpression. One protein capable of encoding such a state is Psp1. Psp1 is ...

Watch this Scientific Journal Video about High-throughput Screening for Protein-based Inheritance in S. cerevisiae at JoVE.com

High-throughput Screening for Protein-based Inheritance in S. cerevisiae

This protocol describes a high-throughput methodology to functionally screen for protein-based inheritance in S. cerevisiae.

High-throughput Screening for Protein-based Inheritance in S. cerevisiae

The encoding of biological information that is accessible to future generations is generally achieved via changes to the DNA sequence. Long-lived ...

The overall goal of this high-throughput yeast phenotyping is to screen for proteins that illicit a lasting phenotypic memory of passed over expression, as a proxy for protein-based inheritance. This method can help answer key questions in the yeast Prion field, such as, how many proteins can it illicit inheritance of this type. The main advantage of this technique is that you can screen many proteins and pathways in an unbiased fashion.Start this procedure by growing the appropriate yeast cells in a 96 well plate at 30 degrees celsius, as described in the text protocol. Visually inspect the cultures to confirm that the cultures are saturated, cells should be visible by eye, at the bottom of each well. Use a liquid handling robot to prepare 384 well plates, containing 45 microliters of the appropriate medium per well.First, dispense Scal-URA into the wells of a 384 well plate. Then dispense Scal-URA plus the stressor of interest into the wells of a second plate, 20 millimolar of manganese chloride is used as the stressor in this experiment. Thirdly, dispense SD-URA, which will not induce plasmid expression, plus manganese chloride into another plate.Lower the 96 well plate containing the cultures onto the liquid handling robot and inoculate a one to four array of one microliter from each well of the 96 well plate, into four separate wells of each 384 well plate filled with a different media. Immediately place the plates with cells on a microplate stacker at room temperature and atmospheric carbon dioxide. Set the protocol for a 72 hour continuous loop, measuring the optical density at 600 nanometers with the microplate reader.After the growth measurements, transfer one microliter per well of the SCal-URA induced cultures that experienced protein over-expression to new 384 well plates, containing 45 microliters per well of ST-URA medium that does not permit protein expression of the plasmid. In parallel, perform analogous inoculations of a second set of 384 well plate containing 45 microliters per well of ST-URA from the cultures that were grown in ST-URA in the presence of the stressor. Place the plates in a humidified chamber and grow the plates for 48 hours at 30 degree celsius to saturation.After 48 hours, use the plates to re-inoculate one microliter per well in 384 well plates containing 45 microliters per well of ST-URA. Then, perform a separate re-inoculation of one microliter per well from the same source plate into a separate 384 well plate containing 45 microliters per well of ST-URA with the stressor. Immediately place the plates with cells of the microstacker at room temperature and atmospheric carbon dioxide and set the protocol for a 48 hour continuous loop, measuring the optical density at 600 nanometers with a microplate reader.When the growth measurements are complete, use the plate reader software to export the time versus optical density at 600 nanometer measurements as an XY table. Group columns of the optical density measurements for each biological replicate together and calculate the mean. Create an XY plot of time versus optical density at 600 nanometers to generate growth curves.For cultures that chose significant growth differences in response to a given stressor, dependent upon ancestral protein over-expression, take one microliter from each biological replicate, dilute in 10 milliliters of water and then plate 50 microliters on plates containing 5-FOA. Grow at 30 degree celsius for three days. If this results in too many or too few colonies per plate, adjust the dilution factor accordingly.100 to 200 colonies per plate is ideal. Pick eight to 32 single colonies with autoclave toothpicks and pin them to 96 well plates containing 150 microliters of SDCSM per well. Place the plates in a humidified chamber and grow to saturation for 48 to 72 hours at 30 degrees celsius.Use these cultures to inoculate two new sets of 96 well plates containing 150 microliters per well of SDCSM, both with and without the stressor. Place the plates on a microplate stacker and set the protocol to measure the optical density at 600 nanometers on a 48 hour continuous loop. After 48 hours, analyze the data as shown earlier and confirm that the significant growth differences seen earlier, are maintained after plasmid loss.The cells that maintain the induced phenotypes are then tested for classic hallmarks of protein-based inheritance as described in the text protocol. This protein-based inheritance screen revealed the transient over-expression of the PSP1 open reading frame, drives a resistance to manganese chloride that was maintained for hundreds of generations in cells, long after over-expression had ceased. Prion predicting algorithms scored the end terminus of PSP1 as moderately Prion-like.In contrast, the algorithms predicted virtually no significant Prion-like sequence features from most inducing proteins recovered on the screen, as shown by this representative analysis. Growth measurements of strains and SDCSM with manganese chloride, normalized to a corresponding naive PSP1 minus control, indicated that inhibition of the HSP104 disaggregase does not impair PSP1 dependent manganese chloride resistance whereas the removal of the HSP70 chaperone and the PSP1 gene, heritably eliminates this phenotype. All spores from single tetrads of crosses between strains, harboring the PSP1 dependent phenotypic state and naive strains, display manganese chloride resistance, indicating non-mendelian inheritance of the phenotype.A comparison of the infectivity for protein transformation between mock lysates and PSP1 harboring lysates as the transmissible material, showed that over 53%of naive cells transformed with seeded PSP1, received the corresponding manganese chloride resistance phenotype. Once mastered, this technique can be done in a couple of weeks, including incubation steps and the preparation of most screening steps can be done in less than two hours per day, even with a large number of plates. While attempting this procedure, it is important to remember to plan exactly what you wanna test beforehand and keep in mind the scale of the experiment.Now this is especially important to beginners of the technique. Following this procedure, other methods like those described in the text protocol can be performed to determine if the phenotypes observed in the screening display a true, Prion-like pattern of inheritance. After its development, this technique paved the way for researchers in the field of epigenetics to explore the breadth of Prion biology in sacralis service CI.After watching this video, you should have a good understanding of how to design a high throughput screen for new forms of protein-based inheritance in yeast, in both an unbiased and targeted fashion.Don't forget, that certain chemical stressors such as DNA damaging agents can be extremely hazardous and precautions, such as wearing personal protective equipment, should always be taken while performing this procedure.

high-throughput-screening-for-protein-based-inheritance-s

Research

JoVE Journal

Biology

Assay for Adhesion and Agar Invasion in S. cerevisiae

Yeasts are found in natural biofilms, where many microorganisms colonize surfaces. In artificial environments, such as surfaces of man-made objects, biofilms can reduce industrial productivity, destroy structures, and threaten human life. 1-3 On the other hand, harnessing the power of biofilms can help clean the environment and generate sustainable energy. 4-8
The ability of S. cerevisiae to colonize surfaces and participate in complex biofilms was mostly ignored until the rediscovery of the differentiation programs triggered by various signaling pathways and environmental cues in this organism. 9, 10 The continuing interest in using S. cerevisiae as a model organism to understand the interaction and convergence of signaling pathways, such as the Ras-PKA, Kss1 MAPK, and Hog1 osmolarity pathways, quickly placed S. cerevisiae in the junction of biofilm biology and signal transduction research. 11-20 To this end, differentiation of yeast cells into long, adhesive, pseudohyphal filaments became a convenient readout for the activation of signal transduction pathways upon various environmental changes. However, filamentation is a complex collection of phenotypes, which makes assaying for it as if it were a simple phenotype misleading. In the past decade, several assays were successfully adopted from bacterial biofilm studies to yeast research, such as MAT formation assays to measure colony spread on soft agar and crystal violet staining to quantitatively measure cell-surface adherence. 12, 21 However, there has been some confusion in assays developed to qualitatively assess the adhesive and invasive phenotypes of yeast in agar.
Here, we present a simple and reliable method for assessing the adhesive and invasive quality of yeast strains with easy-to-understand steps to isolate the adhesion assessment from invasion assessment. Our method, adopted from previous studies, 10, 16 involves growing cells in liquid media and plating on differential nutrient conditions for growth of large spots, which we then wash with water to assess adhesion and rub cells completely off the agar surface to assess invasion into the agar. We eliminate the need for streaking cells onto agar, which affects the invasion of cells into the agar. In general, we observed that haploid strains that invade agar are always adhesive, yet not all adhesive strains can invade agar medium. Our approach can be used in conjunction with other assays to carefully dissect the differentiation steps and requirements of yeast signal transduction, differentiation, quorum sensing, and biofilm formation.

We describe a qualitative assay for yeast adhesion and agar invasion as a measure of invasive and pseudohyphal differentiation. This simple assay can be used to assess the invasive phenotype of various mutants as well as the effects environmental cues and signaling pathways on yeast differentiation.

Yeasts are found in natural biofilms, where many microorganisms colonize surfaces. In artificial environments, such as surfaces of man-made objects, ...

A high-throughput method to globally study the organelle morphology in S. cerevisiae

High-throughput methods to examine protein localization or organelle morphology is an effective tool for studying protein interactions and can help achieve an comprehensive understanding of molecular pathways. In Saccharomyces cerevisiae, with the development of the non-essential gene deletion array, we can globally study the morphology of different organelles like the endoplasmic reticulum (ER) and the mitochondria using GFP (or variant)-markers in different gene backgrounds. However, incorporating GFP markers in each single mutant individually is a labor-intensive process. Here, we describe a procedure that is routinely used in our laboratory. By using a robotic system to handle high-density yeast arrays and drug selection techniques, we can significantly shorten the time required and improve reproducibility. In brief, we cross a GFP-tagged mitochondrial marker (Apc1-GFP) to a high-density array of 4,672 nonessential gene deletion mutants by robotic replica pinning.  Through diploid selection, sporulation, germination and dual marker selection, we recover both alleles. As a result, each haploid single mutant contains Apc1-GFP incorporated at its genomic locus. Now, we can study the morphology of mitochondria in all non-essential mutant background. Using this high-throughput approach, we can conveniently study and delineate the pathways and genes involved in the inheritance and the formation of organelles in a genome-wide setting.

GFP-fusion proteins are widely used to visualize organelles by confocal microscopy. However, screening for mutations that affect the morphology of organelles generally requires individual mutagenesis and is time consuming. Here, we demonstrate a method to simultaneously incorporate organelle-GFP markers in almost 5,000 non-essential genes in yeast.

High-throughput methods to examine protein localization or organelle morphology is an effective tool for studying protein interactions and can help ...

Identification of protein complexes with quantitative proteomics in S. cerevisiae

Lipids are the building blocks of cellular membranes that function as barriers and in compartmentalization of cellular processes, and recently, as important intracellular signalling molecules. However, unlike proteins, lipids are small hydrophobic molecules that traffic primarily by poorly described nonvesicular routes, which are hypothesized to occur at membrane contact sites (MCSs). MCSs are regions where the endoplasmic reticulum (ER) makes direct physical contact with a partnering organelle, e.g., plasma membrane (PM). The ER portion of ER-PM MCSs is enriched in lipid-synthesizing enzymes, suggesting that lipid synthesis is directed to these sites and implying that MCSs are important for lipid traffic. Yeast is an ideal model to study ER-PM MCSs because of their abundance, with over 1000 contacts per cell, and their conserved nature in all eukaryotes. Uncovering the proteins that constitute MCSs is critical to understanding how lipids traffic is accomplished in cells, and how they act as signaling molecules. We have found that an ER called Scs2p localize to ER-PM MCSs and is important for their formation. We are focused on uncovering the molecular partners of Scs2p. Identification of protein complexes traditionally relies on first resolving purified protein samples by gel electrophoresis, followed by in-gel digestion of protein bands and analysis of peptides by mass spectrometry. This often limits the study to a small subset of proteins. Also, protein complexes are exposed to denaturing or non-physiological conditions during the procedure. To circumvent these problems, we have implemented a large-scale quantitative proteomics technique to extract unbiased and quantified data. We use stable isotope labeling with amino acids in cell culture (SILAC) to incorporate staple isotope nuclei in proteins in an untagged control strain. Equal volumes of tagged culture and untagged, SILAC-labeled culture are mixed together and lysed by grinding in liquid nitrogen. We then carry out an affinity purification procedure to pull down protein complexes. Finally, we precipitate the protein sample, which is ready for analysis by high-performance liquid chromatography/ tandem mass spectrometry. Most importantly, proteins in the control strain are labeled by the heavy isotope and will produce a mass/ charge shift that can be quantified against the unlabeled proteins in the bait strain. Therefore, contaminants, or unspecific binding can be easily eliminated. By using this approach, we have identified several novel proteins that localize to ER-PM MCSs. Here we present a detailed description of our approach. 

Here we describe a new quantitative proteomics technique for identifying protein complexes in Saccharomyces cerevisiae. In this study, we have used the SILAC method together with affinity purification followed by tandem mass spectrometry to identify with high specificity the binding partners of an ER protein, Scs2p.

Lipids are the building blocks of cellular membranes that function as barriers and in compartmentalization of cellular processes, and recently, as ...

High-throughput Screening and Biosensing with Fluorescent C. elegans Strains

High-throughput screening (HTS) is a powerful approach for identifying chemical modulators of biological processes. However, many compounds identified in screens using cell culture models are often found to be toxic or pharmacologically inactive in vivo1-2. Screening in whole animal models can help avoid these pitfalls and streamline the path to drug development.
C. elegans is a multicellular model organism well suited for HTS. It is small (&lt;1 mm) and can be economically cultured and dispensed in liquids. C. elegans is also one of the most experimentally tractable animal models permitting rapid and detailed identification of drug mode-of-action3.
We describe a protocol for culturing and dispensing fluorescent strains of C. elegans for high-throughput screening of chemical libraries or detection of environmental contaminants that alter the expression of a specific gene. Large numbers of developmentally synchronized worms are grown in liquid culture, harvested, washed, and suspended at a defined density. Worms are then added to black, flat-bottomed 384-well plates using a peristaltic liquid dispenser. Small molecules from a chemical library or test samples (e.g., water, food, or soil) can be added to wells with worms. In vivo, real-time fluorescence intensity is measured with a fluorescence microplate reader. This method can be adapted to any inducible gene in C. elegans for which a suitable reporter is available. Many inducible stress and developmental transcriptional pathways are well defined in C. elegans and GFP transgenic reporter strains already exist for many of them4. When combined with the appropriate transgenic reporters, our method can be used to screen for pathway modulators or to develop robust biosensor assays for environmental contaminants. 
We demonstrate our C. elegans culture and dispensing protocol with an HTS assay we developed to monitor the C. elegans cap &#x2018;n&#x2019; collar transcription factor SKN-1. SKN-1 and its mammalian homologue Nrf2 activate cytoprotective genes during oxidative and xenobiotic stress5-10. Nrf2 protects mammals from numerous age-related disorders such as cancer, neurodegeneration, and chronic inflammation and has become a major chemotherapeutic target11-13.Our assay is based on a GFP transgenic reporter for the SKN-1 target gene gst-414, which encodes a glutathione-s transferase6. The gst-4 reporter is also a biosensor for xenobiotic and oxidative chemicals that activate SKN-1 and can be used to detect low levels of contaminants such as acrylamide and methyl-mercury15-16.

High-throughput Screening and Biosensing with Fluorescent C. elegans Strains

A procedure for liquid-based culturing and dispensing of C. elegans strains expressing fluorescent reporter proteins is described that does not require expensive sorting equipment. This approach can be applied to numerous inducible C. elegans genes for drug discovery or biosensing of contaminants.

High-throughput screening (HTS) is a powerful approach for identifying chemical modulators of biological processes.  However, many compounds identified in ...

High Throughput Screening of Fungal Endoglucanase Activity in Escherichia coli

Cellulase enzymes (endoglucanases, cellobiohydrolases, and &beta;-glucosidases) hydrolyze cellulose into component sugars, which in turn can be converted into fuel alcohols1. The potential for enzymatic hydrolysis of cellulosic biomass to provide renewable energy has intensified efforts to engineer cellulases for economical fuel production2. Of particular interest are fungal cellulases3-8, which are already being used industrially for foods and textiles processing.
Identifying active variants among a library of mutant cellulases is critical to the engineering process; active mutants can be further tested for improved properties and/or subjected to additional mutagenesis. Efficient engineering of fungal cellulases has been hampered by a lack of genetic tools for native organisms and by difficulties in expressing the enzymes in heterologous hosts. Recently, Morikawa and coworkers developed a method for expressing in E. coli the catalytic domains of endoglucanases from H. jecorina3,9, an important industrial fungus with the capacity to secrete cellulases in large quantities. Functional E. coli expression has also been reported for cellulases from other fungi, including Macrophomina phaseolina10 and Phanerochaete chrysosporium11-12. 
We present a method for high throughput screening of fungal endoglucanase activity in E. coli. (Fig 1) This method uses the common microbial dye Congo Red (CR) to visualize enzymatic degradation of carboxymethyl cellulose (CMC) by cells growing on solid medium. The activity assay requires inexpensive reagents, minimal manipulation, and gives unambiguous results as zones of degradation (&#x201C;halos&#x201D;) at the colony site. Although a quantitative measure of enzymatic activity cannot be determined by this method, we have found that halo size correlates with total enzymatic activity in the cell. Further characterization of individual positive clones will determine , relative protein fitness. 
Traditional bacterial whole cell CMC/CR activity assays13 involve pouring agar containing CMC onto colonies, which is subject to cross-contamination, or incubating cultures in CMC agar wells, which is less amenable to large-scale experimentation. Here we report an improved protocol that modifies existing wash methods14 for cellulase activity: cells grown on CMC agar plates are removed prior to CR staining. Our protocol significantly reduces cross-contamination and is highly scalable, allowing the rapid screening of thousands of clones. In addition to H. jecorina enzymes, we have expressed and screened endoglucanase variants from the Thermoascus aurantiacus and Penicillium decumbens (shown in Figure 2), suggesting that this protocol is applicable to enzymes from a range of organisms.

High Throughput Screening of Fungal Endoglucanase Activity in Escherichia coli

We describe a low cost, high throughput method to screen for fungal endoglucanase activity in E. coli. The method relies on a simple visual readout of substrate degradation, does not require enzyme purification, and is highly scalable. This allows for the rapid screening of large libraries of enzyme variants.

Cellulase enzymes (endoglucanases, cellobiohydrolases, and &beta;-glucosidases) hydrolyze cellulose into component sugars, which in turn can be converted ...

Flow Cytometry-based Purification of S. cerevisiae Zygotes

Zygotes are essential intermediates between haploid and diploid states in the life cycle of many organisms, including yeast (Figure 1) 1. S. cerevisiae zygotes result from the fusion of haploid cells of distinct mating type (MATa, MATalpha) and give rise to corresponding stable diploids that successively generate as many as 20 diploid progeny as a result of their strikingly asymmetric mitotic divisions 2. Zygote formation is orchestrated by a complex sequence of events: In this process, soluble mating factors bind to cognate receptors, triggering receptor-mediated signaling cascades that facilitate interruption of the cell cycle and culminate in cell-cell fusion. Zygotes may be considered a model for progenitor or stem cell function.
Although much has been learned about the formation of zygotes and although zygotes have been used to investigate cell-molecular questions of general significance, almost all studies have made use of mating mixtures in which zygotes are intermixed with a majority population of haploid cells 3-8. Many aspects of the biochemistry of zygote formation and the continuing life of the zygote therefore remain uninvestigated.
Reports of purification of yeast zygotes describe protocols based on their sedimentation properties 9; however, this sedimentation-based procedure did not yield nearly 90% purity in our hands. Moreover, it has the disadvantage that cells are exposed to hypertonic sorbitol. We therefore have developed a versatile purification procedure. For this purpose, pairs of haploid cells expressing red or green fluorescent proteins were co-incubated to allow zygote formation, harvested at various times, and the resulting zygotes were purified using a flow cytometry-based sorting protocol. This technique provides a convenient visual assessment of purity and maturation. The average purity of the fraction is approximately 90%. According to the timing of harvest, zygotes of varying degrees of maturity can be recovered. The purified samples provide a convenient point of departure for "-omic" studies, for recovery of initial progeny, and for systematic investigation of this progenitor cell.

Flow Cytometry-based Purification of S. cerevisiae Zygotes

To purify zygotes of S. cerevisiae, haploid cells of opposite mating type were engineered to express red or green fluorescent proteins, co-incubated to allow zygote formation, and fractionated using a flow cytometry-based protocol. The highly-enriched fraction enables subsequent "-omic" studies, recovery of initial progeny, and systematic investigation of zygote morphogenesis.

Zygotes are essential intermediates between haploid and diploid states in the life cycle of many organisms, including yeast (Figure 1) 1. S. cerevisiae ...

High-throughput Screening for Small-molecule Modulators of Inward Rectifier Potassium Channels

Specific members of the inward rectifier potassium (Kir) channel family are postulated drug targets for a variety of disorders, including hypertension, atrial fibrillation, and pain1,2. For the most part, however, progress toward understanding their therapeutic potential or even basic physiological functions has been slowed by the lack of good pharmacological tools. Indeed, the molecular pharmacology of the inward rectifier family has lagged far behind that of the S4 superfamily of voltage-gated potassium (Kv) channels, for which a number of nanomolar-affinity and highly selective peptide toxin modulators have been discovered3. The bee venom toxin tertiapin and its derivatives are potent inhibitors of Kir1.1 and Kir3 channels4,5, but peptides are of limited use therapeutically as well as experimentally due to their antigenic properties and poor bioavailability, metabolic stability and tissue penetrance. The development of potent and selective small-molecule probes with improved pharmacological properties will be a key to fully understanding the physiology and therapeutic potential of Kir channels.
The Molecular Libraries Probes Production Center Network (MLPCN) supported by the National Institutes of Health (NIH) Common Fund has created opportunities for academic scientists to initiate probe discovery campaigns for molecular targets and signaling pathways in need of better pharmacology6. The MLPCN provides researchers access to industry-scale screening centers and medicinal chemistry and informatics support to develop small-molecule probes to elucidate the function of genes and gene networks. The critical step in gaining entry to the MLPCN is the development of a robust target- or pathway-specific assay that is amenable for high-throughput screening (HTS).
Here, we describe how to develop a fluorescence-based thallium (Tl+) flux assay of Kir channel function for high-throughput compound screening7,8,9,10.The assay is based on the permeability of the K+ channel pore to the K+ congener Tl+. A commercially available fluorescent Tl+ reporter dye is used to detect transmembrane flux of Tl+ through the pore. There are at least three commercially available dyes that are suitable for Tl+ flux assays: BTC, FluoZin-2, and FluxOR7,8. This protocol describes assay development using FluoZin-2. Although originally developed and marketed as a zinc indicator, FluoZin-2 exhibits a robust and dose-dependent increase in fluorescence emission upon Tl+ binding. We began working with FluoZin-2 before FluxOR was available7,8 and have continued to do so9,10. However, the steps in assay development are essentially identical for all three dyes, and users should determine which dye is most appropriate for their specific needs. We also discuss the assay's performance benchmarks that must be reached to be considered for entry to the MLPCN. Since Tl+ readily permeates most K+ channels, the assay should be adaptable to most K+ channel targets.

Methods for developing and validating a quantitative fluorescence assay for measuring the activity of inward rectifier potassium (Kir) channels for high-throughput compound screening is presented.

Specific members of the inward rectifier potassium (Kir) channel family are postulated drug targets for a variety of disorders, including hypertension, ...

High-throughput Functional Screening using a Homemade Dual-glow Luciferase Assay

We present a rapid and inexpensive high-throughput screening protocol to identify transcriptional regulators of alpha-synuclein, a gene associated with Parkinson&#39;s disease. 293T cells are transiently transfected with plasmids from an arrayed ORF expression library, together with luciferase reporter plasmids, in a one-gene-per-well microplate format. Firefly luciferase activity is assayed after 48 hr to determine the effects of each library gene upon alpha-synuclein transcription, normalized to expression from an internal control construct (a hCMV promoter directing Renilla luciferase). This protocol is facilitated by a bench-top robot enclosed in a biosafety cabinet, which performs aseptic liquid handling in 96-well format. Our automated transfection protocol is readily adaptable to high-throughput lentiviral library production or other functional screening protocols requiring triple-transfections of large numbers of unique library plasmids in conjunction with a common set of helper plasmids. We also present an inexpensive and validated alternative to commercially-available, dual luciferase reagents which employs PTC124, EDTA, and pyrophosphate to suppress firefly luciferase activity prior to measurement of Renilla luciferase. Using these methods, we screened 7,670 human genes and identified 68 regulators of alpha-synuclein. This protocol is easily modifiable to target other genes of interest.

We present a rapid and inexpensive screening method for identifying transcriptional regulators using high-throughput robotic transfections and a homemade dual-glow luciferase assay. This protocol rapidly generates direct side-by-side functional data for thousands of genes and is easily modifiable to target any gene of interest.

We present a rapid and inexpensive high-throughput screening protocol to identify transcriptional regulators of alpha-synuclein, a gene associated with ...

High Throughput Quantitative Expression Screening and Purification Applied to Recombinant Disulfide-rich Venom Proteins Produced in E. coli

Escherichia coli (E. coli) is the most widely used expression system for the production of recombinant proteins for structural and functional studies. However, purifying proteins is sometimes challenging since many proteins are expressed in an insoluble form. When working with difficult or multiple targets it is therefore recommended to use high throughput (HTP) protein expression screening on a small scale (1-4&#160;ml cultures) to quickly identify conditions for soluble expression. To cope with the various structural genomics programs of the lab, a quantitative (within a range of 0.1-100 mg/L culture of recombinant protein) and HTP protein expression screening protocol was implemented and validated on thousands of proteins. The protocols were automated with the use of a liquid handling robot but can also be performed manually without specialized equipment.
Disulfide-rich venom proteins are gaining increasing recognition for their potential as therapeutic drug leads. They can be highly potent and selective, but their complex disulfide bond networks make them challenging to produce. As a member of the FP7 European Venomics project (<a href="http://www.venomics.eu">www.venomics.eu</a>), our challenge is to develop successful production strategies with the aim of producing thousands of novel venom proteins for functional characterization. Aided by the redox properties of disulfide bond isomerase DsbC, we adapted our HTP production pipeline for the expression of oxidized, functional venom peptides in the E. coli cytoplasm. The protocols are also applicable to the production of diverse disulfide-rich proteins. Here we demonstrate our pipeline applied to the production of animal venom proteins. With the protocols described herein it is likely that soluble disulfide-rich proteins will be obtained in as little as a week. Even from a small scale, there is the potential to use the purified proteins for validating the oxidation state by mass spectrometry, for characterization in pilot studies, or for sensitive micro-assays.

High Throughput Quantitative Expression Screening and Purification Applied to Recombinant Disulfide-rich Venom Proteins Produced in E. coli

A protocol for the quantitative, high throughput expression screening and analytical purification of fusion proteins from small-scale Escherichia coli cultures is described and applied to the expression of disulfide-rich animal venom protein targets.

Escherichia coli (E. coli) is the most widely used expression system for the production of recombinant proteins for structural and functional studies. ...

High-throughput Screening for Chemical Modulators of Post-transcriptionally Regulated Genes

Both transcriptional and post-transcriptional regulation have a profound impact on genes expression. However, commonly adopted cell-based screening assays focus on transcriptional regulation, being essentially aimed at the identification of promoter-targeting molecules. As a result, post-transcriptional mechanisms are largely uncovered by gene expression targeted drug development. Here we describe a cell-based assay aimed at investigating the role of the 3&#39; untranslated region (3&#8217; UTR) in the modulation of the fate of its mRNA, and at identifying compounds able to modify it. The assay is based on the use of a luciferase reporter construct containing the 3&#8217; UTR of a gene of interest stably integrated into a disease-relevant cell line. The protocol is divided into two parts, with the initial focus on the primary screening aimed at the identification of molecules affecting luciferase activity after 24 hr of treatment. The second part of the protocol describes the counter-screening necessary to discriminate compounds modulating luciferase activity specifically through the 3&#8217; UTR. In addition to the detailed protocol and representative results, we provide important considerations about the assay development and the validation of the hit(s) on the endogenous target. The described cell-based reporter gene assay will allow scientists to identify molecules modulating protein levels via post-transcriptional mechanisms dependent on a 3&#8217; UTR.

Here we describe a cell-based reporter gene assay as a valuable tool to screen chemical libraries for compounds modulating post-transcriptional control mechanisms exerted through 3&#8217; UTR.

Both transcriptional and post-transcriptional regulation have a profound impact on genes expression. However, commonly adopted cell-based screening assays ...