Name: using high content imaging to quantify target engagement in adherent cells
Uploaded: 2018-11-29T14:45:00
Description: Watch this Scientific Journal Video about Using High Content Imaging to Quantify Target Engagement in Adherent Cells at JoVE.com

The authors acknowledge infrastructure support from Science for Life Laboratory and Karolinska Institutet. The authors also acknowledge input and discussions with Michaela Vallin, Magdalena Otrocka and Thomas Lundb&#228;ck.

1. Seeding of Cells
NOTE: For a general overview of the workflow see Figure 1. A detailed list of materials and reagents are available in the Table of Materials.
<ol>
	<li>Prior to seeding of the cells, drill holes with a standard drill in the frame of black 384-well imaging assay plates to avoid air bubbles being trapped under the plate later during the heating step. To avoid plastic particles entering the wells during this ste...

<ol>
	<li>Morgan, P., 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=Impact+of+a+five-dimensional+framework+on+R&amp;D+productivity+at+AstraZeneca.">Impact of a five-dimensional framework on R&amp;D productivity at AstraZeneca.</a> Nature Reviews Drug Discovery. 17 (3), 167-181 (2018).</li><li>Freedman, L. P., Cockburn, I. M., Simcoe, T. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Economics+of+Reproducibility+in+Preclinical+Research.">The Economics of Reproducibility in Preclinical Research.</a> PLOS Biology. 13 (6), e1002165 (2015).</li><li>Waring, M. 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=An+analysis+of+the+attrition+of+drug+candidates+from+four+major+pharmaceutical+companies.">An analysis of the attrition of drug candidates from four major pharmaceutical companies.</a> Nature Reviews Drug Discovery. 14 (7), 475-486 (2015).</li><li>Morgan, P., 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=Can+the+flow+of+medicines+be+improved?+Fundamental+pharmacokinetic+and+pharmacological+principles+toward+improving+Phase+II+survival.">Can the flow of medicines be improved? Fundamental pharmacokinetic and pharmacological principles toward improving Phase II survival.</a> Drug Discovery Today. 17 (9), 419-424 (2012).</li><li>Bunnage, M. E., Chekler, E. L. P., Jones, L. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Target+validation+using+chemical+probes.">Target validation using chemical probes.</a> Nature Chemical Biology. 9 (4), 195-199 (2013).</li><li>Sch&#252;rmann, M., Janning, P., Ziegler, S., Waldmann, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Small-Molecule+Target+Engagement+in+Cells.">Small-Molecule Target Engagement in Cells.</a> Cell Chemical Biology. 23 (4), 435-441 (2016).</li><li>Robers, M. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Target+engagement+and+drug+residence+time+can+be+observed+in+living+cells+with+BRET.">Target engagement and drug residence time can be observed in living cells with BRET.</a> Nature Communications. 6, 10091 (2015).</li><li>Martinez Molina, D., 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=Monitoring+drug+target+engagement+in+cells+and+tissues+using+the+cellular+thermal+shift+assay.">Monitoring drug target engagement in cells and tissues using the cellular thermal shift assay.</a> Science. 341 (6141), 84-87 (2013).</li><li>Martinez Molina, D., Nordlund, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Cellular+Thermal+Shift+Assay:+A+Novel+Biophysical+Assay+for+In+situ+Drug+Target+Engagement+and+Mechanistic+Biomarker+Studies.">The Cellular Thermal Shift Assay: A Novel Biophysical Assay for In situ Drug Target Engagement and Mechanistic Biomarker Studies.</a> Annual Review of Pharmacology and Toxicology. 56, 141-161 (2016).</li><li>Jafari, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+cellular+thermal+shift+assay+for+evaluating+drug+target+interactions+in+cells.">The cellular thermal shift assay for evaluating drug target interactions in cells.</a> Nature Protocols. 9 (9), 2100-2122 (2014).</li><li>Almqvist, 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=CETSA+screening+identifies+known+and+novel+thymidylate+synthase+inhibitors+and+slow+intracellular+activation+of+5-fluorouracil.">CETSA screening identifies known and novel thymidylate synthase inhibitors and slow intracellular activation of 5-fluorouracil.</a> Nature Communications. 7, 11040 (2016).</li><li>Axelsson, 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=In+situ+Target+Engagement+Studies+in+Adherent+Cells.">In situ Target Engagement Studies in Adherent Cells.</a> ACS Chemical Biology. 13 (4), 942-950 (2018).</li><li>Seashore-Ludlow, B., Perspective Lundb&#228;ck, T. E. a. r. l. y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microplate+Application+of+the+Cellular+Thermal+Shift+Assay+(CETSA).">Microplate Application of the Cellular Thermal Shift Assay (CETSA).</a> Journal of Biomolecular Screening. 21 (10), 1019-1033 (2016).</li><li>Axelsson, H., Almqvist, H., Seashore-Ludlow, B., Lundback, T., Sittampalam, G. 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=.">.</a> Assay Guidance Manual [Internet]. , (2016).</li><li>Mateus, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prediction+of+intracellular+exposure+bridges+the+gap+between+target-+and+cell-based+drug+discovery.">Prediction of intracellular exposure bridges the gap between target- and cell-based drug discovery.</a> Proceedings of the National Academy of Sciences of the United States of America. 114 (30), E6231-E6239 (2017).</li></ol>

As discussed in the results section, there are several key steps to the procedure. First, it is important to identify a high-quality affinity reagent. We recommend screening a small library of antibodies for each desired target. After a primary antibody has been selected, it is also important to validate the system for a number of different binding sites of the protein target if appropriate. Counter-screening for compounds that interfere with the assay signal as shown in Figure 2C by omittin...

When developing new drugs or chemical probes it is essential to couple the observed pharmacological effect or functional readout to measurements of target occupancy or engagement in live cells1,2,3. These data are necessary both to ensure that the small molecule in fact reaches its desired target and to validate the biological hypothesis behind protein target selection4,5. Furthermore, during drug development, model systems of increasing complexity are used to select and corroborate a lead compound prior to clinical trials. To confirm translation of biology across these preclinical systems, methods for tracing drug-target engagement and accompanying biology throughout this development process are critical.
Drug-target engagement has traditionally been challenging to monitor in live cells with unfunctionalized small molecules and proteins, especially at the single-cell level with spatial resolution6,7. One recent method to observe the interaction between unmodified drugs and proteins in live cells is the cellular thermal shift assay (CETSA) in which ligand-induced stabilization of a native protein in response to a heat challenge is quantified8,9,10. This is accomplished by quantifying remaining soluble protein after exposure to a heat challenge. In the initial disclosure of CETSA, western blot was used for detection. To enable screening campaigns and hit triaging of larger compound collections, efforts to increase the throughput of CETSA experiments have lead to the development of several homogenous, microplate-based assays10,11. However, one limitation with these methods is that they are currently best suited to compound treatment in cell suspensions and the detection requires cell lysis, leading to loss of spatial information. CETSA can be applied experimentally either as a ligand-induced shift in thermal aggregation temperature (Tagg) at a single concentration of the small molecule or the ligand concentration necessary to stabilize the protein at a single temperature. The latter is termed isothermal dose response fingerprints (ITDRF) to signify the dependence of these measurements on the specific experimental conditions.
The goal of this protocol is to measure target engagement using CETSA in adherent cells by immunofluorescent (IF) antibody detection with high-content microscopy12. This procedure extends the original CETSA platform to allow for single-cell quantification of target engagement with conservation of subcellular localization. Notably, unlike many previous reports, in this procedure compound treatment is performed in live adherent cells without surface detachment or washing prior to the heat challenge, thus preserving the established binding equilibrium we aim to measure13. Currently, the method is validated for one target protein p38&#945; (MAPK14) in several cell lines, and we hope that by sharing this procedure the technique can be applied broadly across the melting proteome. We anticipate that this protocol can be adapted throughout the drug development pipeline from screening, hit triaging through to monitoring of target engagement in vivo.

<table>
	<tbody>
		<tr>
			<td>Phosphate-buffered saline (PBS)</td>
			<td>Medicago</td>
			<td>09-9400-100</td>
			<td></td>
		</tr>
		<tr>
			<td>TrypLE Express</td>
			<td>ThermoFisher Scientific</td>
			<td>12604013</td>
			<td>for detaching cells and subculturing</td>
		</tr>
		<tr>
			<td>16% paraformaldehyde (PFA)</td>
			<td>ThermoFisher Scientific</td>
			<td>28908</td>
			<td>fixative</td>
		</tr>
		<tr>
			<td>Goat anti-rabbit IgG (H+L), Alexa Fluor 488 conjugated antibody</td>
			<td>ThermoFisher Scientific</td>
			<td>A11008</td>
			<td>secondary antibody</td>
		</tr>
		<tr>
			<td>HCS CellMask Red stain</td>
			<td>ThermoFisher Scientific</td>
			<td>H32712</td>
			<td>Cytoplasm stain</td>
		</tr>
		<tr>
			<td>NP-40</td>
			<td>Sigma-Aldrich</td>
			<td>56741</td>
			<td>for permeabilization</td>
		</tr>
		<tr>
			<td>Hoechst stain 33342</td>
			<td>Sigma-Aldrich</td>
			<td>B2261</td>
			<td>nuclear stain</td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s modified Eagle&#8217;s medium (DMEM) - high Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>6429</td>
			<td>cell culture media component</td>
		</tr>
		<tr>
			<td>Heat-inactivated fetal bovine serum (FBS)</td>
			<td>Sigma-Aldrich</td>
			<td>F9665</td>
			<td>cell culture media component</td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>Sigma-Aldrich</td>
			<td>P4333</td>
			<td>cell culture media component</td>
		</tr>
		<tr>
			<td>Corning, breathable plate seal</td>
			<td>Sigma-Aldrich</td>
			<td>CLS3345</td>
			<td>for copound incubation step</td>
		</tr>
		<tr>
			<td>Rabbit anti-p38 antibody [E229]</td>
			<td>Abcam</td>
			<td>ab170099</td>
			<td>primary antibody, LOT:GR305364-16</td>
		</tr>
		<tr>
			<td>Falcon, Black 384-well clear bottom imaging plates</td>
			<td>VWR</td>
			<td>736-2044</td>
			<td>imaging plates</td>
		</tr>
		<tr>
			<td>Greiner, 384-well low volume polypropylene plates</td>
			<td>VWR</td>
			<td>784201</td>
			<td></td>
		</tr>
		<tr>
			<td>Adhesive aluminum foil</td>
			<td>VWR</td>
			<td>30127790</td>
			<td></td>
		</tr>
		<tr>
			<td>Peelable aluminium seal</td>
			<td>Agilent</td>
			<td>24210-001</td>
			<td>for PlateLoc</td>
		</tr>
		<tr>
			<td>LY2228820</td>
			<td>Selleckchem</td>
			<td>S1494</td>
			<td>p38&#945; inhibitor</td>
		</tr>
		<tr>
			<td>PH797804</td>
			<td>Selleckchem</td>
			<td>PH797804</td>
			<td>p38&#945; inhibitor</td>
		</tr>
		<tr>
			<td>BIRB796</td>
			<td>Selleckchem</td>
			<td>S1574</td>
			<td>p38&#945; inhibitor</td>
		</tr>
		<tr>
			<td>SB203580</td>
			<td>Tocris</td>
			<td>1202</td>
			<td>p38&#945; inhibitor</td>
		</tr>
		<tr>
			<td>AMG 548</td>
			<td>Tocris</td>
			<td>3920</td>
			<td>p38&#945; inhibitor</td>
		</tr>
		<tr>
			<td>RWJ 67657</td>
			<td>Tocris</td>
			<td>2999</td>
			<td>p38&#945; inhibitor</td>
		</tr>
		<tr>
			<td>L-Skepinone</td>
			<td>CBCS compound collection</td>
			<td></td>
			<td>p38&#945; inhibitor</td>
		</tr>
		<tr>
			<td>Bovine serum albumin (BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>A7030</td>
			<td>blocking agent</td>
		</tr>
		<tr>
			<td>SDS (sodium dodecyl sulfate)</td>
			<td>BDH</td>
			<td>44244</td>
			<td>used in antigen retrieval</td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Sigma-Aldrich</td>
			<td>G8898</td>
			<td>used in antigen retrieval</td>
		</tr>
		<tr>
			<td>A-431 cells</td>
			<td>ATCC</td>
			<td>ATC-CRL-1555</td>
			<td></td>
		</tr>
		<tr>
			<td>Echo 550</td>
			<td>Labcyte</td>
			<td></td>
			<td>For preparation of compound plates</td>
		</tr>
		<tr>
			<td>Plate sealer</td>
			<td>Agilent</td>
			<td></td>
			<td>PlateLoc</td>
		</tr>
		<tr>
			<td>Bulk reagent dispenser</td>
			<td>Thermo Scientific</td>
			<td>5840300</td>
			<td>Multidrop Combi</td>
		</tr>
		<tr>
			<td>Automated liquid handling</td>
			<td>Agilent</td>
			<td></td>
			<td>Bravo liquid handling platform; used for compound plate preparation</td>
		</tr>
		<tr>
			<td>Plate washer</td>
			<td>Tecan</td>
			<td></td>
			<td>Hydrospeed</td>
		</tr>
		<tr>
			<td>Water bath</td>
			<td>Julabo</td>
			<td>TW12</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermocouple</td>
			<td>VWR</td>
			<td></td>
			<td>Thermocouple traceable lab thermometer</td>
		</tr>
		<tr>
			<td>High content imager</td>
			<td>Molecular Devices</td>
			<td></td>
			<td>ImageXpress Micro XLS Widefield High-Content Analysis System</td>
		</tr>
	</tbody>
</table>

using high content imaging to quantify target engagement in adherent cells

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

The protocol outlined in Figure 1 describes the basic workflow for running CETSA assays on adherent cells with detection of remaining soluble protein by high content imaging. This workflow can be easily adapted to all stages of assay development by modifying the plate layout of the compounds or reagents14. We detail expected results for several anticipated use cases below.
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Watch this Scientific Journal Video about Using High Content Imaging to Quantify Target Engagement in Adherent Cells at JoVE.com

Using High Content Imaging to Quantify Target Engagement in Adherent Cells

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

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

This method can help answer key questions in chemical biology and drug discovery. Such as, does your compound bind to the target protein? The main advantages for this technique are that there's no requirement of detachment of the adherent cells.And spatial localization can be determined by imaging. Though we've applied this method in cell lines, it's also possible to apply this method to other cell systems such as primary cultures and cocultures. Before seeding the cells, place black 384-well imaging assay plates in a tissue culture hood, and cover the plates with aluminum foil before using a standard drill to make three 3.5-millimeter-diameter holes on both ends of each plate.When the plates are ready, use aseptic technique to wash an A-431 cell culture with 5 to 10 milliliters of PBS. And incubate the cells with two milliliters of trypsin at 37 degrees Celsius until the cells detach. After counting, dilute the cells to 5 times 10 to the 4th cells per milliliter in culture medium, and seed 40 microliters of cells to each well of each assay plate.Gently shaking each plate from side to side after seeding to ensure a homogenous distribution of the cells across the well bottoms. To minimize plate edge effects, allow the cells to settle at the bottom of the assay plates for 20 minutes at room temperature in the back of the laminar flow hood before placing the plates in a custom humidified chamber for two to three days at 37 degrees Celsius and 5%carbon dioxide. On the day of the experiment, use a plate washer to aspirate the medium from each well.And add 30 microliters of the compound of interest at the appropriate experimental concentration to the appropriate experimental wells. Seal the compound-treated assay plates with breathable plate seals. And return the plates to the cell culture incubator for 30 minutes.To expose the cells to a heat challenge, first set the water bath to the appropriate experimental temperature, and place an unsealed dummy plate containing the same volume of medium per well as the assay plate into the bath, along with a thermocouple thermometer for monitoring the temperature within the wells. When the appropriate experimental temperature has been reached, remove the breathable seal from each assay plate and reseal the plates with a tight adhesive aluminum foil to ensure that no water leaks into the wells during their subsequent heating in the water bath. Keeping the drilled holes within the plate frame accessible.Place the assay plates and a new dummy plate into the water bath, with the bottoms of the plates angled toward the water surface to force any remaining air from under the plates, and begin monitoring the temperature of the new dummy plate. An even heating of the plate is critical for assay performance. Take care to place the plate in the water bath such that there are no air bubbles trapped underneath.After three minutes, immediately cool the plates in a second water bath of room-temperature water for five minutes before their analysis. To image the cells, first add 10 microliters of 16%paraformaldehyde directly to the assay plates for a 20-minute incubation at room temperature. At the end of the fixation period, wash the cells with 300 microliters of PBS on the plate washer, and add 20 microliters of 0.1%NP40 for a 10-minute incubation at room temperature.At the end of the incubation, wash the cells as demonstrated. And block the cells with 15 microliters of 1%bovine serum albumin, or BSA, for one hour at room temperature. Next, use the plate washer to aspirate the blocking serum, and add 10 microliters of the primary antibody of interest to the appropriate wells for a one-hour incubation at room temperature.At the end of the incubation, wash each well with 300 microliters of PBS, and label the cells with 10 microliters of the appropriate secondary antibody for one hour at room temperature protected from light. For nuclear staining of the cells, add 10 microliters of an appropriate nuclear dye to each well for 10 minutes at room temperature. And wash the cells in PBS as demonstrated.Label the cells with 10 microliters of cell mask per well for 30 minutes at room temperature. Followed by a last wash with PBS. Then dispense 60 microliters of fresh PBS to each well, and seal the plates with aluminum foil until imaging.To image the cells, capture four images per well on a high-content imager using the appropriate fluorescent channels under the 10-times objective using automated laser autofocus and apply binning to during the acquisition. Then store the images as 16-bit grayscale dot-tiff files along with the metadata. Antibody recognition should not be disrupted by conformational changes in the target protein that may be induced by ligand binding.For example, BIRB796 has a long off rate, and quantification of the target engagement is only possible by applying an antigen retrieval step. This representative thermal aggregation curve experiment for cells treated with positive and negative control compounds illustrates typical protein stabilization ranges after treatment of the cells with the compounds at various temperatures. Here a typical isothermal dose-response fingerprint experiment is shown to demonstrate representative ranges of protein stabilization in response to different doses of experimental compound.The application of isothermal heat challenges for compound screening to identify novel binders of the target protein allows the analysis of a large number of compounds at a single concentration at one time, before isothermal dose-response fingerprinting of the hits to confirm target protein stabilization. While attempting this procedure, it's important to remember that the exact experimental conditions, such as the length and temperature of the heat challenge impact the observed potency of the compounds. Don't forget that working with paraformaldehyde can be extremely hazardous.And precautions, such as following institutional safety guidelines, should always be taken while performing this procedure.

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Research

JoVE Journal

Biochemistry

Determination of the Glycogen Content in Cyanobacteria

Cyanobacteria accumulate glycogen as a major intracellular carbon and energy storage&#160;during photosynthesis. Recent developments in research have highlighted complex mechanisms of glycogen metabolism, including the diel cycle of biosynthesis and catabolism, redox regulation, and the involvement of non-coding RNA. At the same time, efforts are being made to redirect carbon from glycogen to desirable products in genetically engineered cyanobacteria to enhance product yields. Several methods are used to determine the glycogen contents in cyanobacteria, with variable accuracies and technical complexities. Here, we provide a detailed protocol for the reliable determination of the glycogen content in cyanobacteria that can be performed in a standard life science laboratory. The protocol entails the selective precipitation of glycogen from the cell lysate and the enzymatic depolymerization of glycogen to generate glucose monomers, which are detected by a glucose oxidase-peroxidase (GOD-POD) enzyme coupled assay. The method has been applied to Synechocystis sp. PCC 6803 and Synechococcus sp. PCC 7002, two model cyanobacterial species that are widely used in metabolic engineering. Moreover, the method successfully showed differences in the glycogen contents between the wildtype and mutants defective in regulatory elements or glycogen biosynthetic genes.

Here, we present a reliable and easy assay to measure the glycogen content in cyanobacterial cells. The procedure entails precipitation, selectable depolymerization, and the detection of glucose residues. This method is suitable for both wildtype and genetically engineered strains and can facilitate the metabolic engineering of cyanobacteria.

Cyanobacteria accumulate glycogen as a major intracellular carbon and energy storage&#160;during photosynthesis. Recent developments in research have ...

High Throughput, Absolute Determination of the Content of a Selected Protein at Tissue Levels Using Quantitative Dot Blot Analysis (QDB)

Lacking a convenient, quantitative, high throughput immunoblot method for absolute determination of the content of a specific protein at cellular and tissue level significantly hampers the progress in proteomic research. Results derived from currently available immunoblot techniques are also relative, preventing any efforts to combine independent studies with a large-scale analysis of protein samples. In this study, we demonstrate the process of quantitative dot blot analysis (QDB) to achieve absolute quantification in a high throughput format. Using a commercially available protein standard, we are able to determine the absolute content of capping actin protein, gelsolin-like (CAPG) in protein samples prepared from three different mouse tissues (kidney, spleen, and prostate) together with a detailed explanation of the experimental details. We propose the QDB analysis as a convenient, quantitative, high throughput immunoblot method of absolute quantification of individual proteins at the cellular and tissue level. This method will substantially aid biomarker validation and pathway verification in various areas of biological and biomedical research.

High Throughput, Absolute Determination of the Content of a Selected Protein at Tissue Levels Using Quantitative Dot Blot Analysis QDB

Here we demonstrate a detailed process of quantitative dot blot analysis (QDB) by determining the absolute content of a targeted protein, capping actin protein, gelsolin-like (CAPG), in three different mouse tissues. We demonstrate a high throughput, convenient, quantitative immunoblot technique for biomarker validation at the cellular and tissue level.

Lacking a convenient, quantitative, high throughput immunoblot method for absolute determination of the content of a specific protein at cellular and ...

A Colorimetric Method for Measuring Iron Content in Plants

Iron, one of the most important micronutrients in living organisms, is involved in basic processes, such as respiration and photosynthesis. Iron content is rather low in all organisms, amounting in plants to about 0.009% of dry weight. To date, one of the most accurate methods for measuring iron concentration in plant tissues is flame absorption atomic spectroscopy. However, this approach is time-consuming and expensive and requires specific equipment not commonly found in plant laboratories. Therefore, a simpler, yet accurate method that can be routinely used is needed. The colorimetric Prussian Blue method is regularly used for qualitative iron staining in animal and plant histological sections. In this study, we adapted the Prussian Blue method for quantitative measurements of iron in tobacco leaves. We validated the accuracy of this method using both atomic spectroscopy and Prussian Blue staining to measure iron content in the same samples and found a linear regression (R2 = 0.988) between the two procedures. We conclude that the Prussian Blue method for quantitative iron measurement in plant tissues is precise, simple, and inexpensive. However, the linear regression presented here may not be appropriate for other plant species, due to potential interactions between the sample and the reagent. Establishment of a regression curve is thus needed for different plant species.

We present a simple and reliable protocol for measuring iron content in plant tissues using the colorimetric Prussian Blue method.

Iron, one of the most important micronutrients in living organisms, is involved in basic processes, such as respiration and photosynthesis. Iron content ...

Dissipative Microgravimetry to Study the Binding Dynamics of the Phospholipid Binding Protein Annexin A2 to Solid-supported Lipid Bilayers Using a Quartz Resonator

The dissipative quartz crystal microbalance technique is a simple and label-free approach to measure simultaneously the mass uptake and viscoelastic properties of the absorbed/immobilized mass on sensor surfaces, allowing the measurements of the interaction of proteins with solid-supported surfaces, such as lipid bilayers, in real-time and with a high sensitivity. Annexins are a highly conserved group of phospholipid-binding proteins that interact reversibly with the negatively charged headgroups via the coordination of calcium ions. Here, we describe a protocol that was employed to quantitatively analyze the binding of annexin A2 (AnxA2) to planar lipid bilayers prepared on the surface of a quartz sensor. This protocol is optimized to obtain robust and reproducible data and includes a detailed step-by-step description. The method can be applied to other membrane-binding proteins and bilayer compositions.

Here, we present an experimental protocol that can be employed to determine the binding affinities and mode of interaction of label-free phospholipid-binding protein annexin A2 with immobilized solid-supported bilayers (SLB) by simultaneously measuring the mass uptake and the viscoelastic properties of the protein annexin A2.

The dissipative quartz crystal microbalance technique is a simple and label-free approach to measure simultaneously the mass uptake and viscoelastic ...

How to Quantify the Fraction of Photoactivated Fluorescent Proteins in Bulk and in Live Cells

Photoactivatable and -convertible fluorescent proteins (PA-FPs) have been used in fluorescence live-cell microscopy for analyzing the dynamics of cells and protein ensembles. Thus far, no method has been available to quantify in bulk and in live cells how many of the PA-FPs expressed are photoactivated to fluoresce.
Here, we present a protocol involving internal rulers, i.e., genetically coupled spectrally distinct (photoactivatable) fluorescent proteins, to ratiometrically quantify the fraction of all PA-FPs expressed in a cell that are switched on to be fluorescent. Using this protocol, we show that different modes of photoactivation yielded different photoactivation efficiencies. Short high-power photoactivation with a confocal laser scanning microscope (CLSM) resulted in up to four times lower photoactivation efficiency than hundreds of low-level exposures applied by CLSM or a short pulse applied by widefield illumination. While the protocol has been exemplified here for (PA-)GFP and (PA-)Cherry, it can in principle be applied to any spectrally distinct photoactivatable or photoconvertible fluorescent protein pair and any experimental set-up.

Here, we present a protocol that involves genetically coupled spectrally distinct photoactivatable and fluorescent proteins. These fluorescent protein chimeras permit quantification of the PA-FP fraction that is photoactivated to be fluorescent, i.e., the photoactivation efficiency. The protocol reveals that different modes of photoactivation yield different photoactivation efficiencies.

Photoactivatable and -convertible fluorescent proteins (PA-FPs) have been used in fluorescence live-cell microscopy for analyzing the dynamics of cells ...

Direct Measurement of KDM1A Target Engagement Using Chemoprobe-based Immunoassays

The assessment of the target engagement, defined as the interaction of a drug with the protein it was designed for, is a basic requirement for the interpretation of the biological activity of any compound in drug development or in basic research projects. In epigenetics, target engagement is most often assessed by the analysis of proxy markers instead of measuring the union of the compound to the target. Downstream biological readouts that have been analyzed include the histone mark modulation or gene expression changes. KDM1A is a lysine demethylase that removes methyl groups from mono- and dimethylated H3K4, a modification associated with the silencing of gene expression. Modulation of the proxy markers is dependent on the cell type and function of the genetic make-up of the cells investigated, which can make interpretation and cross-case comparison quite difficult. To circumvent these problems, a versatile protocol is presented to assess the dose effects and dynamics of the direct KDM1A target engagement. The assay described makes use of a KDM1A chemoprobe to capture and quantify uninhibited enzyme, can be broadly applied to cells or tissue samples without the need for genetic modification, has an excellent window of detection, and can be used both for basic research and analysis of clinical samples.

Here, we present a protocol to measure KDM1A target engagement in a human or animal cell, tissue or blood samples treated with KDM1A inhibitors. The protocol employs chemoprobe tagging of the free KDM1A enzyme and direct quantification of the target occupation using chemoprobe-based immunoassays and can be used in preclinical and clinical studies.

The assessment of the target engagement, defined as the interaction of a drug with the protein it was designed for, is a basic requirement for the ...

Detection of Total Reactive Oxygen Species in Adherent Cells by 2',7'-Dichlorodihydrofluorescein Diacetate Staining

Oxidative stress is an important event under both physiological and pathological conditions. In this study, we demonstrate how to quantify oxidative stress by measuring total reactive oxygen species (ROS) using 2&#39;,7&#39;-dichlorodihydrofluorescein diacetate (DCFH-DA) staining in colorectal cancer cell lines as an example. This protocol describes detailed steps including preparation of DCFH-DA solution, incubation of cells with DCFH-DA solution, and measurement of normalized intensity. DCFH-DA staining is a simple and cost-effective way to detect ROS in cells. It can be used to measure ROS generation after chemical treatment or genetic modifications. Therefore, it is useful for determining cellular oxidative stress upon environment stress, providing clues to mechanistic studies.

Detection of Total Reactive Oxygen Species in Adherent Cells by 2&#039;,7&#039;-Dichlorodihydrofluorescein Diacetate Staining

Here, we present a protocol to detect total cellular reactive oxygen species (ROS) using 2&#39;,7&#39;-dichlorodihydrofluorescein diacetate (DCFH-DA). This method can visualize cellular ROS localization in adherent cells with a fluorescence microscope and quantify ROS intensity with a fluorescence plate reader. This protocol is simple, efficient and cost-effective.

Oxidative stress is an important event under both physiological and pathological conditions. In this study, we demonstrate how to quantify oxidative ...

Estimation of Plant Biomass Lignin Content using Thioglycolic Acid (TGA)

Lignin is a natural polymer that is the second most abundant polymer on Earth after cellulose. Lignin is mainly deposited in plant secondary cell walls and is an aromatic heteropolymer primarily composed of three monolignols with significant industrial importance. Lignin plays an important role in plant growth and development, protects&#160;from biotic and abiotic stresses, and in the quality of animal fodder, the wood, and industrial lignin products. Accurate estimation of lignin content is essential for both fundamental understanding of the lignin biosynthesis and industrial applications of biomass. The thioglycolic acid (TGA) method is a highly reliable method of estimating the total lignin content in the plant biomass. This method estimates the lignin content by forming thioethers with the benzyl alcohol groups of lignin, which are soluble in alkaline conditions and insoluble in acidic conditions. The total lignin content is estimated using a standard curve generated from commercial bamboo lignin.

Estimation of Plant Biomass Lignin Content using Thioglycolic Acid TGA

Here, we present a modified TGA method for estimation of lignin content in herbaceous plant biomass. This method estimates the lignin content by forming specific thioether bonds with lignin and presents an advantage over the Klason method, as it requires a relatively small sample for lignin content estimation.

Lignin is a natural polymer that is the second most abundant polymer on Earth after cellulose. Lignin is mainly deposited in plant secondary cell walls ...

F&#246;rster Resonance Energy Transfer Measurements in Living Plant Cells

Sensitized emission-based F&#246;rster resonance energy transfer (FRET) experiments are easily done but depend on the microscopic setup. Confocal laser scanning microscopes have become a workhorse for biologists. Commercial systems offer high flexibility in laser power adjustment and detector sensitivity and often combine different detectors to obtain the perfect image. However, the comparison of intensity-based data from different experiments and setups is often impossible due to this flexibility. Biologist-friendly procedures are of advantage and allow for simple and reliable adjustment of laser and detector settings. 
Furthermore, as FRET experiments in living cells are affected by the variability in protein expression and donor-acceptor ratios, protein expression levels must be considered for data evaluation. Described here is a simple protocol for reliable and reproducible FRET measurements, including routines for the estimation of protein expression and adjustment of laser intensity and detector settings. Data evaluation will be performed by calibration with a fluorophore fusion of known FRET efficiency. To improve simplicity, correction factors have been compared that have been obtained in cells and by measuring recombinant fluorescent proteins.

F&amp;#246;rster Resonance Energy Transfer Measurements in Living Plant Cells

A protocol is provided for setting up a standard confocal laser-scanning microscope for in vivo F&#246;rster resonance energy transfer measurements, followed by data evaluation.

Sensitized emission-based F&#246;rster resonance energy transfer (FRET) experiments are easily done but depend on the microscopic setup. Confocal laser ...

Advancing High-Resolution Imaging of Virus Assemblies in Liquid and Ice

Interest in liquid-electron microscopy (liquid-EM) has skyrocketed in recent years as scientists can now observe real-time processes at the nanoscale. It is extremely desirable to pair high-resolution cryo-EM information with dynamic observations as many events occur at rapid timescales - in the millisecond range or faster. Improved knowledge of flexible structures can also assist in the design of novel reagents to combat emerging pathogens, such as SARS-CoV-2. More importantly, viewing biological materials in a fluid environment provides a unique glimpse of their performance in the human body. Presented here are newly developed methods to investigate the nanoscale properties of virus assemblies in liquid and vitreous ice. To accomplish this goal, well-defined samples were used as model systems. Side-by-side comparisons of sample preparation methods and representative structural information are presented. Sub-nanometer features are shown for structures resolved in the range of ~3.5-&#197;-10 &#197;. Other recent results that support this complementary framework include dynamic insights of vaccine candidates and antibody-based therapies imaged in liquid. Overall, these correlative applications advance our ability to visualize molecular dynamics, providing a unique context for their use in human health and disease.

Here protocols are described to prepare virus assemblies suitable for liquid-EM and cryo-EM analysis at the nanoscale using transmission electron microscopy.

Interest in liquid-electron microscopy (liquid-EM) has skyrocketed in recent years as scientists can now observe real-time processes at the nanoscale. It ...