Name: analysis of histone antibody specificity with peptide microarrays
Uploaded: 2017-08-01T14:00:00
Description: Watch this Scientific Journal Video about Analysis of Histone Antibody Specificity with Peptide Microarrays at JoVE.com

This work was supported in part by the Van Andel Research Institute and a research grant from the National Institutes of Health (CA181343) to S.B.R.

1. Installing and Running ArrayNinja
<ol>
	<li>Download and install Oracle Virtual Box from www.virtualbox.org.</li>
	<li>Download and uncompress the ArrayNinja virtual machine (VM) from http://research.vai.org/Tools/arrayninja.</li>
	<li>Open Virtual Box and add the ArrayNinja VM by clicking &#39;Machine,&#39; &#39;Add,&#39; and select arrayninja.vbox from the folder where ArrayNinja VM was saved.</li>
	<li>Start ArrayNinja by selecting it inside Virtual Box and clicking the green &#39;start&#39; arrow.</li>
	<li>Virt...

Antibody reliability in biomedical research applications is paramount46,47. This is especially true in chromatin biochemistry given the position of antibodies as key tools for the majority of techniques developed to characterize the abundance and distribution of histone PTMs. The protocol presented here details an optimized pipeline for the design, fabrication, and use of peptide microarrays to analyze histone PTM antibody specificity. This pipeline has been used...

Genomic DNA is elegantly packaged inside the eukaryotic cell nucleus with histone proteins to form chromatin. The repeating subunit of chromatin is the nucleosome, which consists of 147 base pairs of DNA wrapped around an octameric core of histone proteins &#8211; H2A, H2B, H3, and H41. Chromatin is broadly organized into loosely packed euchromatin and tightly packed heterochromatin domains. The degree of chromatin compaction regulates the extent to which protein machineries can access the underlying DNA to carry out fundamental DNA-templated processes like replication, transcription, and repair.
Key regulators of genome accessibility in the context of chromatin are PTMs on the unstructured tail and core domains of histone proteins2,3. Histone PTMs function directly by influencing the structure of chromatin4 and indirectly through the recruitment of reader proteins and their associated macromolecular complexes that have chromatin remodeling, enzymatic, and scaffolding activities5. Studies of histone PTM function over the past two decades overwhelmingly suggest these marks play key roles in regulating cell fate, organismal development, and disease initiation/progression. Fueled by advances in mass spectrometry-based proteomic technology, more than 20 unique histone PTMs on more than 80 distinct histone residues have been discovered6. Notably, these modifications often occur in combinations, and consistent with the &#34;histone code&#34; hypothesis, numerous studies suggest that reader proteins are targeted to discrete regions of chromatin through recognition of specific combinations of histone PTMs7,8,9. A key challenge moving forward will be to assign functions to the growing list of histone PTMs and to determine how specific combinations of histone PTMs orchestrate the dynamic functions associated with chromatin.
Antibodies are the lynchpin reagents for the detection of histone PTMs. As such, more than 1,000 histone PTM-specific antibodies have been commercially developed for use in chromatin biochemistry research. With the rapid development of high-throughput DNA sequencing technology, these reagents are being used extensively by individual investigators and large-scale epigenomics &#34;roadmap&#34; initiatives (e.g., ENCODE and BLUEPRINT) in ChIP-seq (chromatin immunoprecipitation coupled with next-generation sequencing) pipelines to generate high-resolution spatial maps of histone PTM distribution genome-wide10,11. However, recent studies have shown that the specificity of histone PTM antibodies can be highly variable and that these reagents exhibit unfavorable properties such as off-target epitope recognition, strong positive and negative influence by neighboring PTMs, and difficulty discriminating the modification order on a particular residue (e.g., mono-, di-, or tri-methyllysine)12,13,14,15,16,17,18. Therefore, rigorous quality control of histone PTM-specific antibody reagents is necessary to accurately interpret data generated with these valuable reagents.
Microarray technology enables the simultaneous interrogation of thousands of macromolecular interactions in a high-throughput, reproducible, and miniaturized format. For this reason, a variety of microarray platforms have been created to analyze protein-DNA19,20, protein-protein 21, and protein-peptide interactions22. Indeed, histone peptide microarrays have emerged as an informative discovery platform for chromatin biochemistry research, enabling high-throughput profiling of the writers, erasers, and readers of histone PTMs15,23,24, and also for the analysis of histone antibody specificity17,25. Beyond their application in chromatin and epigenetics research, histone peptide arrays have potential utility as a diagnostic/prognostic test for systemic lupus erythematosus and other autoimmune diseases where anti-chromatin autoantibodies are generated26,27.
Here, we describe an integrated pipeline that we have developed for designing, fabricating, and querying histone peptide microarrays to generate specificity profiles for antibodies that recognize histones and their PTMs. The pipeline is facilitated by ArrayNinja, an open-source, interactive software application that we recently developed, which integrates the design and analysis stages of microarray experiments28. ArrayNinja works best in Google Chrome. Briefly, a robotic contact microarray printer is used to deposit a library of biotin-conjugated histone peptides at defined positions on streptavidin-coated glass microscope slides. Arrays can then be used in a competitive and parallel assay format to interrogate antibody-epitope interactions (Figure 1). The peptide library consists of hundreds of unique synthetic peptides harboring PTMs (lysine acetylation, lysine/arginine methylation, and serine/threonine phosphorylation) alone and in relevant combinations largely derived from proteomics datasets. Methods for peptide synthesis and validation are detailed elsewhere23. Data generated from our ongoing histone PTM antibody screening efforts utilizing this array platform are archived on a public web resource, the Histone Antibody Specificity Database (www.histoneantibodies.com). Notably, histone peptide microarrays fabricated with variations of this protocol have also been used extensively to characterize the activity of histone PTM reader domains8,29,30,31,32,33,34,35,36,37 and more recently to profile histone PTM writer and eraser activities24.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55912/55912fig1.jpg" /> 
Figure 1: Cartoon Depiction of the Stepwise Procedure for Antibody Screening on a Histone Peptide microarray. Biotinylated histone peptides harboring defined post-translational modifications (red and blue circles) are co-printed with biotin-fluorescein on streptavidin-coated glass. Positive interactions are visualized as red fluorescence. <a href="http://cloudflare.jove.com/files/ftp_upload/55912/55912fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table border="0" cellpadding="0" cellspacing="0" width="746">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Printing Buffer</td>
			<td style="width:107px;">ArrayIt</td>
			<td style="width:105px;">PPB</td>
			<td style="width:281px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">BSA</td>
			<td style="width:107px;">Omnipure</td>
			<td align="right" style="width:105px;">2390</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">Streptavidin-coated glass microscope slides</td>
			<td style="width:107px;">Greiner Bio-one</td>
			<td>439003-25</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">polypropylene 384 well plate</td>
			<td style="width:107px;">Greiner Bio-one</td>
			<td align="right" style="width:105px;">784201</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Biotin-fluorescein</td>
			<td style="width:107px;">Sigma</td>
			<td align="right" style="width:105px;">53608</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">contact microarray printer</td>
			<td style="width:107px;">Aushon</td>
			<td align="right" style="width:105px;">2470</td>
			<td style="width:281px;">Aushon 2470 Microarray Printer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">contact microarray printer</td>
			<td style="width:107px;">Gene Machines</td>
			<td style="width:105px;">OmniGrid 100</td>
			<td style="width:281px;">OmniGrid Microarray Printer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">PBS</td>
			<td style="width:107px;">Invitrogen</td>
			<td align="right" style="width:105px;">14190</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Blocking Buffer</td>
			<td style="width:107px;">ArrayIt</td>
			<td style="width:105px;">SBB</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Hydrophobic wax pen</td>
			<td style="width:107px;">Vector Labs</td>
			<td style="width:105px;">H-4000</td>
			<td>ImmEdge Hydrophobic Barrier PAP Pen</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Silicon Gasket</td>
			<td style="width:107px;">Grace Bio-labs</td>
			<td align="right" style="width:105px;">622511</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">Hybridization Vessel</td>
			<td style="width:107px;">Thermo Scientific</td>
			<td align="right">267061</td>
			<td>or similar vessel</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">Fluorescent-dye conjugated secondary antibody</td>
			<td style="width:107px;">Life Technologies</td>
			<td>A-21244</td>
			<td style="width:281px;">Alexa Fluor 647 (anti-rabbit)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">Fluorescent-dye conjugated secondary antibody</td>
			<td style="width:107px;">Life Technologies</td>
			<td>A-21235</td>
			<td style="width:281px;">Alexa Fluor 647 (anti-mouse)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Wax Imprinter</td>
			<td style="width:107px;">ArrayIt</td>
			<td>MSI48</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Tween-20</td>
			<td style="width:107px;">Omnipure</td>
			<td align="right" style="width:105px;">9490</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Microarray Scanner</td>
			<td style="width:107px;">Innopsys</td>
			<td style="width:105px;">InnoScan 1100AL</td>
			<td>or equivalent microarray scanner</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">EipTitan Histone Peptide Microarray</td>
			<td style="width:107px;">Epicypher</td>
			<td align="right" style="width:105px;">112001</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">AbSurance Pro Histone Peptide Microarray</td>
			<td style="width:107px;">Millipore</td>
			<td align="right" style="width:105px;">16668</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">MODified Histone Peptide Array</td>
			<td style="width:107px;">Active Motif</td>
			<td align="right" style="width:105px;">13001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Histone Code Peptide Microarrays</td>
			<td style="width:107px;">JPT</td>
			<td style="width:105px;">His_MA_01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Wax</td>
			<td style="width:107px;">Royal Oak</td>
			<td style="width:105px;">GulfWax</td>
			<td>for wax imprinter</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">Humidified Microarray Slide Hybridization Chamber</td>
			<td style="width:107px;">VWR</td>
			<td style="width:105px;">97000-284</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:255px;">High throughput microscope slide washing chamber</td>
			<td style="width:107px;">ArrayIt</td>
			<td style="width:105px;">HTW</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Microscope slide centrifuge</td>
			<td style="width:107px;">VWR</td>
			<td>93000-204</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Antibody 1</td>
			<td>Abcam</td>
			<td align="right" style="width:105px;">8898</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Antibody 2</td>
			<td style="width:107px;">Millipore</td>
			<td style="width:105px;">07-473</td>
			<td></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:255px;">Biotinylated histone peptide</td>
			<td style="width:107px;">EpiCypher</td>
			<td>12-0001</td>
			<td style="width:281px;">Example peptide. Similar peptides with various modifications are available from several commercial sources.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">ImageMagick</td>
			<td style="width:107px;"></td>
			<td style="width:105px;"></td>
			<td>https://www.imagemagick.org/script/index.php</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">ArrayNinja</td>
			<td style="width:107px;"></td>
			<td style="width:105px;"></td>
			<td>https://rothbartlab.vai.org/tools/</td>
		</tr>
	</tbody>
</table>

analysis of histone antibody specificity with peptide microarrays

Post-translational modifications (PTMs) on histone proteins are widely studied for their roles in regulating chromatin structure and gene expression. The mass production and distribution of antibodies specific to histone PTMs has greatly facilitated research on these marks. As histone PTM antibodies are key reagents for many chromatin biochemistry applications, rigorous analysis of antibody specificity is necessary for accurate data interpretation and continued progress in the field. This protocol describes an integrated pipeline for the design, fabrication and use of peptide microarrays for profiling the specificity of histone antibodies. The design and analysis aspects of this procedure are facilitated by ArrayNinja, an open-source and interactive software package we recently developed to streamline the customization of microarray print formats. This pipeline has been used to screen a large number of commercially available and widely used histone PTM antibodies, and data generated from these experiments are freely available through an online and expanding Histone Antibody Specificity Database. Beyond histones, the general methodology described herein can be applied broadly to the analysis of PTM-specific antibodies.

This protocol has been used to design and fabricate a peptide microarray platform for the analysis of histone PTM antibody specificity. The array queries a library of more than 300 unique peptide features (20 - 40 residues in length) representing many of the known combinations of PTMs found on core and variant histone proteins38. This pipeline has been a workhorse for the screening of many widely used and commercially available histone PTM antibodies, and full data...

Watch this Scientific Journal Video about Analysis of Histone Antibody Specificity with Peptide Microarrays at JoVE.com

Analysis of Histone Antibody Specificity with Peptide Microarrays

This manuscript describes methods for applying peptide microarray technology to specificity profiling of antibodies that recognize histones and their post-translational modifications.

Post-translational modifications (PTMs) on histone proteins are widely studied for their roles in regulating chromatin structure and gene expression. The ...

The goal of this video is to describe an integrated pipeline for the design fabrication and use of peptide microarrays for profiling the specificities of histone antibodies. Antibodies that recognize histones and their diverse post-translational modifications are key reagents in chromatin biochemistry research. We rely on these tools to deepen our understanding of histone modification function.Recent studies reveal inconsistencies in histone antibody behavior. As antibody choice is the most critical element in epigenetics experiments, vigorous incomprehensive quality control measures are demanded for these reagents. Here, we demonstrate an integrated pipeline we'd developed for designing, fabricating and analyzing peptide microarrays to generate specificity profiles for antibodies that recognize histones and their post-translational modifications.The pipeline is facilitated by Array Ninja, an open source interactive software application that we developed, which integrates the design and analysis stages of microarray experiments. To begin designing the array slide, under the plan a slide layout heading, select the microarray printer that will be used. Then, type, empty in the load plate field and press enter.Set the spot diameter to 275 micrometers and the spot spacing to 100 micrometers. Fill in the remaining parameters appropriately for the experiment, ensuring that the layout allows for sufficient replicates. At the resulting layout preview, mouse over each unique peptide feature on the slide and enter a feature identifier in the popup text box.Once each unique feature has been labeled, click populate. Name the slide layout, and click commit your plate to save the layout and generate a map at the physical locations of each feature in the source plates. Guided by the source plate map, load one to two microliters of each peptide feature into the designated wells of one or more 384 wells, small volume plates, dilute each feature 10 fold with 1x protein microarray printing buffer, supplemented with 1%bovine serum albumin and five micrograms per microliter fluorescin labeled biotin.Then, centrifuge the plates at 500 x G at room temperature for two minutes. Next, empty the waste container at the microarray printer. Fill the washed solution in humidifier containers with sterile distilled water.Enter the array slide parameters in the microarray printer software. Set the washing procedure to a one second wash with the single immersion, the post washed to redip the pins five times, and the humidity to 60%Then, insert encoated glass slides into the substrate platinums. Load the platinums into the platinum elevator.Insert the source plates into the plate holders and load the holders into the source plate elevator. Run the printing process, then, remove the substrate platinums from the instrument. Block the printed slides with 1x protein microarray blocking buffer for 30 minutes while shaking.Then, wash the slides in room temperature, pH 7.6 phosphate buffered saline for 10 minutes. Repeat the wash with a fresh batch of PBS. Dry the slides by centrifugation for 30 seconds at room temperature.Next, pre-heat a microarray wax imprinter at 85 degrees celsius for 30 minutes, or until the wax has melted. Then, insert a slide printed side down, into the holder and align the holder with the imprinter mold. Bring the mold into contact with the slide and hold for two seconds, then, quickly remove the slide from the holder and inspect the wax borders to verify that the arrays are properly enclosed.Store the partitioned slides at four degrees celsius, in a dry dark area. To begin the hybridization procedure, place a partitioned array slide in a plastic dish and cover the slide with hybridization buffer. Equilibrate the slide for 30 minutes at four degree celsius, while shaking at low speed.Dry the slide by spinning in a microarray slide centrifuge at room temperature. Then, add five microliters of each histone PTM antibody solution to at least two wells of the array and incubate at four degree celsius for one hour. Following incubation, remove the antibody solution and wash the array with cold PBS three times for five minutes each at four degrees celsius.Next, incubate the array in a fluorescent dye-conjugated secondary antibody solution. For 30 minutes at four degrees celsius, in the absence of light. Wash the slide three times with cold PBS as before.Dip the array in room temperature 0.1x PBS to remove excess salt and dry the slide by brief centrifugation at room temperature. Image the slide with a microarray scanner at a resolution of at least, 25 microns. To begin the analysis, use image processing software to merge the single channel files from the microarray scanner.Then, open Array Ninja and select the appropriate microarray printer under the, to quantify images header. Fill in the name of the same slide layout in the load plate dialog box, and press enter. Load the merged image file, and adjust the contrast, brightness and mid point as desired.Fill in the array scanner resolution, adjust the top and side margins to align slide layout grid with the image. To analyze a set of wells as replicates or perform other selective analysis, fill in the well coordinates in the iPin, jPin, and subA fields and press enter. Click to toggle zoom, to display a magnified image of the area under the cursor.Then, click spot seek and wait for the process to finish. Repeat the seek function as needed to center the grid circles on the array spots. Reference spots can be selected by pressing the R key and spot showing debris or widely bearing morphology can be deactivated by pressing the A key while hovering over the spot.Once the background reference spots have been selected, and spots with pore morphology or contamination have been deactivated, click populate, followed by, submit to perform the quantification. A bar graph and table will be displayed in a new page. The binding specificities of two histone PTM antibodies were evaluated using this method.A histone PTM antibody designed to target trimethylated lysine 9 on histone H3 was also found to bind to three other trimethylated lysine groups. A silylation of neighboring lysine residues was observed to positively influence targeting of lysine 9 on H3.A histone PTM antibody targeting trimethylated lysine 4 on histone H3, was found to interact with singlely methylated and dimethylated lysine 4 on H3 as well. Phosphorelation of the neighboring three anine six, was observed to negatively impact binding at lysine four in this assay.This pipeline has been used to screen many of the most widely used, commercially available histone antibodies and data generated from these experiments is freely available through the histone antibody specificity database. Variations to this pipeline have been previously described for the analysis of histone readers, writers and erasers, modifying this platform before utility beyond epigenetics research could be easily for any printable library of interest. Several histone peptide microarray platforms are available commercially for users who do not have access to the specialized equipment needed to synthesize peptides and fabricate arrays.

analysis-of-histone-antibody-specificity-with-peptide-microarrays

Research

JoVE Journal

Biochemistry

Easy Manipulation of Architectures in Protein-based Hydrogels for Cell Culture Applications

Hydrogels are recognized as promising materials for cell culture applications due to their ability to provide highly hydrated cell environments. The field of 3D templates is rising due to the potential resemblance of those materials to the natural extracellular matrix. Protein-based hydrogels are particularly promising because they can easily be functionalized and can achieve defined structures with adjustable physicochemical properties. However, the production of macroporous 3D templates for cell culture applications using natural materials is often limited by their weaker mechanical properties compared to those of synthetic materials. Here, different methods were evaluated to produce macroporous bovine serum albumin (BSA)-based hydrogel systems, with adjustable pore sizes in the range of 10 to 70 &#181;m in radius. Furthermore, a method to generate channels in this protein-based material that are several hundred microns long was established. The different methods to produce pores, as well as the influence of pore size on material properties such as swelling ratio, pH, temperature stability, and enzymatic degradation behavior, were analyzed. Pore sizes were investigated in the native, swollen state of the hydrogels using confocal laser scanning microscopy. The feasibility for cell culture applications was evaluated using a cell-adhesive RGD peptide modification of the protein system and two model cell lines: human breast cancer cells (A549) and adenocarcinomic human alveolar basal epithelial cells (MCF7).

Different methods to manipulate three-dimensional architecture in protein-based hydrogels are evaluated here with respect to material properties. The macroporous networks are functionalized with a cell-adhesive peptide, and their feasibility in cell culture is evaluated using two different model cell lines.

Hydrogels are recognized as promising materials for cell culture applications due to their ability to provide highly hydrated cell environments. The field ...

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

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

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

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

The Determination of Protease Specificity in Mouse Tissue Extracts by MALDI-TOF Mass Spectrometry: Manipulating PH to Cause Specificity Changes

Proteases have several biological functions, including protein activation/inactivation and food digestion. Identifying protease specificity is important for revealing protease function. The method proposed in this study determines protease specificity by measuring the molecular weight of unique substrates using Matrix-assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) mass spectrometry. The substrates contain iminobiotin, while the cleaved site consists of amino acids, and the spacer consists of polyethylene glycol. The cleaved substrate will generate a unique molecular weight using a cleaved amino acid. One of the merits of this method is that it may be carried out in one pot using crude samples, and it is also suitable for assessing multiple samples. In this article, we describe a simple experimental method optimized with samples extracted from mouse lung tissue, including tissue extraction, placement of digestive substrates into samples, purification of digestive substrates under different pH conditions, and measurement of the substrates&#39; molecular weight using MALDI-TOF mass spectrometry. In summary, this technique allows for the identification of protease specificity in crude samples derived from tissue extracts using MALDI-TOF mass spectrometry, which may easily be scaled up for multiple sample processing.

Here, we present a protocol to determine protease specificity in crude mouse tissue extracts using MALDI-TOF spectrometry.

Proteases have several biological functions, including protein activation/inactivation and food digestion. Identifying protease specificity is important ...

Kinase Inhibitor Screening In Self-assembled Human Protein Microarrays

The screening of kinase inhibitors is crucial for better understanding properties of a drug and for the identification of potentially new targets with clinical implications. Several methodologies have been reported to accomplish such screening. However, each has its own limitations (e.g., the screening of only ATP analogues, restriction to using purified kinase domains, significant costs associated with testing more than a few kinases at a time, and lack of flexibility in screening protein kinases with novel mutations). Here, a new protocol that overcomes some of these limitations and can be used for the unbiased screening of kinase inhibitors is presented. A strength of this method is its ability to compare the activity of kinase inhibitors across multiple proteins, either between different kinases or different variants of the same kinase. Self-assembled protein microarrays generated through the expression of protein kinases by a human-based in vitro transcription and translation system (IVTT) are employed. The proteins displayed on the microarray are active, allowing for measurement of the effects of kinase inhibitors. The following procedure describes the protocol steps in detail, from the microarray generation and screening to the data analysis.

A detailed protocol for the generation of self-assembled human protein microarrays for the screening of kinase inhibitors is presented.

The screening of kinase inhibitors is crucial for better understanding properties of a drug and for the identification of potentially new targets with ...

Isolation of Histone from Sorghum Leaf Tissue for Top Down Mass Spectrometry Profiling of Potential Epigenetic Markers

Histones belong to a family of highly conserved proteins in eukaryotes. They pack DNA into nucleosomes as functional units of chromatin. Post-translational modifications (PTMs) of histones, which are highly dynamic and can be added or removed by enzymes, play critical roles in regulating gene expression. In plants, epigenetic factors, including histone PTMs, are related to their adaptive responses to the environment. Understanding the molecular mechanisms of epigenetic control can bring unprecedented opportunities for innovative bioengineering solutions. Herein, we describe a protocol to isolate the nuclei and purify histones from sorghum leaf tissue. The extracted histones can be analyzed in their intact forms by top-down mass spectrometry (MS) coupled with online reversed-phase (RP) liquid chromatography (LC). Combinations and stoichiometry of multiple PTMs on the same histone proteoform can be readily identified. In addition, histone tail clipping can be detected using the top-down LC-MS workflow, thus, yielding the global PTM profile of core histones (H4, H2A, H2B, H3). We have applied this protocol previously to profile histone PTMs from sorghum leaf tissue collected from a large-scale field study, aimed at identifying epigenetic markers of drought resistance. The protocol could potentially be adapted and optimized for chromatin immunoprecipitation-sequencing (ChIP-seq), or for studying histone PTMs in similar plants.

The protocol has been developed to effectively extract intact histones from sorghum leaf materials for profiling of histone post-translational modifications that can serve as potential epigenetic markers to aid engineering drought resistant crops.

Histones belong to a family of highly conserved proteins in eukaryotes. They pack DNA into nucleosomes as functional units of chromatin. ...

Rapid Determination of Antibody-Antigen Affinity by Mass Photometry

Measurements of the specificity and affinity of antigen-antibody interactions are critically important for medical and research applications. In this protocol, we describe the implementation of a new single-molecule technique, mass photometry (MP), for this purpose. MP is a label- and immobilization-free technique that detects and quantifies molecular masses and populations of antibodies and antigen-antibody complexes on a single-molecule level. MP analyzes the antigen-antibody sample within minutes, allowing for the precise determination of the binding affinity and simultaneously providing information on the stoichiometry and the oligomeric state of the proteins. This is a simple and straightforward technique that requires only picomole quantities of protein and no expensive consumables. The same procedure can be used to study protein-protein binding for proteins with a molecular mass larger than 50 kDa. For multivalent protein interactions, the affinities of multiple binding sites can be obtained in a single measurement. However, the single-molecule mode of measurement and the lack of labeling imposes some experimental limitations. This method gives the best results when applied to measurements of sub-micromolar interaction affinities, antigens with a molecular mass of 20 kDa or larger, and relatively pure protein samples. We also describe the procedure for performing the required fitting and calculation steps using basic data analysis software.

We describe a single-molecule approach to antigen-antibody affinity measurements using mass photometry (MP). The MP-based protocol is fast, accurate, uses a very small amount of material, and does not require protein modification.

Measurements of the specificity and affinity of antigen-antibody interactions are critically important for medical and research applications. In this ...

Cell-Free Production of Proteoliposomes for Functional Analysis and Antibody Development Targeting Membrane Proteins

Membrane proteins play essential roles in a variety of cellular processes and perform vital functions. Membrane proteins are medically important in drug discovery because they are the targets of more than half of all drugs. An obstacle to conducting biochemical, biophysical, and structural studies of membrane proteins as well as antibody development has been the difficulty in producing large amounts of high-quality membrane protein with correct conformation and activity. Here we describe a &#8220;bilayer-dialysis method&#8221; using a wheat germ cell-free system, liposomes, and dialysis cups to efficiently synthesize membrane proteins and prepare purified proteoliposomes in a short time with a high success rate. Membrane proteins can be produced as much as in several milligrams, such as GPCRs, ion channels, transporters, and tetraspanins. This cell-free method contributes to reducing the time, cost and effort for preparing high-quality proteoliposomes, and provides suitable means for functional analysis of membrane proteins, drug targets screening, and antibody development.

This protocol describes an efficient cell-free method for production of high-quality proteoliposome by bilayer-dialysis method using wheat cell-free system and liposomes. This method provides suitable means for functional analysis of membrane proteins, drug targets screening, and antibody development.

Membrane proteins play essential roles in a variety of cellular processes and perform vital functions. Membrane proteins are medically important in drug ...

In Vitro Characterization of Histone Chaperones using Analytical, Pull-Down and Chaperoning Assays

Histone proteins associate with DNA to form the eukaryotic chromatin. The basic unit of chromatin is a nucleosome, made up of a histone octamer consisting of two copies of the core histones H2A, H2B, H3, and H4, wrapped around by the DNA. The octamer is composed of two copies of an H2A/H2B dimer and a single copy of an H3/H4 tetramer. The highly charged core histones are prone to non-specific interactions with several proteins in the cellular cytoplasm and the nucleus. Histone chaperones form a diverse class of proteins that shuttle histones from the cytoplasm into the nucleus and aid their deposition onto the DNA, thus assisting the nucleosome assembly process. Some histone chaperones are specific for either H2A/H2B or H3/H4, and some function as chaperones for both. This protocol describes how in vitro laboratory techniques such as pull-down assays, analytical size-exclusion chromatography, analytical ultra-centrifugation, and histone chaperoning assay could be used in tandem to confirm whether a given protein is functional as a histone chaperone.

In Vitro Characterization of Histone Chaperones using Analytical, Pull-Down and Chaperoning Assays

This protocol describes a battery of methods that includes analytical size-exclusion chromatography to study histone chaperone oligomerization and stability, pull-down assay to unravel histone chaperone-histone interactions, AUC to analyze the stoichiometry of the protein complexes, and histone chaperoning assay to functionally characterize a putative histone chaperone in vitro.

Histone proteins associate with DNA to form the eukaryotic chromatin. The basic unit of chromatin is a nucleosome, made up of a histone octamer consisting ...

Deciphering Molecular Mechanism of Histone Assembly by DNA Curtain Technique

Chromatin is a higher-order structure that packages eukaryotic DNA. Chromatin undergoes dynamic alterations according to the cell cycle phase and in response to environmental stimuli. These changes are essential for genomic integrity, epigenetic regulation, and DNA metabolic reactions such as replication, transcription, and repair. Chromatin assembly is crucial for chromatin dynamics and is catalyzed by histone chaperones. Despite extensive studies, the mechanisms by which histone chaperones enable chromatin assembly remains elusive. Moreover, the global features of nucleosomes organized by histone chaperones are poorly understood. To address these problems, this work describes a unique single-molecule imaging technique named DNA curtain, which facilitates the investigation of the molecular details of nucleosome assembly by histone chaperones. DNA curtain is a hybrid technique that combines lipid fluidity, microfluidics, and total internal reflection fluorescence microscopy (TIRFM) to provide a universal platform for real-time imaging of diverse protein-DNA interactions.Using DNA curtain, the histone chaperone function of Abo1, the Schizosaccharomyces pombe bromodomain-containing AAA+ ATPase, is investigated, and the molecular mechanism underlying histone assembly of Abo1 is revealed. DNA curtain provides a unique approach for studying chromatin dynamics.

DNA curtain, a high-throughput single-molecule imaging technique, provides a platform for real-time visualization of diverse protein-DNA interactions. The present protocol utilizes the DNA curtain technique to investigate the biological role and molecular mechanism of Abo1, a Schizosaccharomyces pombe bromodomain-containing AAA+ ATPase.

Chromatin is a higher-order structure that packages eukaryotic DNA. Chromatin undergoes dynamic alterations according to the cell cycle phase and in ...

Routine Collection of High-Resolution cryo-EM Datasets Using 200 KV Transmission Electron Microscope

Cryo-electron microscopy (cryo-EM) has been established as a routine method for protein structure determination during the past decade, taking an ever-increasing share of published structural data. Recent advances in TEM technology and automation have boosted both the speed of data collection and quality of acquired images while simultaneously decreasing the required level of expertise for obtaining cryo-EM maps at sub-3 &#197; resolutions. While most of such high-resolution structures have been obtained using state-of-the-art 300 kV cryo-TEM systems, high-resolution structures can be also obtained with 200 kV cryo-TEM systems, especially when equipped with an energy filter. Additionally, automation of microscope alignments and data collection with real-time image quality assessment reduces system complexity and assures optimal microscope settings, resulting in increased yield of high-quality images and overall throughput of data collection. This protocol demonstrates the implementation of recent technological advances and automation features on a 200 kV cryo-transmission electron microscope and shows how to collect data for the reconstruction of 3D maps that are sufficient for de novo atomic model building. We focus on best practices, critical variables, and common issues that must be considered to enable the routine collection of such high-resolution cryo-EM datasets. Particularly the following essential topics are reviewed in detail: i) automation of microscope alignments, ii) selection of suitable areas for data acquisition, iii) optimal optical parameters for high-quality, high-throughput data collection, iv) energy filter tuning for zero-loss imaging, and v) data management and quality assessment. Application of the best practices and improvement of achievable resolution using an energy filter will be demonstrated on the example of apo-ferritin that was reconstructed to 1.6 &#197;, and Thermoplasma acidophilum 20S proteasome reconstructed to 2.1-&#197; resolution using a 200 kV TEM equipped with an energy filter and a direct electron detector.

High-resolution cryo-EM maps of macromolecules can be also achieved by using 200 kV TEM microscopes. This protocol shows the best practices for setting accurate optics alignments, data acquisition schemes, and selection of imaging areas that are all essential for the successful collection of high-resolution datasets using a 200 kV TEM.