Name: in vitro characterization of histone chaperones using analytical, pull-down and chaperoning assays
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The extramural grants to Dileep Vasudevan from the Science and Engineering Research Board, Government of India [CRG/2018/000695/PS] and the Department of Biotechnology, Ministry of Science and Technology, Government of India [BT/INF/22/SP33046/2019], as well as the intramural support from the Institute of Life Sciences, Bhubaneswar are greatly acknowledged.&#160;We thank Ms. Sudeshna Sen and Ms. Annapurna Sahoo for their help with histone preparation. The discussions with our colleagues Dr. Chinmayee Mohapatra, Mr. Manas Kumar Jagdev, and Dr. Shaikh Nausad Hossain are also acknowledged.

1. Analytical size-exclusion chromatography to elucidate the oligomeric status and stability of histone chaperones
<ol>
	<li>Analysis of the oligomeric status of histone chaperones
	<ol>
		<li>Equilibrate a 24 mL analytical size-exclusion chromatography (SEC) column with 1.2 column volume (CV), i.e., 28.8 mL of degassed SEC buffer [20 mM of Tris-HCl (pH 7.5), 300 of mM NaCl, and 1 mM of &#946;-mercaptoethanol (&#946;-ME)] at 4 &#176;C (see Table of Materials). 
		NOTE: Column type...

<ol>
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This work demonstrates and validates a comprehensive set of protocols for the biochemical and biophysical characterization of a putative histone chaperone. Herein, recombinantly expressed and purified NAP family proteins, AtNRP1 and AtNRP2, and the N-terminal nucleoplasmin domain of AtFKBP53 were used to demonstrate the protocols. The same set of experiments could very well be used to delineate the functional attributes of previously uncharacterized histone chaperones from any organism.
The fi...

Nucleosomes composed of DNA and histone proteins form the structural unit of chromatin and regulate several critical cellular events. Nucleosomes are dynamically repositioned and remodeled to make DNA accessible to various processes such as replication, transcription, and translation1,2. Histones that are highly basic either tend to interact with acidic proteins in the cellular milieu or undergo aggregation, thus leading to various cellular defects3,4,5. A group of dedicated proteins called histone chaperones aid the transport of histones from the cytoplasm to the nucleus and prevent aberrant histone-DNA aggregation events6,7. Fundamentally, most histone chaperones store and transfer histones onto DNA at physiological ionic strength, thereby aiding the formation of nucleosomes8,9. Some histone chaperones have a definite preference for the histone oligomers H2A/H2B or H3/H410.
Histone chaperones are characterized based on their ability to assemble nucleosomes dependent or independent of DNA synthesis11. For example, chromatin assembly factor-1 (CAF-1) is dependent while histone regulator A (HIRA) is independent of DNA synthesis12,13. Similarly, the nucleoplasmin family of histone chaperones is involved in sperm chromatin decondensation and nucleosome assembly14. The nucleosome assembly protein (NAP) family members facilitate the formation of nucleosome-like structures in vitro and are involved in the shuttling of histones between cytoplasm and nucleus15. Nucleoplasmins and NAP family proteins are both functional histone chaperones but do not share any structural features. Essentially, no single structural feature allows the classification of a protein as a histone chaperone16. The usage of functional and biophysical assays along with structural studies work best in characterizing histone chaperones.
This work describes biochemical and biophysical methods to characterize a protein as a histone chaperone that aids nucleosome assembly. First, analytical size-exclusion chromatography was carried out to analyze the oligomeric status and stability of histone chaperones. Next, a pull-down assay was performed to determine the driving forces and the competitive nature of histone chaperone-histone interactions. However, the hydrodynamic parameters of these interactions could not be accurately calculated using analytical size-exclusion chromatography because of the protein&#39;s shape and its complexes that impact their migration through the column. Therefore, analytical ultracentrifugation was used, which provides in-solution macromolecular properties that include accurate molecular weight, the stoichiometry of interaction, and the shape of the biological molecules. Past studies have extensively used in vitro histone chaperoning assay to functionally characterize histone chaperones such as yScS11617, DmACF18, ScRTT106p19, HsNPM120. Histone chaperoning assay was also used to functionally characterize the proteins as histone chaperones.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acetic acid (glacial)</td>
			<td>Sigma</td>
			<td>A6283</td>
			<td></td>
		</tr>
		<tr>
			<td>Acrylamide</td>
			<td>MP Biomedicals</td>
			<td>814326</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>MP Biomedicals</td>
			<td>193983</td>
			<td></td>
		</tr>
		<tr>
			<td>AKTA Pure 25M FPLC</td>
			<td>Cytiva</td>
			<td>29018226</td>
			<td>Instrument for protein purification</td>
		</tr>
		<tr>
			<td>Ammonium persulfate (APS)</td>
			<td>Sigma</td>
			<td>A3678</td>
			<td></td>
		</tr>
		<tr>
			<td>An-60Ti rotor</td>
			<td>Beckman Coulter</td>
			<td>361964</td>
			<td>Rotor for analytical ultracentrifugation</td>
		</tr>
		<tr>
			<td>Bovine serum albumin (BSA)</td>
			<td>Sigma</td>
			<td>A7030</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform</td>
			<td>Sigma</td>
			<td>C2432</td>
			<td></td>
		</tr>
		<tr>
			<td>Coomassie brilliant blue R 250</td>
			<td>Sigma</td>
			<td>1.15444</td>
			<td></td>
		</tr>
		<tr>
			<td>Dialysis tubing (7 kDa cut-off)</td>
			<td>Thermo Fisher</td>
			<td>68700</td>
			<td>For dialysing protein samples</td>
		</tr>
		<tr>
			<td>Dithiothreitol (DTT)</td>
			<td>MP Biomedicals</td>
			<td>100597</td>
			<td></td>
		</tr>
		<tr>
			<td>DNA Loading Dye</td>
			<td>New England Biolabs</td>
			<td>B7025S</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA disodium salt</td>
			<td>MP Biomedicals</td>
			<td>194822</td>
			<td></td>
		</tr>
		<tr>
			<td>Electronic balance</td>
			<td>Shimadzu</td>
			<td>ATX224R</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma</td>
			<td>E7023</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethidium bromide (EtBr)</td>
			<td>Sigma</td>
			<td>E8751</td>
			<td></td>
		</tr>
		<tr>
			<td>Gel Doc System</td>
			<td>Bio-Rad</td>
			<td>12009077</td>
			<td>For imaging gels after staining</td>
		</tr>
		<tr>
			<td>Horizontal gel electrophoresis apparatus</td>
			<td>Bio-Rad</td>
			<td>1704405</td>
			<td>Instrument for agarose gel electrophoresis</td>
		</tr>
		<tr>
			<td>Hydrochloric acid (HCl)</td>
			<td>Sigma</td>
			<td>320331</td>
			<td></td>
		</tr>
		<tr>
			<td>Imidazole</td>
			<td>MP Biomedicals</td>
			<td>102033</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride (MgCl2)</td>
			<td>Sigma</td>
			<td>M8266</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipettes</td>
			<td>Eppendorf</td>
			<td>Z683779</td>
			<td>For pipetting of micro-volumes</td>
		</tr>
		<tr>
			<td>Mini-PROTEAN electrophoresis system</td>
			<td>Bio-Rad</td>
			<td>1658000</td>
			<td>Instrument for SDS-PAGE</td>
		</tr>
		<tr>
			<td>N,N-methylene-bis-acrylamide</td>
			<td>MP Biomedicals</td>
			<td>800172</td>
			<td></td>
		</tr>
		<tr>
			<td>Nano drop</td>
			<td>Thermo Fisher</td>
			<td>ND-2000</td>
			<td>For measurement of protein and DNA concentrations</td>
		</tr>
		<tr>
			<td>Ni-NTA agarose</td>
			<td>Invitrogen</td>
			<td>R901-15</td>
			<td>Resin beads for pull-down assay</td>
		</tr>
		<tr>
			<td>Optima AUC analytical ultracentrifuge</td>
			<td>Beckman Coulter</td>
			<td>B86437</td>
			<td>Instrument for analytical ultracentrifugation</td>
		</tr>
		<tr>
			<td>pH Meter</td>
			<td>Mettler Toledo</td>
			<td>MT30130863</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenol</td>
			<td>Sigma</td>
			<td>P4557</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasmid isolation kit</td>
			<td>Qiagen</td>
			<td>27104</td>
			<td></td>
		</tr>
		<tr>
			<td>Proteinase K</td>
			<td>Sigma-Aldrich</td>
			<td>1.07393</td>
			<td></td>
		</tr>
		<tr>
			<td>pUC19</td>
			<td>Thermo Fisher</td>
			<td>SD0061</td>
			<td>Plasmid for supercoiling assay</td>
		</tr>
		<tr>
			<td>Refrigerated high-speed centrifuge</td>
			<td>Thermo Fisher</td>
			<td>75002402</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS-PAGE protein marker</td>
			<td>Bio-Rad</td>
			<td>1610317</td>
			<td></td>
		</tr>
		<tr>
			<td>SEDFIT</td>
			<td></td>
			<td></td>
			<td>Free software program for analytical ultracentrifugation data analysis</td>
		</tr>
		<tr>
			<td>SEDNTERP</td>
			<td></td>
			<td></td>
			<td>Free software program to estimate viscosity and density of buffer and partial specific volume of a protein</td>
		</tr>
		<tr>
			<td>SigmaPrep Spin Columns</td>
			<td>Sigma</td>
			<td>SC1000</td>
			<td>For pull-down assay</td>
		</tr>
		<tr>
			<td>Sodium acetate</td>
			<td>Sigma</td>
			<td>S2889</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride (NaCl)</td>
			<td>Merck</td>
			<td>S9888</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate (SDS)</td>
			<td>MP Biomedicals</td>
			<td>102918</td>
			<td></td>
		</tr>
		<tr>
			<td>Superdex 200 Increase 10/300 GL</td>
			<td>Cytiva</td>
			<td>28990944</td>
			<td>Column for analytical size-exclusion chromatography</td>
		</tr>
		<tr>
			<td>Superdex 75 Increase 10/300 GL</td>
			<td>Cytiva</td>
			<td>29148721</td>
			<td>Column for analytical size-exclusion chromatography</td>
		</tr>
		<tr>
			<td>TEMED</td>
			<td>Sigma</td>
			<td>1.10732</td>
			<td></td>
		</tr>
		<tr>
			<td>Topoisomerase I</td>
			<td>Inspiralis</td>
			<td>WGT102</td>
			<td>Enzyme used in plasmid supercoiling assay</td>
		</tr>
		<tr>
			<td>Tris base</td>
			<td>Merck</td>
			<td>T1503</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween-20</td>
			<td>Sigma</td>
			<td>P1379</td>
			<td></td>
		</tr>
		<tr>
			<td>Urea</td>
			<td>MP Biomedicals</td>
			<td>191450</td>
			<td></td>
		</tr>
		<tr>
			<td>Water bath</td>
			<td>N&#252;ve</td>
			<td>NB 5</td>
			<td>For heat treatment of protein samples</td>
		</tr>
		<tr>
			<td>&#946;-mercaptoethanol (&#946;-ME)</td>
			<td>Sigma</td>
			<td>M6250</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

The recombinant N-terminal nucleoplasmin domain of the protein FKBP53 from Arabidopsis thaliana was subjected to analytical SEC. The elution peak volume was plotted against the standard curve to identify its oligomeric state. The analytical SEC results revealed that the domain exists as a pentamer in solution, with an approximate molecular mass of 58 kDa (Figure 1A,B). Further, the nucleoplasmin domain was analyzed for thermal and chemical stability in conjunction w...

Watch this Scientific Journal Video about In Vitro Characterization of Histone Chaperones using Analytical, Pull-Down and Chaperoning Assays at JoVE.com

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.

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 ...

Our protocol describes how techniques like pull-down assays analytical size exclusion chromatography, analytical ultra-centrifugation, and histone chaperoning assay could be used to confirm whether a protein is a histone chaperone. The techniques covered here, when using tandem, could be applied directly to characterize a putative chaperone. his could go along with the structural biology technique.The techniques are applicable to the field of chromatin research. However, the individual methods could be applied to any other protein of interest, as required. Demonstrating the procedure will be Mr.Surajit Gandhi, a PhD student from my laboratory, for the complicated pull-down assay;Ms.Archana Samal, a PhD student, along with Mr.Ruchir C.Bobde for the analytical ultra-centrifugation experiment;Mr. Somanath Baral, a PhD student;along with Mr.Ketul Saharan for the plasmid super-coiling assay First, mix five-micromolar histone chaperones with 20-micromolar H2A/H2B dimers in 300 microliters of equilibration buffer. Centrifuge the histone chaperone H2A/H2B complex to remove any precipitate.Load the sample on the spin column pre-equilibrated with equilibration buffer. Wash the column with 100 column volumes or four milliliters of wash buffer to remove excess H2A/H2B dimer. Next, mix the histone chaperone H2A/H2B complex with 20-to 60-micromolar H3/H4 tetramer.Rewash the column with 100 column volumes or four milliliters of wash buffer to remove any unbound H3/H4 tetramer, then elute the samples with elution buffer. Subject the eluted samples to 18%SDS-PAGE. Then, stain with Coomassie brilliant blue R250 and visualize the gel.Purify the H2A/H2B dimer, H3/H4 tetramer in the histone chaperone individually with the dialysis buffer using analytical size exclusion chromatography. Save the buffer from the run to prepare further dilutions later on and to use as a reference in the AUC cell. For AUC samples, mix the purified chaperones with dimer or tetramer in separate tubes to a final volume of 450 microliters using the saved dialysis buffer to reach an OD280 of 0.3 to 0.6.Assemble the cell with a double-sector centerpiece and quartz windows provided with an analytical ultra centrifuge with an absorbance detector. Fill 400 microliters of the sample solution and 420 microliters of dialysis buffer into the reference and sample sectors of the cell, respectively. Weigh and accurately balance the cells and load them into a four-hole titanium rotor.Align the cells using the marks at the bottom of the cells and the rotor. Load the rotor in the centrifuge, close the lid, and start the run, which allows a vacuum to develop and the temperature to stabilize. For data analysis, calculate the density and viscosity for the proteins buffer components and partial specific volume based on the amino acid composition of the protein using the program SEDNTERP.Load the data from the AUC machine into the program SEDFIT. Define the meniscus, red line, the cell bottom, blue line, and data analysis boundaries green lines. Choose Continuous CS distribution as a model.In the parameters section, set resolution maximum up to 100. Next, set sedimentation coefficient minimum to zero and maximum to 10 to 15. Set the frictional ratio to 1.2 initially and opt to float to derive the ratio from the data.Set the F-ratio to 0.68 for one sigma regularization. Set partial specific volume, buffer density, and viscosity as obtained from the SEDNTURP. Press Run to allow the software to solve the lam equation.Press Fit to refine. Choose Show Peak Mw in CS in the display function of the main toolbar to estimate molecular masses. Mix two-micromolar H3/H4 tetramer and four-micromolar H2A/H2B dimer with increasing concentrations of histone chaperone, ranging from one-to six-micromolar, in an assembly buffer to a final volume of 50 microliters.Incubate the mixture at four degrees Celsius for 30 minutes. Simultaneously, pretreat 500 nanograms of the negatively super-coiled PUC-19 plasmid with one microgram of topoisomerase I enzyme in the assembly buffer in a final volume at 50 microliters. Next, combine the pre-mixed solution containing tetramer, dimer, and histone chaperone with the relaxed plasma DNA.Add 100 microliters of 2X stop buffer and incubate to end the assembly reaction by deproteinizing the plasmid DNA. Add an equal volume of Tris-saturated phenol in the tube containing the reaction mixture and mix the contents of the reaction mixture well. Then, centrifuge the sample.Gently collect the upper aqueous phase containing the plasmid DNA with a micropipette and mix an equal volume of chloroform. Vortex the mixture. Next, collect the upper aqueous phase, add a 1/10 volume of three-molar sodium acetate of pH 5.5, and 2.5 volumes of ice-cold ethanol.Mix the solution well by inverting the tube three to four times. Centrifuge the sample at 16, 200 G for 10 minutes and gently discard the supernatant. Keep the tubes open at room temperature until even trace amounts of ethanol evaporate, leaving the precipitated plasmid DNA in the tube.The analytical SEC results revealed that the recombinant N-terminal nucleoplasmin domain of the Arabidopsis thaliana protein FKBP53 is a pentamer of 65 kilodaltons in solution. The nucleoplasmin sample subjected to heat treatment showed that the domain is highly thermo-stable. The nucleoplasmin domain displayed salt stability up to two molars of sodium chloride and urea stability up to four molars.A pull-down assay revealed that the interaction of the nucleoplasmin domain with H2A/H2B dimer was stable up to 0.4-molar sodium chloride, whereas the association with H3/H4 was stable up to 0.7 molars. The chaperone binds H2A/H2B dimer and H3/H4 tetramer simultaneously, irrespective of the order in which they are added to the chaperone, indicating separate interaction sites for the oligomers. The estimated molecular masses through AUC-SV reveal a 1:1 stoichiometry of nucleoplasmin domain with the histone oligomers.In the plasmid super-coiling assay, recombinant plant histone chaperones AtNRP1 and AtNRP2 increased the amount of super-coiled plasmid, suggesting it could deposit histones onto the DNA to form nucleosomes, causing DNA super coiling. Plasmid super-coiling assay needs special care and possible optimization for histone DNA and chaperone characterization. Isomeric characterization telemetry can be used as a follow-up to analytical size-exclusion experiments to confirm the binding stability.

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Research

JoVE Journal

Biochemistry

Species Determination and Quantitation in Mixtures Using MRM Mass Spectrometry of Peptides Applied to Meat Authentication

We describe a simple protocol for identifying and quantifying the two components in binary mixtures of species possessing one or more similar proteins. Central to the method is the identification of 'corresponding proteins' in the species of interest, in other words proteins that are nominally the same but possess species-specific sequence differences. When subject to proteolysis, corresponding proteins will give rise to some peptides which are likewise similar but with species-specific variants. These are 'corresponding peptides'. Species-specific peptides can be used as markers for species determination, while pairs of corresponding peptides permit relative quantitation of two species in a mixture. The peptides are detected using multiple reaction monitoring (MRM) mass spectrometry, a highly specific technique that enables peptide-based species determination even in complex systems. In addition, the ratio of MRM peak areas deriving from corresponding peptides supports relative quantitation. Since corresponding proteins and peptides will, in the main, behave similarly in both processing and in experimental extraction and sample preparation, the relative quantitation should remain comparatively robust. In addition, this approach does not need the standards and calibrations required by absolute quantitation methods. The protocol is described in the context of red meats, which have convenient corresponding proteins in the form of their respective myoglobins. This application is relevant to food fraud detection: the method can detect 1% weight for weight of horse meat in beef. The corresponding protein, corresponding peptide (CPCP) relative quantitation using MRM peak area ratios gives good estimates of the weight for weight composition of a horse plus beef mixture.

We present a protocol for identifying and quantifying the components in mixtures of species possessing similar proteins. Mass spectrometry detects peptides for identification, and gives relative quantitation by ratios of peak areas. As a tool food for fraud detection, the method can detect 1% horse in beef.

We describe a simple protocol for identifying and quantifying the two components in binary mixtures of species possessing one or more similar proteins. ...

Differential Scanning Calorimetry &#8212; A Method for Assessing the Thermal Stability and Conformation of Protein Antigen

Differential scanning calorimetry (DSC) is an analytical technique that measures the molar heat capacity of samples as a function of temperature. In the case of protein samples, DSC profiles provide information about thermal stability, and to some extent serves as a structural &#8220;fingerprint&#8221; that can be used to assess structural conformation. It is performed using a differential scanning calorimeter that measures the thermal transition temperature (melting temperature; Tm) and the energy required to disrupt the interactions stabilizing the tertiary structure (enthalpy; &#8710;H) of proteins. Comparisons are made between formulations as well as production lots, and differences in derived values indicate differences in thermal stability and structural conformation. Data illustrating the use of DSC in an industrial setting for stability studies as well as monitoring key manufacturing steps are provided as proof of the effectiveness of this protocol. In comparison to other methods for assessing the thermal stability of protein conformations, DSC is cost-effective, requires few sample preparation steps, and also provides a complete thermodynamic profile of the protein unfolding process.

Differential scanning calorimetry measures the thermal transition temperature(s) and total heat energy required to denature a protein. Results obtained are used to assess the thermal stability of protein antigens in vaccine formulations.

Differential scanning calorimetry (DSC) is an analytical technique that measures the molar heat capacity of samples as a function of temperature. In the ...

Enhanced Sample Multiplexing of Tissues Using Combined Precursor Isotopic Labeling and Isobaric Tagging (cPILOT)

There is an increasing demand to analyze many biological samples for disease understanding and biomarker discovery. Quantitative proteomics strategies that allow simultaneous measurement of multiple samples have become widespread and greatly reduce experimental costs and times. Our laboratory developed a technique called combined precursor isotopic labeling and isobaric tagging (cPILOT), which enhances sample multiplexing of traditional isotopic labeling or isobaric tagging approaches. Global cPILOT can be applied to samples originating from cells, tissues, bodily fluids, or whole organisms and gives information on relative protein abundances across different sample conditions. cPILOT works by 1) using low pH buffer conditions to selectively dimethylate peptide N-termini and 2) using high pH buffer conditions to label primary amines of lysine residues with commercially-available isobaric reagents (see Table of Materials/Reagents). The degree of sample multiplexing available is dependent on the number of precursor labels used and the isobaric tagging reagent. Here, we present a 12-plex analysis using light and heavy dimethylation combined with six-plex isobaric reagents to analyze 12 samples from mouse tissues in a single analysis. Enhanced multiplexing is helpful for reducing experimental time and cost and more importantly, allowing comparison across many sample conditions (biological replicates, disease stage, drug treatments, genotypes, or longitudinal time-points) with less experimental bias and error. In this work, the global cPILOT approach is used to analyze brain, heart, and liver tissues across biological replicates from an Alzheimer&#39;s disease mouse model and wild-type controls. Global cPILOT can be applied to study other biological processes and adapted to increase sample multiplexing to greater than 20 samples.

Enhanced Sample Multiplexing of Tissues Using Combined Precursor Isotopic Labeling and Isobaric Tagging cPILOT

Combined precursor isotopic labeling and isobaric tagging (cPILOT) is a quantitative proteomics strategy that enhances sample multiplexing capabilities of isobaric tags. This protocol describes the application of cPILOT to tissues from an Alzheimer's disease mouse model and wild-type controls.

There is an increasing demand to analyze many biological samples for disease understanding and biomarker discovery. Quantitative proteomics strategies ...

Structural Characterization of Mannan Cell Wall Polysaccharides in Plants Using PACE

Plant cell wall polysaccharides are notoriously difficult to analyze, and most methods require expensive equipment, skilled operators, and large amounts of purified material. Here, we describe a simple method for gaining detailed polysaccharide structural information, including resolution of structural isomers. For polysaccharide analysis by gel electrophoresis (PACE), plant cell wall material is hydrolyzed with glycosyl hydrolases specific to the polysaccharide of interest (e.g., mannanases for mannan). Large format polyacrylamide gels are then used to separate the released oligosaccharides, which have been fluorescently labeled. Gels can be visualized with a modified gel imaging system (see Table of Materials). The resulting oligosaccharide fingerprint can either be compared qualitatively or, with replication, quantitatively. Linkage and branching information can be established using additional glycosyl hydrolases (e.g., mannosidases and galactosidases). Whilst this protocol describes a method for analyzing glucomannan structure, it can be applied to any polysaccharide for which characterized glycosyl hydrolases exist. Alternatively, it can be used to characterize novel glycosyl hydrolases using defined polysaccharide substrates.

A protocol for the structural analysis of polysaccharides by gel electrophoresis (PACE), using mannan as an example, is described.

Plant cell wall polysaccharides are notoriously difficult to analyze, and most methods require expensive equipment, skilled operators, and large amounts ...

In Vitro Ubiquitination and Deubiquitination Assays of Nucleosomal Histones

Ubiquitination is a post-translational modification that plays important roles in various signaling pathways and is notably involved in the coordination of chromatin function and DNA-associated processes. This modification involves a sequential action of several enzymes including E1 ubiquitin-activating, E2 ubiquitin-conjugating and E3 ubiquitin-ligase and is reversed by deubiquitinases (DUBs). Ubiquitination induces degradation of proteins or alteration of protein function including modulation of enzymatic activity, protein-protein interaction and subcellular localization. A critical step in demonstrating protein ubiquitination or deubiquitination is to perform in vitro reactions with purified components. Effective ubiquitination and deubiquitination reactions could be greatly impacted by the different components used, enzyme co-factors, buffer conditions, and the nature of the substrate.&#160; Here, we provide step-by-step protocols for conducting ubiquitination and deubiquitination reactions. We illustrate these reactions using minimal components of the mouse Polycomb Repressive Complex 1 (PRC1), BMI1, and RING1B, an E3 ubiquitin ligase that monoubiquitinates histone H2A on lysine 119. Deubiquitination of nucleosomal H2A is performed using a minimal Polycomb Repressive Deubiquitinase (PR-DUB) complex formed by the human deubiquitinase BAP1 and the DEUBiquitinase ADaptor (DEUBAD) domain of its co-factor ASXL2. These ubiquitination/deubiquitination assays can be conducted in the context of either recombinant nucleosomes reconstituted with bacteria-purified proteins or native nucleosomes purified from mammalian cells. We highlight the intricacies that can have a significant impact on these reactions and we propose that the general principles of these protocols can be swiftly adapted to other E3 ubiquitin ligases and deubiquitinases.

Ubiquitination is a post-translational modification that plays important roles in cellular processes and is tightly coordinated by deubiquitination. Defects in both reactions underlie human pathologies. We provide protocols for conducting ubiquitination and deubiquitination reaction in vitro using purified components.

Ubiquitination is a post-translational modification that plays important roles in various signaling pathways and is notably involved in the coordination ...

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

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

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

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

Stepwise Dosing Protocol for Increased Throughput in Label-Free Impedance-Based GPCR Assays

Label-free impedance-based assays are increasingly used to non-invasively study ligand-induced GPCR activation in cell culture experiments. The approach provides real-time cell monitoring with a device-dependent time resolution down to several tens of milliseconds and it is highly automated. However, when sample numbers get high (e.g., dose-response studies for various different ligands), the cost for the disposable electrode arrays as well as the available time resolution for sequential well-by-well recordings may become limiting. Therefore, we here present a serial agonist addition protocol which has the potential to significantly increase the output of label-free GPCR assays. Using the serial agonist addition protocol, a GPCR agonist is added sequentially in increasing concentrations to a single cell layer while continuously monitoring the sample&#39;s impedance (agonist mode). With this serial approach, it is now possible to establish a full dose-response curve for a GPCR agonist from just one single cell layer. The serial agonist addition protocol is applicable to different GPCR coupling types, Gq Gi/0 or Gs and it is compatible with recombinant and endogenous expression levels of the receptor under study. Receptor blocking by GPCR antagonists is assessable as well (antagonist mode).

This protocol demonstrates real-time recording of full dose-response relationships for agonist-induced GPCR activation from a single cell layer grown on a single microelectrode using label-free impedance measurements. The new dosing scheme significantly increases throughput without loss in time resolution.

Label-free impedance-based assays are increasingly used to non-invasively study ligand-induced GPCR activation in cell culture experiments. The approach ...

Characterization of Amyloid Structures in Aging C. Elegans Using Fluorescence Lifetime Imaging

Amyloid fibrils are associated with a number of neurodegenerative diseases such as Huntington&#39;s, Parkinson&#39;s, or Alzheimer&#39;s disease. These amyloid fibrils can sequester endogenous metastable proteins as well as components of the proteostasis network (PN) and thereby exacerbate protein misfolding in the cell. There are a limited number of tools available to assess the aggregation process of amyloid proteins within an animal. We present a protocol for fluorescence lifetime microscopy (FLIM) that allows monitoring as well as quantification of the amyloid fibrilization in specific cells, such as neurons, in a noninvasive manner and with the progression of aging and upon perturbation of the PN. FLIM is independent of the expression levels of the fluorophore and enables an analysis of the aggregation process without any further staining or bleaching. Fluorophores are quenched when they are in close vicinity of amyloid structures, which results in a decrease of the fluorescence lifetime. The quenching directly correlates with the aggregation of the amyloid protein. FLIM is a versatile technique that can be applied to compare the fibrilization process of different amyloid proteins, environmental stimuli, or genetic backgrounds in vivo in a non-invasive manner.

Characterization of Amyloid Structures in Aging C. Elegans Using Fluorescence Lifetime Imaging

Fluorescence lifetime imaging monitors, quantifies and distinguishes the aggregation tendencies of proteins in living, aging, and stressed C. elegans disease models.

Amyloid fibrils are associated with a number of neurodegenerative diseases such as Huntington&#39;s, Parkinson&#39;s, or Alzheimer&#39;s disease. These ...

Myosin-Specific Adaptations of In vitro Fluorescence Microscopy-Based Motility Assays

Myosin proteins bind and interact with filamentous actin (F-actin) and are found in organisms across the phylogenetic tree. Their structure and enzymatic properties are adapted for the particular function they execute in cells. Myosin 5a processively walks on F-actin to transport melanosomes and vesicles in cells. Conversely, nonmuscle myosin 2b operates as a bipolar filament containing approximately 30 molecules. It moves F-actin of opposite polarity toward the center of the filament, where the myosin molecules work asynchronously to bind actin, impart a power stroke, and dissociate before repeating the cycle. Nonmuscle myosin 2b, along with its other nonmuscle myosin 2 isoforms, has roles that include&#160;cell adhesion, cytokinesis, and tension maintenance. The mechanochemistry of myosins can be studied by performing in vitro motility assays using purified proteins. In the gliding actin filament assay, the myosins are bound to a microscope coverslip surface and translocate fluorescently labeled F-actin, which can be tracked. In the single molecule/ensemble motility assay, however, F-actin is bound to a coverslip and the movement of fluorescently labeled myosin molecules on the F-actin is observed. In this report, the purification of recombinant myosin 5a from Sf9 cells using affinity chromatography is outlined. Following this, we outline two fluorescence microscopy-based assays: the gliding actin filament assay and the inverted motility assay. From these assays, parameters such as actin translocation velocities and single molecule run lengths and velocities can be extracted using the image analysis software. These techniques can also be applied to study the movement of single filaments of the nonmuscle myosin 2 isoforms, discussed herein in the context of nonmuscle myosin 2b. This workflow represents a protocol and a set of quantitative tools that can be used to study the single molecule and ensemble dynamics of nonmuscle myosins.

Presented here is a procedure to express and purify myosin 5a followed by a discussion of its characterization, using both ensemble and single molecule in vitro fluorescence microscopy-based assays, and how these methods can be modified for the characterization of nonmuscle myosin 2b.

Myosin proteins bind and interact with filamentous actin (F-actin) and are found in organisms across the phylogenetic tree. Their structure and enzymatic ...

An Optimized Single-Molecule Pull-Down Assay for Quantification of Protein Phosphorylation

Phosphorylation is a necessary posttranslational modification that regulates protein function and directs cell signaling outcomes. Current methods to measure protein phosphorylation cannot preserve the heterogeneity in phosphorylation across individual proteins. The single-molecule pull-down (SiMPull) assay was developed to investigate the composition of macromolecular complexes via immunoprecipitation of proteins on a glass coverslip followed by single-molecule imaging. The current technique is an adaptation of SiMPull that provides robust quantification of the phosphorylation state of full-length membrane receptors at the single-molecule level. Imaging thousands of individual receptors in this way allows for quantifying protein phosphorylation patterns. The present protocol details the optimized SiMPull procedure, from sample preparation to imaging. Optimization of glass preparation and antibody fixation protocols further enhances data quality. The current protocol provides code for the single-molecule data analysis that calculates the fraction of receptors phosphorylated within a sample. While this work focuses on phosphorylation of the epidermal growth factor receptor (EGFR), the protocol can be generalized to other membrane receptors and cytosolic signaling molecules.

The present protocol describes sample preparation and data analysis to quantify protein phosphorylation using an improved single-molecule pull-down (SiMPull) assay.

Phosphorylation is a necessary posttranslational modification that regulates protein function and directs cell signaling outcomes. Current methods to ...