We thank the UAMS Proteomics Facility for mass spectrometric support. Funding for this project was provided by NIH grants P20RR015569, P20RR016460 and R01DA025755.

This protocol is modified from Blair et al. 6.
1. LSD1 Demethylation Assay
<ol>
	<li>In a final volume of 20 &mu;L, combine 125 ng recombinant LSD1 with 0.25 &mu;g di-methyl histone H3 peptide (ARTKme2QTARKSTGGKAPRKQLYK-biotin) in demethylase buffer (50 mM Tris-Cl pH 8.5, 50 mM KCl, 5 mM MgCl2, 5% glycerol). Additionally, perform a peptide alone control with no enzyme. The control is for section 3 and does not need reductive methylation.</li>
	<li>Incubate for 2 hours at 37&deg;C.</li>
	<li>To collect the peptides, add 8 &mu;L POROS R2 20 micron beads to each sample and agitate for 15 minutes at room temperature. Prepare POROS beads by suspending 1 volume of beads with 1 volume of methanol, and then add 10 volumes of 5% formic acid / 0.2% TFA.</li>
	<li>Condition two C18 ZipTips by aspirating 20 &mu;L of 0.1% TFA into the tip and pushing it back out with a pipettor. Do this twice with 0.1% TFA, four times with 70% acetonitrile / 0.1% TFA, and four times again with 0.1% TFA.</li>
	<li>Load the two samples (control and the demethylase reaction) onto the conditioned C18 ZipTips by pipetting the bead slurry behind the C18 resin in the ZipTips and pushing the volume through with a pipettor.</li>
	<li>Wash ZipTips twice with 20 &mu;L of 0.1% TFA.</li>
	<li>Elute in 40 &mu;L of 70% acetonitrile / 0.1% TFA.</li>
	<li>Lyophilize each eluant completely with a SpeedVac concentrator.</li>
</ol>
2. Reductive Methylation
This portion of the protocol is modified from Blair et al. and Rayment et al. 6,7.
<ol>
	<li>Re-suspend the demethylase reaction in 100 &mu;L of 50 mM phosphate buffer, pH 7.4.</li>
	<li>To the demethylase reaction, add 8 &mu;L of 15 mg/mL borane dimethylamine. Borane dimethylamine is dissolved in 50 mM phosphate buffer, pH 7.4, to give the 15 mg/mL stock solution. This should be made fresh.</li>
	<li>To the demethylase reaction, add 16 &mu;L of 250 mM deuterated formaldehyde. The 250 mM deuterated formaldehyde is prepared by diluting the stock in H20. This should be made fresh.</li>
	<li>Incubate at 4&deg;C for 2 hours.</li>
	<li>Repeat steps 2.2, 2.3 &amp; 2.4.</li>
	<li>Repeat step 2.2.</li>
	<li>Incubate at 4&deg;C for ~15 hours.</li>
	<li>To the demethylase sample, add 12.5 &mu;L of 1M Tris, pH 7.4 to quench the reductive methylation reaction.</li>
</ol>
3. MALDI Mass Spectrometry
<ol>
	<li>Add POROS R2 20 micron beads to the demethylase reaction, and collect on ZipTips as described in steps 1.3-1.6.</li>
</ol>
Note: Re-suspend the control in 100 &mu;L of 50 mM phosphate buffer, pH 7.4 and treat as the other sample starting at step 3.1.
<ol start="2">
	<li>Elute the control and demethylase reaction samples from the ZipTips onto a MALDI sample plate using 2 &mu;L of 33% saturated 2,5-dihydroxybenzoic acid. To prepare the 33% 2,5-dihydroxybenzoic acid, make a saturated solution of 2,5-dihydroxybenzoic acid in 70% acetonitrile / 0.1% TFA and then dilute to 33% saturated in 70% acetonitrile / 0.1% TFA. Allow the eluted samples to dry and crystallize.</li>
	<li>Collect mass spectra using a PerkinElmerSciex MALDI-prOTOF mass spectrometer or available high resolution MALDI mass spectrometer 8,9,10.</li>
	<li>View spectra and extract peak areas using PerkinElmerSciex TOFworks software or software provided by the mass spectrometer manufacturer.</li>
	<li>Verify reaction products by MS2 with an available mass spectrometric system providing tandem mass spectrometric capabilities.</li>
</ol>
4. Data Analysis
<ol>
	<li>In order to compensate for the isotopic overlap created by using heavy formaldehyde (Figure 1B), determine the peak area (A) ratio of 13C2 and 13C4 isotopes relative to the monoisotopic peak for the control sample, which has not undergone reductive methylation (Fig. 2A). 
	Eq 1: A13C2/A12C = r1 
	Eq 2: A13C4/A12C = r2 
	This will give you the ratio of peptide existing in these isotopic states (r1 &amp; r2) specific to your experiment and mass spectrometer.</li>
	<li>Use the r1 &amp; r2 values in the following formulas for quantifying the relative amount of peptide existing in each modification state in the demethylase reaction sample (Fig. 2B): 
	Eq 3: H3K4me2= A1 
	Eq 4: H3K4me = A2 - r1(A1) 
	Eq 5: H3K4 =A3 - r2(A1) - [r1(A2 - r1(A1))]</li>
</ol>
5. Representative Results
Using LSD1, we show the effectiveness of MassSQUIRM for quantifying lysine demethylation. As described in the Protocol Text section, we performed a demethylase assay with 125 ng of LSD1 and 0.25 &mu;g di-methyl histone H3 peptide (ARTKme2QTARKSTGGKAPRKQLYK-biotin). The control and demethylase reaction samples were subjected to reductive methylation and MALDI mass spectrometry. The control reaction that did not undergo reductive methylation showed the typical isotopic envelope for this peptide and provided peak areas for equations 1 and 2 (Figure 2A). The mass spectrum for the demethylase reaction provided peak areas for equations 3-5 (Figure 2B). Using the peak areas from the control and demethylase reaction, we determined that LSD1 demethylated the peptide to give the following reaction products: 33.7% di-methyl Lys4, 42.3% mono-methyl Lys4, and 24% un-methylated Lys 4. Refer to Blair et al. for the full analysis of LSD1 demethylase activity as well as inhibitor studies 6. Note that changing variables such as reaction time, enzyme concentration and substrate concentration will allow for an in-depth analysis of activity.
<img alt="Figure 1" src="/files/ftp_upload/3604/3604fig1.jpg" /> 
Figure 1. MassSQUIRM overview. (A) An N-terminal peptide from histone H3 is shown as being un- (green), mono- (red), or di- (blue) methylated at lysine 4. Variation in the chemical composition of each peptide leads to differential ionization making quantification complex. (B) Reductive methylation converts all lysine residues to the di-methyl state which causes all peptides to ionize similarly. The use of heavy formaldehyde in the reductive methylation reaction allows retention of the identity of the original methylation. Open circles indicate light methylation while closed circles indicate heavy methylation. Modified from Blair et al. 20116.
<img alt="Figure 2" src="/files/ftp_upload/3604/3604fig2.jpg" /> 
Figure 2. MassSQUIRM can be used to quantify differentially methylated peptides. (A) A di-methylated synthetic histone H3 peptide (ARTKme2QTARKSTGGKAPRKQLYK-biotin) was analyzed using mass spectrometry and peak ratios relative to the monoisotopic peak were noted as r1 and r2 in equations 1 and 2. (B) The same synthetic peptide was incubated with 125 ng LSD1 in demethylase buffer for two hours at 37&deg;C. Samples were then subjected to MassSQUIRM analysis. A mixed population of overlapping peaks represents three different methylation states as seen in Figure 1B. Areas under the monoisotopic peaks were noted as A1, A2, and A3. Peak areas were used in equations 3-5. Open circles indicate light methylation while closed circles indicate heavy methylation. Modified from Blair et al. 20116.

<ol>
	<li>Goldberg, A. D., Allis, C. D., Bernstein, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epigenetics:+a+landscape+takes+shape.">Epigenetics: a landscape takes shape.</a> Cell. 128, 635-638 (2007).</li><li>Kouzarides, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chromatin+modifications+and+their+function.">Chromatin modifications and their function.</a> Cell. 128, 693-705 (2007).</li><li>Blair, L. P., Cao, J., Zou, M. R., Sayegh, J., Yan, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Epigenetic+Regulation+by+Lysine+Demethylase+5+(KDM5)+Enzymes+in+Cancer.">Epigenetic Regulation by Lysine Demethylase 5 (KDM5) Enzymes in Cancer.</a> Cancers (Basel). 3, 1383-1404 (2011).</li><li>Cole, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+probes+for+histone-modifying+enzymes.">Chemical probes for histone-modifying enzymes.</a> Nat. Chem. Biol. 4, 590-597 (2008).</li><li>Shi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histone+demethylation+mediated+by+the+nuclear+amine+oxidase+homolog+LSD1.">Histone demethylation mediated by the nuclear amine oxidase homolog LSD1.</a> Cell. 119, 941-953 (2004).</li><li>Blair, L. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MassSQUIRM:+An+assay+for+quantitative+measurement+of+lysine+demethylase+activity.">MassSQUIRM: An assay for quantitative measurement of lysine demethylase activity.</a> Epigenetics. 6, 490-499 (2011).</li><li>Rayment, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+structure+of+myosin+subfragment-1:+a+molecular+motor.">Three-dimensional structure of myosin subfragment-1: a molecular motor.</a> Science. 261, 50-508 (1993).</li><li>Collom, S. L., Jamakhandi, A. P., Tackett, A. J., Radominska-Pandya, A., Miller, G. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CYP2E1+active+site+residues+in+substrate+recognition+sequence+5+identified+by+photoaffinity+labeling+and+homology+modeling.">CYP2E1 active site residues in substrate recognition sequence 5 identified by photoaffinity labeling and homology modeling.</a> Arch. Biochem. Biophys. 459, 59-69 (2007).</li><li>Gradolatto, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Saccharomyces+cerevisiae+Yta7+Regulates+Histone+Gene+Expression.">Saccharomyces cerevisiae Yta7 Regulates Histone Gene Expression.</a> Genetics. 179, 291-304 (2008).</li><li>Taverna, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Yng1+PHD+finger+binding+to+histone+H3+trimethylated+at+lysine+4+promotes+NuA3+HAT+activity+at+Lysine+14+of+H3+and+transcripiton+at+a+subset+of+targeted+ORFs.">Yng1 PHD finger binding to histone H3 trimethylated at lysine 4 promotes NuA3 HAT activity at Lysine 14 of H3 and transcripiton at a subset of targeted ORFs.</a> Mol. Cell. 24, 785-796 (2006).</li></ol>

We have nothing to disclose.

MassSQUIRM is an inexpensive and quantitative method for comprehensive analysis of the activity of lysine demethylases involved in mono- and di-methylation. MassSQUIRM offers quantitation not only of the product of the reaction but also for the intermediates. This assay can be used as a powerful tool in studying the mechanism of LSD1 and other histone demethylases. It will also be useful for classifying many newly discovered lysine demethylase enzymes such as PHF8 and could be used for certain methyltransferase enzymes.

<table border="1">
	<tbody>
		<tr>
			<td>Name of the reagent</td>
			<td>Company</td>
			<td>Catalogue number</td>
		</tr>
		<tr>
			<td>LSD1</td>
			<td>BPS Biosciences</td>
			<td>50100</td>
		</tr>
		<tr>
			<td>H3K4me2-biotin peptide</td>
			<td>prepared in-house</td>
			<td>none</td>
		</tr>
		<tr>
			<td>POROS R2 20 micron beads</td>
			<td>Applied Biosystems</td>
			<td>1-1129-06</td>
		</tr>
		<tr>
			<td>C18 ZipTip</td>
			<td>Millipore</td>
			<td>ZTC18M</td>
		</tr>
		<tr>
			<td>Trifluoroacetic acid (TFA)</td>
			<td>Thermo</td>
			<td>28904</td>
		</tr>
		<tr>
			<td>acetonitrile</td>
			<td>Fisher</td>
			<td>A996</td>
		</tr>
		<tr>
			<td>2,5-dihydroxybenzoic acid</td>
			<td>Sigma</td>
			<td>85707</td>
		</tr>
		<tr>
			<td>Borane dimethylamine</td>
			<td>Sigma</td>
			<td>180238</td>
		</tr>
		<tr>
			<td>isotopically heavy d2-formaldehyde</td>
			<td>Cambridge Isotope Laboratories</td>
			<td>DLM-805-20</td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Fisher</td>
			<td>BP154</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Fisher</td>
			<td>BP366</td>
		</tr>
		<tr>
			<td>MgCl2</td>
			<td>Fisher</td>
			<td>BP214</td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Fisher</td>
			<td>G33</td>
		</tr>
		<tr>
			<td>Formic acid</td>
			<td>Fluka</td>
			<td>06440</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Fisher</td>
			<td>A452</td>
		</tr>
		<tr>
			<td>Na-phosphate</td>
			<td>Fisher</td>
			<td>BP329</td>
		</tr>
		<tr>
			<td>SpeedVac Concentrator</td>
			<td>Savant</td>
			<td>DNA110</td>
		</tr>
		<tr>
			<td>MALDI-prOTOF mass spectrometer and TOFworks software</td>
			<td>PerkinElmerSciex</td>
			<td>none</td>
		</tr>
	</tbody>
</table>

application of masssquirm for quantitative measurements of lysine demethylase activity

Recently, epigenetic regulators have been discovered as key players in many different diseases 1-3. As a result, these enzymes are prime targets for small molecule studies and drug development 4. Many epigenetic regulators have only recently been discovered and are still in the process of being classified. Among these enzymes are lysine demethylases which remove methyl groups from lysines on histones and other proteins. Due to the novel nature of this class of enzymes, few assays have been developed to study their activity. This has been a road block to both the classification and high throughput study of histone demethylases. Currently, very few demethylase assays exist. Those that do exist tend to be qualitative in nature and cannot simultaneously discern between the different lysine methylation states (un-, mono-, di- and tri-). Mass spectrometry is commonly used to determine demethylase activity but current mass spectrometric assays do not address whether differentially methylated peptides ionize differently. Differential ionization of methylated peptides makes comparing methylation states difficult and certainly not quantitative (Figure 1A). Thus available assays are not optimized for the comprehensive analysis of demethylase activity.
Here we describe a method called MassSQUIRM (mass spectrometric quantitation using isotopic reductive methylation) that is based on reductive methylation of amine groups with deuterated formaldehyde to force all lysines to be di-methylated, thus making them essentially the same chemical species and therefore ionize the same (Figure 1B). The only chemical difference following the reductive methylation is hydrogen and deuterium, which does not affect MALDI ionization efficiencies. The MassSQUIRM assay is specific for demethylase reaction products with un-, mono- or di-methylated lysines. The assay is also applicable to lysine methyltransferases giving the same reaction products. Here, we use a combination of reductive methylation chemistry and MALDI mass spectrometry to measure the activity of LSD1, a lysine demethylase capable of removing di- and mono-methyl groups, on a synthetic peptide substrate 5. This assay is simple and easily amenable to any lab with access to a MALDI mass spectrometer in lab or through a proteomics facility. The assay has ~8-fold dynamic range and is readily scalable to plate format 5.

Watch this Scientific Journal Video about Application of MassSQUIRM for Quantitative Measurements of Lysine Demethylase Activity at JoVE.com

Application of MassSQUIRM for Quantitative Measurements of Lysine Demethylase Activity

We present a method for using MALDI mass spectrometry and reductive methylation chemistry to quantify changes in lysine methylation.

Recently, epigenetic regulators have been discovered as key players in many different diseases 1-3. As a result, these enzymes are prime targets for small ...

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13.3K Views.  University of Arkansas for Medical Sciences. We present a method for using MALDI mass spectrometry and reductive methylation chemistry to quantify changes in lysine methylation.

Video: Application of MassSQUIRM for Quantitative Measurements of Lysine Demethylase Activity

An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

Escherichia coli is an enteric bacterium that is capable of growing over a wide range of pH values (pH 5 - 9)1 and, incredibly, is able to survive extreme acid stresses including passage through the mammalian stomach where the pH can fall to as low as pH 1 - 22. To enable such a broad range of acidic pH survival, E. coli possesses four different inducible amino acid decarboxylases that decarboxylate their substrate amino acids in a proton-dependent manner thus raising the internal pH. The decarboxylases include the glutamic acid decarboxylases GadA and GadB3, the arginine decarboxylase AdiA4, the lysine decarboxylase LdcI5, 6 and the ornithine decarboxylase SpeF7. All of these enzymes utilize pyridoxal-5'-phospate as a co-factor8 and function together with inner-membrane substrate-product antiporters that remove decarboxylation products to the external medium in exchange for fresh substrate2. In the case of LdcI, the lysine-cadaverine antiporter is called CadB. Recently, we determined the X-ray crystal structure of LdcI to 2.0 &#197;, and we discovered a novel small-molecule bound to LdcI the stringent response regulator guanosine 5'-diphosphate,3'-diphosphate (ppGpp) 14. The stringent response occurs when exponentially growing cells experience nutrient deprivation or one of a number of other stresses9. As a result, cells produce ppGpp which leads to a signaling cascade culminating in the shift from exponential growth to stationary phase growth10. We have demonstrated that ppGpp is a specific inhibitor of LdcI 14. Here we describe the lysine decarboxylase assay, modified from the assay developed by Phan et al.11, that we have used to determine the activity of LdcI and the effect of pppGpp/ppGpp on that activity. The LdcI decarboxylation reaction removes the &alpha;-carboxy group of L-lysine and produces carbon dioxide and the polyamine cadaverine (1,5-diaminopentane)5. L-lysine and cadaverine can be reacted with 2,4,6-trinitrobenzensulfonic acid (TNBS) at high pH to generate N,N'-bistrinitrophenylcadaverine (TNP-cadaverine) and N,N&#8242;-bistrinitrophenyllysine (TNP-lysine), respectively11. The TNP-cadaverine can be separated from the TNP-lysine as the former is soluble in organic solvents such as toluene while the latter is not (See Figure 1). The linear range of the assay was determined empirically using purified cadaverine.

An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

The activity of the inducible lysine decarboxylase is monitored by reacting the substrate L-lysine and the product cadaverine with 2,4,6-trinitrobenzensulfonic acid to form adducts that have differential solubility in toluene.

Escherichia coli is an enteric bacterium that is capable of growing over a wide range of pH values (pH 5 - 9)1 and, incredibly, is able to survive extreme ...

Quantitative, Real-time Analysis of Base Excision Repair Activity in Cell Lysates Utilizing Lesion-specific Molecular Beacons

We describe a method for the quantitative, real-time measurement of DNA glycosylase and AP endonuclease activities in cell nuclear lysates using base excision repair (BER) molecular beacons. The substrate (beacon) is comprised of a deoxyoligonucleotide containing a single base lesion with a 6-Carboxyfluorescein (6-FAM) moiety conjugated to the 5'end and a Dabcyl moiety conjugated to the 3' end of the oligonucleotide. The BER molecular beacon is 43 bases in length and the sequence is designed to promote the formation of a stem-loop structure with 13 nucleotides in the loop and 15 base pairs in the stem1,2. When folded in this configuration the 6-FAM moiety is quenched by Dabcyl in a non-fluorescent manner via F&ouml;rster Resonance Energy Transfer (FRET)3,4. The lesion is positioned such that following base lesion removal and strand scission the remaining 5 base oligonucleotide containing the 6-FAM moiety is released from the stem. Release and detachment from the quencher (Dabcyl) results in an increase of fluorescence that is proportionate to the level of DNA repair. By collecting multiple reads of the fluorescence values, real-time assessment of BER activity is possible. The use of standard quantitative real-time PCR instruments allows the simultaneous analysis of numerous samples. The design of these BER molecular beacons, with a single base lesion, is amenable to kinetic analyses, BER quantification and inhibitor validation and is adaptable for quantification of DNA Repair activity in tissue and tumor cell lysates or with purified proteins. The analysis of BER activity in tumor lysates or tissue aspirates using these molecular beacons may be applicable to functional biomarker measurements. Further, the analysis of BER activity with purified proteins using this quantitative assay provides a rapid, high-throughput method for the discovery and validation of BER inhibitors.

We describe a method for the quantitative, real-time measurement of DNA glycosylase and AP endonuclease activities in cell nuclear lysates. The assay yields rates of DNA Repair activity amenable to kinetic analysis and is adaptable for quantification of DNA Repair activity in tissue and tumor lysates or with purified proteins.

We describe a method for the quantitative, real-time measurement of DNA glycosylase and AP endonuclease activities in cell nuclear lysates using base ...

Visualization and Analysis of mRNA Molecules Using Fluorescence In Situ Hybridization in Saccharomyces cerevisiae

The Fluorescence in situ Hybridization (FISH) method allows one to detect nucleic acids in the native cellular environment. Here we provide a protocol for using FISH to quantify the number of mRNAs in single yeast cells. Cells can be grown in any condition of interest and then fixed and made permeable. Subsequently, multiple single-stranded deoxyoligonucleotides conjugated to fluorescent dyes are used to label and visualize mRNAs. Diffraction-limited fluorescence from single mRNA molecules is quantified using a spot-detection algorithm to identify and count the number of mRNAs per cell. While the more standard quantification methods of northern blots, RT-PCR and gene expression microarrays provide information on average mRNAs in the bulk population, FISH facilitates both the counting and localization of these mRNAs in single cells at single-molecule resolution.

Visualization and Analysis of mRNA Molecules Using Fluorescence In Situ Hybridization in Saccharomyces cerevisiae

This protocol describes an experimental procedure for performing Fluorescence in situ Hybridization (FISH) for counting mRNAs in single cells at single-molecule resolution.

The Fluorescence in situ Hybridization (FISH) method allows one to detect nucleic acids in the native cellular environment. Here we provide a protocol for ...

Cytosolic Calcium Measurements in Renal Epithelial Cells by Flow Cytometry

A variety of cellular processes, both physiological and pathophysiological, require or are governed by calcium, including exocytosis, mitochondrial function, cell death, cell metabolism and cell migration to name but a few. Cytosolic calcium is normally maintained at low nanomolar concentrations; rather it is found in high micromolar to millimolar concentrations in the endoplasmic reticulum, mitochondrial matrix and the extracellular compartment. Upon stimulation, a transient increase in cytosolic calcium serves to signal downstream events. Detecting changes in cytosolic calcium is normally performed using a live cell imaging set up with calcium binding dyes that exhibit either an increase in fluorescence intensity or a shift in the emission wavelength upon calcium binding. However, a live cell imaging set up is not freely accessible to all researchers. Alternative detection methods have been optimized for immunological cells with flow cytometry and for non-immunological adherent cells with a fluorescence microplate reader. Here, we describe an optimized, simple method for detecting changes in epithelial cells with flow cytometry using a single wavelength calcium binding dye. Adherent renal proximal tubule epithelial cells, which are normally difficult to load with dyes, were loaded with a fluorescent cell permeable calcium binding dye in the presence of probenecid, brought into suspension and calcium signals were monitored before and after addition of thapsigargin, tunicamycin and ionomycin.

Calcium is involved in numerous physiological and pathophysiological signaling pathways. Live cell imaging requires specialized equipment and can be time consuming. A quick, simple method using a flow cytometer to determine relative changes in cytosolic calcium in adherent epithelial cells brought into suspension was optimized.

A variety of cellular processes, both physiological and pathophysiological, require or are governed by calcium, including exocytosis, mitochondrial ...

Specificity Analysis of Protein Lysine Methyltransferases Using SPOT Peptide Arrays

Lysine methylation is an emerging post-translation modification and it has been identified on several histone and non-histone proteins, where it plays crucial roles in cell development and many diseases. Approximately 5,000 lysine methylation sites were identified on different proteins, which are set by few dozens of protein lysine methyltransferases. This suggests that each PKMT methylates multiple proteins, however till now only one or two substrates have been identified for several of these enzymes. To approach this problem, we have introduced peptide array based substrate specificity analyses of PKMTs. Peptide arrays are powerful tools to characterize the specificity of PKMTs because methylation of several substrates with different sequences can be tested on one array. We synthesized peptide arrays on cellulose membrane using an Intavis SPOT synthesizer and analyzed the specificity of various PKMTs. Based on the results, for several of these enzymes, novel substrates could be identified. For example, for NSD1 by employing peptide arrays, we showed that it methylates K44 of H4 instead of the reported H4K20 and in addition H1.5K168 is the highly preferred substrate over the previously known H3K36. Hence, peptide arrays are powerful tools to biochemically characterize the PKMTs.

Peptide arrays synthesized by the SPOT method can be used to analyze the substrate specificity of Protein lysine methyltransferases (PKMTs) and to define the substrate spectrum of PKMTs to understand their biological role. This protocol describes how to synthesize peptide arrays, methylate them with PKMTs, and analyze the results.

Lysine methylation is an emerging post-translation modification and it has been identified on several histone and non-histone proteins, where it plays ...

Functional Reconstitution and Channel Activity Measurements of Purified Wildtype and Mutant CFTR Protein

The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a unique channel-forming member of the ATP Binding Cassette (ABC) superfamily of transporters. The phosphorylation and nucleotide dependent chloride channel activity of CFTR has been frequently studied in whole cell systems and as single channels in excised membrane patches. Many Cystic Fibrosis-causing mutations have been shown to alter this activity. While a small number of purification protocols have been published, a fast reconstitution method that retains channel activity and a suitable method for studying population channel activity in a purified system have been lacking. Here rapid methods are described for purification and functional reconstitution of the full-length CFTR protein into proteoliposomes of defined lipid composition that retains activity as a regulated halide channel. This reconstitution method together with a novel flux-based assay of channel activity is a suitable system for studying the population channel properties of wild type CFTR and the disease-causing mutants F508del- and G551D-CFTR. Specifically, the method has utility in studying the direct effects of phosphorylation, nucleotides and small molecules such as potentiators and inhibitors on CFTR channel activity. The methods are also amenable to the study of other membrane channels/transporters for anionic substrates.

Described here is a rapid and effective procedure for functional reconstitution of purified wild-type and mutant CFTR protein that preserves activity for this chloride channel, which is defective in Cystic Fibrosis. Iodide efflux from reconstituted proteoliposomes mediated by CFTR allows studies of channel activity and the effects of small molecules.

The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a unique channel-forming member of the ATP Binding Cassette (ABC) superfamily of ...

Development and Characterization of In Vitro Microvessel Network and Quantitative Measurements of Endothelial [Ca2+]i and Nitric Oxide Production

Endothelial cells (ECs) lining the blood vessel walls in vivo are constantly exposed to flow, but cultured ECs are often grown under static conditions and exhibit a pro-inflammatory phenotype. Although the development of microfluidic devices has been embraced by engineers over two decades, their biological applications remain limited. A more physiologically relevant in vitro microvessel model validated by biological applications is important to advance the field and bridge the gaps between in vivo and in vitro studies. Here, we present detailed procedures for the development of cultured microvessel network using a microfluidic device with a long-term perfusion capability. We also demonstrate its applications for quantitative measurements of agonist-induced changes in EC [Ca2+]i and nitric oxide (NO) production in real time using confocal and conventional fluorescence microscopy. The formed microvessel network with continuous perfusion showed well-developed junctions between ECs. VE-cadherin distribution was closer to that observed in intact microvessels than statically cultured EC monolayers. ATP-induced transient increases in EC [Ca2+]i and NO production were quantitatively measured at individual cell levels, which validated the functionality of the cultured microvessels. This microfluidic device allows ECs to grow under a well-controlled, physiologically relevant flow, which makes the cell culture environment closer to in vivo than that in the conventional, static 2D cultures. The microchannel network design is highly versatile, and the fabrication process is simple and repeatable. The device can be easily integrated to the confocal or conventional microscopic system enabling high resolution imaging. Most importantly, because the cultured microvessel network can be formed by primary human ECs, this approach will serve as a useful tool to investigate how pathologically altered blood components from patient samples affect human ECs and provide insight into clinical issues. It also can be developed as a platform for drug screening.

Development and Characterization of In Vitro Microvessel Network and Quantitative Measurements of Endothelial [Ca2+]i and Nitric Oxide Production

Primary human umbilical vein endothelial cells (HUVECs) were grown to confluence within a microfluidic network device. The endothelial cell junction and F-actin distributions were illustrated and the changes in intracellular calcium concentration and nitric oxide production in response to adenosine triphosphate (ATP) were quantified in real-time at individual cell levels.

Endothelial cells (ECs) lining the blood vessel walls in vivo are constantly exposed to flow, but cultured ECs are often grown under static conditions and ...

Application of Electrophysiology Measurement to Study the Activity of Electro-Neutral Transporters

The transport of ions through cell membranes ensures the fine control of ion content within and outside the cell that is indispensable for cell survival. These transport mechanisms are mediated by the activities of specialized transporter proteins. Specifically,pH dynamics are finely controlled by plasma membrane proton (H+) extrusion systems, such as the Na+/H+ exchanger (NHE) protein family. Despite extensive efforts to study the mechanisms underlying NHE regulation, our current understanding of the biophysical and molecular properties of the NHE family is inadequate because of the limited availability of methods to effectively measure NHE activity. In this manuscript, we used H+-selective electrodes during whole-cell patch clamping recording to measure NHE-induced H+ flux. We proposed this approach to overcome some limitations of typically used methods to measure NHE activity, such as radioactive uptake and fluorescent membrane permeants. Measurement of NHE activity using the described method enables high sensitivity and time resolution and more efficient control of intracellular H+ concentrations. H+-selective electrodes are based on the fact that transporter activity creates an ion gradient in close proximity to the cell membrane. An H+-selective electrode moving up to and away from the cell membrane in a repetitive, oscillatory fashion records a voltage difference that is dependent on H+ flux. While H+-selective electrodes are used to detect H+ flux moving out of the cell, the patch clamp method in the whole-cell configuration is used to control the intracellular ion composition. Moreover, application of the giant patch clamp technique allows modification of the intracellular composition of not only ions but also lipids. The transporter activity of NHE isoform 3 (NHE3) was measured using this technical approach to study the molecular basis of NHE3 regulation by phosphoinositides.

This manuscript describes the applications of proton-selective electrodes and patch clamping methods to measure the activity of proton transport systems. These methods overcome some limitations of techniques commonly used to study proton transport activity, such as moderate sensitivity, time resolution and insufficient intracellular milieu control.

The transport of ions through cell membranes ensures the fine control of ion content within and outside the cell that is indispensable for cell survival. ...

Quantification of Site-specific Protein Lysine Acetylation and Succinylation Stoichiometry Using Data-independent Acquisition Mass Spectrometry

Post-translational modification (PTM) of protein lysine residues by N&#400;-acylation induces structural changes that can dynamically regulate protein functions, for example, by changing enzymatic activity or by mediating interactions. Precise quantification of site-specific protein acylation occupancy, or stoichiometry, is essential for understanding the functional consequences of both global low-level stoichiometry and individual high-level acylation stoichiometry of specific lysine residues. Other groups have reported measurement of lysine acetylation stoichiometry by comparing the ratio of peptide precursor isotopes from endogenous, natural abundance acylation and exogenous, heavy isotope-labeled acylation introduced after quantitative chemical acetylation of proteins using stable isotope-labeled acetic anhydride. This protocol describes an optimized approach featuring several improvements, including: (1) increased chemical acylation efficiency, (2) the ability to measure protein succinylation in addition to acetylation, and (3) improved quantitative accuracy due to reduced interferences using fragment ion quantification from data-independent acquisitions (DIA) instead of precursor ion signal from data-dependent acquisition (DDA). The use of extracted peak areas from fragment ions for quantification also uniquely enables differentiation of site-level acylation stoichiometry from proteolytic peptides containing more than one lysine residue, which is not possible using precursor ion signals for quantification. Data visualization in Skyline, an open source quantitative proteomics environment, allows for convenient data inspection and review. Together, this workflow offers unbiased, precise, and accurate quantification of site-specific lysine acetylation and succinylation occupancy of an entire proteome, which may reveal and prioritize biologically relevant acylation sites.

Here, we present unbiased quantification of site-specific protein acetylation and/or succinylation occupancy (stoichiometry) of an entire proteome through a ratiometric analysis of endogenous modifications to modifications introduced after quantitative chemical acylation using stable isotope-labeled anhydrides. In combination with sensitive data-independent acquisition mass spectrometry, accurate site occupancy measurements are obtained.

Post-translational modification (PTM) of protein lysine residues by N&#400;-acylation induces structural changes that can dynamically regulate protein ...

Particle Templated Emulsification enables Microfluidic-Free Droplet Assays

Reactions performed in monodispersed droplets afford enhanced accuracy and sensitivity compared to equivalent ones performed in bulk. However, the requirement of microfluidics to form controlled droplets imposes a barrier to non-experts, limiting their use. Here, we describe particle templated emulsification, an approach to generate monodisperse droplets without microfluidics. Using templating hydrogel spheres, we encapsulate samples in monodispersed droplets by simple vortexing. We demonstrate the approach by using it to perform microfluidic-free digital PCR.

Water-in-oil droplet assays are useful for analytical chemistry, enzyme evolution, and single cell analysis, but typically require microfluidics to form the droplets. Here, we describe particle templated emulsification, a microfluidic-free approach to perform droplet assays.