The authors thank K. Woolfrey for advice and input on the APEGS assay. These studies were funded by research grants to E.D. from the Whitehall Foundation and the NIH-NIMH (1R01MH119347).

All animal procedures followed guidelines set forth by the National Institutes of Health (NIH) and have been approved by the Institutional Animal Care and Use Committee at the University of California, Davis.
1. Preparation of mouse brain membranes
<ol>
	<li>Decapitate mouse using a guillotine apparatus and dissect brain out rapidly (in &#60;1 min, if possible, to minimize palmitoylation changes that may occur during dissection procedure). Homogenize immediately in 10 mL of homogenization buffer (Table 1) in a glass homogenizer (~12 strokes) on ice.</li>
	<li>Centrifuge lysates for 15 min at 1,400 x g at 4 &#176;C. Transfer the supernatant to a new tube on ice. Resuspend the pellet (~6 strokes) in an equal volume of homogenization buffer and centrifuge at 710 x g for 10 min at 4 &#176;C.</li>
	<li>Combine the supernatants from step 1.2 and centrifuge at 40,000 x g for 20 min at 4 &#176;C.</li>
	<li>Discard the supernatant (cytosolic fraction) and resuspend the pelleted membrane (P2) fraction in homogenization buffer. 
	NOTE: Samples can be flash frozen and stored at -80 &#176;C for later use.</li>
	<li>Perform a bicinchoninic acid (BCA) assay to quantitate protein levels. For the APEGS assay, begin with ~100&#8722;200 mg protein (maximum 250 mg) in a volume of 470 &#181;L of buffer A (Table 1) in a 1.5 mL tube. Sonicate and centrifuge at &#62;13,000 x g for 10 min at 25 &#176;C to remove insoluble protein. Transfer solubilized protein to a new 1.5 mL tube.</li>
</ol>
2. Acyl-PEGyl exchange gel-shift (APEGS) assay
<ol>
	<li>Disrupt disulfide bonds and block free cysteines.
	<ol>
		<li>Disrupt disulfide bonds by incubating in 25 mM tris(2-carboxyethyl)phosphine (TCEP; 25 &#181;L, added from a stock solution; Table 1) for 60 min at 55 &#176;C.</li>
		<li>Block free cysteines with 50 mM N-ethylmaleimide (NEM; 12.5 &#181;L, added from a stock solution; Table 1) at room temperature for 3 h. 
		NOTE: The reaction can be extended overnight.</li>
	</ol>
	</li>
	<li>Perform chloroform methanol (CM) precipitation.
	<ol>
		<li>Transfer the protein solution from 1.5 mL tube to a polypropylene or glass tube that can be centrifuged in a swinging bucket rotor at modest speed. A 5 mL tube is ideal. Add four volumes (2 mL) of methanol (MeOH) and vortex briefly.</li>
		<li>Add two volumes (1 mL) of chloroform and vortex briefly.</li>
		<li>Add three volumes (1.5 mL) of dH2O and vortex briefly.</li>
		<li>Centrifuge the samples at 3,000 x g for 30 min at 25 &#176;C in a swinging bucket rotor.</li>
		<li>Carefully remove and discard the upper phase.</li>
		<li>Add 3 volumes (1.5 mL) of MeOH and mix gently but thoroughly, being careful not to fragment the opaque protein pancake.</li>
		<li>Centrifuge at 3,000 x g for 10 min at 25 &#176;C in a swinging bucket rotor.</li>
		<li>Using a glass serological pipet, remove as much of the top phase as possible without disturbing the protein pancake.</li>
		<li>Carefully rinse the pellet with 1 mL of MeOH.</li>
		<li>Air dry the pellet for at least 10 min. 
		NOTE: Dried pellet can be stored at -20 &#176;C.</li>
	</ol>
	</li>
	<li>Perform cleavage of palmitoyl-thioester linkages with hydroxylamine (NH2OH, HAM).
	<ol>
		<li>Resuspend protein precipitate in 125 &#181;L of buffer A and sonicate briefly. Centrifuge at &#62;13,000 x g for 10 min at 25 &#176;C to remove insoluble material. Transfer solubilized protein to a new 1.5 mL tube.</li>
		<li>Add 375 &#181;L of buffer H (HAM+; Table 1) or buffer T (HAM-; Table 1) and incubate samples for 60 min at 25 &#176;C.</li>
	</ol>
	</li>
	<li>Repeat the CM precipitation described in step 2.2. 
	NOTE: Dried pellet can be stored at -20 &#176;C.</li>
	<li>Add mPEG to unprotected cysteines.
	<ol>
		<li>Resuspend pellet in 100 &#181;L of buffer A containing 10 mM TCEP. Transfer to a 1.5 mL tube. 
		NOTE: It is normal for significant loss of protein to have occurred during CM precipitation steps. All subsequent steps will be performed in a 1.5 mL tube, constraining the volume of protein to a maximum of ~120&#8722;130 &#181;L. This will reduce protein loss during the final CM precipitation.</li>
		<li>Add 20 mM mPEG-5k (25 &#181;L, added from a stock solution; Table 1) to protein sample and mix by pipetting. Incubate for 60 min at 25 &#176;C with end-over-end rotation.</li>
		<li>To remove unincorporated mPEG-5k, perform CM precipitation as described in step 2.2 using these adjusted volumes: 4 volumes of MeOH (500 &#181;L), 2 volumes of chloroform (250 &#181;L), and 3 volumes of dH2O (375 &#181;L). Centrifuge at &#62;13,000 x g for 10 min at 25 &#176;C.</li>
		<li>Carefully remove the upper phase as before, avoiding the thick, flocculent pancake. Add 1 mL of MeOH and mix gently but thoroughly. Centrifuge at &#62;13,000 x g for 10 min at 25 &#176;C.</li>
		<li>Carefully remove the supernatant and rinse the pellet with 1 mL of MeOH. Centrifuge at &#62;13,000 x g for 10 min at 25 &#176;C. Air dry pellet. 
		NOTE: Dried pellet can be stored at -20 &#176;C.</li>
		<li>Resuspend the dried pellet in 50 &#181;L of buffer A (without TCEP or any reducing agent). Reserve 5 &#181;L for BCA protein quantitation. After quantitation, add an appropriate amount of 4x Laemmli sample buffer and, depending on the protein of interest, potentially heat the sample to 70&#8722;100 &#176;C for 10 min. 
		NOTE: Boiling may cause aggregation of some membrane proteins.</li>
	</ol>
	</li>
</ol>
3. Western blot analysis of PEGylated proteins
<ol>
	<li>Load the sample onto an sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gel13. 
	NOTE: In this protocol 10% polyacrylamide was used.</li>
	<li>Use standard separation, transfer and detection protocols for Western blotting14.</li>
	<li>Use densitometry14 to determine the relative amounts of PEGylated versus nonPEGylated proteins.</li>
</ol>

<ol>
	<li>Blaskovic, S., Blanc, M., van der Goot, F. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=What+does+S-palmitoylation+do+to+membrane+proteins?.">What does S-palmitoylation do to membrane proteins?.</a> FEBS Journal. 280, 2766-2774 (2013).</li><li>Fukata, Y., Fukata, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+palmitoylation+in+neuronal+development+and+synaptic+plasticity.">Protein palmitoylation in neuronal development and synaptic plasticity.</a> Nature Reviews Neuroscience. 11, 161-175 (2010).</li><li>Globa, A. K., Bamji, S. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+palmitoylation+in+the+development+and+plasticity+of+neuronal+connections.">Protein palmitoylation in the development and plasticity of neuronal connections.</a> Current Opinion in Neurobiology. 45, 210-220 (2017).</li><li>Thomas, G. M., Huganir, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Palmitoylation-dependent+regulation+of+glutamate+receptors+and+their+PDZ+domain-containing+partners.">Palmitoylation-dependent regulation of glutamate receptors and their PDZ domain-containing partners.</a> Biochemical Society Transactions. 41, 72-78 (2013).</li><li>Kalashnikova, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SynDIG1:+an+activity-regulated,+AMPA-+receptor-interacting+transmembrane+protein+that+regulates+excitatory+synapse+development.">SynDIG1: an activity-regulated, AMPA- receptor-interacting transmembrane protein that regulates excitatory synapse development.</a> Neuron. 65, 80-93 (2010).</li><li>Kaur, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activity-Dependent+Palmitoylation+Controls+SynDIG1+Stability,+Localization,+and+Function.">Activity-Dependent Palmitoylation Controls SynDIG1 Stability, Localization, and Function.</a> Journal of Neuroscience. 36, 7562-7568 (2016).</li><li>Wan, J., Roth, A. F., Bailey, A. O., Davis, N. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Palmitoylated+proteins:+purification+and+identification.">Palmitoylated proteins: purification and identification.</a> Nature Protocols. 2, 1573-1584 (2007).</li><li>Howie, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Substrate+recognition+by+the+cell+surface+palmitoyl+transferase+DHHC5.">Substrate recognition by the cell surface palmitoyl transferase DHHC5.</a> Proceedings of the National Academy of Sciences of the United States of America. 111, 17534-17539 (2014).</li><li>Kanadome, T., Yokoi, N., Fukata, Y., Fukata, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systematic+Screening+of+Depalmitoylating+Enzymes+and+Evaluation+of+Their+Activities+by+the+Acyl-PEGyl+Exchange+Gel-Shift+(APEGS)+Assay.">Systematic Screening of Depalmitoylating Enzymes and Evaluation of Their Activities by the Acyl-PEGyl Exchange Gel-Shift (APEGS) Assay.</a> Methods in Molecular Biology. 2009, 83-98 (2019).</li><li>Percher, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass-tag+labeling+reveals+site-specific+and+endogenous+levels+of+protein+S-fatty+acylation.">Mass-tag labeling reveals site-specific and endogenous levels of protein S-fatty acylation.</a> Proceedings of the National Academy of Sciences of the United States of America. 113, 4302-4307 (2016).</li><li>Percher, A., Thinon, E., Hang, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass-Tag+Labeling+Using+Acyl-PEG+Exchange+for+the+Determination+of+Endogenous+Protein+S-Fatty+Acylation.">Mass-Tag Labeling Using Acyl-PEG Exchange for the Determination of Endogenous Protein S-Fatty Acylation.</a> Current Protocols in Protein Science. 89, 14.17.1-14.17.11 (2017).</li><li>Yokoi, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+PSD-95+Depalmitoylating+Enzymes.">Identification of PSD-95 Depalmitoylating Enzymes.</a> Journal of Neuroscience. 36, 6431-6444 (2016).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=JoVE+Science+Education+Database.+Separating+Protein+with+SDS-PAGE.">JoVE Science Education Database. Separating Protein with SDS-PAGE.</a> Basic Methods in Cellular and Molecular Biology. , (2019).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Science+Education+Database.+The+Western+Blot.">Science Education Database. The Western Blot.</a> Basic Methods in Cellular and Molecular Biology. , (2019).</li><li>Chenaux, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Loss+of+SynDIG1+Reduces+Excitatory+Synapse+Maturation+But+Not+Formation+In+Vivo.">Loss of SynDIG1 Reduces Excitatory Synapse Maturation But Not Formation In Vivo.</a> eNeuro. 3 (5), (2016).</li><li>Matt, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=SynDIG4/Prrt1+Is+Required+for+Excitatory+Synapse+Development+and+Plasticity+Underlying+Cognitive+Function.">SynDIG4/Prrt1 Is Required for Excitatory Synapse Development and Plasticity Underlying Cognitive Function.</a> Cell Reports. 22, 2246-2253 (2018).</li><li>Purkey, A. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AKAP150+Palmitoylation+Regulates+Synaptic+Incorporation+of+Ca(2+)-Permeable+AMPA+Receptors+to+Control+LTP.">AKAP150 Palmitoylation Regulates Synaptic Incorporation of Ca(2+)-Permeable AMPA Receptors to Control LTP.</a> Cell Reports. 25, 974-987 (2018).</li><li>Woolfrey, K. M., Sanderson, J. L., Dell'Acqua, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+palmitoyl+acyltransferase+DHHC2+regulates+recycling+endosome+exocytosis+and+synaptic+potentiation+through+palmitoylation+of+AKAP79/150.">The palmitoyl acyltransferase DHHC2 regulates recycling endosome exocytosis and synaptic potentiation through palmitoylation of AKAP79/150.</a> Journal of Neuroscience. 35, 442-456 (2015).</li></ol>

The authors have nothing to disclose.

In our previous work, we utilized the ABE assay to demonstrate that SynDIG1 is palmitoylated at two conserved juxta-transmembrane Cys residues (found in all SynDIG proteins) in an activity-dependent manner to regulate stability, localization, and function6. A limitation is that the ABE assay requires affinity purification with agarose resins conjugated to avidin moieties as the final step in the procedure, resulting in significant loss of signal that complicate quantitative analysis. Furthermore, ...

S-palmitoylation is a reversible post-translational modification of target proteins that regulates stable membrane association, protein trafficking, and protein-protein interactions1. It involves addition of a 16-carbon palmitate moiety to cysteine residues via thioester linkage catalyzed by palmitoyl acyltransferase (PAT) enzymes. Many synaptic proteins in the brain are palmitoylated, including AMPA-Rs and PSD-95, in an activity-dependent manner to regulate stability, localization, and function2,3,4. Alterations in the levels of synaptic AMPARs in the PSD via interaction of auxiliary factors with synaptic scaffolds such as PSD-95 underlies synaptic plasticity; thus, methods to determine the palmitoylation state of synaptic proteins provides important insight into mechanisms of synaptic plasticity.
Previously, we identified the SynDIG family of four genes (SynDIG1-4) encoding brain-specific transmembrane proteins that associate with AMPARs5. Overexpression or knock-down of SynDIG1 in dissociated rat hippocampal neurons increases or decreases, respectively, AMPA-R synapse size and number by ~50% as detected using immunocytochemistry and electrophysiology5. We utilized the acyl-biotin exchange (ABE) assay to demonstrate that SynDIG1 is palmitoylated at two conserved juxta-transmembrane Cys residues (found in all SynDIG proteins) in an activity-dependent manner to regulate stability, localization, and function6. The ABE assay relies on exchange of biotin on cysteines protected by modification and subsequent affinity purification7. Here, we describe an innovative biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay8,9,10,11,12, which does not require affinity purification and instead utilizes changes in gel mobility to determine the number of modifications for a protein of interest. The protocol is described for investigation of endogenous membrane proteins from mouse brain for which suitable antibodies are available.

<table><tbody><tr><td>Hydroxylamine (HAM)</td><td>ThermoFisher</td><td>26103</td><td></td></tr><tr><td>Methoxy-PEG-(CH&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;NHCO(CH&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;-MAL (mPEG)</td><td>NOF</td><td>ME-050MA</td><td>MW ~5000 kDa</td></tr><tr><td>Microfuge</td><td>Eppendorf</td><td>5415R</td><td>or equivalent equipment</td></tr><tr><td>N-ethylmalemide (NEM)</td><td>Calbiochem</td><td>34115</td><td>Highly toxic.</td></tr><tr><td>Optical imager for densitometry</td><td>Azure Biosystems</td><td>Sapphire Biomolecular Imager</td><td>or equivalent equipment</td></tr><tr><td>Polypropylene tubes with cap</td><td>Fisher Scientific</td><td>14-956-1D</td><td></td></tr><tr><td>Serological pipets (glass)</td><td>Fisher Scientific</td><td>13-678-27D</td><td></td></tr><tr><td>Table top centrifuge</td><td>Beckman</td><td>Allegra X-15R</td><td>or equivalent equipment</td></tr><tr><td>Tris(2-carboxyethyl) phosphine-hydrochloride (TCEP)</td><td>EMD Millipore</td><td>580560</td><td></td></tr></tbody></table>

acyl-pegyl exchange gel shift assay for quantitative determination of palmitoylation of brain membrane proteins

Activity-dependent alterations in the levels of synaptic AMPA receptors (AMPARs) within the postsynaptic density (PSD) is thought to represent a cellular mechanism for learning and memory. Palmitoylation regulates localization and function of many synaptic proteins including AMPA-Rs, auxiliary factors and synaptic scaffolds in an activity-dependent manner. We identified the synapse differentiation induced gene (SynDIG) family of four genes (SynDIG1-4) encoding brain-specific transmembrane proteins that associate with AMPARs and regulate synapse strength. SynDIG1 is palmitoylated at two cysteine residues located at positions 191 and 192 in the juxta-transmembrane region important for activity-dependent excitatory synapse development. Here, we describe an innovative biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay, to investigate the palmitoylation state of any protein of interest and demonstrate its utility with the SynDIG family of proteins in mouse brain lysates.

Immunoblotting with antibodies against the protein of interest reveals the palmitoylated state (non, singly, doubly, etc.) in mouse brain lysates as determined by mobility shift compared with samples in which HAM was not included. Previously, we had demonstrated that SynDIG1 was palmitoylated at two sites using the ABE assay6; however, we could not determine whether both sites were modified in brain tissue. Here we show that SynDIG1, SynDIG4/Prrt1, and Prrt2 are pa...

Watch this Scientific Journal Video about Acyl-PEGyl Exchange Gel Shift Assay for Quantitative Determination of Palmitoylation of Brain Membrane Proteins at JoVE.com

Acyl-PEGyl Exchange Gel Shift Assay for Quantitative Determination of Palmitoylation of Brain Membrane Proteins

Palmitoylation entails the incorporation of a 16-carbon palmitate moiety to cysteine residues of target proteins in a reversible manner. Here, we describe a biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay, to investigate the palmitoylation state of any protein of interest in mouse brain lysates.

Activity-dependent alterations in the levels of synaptic AMPA receptors (AMPARs) within the postsynaptic density (PSD) is thought to represent a cellular ...

acyl-pegyl-exchange-gel-shift-assay-for-quantitative-determination

Research

JoVE Journal

Biochemistry

6.5K Views.  UC Davis School of Medicine. Palmitoylation entails the incorporation of a 16-carbon palmitate moiety to cysteine residues of target proteins in a reversible manner. Here, we describe a biochemical approach, the acyl-PEGyl exchange gel shift (APEGS) assay, to investigate the palmitoylation state of any protein of interest in mouse brain lysates.

Video: Acyl-PEGyl Exchange Gel Shift Assay for Quantitative Determination of Palmitoylation of Brain Membrane Proteins

Single-molecule Super-resolution Imaging of Phosphatidylinositol 4,5-bisphosphate in the Plasma Membrane with Novel Fluorescent Probes

Phosphoinositides in the cell membrane are signaling lipids with multiple cellular functions. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is a determinant phosphoinositide of the plasma membrane (PM), and it is required to modulate ion channels, actin dynamics, exocytosis, endocytosis, intracellular signaling, and many other cellular processes. However, the spatial organization of PI(4,5)P2 in the PM is controversial, and its nanoscale distribution is poorly understood due to the technical limitations of research approaches. Here by utilizing single molecule localization microscopy and the Pleckstrin Homology (PH) domain based dual color fluorescent probes, we describe a novel method to visualize the nanoscale distribution of PI(4,5)P2 in the PM in fixed membrane sheets as well as live cells.

PI(4,5)P2 regulates various cellular functions, but its nanoscale organization in the cell plasma membrane is poorly understood. By labeling PI(4,5)P2 with a dual-color fluorescent probe fused to the Pleckstrin Homology domain, we describe a novel approach to study the PI(4,5)P2 spatial distribution in the plasma membrane at the nanometer scale.

Phosphoinositides in the cell membrane are signaling lipids with multiple cellular functions. Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is a ...

Detection of Protein Palmitoylation in Cultured Hippocampal Neurons by Immunoprecipitation and Acyl-Biotin Exchange (ABE)

Palmitoylation is a post-translational lipid modification involving the attachment of a 16-carbon saturated fatty acid, palmitate, to cysteine residues of substrate proteins through a labile thioester bond [reviewed in1]. Palmitoylation of a substrate protein increases its hydrophobicity, and typically facilitates its trafficking toward cellular membranes. Recent studies have shown palmitoylation to be one of the most common lipid modifications in neurons1, 2, suggesting that palmitate turnover is an important mechanism by which these cells regulate the targeting and trafficking of proteins. The identification and detection of palmitoylated substrates can therefore better our understanding of protein trafficking in neurons.
Detection of protein palmitoylation in the past has been technically hindered due to the lack of a consensus sequence among substrate proteins, and the reliance on metabolic labeling of palmitoyl-proteins with 3H-palmitate, a time-consuming biochemical assay with low sensitivity. Development of the Acyl-Biotin Exchange (ABE) assay enables more rapid and high sensitivity detection of palmitoylated proteins2-4, and is optimal for measuring the dynamic turnover of palmitate on neuronal proteins. The ABE assay is comprised of three biochemical steps (Figure 1): 1) irreversible blockade of unmodified cysteine thiol groups using N-ethylmaliemide (NEM), 2) specific cleavage and unmasking of the palmitoylated cysteine's thiol group by hydroxylamine (HAM), and 3) selective labeling of the palmitoylated cysteine using a thiol-reactive biotinylation reagent, biotin-BMCC. Purification of the thiol-biotinylated proteins following the ABE steps has differed, depending on the overall goal of the experiment.
Here, we describe a method to purify a palmitoylated protein of interest in primary hippocampal neurons by an initial immunoprecipitation (IP) step using an antibody directed against the protein, followed by the ABE assay and western blotting to directly measure palmitoylation levels of that protein, which is termed the IP-ABE assay. Low-density cultures of embryonic rat hippocampal neurons have been widely used to study the localization, function, and trafficking of neuronal proteins, making them ideally suited for studying neuronal protein palmitoylation using the IP-ABE assay. The IP-ABE assay mainly requires standard IP and western blotting reagents, and is only limited by the availability of antibodies against the target substrate. This assay can easily be adapted for the purification and detection of transfected palmitoylated proteins in heterologous cell cultures, primary neuronal cultures derived from various brain tissues of both mouse and rat, and even primary brain tissue itself.

Detection of Protein Palmitoylation in Cultured Hippocampal Neurons by Immunoprecipitation and Acyl-Biotin Exchange ABE

The reversible addition of palmitate to proteins is an important regulator of intracellular protein trafficking. This is of particular interest in neurons where many synaptic proteins are palmitoylated. We utilize a simple biochemical method to detect palmitoylated proteins in cultured neurons, which can be adapted for multiple cell types and tissues.

Palmitoylation is a post-translational lipid  modification involving the attachment of a 16-carbon saturated fatty acid,  palmitate, to cysteine residues ...

Neuroscience

Detection of Protein S-Acylation using Acyl-Resin Assisted Capture

Protein S-acylation, also referred to as S-palmitoylation, is a reversible post-translational modification of cysteine residues with long-chain fatty acids via a labile thioester bond. S-acylation, which is emerging as a widespread regulatory mechanism, can modulate almost all aspects of the biological activity of proteins, from complex formation to protein trafficking and protein stability. The recent progress in understanding of the biological function of protein S-acylation was achieved largely due to the development of novel biochemical tools allowing robust and sensitive detection of protein S-acylation in a variety of biological samples. Here, we describe acyl resin-assisted capture (Acyl-RAC), a recently developed method based on selective capture of endogenously S-acylated proteins by thiol-reactive Sepharose beads. Compared to existing approaches, Acyl-RAC requires fewer steps and can yield more reliable results when coupled with mass spectrometry for identification of novel S-acylation targets. A major limitation in this technique is the lack of ability to discriminate between fatty acid species attached to cysteines via the same thioester bond.

Acyl-RAC (Acyl-Resin Assisted Capture) is a highly sensitive, reliable and easy to perform method to detect reversible lipid modification of cysteine residues (S-acylation) in a variety of biological samples.

Protein S-acylation, also referred to as S-palmitoylation, is a reversible post-translational modification of cysteine residues with long-chain fatty ...

Click-Chemistry Based Fluorometric Assay for Apolipoprotein N-acyltransferase from Enzyme Characterization to High-Throughput Screening

Lipoproteins from proteobacteria are posttranslationally modified by fatty acids derived from membrane phospholipids by the action of three integral membrane enzymes, resulting in triacylated proteins. The first step in the lipoprotein modification pathway involves the transfer of a diacylglyceryl group from phosphatidylglycerol onto the prolipoprotein, resulting in diacylglyceryl prolipoprotein. In the second step, the signal peptide of prolipoprotein is cleaved, forming an apolipoprotein, which in turn is modified by a third fatty acid derived from a phospholipid. This last step is catalyzed by apolipoprotein N-acyltransferase (Lnt). The lipoprotein modification pathway is essential in most &#947;-proteobacteria, making it a potential target for the development of novel antibacterial agents. Described here is a sensitive assay for Lnt that is compatible with high-throughput screening of small inhibitory molecules. The enzyme and substrates are membrane-embedded molecules; therefore, the development of an in vitro test is not straightforward. This includes the purification of the active enzyme in the presence of detergent, the availability of alkyne-phospholipids and diacylglyceryl peptide substrates, and the reaction conditions in mixed micelles. Furthermore, in order to use the activity test in a high-throughput screening (HTS) setup, direct readout of the reaction product is preferred over coupled enzymatic reactions. In this fluorometric enzyme assay, the alkyne-triacylated peptide product is rendered fluorescent through a click-chemistry reaction and detected in a multiwell plate format. This method is applicable to other acyltransferases that use fatty acid-containing substrates, including phospholipids and acyl-CoA.

Presented here is a sensitive fluorescence assay to monitor apolipoprotein N-acyltransferase activity using diacylglyceryl peptide and alkyne-phospholipids as substrates with click-chemistry.

Lipoproteins from proteobacteria are posttranslationally modified by fatty acids derived from membrane phospholipids by the action of three integral ...

Optimized Incorporation of Alkynyl Fatty Acid Analogs for the Detection of Fatty Acylated Proteins using Click Chemistry

Fatty acylation, the covalent addition of saturated fatty acids to protein substrates, is important in regulating a myriad of cellular functions in addition to its implications in cancer and neurodegenerative diseases. Recent developments in fatty acylation detection methods have enabled efficient and non-hazardous detection of fatty acylated proteins, particularly through the use of click chemistry with bio-orthogonal labeling. However, click chemistry detection can be limited by the poor solubility and potential toxic effects of adding long chain fatty acids to cell culture. Described here is a labeling approach with optimized delivery using saponified fatty acids in combination with fatty-acid free BSA, as well as delipidated media, which can improve detection of hard to detect fatty acylated proteins. This effect was most pronounced with the alkynyl-stearate analog, 17-ODYA, which has been the most commonly used fatty acid analog in click chemistry detection of acylated proteins. This modification will improve cellular incorporation and increase sensitivity to acylated protein detection. In addition, this approach can be applied in a variety of cell types and combined with other assays such as pulse-chase analysis, stable isotope labeling with amino acids in cell culture, and mass spectrometry for quantitative profiling of fatty acylated proteins.

The study of fatty acylation has important implications in cellular protein interactions and diseases. Presented here is a modified protocol to improve click chemistry detection of fatty acylated proteins, which can be applied in various cell types and combined with other assays, including pulse-chase and mass spectrometry.

Fatty acylation, the covalent addition of saturated fatty acids to protein substrates, is important in regulating a myriad of cellular functions in ...

Fluorescence-Based Measurements of Phosphatidylserine/Phosphatidylinositol 4-Phosphate Exchange Between Membranes

Several members of the evolutionarily conserved oxysterol-binding protein (OSBP)-related proteins(ORP)/OSBP homologs (Osh) family have recently been found to represent a novel lipid transfer protein (LTP) group in yeast and human cells. They transfer phosphatidylserine (PS) from the endoplasmic reticulum (ER) to the plasma membrane (PM) via PS/phosphatidylinositol 4-phosphate (PI(4)P) exchange cycles. This finding allows a better understanding of how PS, which is critical for signaling processes, is distributed throughout the cell and the investigation of the link between this process and phosphoinositide (PIP) metabolism. The development of new fluorescence-based protocols has been instrumental in the discovery and characterization of this new cellular mechanism in vitro at the molecular level. This paper describes the production and the use of two fluorescently labelled lipid sensors, NBD-C2Lact and NBD-PHFAPP, to measure the ability of a protein to extract PS or PI(4)P and to transfer these lipids between artificial membranes. First, the protocol describes how to produce, label, and obtain high-purity samples of these two constructs. Secondly, this paper explains how to use these sensors with a fluorescence microplate reader to determine whether a protein can extract PS or PI(4)P from liposomes, using Osh6p as a case study. Finally, this protocol shows how to accurately measure the kinetics of PS/PI(4)P exchange between liposomes of defined lipid composition and to determine lipid transfer rates by fluorescence resonance energy transfer (FRET) using a standard fluorometer.

Here, we describe protocols using fluorescent lipid sensors and liposomes to determine whether a protein extracts and transports phosphatidylserine or phosphatidylinositol 4-phosphate in vitro.

Several members of the evolutionarily conserved oxysterol-binding protein (OSBP)-related proteins(ORP)/OSBP homologs (Osh) family have recently been found ...

Measuring Plasma Membrane Protein Endocytic Rates by Reversible Biotinylation

Plasma membrane proteins are a large, diverse group of proteins comprised of receptors, ion channels, transporters and pumps.  Activity of these proteins is responsible for a variety of key cellular events, including nutrient delivery, cellular excitability, and chemical signaling.  Many plasma membrane proteins are dynamically regulated by endocytic trafficking, which modulates protein function by altering protein surface expression.  The mechanisms that facilitate protein endocytosis are complex and are not fully understood for many membrane proteins.  In order to fully understand the mechanisms that control the endocytic trafficking of a given protein, it is critical that the protein s endocytic rate be precisely measured.  For many receptors, direct endocytic rate measurements are frequently achieved utilizing labeled receptor ligands.  However, for many classes of membrane proteins, such as transporters, pumps and ion channels, there is no convenient ligand that can be used to measure the endocytic rate.  In the present report, we describe a reversible biotinylation method that we employ to measure the dopamine transporter (DAT) endocytic rate.  This method provides a straightforward approach to measuring internalization rates, and can be easily employed for trafficking studies of most membrane proteins.

Regulated endocytosis governs the cell surface expression levels of the majority of membrane proteins. Here we utilize reducible, membrane impermeant biotinylation reagents to measure the endocytic rate of the dopamine transporter (DAT), a polytopic membrane protein. The method facilitates a straightforward approach to measuring the endocytic rate of most plasma membrane proteins.

Plasma membrane proteins are a large, diverse group of proteins comprised of receptors, ion channels, transporters and pumps.  Activity of these proteins ...

Biology

Brain Slice Biotinylation: An Ex Vivo Approach to Measure Region-specific Plasma Membrane Protein Trafficking in Adult Neurons

Regulated endocytic trafficking is the central mechanism facilitating a variety of neuromodulatory events, by dynamically controlling receptor, ion channel, and transporter cell surface presentation on a minutes time scale.&#160;There is a broad diversity of mechanisms that control endocytic trafficking of individual proteins. Studies investigating the molecular underpinnings of trafficking have primarily relied upon surface biotinylation to quantitatively measure changes in membrane protein surface expression in response to exogenous stimuli and gene manipulation.&#160;However, this approach has been mainly limited to cultured cells, which may not faithfully reflect the physiologically relevant mechanisms at play in adult neurons.&#160;Moreover, cultured cell approaches may underestimate region-specific differences in trafficking mechanisms.&#160;Here, we describe an approach that extends cell surface biotinylation to the acute brain slice preparation.&#160;We demonstrate that this method provides a high-fidelity approach to measure rapid changes in membrane protein surface levels in adult neurons.&#160;This approach is likely to have broad utility in the field of neuronal endocytic trafficking.

Brain Slice Biotinylation: An Ex Vivo Approach to Measure Region-specific Plasma Membrane Protein Trafficking in Adult Neurons

Neuronal membrane trafficking dynamically controls plasma membrane protein availability and significantly impacts neurotransmission.&#160;To date, it has been challenging to measure neuronal endocytic trafficking in adult neurons.&#160;Here, we describe a highly effective, quantitative method to measure rapid changes in surface protein expression ex vivo in acute brain slices.

Regulated endocytic trafficking is the central mechanism facilitating a variety of neuromodulatory events, by dynamically controlling receptor, ion ...

Metabolomic Analysis of Rat Brain by High Resolution Nuclear Magnetic Resonance Spectroscopy of Tissue Extracts

Studies of gene expression on the RNA and protein levels have long been used to explore biological processes underlying disease. More recently, genomics and proteomics have been complemented by comprehensive quantitative analysis of the metabolite pool present in biological systems. This strategy, termed metabolomics, strives to provide a global characterization of the small-molecule complement involved in metabolism. While the genome and the proteome define the tasks cells can perform, the metabolome is part of the actual phenotype. Among the methods currently used in metabolomics, spectroscopic techniques are of special interest because they allow one to simultaneously analyze a large number of metabolites without prior selection for specific biochemical pathways, thus enabling a broad unbiased approach. Here, an optimized experimental protocol for metabolomic analysis by high-resolution NMR spectroscopy is presented, which is the method of choice for efficient quantification of tissue metabolites. Important strengths of this method are (i) the use of crude extracts, without the need to purify the sample and/or separate metabolites; (ii) the intrinsically quantitative nature of NMR, permitting quantitation of all metabolites represented by an NMR spectrum with one reference compound only; and (iii) the nondestructive nature of NMR enabling repeated use of the same sample for multiple measurements. The dynamic range of metabolite concentrations that can be covered is considerable due to the linear response of NMR signals, although metabolites occurring at extremely low concentrations may be difficult to detect. For the least abundant compounds, the highly sensitive mass spectrometry method may be advantageous although this technique requires more intricate sample preparation and quantification procedures than NMR spectroscopy. We present here an NMR protocol adjusted to rat brain analysis; however, the same protocol can be applied to other tissues with minor modifications.

The neurochemistry of mammalian brain is changed in many neurological and systemic diseases. Characteristic profiles of cerebral metabolites can be efficiently obtained based on crude extracts of brain tissue. To this end, high-resolution NMR spectroscopy is employed, enabling detailed quantitative analysis of metabolite concentrations (metabolomics).

Studies of gene expression on the RNA and protein levels have long been used to explore biological processes underlying disease. More recently, genomics ...

Lipid Exchange Assay in Living Cells

Lipid rafts are dynamic, ordered domains in the plasma membrane often formed during membrane protein clustering and signaling. The lipid identity of the outer leaflet drives the membrane&#39;s propensity to form lipid rafts. The transient nature of lipid rafts makes it difficult to study in living cells. Therefore, methods that add or remove raft-forming lipids at&#160;the outer leaflet of living cells facilitate studying the characteristics of rafts, such as their effects on membrane proteins. Lipid exchange experiments developed in our lab utilize lipid-loaded cyclodextrins to remove and add exogenous phospholipids to change the lipid constitution of the plasma membrane. Substituting the membrane with a raft or non-raft-forming lipid can aid in studying the effects on transmembrane protein activity. Here, we describe a method for lipid exchange on the outer leaflet of the plasma membrane using lipid-loaded cyclodextrin. We demonstrate the preparation of the exchange media and the subsequent treatment of attached mammalian cells. We also showcase how to measure the efficiency of exchange using HP-TLC. This protocol yields a nearly complete replacement of the outer leaflet with exogenous lipids without altering cellular viability, permitting further experimentation on modified intact plasma membranes.

We describe a method for using cyclodextrin to mediate exchange between lipids of the plasma membrane with exogenous lipids. This technique can be paired with experiments studying transmembrane proteins, which behave differently in lipid raft-like environments than they do in non-raft-like environments.

Lipid rafts are dynamic, ordered domains in the plasma membrane often formed during membrane protein clustering and signaling. The lipid identity of the ...

Acyl-PEGyl Exchange Gel Shift Assay for Quantitative Determination of Palmitoylation of Brain Membrane Proteins

Summary

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Chapters in this video

Single-molecule Super-resolution Imaging of Phosphatidylinositol 4,5-bisphosphate in the Plasma Membrane with Novel Fluorescent Probes

Detection of Protein Palmitoylation in Cultured Hippocampal Neurons by Immunoprecipitation and Acyl-Biotin Exchange (ABE)

Detection of Protein S-Acylation using Acyl-Resin Assisted Capture

Click-Chemistry Based Fluorometric Assay for Apolipoprotein N-acyltransferase from Enzyme Characterization to High-Throughput Screening

Optimized Incorporation of Alkynyl Fatty Acid Analogs for the Detection of Fatty Acylated Proteins using Click Chemistry

Fluorescence-Based Measurements of Phosphatidylserine/Phosphatidylinositol 4-Phosphate Exchange Between Membranes

Measuring Plasma Membrane Protein Endocytic Rates by Reversible Biotinylation

Brain Slice Biotinylation: An Ex Vivo Approach to Measure Region-specific Plasma Membrane Protein Trafficking in Adult Neurons

Metabolomic Analysis of Rat Brain by High Resolution Nuclear Magnetic Resonance Spectroscopy of Tissue Extracts

Lipid Exchange Assay in Living Cells