Name: capturing the interaction kinetics of an ion channel protein with small molecules by the bio-layer interferometry assay
Uploaded: 2018-03-07T13:30:00
Description: Watch this Scientific Journal Video about Capturing the Interaction Kinetics of an Ion Channel Protein with Small Molecules by the Bio-layer Interferometry Assay at JoVE.com

This work was supported by Bio-ID Center and SJTU Cross-Disciplinary Research Fund in Medicine and Engineering (YG2016QN66), National Natural Science Foundation of China (31271217), and National Basic Research Program of China (2014CB910304).

NOTE: The HEK-293T cell line continuously expressing FLAG-tagged hEAG1 channel protein is constructed by transfecting a pCDH lentiviral plasmid containing the DNA sequence of hEAG1 with a FLAG at the distal C-terminus into HEK-293T cells followed by the puromycin-resistant selection as previously described15.
1. Affinity Purification of FLAG-tagged hEAG1 Channel Protein from HEK-293T Cells
<ol>
	<li>Thaw cells stably expressing hEAG1 channels from liquid nitrogen into...

<ol>
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Membrane ion channels have been verified as the primary therapeutic targets of over 13% of currently known drugs for the treatment of a variety of human diseases, including cardiovascular and neurological disorders18. Patch-clamp recording, the golden standard for measuring the functional of ion channels with small molecules, has been widely used for ion channel ligands screening. However, such electrophysiological approaches cannot demonstrate whether the small molecules binds to the channel dire...

Targeting the cell surface-accessible ion channel proteins with small molecules offers a tremendous potential for the ligand screening and biological drug discovery1,2,3. Thus, an appropriate tool is needed for studying the interaction between ion channel and&#160;small molecules and their corresponding function. The patch-clamp recording has been demonstrated to be a unique and irreplaceable technique in ion channel functional assay. However, determining whether the small molecules directly target ion channels require other technologies. Traditionally, the radioactive ligand binding assay was used to observe the kinetics of binding between small molecule and its target ion channel protein. However, the usage of this technique is limited because of its requirement in radioactive labeling and detection. Moreover, the prerequisite step to label the small ligand in the study prevents its using in many types of ion channels without known specific ligand. Some label-free techniques such as NMR spectroscopy, X-ray diffraction, microscale thermophoresis (MST)4 and surface plasmon resonance (SPR) have been used to measure the protein-small molecule interactions. But these types of assays usually cannot provide sufficient information because of the difficulty to get the full-length protein, low resolution of dynamics, low throughput, and high cost5. In contrast with these techniques, bio-layer Interferometry (BLI) is emerging as a novel label-free methodology to overcome these drawbacks for detecting protein-small molecule interactions by immobilizing a tiny amounts of protein sample on the surfaces of biosensor and measuring the optical changing signals6,7. As a promising biosensor platform, BLI technique is already performed to observe the interaction of small molecules with natural water soluble proteins such as a human monoclonal antibody CR80208 and the detailed assay procedure has been reported in a previous article9. Although the key role of ion channel protein for new therapeutic targets discovery has been recognized, the ion channel protein-small molecule interaction assay based on BLI has not been described.
The human Ether &#224; go-go channels (hEAG1) are expressed in various types of cancer cells and central nervous system which makes the channel a potential therapeutic target of many cancers and neuronal disorders10,11,12,13,14. The electrophysiological study in our lab has confirmed the inhibitory effect of phosphatidylinositol 4, 5-bisphosphate (PIP2) on hEAG1 channel15. Based on our results, testing PIP2 directly interaction with the hEAG1 by using BLI technique can be as a model for other types of ion channel protein-small molecule compound interaction especially for those channels lacking specific ligands. According to the instructions of BLI assay, we prepared biotinylated hEAG1 proteins and immobilized them on the surface of streptavidin (SA) biosensor tips followed by interaction them to PIP2 solutions to observe their direct binding between the protein and the lipid. After the attachment of PIP2 to the hEAG1 protein coated surface, the thickness of the layer on the surface increases, which directly correlates the spectral shift and can be measured in real-time16. The binding kinetics can be determined due to a positive shift in association step and a negative shift in dissociation step. According to this principle, we purified the functional hEAG1 ion channel protein from HEK-239T stable expression system by using affinity purification method to maintain the in vitro functional state, then measured the kinetics of binding of different concentration PIP2, and yielded a semblable kinetic data as observed in electrophysiological measurements15. The close correspondence between the results from the BLI and electrophysiological measurements demonstrate for the first time the suitability of BLI as an appropriate analytical tool for ion channel membrane protein-small molecule interaction.

<table>
	<tbody>
		<tr>
			<td>DMEM/High Glucose Medium</td>
			<td>HyClone</td>
			<td>SH30243.01</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate Buffered Saline (1x)</td>
			<td>HyClone</td>
			<td>SH30256.01</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Gibco</td>
			<td>10270</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin</td>
			<td>Gibco</td>
			<td>1697550</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell Culture Dish</td>
			<td>Corning</td>
			<td>430599</td>
			<td>150 mm X 25 mm</td>
		</tr>
		<tr>
			<td>Nonidet P-40 Substitute</td>
			<td>Amresco</td>
			<td>E109</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>BBI Life Sciences</td>
			<td>A610476</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>BBI Life Sciences</td>
			<td>A610440</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin</td>
			<td>BBI Life Sciences</td>
			<td>A600332</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyoxyethylene-20-Sorbitan Monolaurate</td>
			<td>BBI Life Sciences</td>
			<td>A600560</td>
			<td></td>
		</tr>
		<tr>
			<td>ANTI-FLAG M2 Affinity Gel</td>
			<td>Sigma</td>
			<td>A2220</td>
			<td></td>
		</tr>
		<tr>
			<td>3x FLAG peptide</td>
			<td>Sigma</td>
			<td>F4799</td>
			<td></td>
		</tr>
		<tr>
			<td>Octet-RED96</td>
			<td>Pall/Fort&#233;Bio</td>
			<td>30-5048</td>
			<td></td>
		</tr>
		<tr>
			<td>Data Acquisition software</td>
			<td>Pall/Fort&#233;Bio</td>
			<td>Version 7.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Data Analysis software</td>
			<td>Pall/Fort&#233;Bio</td>
			<td>Version 7.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Biosensor/Streptavidin</td>
			<td>Pall/Fort&#233;Bio</td>
			<td>18-5019</td>
			<td></td>
		</tr>
		<tr>
			<td>Microtiter plate</td>
			<td>Greiner Bio-one</td>
			<td>655209</td>
			<td></td>
		</tr>
		<tr>
			<td>Sulfo-NHS-LC-LC-Biotin</td>
			<td>ThermoFisher</td>
			<td>21338</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifugal Machine</td>
			<td>ThermoFisher</td>
			<td>75004250</td>
			<td></td>
		</tr>
		<tr>
			<td>PageRuler Prestained Protein Ladder</td>
			<td>ThermoScientific</td>
			<td>318120</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrafiltration device</td>
			<td>MILLIPORE</td>
			<td>UFC503008</td>
			<td>NMWL of 30 kDa</td>
		</tr>
		<tr>
			<td>phosphatidylinositol 4, 5-bisphosphate (PIP2)</td>
			<td>Sigma</td>
			<td>P9763</td>
			<td></td>
		</tr>
		<tr>
			<td>Monoclonal ANTI-FLAG M2 antibody</td>
			<td>Sigma</td>
			<td>F1804</td>
			<td>1:2000 dilution</td>
		</tr>
		<tr>
			<td>goat anti-mouse HRP-conjugated secondary antibody</td>
			<td>Santa Cruz Biotechnology</td>
			<td>sc-2005</td>
			<td>1:5000 dilution</td>
		</tr>
		<tr>
			<td>Enhanced BCA Protein Assay Kit</td>
			<td>Beyotime</td>
			<td>P0010</td>
			<td></td>
		</tr>
		<tr>
			<td>Protease Inhibitor Cocktail Tablets</td>
			<td>Roche</td>
			<td>04693159001</td>
			<td></td>
		</tr>
		<tr>
			<td>Amersham Imager 600 Imaging System</td>
			<td>GE Healthcare Bio-Sciences</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Western blot system</td>
			<td>BIO-RAD</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

capturing the interaction kinetics of an ion channel protein with small molecules by the bio-layer interferometry assay

The bio-layer interferometry (BLI) assay is a valuable tool for measuring protein-protein and protein-small molecule interactions. Here, we first describe the application of this novel label-free technique to study the interaction of human EAG1 (hEAG1) channel proteins with the small molecule PIP2. hEAG1 channel has been recognized as potential therapeutic target because of its aberrant overexpression in cancers and a few gain-of-function mutations involved in some types of neurological diseases. We purified&#160;hEAG1 channel proteins from a mammalian stable expression system and measured the interaction with PIP2 by BLI. The successful measurement of the kinetics of binding between hEAG1 protein and PIP2 demonstrates that the BLI assay is a potential high-throughput approach used for novel small-molecule ligand screening in ion channel pharmacology.

We purified&#160;the FLAG fusion hEAG1 channel protein from HEK-293T cells stably overexpressed hEAG1. The function of this fusion protein has been demonstrated by using the patch-clamp method and the quality and specificity of purified protein are confirmed by Western blot (Figure 1). The purified channel protein is biotinylated to perform an interaction assay with the lipids (PIP2) by using the real-time BLI assay. The BLI binding assay configura...

Watch this Scientific Journal Video about Capturing the Interaction Kinetics of an Ion Channel Protein with Small Molecules by the Bio-layer Interferometry Assay at JoVE.com

Capturing the Interaction Kinetics of an Ion Channel Protein with Small Molecules by the Bio-layer Interferometry Assay

The protocol here describes the interactions of purified hEAG1 ion channel protein with the small molecule lipid ligand phosphatidylinositol 4, 5-bisphosphate (PIP2). The measurement demonstrates that BLI could be a potential method for novel small-molecule ion channel ligand screening.

The bio-layer interferometry (BLI) assay is a valuable tool for measuring protein-protein and protein-small molecule interactions. Here, we first describe ...

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