Our work has been supported by grants from American Heart Association (Greater Southeast Affiliate) Beginning-grant-in-aid 0765185B, the Elsa U. Pardee Foundation research grant, and Wayne State University intramural startup fund and Cardiovascular Research Institute Isis Initiative award. This method of in vitro CFTR macromolecular complex assembly was originally pioneered by Dr. A.P. Naren (University of Tennessee Health Science Center).

1. Expression and Purification of Recombinant Tagged Fusion Proteins in Bacteria
<ol>
	<li>Amplify defined regions of the C-tails (the last 50-100 amino acids containing the PDZ motifs at C-terminus) for CFTR, LPA2, MRP2, MRP4, &beta;2AR, and NHERFs (full-length or PDZ1 or PDZ2 domains) by PCR approach.</li>
	<li>Clone the PCR products into pGEX4T-1 vector for GST-fusion proteins (such as GST-NHERFs, GST-MRP4 CT), pMAL-C2 vector for MBP-fusion proteins (such as MBP-&beta;2AR CT, MBP-CFT...

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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chloride+impermeability+in+cystic+fibrosis.">Chloride impermeability in cystic fibrosis.</a> Nature. 301, 421-422 (1983).</li><li>Cheng, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Defective+intracellular+transport+and+processing+of+CFTR+is+the+molecular+basis+of+most+cystic+fibrosis.">Defective intracellular transport and processing of CFTR is the molecular basis of most cystic fibrosis.</a> Cell. 63, 827-834 (1990).</li><li>Gabriel, S. E., Brigman, K. N., Koller, B. H., Boucher, R. C., Stutts, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cystic+fibrosis+heterozygote+resistance+to+cholera+toxin+in+the+cystic+fibrosis+mouse+model.">Cystic fibrosis heterozygote resistance to cholera toxin in the cystic fibrosis mouse model.</a> Science. 266, 107-109 (1994).</li><li>Li, C., Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CFTR+chloride+channel+in+the+apical+compartments:+spatiotemporal+coupling+to+its+interacting+partners.">CFTR chloride channel in the apical compartments: spatiotemporal coupling to its interacting partners.</a> Integr. Biol (Camb). 2, 161-177 (2010).</li><li>Chao, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Activation+of+intestinal+CFTR+Cl-+channel+by+heat-stable+enterotoxin+and+guanylin+via+cAMP-dependent+protein+kinase.">Activation of intestinal CFTR Cl- channel by heat-stable enterotoxin and guanylin via cAMP-dependent protein kinase.</a> Embo. J. 13, 1065-1072 (1994).</li><li>Gabriel, S. E., Clarke, L. L., Boucher, R. C., Stutts, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CFTR+and+outward+rectifying+chloride+channels+are+distinct+proteins+with+a+regulatory+relationship.">CFTR and outward rectifying chloride channels are distinct proteins with a regulatory relationship.</a> Nature. 363, 263-268 (1993).</li><li>McNicholas, C. 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Physiol. 276, 16-25 (1999).</li><li>Ahn, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulatory+interaction+between+the+cystic+fibrosis+transmembrane+conductance+regulator+and+HCO3-+salvage+mechanisms+in+model+systems+and+the+mouse+pancreatic+duct.">Regulatory interaction between the cystic fibrosis transmembrane conductance regulator and HCO3- salvage mechanisms in model systems and the mouse pancreatic duct.</a> J. Biol. Chem. 276, 17236-17243 (2001).</li><li>Sugita, M., Yue, Y., Foskett, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CFTR+Cl-+channel+and+CFTR-associated+ATP+channel:+distinct+pores+regulated+by+common+gates.">CFTR Cl- channel and CFTR-associated ATP channel: distinct pores regulated by common gates.</a> Embo. J. 17, 898-908 (1998).</li><li>Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+CFTR+chloride+channels+by+syntaxin+and+Munc18+isoforms.">Regulation of CFTR chloride channels by syntaxin and Munc18 isoforms.</a> Nature. 390, 302-305 (1997).</li><li>Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Syntaxin+1A+is+expressed+in+airway+epithelial+cells,+where+it+modulates+CFTR+Cl(-)+currents.">Syntaxin 1A is expressed in airway epithelial cells, where it modulates CFTR Cl(-) currents.</a> J. Clin. Invest. 105, 377-386 (2000).</li><li>Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+macromolecular+complex+of+beta+2+adrenergic+receptor,+CFTR,+and+ezrin/radixin/moesin-binding+phosphoprotein+50+is+regulated+by+PKA.">A macromolecular complex of beta 2 adrenergic receptor, CFTR, and ezrin/radixin/moesin-binding phosphoprotein 50 is regulated by PKA.</a> Proc. Natl. Acad. Sci. USA. 100, 342-346 (1073).</li><li>Li, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lysophosphatidic+acid+inhibits+cholera+toxin-induced+secretory+diarrhea+through+CFTR-dependent+protein+interactions.">Lysophosphatidic acid inhibits cholera toxin-induced secretory diarrhea through CFTR-dependent protein interactions.</a> J. Exp. Med. 202, 975-986 (2005).</li><li>Li, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatiotemporal+coupling+of+cAMP+transporter+to+CFTR+chloride+channel+function+in+the+gut+epithelia.">Spatiotemporal coupling of cAMP transporter to CFTR chloride channel function in the gut epithelia.</a> Cell. 131, 940-951 (2007).</li><li>Li, C., Schuetz, J. D., Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tobacco+carcinogen+NNK+transporter+MRP2+regulates+CFTR+function+in+lung+epithelia:+implications+for+lung+cancer.">Tobacco carcinogen NNK transporter MRP2 regulates CFTR function in lung epithelia: implications for lung cancer.</a> Cancer Lett. 292, 246-253 (2010).</li><li>Hall, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+C-terminal+motif+found+in+the+beta2-adrenergic+receptor,+P2Y1+receptor+and+cystic+fibrosis+transmembrane+conductance+regulator+determines+binding+to+the+Na+/H++exchanger+regulatory+factor+family+of+PDZ+proteins.">A C-terminal motif found in the beta2-adrenergic receptor, P2Y1 receptor and cystic fibrosis transmembrane conductance regulator determines binding to the Na+/H+ exchanger regulatory factor family of PDZ proteins.</a> Proc. Natl. Acad. Sci. U.S.A. 95, 8496-8501 (1998).</li><li>Short, D. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+apical+PDZ+protein+anchors+the+cystic+fibrosis+transmembrane+conductance+regulator+to+the+cytoskeleton.">An apical PDZ protein anchors the cystic fibrosis transmembrane conductance regulator to the cytoskeleton.</a> J. Biol. Chem. 273, 19797-19801 (1998).</li><li>Wang, S., Yue, H., Derin, R. B., Guggino, W. B., Li, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Accessory+protein+facilitated+CFTR-CFTR+interaction,+a+molecular+mechanism+to+potentiate+the+chloride+channel+activity.">Accessory protein facilitated CFTR-CFTR interaction, a molecular mechanism to potentiate the chloride channel activity.</a> Cell. 103, 169-179 (2000).</li><li>Sun, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=E3KARP+mediates+the+association+of+ezrin+and+protein+kinase+A+with+the+cystic+fibrosis+transmembrane+conductance+regulator+in+airway+cells.">E3KARP mediates the association of ezrin and protein kinase A with the cystic fibrosis transmembrane conductance regulator in airway cells.</a> J. Biol. 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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+regulation+of+cystic+fibrosis+transmembrane+conductance+regulator+by+competitive+interactions+of+molecular+adaptors.">Dynamic regulation of cystic fibrosis transmembrane conductance regulator by competitive interactions of molecular adaptors.</a> The Journal of biological chemistry. 282, 10414-10422 (2007).</li><li>Gee, H. Y., Noh, S. H., Tang, B. L., Kim, K. H., Lee, M. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rescue+of+DeltaF508-CFTR+trafficking+via+a+GRASP-dependent+unconventional+secretion+pathway.">Rescue of DeltaF508-CFTR trafficking via a GRASP-dependent unconventional secretion pathway.</a> Cell. 146, 746-760 (2011).</li><li>Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+for+the+study+of+intermolecular+and+intramolecular+interactions+regulating+CFTR+function.">Methods for the study of intermolecular and intramolecular interactions regulating CFTR function.</a> Met. Molecul. Med. 70, 175-186 (2002).</li><li>Li, C., Roy, K., Dandridge, K., Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+assembly+of+cystic+fibrosis+transmembrane+conductance+regulator+in+plasma+membrane.">Molecular assembly of cystic fibrosis transmembrane conductance regulator in plasma membrane.</a> The Journal of biological chemistry. 279, 24673-24684 (2004).</li><li>Li, C., Naren, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+CFTR+Interactome+in+the+Macromolecular+Complexes.">Analysis of CFTR Interactome in the Macromolecular Complexes.</a> Met. Molecul. Med. 741, 255-270 (2011).</li><li>Wu, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+chemokine+receptor+CXCR2+macromolecular+complex+regulates+neutrophil+functions+in+inflammatory+diseases.">A chemokine receptor CXCR2 macromolecular complex regulates neutrophil functions in inflammatory diseases.</a> J. Biol. Chem. , (2011).</li></ol>

In this protocol we demonstrated a method for in vitro assembling and detection of a CFTR containing macromolecular signaling complex using purified proteins (or protein fragments) and/or cell lysates as reported previously16-19,29,30. To achieve best results the following critical points during the preparation process require special attention:
<ul>
	<li>It is important that the pH of the elution buffer be adjusted to 8.0 after adding reduced glutathione when purifying the GST-fusion protein as d...

<table border="1">
	<tbody>
		<tr>
			<td>Name of the reagent</td>
			<td>Company</td>
			<td>Catalog number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>pGEX4T-1 vector</td>
			<td>GE Healthcare</td>
			<td>28-9545-49</td>
			<td>formerly Amersham Biosciences</td>
		</tr>
		<tr>
			<td>pMAL-C2 vector</td>
			<td>New England BioLabs</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>pET30 vector</td>
			<td>EMD Chemicals</td>
			<td>69077-3</td>
			<td>formerly Novagen</td>
		</tr>
		<tr>
			<td>Glutathione agarose beads</td>
			<td>BD Biosciences</td>
			<td>554780</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Amylose resin</td>
			<td>New England BioLabs</td>
			<td>E8021S</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Talon beads</td>
			<td>Clontech</td>
			<td>635501</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>reduced glutathione</td>
			<td>BD Biosciences</td>
			<td>554782</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>imidazole</td>
			<td>Fisher</td>
			<td>BP305-50</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>maltose</td>
			<td>Fisher</td>
			<td>BP684-500</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>S-protein agarose</td>
			<td>EMD Chemicals</td>
			<td>69704-3</td>
			<td>formerly Novagen</td>
		</tr>
		<tr>
			<td>Anti-Flag HRP</td>
			<td>Sigma</td>
			<td>A8592</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Anti-CFTR IgG</td>
			<td>Custom-made</td>
			<td>R1104</td>
			<td>mAb recognizing CFTR epitope at a.a. 722-734</td>
		</tr>
		<tr>
			<td>Anti-MRP2 IgG</td>
			<td>Chemicon International</td>
			<td>MAB4148</td>
			<td>Now a part of Millipore</td>
		</tr>
	</tbody>
</table>
Table 2. Specific reagents and equipment.

in vitro analysis of pdz-dependent cftr macromolecular signaling complexes

Cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel located primarily at the apical membranes of epithelial cells, plays a crucial role in transepithelial fluid homeostasis1-3. CFTR has been implicated in two major diseases: cystic fibrosis (CF)4 and secretory diarrhea5. In CF, the synthesis or functional activity of the CFTR Cl- channel is reduced. This disorder affects approximately 1 in 2,500 Caucasians in the United States6. Excessive CFTR activity has also been implicated in cases of toxin-induced secretory diarrhea (e.g., by cholera toxin and heat stable E. coli enterotoxin) that stimulates cAMP or cGMP production in the gut7.
Accumulating evidence suggest the existence of physical and functional interactions between CFTR and a growing number of other proteins, including transporters, ion channels, receptors, kinases, phosphatases, signaling molecules, and cytoskeletal elements, and these interactions between CFTR and its binding proteins have been shown to be critically involved in regulating CFTR-mediated transepithelial ion transport in vitro and also in vivo8-19. In this protocol, we focus only on the methods that aid in the study of the interactions between CFTR carboxyl terminal tail, which possesses a protein-binding motif [referred to as PSD95/Dlg1/ZO-1 (PDZ) motif], and a group of scaffold proteins, which contain a specific binding module referred to as PDZ domains. So far, several different PDZ scaffold proteins have been reported to bind to the carboxyl terminal tail of CFTR with various affinities, such as NHERF1, NHERF2, PDZK1, PDZK2, CAL (CFTR-associated ligand), Shank2, and GRASP20-27. The PDZ motif within CFTR that is recognized by PDZ scaffold proteins is the last four amino acids at the C terminus (i.e., 1477-DTRL-1480 in human CFTR)20. Interestingly, CFTR can bind more than one PDZ domain of both NHERFs and PDZK1, albeit with varying affinities22. This multivalency with respect to CFTR binding has been shown to be of functional significance, suggesting that PDZ scaffold proteins may facilitate formation of CFTR macromolecular signaling complexes for specific/selective and efficient signaling in cells16-18.
Multiple biochemical assays have been developed to study CFTR-involving protein interactions, such as co-immunoprecipitation, pull-down assay, pair-wise binding assay, colorimetric pair-wise binding assay, and macromolecular complex assembly assay16-19,28,29. Here we focus on the detailed procedures of assembling a PDZ motif-dependent CFTR-containing macromolecular complex in vitro, which is used extensively by our laboratory to study protein-protein or domain-domain interactions involving CFTR16-19,28,29.

Watch this Scientific Journal Video about In Vitro Analysis of PDZ-dependent CFTR Macromolecular Signaling Complexes at JoVE.com

In Vitro Analysis of PDZ-dependent CFTR Macromolecular Signaling Complexes

Cystic fibrosis transmembrane conductance regulator (CFTR), an epithelial chloride channel, has been reported to interact with various proteins and regulate important cellular processes; among them the CFTR PDZ motif-mediated interactions have been well documented. This protocol describes methods we developed to assemble a PDZ-dependent CFTR macromolecular signaling complex in vitro.

In Vitro Analysis of PDZ-dependent CFTR Macromolecular Signaling Complexes

Cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel located primarily at the apical membranes of epithelial cells, plays a ...

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10.3K 조회수.  Wayne State University School of Medicine. 낭성 섬유증의 transmembrane의 전도성 조정기 (CFTR), 상피 염화물 채널, 각종 단백질과 상호 작용하고 중요한 세포 과정을 조절하는 것으로보고되었습니다; 그들 가운데 CFTR PDZ 모티프-매개 상호 작용이 잘 문서화되었습니다. 이 프로토콜은 우리가 복잡한 신호 PDZ-의존 CFTR의 macromolecular를 조립하기 위해 개발된 방법을 설명합니다 체외에서.