Name: functional reconstitution and channel activity measurements of purified wildtype and mutant cftr protein
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Description: Watch this Scientific Journal Video about Functional Reconstitution and Channel Activity Measurements of Purified Wildtype and Mutant CFTR Protein Video at JoVE.com

The authors declare that they have no competing financial interests.

1. Purification of CFTR
NOTE: Please see Table of Materials and Equipment for a list of equipment and materials used in this protocol. A detailed protocol exists for overexpression of human Wt-CFTR and mutants in the Sf9-baculovirus expression system17,28. Overexpress CFTR and prepare pellets of Sf9 cells according to this protocol.
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	<li>Crude membrane preparation
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		<li>Obtain a fresh or thaw a frozen Sf9 cell pellet from a 500 ml culture of c...

<ol>
	<li>Kim Chiaw, P., Eckford, P. D., Bear, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insights+into+the+mechanisms+underlying+CFTR+channel+activity,+the+molecular+basis+for+cystic+fibrosis+and+strategies+for+therapy.">Insights into the mechanisms underlying CFTR channel activity, the molecular basis for cystic fibrosis and strategies for therapy.</a> Essays Biochem. 50 (1), 233-248 (2011).</li><li>Bear, C. 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=Purification+and+functional+reconstitution+of+the+cystic+fibrosis+transmembrane+conductance+regulator+(CFTR).">Purification and functional reconstitution of the cystic fibrosis transmembrane conductance regulator (CFTR).</a> Cell. 68 (4), 809-818 (1992).</li><li>Cai, Z., Sohma, Y., Bompadre, S. G., Sheppard, D. N., Hwang, T. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+high-resolution+single-channel+recording+to+functional+studies+of+cystic+fibrosis+mutants.">Application of high-resolution single-channel recording to functional studies of cystic fibrosis mutants.</a> Methods Mol Biol. 741, 419-441 (2011).</li><li>Kerem, B., 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+the+cystic+fibrosis+gene:+genetic+analysis.">Identification of the cystic fibrosis gene: genetic analysis.</a> Science. 245 (4922), 1073-1080 (1989).</li><li>Yang, Y., 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=Molecular+basis+of+defective+anion+transport+in+L+cells+expressing+recombinant+forms+of+CFTR.">Molecular basis of defective anion transport in L cells expressing recombinant forms of CFTR.</a> Hum Mol Genet. 2 (8), 1253-1261 (1993).</li><li>Mendoza, J. 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=Requirements+for+efficient+correction+of+DeltaF508+CFTR+revealed+by+analyses+of+evolved+sequences.">Requirements for efficient correction of DeltaF508 CFTR revealed by analyses of evolved sequences.</a> Cell. 148 (1-2), 164-274 (2012).</li><li>Rabeh, W. 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=Correction+of+both+NBD1+energetics+and+domain+interface+is+required+to+restore+DeltaF508+CFTR+folding+and+function.">Correction of both NBD1 energetics and domain interface is required to restore DeltaF508 CFTR folding and function.</a> Cell. 148 (1-2), 150-163 (2012).</li><li>Aleksandrov, A. 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=Allosteric+modulation+balances+thermodynamic+stability+and+restores+function+of+DeltaF508.">Allosteric modulation balances thermodynamic stability and restores function of DeltaF508.</a> CFTR. J Mol Biol. 419 (1-2), 41-60 (2012).</li><li>Ramsey, B. W., 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=A+CFTR+potentiator+in+patients+with+cystic+fibrosis+and+the+G551D+mutation.">A CFTR potentiator in patients with cystic fibrosis and the G551D mutation.</a> N Engl J Med. 365 (18), 1663-1672 (2011).</li><li>Riordan, C. R., 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=Purification+and+characterization+of+recombinant+cystic+fibrosis+transmembrane+conductance+regulator+from+Chinese+hamster+ovary+and+insect+cells.">Purification and characterization of recombinant cystic fibrosis transmembrane conductance regulator from Chinese hamster ovary and insect cells.</a> J. Biol. Chem. 270 (28), 17033-17043 (1995).</li><li>Ryan, L., Rimington, T., Cant, N., Ford, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+and+purification+of+the+cystic+fibrosis+transmembrane+conductance+regulator+protein+in+Saccharomyces+cerevisiae.">Expression and purification of the cystic fibrosis transmembrane conductance regulator protein in Saccharomyces cerevisiae.</a> JoVE. (61), (2012).</li><li>Ostedgaard, L. S., Welsh, 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=Partial+purification+of+the+cystic+fibrosis+transmembrane+conductance+regulator.">Partial purification of the cystic fibrosis transmembrane conductance regulator.</a> J Biol Chem. 267 (36), 26142-26149 (1992).</li><li>Peng, S., 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=One-step+affinity+isolation+of+recombinant+protein+using+the+baculovirus/insect+cell+expression+system.">One-step affinity isolation of recombinant protein using the baculovirus/insect cell expression system.</a> Protein Expr Purif. 4 (2), 95-100 (1993).</li><li>Ramjeesingh, 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=A+novel+procedure+for+the+efficient+purification+of+the+cystic+fibrosis+transmembrane+conductance+regulator+(CFTR).">A novel procedure for the efficient purification of the cystic fibrosis transmembrane conductance regulator (CFTR).</a> Biochem J. 327 (1), 17-21 (1997).</li><li>Rosenberg, M. F., Kamis, A. B., Aleksandrov, L. A., Ford, R. C., Riordan, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+and+crystallization+of+the+cystic+fibrosis+transmembrane+conductance+regulator+(CFTR).">Purification and crystallization of the cystic fibrosis transmembrane conductance regulator (CFTR).</a> J Biol Chem. 279 (37), 39051-39057 (2004).</li><li>Ramjeesingh, 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=Purification+and+reconstitution+of+epithelial+chloride+channel+cystic+fibrosis+transmembrane+conductance+regulator.">Purification and reconstitution of epithelial chloride channel cystic fibrosis transmembrane conductance regulator.</a> Methods Enzymol. 294, 227-246 (1999).</li><li>Sorscher, E. J., Sommerfelt, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+of+recombinant+protein+derived+from+the+baculovirus+expression+system+using+glutathione+affinity+agarose.">Purification of recombinant protein derived from the baculovirus expression system using glutathione affinity agarose.</a> Methods Mol Biol. 3, 337-348 (1995).</li><li>Eckford, P. D., Li, C., Ramjeesingh, M., Bear, C. E. <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+transmembrane+conductance+regulator+(CFTR)+potentiator+VX-770+(ivacaftor)+opens+the+defective+channel+gate+of+mutant+CFTR+in+a+phosphorylation-dependent+but+ATP-independent+manner.">Cystic fibrosis transmembrane conductance regulator (CFTR) potentiator VX-770 (ivacaftor) opens the defective channel gate of mutant CFTR in a phosphorylation-dependent but ATP-independent manner.</a> J Biol Chem. 287 (44), 36639-36649 (2012).</li><li>Alkhouri, B., 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=Synthesis+and+properties+of+molecular+probes+for+the+rescue+site+on+mutant+cystic+fibrosis+transmembrane+conductance+regulator.">Synthesis and properties of molecular probes for the rescue site on mutant cystic fibrosis transmembrane conductance regulator.</a> J Med Chem. 54 (24), 8693-8701 (2011).</li><li>Eckford, P. D., 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=VX-809+and+Related+Corrector+Compounds+Exhibit+Secondary+Activity+Stabilizing+Active+F508del-CFTR+after+Its+Partial+Rescue+to+the+Cell+Surface.">VX-809 and Related Corrector Compounds Exhibit Secondary Activity Stabilizing Active F508del-CFTR after Its Partial Rescue to the Cell Surface.</a> Chem Biol. 21 (5), 666-678 (2014).</li><li>Kim Chiaw, P., Wellhauser, L., Huan, L. J., Ramjeesingh, M., Bear, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+chemical+corrector+modifies+the+channel+function+of+F508del-CFTR.">A chemical corrector modifies the channel function of F508del-CFTR.</a> Mol.Pharmacol. 78 (3), 411-418 (2010).</li><li>Verkman, A. S., Galietta, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chloride+channels+as+drug+targets.">Chloride channels as drug targets.</a> Nat Rev Drug Discov. 8 (2), 153-171 (2009).</li><li>Pasyk, S., Li, C., Ramjeesingh, M., Bear, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+interaction+of+a+small-molecule+modulator+with+G551D-CFTR,+a+cystic+fibrosis-causing+mutation+associated+with+severe+disease.">Direct interaction of a small-molecule modulator with G551D-CFTR, a cystic fibrosis-causing mutation associated with severe disease.</a> Biochem J. 418 (1), 185-190 (2009).</li><li>Norez, C., 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=Determination+of+CFTR+chloride+channel+activity+and+pharmacology+using+radiotracer+flux+methods.">Determination of CFTR chloride channel activity and pharmacology using radiotracer flux methods.</a> J Cyst Fibros. 3 (2), 119-121 (2004).</li><li>Whitney, J. C., 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=Structural+basis+for+alginate+secretion+across+the+bacterial+outer+membrane.">Structural basis for alginate secretion across the bacterial outer membrane.</a> Proc Natl Acad Sci U S A. 108 (32), 13083-13088 (2011).</li><li>Islam, S. T., 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=Proton-dependent+gating+and+proton+uptake+by+Wzx+support+O-antigen-subunit+antiport+across+the+bacterial+inner+membrane.">Proton-dependent gating and proton uptake by Wzx support O-antigen-subunit antiport across the bacterial inner membrane.</a> mBio. 4 (5), e00678-e00613 (2013).</li><li>Ramjeesingh, M., Conn, P. 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=Ch.+16.">Ch. 16.</a> Reliable Lab Solutions: Essential Ion Channel MethodsReliable Lab Solutions. , 337-357 (2010).</li><li>Wellhauser, 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=A+small-molecule+modulator+interacts+directly+with+deltaPhe508-CFTR+to+modify+its+ATPase+activity+and+conformational+stability.">A small-molecule modulator interacts directly with deltaPhe508-CFTR to modify its ATPase activity and conformational stability.</a> Mol Pharmacol. 75 (6), 1430-1438 (2009).</li><li>Lee, S. Y., Letts, J. A., MacKinnon, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+reconstitution+of+purified+human+Hv1+H++channels.">Functional reconstitution of purified human Hv1 H+ channels.</a> J Mol Biol. 387 (5), 1055-1060 (2009).</li><li>Chang, X. B., 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=Protein+kinase+A+(PKA)+still+activates+CFTR+chloride+channel+after+mutagenesis+of+all+10+PKA+consensus+phosphorylation+sites.">Protein kinase A (PKA) still activates CFTR chloride channel after mutagenesis of all 10 PKA consensus phosphorylation sites.</a> J. Biol. Chem. 268 (15), 11304-11311 (1993).</li><li>Gadsby, D. C., Nairn, 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=Regulation+of+CFTR+Cl-+ion+channels+by+phosphorylation+and+dephosphorylation.">Regulation of CFTR Cl- ion channels by phosphorylation and dephosphorylation.</a> Adv.Second Messenger Phosphoprotein Res. 33, 79-106 (1999).</li><li>Li, C., 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=ATPase+activity+of+the+cystic+fibrosis+transmembrane+conductance+regulator.">ATPase activity of the cystic fibrosis transmembrane conductance regulator.</a> J Biol Chem. 271 (45), 28463-28468 (1996).</li><li>Ma, T., 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=Thiazolidinone+CFTR+inhibitor+identified+by+high-throughput+screening+blocks+cholera+toxin-induced+intestinal+fluid+secretion.">Thiazolidinone CFTR inhibitor identified by high-throughput screening blocks cholera toxin-induced intestinal fluid secretion.</a> J Clin Invest. 110 (11), 1651-1658 (2002).</li><li>Kopeikin, Z., Sohma, Y., Li, M., Hwang, T. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+mechanism+of+CFTR+inhibition+by+a+thiazolidinone+derivative.">On the mechanism of CFTR inhibition by a thiazolidinone derivative.</a> J Gen Physiol. 136 (6), 659-671 (2010).</li><li>Wang, X. F., Reddy, M. M., Quinton, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+a+new+cystic+fibrosis+transmembrane+conductance+regulator+inhibitor+on+Cl-+conductance+in+human+sweat+ducts.">Effects of a new cystic fibrosis transmembrane conductance regulator inhibitor on Cl- conductance in human sweat ducts.</a> Exp Physiol. 89 (4), 417-425 (2004).</li></ol>

There have been a limited number of purification protocols for full-length, functional CFTR isolation, from a variety of cellular overexpression systems. The method described here is advantageous as it allows rapid purification of Wt-CFTR or high enrichment of F508del- and G551D-CFTR in moderate quantities that is highly functional in assays including ATPase and direct measurements of channel function, including single channel measurements in planar bilayer systems and demonstrated measures of CFTR population channel fun...

Chloride transport across the apical membranes of epithelial cells in such tissues as the lung, intestine, pancreas and sweat glands is primarily mediated by the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR), an ATP- and phosphorylation-regulated member of the ABC (ATP-Binding Cassette) C subfamily of membrane proteins (reviewed in1). Like other members of the ABCC subfamily, CFTR is a large, multi-spanning integral membrane protein that binds ATP at two nucleotide binding sites formed at the interface of its nucleotide-binding domains (NBDs), where it possesses modest ATPase activity at a single site. However, unlike other ABCC subfamily members, CFTR has evolved as a unique regulated Cl channel rather than as an active solute transporter.
Mutations in CFTR cause Cystic Fibrosis, a disease affecting multiple organs including the lungs, gastrointestinal tract, pancreatic and reproductive tract, leading to morbidity and mortality in young adults. Lung disease typically accounts for early mortality in Cystic Fibrosis and in most cases is caused by the loss of CFTR function on the surface epithelium of the conducting airways. The lack of CFTR chloride channel activity causes a reduction in both Cl- and water movement across the surface epithelium to modify the fluid layer on the apical surface of the ciliated respiratory epithelium. This results in a viscous airway surface liquid that impairs the ability of ciliated respiratory epithelial cells to effectively clear pathogens out of the airways. As a consequence, most CF patients suffer from recurrent bouts of lung infection and lung damage due to inflammation.
As expected, studies of the mechanism of action of the normal CFTR protein focused primarily on detailed electrophysiological studies of its channel gating activity. Single channel studies have shown directly that CFTR functions as a PKA-dependent Cl- channel which possesses an ATP regulated gate2. Detailed electrophysiological studies provide a great deal of information on single CFTR channels1,3, however there may be concern as to whether the characteristics of any particular single channel that has been studied is reflective of the entire population of CFTR channels and therefore the single channel results should always be considered along with methods to study the macroscopic population. Direct assay of the population channel activity of purified CFTR has the potential to provide insight into the molecular defect associated with disease-causing mutations and to drive discovery of chemical modulators which repair mutant CFTR proteins. To date, there are in excess of 1,900 different mutations in CFTR thought to cause Cystic Fibrosis4. The major mutation, F508del-CFTR, found on at least one allele in approximately 90% of patients in North America and Europe leads to protein misfolding and retention in the endoplasmic reticulum5. F508del-CFTR also has other consequences, including defective channel activity6-9. The resultant absence of CFTR from the cell surface is associated with severe disease. G551D-CFTR, a less common mutation, is thought to be properly folded yet is dysfunctional as a chloride channel at the cell surface6. The development of small molecule correctors and potentiators has the goal of correcting folding and/or trafficking of mutants such as F508del-CFTR to the cell surface, and potentiating or increasing the channel activity of mutations such as G551D when present on the cell surface, respectively. While the correctors VX-809 and VX-661 (are not yet approved for use in patients, the potentiator Kalydeco (ivacaftor; VX-770) is being used at 150 mg every 12 hr in CF patients &#62;6 years with at least one G551D-CFTR mutation, and more recently for patients with one of G178R, S549N, S549R, G551S, G1244E, S1251N, S1255P and G1349D. Kalydeco is both safe and results in improvement of clinical measures of CF disease10, however the mechanism of action of this small molecule was poorly understood at the time of FDA approval for use in patients.
A handful of CFTR purification methods have been described previously2,11-18, many of which require a considerable length of time to complete. In a recent publication19, a unique rapid purification and reconstitution method was described for CFTR overexpressed in the Sf9 cell expression system, and this purified protein in defined lipid systems was used to develop a CFTR halide channel activity assay for a population of CFTR molecules. The assay recapitulates the known effects of phosphorylation, nucleotides and inhibitors on CFTR function. The system was used to interrogate the effects of the potentiator VX-770/Kalydeco on Wt- (wild-type), F508del- and G551D-CFTR and it was shown for the first time that the drug interacts directly with the CFTR protein to potentiate its channel activity in an ATP-independent manner, demonstrating the utility and applicability of these methods to the study of the interaction of CFTR and mutants with nucleotides and small molecules from a population perspective to answer clinically relevant questions about the protein. The methods have also been used to study other potentiator molecules and their derivatives20, as well as the effects of a small molecule corrector on the activity of the protein21.
Efflux assays have been used in many studies previously to investigate the activity of CFTR mutants and the effects of CFTR-modulatory compounds on its activity, including whole cell assays using electrodes, radioactive tracers and fluorophores22,23, membrane vesicles with ion selective electrodes24, and purified reconstituted CFTR with radioactive tracers25. However the use of ion selective electrodes to study purified reconstituted CFTR was first reported recently19. An adaptation of the current method has been used for reconstitution and functional characterization of two membrane proteins in Pseudomonas aeruginosa, a common CF pathogen. Reconstitution of purified AlgE outer membrane protein coupled with iodide efflux measurements were used to support a model for anionic alginate secretion through this transporter26. Reconstitution and iodide efflux measurements were applied to the purified Wzx protein, which allowed a model to be proposed that suggests an H+-dependent antiport mechanism for lipid-linked oligosaccharide translocation across the bacterial inner membrane by this protein27. In both cases iodide was used as a surrogate for the anionic substrate, albeit at lower throughput than one might expect for a native substrate. The method may be suitable for adaptation to other proteins with cationic transport or conduction pathways for anionic substrates.
Here a rapid purification procedure is described for the CFTR protein and its reconstitution into proteoliposomes of defined lipid. The rapid reconstitution procedure can easily be tailored for use with CFTR purified by other methods, provided that the type of detergent used in the purification is amenable to removal by the methods used here or can be exchanged for a suitable detergent before the reconstitution procedure. The iodide efflux method for measurement of channel activity of purified and reconstituted CFTR protein is described in detail and some typical results that can be obtained from this method are presented.

<table border="0" cellpadding="0" cellspacing="0" width="1269">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:403px;">fos-choline 14 detergent</td>
			<td style="width:515px;">Anatrace Affymetrix (www.anatrace.affymetrix.com)</td>
			<td style="width:145px;">F312</td>
			<td style="width:207px;">Affymetrix: Anatrace Products; CAS#&#160;:77733-28-9</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">cOmplete EDTA-free protease inhibitor cocktail tablets</td>
			<td>Roche (www.roche-applied-science.com)</td>
			<td>04 693 132 001</td>
			<td>EDTA-free Protease inhibitor cocktail tablets (1 in 50 ml or mini:1 in 10 mL) (Roche Diagnostics GmbH; Ref: 11873 580 001</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">cOmplete ULTRA Tablets, Mini, EDTA-free, EASYpack&#160;</td>
			<td>Roche (www.roche-applied-science.com)</td>
			<td>05 892 791 001</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ni-NTA Agarose</td>
			<td>Qaigen GmbH</td>
			<td align="right">1018240</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Fisherbrand Screening columns</td>
			<td>Fisher Healthcare</td>
			<td>11-387-50</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Amicon Ultra Centrifugal filters, Ultracel-100K</td>
			<td>Millipore (www.millipore.com)</td>
			<td>UFC910008</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">cAMP-Dependent Protein Kinase A (PKA), Catalytic Subunit</td>
			<td colspan="2">New England Biolabs (www.neb.com/products/p6000-camp-dependent-protein-kinase-pka-catalytic-subunit)</td>
			<td>Peirce PKA is also suitable</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PC, Chicken Egg</td>
			<td>Avanti Polar Lipids (www.avantilipids.com)</td>
			<td>840051C</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">POPC</td>
			<td>Avanti Polar Lipids (www.avantilipids.com)</td>
			<td>850457C</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PS, Porcine Brain</td>
			<td>Avanti Polar Lipids (www.avantilipids.com)</td>
			<td>840032C</td>
			<td>(CFTR has been successfully reconstituted into Egg PC, POPC, 2:1 (w/w) Egg PC:POPC, or a mixture of PE:PS:PC:ergosterol, 5:2:2:1 (w/w))</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PE, Chicken Egg</td>
			<td>Avanti Polar Lipids (www.avantilipids.com)</td>
			<td>841118C</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ergosterol</td>
			<td>Sigma (www.sigmaaldrich.com)</td>
			<td align="right">45480</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Pierce Detergent removal spin column</td>
			<td>Thermo Scientific</td>
			<td align="right">87779</td>
			<td>1 ml capacity columns</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">valinomycin</td>
			<td>Sigma (www.sigmaaldrich.com)</td>
			<td>V-0627</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">VX-770 (ivacaftor)</td>
			<td>Selleck Chemicals</td>
			<td>S1144</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">iodide selective microelectrode</td>
			<td>Lazar Research Laboratories (www.shelfscientific.com/cgi-bin/tame/newlaz/microionn.tam)</td>
			<td>LIS-146ICM</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Clampex 8.1 software</td>
			<td>Axon Instruments (www.axon.com)</td>
			<td></td>
			<td>we use components of the ClampX system with a home made filter to monitor and record the response to our electrode</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Alternate Software: ArrowLabb System&#160;</td>
			<td>Lazar Research Laboratories (www.shelfscientific.com/cgi-bin/tame/newlaz/ionsystems.tam)</td>
			<td>LIS-146LICM-XS</td>
			<td>Lazar Research sells a meter that can interface with a computer and software to record the probe response.&#160; This software should serve a similar function to our setup</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">small stir bars</td>
			<td>Big Science Inc (www.stirbars.com)</td>
			<td>SBM-0502-CMB</td>
			<td>choose a stir bar small enough to easily fit into a well of a 96-well plate</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sephadex G50, fine</td>
			<td>GE Health Care (www.gelifesciences.com)</td>
			<td>17-0042-01</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sonicator</td>
			<td>Laboratory Supplies Co, Inc.</td>
			<td>G112SP1G</td>
			<td>Bath sonicators from other manufacturers should also be suitable</td>
		</tr>
	</tbody>
</table>

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 in this written publication are methods to purify, reconstitute and measure regulated channel activity of the CFTR protein. Figure 1a shows the workflow for the purification, reconstitution and iodide efflux procedures. Methods for reconstitution and channel activity measurements by iodide flux are also shown in further detail in the associated video.
Purification and reconstitution of CFTR into proteoliposomes
CFTR can be functionally exp...

Watch this Scientific Journal Video about Functional Reconstitution and Channel Activity Measurements of Purified Wildtype and Mutant CFTR Protein Video at JoVE.com

Functional Reconstitution and Channel Activity Measurements of Purified Wildtype and Mutant CFTR Protein Video (Video) | JoVE

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.

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 ...

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