CFTR (cystic fibrosis transmembrane conductance regulator), encoded by the gene mutated in CF patients, is one of approximately 50 human ATP-binding cassette (ABC) proteins, and belongs to subfamily ABC-C which also includes SUR (sulfonylurea receptor) and MRP (multidrug resistance related) proteins. Unlike other ABC proteins, CFTR is an ion channel; it allows the Cl- flow needed for transepithelial fluid movement. Opening and closing of the CFTR channel pore are controlled by ATP binding to CFTR's two nucleotide binding domains (NBDs) and by ATP hydrolysis. Transduction of these NBD events to the channel gates is regulated by phosphorylation, by cAMP-dependent protein kinase, of multiple serines in CFTR's regulatory (R) domain. The goal of the proposed research is to understand, in molecular detail, the mechanisms regulating NBD function and channel gating. Knowing the precise mechanisms that control CFTR channel opening and closing might help pharmacological rescue in CF patients of cells with inadequate ion flow due to expression of mutant CFTR channels; this includes mutants that reach the cell surface in inadequate numbers, those with diminished pore conductance, and those that spend an insufficient time open.
The specific aims are essentially unchanged. The first addresses what the NBDs look like, how they function, how they interact, and how they control the channel's gates. The working hypothesis is that CFTR's two NBDs are structurally dissimilar (a characteristic of ABC-C family members), that upon ATP binding they form head-to-tail dimers that enclose two ATP molecules in composite catalytic sites within the dimer interface, that the dimerization drives channel opening, and that hydrolysis of the ATP at the NBD2 catalytic site prompts channel closing; ATP remains bound at the NBD1 catalytic site for several minutes without being hydrolyzed.
The second aim addresses how phosphorylation (and at which site or sites) permits channel opening, and how additional phosphorylation promotes stabilization of the channel open state. Wild-type and mutant CFTR channels will be expressed in oocytes and mammalian cells, and their structure and function analyzed using biophysical, electrophysiological, and biochemical methods. Mutant cycle measurements of single-channel gating kinetics will probe energetic interactions between residues and domains of CFTR. Photolabeling will probe nucleotide interactions with the NBDs. Structural analysis of prokaryotic NBD heterodimers, with an active and a dead catalytic site as in CFTR, will elucidate mechanisms in CFTR's NBDs.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
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Cellular and Molecular Biology of the Kidney Study Section (CMBK)
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Mckeon, Catherine T
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Rockefeller University
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New York
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Chaves, Luiz A Poletto; Gadsby, David C (2015) Cysteine accessibility probes timing and extent of NBD separation along the dimer interface in gating CFTR channels. J Gen Physiol 145:261-83
Csanády, László; Töröcsik, Beáta (2014) Catalyst-like modulation of transition states for CFTR channel opening and closing: new stimulation strategy exploits nonequilibrium gating. J Gen Physiol 143:269-87
Csanády, László; Töröcsik, Beáta (2014) Structure-activity analysis of a CFTR channel potentiator: Distinct molecular parts underlie dual gating effects. J Gen Physiol 144:321-36
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Csanády, László; Vergani, Paola; Gulyás-Kovács, Attila et al. (2011) Electrophysiological, biochemical, and bioinformatic methods for studying CFTR channel gating and its regulation. Methods Mol Biol 741:443-69
Csanády, László; Vergani, Paola; Gadsby, David C (2010) Strict coupling between CFTR's catalytic cycle and gating of its Cl- ion pore revealed by distributions of open channel burst durations. Proc Natl Acad Sci U S A 107:1241-6
Muallem, Daniella; Vergani, Paola (2009) Review. ATP hydrolysis-driven gating in cystic fibrosis transmembrane conductance regulator. Philos Trans R Soc Lond B Biol Sci 364:247-55
Csanady, Laszlo (2009) Application of rate-equilibrium free energy relationship analysis to nonequilibrium ion channel gating mechanisms. J Gen Physiol 134:129-36
Gadsby, David C (2009) Ion channels versus ion pumps: the principal difference, in principle. Nat Rev Mol Cell Biol 10:344-52

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