scholarly journals Preferential Phosphorylation of R-domain Serine 768 Dampens Activation of CFTR Channels by PKA

2005 ◽  
Vol 125 (2) ◽  
pp. 171-186 ◽  
Author(s):  
László Csanády ◽  
Donna Seto-Young ◽  
Kim W. Chan ◽  
Cristina Cenciarelli ◽  
Benjamin B. Angel ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Chloride Ion ◽  
Spectrometric Analysis ◽  
Inhibitory Influence ◽  
Open Probability ◽  
Principal Mechanism ◽  
Binding Domains ◽  
Excised Patches ◽  
The Right ◽  
R Domain

CFTR (cystic fibrosis transmembrane conductance regulator), the protein whose dysfunction causes cystic fibrosis, is a chloride ion channel whose gating is controlled by interactions of MgATP with CFTR's two cytoplasmic nucleotide binding domains, but only after several serines in CFTR's regulatory (R) domain have been phosphorylated by cAMP-dependent protein kinase (PKA). Whereas eight R-domain serines have previously been shown to be phosphorylated in purified CFTR, it is not known how individual phosphoserines regulate channel gating, although two of them, at positions 737 and 768, have been suggested to be inhibitory. Here we show, using mass spectrometric analysis, that Ser 768 is the first site phosphorylated in purified R-domain protein, and that it and five other R-domain sites are already phosphorylated in resting Xenopus oocytes expressing wild-type (WT) human epithelial CFTR. The WT channels have lower activity than S768A channels (with Ser 768 mutated to Ala) in resting oocytes, confirming the inhibitory influence of phosphoserine 768. In excised patches exposed to a range of PKA concentrations, the open probability (Po) of mutant S768A channels exceeded that of WT CFTR channels at all [PKA], and the half-maximally activating [PKA] for WT channels was twice that for S768A channels. As the open burst duration of S768A CFTR channels was almost double that of WT channels, at both low (55 nM) and high (550 nM) [PKA], we conclude that the principal mechanism by which phosphoserine 768 inhibits WT CFTR is by hastening the termination of open channel bursts. The right-shifted Po-[PKA] curve of WT channels might explain their slower activation, compared with S768A channels, at low [PKA]. The finding that phosphorylation kinetics of WT or S768A R-domain peptides were similar provides no support for an alternative explanation, that early phosphorylation of Ser 768 in WT CFTR might also impair subsequent phosphorylation of stimulatory R-domain serines. The observed reduced sensitivity to activation by [PKA] imparted by Ser 768 might serve to ensure activation of WT CFTR by strong stimuli while dampening responses to weak signals.

scholarly journals Structure and Function of the CFTR Chloride Channel

1999 ◽  
Vol 79 (1) ◽  
pp. S23-S45 ◽  
Author(s):  
DAVID N. SHEPPARD ◽  
MICHAEL J. WELSH
Keyword(s):  
Cystic Fibrosis ◽  
Chloride Channel ◽  
Atp Hydrolysis ◽  
Current Knowledge ◽  
Structure And Function ◽  
Binding Domains ◽  
Transporter Family ◽  
Membrane Spanning ◽  
And Function ◽  
R Domain

Sheppard, David N., and Michael J. Welsh. Structure and Function of the CFTR Chloride Channel. Physiol. Rev. 79 , Suppl.: S23–S45, 1999. — The cystic fibrosis transmembrane conductance regulator (CFTR) is a unique member of the ABC transporter family that forms a novel Cl− channel. It is located predominantly in the apical membrane of epithelia where it mediates transepithelial salt and liquid movement. Dysfunction of CFTR causes the genetic disease cystic fibrosis. The CFTR is composed of five domains: two membrane-spanning domains (MSDs), two nucleotide-binding domains (NBDs), and a regulatory (R) domain. Here we review the structure and function of this unique channel, with a focus on how the various domains contribute to channel function. The MSDs form the channel pore, phosphorylation of the R domain determines channel activity, and ATP hydrolysis by the NBDs controls channel gating. Current knowledge of CFTR structure and function may help us understand better its mechanism of action, its role in electrolyte transport, its dysfunction in cystic fibrosis, and its relationship to other ABC transporters.

scholarly journals Molecular pathology of the R117H cystic fibrosis mutation is explained by loss of a hydrogen bond

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Márton A Simon ◽  
László Csanády
Keyword(s):  
Cystic Fibrosis ◽  
Hydrogen Bond ◽  
Molecular Pathology ◽  
Atp Hydrolysis ◽  
Salt Water ◽  
Anion Channel ◽  
Open Probability ◽  
Binding Domains ◽  
State Dependent ◽  
Cftr Mutations

The phosphorylation-activated anion channel CFTR is gated by an ATP hydrolysis cycle at its two cytosolic nucleotide binding domains, and is essential for epithelial salt-water transport. A large number of CFTR mutations cause cystic fibrosis. Since recent breakthrough in targeted pharmacotherapy, CFTR mutants with impaired gating are candidates for stimulation by potentiator drugs. Thus, understanding the molecular pathology of individual mutations has become important. The relatively common R117H mutation affects an extracellular loop, but nevertheless causes a strong gating defect. Here we identify a hydrogen bond between the side chain of arginine 117 and the backbone carbonyl group of glutamate 1124 in the cryo-electronmicroscopic structure of phosphorylated, ATP-bound CFTR. We address the functional relevance of that interaction for CFTR gating using macroscopic and microscopic inside-out patch-clamp recordings. Employing thermodynamic double-mutant cycles, we systematically track gating-state dependent changes in the strength of the R117-E1124 interaction. We find that the H-bond is formed only in the open state, but neither in the short-lived "flickery" nor in the long-lived 'interburst' closed state. Loss of this H-bond explains the strong gating phenotype of the R117H mutant, including robustly shortened burst durations and strongly reduced intraburst open probability. The findings may help targeted potentiator design.

scholarly journals Functional and pharmacological importance of the composite ATP binding site 1 in CFTR chloride channels

2010 ◽  
Author(s):  
◽  
Ming-Feng Tsai
Keyword(s):  
Cystic Fibrosis ◽  
Chloride Channels ◽  
Molecular Model ◽  
Chloride Ion ◽  
Atp Binding ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Atp Binding Site ◽  
Binding Domains ◽  
Opening And Closing

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride ion channel whose defects cause the deadly genetic disease cystic fibrosis (CF). Like other ATP binding cassette (ABC) proteins, CFTR encompasses two cytoplasmic nucleotide binding domains (NBDs). Upon ATP binding, the two NBDs can coalesce into a head-to-tail dimer with ATP buried at two interfacial composite sites (sites 1 and 2). Although evidence suggests that gating of CFTR is mainly controlled by site 2, the role of site 1 remains less understood. I have used pyrophosphate as a probe or adopted a ligand exchange protocol to investigate ATP binding status in site 1 in real time. With these novel approaches, I have identified a “partial” NBD dimer state mediated by an ATP molecule tightly bound in site 1. A molecular model of CFTR gating was then established with opening and closing of CFTR coupled to the formation and partial separation of the NBD dimer. Moreover, I discovered several mutations that enhance ATP binding in site 1 and demonstrated that the activity of CF-associated mutant channels, Î"F508- and G551D-CFTR, can be significantly improved by these mutations, thus providing evidence that site 1 is a potential target for developing pharmaceutical reagents to treat patients with CF.

scholarly journals Catalyst-like modulation of transition states for CFTR channel opening and closing: New stimulation strategy exploits nonequilibrium gating

2014 ◽  
Vol 143 (2) ◽  
pp. 269-287 ◽  
Author(s):  
László Csanády ◽  
Beáta Töröcsik
Keyword(s):  
Cystic Fibrosis ◽  
Ion Channels ◽  
Single Channel ◽  
Transition States ◽  
Chloride Ion ◽  
Open Probability ◽  
Gating Mechanism ◽  
Channel Opening ◽  
The Stability ◽  
Opening And Closing

Cystic fibrosis transmembrane conductance regulator (CFTR) is the chloride ion channel mutated in cystic fibrosis (CF) patients. It is an ATP-binding cassette protein, and its resulting cyclic nonequilibrium gating mechanism sets it apart from most other ion channels. The most common CF mutation (ΔF508) impairs folding of CFTR but also channel gating, reducing open probability (Po). This gating defect must be addressed to effectively treat CF. Combining single-channel and macroscopic current measurements in inside-out patches, we show here that the two effects of 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB) on CFTR, pore block and gating stimulation, are independent, suggesting action at distinct sites. Furthermore, detailed kinetic analysis revealed that NPPB potently increases Po, also of ΔF508 CFTR, by affecting the stability of gating transition states. This finding is unexpected, because for most ion channels, which gate at equilibrium, altering transition-state stabilities has no effect on Po; rather, agonists usually stimulate by stabilizing open states. Our results highlight how for CFTR, because of its unique cyclic mechanism, gating transition states determine Po and offer strategic targets for potentiator compounds to achieve maximal efficacy.

scholarly journals Curcumin Opens Cystic Fibrosis Transmembrane Conductance Regulator Channels by a Novel Mechanism That Requires neither ATP Binding nor Dimerization of the Nucleotide-binding Domains

2006 ◽  
Vol 282 (7) ◽  
pp. 4533-4544 ◽  
Author(s):  
Wei Wang ◽  
Karen Bernard ◽  
Ge Li ◽  
Kevin L. Kirk
Keyword(s):  
Cystic Fibrosis ◽  
Nucleotide Binding ◽  
Salt Transport ◽  
Atp Binding ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
Binding Domains ◽  
Channel Opening ◽  
Cystic Fibrosis Transmembrane ◽  
R Domain

Cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels are essential mediators of salt transport across epithelia. Channel opening normally requires ATP binding to both nucleotide-binding domains (NBDs), probable dimerization of the two NBDs, and phosphorylation of the R domain. How phosphorylation controls channel gating is unknown. Loss-of-function mutations in the CFTR gene cause cystic fibrosis; thus, there is considerable interest in compounds that improve mutant CFTR function. Here we investigated the mechanism by which CFTR is activated by curcumin, a natural compound found in turmeric. Curcumin opened CFTR channels by a novel mechanism that required neither ATP nor the second nucleotide-binding domain (NBD2). Consequently, this compound potently activated CF mutant channels that are defective for the normal ATP-dependent mode of gating (e.g. G551D and W1282X), including channels that lack NBD2. The stimulation of NBD2 deletion mutants by curcumin was strongly inhibited by ATP binding to NBD1, which implicates NBD1 as a plausible activation site. Curcumin activation became irreversible during prolonged exposure to this compound following which persistently activated channels gated dynamically in the absence of any agonist. Although CFTR activation by curcumin required neither ATP binding nor heterodimerization of the two NBDs, it was strongly dependent on prior channel phosphorylation by protein kinase A. Curcumin is a useful functional probe of CFTR gating that opens mutant channels by circumventing the normal requirements for ATP binding and NBD heterodimerization. The phosphorylation dependence of curcumin activation indicates that the R domain can modulate channel opening without affecting ATP binding to the NBDs or their heterodimerization.

Conformational changes opening and closing the CFTR chloride channel: Insights from cysteine scanning mutagenesis

2014 ◽  
Vol 92 (6) ◽  
pp. 481-488 ◽  
Author(s):  
Yassine El Hiani ◽  
Paul Linsdell
Keyword(s):  
Cystic Fibrosis ◽  
Conformational Changes ◽  
Large Family ◽  
Chloride Ion ◽  
Channel Structure ◽  
Patch Clamp Recording ◽  
Binding Domains ◽  
Substituted Cysteine Accessibility ◽  
Cysteine Scanning Mutagenesis ◽  
Opening And Closing

Cystic fibrosis, the most common lethal genetic disease affecting young people in North America, is caused by failure of the chloride ion channel known as CFTR (cystic fibrosis transmembrane conductance regulator). CFTR belongs to the large family of ATP-binding cassette (ABC) membrane transporters. In CFTR, ATP-driven events at the nucleotide-binding domains (NBDs) open and close a gate that controls chloride permeation. However, the conformational changes concomitant with opening and closing of the CFTR gate are unknown. Diverse techniques including substituted cysteine accessibility method, disulfide cross-linking, and patch-clamp recording have been used to explore CFTR channel structure. Here, we consider the architecture of both the open and the closed CFTR channel. We review how CFTR channel structure changes between the closed and the open channel conformations and portray the relative function of both cytoplasmic and vestigial gates during the gating cycle. Understanding how the CFTR channel gates chloride permeation is central for understanding how CFTR defects lead to CF. Such knowledge opens the door for novel ways to maximize CFTR channel activity in a CF setting.

scholarly journals Functional Roles of Nonconserved Structural Segments in CFTR's NH2-terminal Nucleotide Binding Domain

2004 ◽  
Vol 125 (1) ◽  
pp. 43-55 ◽  
Author(s):  
László Csanády ◽  
Kim W. Chan ◽  
Angus C. Nairn ◽  
David C. Gadsby
Keyword(s):  
Cystic Fibrosis ◽  
Conformational Changes ◽  
Single Channel ◽  
Channel Gating ◽  
Essential Element ◽  
Nucleotide Binding ◽  
Transmembrane Conductance Regulator ◽  
Functional Roles ◽  
Binding Domains ◽  
Excised Patches

The cystic fibrosis transmembrane conductance regulator (CFTR), encoded by the gene mutated in cystic fibrosis patients, belongs to the family of ATP-binding cassette (ABC) proteins, but, unlike other members, functions as a chloride channel. CFTR is activated by protein kinase A (PKA)-mediated phosphorylation of multiple sites in its regulatory domain, and gated by binding and hydrolysis of ATP at its two nucleotide binding domains (NBD1, NBD2). The recent crystal structure of NBD1 from mouse CFTR (Lewis, H.A., S.G. Buchanan, S.K. Burley, K. Conners, M. Dickey, M. Dorwart, R. Fowler, X. Gao, W.B. Guggino, W.A. Hendrickson, et al. 2004. EMBO J. 23:282–293) identified two regions absent from structures of all other NBDs determined so far, a “regulatory insertion” (residues 404–435) and a “regulatory extension” (residues 639–670), both positioned to impede formation of the putative NBD1–NBD2 dimer anticipated to occur during channel gating; as both segments appeared highly mobile and both contained consensus PKA sites (serine 422, and serines 660 and 670, respectively), it was suggested that their phosphorylation-linked conformational changes might underlie CFTR channel regulation. To test that suggestion, we coexpressed in Xenopus oocytes CFTR residues 1–414 with residues 433–1480, or residues 1–633 with 668–1480, to yield split CFTR channels (called 414+433 and 633+668) that lack most of the insertion, or extension, respectively. In excised patches, regulation of the resulting CFTR channels by PKA and by ATP was largely normal. Both 414+433 channels and 633+668 channels, as well as 633(S422A)+668 channels (lacking both the extension and the sole PKA consensus site in the insertion), were all shut during exposure to MgATP before addition of PKA, but activated like wild type (WT) upon phosphorylation; this indicates that inhibitory regulation of nonphosphorylated WT channels depends upon neither segment. Detailed kinetic analysis of 414+433 channels revealed intact ATP dependence of single-channel gating kinetics, but slightly shortened open bursts and faster closing from the locked-open state (elicited by ATP plus pyrophosphate or ATP plus AMPPNP). In contrast, 633+668 channel function was indistinguishable from WT at both macroscopic and microscopic levels. We conclude that neither nonconserved segment is an essential element of PKA- or nucleotide-dependent regulation.

scholarly journals Cryo-EM visualization of an active high open probability CFTR ion channel

2018 ◽  
Author(s):  
Jonathan F. Fay ◽  
Luba A. Aleksandrov ◽  
Timothy J. Jensen ◽  
Liying L. Cui ◽  
Joseph N. Kousouros ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Bound States ◽  
Structural Changes ◽  
Large Family ◽  
Anion Channel ◽  
List Type ◽  
Open Probability ◽  
Its Gene ◽  
Functional States ◽  
R Domain

AbstractThe Cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, crucial to epithelial salt and water homeostasis, and defective due to mutations in its gene in patients with cystic fibrosis is a unique member of the large family of ATP-binding cassette transport proteins. Regulation of CFTR channel activity is stringently controlled by phosphorylation and nucleotide binding. Structural changes that underlie transitions between active and inactive functional states are not yet fully understood. Indeed the first 3D structures of dephosphorylated, ATP-free and phosphorylated ATP-bound states were only recently reported. Here we have determined the structure of inactive and active states of a thermally stabilized CFTR with very high channel open probability, confirmed after reconstitution into proteoliposomes. The unique repositioning of the TMHs and R domain density that we observe provide insights into the structural transition between active and inactive functional states of CFTR.HighlightsStructures of thermostabilized avian CFTR in dephosphorylated or phosphorylated forms at 4.3 Å and 6.6 Å resolution, respectively.Conformational differences of transmembrane helices 7 & 8 compared to zebra fish and human CFTR structures reveal an extracellular vestibule that may provide anion access to the pore.R-domain density appears to “plug” the intercellular vestibule in the dephosphorylated avian CFTR cryo-EM map.

scholarly journals Molecular pathology of a cystic fibrosis mutation is explained by loss of a hydrogen bond

2021 ◽  
Author(s):  
Márton A Simon ◽  
LászlÓ Csanády
Keyword(s):  
Cystic Fibrosis ◽  
Hydrogen Bond ◽  
Molecular Pathology ◽  
Atp Hydrolysis ◽  
Salt Water ◽  
Anion Channel ◽  
Open Probability ◽  
Binding Domains ◽  
State Dependent ◽  
Cftr Mutations

The phosphorylation-activated anion channel CFTR is gated by an ATP hydrolysis cycle at its two cytosolic nucleotide binding domains, and is essential for epithelial salt-water transport. A large number of CFTR mutations cause cystic fibrosis. Since recent breakthrough in targeted pharmacotherapy, CFTR mutants with impaired gating are candidates for stimulation by potentiator drugs. Thus, understanding the molecular pathology of individual mutations has become important. The relatively common R117H mutation affects an extracellular loop, but nevertheless causes a strong gating defect. Here we identify a hydrogen bond between the side chain of arginine 117 and the backbone carbonyl group of glutamate 1124 in the cryo-electronmicroscopic structure of phosphorylated, ATP-bound CFTR. We address the functional relevance of that interaction for CFTR gating using macroscopic and microscopic inside-out patch-clamp recordings. Employing thermodynamic double-mutant cycles, we systematically track gating-state dependent changes in the strength of the R117-E1124 interaction. We find that the H-bond is formed only in the open state, but neither in the short-lived "flickery" nor in the long-lived "interburst" closed state. Loss of this H-bond explains the entire gating phenotype of the R117H mutant, including robustly shortened burst durations and strongly reduced intraburst open probability. The findings may help targeted potentiator design.

scholarly journals Structure, Gating, and Regulation of the CFTR Anion Channel

2019 ◽  
Vol 99 (1) ◽  
pp. 707-738 ◽  
Author(s):  
László Csanády ◽  
Paola Vergani ◽  
David C. Gadsby
Keyword(s):  
Cystic Fibrosis ◽  
Molecular Mechanisms ◽  
Anion Channel ◽  
Atp Binding ◽  
Electron Microscopic ◽  
Binding Domains ◽  
Cytosolic Domains ◽  
Cftr Protein ◽  
Atp Binding And Hydrolysis ◽  
R Domain

The cystic fibrosis transmembrane conductance regulator (CFTR) belongs to the ATP binding cassette (ABC) transporter superfamily but functions as an anion channel crucial for salt and water transport across epithelial cells. CFTR dysfunction, because of mutations, causes cystic fibrosis (CF). The anion-selective pore of the CFTR protein is formed by its two transmembrane domains (TMDs) and regulated by its cytosolic domains: two nucleotide binding domains (NBDs) and a regulatory (R) domain. Channel activation requires phosphorylation of the R domain by cAMP–dependent protein kinase (PKA), and pore opening and closing (gating) of phosphorylated channels is driven by ATP binding and hydrolysis at the NBDs. This review summarizes available information on structure and mechanism of the CFTR protein, with a particular focus on atomic-level insight gained from recent cryo-electron microscopic structures and on the molecular mechanisms of channel gating and its regulation. The pharmacological mechanisms of small molecules targeting CFTR’s ion channel function, aimed at treating patients suffering from CF and other diseases, are briefly discussed.

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