ABCMdb

ABCC7 p.Arg347Cys

ClinVar:	c.1039C>T , p.Arg347Cys ? , not provided c.1040G>A , p.Arg347His D , Pathogenic c.1040G>T , p.Arg347Leu D , Pathogenic c.1040G>C , p.Arg347Pro D , Pathogenic
CF databases:	c.1040G>C , p.Arg347Pro D , CF-causing ; CFTR1: This mutation destroys a Hha I restriciton site and creates an NcoI site and occurred in a family diagnosed as PS. The mutation have been identified and analyzed using the SSCP technique. c.1040G>A , p.Arg347His D , CF-causing ; CFTR1: The patient is of Italian origin and carries the [delta]F508 mutation on the other chromosome. Initially we thought this was the same mutation as R347 because it destroys the same hhai site; however, R347H does not create the NcoI site. c.1040G>T , p.Arg347Leu (CFTR1) D , A nucleotide change, G->T at position 1172, was detected leading to R347L. The other chromosome carries a [delta]F508. This mutation was found on one chromosome among 150 CF chromosomes screened. c.1039C>T , p.Arg347Cys (CFTR1) ? , This mutation was identified by DGGE and direct sequencing.
Predicted by SNAP2:	A: D (95%), C: D (95%), D: D (95%), E: D (95%), F: D (95%), G: D (95%), H: D (71%), I: D (95%), K: D (95%), L: D (80%), M: D (95%), N: D (95%), P: D (75%), Q: D (95%), S: D (95%), T: D (95%), V: D (95%), W: D (95%), Y: D (95%),
Predicted by PROVEAN:	A: N, C: D, D: D, E: N, F: D, G: D, H: N, I: D, K: N, L: N, M: N, N: N, P: N, Q: N, S: N, T: N, V: D, W: D, Y: D,

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Publications
[hide] Insight in eukaryotic ABC transporter function by ... FEBS Lett. 2006 Feb 13;580(4):1064-84. Epub 2006 Jan 19. Frelet A, Klein M
Insight in eukaryotic ABC transporter function by mutation analysis.
FEBS Lett. 2006 Feb 13;580(4):1064-84. Epub 2006 Jan 19., 2006-02-13 [PMID:16442101]

Abstract [show]
With regard to structure-function relations of ATP-binding cassette (ABC) transporters several intriguing questions are in the spotlight of active research: Why do functional ABC transporters possess two ATP binding and hydrolysis domains together with two ABC signatures and to what extent are the individual nucleotide-binding domains independent or interacting? Where is the substrate-binding site and how is ATP hydrolysis functionally coupled to the transport process itself? Although much progress has been made in the elucidation of the three-dimensional structures of ABC transporters in the last years by several crystallographic studies including novel models for the nucleotide hydrolysis and translocation catalysis, site-directed mutagenesis as well as the identification of natural mutations is still a major tool to evaluate effects of individual amino acids on the overall function of ABC transporters. Apart from alterations in characteristic sequence such as Walker A, Walker B and the ABC signature other parts of ABC proteins were subject to detailed mutagenesis studies including the substrate-binding site or the regulatory domain of CFTR. In this review, we will give a detailed overview of the mutation analysis reported for selected ABC transporters of the ABCB and ABCC subfamilies, namely HsCFTR/ABCC7, HsSUR/ABCC8,9, HsMRP1/ABCC1, HsMRP2/ABCC2, ScYCF1 and P-glycoprotein (Pgp)/MDR1/ABCB1 and their effects on the function of each protein.

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394 They are positively charged amino acids [171], conserved across species and associated with CF: R334Q/W and R347C/H/L/P. Login to comment

[hide] Cystic fibrosis-associated mutations at arginine 3... J Biol Chem. 1999 Feb 26;274(9):5429-35. Cotten JF, Welsh MJ
Cystic fibrosis-associated mutations at arginine 347 alter the pore architecture of CFTR. Evidence for disruption of a salt bridge.
J Biol Chem. 1999 Feb 26;274(9):5429-35., 1999-02-26 [PMID:10026154]

Abstract [show]
Arginine 347 in the sixth transmembrane domain of cystic fibrosis transmembrane conductance regulator (CFTR) is a site of four cystic fibrosis-associated mutations. To better understand the function of Arg-347 and to learn how mutations at this site disrupt channel activity, we mutated Arg-347 to Asp, Cys, Glu, His, Leu, or Lys and examined single-channel function. Every Arg-347 mutation examined, except R347K, had a destabilizing effect on the pore, causing the channel to flutter between two conductance states. Chloride flow through the larger conductance state was similar to that of wild-type CFTR, suggesting that the residue at position 347 does not interact directly with permeating anions. We hypothesized that Arg-347 stabilizes the channel through an electrostatic interaction with an anionic residue in another transmembrane domain. To test this, we mutated anionic residues (Asp-924, Asp-993, and Glu-1104) to Arg in the context of either R347E or R347D mutations. Interestingly, the D924R mutation complemented R347D, yielding a channel that behaved like wild-type CFTR. These data suggest that Arg-347 plays an important structural role in CFTR, at least in part by forming a salt bridge with Asp-924; cystic fibrosis-associated mutations disrupt this interaction.

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1 To better understand the function of Arg-347 and to learn how mutations at this site disrupt channel activity, we mutated Arg-347 to Asp, Cys, Glu, His, Leu, or Lys and examined single-channel function. Login to comment
12 At least four CF-associated mutations have been identified at position 347 in M6: R347C, R347H, R347L, and R347P, suggesting that Arg-347 is important for CFTR structure and function (13-15).2 Early studies by Sheppard et al. (7) showed that mutation of Arg-347 to proline significantly decreased single-channel conductance with little effect on CFTR trafficking to the plasma membrane. Login to comment
24 To better understand the role of Arg-347 in CFTR structure and function, we examined the effect of mutating Arg-347 to cysteine, aspartic acid, glutamic acid, lysine, and leucine on CFTR conductance. Login to comment
25 We examined the cytosolic pH (pHc)-dependent behavior of CFTR-R347H and that of the other residue 347 mutants both with (R347C, R347D, R347E, and R347K) and without (R347L) a pHc-titratable residue. Login to comment
86 Visual inspection suggested that the lifetimes of OL and OB states were also influenced by the nature of the residue at position 347: R347E and R347H tended to have longer dwell times in the OL and OB states, whereas R347L, R347C, and R347D tended to display shorter dwell times. Login to comment
113 The observable pK (0 mV) for the equilibrium between OL and OB of R347E and R347H were 6.4 and 6.3, respectively. The faster kinetics of R347D, R347C, and R347L made dwell-time analysis for these mutants less reliable. Login to comment
117 Fig. 3B shows that R347C, R347D, and R347L did not reach a peak variance over the range of pHc studied, suggesting that their apparent pK is less than 5.0-5.5. Login to comment
136 B, open-channel current variance of the R347C, R347D, R347L, and R347E mutants versus pHc. Login to comment
210 The Arg-347 residue is targeted by several CF-associated mutations, R347C, R347H, R347L, and R347P (13-15).2 Our data suggest that CF-associated as well as other mutations at residue 347 affect CFTR similarly. Login to comment

[hide] Two mild cystic fibrosis-associated mutations resu... J Biol Chem. 2001 Mar 23;276(12):9045-9. Epub 2000 Dec 15. Clain J, Fritsch J, Lehmann-Che J, Bali M, Arous N, Goossens M, Edelman A, Fanen P
Two mild cystic fibrosis-associated mutations result in severe cystic fibrosis when combined in cis and reveal a residue important for cystic fibrosis transmembrane conductance regulator processing and function.
J Biol Chem. 2001 Mar 23;276(12):9045-9. Epub 2000 Dec 15., 2001-03-23 [PMID:11118444]

Abstract [show]
The number of complex cystic fibrosis transmembrane conductance regulator (CFTR) genotypes identified as having double-mutant alleles with two mutations inherited in cis has been growing. We investigated the structure-function relationships of a severe cystic fibrosis (CF)-associated double mutant (R347H-D979A) to evaluate the contribution of each mild mutation to the phenotype. CFTR mutants expressed in HeLa cells were analyzed for protein biosynthesis and Cl(-) channel activity. Our data show that R347H is associated with mild defective Cl(-) channel activity and that the D979A defect leads to misprocessing. The mutant R347H-D979A combines both defects for a dramatic decrease in Cl(-) current. To decipher the molecular mechanism of this phenotype, single and double mutants with different charge combinations at residues 347 and 979 were constructed as charged residues were involved in this complex genotype. These studies revealed that residue 979, located in the third cytoplasmic loop, is critical for CFTR processing and Cl(-) channel activity highlighting the role of charged residues. These results have also important implications for CF, as they show that two mutations in cis can act in concert to alter dramatically CFTR function contributing to the wide phenotypic variability of CF disease.

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14 At least four CF-associated mutations have been identified in isolation at position 347 (R347C, R347H, R347L, and R347P) and two at position 979 (D979A and D979V), suggesting that Arg-347 and Asp-979 are important for CFTR structure and/or function. Login to comment

[hide] CFTR: covalent and noncovalent modification sugges... J Gen Physiol. 2001 Oct;118(4):407-31. Smith SS, Liu X, Zhang ZR, Sun F, Kriewall TE, McCarty NA, Dawson DC
CFTR: covalent and noncovalent modification suggests a role for fixed charges in anion conduction.
J Gen Physiol. 2001 Oct;118(4):407-31., [PMID:11585852]

Abstract [show]
The goal of the experiments described here was to explore the possible role of fixed charges in determining the conduction properties of CFTR. We focused on transmembrane segment 6 (TM6) which contains four basic residues (R334, K335, R347, and R352) that would be predicted, on the basis of their positions in the primary structure, to span TM6 from near the extracellular (R334, K335) to near the intracellular (R347, R352) end. Cysteines substituted at positions 334 and 335 were readily accessible to thiol reagents, whereas those at positions 347 and 352 were either not accessible or lacked significant functional consequences when modified. The charge at positions 334 and 335 was an important determinant of CFTR channel function. Charge changes at position 334--brought about by covalent modification of engineered cysteine residues, pH titration of cysteine and histidine residues, and amino acid substitution--produced similar effects on macroscopic conductance and the shape of the I-V plot. The effect of charge changes at position 334 on conduction properties could be described by electrodiffusion or rate-theory models in which the charge on this residue lies in an external vestibule of the pore where it functions to increase the concentration of Cl adjacent to the rate-limiting portion of the conduction path. Covalent modification of R334C CFTR increased single-channel conductance determined in detached patches, but did not alter open probability. The results are consistent with the hypothesis that in wild-type CFTR, R334 occupies a position where its charge can influence the distribution of anions near the mouth of the pore.

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25 R347C and R352C were gifts of M. Akabas (Albert Einstein College of Medicine, Bronx, NY) and used in their parent vector, pMN. Login to comment
107 The Function of R334C and K335C CFTR Was Modified by External MTSES or MTSET but the Function of R347C and R352C CFTR Was Not Modified by these Polar Thiol Reagents Fig. 3 summarizes the results of experiments in which MTSES, MTSET, or MTSEA (100 ␮M-10 mM) were added to the solution bathing oocytes expressing wt, R334C, K335C, R347C, or R352C CFTR. Login to comment
122 Shown in Fig. 4 is a representative experiment in which an oocyte expressing R347C CFTR was exposed to MTS reagents. Login to comment
124 The experiments were repeated with each of the compounds individually, both with and without prior exposure to 2-ME and in no case were we able to detect an effect on the function of R347C CFTR. Login to comment
125 Cheung and Akabas (1996) initially reported that there was a ‫%05ف‬ decrease in the normalized current (@ -100 mV) after exposure of oocytes expressing R347C CFTR to 10 mM MTSES, 1 mM MTSET or 2.5 mM MTSEA. Login to comment
126 However, in the course of subsequent studies by Cheung and Akabas (1997), it was discovered that the R347C construct had a substantial deletion. Login to comment
127 MTSES or MTSET were reported as not reacting with the full-length R347C CFTR, and MTSEA was reported to cause a 19% inhibition. Login to comment
133 Comparison of the effects of MTSES, MTSET, and MTSEA on the conductance of oocytes expressing R334C, K335C, R347C, or R352C CFTR. Login to comment
137 MTS reagents did not discernibly alter the function of R347C CFTR expressed in oocytes. Login to comment

[hide] DHPLC screening of cystic fibrosis gene mutations. Hum Mutat. 2002 Apr;19(4):374-83. Ravnik-Glavac M, Atkinson A, Glavac D, Dean M
DHPLC screening of cystic fibrosis gene mutations.
Hum Mutat. 2002 Apr;19(4):374-83., [PMID:11933191]

Abstract [show]
Denaturing high performance liquid chromatography (DHPLC) using ion-pairing reverse phase chromatography (IPRPC) columns is a technique for the screening of gene mutations. In order to evaluate the potential utility of this assay method in a clinical laboratory setting, we subjected the PCR products of 73 CF patients known to bear CFTR mutations to this analytic technique. We used thermal denaturation profile parameters specified by the MELT program tool, made available by Stanford University. Using this strategy, we determined an initial analytic sensitivity of 90.4% for any of 73 known CFTR mutations. Most of the mutations not detected by DHPLC under these conditions are alpha-substitutions. This information may eventually help to improve the MELT algorithm. Increasing column denaturation temperatures for one or two degrees above those recommended by the MELT program allowed 100% detection of CFTR mutations tested. By comparing DHPLC methodology used in this study with the recently reported study based on Wavemaker 3.4.4 software (Transgenomic, Omaha, NE) [Le Marechal et al., 2001) and with previous SSCP analysis of CFTR mutations [Ravnik-Glavac et al., 1994] we emphasized differences and similarities in order to refine the DHPLC system and discuss the relationship to the alternative approaches. We conclude that the DHPLC method, under optimized conditions, is highly accurate, rapid, and efficient in detecting mutations in the CFTR gene and may find high utility in screening individuals for CFTR mutations. Hum Mutat 19:374-383, 2002. Published 2002 Wiley-Liss, Inc.

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No. Sentence Comment
42 The following mutations have been studied: exon 3: W57G, R74W, R75Q, G85E, 394delTT, 405+ 1G>A; exon 4: E92X, P99L, 441delA, 444delA, 457TAT>G, D110H, R117C, R117H, A120T, 541delC, 544delCA, Q151X, 621+1G>T, 662- 2A>C; exon 7: 1078delT, F331L, R334W, I336K, R347C, R347P, A349V, R352Q, 1221delCT; exon 10: S492F, Q493X, 1609delCA, deltaI507, deltaF508; exon 11: G542X, S549N, G551D, R553X, A559T, R560K, R560T; exon 13: K716X, Q685X, G628R, L719X; exon 17b: H1054D, G1061R, 3320ins5, R1066H, R1066L, R1070Q, 3359delCT, L1077P, H1085R, Y1092X; exon 19: R1162X, 3659delC, 3662delA, 3667del4, 3737delA, I1234V, S1235R, 3849G>A; exon 20: 3860ins31,S1255X,3898insC,3905insT,D1270N, W1282X, Q1291R; and exon 21: N1303H, N1303K, W1316X. Login to comment
100 Optimization of Temperature (OTm) for Undetected Mutations Nucleotide RTm OTm Exon Mutation change (°C) (°C) 3 W57G 301 T>G 55 57 R74W 352 C>T 55 57 7 R334W 1132 C>T 58 60 R347C 1171 C>T 58 60 10 Q493X 609 C>T 55 56 20 3905 insT 3905 insT 55 56 D1270N 3940 G>A 57 58 RTm, recommended temperature by the MELT program; OTm, optimized temperature. Login to comment

[hide] Pharmacological induction of CFTR function in pati... Pediatr Pulmonol. 2005 Sep;40(3):183-96. Kerem E
Pharmacological induction of CFTR function in patients with cystic fibrosis: mutation-specific therapy.
Pediatr Pulmonol. 2005 Sep;40(3):183-96., [PMID:15880796]

Abstract [show]
CFTR mutations cause defects of CFTR protein production and function by different molecular mechanisms. Mutations can be classified according to the mechanisms by which they disrupt CFTR function. This understanding of the different molecular mechanisms of CFTR dysfunction provides the scientific basis for the development of targeted drugs for mutation-specific therapy of cystic fibrosis (CF). Class I mutations are nonsense mutations that result in the presence of a premature stop codon that leads to the production of unstable mRNA, or the release from the ribosome of a short, truncated protein that is not functional. Aminoglycoside antibiotics can suppress premature termination codons by disrupting translational fidelity and allowing the incorporation of an amino acid, thus permitting translation to continue to the normal termination of the transcript. Class II mutations cause impairment of CFTR processing and folding in the Golgi. As a result, the mutant CFTR is retained in the endoplasmic reticulum (ER) and eventually targeted for degradation by the quality control mechanisms. Chemical and molecular chaperones such as sodium-4-phenylbutyrate can stabilize protein structure, and allow it to escape from degradation in the ER and be transported to the cell membrane. Class III mutations disrupt the function of the regulatory domain. CFTR is resistant to phosphorylation or adenosine tri-phosphate (ATP) binding. CFTR activators such as alkylxanthines (CPX) and the flavonoid genistein can overcome affected ATP binding through direct binding to a nucleotide binding fold. In patients carrying class IV mutations, phosphorylation of CFTR results in reduced chloride transport. Increases in the overall cell surface content of these mutants might overcome the relative reduction in conductance. Alternatively, restoring native chloride pore characteristics pharmacologically might be effective. Activators of CFTR at the plasma membrane may function by promoting CFTR phosphorylation, by blocking CFTR dephosphorylation, by interacting directly with CFTR, and/or by modulation of CFTR protein-protein interactions. Class V mutations affect the splicing machinery and generate both aberrantly and correctly spliced transcripts, the levels of which vary among different patients and among different organs of the same patient. Splicing factors that promote exon inclusion or factors that promote exon skipping can promote increases of correctly spliced transcripts, depending on the molecular defect. Inconsistent results were reported regarding the required level of corrected or mutated CFTR that had to be reached in order to achieve normal function.

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No. Sentence Comment
58 C-D565G II DF508 D1507 S549R S549I S549N S549R S945D S945L H1054D G1061R L1065P R1066C R1066M L1077P H1085R N1303K G85E III G551D S492F V520F R553G R560T R560S Y569D IV R117H, R117C, R117P, R117L D1152H, L88S, G91R, E92K, Q98R, P205S, L206W, L227R, F311L, G314E, R334W, R334Q, I336K, T338I, L346P, R347C, R347H, R347L, R347P, L927P, R1070W, R1070Q V 3849 þ 10 kb C ! Login to comment

[hide] Conformational changes in a pore-lining helix coup... J Biol Chem. 2008 Feb 22;283(8):4957-66. Epub 2007 Dec 3. Beck EJ, Yang Y, Yaemsiri S, Raghuram V
Conformational changes in a pore-lining helix coupled to cystic fibrosis transmembrane conductance regulator channel gating.
J Biol Chem. 2008 Feb 22;283(8):4957-66. Epub 2007 Dec 3., 2008-02-22 [PMID:18056267]

Abstract [show]
Cystic fibrosis transmembrane conductance regulator (CFTR), the protein dysfunctional in cystic fibrosis, is unique among ATP-binding cassette transporters in that it functions as an ion channel. In CFTR, ATP binding opens the channel, and its subsequent hydrolysis causes channel closure. We studied the conformational changes in the pore-lining sixth transmembrane segment upon ATP binding by measuring state-dependent changes in accessibility of substituted cysteines to methanethiosulfonate reagents. Modification rates of three residues (resides 331, 333, and 335) near the extracellular side were 10-1000-fold slower in the open state than in the closed state. Introduction of a charged residue by chemical modification at two of these positions (resides 331 and 333) affected CFTR single-channel gating. In contrast, modifications of pore-lining residues 334 and 338 were not state-dependent. Our results suggest that ATP binding induces a modest conformational change in the sixth transmembrane segment, and this conformational change is coupled to the gating mechanism that regulates ion conduction. These results may establish a structural basis of gating involving the dynamic rearrangement of transmembrane domains necessary for vectorial transport of substrates in ATP-binding cassette transporters.

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100 The oocytes 750 500 250 0 µS 180012006000 s IBMX MTSEA Cd 2+ DTT 200 100 0 µS 180012006000 s IBMX DTT Cd 2+ MTSEA A B C -100 -80 -60 -40 -20 0 20 40 % Change in conductance Y325C A326C L327C I328C K329C G330C I331C I332C L333C R334C K335C I336C F337C T338C T339C I340C S341C F342C WT I344C V345C R347C M348C A349C V350C T351C Q353C * * * * * Cd 2+ 1mM MTSEA 1mM D FIGURE 1. Login to comment
218 Finally, the MTSEA reactivity was restricted to only five of twenty-six residues in and flanking TM6 in our study, whereas in the earlier study, residues F337C, S341C, I344C, R347C, T351C, R352C, and Q353C were also shown to be accessible to MTS reagents. Login to comment
220 However, our observations on the accessibility of R334C, K335C, and T338C and the inaccessibility of R347C are consistent with other studies (10, 11). Login to comment

[hide] Evidence for direct CFTR inhibition by CFTR(inh)-1... Biochem J. 2008 Jul 1;413(1):135-42. Caci E, Caputo A, Hinzpeter A, Arous N, Fanen P, Sonawane N, Verkman AS, Ravazzolo R, Zegarra-Moran O, Galietta LJ
Evidence for direct CFTR inhibition by CFTR(inh)-172 based on Arg347 mutagenesis.
Biochem J. 2008 Jul 1;413(1):135-42., 2008-07-01 [PMID:18366345]

Abstract [show]
CFTR (cystic fibrosis transmembrane conductance regulator) is an epithelial Cl- channel inhibited with high affinity and selectivity by the thiazolidinone compound CFTR(inh)-172. In the present study, we provide evidence that CFTR(inh)-172 acts directly on the CFTR. We introduced mutations in amino acid residues of the sixth transmembrane helix of the CFTR protein, a domain that has an important role in the formation of the channel pore. Basic and hydrophilic amino acids at positions 334-352 were replaced with alanine residues and the sensitivity to CFTR(inh)-172 was assessed using functional assays. We found that an arginine-to-alanine change at position 347 reduced the inhibitory potency of CFTR(inh)-172 by 20-30-fold. Mutagenesis of Arg347 to other amino acids also decreased the inhibitory potency, with aspartate producing near total loss of CFTR(inh)-172 activity. The results of the present study provide evidence that CFTR(inh)-172 interacts directly with CFTR, and that Arg347 is important for the interaction.

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127 CFTR form CFTRinh-172 Ki (μM) Hill coefficient I- influx (mM/s) n Wild-type 1.32 + - 0.25 1.03 + - 0.07 0.1336 + - 0.0107 10 S341A 0.57 + - 0.17 1.21 + - 0.37 0.0297 + - 0.0064 4 T338A 3.20 + - 0.86 1.13 + - 0.20 0.1260 + - 0.0225 4 R347A 44.98 + - 4.71** 0.91 + - 0.04 0.1288 + - 0.0154 7 R334A 2.39 + - 0.74 0.93 + - 017 0.0313 + - 0.062 4 A349S 1.23 + - 0.41 1.11 + - 0.25 0.1500 + - 0.011 4 R347D >50 Not determined 0.1160 + - 0.0136 7 R347D/D924R >50 Not determined 0.1008 + - 0.0504 4 R347C >50 Not determined 0.1437 + - 0.0123 4 Mock 0.003 + - 0.001 10 introduced a mutation at position 349 (an alanine residue replaced by a serine residue). Login to comment
132 As found for R347A, the mutants R347C and R347D also showed a normal rate of anion transport but altered sensitivity to CFTRinh-172 (Figures 2A and 2B). Login to comment

[hide] Mutations at arginine 352 alter the pore architect... J Membr Biol. 2008 Mar;222(2):91-106. Epub 2008 Apr 18. Cui G, Zhang ZR, O'Brien AR, Song B, McCarty NA
Mutations at arginine 352 alter the pore architecture of CFTR.
J Membr Biol. 2008 Mar;222(2):91-106. Epub 2008 Apr 18., [PMID:18421494]

Abstract [show]
Arginine 352 (R352) in the sixth transmembrane domain of the cystic fibrosis transmembrane conductance regulator (CFTR) previously was reported to form an anion/cation selectivity filter and to provide positive charge in the intracellular vestibule. However, mutations at this site have nonspecific effects, such as inducing susceptibility of endogenous cysteines to chemical modification. We hypothesized that R352 stabilizes channel structure and that charge-destroying mutations at this site disrupt pore architecture, with multiple consequences. We tested the effects of mutations at R352 on conductance, anion selectivity and block by the sulfonylurea drug glipizide, using recordings of wild-type and mutant channels. Charge-altering mutations at R352 destabilized the open state and altered both selectivity and block. In contrast, R352K-CFTR was similar to wild-type. Full conductance state amplitude was similar to that of wild-type CFTR in all mutants except R352E, suggesting that R352 does not itself form an anion coordination site. In an attempt to identify an acidic residue that may interact with R352, we found that permeation properties were similarly affected by charge-reversing mutations at D993. Wild-type-like properties were rescued in R352E/D993R-CFTR, suggesting that R352 and D993 in the wild-type channel may interact to stabilize pore architecture. Finally, R352A-CFTR was sensitive to modification by externally applied MTSEA+, while wild-type and R352E/D993R-CFTR were not. These data suggest that R352 plays an important structural role in CFTR, perhaps reflecting its involvement in forming a salt bridge with residue D993.

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98 Previous studies showed that both R347C and R352C either were not accessible to membrane-impermeant MTS reagents (methanethiosulfonate ethyltrimethylammonium [MTSET+ ] or methanethiosulfonate ethylsulfonate [MTSES- ]) applied to the extracellular solution or lacked significant functional consequences when modified; this suggested that both sites either were at the predicted cytoplasmic end of the pore, and therefore cytoplasmic to the narrow region, or were not pore-facing residues (Smith et al. 2001). Login to comment

[hide] Cystic fibrosis transmembrane conductance regulato... Biochemistry. 2009 Oct 27;48(42):10078-88. Alexander C, Ivetac A, Liu X, Norimatsu Y, Serrano JR, Landstrom A, Sansom M, Dawson DC
Cystic fibrosis transmembrane conductance regulator: using differential reactivity toward channel-permeant and channel-impermeant thiol-reactive probes to test a molecular model for the pore.
Biochemistry. 2009 Oct 27;48(42):10078-88., 2009-10-27 [PMID:19754156]

Abstract [show]
The sixth transmembrane segment (TM6) of the CFTR chloride channel has been intensively investigated. The effects of amino acid substitutions and chemical modification of engineered cysteines (cysteine scanning) on channel properties strongly suggest that TM6 is a key component of the anion-conducting pore, but previous cysteine-scanning studies of TM6 have produced conflicting results. Our aim was to resolve these conflicts by combining a screening strategy based on multiple, thiol-directed probes with molecular modeling of the pore. CFTR constructs were screened for reactivity toward both channel-permeant and channel-impermeant thiol-directed reagents, and patterns of reactivity in TM6 were mapped onto two new, molecular models of the CFTR pore: one based on homology modeling using Sav1866 as the template and a second derived from the first by molecular dynamics simulation. Comparison of the pattern of cysteine reactivity with model predictions suggests that nonreactive sites are those where the TM6 side chains are occluded by other TMs. Reactive sites, in contrast, are generally situated such that the respective amino acid side chains either project into the predicted pore or lie within a predicted extracellular loop. Sites where engineered cysteines react with both channel-permeant and channel-impermeant probes occupy the outermost extent of TM6 or the predicted TM5-6 loop. Sites where cysteine reactivity is limited to channel-permeant probes occupy more cytoplasmic locations. The results provide an initial validation of two, new molecular models for CFTR and suggest that molecular dynamics simulation will be a useful tool for unraveling the structural basis of anion conduction by CFTR.

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52 We proposed that these spontaneous changes, that are not seen in either wt or Cys-less CFTR, reflect the coordination of trace Table 1: Percent Change in Oocyte Conductance in the Presence of Compounda MTSETþ MTSES- [Ag(CN)2]- [Au(CN)2]- G330C O O O O I331C -51.6 ( 6.3 -28.9 ( 2.1 -63.1 ( 8.8 O I332C O O O O L333C -58.5 ( 4.8 -47.5 ( 7.6 -83.1 ( 2.2 O R334C þ76.9 ( 11.3 -84.4 ( 1.5 -67.4 ( 7.4 -41.4 ( 3.1 K335C þ10.7 ( 2.4 -37.3 ( 1.5 -29.1 ( 6.4 -54.6 ( 4.7 I336C -54.4 ( 7.9 -75.0 ( 0.6 -81.2 ( 10.5 O F337C O O -89.6 ( 1.9 -90.1 ( 1.3 T338C -37.1 ( 3.3 -85.4 ( 2.5 -75.0 ( 5.2 -88.3 ( 1.6 T339C O O -24.5 ( 7.2 O I340C O O -93.8 ( 1.0 O S341C O O -49.3 ( 4.8 O F342C O O -84.7 ( 1.8 O C343 O O O O I344C O O -66.9 ( 9.3 -77.9 ( 2.1 V345C O O -49.1 ( 9.3 O L346C O O O O R347C O O O O M348C O O -47.9 ( 8.8 -50.1 ( 3.3 A349C O O -19.0 ( 2.0 O V350C O O O O T351C O O O O R352C O O -77.5 ( 1.3 O Q353C O O -72.6 ( 4.5 -76.7 ( 2.8 a Values are means ( SE of three or more oocytes. Login to comment
281 Note the lack of consistent results reported for F337C, S341C, I344C, R347C, T351C, R352C, and Q353C (shaded). Login to comment

[hide] Dual roles of the sixth transmembrane segment of t... J Gen Physiol. 2010 Sep;136(3):293-309. Bai Y, Li M, Hwang TC
Dual roles of the sixth transmembrane segment of the CFTR chloride channel in gating and permeation.
J Gen Physiol. 2010 Sep;136(3):293-309., [PMID:20805575]

Abstract [show]
Cystic fibrosis transmembrane conductance regulator (CFTR) is the only member of the adenosine triphosphate-binding cassette (ABC) transporter superfamily that functions as a chloride channel. Previous work has suggested that the external side of the sixth transmembrane segment (TM6) plays an important role in governing chloride permeation, but the function of the internal side remains relatively obscure. Here, on a cysless background, we performed cysteine-scanning mutagenesis and modification to screen the entire TM6 with intracellularly applied thiol-specific methanethiosulfonate reagents. Single-channel amplitude was reduced in seven cysteine-substituted mutants, suggesting a role of these residues in maintaining the pore structure for normal ion permeation. The reactivity pattern of differently charged reagents suggests that the cytoplasmic part of TM6 assumes a secondary structure of an alpha helix, and that reactive sites (341, 344, 345, 348, 352, and 353) reside in two neighboring faces of the helix. Although, as expected, modification by negatively charged reagents inhibits anion permeation, interestingly, modification by positively charged reagents of cysteine thiolates on one face (344, 348, and 352) of the helix affects gating. For I344C and M348C, the open time was prolonged and the closed time was shortened after modification, suggesting that depositions of positive charges at these positions stabilize the open state but destabilize the closed state. For R352C, which exhibited reduced single-channel amplitude, modifications by two positively charged reagents with different chemical properties completely restored the single-channel amplitude but had distinct effects on both the open time and the closed time. These results corroborate the idea that a helix rotation of TM6, which has been proposed to be part of the molecular motions during transport cycles in other ABC transporters, is associated with gating of the CFTR pore.

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82 7 out of the 25 mutant channels exhibited a reduced single-channel current amplitude, including, from extracellular to intracellular, R334C, K335C, F337C, T338C, S341C, R347C, and R352C (Fig. 2). Login to comment
83 The single-channel amplitude is unsolv- able in the cases of R334C, S341C, R347C, and R352C due to a limited bandwidth, whereas it is 0.2-0.3 pA for Data analysis Current traces containing fewer than three channel opening levels and lasting for >1 min were selected for single-channel kinetic analysis using a program developed by L. Csanády (2000). Login to comment
345 Indeed, in the current study, R347C is insensitive to either MTSET or MTSES. Login to comment

[hide] Structure and function of the CFTR chloride channe... Physiol Rev. 1999 Jan;79(1 Suppl):S23-45. Sheppard DN, Welsh MJ
Structure and function of the CFTR chloride channel.
Physiol Rev. 1999 Jan;79(1 Suppl):S23-45., [PMID:9922375]

Abstract [show]
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.

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98 These residues are conserved across spe- because I0 blocks the pore, it appears that I0 is less per- cies, and two are the site of mutations associated with meable under some conditions, including the whole cell CF: R334Q/W and R347C/H/L/P (142). Login to comment

[hide] CFTR: mechanism of anion conduction. Physiol Rev. 1999 Jan;79(1 Suppl):S47-75. Dawson DC, Smith SS, Mansoura MK
CFTR: mechanism of anion conduction.
Physiol Rev. 1999 Jan;79(1 Suppl):S47-75., [PMID:9922376]

Abstract [show]
CFTR: Mechanism of Anion Conduction. Physiol. Rev. 79, Suppl.: S47-S75, 1999. - The purpose of this review is to collect together the results of recent investigations of anion conductance by the cystic fibrosis transmembrane conductance regulator along with some of the basic background that is a prerequisite for developing some physical picture of the conduction process. The review begins with an introduction to the concepts of permeability and conductance and the Nernst-Planck and rate theory models that are used to interpret these parameters. Some of the physical forces that impinge on anion conductance are considered in the context of permeability selectivity and anion binding to proteins. Probes of the conduction process are considered, particularly permeant anions that bind tightly within the pore and block anion flow. Finally, structure-function studies are reviewed in the context of some predictions for the origin of pore properties.

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480 Three residues, R334C, R347C, neered cysteines can react with the charged MTS reagents in the pore interior. The potential flaw in this assumptionand R352C, were also inhibited by the larger cation MTSET0 . Login to comment

[hide] Locating the anion-selectivity filter of the cysti... J Gen Physiol. 1997 Mar;109(3):289-99. Cheung M, Akabas MH
Locating the anion-selectivity filter of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel.
J Gen Physiol. 1997 Mar;109(3):289-99., [PMID:9089437]

Abstract [show]
The cystic fibrosis transmembrane conductance regulator forms an anion-selective channel; the site and mechanism of charge selectivity is unknown. We previously reported that cysteines substituted, one at a time, for Ile331, Leu333, Arg334, Lys335, Phe337, Ser341, Ile344, Arg347, Thr351, Arg352, and Gln353, in and flanking the sixth membrane-spanning segment (M6), reacted with charged, sulfhydryl-specific, methanethiosulfonate (MTS) reagents. We inferred that these residues are on the water-accessible surface of the protein and may line the ion channel. We have now measured the voltage-dependence of the reaction rates of the MTS reagents with the accessible, engineering cysteines. By comparing the reaction rates of negatively and positively charged MTS reagents with these cysteines, we measured the extent of anion selectivity from the extracellular end of the channel to eight of the accessible residues. We show that the major site determining anion vs. cation selectivity is near the cytoplasmic end of the channel; it favors anions by approximately 25-fold and may involve the residues Arg347 and Arg 352. From the voltage dependence of the reaction rates, we calculated the electrical distance to the accessible residues. For the residues from Leu333 to Ser341 the electrical distance is not significantly different than zero; it is significantly different than zero for the residues Thr351 to Gln353. The maximum electrical distance measured was 0.6 suggesting that the channel extends more cytoplasmically and may include residues flanking the cytoplasmic end of the M6 segment. Furthermore, the electrical distance calculations indicate that R352C is closer to the extracellular end of the channel than either of the adjacent residues. We speculate that the cytoplasmic end of the M6 segment may loop back into the channel narrowing the lumen and thereby forming both the major resistance to current flow and the anion-selectivity filter.

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107 We did not measure the reaction rate constants for the most extracellular residue, I331C, because we thought that it was unlikely that the reaction rates would be voltage dependent given the absence of voltage dependence at the adjacent, more cytoplasmic residues. We also did not measure the reaction rate constants for the mutants I344C and R347C because, although MTSEAϩ reacted with these residues, MTSES- and MTSETϩ did not react with these k ψ( )( )ln k Ψ 0=( )( ) zFδ RT/( )-ln ψ= t a b l e i Second-order Rate Constants for the Reaction of the MTS Reagents with the Water-exposed Cysteine Mutants k ES (M-1s-1) k EA (M-1s-1) k ET (M-1s-1) mutant -25 mV -50 mV -75 mV -25 mV -50 mV -75 mV -25 mV -50 mV -75 mV L333C 71 Ϯ 3(3) 71 Ϯ 20(2) 71 Ϯ 23(3) 320 Ϯ 89(2) 320 Ϯ 128(2) 333 Ϯ 139(3) 952 Ϯ 136(2) 1,000 Ϯ 350(2) 1,053 Ϯ 443(2) R334C 48 Ϯ 14(2) 48 Ϯ 6(3) 44 Ϯ 8(4) 145 Ϯ 32(2) 163 Ϯ 7(2) 182 Ϯ 21(3) 444 Ϯ 49(2) 454 Ϯ 124(2) 588 Ϯ 95(3) K335C 36 Ϯ 20(3) 23 Ϯ 11(3) 27 Ϯ 16(3) 222 Ϯ 80(3) 121 Ϯ 51(4) 107 Ϯ 30(3) 217 Ϯ 111(3) 235 Ϯ 28(3) 217 Ϯ 95(4) F337C 91 Ϯ 17(2) 80 Ϯ 22(3) 71 Ϯ 20(4) 222 Ϯ 74(2) 222 Ϯ 86(3) 285 Ϯ 81(3) 740 Ϯ 246(3) 740 Ϯ 82(2) 714 Ϯ 51(2) S341C 56 Ϯ 18(3) 56 Ϯ 40(2) 43 Ϯ 12(3) 93 Ϯ 6(3) 110 Ϯ 22(3) 138 Ϯ 34(3) 690 Ϯ 356(3) 556 Ϯ 246(3) 800 Ϯ 224(4) T351C 100 Ϯ 25(5) 57 Ϯ 6(3) 26 Ϯ 9(6) 146 Ϯ 30(4) 195 Ϯ 42(4) 296 Ϯ 18(3) 308 Ϯ 47(10) 392 Ϯ 78(6) 769 Ϯ 89(5) R352C 42 Ϯ 4(3) 26 Ϯ 4(5) 21 Ϯ 6(4) 105 Ϯ 76(3) 137 Ϯ 46(3) 205 Ϯ 58(2) 417 Ϯ 138(4) 800 Ϯ 128(2) 952 Ϯ 408(2) Q353C 125 Ϯ 23(4) 51 Ϯ 12(4) 42 Ϯ 8(4) 83 Ϯ 24(4) 116 Ϯ 42(4) 160 Ϯ 92(3) 189 Ϯ 48(6) 220 Ϯ 48(3) 625 Ϯ 273(4) residues and therefore we could not determine the charge selectivity at these positions.2 The reaction rate constants that we have measured are between 10-and 500-fold slower than the rates of reaction with sulfhydryls in free solution (Table II) (Stauffer and Karlin, 1994). Login to comment
120 2In the course of these experiments we discovered that the R347C construct that we had used previously contained a large truncation, deleting most of the R-domain to the COOH terminus. Login to comment
121 In the full length CFTR construct the R347C mutant is accessible to MTSEAϩ which causes 19% inhibition, however, MTSES- and MTSETϩ do not react with this mutant. Login to comment

[hide] Disulphonic stilbene block of cystic fibrosis tran... J Physiol. 1996 Nov 1;496 ( Pt 3):687-93. Linsdell P, Hanrahan JW
Disulphonic stilbene block of cystic fibrosis transmembrane conductance regulator Cl- channels expressed in a mammalian cell line and its regulation by a critical pore residue.
J Physiol. 1996 Nov 1;496 ( Pt 3):687-93., [PMID:8930836]

Abstract [show]
1. The disulphonic stilbenes 4,4'-dinitrostilbene-2,2'-disulphonic acid (DNDS) and 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS) were shown to cause a voltage-dependent inhibition of macroscopic cystic fibrosis transmembrane conductance regulator (CFTR) Cl- currents expressed in baby hamster kidney cells when applied to the cytoplasmic face of the membrane. These compounds are known to be relatively ineffective at blocking CFTR from the extracellular side of the membrane. 2. Mutation of a positively charged arginine, previously suggested to be located in the channel pore (R347), to a negatively charged aspartate significantly reduced the affinity of block by both DNDS and DIDS, suggesting that this residue contributes to the binding site for disulphonic stilbenes. 3. It is suggested that the CFTR Cl- channel may contain a relatively large inner vestibule in which a number of large anions bind and block Cl- permeation. Arginine 347 may be involved in anion binding within this region.

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102 Since MTSET reacts covalently with cysteine residues, a very low rate of MTSET permeation would presumably be sufficient to block cysteine-substitutecl forms of CFTR such as R347C and R352C, whereas a similarly low rate of permeation byv a reversible blocker such as gluconate may not affect Cl- permeation. Login to comment

[hide] Identification of cystic fibrosis transmembrane co... Biophys J. 1996 Jun;70(6):2688-95. Cheung M, Akabas MH
Identification of cystic fibrosis transmembrane conductance regulator channel-lining residues in and flanking the M6 membrane-spanning segment.
Biophys J. 1996 Jun;70(6):2688-95., [PMID:8744306]

Abstract [show]
The cystic fibrosis transmembrane conductance regulator (CFTR) forms a chloride channel that is regulated by phosphorylation and ATP binding. Work by others suggested that some residues in the sixth transmembrane segment (M6) might be exposed in the channel and play a role in ion conduction and selectivity. To identify the residues in M6 that are exposed in the channel and the secondary structure of M6, we used the substituted cysteine accessibility method. We mutated to cysteine, one at a time, 24 consecutive residues in and flanking the M6 segment and expressed these mutants in Xenopus oocytes. We determined the accessibility of the engineered cysteines to charged, lipophobic, sulfhydryl-specific methanethiosulfonate (MTS) reagents applied extracellularly. The cysteines substituted for Ile331, Leu333, Arg334, Lys335, Phe337, Ser341, Ile344, Arg347, Thr351, Arg352, and Gln353 reacted with the MTS reagents, and we infer that they are exposed on the water-accessible surface of the protein. From the pattern of the exposed residues we infer that the secondary structure of the M6 segment includes both alpha-helical and extended regions. The diameter of the channel from the extracellular end to the level of Gln353 must be at least 6 A to allow the MTS reagents to reach these residues.

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86 The peak current at -100 mV was -7117 ± 511 nA for the wild type, and ranged from -1709 ± 124 nA for the R347C mutant to -7709 + 700 nA for the T339C mutant (Fig. 2 A). Login to comment
91 Effects of MTS reagents on wild-type cysteines RESULTS in CFTR To identify the residues in and flanking the M6 membrane-spanning segment that are on the water-exposed surface of As reported previously (Akabas et al., 1994b), extracellular applications of the MTS reagents to Xenopus oocytes ex- L2j K329C L. _J *G330C 1331C 1332C L333C R334C K335C 1336C F337C T338C T339C 1340C S341C T342C C343,WT 1344C V345C L346C R347C M348C A349C V350C T351C R352C Q353C 0 2000 4000 6000 8000 0 25 50 PEAK CURRENTS (nA) TIME TO REACH PLATEAU (min) FIGURE 2 Peak CFTR-induced currents and time to reach the plateau current after stimulation with cAMP-activating reagents for 24 cysteine-substitution mutants and wild-type CFTR. Login to comment
99 .0 %0-0 0 10 20 30 40 50 MTSET' d]I 0-0 cAMP 0 0 0 10 20 30 40 50 Time (min) FIGURE 3 Effect of the MTS reagents on the CFTR-induced current in oocytes expressing the R347C mutant. Login to comment
109 Accessibility of substituted cysteines to MTSES- A 1-min application of 10 mM MTSES- significantly inhibited the CFIR-induced currents of 9 of the 24 cysteine-substituted mutants (Fig. 4 A), L333C, R334C, K335C, F337C, S341C, R347C, T351C, R352C, and Q353C. Login to comment
116 We also examined the ability of a larger, permanently positively charged reagent, MTSET+, to react with three of the mutants, R334C, R347C, and R352C, that were susceptible to MTSEA+. Login to comment
117 One-minute and 8-min applications of 1 mM MTSET+ inhibited the CFTIR-mediated current of the mutants R334C by 53 ± 6% and 52 ± 7% (n = 3); R347C by 44 ± 2% and 36 + 3% (n = 3) (Fig. 3 D); and R352C by 46 ± 11% and 54.6 ± 10.5% (n = 3). Login to comment
85 The peak current at -100 mV was -7117 &#b1; 511 nA for the wild type, and ranged from -1709 &#b1; 124 nA for the R347C mutant to -7709 + 700 nA for the T339C mutant (Fig. 2 A). Login to comment
90 Effects of MTS reagents on wild-type cysteines RESULTS in CFTR To identify the residues in and flanking the M6 membrane-spanning segment that are on the water-exposed surface of As reported previously (Akabas et al., 1994b), extracellular applications of the MTS reagents to Xenopus oocytes ex- L2j K329C L. _J *G330C 1331C 1332C L333C R334C K335C 1336C F337C T338C T339C 1340C S341C T342C C343,WT 1344C V345C L346C R347C M348C A349C V350C T351C R352C Q353C 0 2000 4000 6000 8000 0 25 50 PEAK CURRENTS (nA) TIME TO REACH PLATEAU (min) FIGURE 2 Peak CFTR-induced currents and time to reach the plateau current after stimulation with cAMP-activating reagents for 24 cysteine-substitution mutants and wild-type CFTR. Login to comment
98 .0 %0-0 0 10 20 30 40 50 MTSET' d]I 0-0 cAMP 0 0 0 10 20 30 40 50 Time (min) FIGURE 3 Effect of the MTS reagents on the CFTR-induced current in oocytes expressing the R347C mutant. Login to comment
108 Accessibility of substituted cysteines to MTSES- A 1-min application of 10 mM MTSES- significantly inhibited the CFIR-induced currents of 9 of the 24 cysteine-substituted mutants (Fig. 4 A), L333C, R334C, K335C, F337C, S341C, R347C, T351C, R352C, and Q353C. Login to comment
115 We also examined the ability of a larger, permanently positively charged reagent, MTSET+, to react with three of the mutants, R334C, R347C, and R352C, that were susceptible to MTSEA+. Login to comment

[hide] Independent origins of cystic fibrosis mutations R... Am J Hum Genet. 1994 Nov;55(5):890-8. Morral N, Llevadot R, Casals T, Gasparini P, Macek M Jr, Dork T, Estivill X
Independent origins of cystic fibrosis mutations R334W, R347P, R1162X, and 3849 + 10kbC-->T provide evidence of mutation recurrence in the CFTR gene.
Am J Hum Genet. 1994 Nov;55(5):890-8., [PMID:7526685]

Abstract [show]
Microsatellite analysis of chromosomes carrying particular cystic fibrosis mutations has shown different haplotypes in four cases: R334W, R347P, R1162X, and 3849 + 10kbC-->T. To investigate the possibility of recurrence of these mutations, analysis of intra- and extragenic markers flanking these mutations has been performed. Recurrence is the most plausible explanation, as it becomes necessary to postulate either double recombinations or single recombinations in conjunction with slippage at one or more microsatellite loci, to explain the combination of mutations and microsatellites if the mutations arose only once. Also in support of recurrence, mutations R334W, R347P, R1162X, and 3849 + 10kbC-->T involve CpG dinucleotides, which are known to have an increased mutation rate. Although only 15.7% of point mutations in the coding sequence of CFTR have occurred at CpG dinucleotides, approximately half of these CpG sites have mutated at least once. Specific nucleotide positions of the coding region of CFTR, distinct from CpG sequences, also seem to have a higher mutation rate, and so it is possible that the mutations observed are recurrent. G-->A transitions are the most common change found in those positions involved in more than one mutational event in CFTR.

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107 1990 G--*-T R117L G. Novelli, personal communication 1171 ......... CT R347C C. Ferec, personal communication 1172 ......... G--A R347H Cremonesi et al. 1992 G I. Login to comment
124 Two other mutations (R347H and R347L) (Cremonesi et al. 1992; Audrezet et al. 1993) have occurred at nucleotide 1172 (G--A and G--T), and another one (R347C) has occurred at nucleotide 1171, which consists of a C-*T transition (C. Ferec, personal communication). Login to comment

[hide] Three charged amino acids in extracellular loop 1 ... J Gen Physiol. 2014 Aug;144(2):159-79. doi: 10.1085/jgp.201311122. Epub 2014 Jul 14. Cui G, Rahman KS, Infield DT, Kuang C, Prince CZ, McCarty NA
Three charged amino acids in extracellular loop 1 are involved in maintaining the outer pore architecture of CFTR.
J Gen Physiol. 2014 Aug;144(2):159-79. doi: 10.1085/jgp.201311122. Epub 2014 Jul 14., [PMID:25024266]

Abstract [show]
The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) bears six extracellular loops (ECL1-6); ECL1 is the site of several mutations associated with CF. Mutation R117H has been reported to reduce current amplitude, whereas D110H, E116K, and R117C/L/P may impair channel stability. We hypothesized that these amino acids might not be directly involved in ion conduction and permeation but may contribute to stabilizing the outer vestibule architecture in CFTR. We used cRNA injected oocytes combined with electrophysiological techniques to test this hypothesis. Mutants bearing cysteine at these sites were not functionally modified by extracellular MTS reagents and were blocked by GlyH-101 similarly to WT-CFTR. These results suggest that these three residues do not contribute directly to permeation in CFTR. In contrast, mutants D110R-, E116R-, and R117A-CFTR exhibited instability of the open state and significantly shortened burst duration compared with WT-CFTR and failed to be locked into the open state by AMP-PNP (adenosine 5'-(beta,gamma-imido) triphosphate); charge-retaining mutants showed mainly the full open state with comparably longer open burst duration. These interactions suggest that these ECL1 residues might be involved in maintaining the outer pore architecture of CFTR. A CFTR homology model suggested that E116 interacts with R104 in both the closed and open states, D110 interacts with K892 in the fully closed state, and R117 interacts with E1126 in the open state. These interactions were confirmed experimentally. The results suggest that D110, E116, and R117 may contribute to stabilizing the architecture of the outer pore of CFTR by interactions with other charged residues.

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130 This is similar to our previous findings for TM6 mutants R334C-, R352A-, R347C/H-CFTR (Cotten and Welsh, 1999; Zhang et al., 2005b; Cui et al., 2008). Login to comment