ABCMdb

ABCC7 p.Thr338His

ClinVar:	c.1012A>G , p.Thr338Ala ? , not provided c.1013C>T , p.Thr338Ile D , Pathogenic
CF databases:	c.1013C>T , p.Thr338Ile D , CF-causing ; CFTR1: A nucleotide change C->T at position 1145 which causes the replacement of a Threonine by Isoleucine residue in codon 338 of exon 7. c.1012A>G , p.Thr338Ala (CFTR1) ? , This mutation was identified in one Iranian CBAVD patient.
Predicted by SNAP2:	A: D (85%), C: D (91%), D: D (95%), E: D (95%), F: D (95%), G: D (95%), H: D (95%), I: D (53%), K: D (95%), L: D (95%), M: D (95%), N: D (91%), P: D (95%), Q: D (95%), R: D (95%), S: D (91%), V: D (85%), W: D (95%), Y: D (95%),
Predicted by PROVEAN:	A: N, C: D, D: D, E: D, F: D, G: D, H: D, I: D, K: D, L: D, M: D, N: N, P: N, Q: D, R: D, S: N, V: N, W: D, Y: D,

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Publications
[hide] CFTR: what's it like inside the pore? J Exp Zool A Comp Exp Biol. 2003 Nov 1;300(1):69-75. Liu X, Smith SS, Dawson DC
CFTR: what's it like inside the pore?
J Exp Zool A Comp Exp Biol. 2003 Nov 1;300(1):69-75., 2003-11-01 [PMID:14598388]

Abstract [show]
The Cystic Fibrosis Conductance Regulator (CFTR) functions as a cAMP-activated, anion-selective channel, but the structural basis for anion permeation is not well understood. Here we summarize recent studies aimed at understanding how anions move through the CFTR channel, and the nature of the environment anions experience inside the pore. From these studies it is apparent that anion permeability selectivity and anion binding selectivity of the pore are consistent with a model based on a "dielectric tunnel." The selectivity pattern for halides and pseudohalides can be predicted if it is assumed that permeant anions partition between bulk water and a polarizable space that is characterized by an effective dielectric constant of about 19. Covalent labeling of engineered cysteines and pH titration of engineered cysteines and histidines lead to the conclusion that the CFTR anion conduction path includes a positively charged outer vestibule. A residue in transmembrane segment 6 (TM6) (R334) appears to reside in the outer vestibule of the CFTR pore where it creates a positive electrostatic potential that enhances anion conduction.

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Sentences [show]
No. Sentence Comment
117 Titration of the macroscopic conductance due to T338C and T338H CFTR indicates that positive charges at R334, perhaps at K335, and perhaps elsewhere may cause the pKa of T338C CFTR to become more acidic than in free solution (E7.4) and to render T338H CFTR non-titratable. Login to comment
118 Changing the charge at position 334 either by modification of R334C/T338H CFTR with polar thiol reactive reagents or by amino acid substitution (R334A/T338C) shifts the titration curve in a direction that was predicted on the basis of a nearby positive charge being able to stabilize a titratable group (Liu et al., 2001). Login to comment

[hide] Variable reactivity of an engineered cysteine at p... J Biol Chem. 2006 Mar 24;281(12):8275-85. Epub 2006 Jan 24. Liu X, Alexander C, Serrano J, Borg E, Dawson DC
Variable reactivity of an engineered cysteine at position 338 in cystic fibrosis transmembrane conductance regulator reflects different chemical states of the thiol.
J Biol Chem. 2006 Mar 24;281(12):8275-85. Epub 2006 Jan 24., 2006-03-24 [PMID:16436375]

Abstract [show]
In a previous study of T338C CFTR (cystic fibrosis transmembrane conductance regulator) we found that protons and thiol-directed reagents modified channel properties in a manner consistent with the hypothesis that this residue lies within the conduction path, but the observed reactivity was not consistent with the presence of a single thiolate species in the pore. Here we report results consistent with the notion that the thiol moiety can exist in at least three chemical states, the simple thiol, and two altered states. One of the altered states displays reactivity toward thiols like dithiothreitol and 2-mercaptoethanol as well as reagents: mixed disulfides (methanethiosulfonate reagents: MTSET+, MTSES-) and an alkylating agent (iodoacetamide). The other altered state is unreactive. The phenotype associated with the reactive, altered state could be replicated by exposing oocytes expressing T338C CFTR to CuCl2, but not by glutathionylation or nitrosylation of the thiol or by oxidation with hydrogen peroxide. The results are consistent with the hypothesis that substituting a cysteine at 338 can create an adventitious metal binding site. Metal liganding alters thiol reactivity and may, in some cases, catalyze oxidation of the thiol to an unreactive form such as a sulfinic or sulfonic acid.

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Sentences [show]
No. Sentence Comment
53 RESULTS T338C/WT CFTR Conductance Was Markedly Altered by 2-ME or DTT Prior to Exposure to Exogenous Thiol-directed Reagents5 - Exposing oocytes expressing T338C/WT CFTR to 2-ME or DTT during steady state activation led to increases in conductance (without any discernable change in reversal potential) that were rapid (t1/2 ϭ 20 s), and of variable amplitude and were not seen in oocytes expressing CFTR constructs lacking the cysteine at 338, such as WT, T338A, T338H, T338S CFTR, or Cys-less CFTR. Login to comment

[hide] CFTR: a cysteine at position 338 in TM6 senses a p... Biophys J. 2004 Dec;87(6):3826-41. Epub 2004 Sep 10. Liu X, Zhang ZR, Fuller MD, Billingsley J, McCarty NA, Dawson DC
CFTR: a cysteine at position 338 in TM6 senses a positive electrostatic potential in the pore.
Biophys J. 2004 Dec;87(6):3826-41. Epub 2004 Sep 10., [PMID:15361410]

Abstract [show]
We investigated the accessibility to protons and thiol-directed reagents of a cysteine substituted at position 338 in transmembrane segment 6 (TM6) of CFTR to test the hypothesis that T338 resides in the pore. Xenopus oocytes expressing T338C CFTR exhibited pH-dependent changes in gCl and I-V shape that were specific to the substituted cysteine. The apparent pKa of T338C CFTR was more acidic than that expected for a cysteine or similar simple thiols in aqueous solution. The pKa was shifted toward alkaline values when a nearby positive charge (R334) was substituted with neutral or negatively charged residues, consistent with the predicted influence of the positive charge of R334, and perhaps other residues, on the titration of a cysteine at 338. The relative rates of chemical modification of T338C CFTR by MTSET+ and MTSES- were also altered by the charge at 334. These observations support a model for CFTR that places T338 within the anion conduction path. The apparent pKa of a cysteine substituted at 338 and the relative rates of reaction of charged thiol-directed reagents provide a crude measure of a positive electrostatic potential that may be due to R334 and other residues near this position in the pore.

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Sentences [show]
No. Sentence Comment
94 For ease of comparison, in T338C/R334X (X ¼ A or E) CFTRs and T338H/R334C CFTRs in which the cysteine was always blocked by reaction with MTS reagents or NEM, the titration curves were expressed in a normalized form. Login to comment
190 To test the generality of titration results obtained with T338C CFTR, we compared the titration behavior of T338H CFTR with that of a double mutant, T338H/R334C, in which it was possible to change the charge at position 334 by means of chemical modification. Login to comment
191 Summarized in Fig. 8 B are the results obtained from oocytes expressing either T338H or chemically modified T338H/R334C CFTR (n ¼ 3-4 for each mutant). Login to comment
192 Shown are sample titration curves for T338H and T338H/R334C CFTRs in which the cysteine was modified by MTSET1 , MTSESÿ , and NEM (neutral). Login to comment
194 The conductance of oocytes expressing T338H CFTR was essentially not titratable, as if the pKa of the histidine was more acidic than 4.0. Login to comment
195 Similarly, the conductance due to MTSET1 -modified T338H/R334C CFTR was not very sensitive to pH titration. Login to comment
208 NEM- or MTSESÿ -modified T338H/R334C CFTR were more titratable and the apparent pKa values were shifted toward more basic values. Login to comment
209 Because the range of pH values tolerated by oocytes was limited, the apparent pKa values could not be estimated accurately for T338H and T338H/ R334C variants. Login to comment
221 FIGURE 8 The pH-induced changes in the conductances of oocytes expressing T338C/R334A, T338C/R334E, T338H, or T338H/R334C CFTR. Login to comment
222 (A) Sample titration curves of conductances of oocytes expressing T338C CFTR (solid circles), T338C/R334A (open squares), or T338C/ R334E CFTRs (shaded triangles). Login to comment
225 (B) Sample titration curves for T338H (open triangle) and T338H/R334C CFTR modified by MTSET1 (solid circles), MTSESÿ (open circles), and NEM (shaded triangles). Login to comment
193 Shown are sample titration curves for T338H and T338H/R334C CFTRs in which the cysteine was modified by MTSET1 , MTSES , and NEM (neutral). Login to comment
196 Similarly, the conductance due to MTSET1 -modified T338H/R334C CFTR was not very sensitive to pH titration. Login to comment
210 Because the range of pH values tolerated by oocytes was limited, the apparent pKa values could not be estimated accurately for T338H and T338H/ R334C variants. Login to comment
226 (B) Sample titration curves for T338H (open triangle) and T338H/R334C CFTR modified by MTSET1 (solid circles), MTSES (open circles), and NEM (shaded triangles). Login to comment