ABCMdb

ABCC7 p.Cys1344Ala

Predicted by SNAP2:	A: N (93%), D: N (72%), E: N (82%), F: N (87%), G: N (87%), H: N (93%), I: N (93%), K: N (78%), L: N (87%), M: N (93%), N: N (87%), P: N (61%), Q: N (87%), R: N (78%), S: N (93%), T: N (93%), V: N (93%), W: N (78%), Y: N (93%),
Predicted by PROVEAN:	A: N, D: N, E: N, F: N, G: N, H: N, I: N, K: N, L: N, M: N, N: N, P: N, Q: N, R: N, S: N, T: N, V: N, W: N, Y: N,

[switch to compact view]
Comments [show]

None has been submitted yet.

Publications
[hide] Reversible silencing of CFTR chloride channels by ... J Gen Physiol. 2005 Feb;125(2):127-41. Epub 2005 Jan 18. Wang W, Oliva C, Li G, Holmgren A, Lillig CH, Kirk KL
Reversible silencing of CFTR chloride channels by glutathionylation.
J Gen Physiol. 2005 Feb;125(2):127-41. Epub 2005 Jan 18., [PMID:15657297]

Abstract [show]
The cystic fibrosis transmembrane conductance regulator (CFTR) is a phosphorylation- and ATP-dependent chloride channel that modulates salt and water transport across lung and gut epithelia. The relationship between CFTR and oxidized forms of glutathione is of potential interest because reactive glutathione species are produced in inflamed epithelia where they may be modulators or substrates of CFTR. Here we show that CFTR channel activity in excised membrane patches is markedly inhibited by several oxidized forms of glutathione (i.e., GSSG, GSNO, and glutathione treated with diamide, a strong thiol oxidizer). Three lines of evidence indicate that the likely mechanism for this inhibitory effect is glutathionylation of a CFTR cysteine (i.e., formation of a mixed disulfide with glutathione): (a) channels could be protected from inhibition by pretreating the patch with NEM (a thiol alkylating agent) or by lowering the bath pH; (b) inhibited channels could be rescued by reducing agents (e.g., DTT) or by purified glutaredoxins (Grxs; thiol disulfide oxidoreductases) including a mutant Grx that specifically reduces mixed disulfides between glutathione and cysteines within proteins; and (c) reversible glutathionylation of CFTR polypeptides in microsomes could be detected biochemically under the same conditions. At the single channel level, the primary effect of reactive glutathione species was to markedly inhibit the opening rates of individual CFTR channels. CFTR channel inhibition was not obviously dependent on phosphorylation state but was markedly slowed when channels were first "locked open" by a poorly hydrolyzable ATP analogue (AMP-PNP). Consistent with the latter finding, we show that the major site of inhibition is cys-1344, a poorly conserved cysteine that lies proximal to the signature sequence in the second nucleotide binding domain (NBD2) of human CFTR. This region is predicted to participate in ATP-dependent channel opening and to be occluded in the nucleotide-bound state of the channel based on structural comparisons to related ATP binding cassette transporters. Our results demonstrate that human CFTR channels are reversibly inhibited by reactive glutathione species, and support an important role of the region proximal to the NBD2 signature sequence in ATP-dependent channel opening.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
169 All CFTR constructs, with the exception of C1344A-CFTR, were markedly inhibited by diamide/GSH (Fig. 7, B and C). Login to comment
170 C1344A-CFTR was largely, although not completely, resistant to each of the three glutathione species at the indicated concentrations (Fig. 7, B and D). Login to comment
212 CFTR channels that lack cys-1344 (C1344A-CFTR) are largely resistant to inhibition by reactive glutathione species. Login to comment
219 (C) Representative current trace showing resistance of C1344A-CFTR to inhibition by diamide/GSH. Login to comment
220 (D) Mean data comparing the sensitivities of WT CFTR and C1344A-CFTR to inhibition by diamide/ GSH (20 ␮M), GSNO (200 ␮M), and GSSG (20 mM). Login to comment
227 However, the fact that C1344A-CFTR was the only cysteine mutant that was highly resistant to inhibition by all three reactive glutathione species (GSNO, GSSG, and diamide/GSH) indicates that this cysteine likely is the functionally important site for glutathionylation. Login to comment

[hide] Modulation of cystic fibrosis transmembrane conduc... J Biol Chem. 2010 Dec 31;285(53):41591-6. Epub 2010 Oct 25. Melani R, Tomati V, Galietta LJ, Zegarra-Moran O
Modulation of cystic fibrosis transmembrane conductance regulator (CFTR) activity and genistein binding by cytosolic pH.
J Biol Chem. 2010 Dec 31;285(53):41591-6. Epub 2010 Oct 25., 2010-12-31 [PMID:20974851]

Abstract [show]
Potentiators are molecules that increase the activity of the cystic fibrosis transmembrane conductance regulator (CFTR). Some potentiators can also inhibit CFTR at higher concentrations. The activating binding site is thought to be located at the interface of the dimer formed by the two nucleotide-binding domains. We have hypothesized that if binding of potentiators involves titratable residues forming salt bridges, then modifications of cytosolic pH (pH(i)) would alter the binding affinity. Here, we analyzed the effect of pH(i) on CFTR activation and on the binding of genistein, a well known CFTR potentiator. We found that pH(i) does modify CFTR maximum current (I(m)) and half-activation concentration (K(d)): I(m) = 127.7, 185.5, and 231.8 muA/cm(2) and K(d) = 32.7, 56.6 and 71.9 mum at pH 6, 7.35, and 8, respectively. We also found that the genistein apparent dissociation constant for activation (K(a)) increased at alkaline pH(i), near cysteine pK (K(a) = 1.83, 1.81 and 4.99 mum at pH(i) 6, 7.35, and 8, respectively), suggesting the involvement of cysteines in the binding site. Mutations of cysteine residues predicted to be within (Cys-491) or outside (Cys-1344) the potentiator-binding site showed that Cys-491 is responsible for the sensitivity of potentiator binding to alkaline pH(i). Effects of pH(i) on inhibition by high genistein doses were also analyzed. Our results extend previous data about multiple effects of pH(i) on CFTR activity and demonstrate that binding of potentiators involves salt bridge formation with amino acids of nucleotide-binding domain 1.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
42 EXPERIMENTAL PROCEDURES Cell Culture-Fisher rat thyroid (FRT) cells stably transfected with WT-CFTR or with CFTR carrying the C491A or C1344A mutation were grown as described previously (23). Login to comment
75 Both C491A and C1344A were produced on a wild-type CFTR background. Login to comment
87 Genistein Potentiation of C1344A-CFTR Maintains the Sensitivity to pH 8-The cysteine mutant outside the putative binding site for potentiators, C1344A, showed a CPT-cAMP maximum current even smaller than C491A, but the equilibrium constant (Kd) was very close to the equilibrium constants of C491A and WT-CFTR (Table 1). Login to comment
88 Similar to the other two proteins, also C1344A-CFTR showed a higher apparent affinity (lower Kd) for CPT-cAMP at pH 6. Login to comment
100 Parameter pH 6.0 7.35 8.0 Im (␮A⅐cm-2 ) WT 127.7 Ϯ 15.8 (10)a 185.5 Ϯ 17.3 (23) 231.8 Ϯ 27.4 (14) C491A 13.9 Ϯ 3.7 (9)a 36.1 Ϯ 4.5 (8) 29.9 Ϯ 2.2 (8) C1344A 2.2 Ϯ 0.5 (5)a 6.2 Ϯ 1.7 (9) 11.7 Ϯ 2.2 (8) Kd (␮M) WT 32.7 Ϯ 6 (10)a 56.6 Ϯ 5.9 (23) 71.9 Ϯ 13.3 (14) C491A 10.3 Ϯ 1.2 (9)a 56.7 Ϯ 6.2 (8) 67.7 Ϯ 8.6 (9) C1344A 11.2 Ϯ 2 (5)a 63.4 Ϯ 9.4 (9) 104.3 Ϯ 12.7 (8) a p Ͻ 0.05 compared with the same parameter on the same protein at pH 7.35. Login to comment
102 Parameter pH 6 7.35 8.0 fA WT 1.24 Ϯ 0.22 (12) 1.87 Ϯ 0.34 (14) 4.36 Ϯ 0.83 (16)a C491A 2.57 Ϯ 0.58 (11) 3.29 Ϯ 0.53 (13) 3.85 Ϯ 0.54 (11) C1344A 1.84 Ϯ 0.64 (4) 4.5 Ϯ 1.2 (9) 5.23 Ϯ 0.89 (13) Ka (␮M) WT 1.83 Ϯ 0.43 (12) 1.81 Ϯ 0.37 (14) 4.99 Ϯ 0.89 (16)a C491A 17.2 Ϯ 4 (11) 17.8 Ϯ 5.44 (13) 16.4 Ϯ 3.29 (11) C1344A 8.2 Ϯ 1.27 (4) 10.1 Ϯ 2.17 (9) 20 Ϯ 3.53 (13)a Ki (␮M) WT 250.9 Ϯ 29.5 (12) 368 Ϯ 50.9 (14) 237.9 Ϯ 44.95 (16) C491A 78.5 Ϯ 21.2 (11) 108.5 Ϯ 24.3 (13) 394.9 Ϯ 70.4 (12)a C1344A 23.8 Ϯ 2.48 (4)a 73.9 Ϯ 12.7 (9) 398.75 Ϯ 87.1 (13)a a p Ͻ 0.05 compared with the same parameter at pH 7.35 on the same protein. Login to comment
104 The Ka was found to be higher than that of the WT-CFTR, but as in the WT channel, the Ka of C1344A-CFTR increased when pHi was set at a value of 8. Login to comment
105 This indicates that, in contrast to what was found with C491A, the C1344A mutation did not modify the sensitivity of genistein binding to the activating site at alkaline pHi (Fig. 3C). Login to comment
120 A, Western blot showing CFTR protein expression in untransfected FRT cells (FRT-null) and in cells stably transfected with WT-, C491A-, and C1344A-CFTR. Login to comment
131 Dose-response relationship of C1344A-CFTR to genistein. Login to comment
132 A, representative traces showing the response of mutant C1344A-CFTR to increasing doses of genistein (indicated by arrows). Login to comment
133 Dashed lines under the curves indicate the zero current level. B, normalized dose-response relationships in experiments on mutant C1344A at pH 6 (n ϭ 4), 7.35 (n ϭ 4), and 8 (n ϭ 4). Login to comment
134 C, course of Ka measured on WT-, C491A-, and C1344A-CFTR at different pHi values. Login to comment
138 However, at pHi 8, the Ka for WT and C1344A-CFTR increased significantly (p Ͻ 0.05), whereas it remained unchanged for mutant C491A. Login to comment
165 Analysis of epithelia stably expressing these mutant CFTR proteins showed that, whereas C1344A-CFTR behaved as WT-CFTR, exhibiting reduced affinity for genistein at pH 8, the C491A mutation kept the same affinity for genistein at the three pHi values (Fig. 3C and Table 2). Login to comment
174 Substitution of either Cys-491 or Cys-1344 with alanine resulted in an increased affinity for the inhibitory site at pHi 6 and 7.35 (Table 2). Login to comment
175 This effect was more marked at pH 6 and for C1344A-CFTR (Ki ϭ 24 ␮M). Login to comment

[hide] Converting nonhydrolyzable nucleotides to strong c... J Biol Chem. 2013 Jun 14;288(24):17122-33. doi: 10.1074/jbc.M112.442582. Epub 2013 Apr 25. Okeyo G, Wang W, Wei S, Kirk KL
Converting nonhydrolyzable nucleotides to strong cystic fibrosis transmembrane conductance regulator (CFTR) agonists by gain of function (GOF) mutations.
J Biol Chem. 2013 Jun 14;288(24):17122-33. doi: 10.1074/jbc.M112.442582. Epub 2013 Apr 25., [PMID:23620589]

Abstract [show]
Cystic fibrosis transmembrane conductance regulator (CFTR) is the only ligand-gated ion channel that hydrolyzes its agonist, ATP. CFTR gating has been argued to be tightly coupled to its enzymatic activity, but channels do open occasionally in the absence of ATP and are reversibly activated (albeit weakly) by nonhydrolyzable nucleotides. Why the latter only weakly activates CFTR is not understood. Here we show that CFTR activation by adenosine 5'-O-(thiotriphosphate) (ATPgammaS), adenosine 5'-(beta,gamma-imino)triphosphate (AMP-PNP), and guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) is enhanced substantially by gain of function (GOF) mutations in the cytosolic loops that increase unliganded activity. This enhancement correlated with the base-line nucleotide-independent activity for several GOF mutations. AMP-PNP or ATPgammaS activation required both nucleotide binding domains (NBDs) and was disrupted by a cystic fibrosis mutation in NBD1 (G551D). GOF mutant channels deactivated very slowly upon AMP-PNP or ATPgammaS removal (taudeac approximately 100 s) implying tight binding between the two NBDs. Despite this apparently tight binding, neither AMP-PNP nor ATPgammaS activated even the strongest GOF mutant as strongly as ATP. ATPgammaS-activated wild type channels deactivated more rapidly, indicating that GOF mutations in the cytosolic loops reciprocally/allosterically affect nucleotide occupancy of the NBDs. A GOF mutation substantially rescued defective ATP-dependent gating of G1349D-CFTR, a cystic fibrosis NBD2 signature sequence mutant. Interestingly, the G1349D mutation strongly disrupted activation by AMP-PNP but not by ATPgammaS, indicating that these analogs interact differently with the NBDs. We conclude that poorly hydrolyzable nucleotides are less effective than ATP at opening CFTR channels even when they bind tightly to the NBDs but are converted to stronger agonists by GOF mutations.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
220 D, mean inhibition by diamide/glutathione of the AMP-PNP activated currents for K978P-CFTR (n afd; 5) and K978P/C1344A- CFTR (n afd; 3) is shown. Login to comment