ABCMdb

ABCC7 p.Ala534Pro

ClinVar:	c.1601C>A , p.Ala534Glu D , Pathogenic
CF databases:	c.1601C>A , p.Ala534Glu (CFTR1) ? , A nucleotide change, C->A at position 1733, was detected by DGGE and direct sequencing leading to A534E in exon 11.
Predicted by SNAP2:	C: N (78%), D: N (78%), E: N (82%), F: D (59%), G: N (66%), H: N (57%), I: N (57%), K: N (78%), L: D (53%), M: N (61%), N: N (57%), P: N (93%), Q: N (87%), R: D (53%), S: N (72%), T: N (66%), V: N (61%), W: D (66%), Y: D (53%),
Predicted by PROVEAN:	C: N, D: N, E: N, F: D, 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: D, Y: D,

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Publications
[hide] Allosteric modulation balances thermodynamic stabi... J Mol Biol. 2012 May 25;419(1-2):41-60. Epub 2012 Mar 8. Aleksandrov AA, Kota P, Cui L, Jensen T, Alekseev AE, Reyes S, He L, Gentzsch M, Aleksandrov LA, Dokholyan NV, Riordan JR
Allosteric modulation balances thermodynamic stability and restores function of DeltaF508 CFTR.
J Mol Biol. 2012 May 25;419(1-2):41-60. Epub 2012 Mar 8., [PMID:22406676]

Abstract [show]
Most cystic fibrosis is caused by a deletion of a single residue (F508) in CFTR (cystic fibrosis transmembrane conductance regulator) that disrupts the folding and biosynthetic maturation of the ion channel protein. Progress towards understanding the underlying mechanisms and overcoming the defect remains incomplete. Here, we show that the thermal instability of human DeltaF508 CFTR channel activity evident in both cell-attached membrane patches and planar phospholipid bilayers is not observed in corresponding mutant CFTRs of several non-mammalian species. These more stable orthologs are distinguished from their mammalian counterparts by the substitution of proline residues at several key dynamic locations in first N-terminal nucleotide-binding domain (NBD1), including the structurally diverse region, the gamma-phosphate switch loop, and the regulatory insertion. Molecular dynamics analyses revealed that addition of the prolines could reduce flexibility at these locations and increase the temperatures of unfolding transitions of DeltaF508 NBD1 to that of the wild type. Introduction of these prolines experimentally into full-length human DeltaF508 CFTR together with the already recognized I539T suppressor mutation, also in the structurally diverse region, restored channel function and thermodynamic stability as well as its trafficking to and lifetime at the cell surface. Thus, while cellular manipulations that circumvent its culling by quality control systems leave DeltaF508 CFTR dysfunctional at physiological temperature, restoration of the delicate balance between the dynamic protein's inherent stability and channel activity returns a near-normal state.

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Sentences [show]
No. Sentence Comment
112 Combination of introduction of a proline into the Q-loop at position 492 together with I539T to generate ΔF/PT was sufficient to allow a high level of maturation even without further addition of the substitutions in the I539 loop (A534P) to generate ΔF/2PT or also in the RI (S422P and S434P) to generate ΔF/4PT. Login to comment
121 With the inclusion of S492P± A534P (ΔF/PT or ΔF/ 2PT), the turnover rates were indistinguishable from WT with a T1/2 of ~14 h. When prolines also replaced residues 422 and 434 in the RI to form ΔF/ 4PT, the rate appeared even slower than WT with a T1/2 of ~16 h. Thus, the biological stability of the Fig. 5. Login to comment
128 (c) Western blot of WT and ΔF508 CFTR expressed in HEK-293 cells and ΔF508 modified with I539T (ΔF/T), S422P/S434P/S492P/A534P (ΔF/4P), I539T/S492P (ΔF/PT), I539T/S492P/A534P (ΔF/2PT), and I539T/S422P/S434P/S492P/A534P (ΔF/4PT). Login to comment
136 Thermostable binding of the nucleotide by the WT, which is lost in ΔF508 CFTR,19 was not restored after rescue in cells grown at 27 °C [(r)ΔF panel], but was to some extent by I539T (ΔF/T panel), to a greater extent when S492P was added (ΔF/PT panel), still further with A534P also added (ΔF/2PT panel), and to near the WT level with proline replacements at residues S492 and A534 as well (ΔF/4PT panel). Login to comment
178 HEK293 cells were transiently transfected with Cys-less CFTR or Cys-less ΔF508-CFTR in the presence or absence of the 4PT mutations (S422P/S434P/S492P/A534P/I539T), with the Cys pair V510C/G1069C introduced at the CL4/NBD1 interface. Login to comment

[hide] Correctors of DeltaF508 CFTR restore global confor... FASEB J. 2013 Feb;27(2):536-45. doi: 10.1096/fj.12-216119. Epub 2012 Oct 26. He L, Kota P, Aleksandrov AA, Cui L, Jensen T, Dokholyan NV, Riordan JR
Correctors of DeltaF508 CFTR restore global conformational maturation without thermally stabilizing the mutant protein.
FASEB J. 2013 Feb;27(2):536-45. doi: 10.1096/fj.12-216119. Epub 2012 Oct 26., [PMID:23104983]

Abstract [show]
Most cystic fibrosis is caused by the deletion of a single amino acid (F508) from CFTR and the resulting misfolding and destabilization of the protein. Compounds identified by high-throughput screening to improve DeltaF508 CFTR maturation have already entered clinical trials, and it is important to understand their mechanisms of action to further improve their efficacy. Here, we showed that several of these compounds, including the investigational drug VX-809, caused a much greater increase (5- to 10-fold) in maturation at 27 than at 37 degrees C (<2-fold), and the mature product remained short-lived (T(1/2) approximately 4.5 h) and thermally unstable, even though its overall conformational state was similar to wild type, as judged by resistance to proteolysis and interdomain cross-linking. Consistent with its inability to restore thermodynamic stability, VX-809 stimulated maturation 2-5-fold beyond that caused by several different stabilizing modifications of NBD1 and the NBD1/CL4 interface. The compound also promoted maturation of several disease-associated processing mutants on the CL4 side of this interface. Although these effects may reflect an interaction of VX-809 with this interface, an interpretation supported by computational docking, it also rescued maturation of mutants in other cytoplasmic loops, either by allosteric effects or via additional sites of action. In addition to revealing the capabilities and some of the limitations of this important investigational drug, these findings clearly demonstrate that DeltaF508 CFTR can be completely assembled and evade cellular quality control systems, while remaining thermodynamically unstable. He, L., Kota, P., Aleksandrov, A. A., Cui, L., Jensen, T., Dokholyan, N. V., Riordan, J. R. Correctors of DeltaF508 CFTR restore global conformational maturation without thermally stabilizing the mutant protein.

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Sentences [show]
No. Sentence Comment
122 4PT, S422P/S434P/S492P/ A534P/I539T. Login to comment
148 A) èc;F508 with NBD1-stabilizing mutations: 4S, I539T/G550E/R553M/R555K; èc;RI, deletion of amino acid residues 404-435; 4PT, S422P/S434P/S492P/A534P/I539T. Login to comment

[hide] Restoration of NBD1 thermal stability is necessary... J Mol Biol. 2015 Jan 16;427(1):106-20. doi: 10.1016/j.jmb.2014.07.026. Epub 2014 Jul 30. He L, Aleksandrov AA, An J, Cui L, Yang Z, Brouillette CG, Riordan JR
Restoration of NBD1 thermal stability is necessary and sufficient to correct F508 CFTR folding and assembly.
J Mol Biol. 2015 Jan 16;427(1):106-20. doi: 10.1016/j.jmb.2014.07.026. Epub 2014 Jul 30., [PMID:25083918]

Abstract [show]
Cystic fibrosis transmembrane conductance regulator (CFTR) (ABCC7), unique among ABC exporters as an ion channel, regulates ion and fluid transport in epithelial tissues. Loss of function due to mutations in the cftr gene causes cystic fibrosis. The most common cystic-fibrosis-causing mutation, the deletion of F508 (DeltaF508) from the first nucleotide binding domain (NBD1) of CFTR, results in misfolding of the protein and clearance by cellular quality control systems. The DeltaF508 mutation has two major impacts on CFTR: reduced thermal stability of NBD1 and disruption of its interface with membrane-spanning domains (MSDs). It is unknown if these two defects are independent and need to be targeted separately. To address this question, we varied the extent of stabilization of NBD1 using different second-site mutations and NBD1 binding small molecules with or without NBD1/MSD interface mutation. Combinations of different NBD1 changes had additive corrective effects on F508 maturation that correlated with their ability to increase NBD1 thermostability. These effects were much larger than those caused by interface modification alone and accounted for most of the correction achieved by modifying both the domain and the interface. Thus, NBD1 stabilization plays a dominant role in overcoming the DeltaF508 defect. Furthermore, the dual target approach resulted in a locked-open ion channel that was constitutively active in the absence of the normally obligatory dependence on phosphorylation by protein kinase A. Thus, simultaneous targeting of both the domain and the interface, as well as being non-essential for correction of biogenesis, may disrupt normal regulation of channel function.

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Sentences [show]
No. Sentence Comment
45 2PT, S492P/A534P/I539T; 4PT, 2PT + S422P/S434P; 3SS, G550E/R553M/R555K; 4SS, 3SS + I539T; ƊRI, deletion of RI amino acids 404-435; combo, ƊRI + 2PT + 3SS. Login to comment
72 2PT, S492P/ A534P/I539T; 3PT, 2PT + S495P. Login to comment
96 The S492P and I539T substitutions had additive affects such that ƊTm increased to 4.4 &#b0;C, and ƊTm was further increased to 8.4 &#b0;C when the additional mutations A534P/G550E/R553M/R555K were introduced. Login to comment
123 Figure 3e shows that both BIA and BEIA further strongly increased maturation of the NBD1 stabilized variant ƊF508/2PT (S492P/A534P/I539T). Login to comment

[hide] Thermal stability of purified and reconstituted CF... Protein Expr Purif. 2015 Dec;116:159-66. doi: 10.1016/j.pep.2015.09.018. Epub 2015 Sep 15. Aleksandrov LA, Jensen TJ, Cui L, Kousouros JN, He L, Aleksandrov AA, Riordan JR
Thermal stability of purified and reconstituted CFTR in a locked open channel conformation.
Protein Expr Purif. 2015 Dec;116:159-66. doi: 10.1016/j.pep.2015.09.018. Epub 2015 Sep 15., [PMID:26384709]

Abstract [show]
CFTR is unique among ABC transporters as the only one functioning as an ion channel and from a human health perspective because mutations in its gene cause cystic fibrosis. Although considerable advances have been made towards understanding CFTR's mechanism of action and the impact of mutations, the lack of a high-resolution 3D structure has hindered progress. The large multi-domain membrane glycoprotein is normally present at low copy number and when over expressed at high levels it aggregates strongly, limiting the production of stable mono-disperse preparations. While the reasons for the strong self-association are not fully understood, its relatively low thermal stability seems likely to be one. The major CF causing mutation, DeltaF508, renders the protein very thermally unstable and therefore a great deal of attention has been paid to this property of CFTR. Multiple second site mutations of CFTR in NBD1 where F508 normally resides and small molecule binders of the domain increase the thermal stability of the mutant. These manipulations also stabilize the wild-type protein. Here we have applied DeltaF508-stabilizing changes and other modifications to generate wild-type constructs that express at much higher levels in scaled-up suspension cultures of mammalian cells. After purification and reconstitution into liposomes these proteins are active in a locked-open conformation at temperatures as high as 50 degrees C and remain monodisperse at 4 degrees C in detergent or lipid for at least a week. The availability of adequate amounts of these and related stable active preparations of homogeneous CFTR will enable stalled structural and ligand binding studies to proceed.

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Sentences [show]
No. Sentence Comment
20 Abbreviations used: CFTR, cystic fibrosis transmembrane conductance regulator; ABC, ATP-binding cassette; NBD1, N-terminal nucleotide-binding domain; CF, cystic fibrosis; CHO, Chinese hamster ovary; HEK, human embryonic kidney; BHK, baby hamster kidney; Tm, melting temperature; Ti, inactivation temperature; RI, Regulatory Insertion (residues 404-435); 2PT, variant with NBD1 mutations S492P, A534P and I539T; Q loop, residues contacting the gamma-phosphate of ATP; SDR, structurally divers region; DMNG, Decyl Maltose Neopentyl Glycol; MALS, multi-angle light scattering analysis; DOPE, 1,2-dioleoyl-sn-glycero-3-phosphoethanola mine; DOPC, 1,2-dioleoyl-sn-glycero-3-phosphocholine; DOPS, 1,2-dioleoyl-sn- glycero-3-phospho-L-serine; SUV, small unilamellar vesicles; LMV, large multilamellar vesicles; LULV, large unilamellar vesicles; PKA, protein kinase A; RIPA, radioimmunoprecipitation assay; ER, endoplasmic reticulum; RAMP, gradual increase with constant slope. Login to comment
107 As seen in Fig. 2a the ''2PT" variant with NBD1 mutations S492P, A534P and I539T and the DRI variant, from which the Regulatory Insertion (residues 404-435) was deleted both increased expression levels substantially compared to the wild type. Login to comment
109 Channel open probability was substantially reduced in 2PT due to the introduction of the two prolines into the mobile Q loop (S492P) and SDR (A534P) regions of NBD1 (third tracing). Login to comment

[hide] Exploiting species differences to understand the C... Biochem Soc Trans. 2015 Oct 1;43(5):975-82. doi: 10.1042/BST20150129. Bose SJ, Scott-Ward TS, Cai Z, Sheppard DN
Exploiting species differences to understand the CFTR Cl- channel.
Biochem Soc Trans. 2015 Oct 1;43(5):975-82. doi: 10.1042/BST20150129., [PMID:26517912]

Abstract [show]
The anion channel cystic fibrosis transmembrane conductance regulator (CFTR) is a unique ATP-binding cassette (ABC) transporter. CFTR plays a pivotal role in transepithelial ion transport as its dysfunction in the genetic disease cystic fibrosis (CF) dramatically demonstrates. Phylogenetic analysis suggests that CFTR first appeared in aquatic vertebrates fulfilling important roles in osmosensing and organ development. Here, we review selectively, knowledge of CFTR structure, function and pharmacology, gleaned from cross-species comparative studies of recombinant CFTR proteins, including CFTR chimeras. The data argue that subtle changes in CFTR structure can affect strongly channel function and the action of CF mutations.

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No. Sentence Comment
120 Hypothesizing that structural differences between human and chicken CFTR account for the thermostability of F508del chicken CFTR, Aleksandrov et al. [41] demonstrated that the F508del revertant I539T and four proline residues at key positions within NBD1 (S422P, S434P, S492P and A534P) were responsible for rescuing the processing, plasma membrane stability and function of human CFTR. Login to comment