ABCMdb

ABCC7 p.Val232Asn

ClinVar:	c.695T>A , p.Val232Asp ? , not provided
CF databases:	c.695T>A , p.Val232Asp (CFTR1) D , This mutation was was detected by DGGE and identified by direct sequencing in the CFTR gene. The defect is a T to A change at nucleotide 827 in exon 6a which would lead to a valine-to-aspartic acid replacement in the protein sequence at residue 232. This nucleotide change has been found in an infertile man with CBAVD having neither manifestation of gastrointestinal nor pulmonary disease but with a sweat teat at mmol/
Predicted by SNAP2:	A: N (53%), C: N (61%), D: D (80%), E: D (71%), F: N (61%), G: D (75%), H: D (75%), I: N (97%), K: D (80%), L: N (93%), M: N (82%), N: D (71%), P: D (75%), Q: D (71%), R: D (80%), S: D (66%), T: D (63%), W: D (85%), Y: D (80%),
Predicted by PROVEAN:	A: N, C: D, D: D, E: D, F: N, G: D, H: D, I: N, K: D, L: N, M: N, N: D, P: D, Q: D, R: D, S: D, T: N, W: D, Y: N,

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[hide] The cystic fibrosis V232D mutation inhibits CFTR m... Biochem Pharmacol. 2014 Mar 1;88(1):46-57. doi: 10.1016/j.bcp.2013.12.027. Epub 2014 Jan 9. Loo TW, Clarke DM
The cystic fibrosis V232D mutation inhibits CFTR maturation by disrupting a hydrophobic pocket rather than formation of aberrant interhelical hydrogen bonds.
Biochem Pharmacol. 2014 Mar 1;88(1):46-57. doi: 10.1016/j.bcp.2013.12.027. Epub 2014 Jan 9., [PMID:24412276]

Abstract [show]
Processing mutations that inhibit folding and trafficking of CFTR are the main cause of cystic fibrosis. Repair of CFTR mutants requires an understanding of the mechanisms of misfolding caused by processing mutations. Previous studies on helix-loop-helix fragments of the V232D processing mutation suggested that its mechanism was to lock transmembrane (TM) segments 3 and 4 together by a non-native hydrogen bond (Asp232(TM4)/Gln207(TM3)). Here, we performed mutational analysis to test for Asp232/Gln207 interactions in full-length CFTR. The rationale was that a V232N mutation should mimic V232D and a V232D/Q207A mutant should mature if the processing defect was caused by hydrogen bonds. We report that only Val232 mutations to charged amino acids severely blocked CFTR maturation. The V232N mutation did not mimic V232D as V232N showed 40% maturation compared to 2% for V232D. Mutation of Val232 to large nonpolar residues (Leu, Phe) had little effect. The Q207L mutation did not rescue V232D because Q207L showed about 50% maturation in the presence of corrector VX-809 while V232D/Q207A could no longer be rescued. These results suggest that V232D inhibits maturation by disrupting a hydrophobic pocket between TM segments rather than forming a non-native hydrogen bond. Disulfide cross-linking analysis of cysteines W356C(TM6) and W1145C(TM12) suggest that the V232D mutation inhibits maturation by trapping CFTR as a partially folded intermediate. Since correctors can efficiently rescue V232D CFTR, the results suggest that hydrophilic processing mutations facing a hydrophobic pocket are good candidates for rescue with pharmacological chaperones.

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No. Sentence Comment
19 The rationale was that a V232N mutation should mimic V232D and a V232D/Q207A mutant should mature if the processing defect was caused by hydrogen bonds. Login to comment
21 The V232N mutation did not mimic V232D as V232N showed 40% maturation compared to 2% for V232D. Login to comment
42 The rationale was that the V232N mutation should be just as effective as V232D to inhibit CFTR maturation and mutation of Gln207 to nonpolar residues should rescue the V232D mutant if the processing defect was caused by Asp232/Gln207 hydrogen bonds. Login to comment
127 Inhibition of CFTR maturation correlates with the polarity of a Val232 mutation If V232D inhibits CFTR maturation by forming a non-native hydrogen bond with Gln207, then it would be expected that V232N and V232Q mutations would also severely inhibit maturation since asparagine and glutamine are structurally similar to aspartate and their amide groups can accept or donate two hydrogen bonds. Login to comment
128 Accordingly, mutants V232N and V232Q were constructed. Login to comment
131 By contrast, the amount of mature protein was about 20-fold higher (about 40%) for mutants V232N and V232Q compared to V232D or V232E (Fig. 3). Login to comment
137 The V232N and V232Q mutations modestly reduced the yield of mature CFTR by about half (80% for wild-type CFTR compared to about 40% for mutants V232N or V232Q) (Fig. 3). Login to comment
138 The V232N and V232Q mutations may have reduced maturation because of a change in polarity or because introduction of a larger side chain caused steric effects that disrupted packing of the TM segments. Login to comment
274 In summary, the results suggest that: (1) the mechanism of how V232D causes protein misfolding is unlikely to involve non-native hydrogen bond interactions with Gln207 because V232N yielded about 20-fold more mature CFTR than V232D; (2) it appears that the mechanism of protein misfolding by V232D mutation involves disruption of a hydrophobic pocket since the hydrophobicity of the substituted amino acid at position 232 correlated with the amount of mature product and the ability to correct the defects with correctors or the V510D suppressor mutation; (3) the V232D mutation traps CFTR as a partially folded intermediate that can be rescued by corrector VX-809 to yield a native structure. Login to comment