ABCMdb

ABCC7 p.Gln220Lys

ClinVar:	c.658C>T , p.Gln220* D , Pathogenic c.659A>G , p.Gln220Arg ? , not provided
CF databases:	c.658C>T , p.Gln220* D , CF-causing c.659A>G , p.Gln220Arg (CFTR1) ? , Found in a patient with CBAVD.
Predicted by SNAP2:	A: N (57%), C: D (59%), D: N (66%), E: N (82%), F: D (75%), G: N (61%), H: N (53%), I: D (71%), K: D (53%), L: D (59%), M: D (71%), N: N (61%), P: D (63%), R: D (63%), S: N (57%), T: N (66%), V: N (57%), W: D (80%), Y: D (71%),
Predicted by PROVEAN:	A: N, C: N, D: N, E: N, F: N, G: N, H: N, I: D, K: N, L: D, M: N, N: N, P: N, R: N, S: N, T: N, V: N, W: N, Y: N,

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Publications
[hide] Topogenesis of cystic fibrosis transmembrane condu... Biochemistry. 1999 Apr 27;38(17):5471-7. Chen M, Zhang JT
Topogenesis of cystic fibrosis transmembrane conductance regulator (CFTR): regulation by the amino terminal transmembrane sequences.
Biochemistry. 1999 Apr 27;38(17):5471-7., 1999-04-27 [PMID:10220334]

Abstract [show]
Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transport superfamily. CFTR folding and assembly appear to involve several events occurred in the cytosol and ER. Misfolding of CFTR causes cystic fibrosis, and thus, understanding the folding mechanism of CFTR is extremely important. Recently, detailed study of membrane insertion process suggests that the first two transmembrane (TM) segments of CFTR have two distinct but independent mechanisms to ensure the correct membrane folding of its amino terminal end [Lu, Y., Xiong, X., Helm, A., Kimani, K., Bragin, A., Skach, W. R. (1998) J. Biol. Chem. 273, 568-576]. To understand how other TM segments are ensured to insert into membranes correctly, we investigated the topogenesis of TM3 and TM4 of CFTR in a cell-free expression system. We found that the correct membrane insertion of TM3 and TM4 of CFTR was ensured by their flanking amino acid sequences and controlled by the correct membrane insertion of their preceding TM1 and TM2. Thus, correct membrane insertion and folding of TM1 and TM2 play an essential role in the membrane insertion and folding of the subsequent TM segments of CFTR.

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No. Sentence Comment
47 Primers carrying various mutations are 5'-AATCTGGAGGTTGTTAAAGGCGTC-3' (E217R/Q220K), 5'-CATCATTTCCCCTAGCCC-3' (R242E), 5'-CT- GATCTTCGTAATTCATCATCAT-3' (K246N/R248E), and 5'-TCCCAGCTTCCTGATCT-3' (R251E). Login to comment
48 To make the CFTR-N4R(-8) and CFTR-N4R(-5) mutants, two PCR reactions were performed as described above using CFTR-N4R(E217R/Q220K) or wild-type CFTR-N4R as templates and the mutant primer 5'-AGGGGAAATGATGATGGAG- TACGAAGATCAGGAAGCTGGGGATATCAG-3'. Login to comment
49 The resulting constructs were named CFTR-N4R(E217R/Q220K), CFTR-N4R(R242E), CFTR-N4R(K246N/R248E), CFTR-N4R(R251E), CFTR-N4R(-8), and CFTR-N4R(-5). Login to comment
50 To remove TM1 and TM2 from CFTR-N4R, CFTR-N4R- (E217R/Q220K), CFTR-N4R(-8), and CFTR-N4R(-5), PCR was performed using a primer 5'-GAGACCATGCA- GATGAGAATAG-3' containing Kozak translation initiation codon and a primer 5'-CACTTTTGCCAACCAG-3' in the glycosylation reporter sequence on templates CFTR-N4R, CFTR-N4R(E217R/Q220K), CFTR-N4R(-8), and CFTR-N4R(-5), respectively. Login to comment
53 The final DNA clones were named CF-TM3,4R, CF-TM3,4R(E217R/Q220K), CF-TM3,4R(-8), and CF-TM3,4R(-5), respectively. To engineer R242E and K246N/R248E mutations into CF-TM3,4R, an EcoRI-EcoNI fragment encoding TM3 and part of TM4 was released from CF-TM3,4R and used to replace the amino terminal-encoding sequence in CFTR-N4R(R242E) and CFTR-N4R(K246N/R248E). Login to comment
72 The mutant molecules used were CF-TM3,4R(E217R/ Q220K), CF-TM3,4R(R242E), and CF-TM3,4R(K246N/ R248E). Login to comment

[hide] Role of the extracellular loop in the folding of a... Biochemistry. 2007 Jun 19;46(24):7099-106. Epub 2007 May 22. Wehbi H, Rath A, Glibowicka M, Deber CM
Role of the extracellular loop in the folding of a CFTR transmembrane helical hairpin.
Biochemistry. 2007 Jun 19;46(24):7099-106. Epub 2007 May 22., 2007-06-19 [PMID:17516627]

Abstract [show]
The folding of membrane-spanning domains into their native functional forms depends on interactions between transmembrane (TM) helices joined by covalent loops. However, the importance of these covalent linker regions in mediating the strength of helix-helix associations has not been systematically addressed. Here we examine the potential structural impact of cystic fibrosis-phenotypic mutations in the extracellular loop 2 (ECL2) on interactions between the TM3 and TM4 helices of the cystic fibrosis transmembrane conductance regulator (CFTR) in constructs containing CFTR residues 194-241. When the effects of replacements in ECL2 (including the CF-phenotypic mutants E217G and Q220R) were evaluated in a library of wild-type and mutant TM3-ECL2-TM4 hairpin constructs, we found that SDS-PAGE gel migration rates differed over a range of nearly 40% +/- the wild-type position and that decreased migration rates correlate with increasing hairpin alpha-helical content as measured by circular dichroism spectra in sodium dodecyl sulfate micelles. The decreased mobility of TM3/4 constructs by introduction of non-native residues is interpreted in terms of an elongation or "opening" of the helical hairpin and concomitant destabilization of membrane-based helix-helix interactions. Our results support a role for short loop regions in dictating the stability of membrane protein folds and highlight the interplay between membrane-embedded helix-helix interactions and loop conformation in influencing the structure of membrane proteins.

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No. Sentence Comment
83 The Q220E replacement migrates faster than TM3/4 WT, the Q220G and Q220N mutants migrate at equivalent rates to TM3/4 WT, while the Q220W, Q220K, and Q220R substitutions migrate more slowly. Login to comment
89 The Q220K and Q220W hairpins migrated identically to Q220R (p ) 0.259 and p ) 0.101, respectively) and to one another (p ) 0.341), making it unlikely that the positive charge on the Arg side chain per se reduced hairpin compactness. Login to comment
97 When the changes in TM3/4 WT hairpin migration were compared to changes in overall hairpin helicity, a strong correlation (R ) 0.79) was observed (Figure 5), leading us to propose that increases in non-native R-helix structure within ECL2 might Table 1: Migration Behavior on SDS-PAGE Gels of Single and Double Mutants in the Loop Region of CFTR TM3/4 Constructs % change in apparent MW on SDS-PAGE mutant vs TM3/4 WT in WT loop mutantsa vs TM3/4 V232D in V232D loop mutantsa Pb E217G 6.8 ( 0.7 E217S 11.1 ( 3.4 5.4 ( 1.4 0.056 Q220R 15.2 ( 1.1 Q220G 0.3 ( 0.4 Q220N 2.1 ( 1.3 0.5 ( 0.3 0.108 Q220K 14.1 ( 1.0 Q220W 13.1 ( 1.3 11.5 ( 0.9 0.157 Q220E -11.1 ( 1.1 -4.0 ( 0.3 <0.001 S222G 12.0 ( 2.1 1.1 ( 0.6 0.001 S222E -0.3 ( 2.4 1.3 ( 0.5 0.512 E217G/S222G 12.4 ( 1.9 E217S/S222E 26.1 ( 4.5 averagec 10.4 ( 7.3 4.0 ( 4.2 0.067 a Values are the percentage difference vs TM3/4 WT or TM3/4 V232D migration of SDS-PAGE gels. Login to comment
146 While there may be a potential charge factor in the migration patterns for certain Q220 mutations (Q220E, Q220K, and Q220R; Figure 3), the migration rates of other ECL2 mutants cannot be rationalized as simple functions of adding or subtracting single charges. Login to comment
147 For example, S222E and WT migrate at approximately the same rate, but Q220E moves at -11% vs WT; both S222G and E217G/S222G are at +12%; Q220K, Q220R, and Q220W are each at +13-15%. Login to comment