ABCMdb

ABCC7 p.Ser222Glu

Predicted by SNAP2:	A: N (53%), C: D (71%), D: D (80%), E: D (85%), F: D (66%), G: D (66%), H: D (85%), I: D (71%), K: D (85%), L: D (80%), M: D (80%), N: N (66%), P: D (85%), Q: D (80%), R: D (85%), T: N (57%), V: D (80%), W: D (91%), Y: D (85%),
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: D, Q: D, R: D, T: N, V: D, W: D, Y: D,

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Publications
[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
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
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
148 Moreover, in construct E217S/S222E, the net charge is not changed vs WT, yet the mutant runs at +26%. Login to comment

[hide] Detergent binding explains anomalous SDS-PAGE migr... Proc Natl Acad Sci U S A. 2009 Feb 10;106(6):1760-5. Epub 2009 Jan 30. Rath A, Glibowicka M, Nadeau VG, Chen G, Deber CM
Detergent binding explains anomalous SDS-PAGE migration of membrane proteins.
Proc Natl Acad Sci U S A. 2009 Feb 10;106(6):1760-5. Epub 2009 Jan 30., 2009-02-10 [PMID:19181854]

Abstract [show]
Migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) that does not correlate with formula molecular weights, termed "gel shifting," appears to be common for membrane proteins but has yet to be conclusively explained. In the present work, we investigate the anomalous gel mobility of helical membrane proteins using a library of wild-type and mutant helix-loop-helix ("hairpin") sequences derived from transmembrane segments 3 and 4 of the human cystic fibrosis transmembrane conductance regulator (CFTR), including disease-phenotypic residue substitutions. We find that these hairpins migrate at rates of -10% to +30% vs. their actual formula weights on SDS-PAGE and load detergent at ratios ranging from 3.4-10 g SDS/g protein. We additionally demonstrate that mutant gel shifts strongly correlate with changes in hairpin SDS loading capacity (R(2) = 0.8), and with hairpin helicity (R(2) = 0.9), indicating that gel shift behavior originates in altered detergent binding. In some cases, this differential solvation by SDS may result from replacing protein-detergent contacts with protein-protein contacts, implying that detergent binding and folding are intimately linked. The CF-phenotypic V232D mutant included in our library may thus disrupt CFTR function via altered protein-lipid interactions. The observed interdependence between hairpin migration, SDS aggregation number, and conformation additionally suggests that detergent binding may provide a rapid and economical screen for identifying membrane proteins with robust tertiary and/or quaternary structures.

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No. Sentence Comment
61 PA/VD and ES/SE denote the P205A/V232D and E217S/S222E hairpins, respectively. Login to comment
62 V232D, V232A, P205S, and Q220W) migrated as WT within statistical significance; 2 were faster (V232D and V232K); and 4 were slower (G228L, E217V, E217F, and E217S/S222E). Login to comment
70 The mutant hairpins ranged in loading levels from 3.4-10 g SDS/g, with V232D binding significantly fewer SDS molecules than WT, and the E217F and E217S/S222E mutants binding significantly more. Login to comment
71 All hairpins load more detergent than do intact cytochrome b5, KcsA, and Glut1 [range 0.7-1.7 g SDS/g protein, (8-10)], and the E217F and E217S/S222E mutants are apparently the highest reported binders among the admittedly limited numbers of membrane proteins evaluated to date. Login to comment
85 Gel shifts, SDS binding, helicity, and column MW of TM3/4 hairpins Hairpin* Gel shift (dMW, %) Bound SDS (g/g) Helicity (MRE X 103)† Column MW (mut-wt, %)‡ V232Dcf -11 Ϯ 2.6 3.4 Ϯ 0.9 -17 Ϯ 1.2 ϩ19 Ϯ 1.5 V232K -10 Ϯ 3.0 3.8 Ϯ 0.6 -16 Ϯ 1.1 ϩ5.6 Ϯ 1.6 A204L -2.2 Ϯ 2.3 6.0 Ϯ 0.7 -18 Ϯ 1.3 ϩ3.4 Ϯ 1.6 P205A/V232Dcf ϩ0.12 Ϯ 5.2 4.7 Ϯ 0.4 -19 Ϯ 2.6 ϩ21 Ϯ 0.6 WT ϩ0.42 Ϯ 4.5 5.4 Ϯ 1.4 -18 Ϯ 2.2 0.0 Ϯ 0.79 V232A ϩ3.6 Ϯ 3.7 5.2 Ϯ 0.4 -18 Ϯ 0.9 ϩ6.1 Ϯ 1.9 P205Scf ϩ4.7 Ϯ 6.0 4.7 Ϯ 1.0 -18 Ϯ 0.7 ϩ4.4 Ϯ 1.6 Q220W ϩ6.3 Ϯ 2.4 5.0 Ϯ 0.7 -21 Ϯ 2.7 -4.9 Ϯ 1.3 G228L ϩ14 Ϯ 5.1 6.9 Ϯ 1.4 -23 Ϯ 1.7 ϩ14 Ϯ 2.6 E217V ϩ28 Ϯ 1.3 6.7 Ϯ 1.0 -25 Ϯ 1.7 ϩ32 Ϯ 4.0 E217F ϩ29 Ϯ 2.8 9.4 Ϯ 1.9 -28 Ϯ 2.6 ϩ17 Ϯ 1.1 E217S/S222E ϩ29 Ϯ 7.6 10 Ϯ 2.3 -25 Ϯ 2.8 ϩ35 Ϯ 0.9 Glycophorin§ - 3.4 Ϯ 0.6 -9.5 Ϯ 1.2 ϩ83 Ϯ 5.1 *Mutant hairpins are listed in order of increasing gel shift. Login to comment
97 PA/VD and ES/SE denote the P205A/V232D and E217S/S222E hairpins, respectively. Login to comment
106 In the presence of the iso-hydropathic mutant E217S/S222E, correlations between each parameter and hydropathy range from R2 values of 0.371 (for bound SDS vs. hydropathy, Fig. 4) to 0.582 (for gel shift vs. hydropathy, Fig. S3). Login to comment
127 It is possible that the 9-10 g SDS/g stoichiometry of E217F and the iso-hydropathic E217S/S222E mutant are representative of detergent loading by a fully ''denatured`` helical membrane protein (such as the ''caterpillar`` structure in Fig. 5F). Login to comment
137 The E217S/S222E mutant is marked with an asterisk. Login to comment
138 Correlation coefficients (R2) of the best fit line in the absence of E217S/S222E (red) or with all mutants (black) are shown. Login to comment
139 Trendline P value in the absence of E217S/S222E is 0.002. Login to comment