ABCMdb

ABCC7 p.Arg134Gln

Predicted by SNAP2:	A: D (75%), C: D (80%), D: D (91%), E: D (85%), F: D (85%), G: D (80%), H: D (75%), I: D (80%), K: D (59%), L: D (66%), M: D (80%), N: D (75%), P: D (91%), Q: D (71%), S: D (71%), T: D (71%), V: D (80%), W: D (91%), Y: D (85%),
Predicted by PROVEAN:	A: N, C: D, D: D, E: N, F: D, G: D, H: N, I: D, K: N, L: D, M: N, N: N, P: D, Q: N, S: N, T: D, V: D, W: D, Y: D,

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[hide] Positive charges at the intracellular mouth of the... J Gen Physiol. 2006 Nov;128(5):535-45. Epub 2006 Oct 16. Aubin CN, Linsdell P
Positive charges at the intracellular mouth of the pore regulate anion conduction in the CFTR chloride channel.
J Gen Physiol. 2006 Nov;128(5):535-45. Epub 2006 Oct 16., [PMID:17043152]

Abstract [show]
Many different ion channel pores are thought to have charged amino acid residues clustered around their entrances. The so-called surface charges contributed by these residues can play important roles in attracting oppositely charged ions from the bulk solution on one side of the membrane, increasing effective local counterion concentration and favoring rapid ion movement through the channel. Here we use site-directed mutagenesis to identify arginine residues contributing important surface charges in the intracellular mouth of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel pore. While wild-type CFTR was associated with a linear current-voltage relationship with symmetrical solutions, strong outward rectification was observed after mutagenesis of two arginine residues (R303 and R352) located near the intracellular ends of the fifth and sixth transmembrane regions. Current rectification was dependent on the charge present at these positions, consistent with an electrostatic effect. Furthermore, mutagenesis-induced rectification was more pronounced at lower Cl(-) concentrations, suggesting that these mutants had a reduced ability to concentrate Cl(-) ions near the inner pore mouth. R303 and R352 mutants exhibited reduced single channel conductance, especially at negative membrane potentials, that was dependent on the charge of the amino acid residue present at these positions. However, the very low conductance of both R303E and R352E-CFTR could be greatly increased by elevating intracellular Cl(-) concentration. Modification of an introduced cysteine residue at position 303 by charged methanethiosulfonate reagents reproduced charge-dependent effects on current rectification. Mutagenesis of arginine residues in the second and tenth transmembrane regions also altered channel permeation properties, however these effects were not consistent with changes in channel surface charges. These results suggest that positively charged arginine residues act to concentrate Cl(-) ions at the inner mouth of the CFTR pore, and that this contributes to maximization of the rate of Cl(-) ion permeation through the pore.

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No. Sentence Comment
131 However, both R134Q and R1030Q did yield functional channels (Fig. 10). Login to comment
132 R134Q Figure 7. Modification of CFTR by intracellular MTSES. Login to comment
143 Measurable single channel activity was not observed after R134Q expression; however, Fig. 10 C shows an example of a very small apparent single channel opening frequently observed in a patch excised from an R134Q-expressing cell. Login to comment
144 This tiny current suggests that R134Q has an extremely small unitary conductance below the accurate resolution of single channel recording. Login to comment
172 (A) Example leak-subtracted macroscopic I-V relationships from R134Q and R1030Q-CFTR in inside-out membrane patches with symmetrical 154 mM Cl- solu- tions, after maximal channel activation. Login to comment
174 * indicates a significant difference from wild type at the same Cl-concentration (P < 10-4, two-tailed t test), † indicates a significant difference from R134Q at 154 mM Cl- (P < 0.005, two-tailed t test). Login to comment
177 For R134Q, the tiny current associated with a putative channel opening is identified by a line above it. Login to comment
207 R134Q and R1030Q do not appear consistent with loss of an intracellular surface charge. Login to comment
208 R134Q is associated with outward rectification (Fig. 10, A and B); however, this effect shows a complex Cl-dependence that, unlike that of R303E, R303Q, and R352Q (Fig. 3 B), is not consistent with a simple surface charge effect. Furthermore, R134Q shows an extremely small apparent unitary conductance (Fig. 10 C). Login to comment