ABCC8 p.Arg74Lys
Predicted by SNAP2: | A: N (53%), C: D (63%), D: D (80%), E: N (53%), F: D (63%), G: D (95%), H: N (82%), I: N (57%), K: N (87%), L: N (78%), M: N (57%), N: N (61%), P: N (53%), Q: N (66%), S: N (61%), T: N (61%), V: N (57%), W: D (91%), Y: D (75%), |
Predicted by PROVEAN: | A: D, C: D, D: D, E: D, F: D, G: D, H: D, I: D, K: N, L: D, M: D, N: D, P: D, Q: D, S: D, T: D, V: D, W: D, Y: D, |
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[hide] N-terminal transmembrane domain of SUR1 controls g... J Gen Physiol. 2011 Mar;137(3):299-314. Epub 2011 Feb 14. Pratt EB, Tewson P, Bruederle CE, Skach WR, Shyng SL
N-terminal transmembrane domain of SUR1 controls gating of Kir6.2 by modulating channel sensitivity to PIP2.
J Gen Physiol. 2011 Mar;137(3):299-314. Epub 2011 Feb 14., [PMID:21321069]
Abstract [show]
Functional integrity of pancreatic adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels depends on the interactions between the pore-forming potassium channel subunit Kir6.2 and the regulatory subunit sulfonylurea receptor 1 (SUR1). Previous studies have shown that the N-terminal transmembrane domain of SUR1 (TMD0) interacts with Kir6.2 and is sufficient to confer high intrinsic open probability (P(o)) and bursting patterns of activity observed in full-length K(ATP) channels. However, the nature of TMD0-Kir6.2 interactions that underlie gating modulation is not well understood. Using two previously described disease-causing mutations in TMD0 (R74W and E128K), we performed amino acid substitutions to study the structural roles of these residues in K(ATP) channel function in the context of full-length SUR1 as well as TMD0. Our results revealed that although R74W and E128K in full-length SUR1 both decrease surface channel expression and reduce channel sensitivity to ATP inhibition, they arrive there via distinct mechanisms. Mutation of R74 uniformly reduced TMD0 protein levels, suggesting that R74 is necessary for stability of TMD0. In contrast, E128 mutations retained TMD0 protein levels but reduced functional coupling between TMD0 and Kir6.2 in mini-K(ATP) channels formed by TMD0 and Kir6.2. Importantly, E128K full-length channels, despite having a greatly reduced P(o), exhibit little response to phosphatidylinositol 4,5-bisphosphate (PIP(2)) stimulation. This is reminiscent of Kir6.2 channel behavior in the absence of SUR1 and suggests that TMD0 controls Kir6.2 gating by modulating Kir6.2 interactions with PIP(2). Further supporting this notion, the E128W mutation in full-length channels resulted in channel inactivation that was prevented or reversed by exogenous PIP(2). These results identify a critical determinant in TMD0 that controls Kir6.2 gating by controlling channel sensitivity to PIP(2). Moreover, they uncover a novel mechanism of K(ATP) channel inactivation involving aberrant functional coupling between SUR1 and Kir6.2.
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No. Sentence Comment
78 Surface expression for every R74X-mutant tested, except the charge-conserving R74K mutation, was significantly reduced to <40% of WT (Fig. 1 B).
X
ABCC8 p.Arg74Lys 21321069:78:78
status: NEW107 R74K, which had surface expression at 74 ± 4% of WT by chemiluminescence (Fig. 1 B), showed both upper and lower glycosylation bands.
X
ABCC8 p.Arg74Lys 21321069:107:0
status: NEW121 R74K had the highest level, with 70% of WT; all other R74 substitutions (alanine, phenylalanine, tyrosine, and tryptophan) resulted in significantly decreased TMD0 levels, with <25% of WT (Fig. 3, A and B), possibly a result of increased degradation.
X
ABCC8 p.Arg74Lys 21321069:121:0
status: NEW122 Next, we examined the surface expression of R74W and R74K fTMD0 when coexpressed with Kir6.2C36 using immunofluorescent obtain the IC50 for ATP inhibition (Fig. 2 B).
X
ABCC8 p.Arg74Lys 21321069:122:53
status: NEW123 As with trafficking, the charge-conserving mutant R74K had minimal effect on ATP inhibition (IC50 = 18 ± 2 and 17 ± 1 µM for WT and R74K, respectively).
X
ABCC8 p.Arg74Lys 21321069:123:50
status: NEWX
ABCC8 p.Arg74Lys 21321069:123:144
status: NEW141 No surface fTMD0 was detected above background signal using anti-FLAG antibody for either mutant construct, even though the R74K mutation exhibited the greatest total TMD0 level (70% of WT; Fig. 3 B); in contrast, surface staining of cells expressing WT mini-KATP channels was clearly visible (Fig. 3 E).
X
ABCC8 p.Arg74Lys 21321069:141:124
status: NEW142 Consistently, in single-channel recordings from cells coexpressing R74K or R74W fTMD0 with Kir6.2C36, no channel kinetics distinct from those characteristic of channels formed by Kir6.2C36 alone were observed (unpublished data).
X
ABCC8 p.Arg74Lys 21321069:142:67
status: NEW149 (E) Cells cotransfected with WT, R74W, R74K, or E128K fTMD0 and Kir6.2C36 were probed with -FLAG antibody 48 h after transfection to detect surface expression of mini-KATP channels.
X
ABCC8 p.Arg74Lys 21321069:149:39
status: NEW150 A rim of surface staining was detected in WTand E128K-transfected cells (green, inset images), but not in either R74W- or R74K-transfected cells.
X
ABCC8 p.Arg74Lys 21321069:150:122
status: NEW258 It may seem surprising that although total R74K TMD0 protein remains at near WT levels (Fig. 3, A and B), no R74K mini-channels were observed at the cell surface either by immunostaining or single-channel recording.
X
ABCC8 p.Arg74Lys 21321069:258:43
status: NEWX
ABCC8 p.Arg74Lys 21321069:258:109
status: NEW259 That the R74K mutation has a more pronounced effect on the surface expression of mini-KATP versus full-length channels (i.e., no detectable surface expression of mini-channels [Fig. 3 C] vs. 80% of WT for full-length channels [Fig. 1, B and C]) suggests a role for extra-TMD0 regions of SUR1 in channel protein folding and assembly.
X
ABCC8 p.Arg74Lys 21321069:259:9
status: NEW288 In addition, the ATP-dependent recovery from inactivation in the E128W mutant suggests that conformational changes in Kir6.2 tertiary structure of R74K TMD0 and its ability to assemble with Kir6.2 to form channels may be contingent upon the SUR1 structures downstream of TMD0.
X
ABCC8 p.Arg74Lys 21321069:288:147
status: NEW