ABCMdb

ABCC8 p.Asp1505Asn

Predicted by SNAP2:	A: D (91%), C: D (91%), E: D (91%), F: D (95%), G: D (95%), H: D (95%), I: D (95%), K: D (95%), L: D (95%), M: D (95%), N: D (91%), P: D (95%), Q: D (75%), R: D (95%), S: D (91%), T: D (91%), V: D (95%), W: D (95%), Y: D (95%),
Predicted by PROVEAN:	A: D, C: D, E: D, F: D, G: D, H: D, I: D, K: D, L: D, M: D, N: D, P: D, Q: D, R: D, S: D, T: D, V: D, W: D, Y: D,

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Publications
[hide] MgATP activates the beta cell KATP channel by inte... Proc Natl Acad Sci U S A. 1998 Jun 9;95(12):7185-90. Gribble FM, Tucker SJ, Haug T, Ashcroft FM
MgATP activates the beta cell KATP channel by interaction with its SUR1 subunit.
Proc Natl Acad Sci U S A. 1998 Jun 9;95(12):7185-90., [PMID:9618560]

Abstract [show]
ATP-sensitive potassium (KATP) channels in the pancreatic beta cell membrane mediate insulin release in response to elevation of plasma glucose levels. They are open at rest but close in response to glucose metabolism, producing a depolarization that stimulates Ca2+ influx and exocytosis. Metabolic regulation of KATP channel activity currently is believed to be mediated by changes in the intracellular concentrations of ATP and MgADP, which inhibit and activate the channel, respectively. The beta cell KATP channel is a complex of four Kir6.2 pore-forming subunits and four SUR1 regulatory subunits: Kir6.2 mediates channel inhibition by ATP, whereas the potentiatory action of MgADP involves the nucleotide-binding domains (NBDs) of SUR1. We show here that MgATP (like MgADP) is able to stimulate KATP channel activity, but that this effect normally is masked by the potent inhibitory effect of the nucleotide. Mg2+ caused an apparent reduction in the inhibitory action of ATP on wild-type KATP channels, and MgATP actually activated KATP channels containing a mutation in the Kir6.2 subunit that impairs nucleotide inhibition (R50G). Both of these effects were abolished when mutations were made in the NBDs of SUR1 that are predicted to abolish MgATP binding and/or hydrolysis (D853N, D1505N, K719A, or K1384M). These results suggest that, like MgADP, MgATP stimulates KATP channel activity by interaction with the NBDs of SUR1. Further support for this idea is that the ATP sensitivity of a truncated form of Kir6.2, which shows functional expression in the absence of SUR1, is unaffected by Mg2+.

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Sentences [show]
No. Sentence Comment
7 Both of these effects were abolished when mutations were made in the NBDs of SUR1 that are predicted to abolish MgATP binding and/or hydrolysis (D853N, D1505N, K719A, or K1384M). Login to comment
106 We therefore explored the effects of mutation of the WB aspartate to asparagine in either the first (D853N) or the second (D1505N) NBD on the sensitivity of the channel to inhibition by ATP. Login to comment
107 Giant patches excised from oocytes coinjected with mRNAs encoding Kir6.2 and either D853N-SUR1 or D1505N-SUR1 developed large Kϩ currents, which were of comparable amplitude to those observed for wild-type channels, after patch excision. Login to comment
108 The mean macroscopic conductance was 95 Ϯ 24 nS (n ϭ 5) for D853N-SUR1 channels, 48 Ϯ 16 nS (n ϭ 8) for D1505N-SUR1 channels, and 49 Ϯ 6 nS (n ϭ 18) for wild-type channels. Login to comment
110 Fig. 2 compares the relationship between ATP concentration and channel inhibition for wild-type, D853N-SUR1, and D1505N-SUR1 currents. Login to comment
112 The Ki for ATP inhibition of D853N-SUR1 currents was 13.4 Ϯ 0.2 ␮M (n ϭ 4), and that of D1505N-SUR1 was 16.0 Ϯ 2.6 ␮M (n ϭ 5), compared with 28 ␮M for wild-type currents (P ϭ 0.05 by ANOVA). Login to comment
134 Mean ATP dose-response relationships for Kir6.2͞SUR1 (f, n ϭ 15), Kir6.2͞SUR1-D853N (⅜, n ϭ 4) or Kir6.2͞SUR1-D1505N (F, n ϭ 5) currents, measured in the presence of Mg2ϩ. Login to comment

[hide] The interaction of nucleotides with the tolbutamid... J Physiol. 1997 Oct 1;504 ( Pt 1):35-45. Gribble FM, Tucker SJ, Ashcroft FM
The interaction of nucleotides with the tolbutamide block of cloned ATP-sensitive K+ channel currents expressed in Xenopus oocytes: a reinterpretation.
J Physiol. 1997 Oct 1;504 ( Pt 1):35-45., [PMID:9350615]

Abstract [show]
1. We have examined the mechanism by which nucleotides modulate the tolbutamide block of the beta-cell ATP-sensitive K+ channel (KATP channel), using wild-type and mutant KATP channels heterologously expressed in Xenopus oocytes. This channel is composed of sulphonylurea receptor (SUR1) and pore-forming (Kir6.2) subunits. 2. The dose-response relation for tolbutamide block of wild-type KATP currents in the absence of nucleotide showed both a high-affinity (Ki = 2.0 microM) and a low-affinity (Ki = 1.8 mM) site. 3. The dose-response relation for tolbutamide block of Kir6.2 delta C36 (a truncated form of Kir6.2 which is expressed independently of SUR1) was best fitted with a single, low-affinity site (Ki = 1.7 mM). This indicates that the high-affinity site resides on SUR1, whereas the low-affinity site is located on Kir6.2. 4. ADP (100 microM) had a dual effect on wild-type KATP currents: the nucleotide enhanced the current in the presence of Mg2+, but was inhibitory in the absence of Mg2+. Kir6.2 delta C36 currents were blocked by 100 microM ADP in the presence of Mg2+. 5. For wild-type KATP currents, the blocking effect of 0.5 mM tolbutamide appeared greater in the presence of 100 microM MgADP (84 +/- 2%) than in its absence (59 +/- 4%). When SUR1 was mutated to abolish MgADP activation of KATP currents (K719A or K1384M), there was no difference in the extent of tolbutamide inhibition in the presence or absence of MgADP. 6. The Ki for tolbutamide interaction with either the high- or low-affinity site was unaffected by 100 microM MgADP, for both wild-type and K719A-K1384M currents. 7. MgGDP (100 microM) enhanced wild-type KATP currents and was without effect on K719A-K1384M currents. It did not affect the Ki for tolbutamide block at either the high- or low-affinity site. 8. Our results indicate that interaction of tolbutamide with the high-affinity site (on SUR1) abolishes the stimulatory action of MgADP. This unmasks the inhibitory effect of ADP and leads to an apparent increase in channel inhibition. Under physiological conditions, abolition of MgADP activation is likely to constitute the principal mechanism by which tolbutamide inhibits the KATP channel.

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Sentences [show]
No. Sentence Comment
127 Mutation of the WB aspartate residues in either NBD1 (D853N) or NBD2 (D1505N) of SURI abolished the stimulatory effects of MgADP on KATP currents (Fig. 4) and prevented the MgADP-dependent enhancement of tolbutamide block (Fig. 3). Login to comment