ABCMdb

ABCC8 p.Ile1424Val

Predicted by SNAP2:	A: D (75%), C: D (63%), D: D (91%), E: D (91%), F: D (80%), G: D (91%), H: D (85%), K: D (91%), L: D (66%), M: D (59%), N: D (91%), P: D (91%), Q: D (85%), R: D (91%), S: D (85%), T: D (75%), V: N (57%), W: D (85%), Y: D (85%),
Predicted by PROVEAN:	A: D, C: D, D: D, E: D, F: D, G: D, H: D, K: D, L: N, M: D, N: D, P: D, Q: D, R: D, S: D, T: D, V: N, W: D, Y: D,

[switch to compact view]
Comments [show]

None has been submitted yet.

Publications
[hide] Review. SUR1: a unique ATP-binding cassette protei... Philos Trans R Soc Lond B Biol Sci. 2009 Jan 27;364(1514):257-67. Aittoniemi J, Fotinou C, Craig TJ, de Wet H, Proks P, Ashcroft FM
Review. SUR1: a unique ATP-binding cassette protein that functions as an ion channel regulator.
Philos Trans R Soc Lond B Biol Sci. 2009 Jan 27;364(1514):257-67., [PMID:18990670]

Abstract [show]
SUR1 is an ATP-binding cassette (ABC) transporter with a novel function. In contrast to other ABC proteins, it serves as the regulatory subunit of an ion channel. The ATP-sensitive (KATP) channel is an octameric complex of four pore-forming Kir6.2 subunits and four regulatory SUR1 subunits, and it links cell metabolism to electrical activity in many cell types. ATPase activity at the nucleotide-binding domains of SUR results in an increase in KATP channel open probability. Conversely, ATP binding to Kir6.2 closes the channel. Metabolic regulation is achieved by the balance between these two opposing effects. Precisely how SUR1 talks to Kir6.2 remains unclear, but recent studies have identified some residues and domains that are involved in both physical and functional interactions between the two proteins. The importance of these interactions is exemplified by the fact that impaired regulation of Kir6.2 by SUR1 results in human disease, with loss-of-function SUR1 mutations causing congenital hyperinsulinism and gain-of-function SUR1 mutations leading to neonatal diabetes. This paper reviews recent data on the regulation of Kir6.2 by SUR1 and considers the molecular mechanisms by which SUR1 mutations produce disease.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
182 The I1425V mutation in NBD2 also shows greater Mg-nucleotide-dependent stimulation of the channel activity (Babenko et al. 2006; I1424V in their notation). Login to comment
185 Such naturally occurring mutations TNDM PNDM DEND TNDM PNDM DEND iDEND WT P206L D212N P45L N72S P207S E208K+Y263D D212I T229I A1185E V1522L+Y229I F132L 0 0.05 0.10 0.15 fractionofcurrentremaining in3mMMgATP(a) (b) (i) (ii) Figure 4. Login to comment

[hide] Activating mutations in the ABCC8 gene in neonatal... N Engl J Med. 2006 Aug 3;355(5):456-66. Babenko AP, Polak M, Cave H, Busiah K, Czernichow P, Scharfmann R, Bryan J, Aguilar-Bryan L, Vaxillaire M, Froguel P
Activating mutations in the ABCC8 gene in neonatal diabetes mellitus.
N Engl J Med. 2006 Aug 3;355(5):456-66., [PMID:16885549]

Abstract [show]
BACKGROUND: The ATP-sensitive potassium (K(ATP)) channel, composed of the beta-cell proteins sulfonylurea receptor (SUR1) and inward-rectifying potassium channel subunit Kir6.2, is a key regulator of insulin release. It is inhibited by the binding of adenine nucleotides to subunit Kir6.2, which closes the channel, and activated by nucleotide binding or hydrolysis on SUR1, which opens the channel. The balance of these opposing actions determines the low open-channel probability, P(O), which controls the excitability of pancreatic beta cells. We hypothesized that activating mutations in ABCC8, which encodes SUR1, cause neonatal diabetes. METHODS: We screened the 39 exons of ABCC8 in 34 patients with permanent or transient neonatal diabetes of unknown origin. We assayed the electrophysiologic activity of mutant and wild-type K(ATP) channels. RESULTS: We identified seven missense mutations in nine patients. Four mutations were familial and showed vertical transmission with neonatal and adult-onset diabetes; the remaining mutations were not transmitted and not found in more than 300 patients without diabetes or with early-onset diabetes of similar genetic background. Mutant channels in intact cells and in physiologic concentrations of magnesium ATP had a markedly higher P(O) than did wild-type channels. These overactive channels remained sensitive to sulfonylurea, and treatment with sulfonylureas resulted in euglycemia. CONCLUSIONS: Dominant mutations in ABCC8 accounted for 12 percent of cases of neonatal diabetes in the study group. Diabetes results from a newly discovered mechanism whereby the basal magnesium-nucleotide-dependent stimulatory action of SUR1 on the Kir pore is elevated and blockade by sulfonylureas is preserved.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
43 A homology model26 of the human SUR1 core was used to map the mutant residues.27 Results ABCC8 Mutations in Patients with Permanent or Transient Neonatal Diabetes We identified seven heterozygous ABCC8 mutations in 9 of 34 patients with neonatal diabetes: L213R and I1424V in 2 with permanent neonatal diabetes and C435R, L582V, H1023Y, R1182Q, and R1379C in patients with transient neonatal diabetes. Login to comment
48 The L213R, H1023Y, and I1424V were noninherited mutations, as were the L582V and R1379C mutations in one family each. Login to comment
67 After identification of the mutations in the patients with permanent neonatal diabetes, glyburide therapy was initiated and found to be successful and insulin was discontinued after 2 days in the proband from Family 12 and after 15 days in the proband from A Permanent Neonatal Diabetes B Transient Neonatal Diabetes NN NN NN NN NN NN NN NNNM NM NM NM NM NMNM NM NM* NM* NA NA NA NA NANANANANA NA NA NA NA Family 12 (L213R) NNNN NM Family 36 (L582V) 16 NN NN NNNM NMNM Family 28 (H1023Y) Family 34 (R1182Q) Family 16 (L582V) Family 17 (R1379C) Family 16 (I1424V) I II III I II III IV V 1 1 2 1 2 3 4 5 2 1 2 1 2 1 2 1 2 3 4 5 6 7 3 1 4 6 NNNN NN NNNM NMNM* Family 13 (C435R) Family 19 (R1379C) Transient Neonatal Diabetes Figure 1. Login to comment
106 Figure 2 shows that the normalized activities of mutant channels (containing the I1424V or H1023Y variant) in intact cells and in 1 mM magnesium ATP are nearly four and seven times as great, respectively, as those of wild-type channels under similar nucleotide conditions. Login to comment
111 To exclude the possibility that overactivity of the mutant I1424V and H1023Y channels is caused by either a gain in the intrinsic, ligand-independent, activity or by attenuation of the inhibitory action of ATP on Kir6.2, we measured the mean ligand-independent PO values and steady-state ATP-inhibitory curves (i.e., without magnesium) (Fig. 3). Login to comment
113 We conclude that mutant I1424V and H1023Y channels overactivate beta-cell KATP channels under physiologic magnesium-nucleotide conditions by increasing the magne- 2006462 sium-nucleotide-dependent stimulatory action of SUR1 on the pore. Login to comment
115 A concentration of 200 μM tolbutamide, which saturates the high-affinity binding site of wild-type SUR1,25 inhibited wild-type and mutant channels (containing the I1424V or H1023Y variant) to a similar degree in the absence of magnesium nucleotides (Fig. 4A). Login to comment
116 This inhibition indicated that tolbutamide binding to SUR1 and its functional coupling to the Kir6.2 pore were not altered by the I1424V or H1023Y mutations. Login to comment
122 Our results are consistent with a report that neonatal diabetes develops in transgenic mice expressing a mutant Kir6.2 subunit with P<0.001 P<0.01 P<0.001 P<0.001 P<0.001 P<0.001 P<0.05 P<0.05 P<0.001 P<0.001 Intact Cells 1 mM Magnesium ATP 1 mM ATP 5% of Ligand- indepen- dent activity 5% of Ligand- indepen- dent activity 5% of Ligand- indepen- dent activity 5% of Ligand- indepen- dent activity Channel with I1424V Mutation Wild-Type Channel Channel with H1023Y Mutation Channels with H1023Y Mutation and Wild-Type Figure 2. Login to comment
142 In clinical practice, there is no way to distin- Ligand-IndependentPO RelativeActivity ofKATPChannels 0.2 0.4 0.0 Channel with I1424V Mutation Wild-Type Channel Channel with H1023Y Mutation 0.6 A B 0.6 0.8 0.4 0.2 0.0 0 1 10 100 1000 ATP (μM) 1.0 Channel with I1424V mutation Channel with H1023Y mutation Wild-type channel IC50(ATP)=7.99±0.42 μM h=1.18±0.06 R2=0.998 IC50(ATP)=8.85±0.36 μM h=1.14±0.1 R2=0.999 IC50(ATP)=6.97±0.39 μM h=1.24±0.08 R2=0.997 Figure 3. Login to comment
149 2006464 Normal Beta Cell Normal Beta Cell Without Nucleotides With 0.5 mM Magnesium ATP and 0.5 mM ADP Mutant Beta Cell Mutant Beta Cell in the Presence of Sulfonylurea RelativeActivityin50mMTIb I1424V Mutant Wild-Type Channel H1023Y Mutant I1424V Mutant Wild-Type Channel H1023Y Mutant Normal SUR1 0.5 ATP K+ K+ Ca2+ 0.4 0.3 0.2 0.1 0.0 RelativeActivityin200mMTIb 0.5 0.4 0.3 0.2 0.1 0.0 Stimulatory action of magnesium nucleotides (low ATP:ADP ratio) Normal SUR1 ATP K+ K+ Ca2+ Stimulatory action of magnesium nucleotides (elevated ATP:ADP ratio) Stimulates insulin secretion Mutant SUR1 ATP Ca2+ Stimulatory action of magnesium nucleotides (elevated ATP:ADP ratio) Mutant SUR1 Sulfonylurea ATP K+ Ca2+ Reduced stimulatory action of magnesium nucleotides (elevated ATP:ADP ratio) Stimulates insulin secretion Decreased insulin secretion Hyperglycemia X X Decreased Ca2+ influx K+ Membrane depolarization Increased glucose Increased glucose Increased glucose Membrane depolarization A C E B D F The New England Journal of Medicine Downloaded from nejm.org at UNIV OF NC/ACQ SRVCS on March 7, 465 guish patients with ABCC8 or KCNJ11 mutations from those with abnormalities in chromosome 6q24. Login to comment
42 A homology model26 of the human SUR1 core was used to map the mutant residues.27 Results ABCC8 Mutations in Patients with Permanent or Transient Neonatal Diabetes We identified seven heterozygous ABCC8 mutations in 9 of 34 patients with neonatal diabetes: L213R and I1424V in 2 with permanent neonatal diabetes and C435R, L582V, H1023Y, R1182Q, and R1379C in patients with transient neonatal diabetes. Login to comment
47 The L213R, H1023Y, and I1424V were noninherited mutations, as were the L582V and R1379C mutations in one family each. Login to comment
66 After identification of the mutations in the patients with permanent neonatal diabetes, glyburide therapy was initiated and found to be successful and insulin was discontinued after 2 days in the proband from Family 12 and after 15 days in the proband from A Permanent Neonatal Diabetes B Transient Neonatal Diabetes NN NN NN NN NN NN NN NN NM NM NM NM NM NM NM NM NM* NM* NA NA NA NA NA NA NA NA NA NA NA NA NA Family 12 (L213R) NN NN NM Family 36 (L582V) 16 NN NN NN NM NM NM Family 28 (H1023Y) Family 34 (R1182Q) Family 16 (L582V) Family 17 (R1379C) Family 16 (I1424V) I II III I II III IV V 1 1 2 1 2 3 4 5 2 1 2 1 2 1 2 1 2 3 4 5 6 7 3 1 4 6 NN NN NN NN NM NM NM* Family 13 (C435R) Family 19 (R1379C) Transient Neonatal Diabetes Figure 1. Login to comment
92 Mutation Sex Wk of Gestation Birth Weight At Diagnosis At Metabolic Testing Current Treatment Age Weight Presentation Glucose Age Height Weight Insulin g (percentile) days g mmol/liter yr cm (SD)ߤ kg (percentile) U/kg/day Permanent neonatal diabetes 12 L213R Male 41 3065 (22) 125 5320 Polyuria, polydipsia 28.6 4.75 107.5 (0) 17 (50) 0.12 Glb, 10 mg/day 16 I1424V Male 40 3080 (25) 33 3360 Ketoacidosis 66 16.5 178 (+0.9) 69 (85) 0.88 Glb, 15 mg/day Transient neonatal diabetes 13 C435R Male 40 3040 (25) 32 3575 Polyuria, polydipsia 44.5 4.75 108.8 (+0.5) 17.5 (75) 16 L582V Male 40 3350 (50) 15 3210 Polyuria, polydipsia 51.4 5.25 117 (+1.9) 18.4 (50) 17 R1379C Female 40 2050 (<3) 3 2100 Hyperglycemia 6.9 5.25 114.5 (+1.6) 19.5 (82) 19 R1379C Female 40 2330 (<3) 60 4900 Polyuria, polydipsia 22 15.7 158 (-0.8) 54 (70) 1.2 Glb, 10 mg/day 28 H1023Y Male 40 3400 (55) 21 NA Ketoacidosis 37.8 16 180 (+1.2) 59.5 (60) 0.5 Glp, 10 mg/day 34 R1182Q Male 34 1830 (8) 4 1680 Hyperglycemia 13.6 2 82 (-1.5) 10.3 (8) 36 L582V Male 40 3570 (67) 74 6100 Polyuria, polydipsia 34 1.8 92 (+2) 14 (90) * Glb denotes glyburide, NA not available, and Glp glipizide. Login to comment
108 Figure 2 shows that the normalized activities of mutant channels (containing the I1424V or H1023Y variant) in intact cells and in 1 mM magnesium ATP are nearly four and seven times as great, respectively, as those of wild-type channels under similar nucleotide conditions. Login to comment
117 A concentration of 200 bc;M tolbutamide, which saturates the high-affinity binding site of wild-type SUR1,25 inhibited wild-type and mutant channels (containing the I1424V or H1023Y variant) to a similar degree in the absence of magnesium nucleotides (Fig. 4A). Login to comment
118 This inhibition indicated that tolbutamide binding to SUR1 and its functional coupling to the Kir6.2 pore were not altered by the I1424V or H1023Y mutations. Login to comment
124 Our results are consistent with a report that neonatal diabetes develops in transgenic mice expressing a mutant Kir6.2 subunit with P<0.001 P<0.01 P<0.001 P<0.001 P<0.001 P<0.001 P<0.05 P<0.05 P<0.001 P<0.001 Intact Cells 1 mM Magnesium ATP 1 mM ATP 5% of Ligand- indepen- dent activity 5% of Ligand- indepen- dent activity 5% of Ligand- indepen- dent activity 5% of Ligand- indepen- dent activity Channel with I1424V Mutation Wild-Type Channel Channel with H1023Y Mutation Channels with H1023Y Mutation and Wild-Type Figure 2. Login to comment
144 In clinical practice, there is no way to distin- Ligand-Independent P O Relative Activity of K ATP Channels 0.2 0.4 0.0 Channel with I1424V Mutation Wild-Type Channel Channel with H1023Y Mutation 0.6 A B 0.6 0.8 0.4 0.2 0.0 0 1 10 100 1000 ATP (bc;M) 1.0 Channel with I1424V mutation Channel with H1023Y mutation Wild-type channel IC50(ATP)=7.99&#b1;0.42 bc;M h=1.18&#b1;0.06 R2=0.998 IC50(ATP)=8.85&#b1;0.36 bc;M h=1.14&#b1;0.1 R2=0.999 IC50(ATP)=6.97&#b1;0.39 bc;M h=1.24&#b1;0.08 R2=0.997 Figure 3. Login to comment
151 Normal Beta Cell Normal Beta Cell Without Nucleotides With 0.5 mM Magnesium ATP and 0.5 mM ADP Mutant Beta Cell Mutant Beta Cell in the Presence of Sulfonylurea Relative Activity in 50 mM TIb I1424V Mutant Wild-Type Channel H1023Y Mutant I1424V Mutant Wild-Type Channel H1023Y Mutant Normal SUR1 0.5 ATP K+ K+ Ca2+ 0.4 0.3 0.2 0.1 0.0 Relative Activity in 200 mM TIb 0.5 0.4 0.3 0.2 0.1 0.0 Stimulatory action of magnesium nucleotides (low ATP:ADP ratio) Normal SUR1 ATP K+ K+ Ca2+ Stimulatory action of magnesium nucleotides (elevated ATP:ADP ratio) Stimulates insulin secretion Mutant SUR1 ATP Ca2+ Stimulatory action of magnesium nucleotides (elevated ATP:ADP ratio) Mutant SUR1 Sulfonylurea ATP K+ Ca2+ Reduced stimulatory action of magnesium nucleotides (elevated ATP:ADP ratio) Stimulates insulin secretion Decreased insulin secretion Hyperglycemia X X Decreased Ca2+ influx K+ Membrane depolarization Increased glucose Increased glucose Increased glucose Membrane depolarization A C E B D F guish patients with ABCC8 or KCNJ11 mutations from those with abnormalities in chromosome 6q24. Login to comment

[hide] ABCC8 and ABCC9: ABC transporters that regulate K+... Pflugers Arch. 2007 Feb;453(5):703-18. Epub 2006 Aug 8. Bryan J, Munoz A, Zhang X, Dufer M, Drews G, Krippeit-Drews P, Aguilar-Bryan L
ABCC8 and ABCC9: ABC transporters that regulate K+ channels.
Pflugers Arch. 2007 Feb;453(5):703-18. Epub 2006 Aug 8., [PMID:16897043]

Abstract [show]
The sulfonylurea receptors (SURs) ABCC8/SUR1 and ABCC9/SUR2 are members of the C-branch of the transport adenosine triphosphatase superfamily. Unlike their brethren, the SURs have no identified transport function; instead, evolution has matched these molecules with K(+) selective pores, either K(IR)6.1/KCNJ8 or K(IR)6.2/KCNJ11, to assemble adenosine triphosphate (ATP)-sensitive K(+) channels found in endocrine cells, neurons, and both smooth and striated muscle. Adenine nucleotides, the major regulators of ATP-sensitive K(+) (K(ATP)) channel activity, exert a dual action. Nucleotide binding to the pore reduces the activity or channel open probability, whereas Mg-nucleotide binding and/or hydrolysis in the nucleotide-binding domains of SUR antagonize this inhibitory action to stimulate channel openings. Mutations in either subunit can alter this balance and, in the case of the SUR1/KIR6.2 channels found in neurons and insulin-secreting pancreatic beta cells, are the cause of monogenic forms of hyperinsulinemic hypoglycemia and neonatal diabetes. Additionally, the subtle dysregulation of K(ATP) channel activity by a K(IR)6.2 polymorphism has been suggested as a predisposing factor in type 2 diabetes mellitus. Studies on K(ATP) channel null mice are clarifying the roles of these metabolically sensitive channels in a variety of tissues.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
141 Analysis of two SUR1 mutant channels, I1424V or H1023Y, demonstrated they were more active than wild-type channels both in on-cell recordings from intact mammalian cells and in isolated patches exposed to a quasiphysiologic concentration of MgATP (1 mM). Login to comment
142 In the absence of Mg2+ , when the stimulatory action of SUR1 on the pore was abolished, there was no significant difference in the ATP inhibitory curves of mutant and wild-type channels, indicating the I1424V or H1023Y receptors exert an enhanced stimulatory action on the pore. Login to comment

[hide] A mutation in the TMD0-L0 region of sulfonylurea r... Diabetes. 2007 May;56(5):1357-62. Epub 2007 Feb 22. Masia R, De Leon DD, MacMullen C, McKnight H, Stanley CA, Nichols CG
A mutation in the TMD0-L0 region of sulfonylurea receptor-1 (L225P) causes permanent neonatal diabetes mellitus (PNDM).
Diabetes. 2007 May;56(5):1357-62. Epub 2007 Feb 22., [PMID:17317760]

Abstract [show]
OBJECTIVE: We sought to examine the molecular mechanisms underlying permanenent neonatal diabetes mellitus (PNDM) in a patient with a heterozygous de novo L225P mutation in the L0 region of the sulfonylurea receptor (SUR)1, the regulatory subunit of the pancreatic ATP-sensitive K(+) channel (K(ATP) channel). RESEARCH DESIGN AND METHODS: The effects of L225P on the properties of recombinant K(ATP) channels in transfected COS cells were assessed by patch-clamp experiments on excised membrane patches and by macroscopic Rb-flux experiments in intact cells. RESULTS: L225P-containing K(ATP) channels were significantly more active in the intact cell than in wild-type channels. In excised membrane patches, L225P increased channel sensitivity to stimulatory Mg nucleotides without altering intrinsic gating or channel inhibition by ATP in the absence of Mg(2+). The effects of L225P were abolished by SUR1 mutations that prevent nucleotide hydrolysis at the nucleotide binding folds. L225P did not alter channel inhibition by sulfonylurea drugs, and, consistent with this, the patient responded to treatment with oral sulfonylureas. CONCLUSIONS: L225P underlies K(ATP) channel overactivity and PNDM by specifically increasing Mg-nucleotide stimulation of the channel, consistent with recent reports of mechanistically similar PNDM-causing mutations in SUR1. The mutation does not affect sulfonylurea sensitivity, and the patient is successfully treated with sulfonylureas.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
149 Two reports have identified three SUR1 mutations associated with PNDM (F132L, L213R, and I1424V) and five associated with transient neonatal diabetes (11,12). Login to comment
150 Common to F132L and I1424V is an increased sensitivity of the channel to Mg nucleotides, such that channel overactivity results at physiological nucleotide concentrations. Login to comment
151 Our results are consistent with these previous studies, as L225P increases channel sensitivity to Mg nucleotides without altering intrinsic gating or inhibition by ATP. Login to comment
152 The effects of L225P are similar to those of the PNDM-associated I1424V mutation (12) but not as severe as those of the DEND (Developmental Delay, Epilepsy, and Neonatal Diabetes Syndrome)-associated F132L mutation (11). Login to comment
157 The carrier of the I1424V mutation (which is mechanistically similar to L225P) has also been successfully treated with sulfonyureas (12). Login to comment
153 The effects of L225P are similar to those of the PNDM-associated I1424V mutation (12) but not as severe as those of the DEND (Developmental Delay, Epilepsy, and Neonatal Diabetes Syndrome)-associated F132L mutation (11). Login to comment
158 The carrier of the I1424V mutation (which is mechanistically similar to L225P) has also been successfully treated with sulfonyureas (12). Login to comment

[hide] Neonatal Diabetes and Congenital Hyperinsulinism C... Front Endocrinol (Lausanne). 2015 Apr 15;6:48. doi: 10.3389/fendo.2015.00048. eCollection 2015. Ortiz D, Bryan J
Neonatal Diabetes and Congenital Hyperinsulinism Caused by Mutations in ABCC8/SUR1 are Associated with Altered and Opposite Affinities for ATP and ADP.
Front Endocrinol (Lausanne). 2015 Apr 15;6:48. doi: 10.3389/fendo.2015.00048. eCollection 2015., [PMID:25926814]

Abstract [show]
ATP-sensitive K(+) (KATP) channels composed of potassium inward-rectifier type 6.2 and sulfonylurea receptor type 1 subunits (Kir6.2/SUR1)4 are expressed in various cells in the brain and endocrine pancreas where they couple metabolic status to membrane potential. In beta-cells, increases in cytosolic [ATP/ADP]c inhibit KATP channel activity, leading to membrane depolarization and exocytosis of insulin granules. Mutations in ABCC8 (SUR1) or KCNJ11 (Kir6.2) can result in gain or loss of channel activity and cause neonatal diabetes (ND) or congenital hyperinsulinism (CHI), respectively. SUR1 is reported to be a Mg(2+)-dependent ATPase. A prevailing model posits that ATP hydrolysis at SUR1 is required to stimulate openings of the pore. However, recent work shows nucleotide binding, without hydrolysis, is sufficient to switch SUR1 to stimulatory conformations. The actions of nucleotides, ATP and ADP, on ND (SUR1E1506D) and CHI (SUR1E1506K) mutants, without Kir6.2, were compared to assess both models. Both substitutions significantly impair hydrolysis in SUR1 homologs. SUR1E1506D has greater affinity for MgATP than wildtype; SUR1E1506K has reduced affinity. Without Mg(2+), SUR1E1506K has a greater affinity for ATP(4-) consistent with electrostatic attraction between ATP(4-), unshielded by Mg(2+), and the basic lysine. Further analysis of ND and CHI ABCC8 mutants in the second transmembrane and nucleotide-binding domains (TMD2 and NBD2) found a relation between their affinities for ATP (+/-Mg(2+)) and their clinical phenotype. Increased affinity for ATP is associated with ND; decreased affinity with CHI. In contrast, MgADP showed a weaker relationship. Diazoxide, known to reduce insulin release in some CHI cases, potentiates switching of CHI mutants from non-stimulatory to stimulatory states consistent with diazoxide stabilizing a nucleotide-bound conformation. The results emphasize the greater importance of nucleotide binding vs. hydrolysis in the regulation of KATP channels in vivo.

Comments [show]

None has been submitted yet.

Sentences [show]
No. Sentence Comment
112 Mutation Reference KG KT (+Mg2+) b2; KT (-Mg2+) b2; KD (+Mg2+) b2; nM &#b5;M &#b5;M &#b5;M E1506Qa (8) 0.6 &#b1; 0.2 0.9 &#b1; 0.2 40 &#b1; 20 94 &#b1; 9 40 &#b1; 11 211 &#b1; 34 7 .6 &#b1; 2.2 E1506Da (15) 0.4 &#b1; 0.04 3.2 &#b1; 1 8.6 &#b1; 1.5 5570 &#b1; 1200 7 .2 &#b1; 1.5 289 &#b1; 122 4.7 &#b1; 2.2 Q1178Rb (24) 1.0 &#b1; 0.1 9.2 &#b1; 1.3 10 &#b1; 1 1030 &#b1; 200 9.1 &#b1; 1.7 13.9 &#b1; 2.0 20.7 &#b1; 8.9 I1424V (24) 0.5 &#b1; 0.03 7 .1 &#b1; 2.2 5.6 &#b1; 0.7 2840 &#b1; 700 7 .6 &#b1; 1.5 12.1 &#b1; 3.7 14.8 &#b1; 6.5 R1182Qb (24) 0.5 &#b1; 0.15 13.1 &#b1; 2.3 10.3 &#b1; 1.4 11100 &#b1; 1600 4.1 &#b1; 0.4 13.1 &#b1; 2.2 16.4 &#b1; 4.6 WT 0.25 &#b1; 0.02 200 &#b1; 18 13 &#b1; 1 10900 &#b1; 3400 16 &#b1; 11 60 &#b1; 16 14 &#b1; 6.6 S1185Ac (9) 0.3 &#b1; 0.05 416 &#b1; 75 4.9 &#b1; 0.5 19100 &#b1; 3600 6.4 &#b1; 1.5 36.6 &#b1; 8 10.4 &#b1; 2.5 C1174Fc (9) 0.5 &#b1; 0.04 2690 &#b1; 725 5.9 &#b1; 2.3 >20000 13 &#b1; 6 66 &#b1; 13 7 .6 &#b1; 1.7 E1506K (25) 0.3 &#b1; 0.03 8450 &#b1; 1200 5.5 &#b1; 0.6 256 &#b1; 55 5.3 &#b1; 0.4 >1000 n.d. G1479R (26) 0.5 &#b1; 0.04 >10000 n.d. >20000 n.d. >1000 n.d. a Includes data from Ref. (8). Login to comment
122 to the current regulatory model, both E1506 substitutions have reduced affinity for MgADP (Figure 4), consistent with electrophysiological data demonstrating that SUR1E1506D/Kir6.2 and 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 0.0 0.2 0.4 0.6 0.8 1.0 E1506Q Q1178R E1506D R1182Q I1424V WT S1185A C1174F E1506K G1479R Specific Bound GBC [MgATP] (&#b5;M) 10 -1 10 0 10 1 10 2 10 3 10 4 10 5 0.0 0.2 0.4 0.6 0.8 1.0 E1506Q E1506K Q1178R I1424V E1506D R1182Q WT S1185A C1174F G1479R Specific Bound GBC [ATP 4- ] (&#b5;M) B A FIGURE 3 | Comparison of nucleotide-induced conformational switching in WT and SUR1 mutants. Login to comment
128 To support this hypothesis we analyzed additional mutations including I1424V (ND) and G1479R (CHI) in NBD2 and a cluster of disease causing mutations in TMD2: C1174F (CHI), S1185A (CHI), Q1178R (ND), and R1182Q (ND). Login to comment
151 Figure 5 shows that diazoxide potentiates the 1 10 100 1000 0.0 0.2 0.4 0.6 0.8 1.0 Q1178R I1424V R1182Q S1185A C1174F WT E1506Q E1506D G1479R E1506K Specific Bound GBC [MgADP] (&#b5;M) FIGURE 4 | MgADP-induced conformational switching in WT and SUR1 mutants. Login to comment