ABCMdb

ABCC8 p.Arg1182Gln

ClinVar:	c.3545T>G , p.Phe1182Cys D , Likely pathogenic
Predicted by SNAP2:	A: D (63%), C: D (66%), D: D (91%), E: D (85%), F: D (71%), G: D (75%), H: D (80%), I: N (66%), K: D (63%), L: N (53%), M: N (53%), N: D (80%), P: D (91%), Q: D (66%), S: D (71%), T: N (53%), V: N (72%), W: D (91%), Y: D (85%),
Predicted by PROVEAN:	A: N, C: D, D: D, E: N, F: D, G: D, H: N, I: N, K: N, L: N, M: N, N: N, P: D, Q: N, S: N, T: N, V: N, W: D, Y: D,

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[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.

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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
49 The L582V and R1397C mutations were also inherited in one family each, as were the C435R and R1182Q mutations. Login to comment
51 The father of the proband with a C435R mutation in Family 13 was given a diagnosis of diabetes mellitus at 13 years of age; after he was found to have the C435R mutation, he discontinued insulin (after 24 years of treatment) after a successful response to glyburide (10 mg per day). Login to comment
52 An oral glucose-tolerance test showed that the father of the proband with an R1182Q mutation in Family 34 had diabetes; he is currently being treated with diet alone. 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
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
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

[hide] Update of mutations in the genes encoding the panc... Hum Mutat. 2009 Feb;30(2):170-80. Flanagan SE, Clauin S, Bellanne-Chantelot C, de Lonlay P, Harries LW, Gloyn AL, Ellard S
Update of mutations in the genes encoding the pancreatic beta-cell K(ATP) channel subunits Kir6.2 (KCNJ11) and sulfonylurea receptor 1 (ABCC8) in diabetes mellitus and hyperinsulinism.
Hum Mutat. 2009 Feb;30(2):170-80., [PMID:18767144]

Abstract [show]
The beta-cell ATP-sensitive potassium (K(ATP)) channel is a key component of stimulus-secretion coupling in the pancreatic beta-cell. The channel couples metabolism to membrane electrical events bringing about insulin secretion. Given the critical role of this channel in glucose homeostasis it is therefore not surprising that mutations in the genes encoding for the two essential subunits of the channel can result in both hypo- and hyperglycemia. The channel consists of four subunits of the inwardly rectifying potassium channel Kir6.2 and four subunits of the sulfonylurea receptor 1 (SUR1). It has been known for some time that loss of function mutations in KCNJ11, which encodes for Kir6.2, and ABCC8, which encodes for SUR1, can cause oversecretion of insulin and result in hyperinsulinism of infancy, while activating mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes. This review focuses on reported mutations in both genes, the spectrum of phenotypes, and the implications for treatment on diagnosing patients with mutations in these genes.

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34 This means that there are discrepancies in nomenclature reported in the literature for mutations that affect residues encoded within exons 17-39 that differ by one amino acid depending on the isoform used (e.g., R1182Q reported by Babenko et al. Login to comment

[hide] New ABCC8 mutations in relapsing neonatal diabetes... Diabetes. 2007 Jun;56(6):1737-41. Epub 2007 Mar 27. Vaxillaire M, Dechaume A, Busiah K, Cave H, Pereira S, Scharfmann R, de Nanclares GP, Castano L, Froguel P, Polak M
New ABCC8 mutations in relapsing neonatal diabetes and clinical features.
Diabetes. 2007 Jun;56(6):1737-41. Epub 2007 Mar 27., [PMID:17389331]

Abstract [show]
Activating mutations in the ABCC8 gene that encodes the sulfonylurea receptor 1 (SUR1) regulatory subunit of the pancreatic islet ATP-sensitive K(+) channel (K(ATP) channel) cause both permanent and transient neonatal diabetes. Recently, we have described the novel mechanism where basal Mg-nucleotide-dependent stimulatory action of SUR1 on the Kir6.2 pore is increased. In our present study, we identified six new heterozygous ABCC8 mutations, mainly in patients presenting the transient form of neonatal diabetes (six of eight), with a median duration of initial insulin therapy of 17 months (range 0.5-38.0). Most of these mutations map to key functional domains of SUR1. Whereas Kir6.2 mutations are a common cause of permanent neonatal diabetes and in a few cases associate with the DEND (developmental delay, epilepsy, and neonatal diabetes) syndrome, SUR1 mutations are more frequent in transient (52%) compared with permanent (14%) neonatal diabetes cases screened for ABCC8 in our series. Although ketoacidosis is frequent at presentation, SUR1 mutations associate mainly with transient hyperglycemia, with possible recurrence later in life. One-half of the SUR1 neonatal diabetic patients presented with de novo mutations. In some familial cases, diabetes is not always present in the adult carriers of SUR1 mutations, supporting variability in their clinical expressivity that remains to be fully explained.

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39 The two other mutations, L582V (c.1744CϾG) and R1182Q (c.3545GϾA), had been previously described by our group in three independent families with TND cases (13). Login to comment
51 The R1182Q and V1523M mutations were not identified in either parent, consistent with de novo mutations. Login to comment
52 The V324M and R1379H mutations tested negative in the mothers, and the two fathers were not available for genetic testing. Login to comment
77 In the ND-SUR1 patients, an apparently mild phenotype, i.e., without neurological features, is observed in the TND families, except in a few cases presenting with PND (13) TABLE1 ClinicalfeaturesinneonataldiabeticpatientsscreenedpositiveforABCC8mutations Patient SGMGKKSLMCNCDDLNJ MutationE208KV324ML582VR825WR1182QR1379HV1523MA269D SexFemaleMaleMaleFemaleFemaleMaleMaleFemale TypeofdiabetesTNDTNDTNDTNDTNDTNDPND Notyet known Atbirth Weight(g/percentile)1,790/321,660/Ͻ33,250/282,300/Ͻ32,930/103,150/432,710/312,390/Ͻ3 Gestationweek33.53739394138.53739 Atpresentation Age(days)1112361013426766 Weight(g)1,7904,2904,3002,5203,0003,6903,6605,100 PresentationGlucose monitoring KetoacidosisKetoacidosisGlucose monitoring WeightlossKetoacidosisKetoacidosisKetoaciduria Glucose(mmol/l)12.424.160.516.824.164.23627.5 Autoantibodies00000000 Insulindose(units⅐kg-1 ⅐day-1 )0.1012.400.300.720.502.500.72 PancreasultrasonographyNANANNNNNN Currentstatus Age(months)712728134833188.7 Height(cm/SD)63/-1.6134.5/-0.790.2/0.672.5/-0.4101.2/0.296/184/1.370/0.8 Weight(kg/percentile)6.15/323.6/Ͻ313.5/759.62/5614.9/5017.5/Ͼ9711/318.52/50 Diabetes(yes[ϩ],no[-])-ϩ(9)*----ϩϩ Insulindose(units⅐kg-1 ⅐day-1 )00†00000.600.62 A1Catlastexamination(%)4.56.05.15.05.45.05.58.9 Neurologicalfeatures MuscleweaknessNoNoNoNoNoNoNoNo MotordevelopmentaldelayNoNoNoNoNoNoNoNo EpilepsyNoNoNoNoNoNoNoNo MentaldevelopmentaldelayNoNoNoNoNoNoNoNo SpeechdevelopmentaldelayNoYesNoNoNoYesNoNo DysmorphicfeaturesNoNoNoNoNoNoNoNo OtherfeaturesNoNoNoNoNoHyperkinesia, troubleof feeding behavior NoHypotonia ParentwithamutationFatherNone‡FatherFatherNoneNone‡NoneMother Glucosetolerance§IGT-NN---N Ageatexamination(year)41-3129---25 A1Catlastexamination(%)¶5.4-6.1NA---5.2 BMIatlastexamination(kg/m2 )27-2422---NA *Ageatrelapse,inyear.†PatientGK-V324Mwassuccessfullyswitchedtoglibenclamide(gliburide)attheageof9.5years(currentdose2.5mg/day;weight25kg).‡Onlythemotherwas screenedforthemutation;thefatherofGK-V324Mdied,andnoinformationisavailableonthebiologicalfatherofCD-R1379H.§Assessedbyanoralglucosetolerancetest.¶Upperlimit ofnormalvaluesforA1C:5.6%.IGT,impairedglucosetolerance;N,normal;NA,notavailable. Login to comment
40 The two other mutations, L582V (c.1744Cb0e;G) and R1182Q (c.3545Gb0e;A), had been previously described by our group in three independent families with TND cases (13). Login to comment

[hide] Two neonatal diabetes mutations on transmembrane h... J Biol Chem. 2012 May 25;287(22):17985-95. doi: 10.1074/jbc.M112.349019. Epub 2012 Mar 27. Ortiz D, Voyvodic P, Gossack L, Quast U, Bryan J
Two neonatal diabetes mutations on transmembrane helix 15 of SUR1 increase affinity for ATP and ADP at nucleotide binding domain 2.
J Biol Chem. 2012 May 25;287(22):17985-95. doi: 10.1074/jbc.M112.349019. Epub 2012 Mar 27., [PMID:22451668]

Abstract [show]
K(ATP) channels, (SUR1/Kir6.2)(4) (sulfonylurea receptor type 1/potassium inward rectifier type 6.2) respond to the metabolic state of pancreatic beta-cells, modulating membrane potential and insulin exocytosis. Mutations in both subunits cause neonatal diabetes by overactivating the pore. Hyperactive channels fail to close appropriately with increased glucose metabolism; thus, beta-cell hyperpolarization limits insulin release. K(ATP) channels are inhibited by ATP binding to the Kir6.2 pore and stimulated, via an uncertain mechanism, by magnesium nucleotides at SUR1. Glibenclamide (GBC), a sulfonylurea, was used as a conformational probe to compare nucleotide action on wild type versus Q1178R and R1182Q SUR1 mutants. GBC binds with high affinity to aporeceptors, presumably in the inward facing ATP-binding cassette configuration; MgATP reduces binding affinity via a shift to the outward facing conformation. To determine nucleotide affinities under equilibrium, non-hydrolytic conditions, Mg(2+) was eliminated. A four-state equilibrium model describes the allosteric linkage. The K(D) for ATP(4-) is ~1 versus 12 mM, Q1178R versus wild type, respectively. The linkage constant is ~10, implying that outward facing conformations bind GBC with a lower affinity, 9-10 nM for Q1178R. Thus, nucleotides cannot completely inhibit GBC binding. Binding of channel openers is reported to require ATP hydrolysis, but diazoxide, a SUR1-selective agonist, concentration-dependently augments ATP(4-) action. An eight-state model describes linkage between diazoxide and ATP(4-) binding; diazoxide markedly increases the affinity of Q1178R for ATP(4-) and ATP(4-) augments diazoxide binding. NBD2, but not NBD1, has a higher affinity for ATP (and ADP) in mutant versus wild type (with or without Mg(2+)). Thus, the mutants spend more time in nucleotide-bound conformations, with reduced affinity for GBC, that activate the pore.

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9 Glibenclamide (GBC), a sulfonylurea, was used as a conformational probe to compare nucleotide action on wild type versus Q1178R and R1182Q SUR1 mutants. Login to comment
47 Here we focus on two mutations, Q1178R and R1182Q, located in the 15th helix (transmembrane helix) of the second transmembrane domain (TMD2). Login to comment
48 These substitutions are in a cluster of mutations that cause either neonatal diabetes (Q1178R, R1182Q, and A1184E) or hyperinsulinism (C1174F and S1185A). Login to comment
58 The results imply that outward facing conformations with dimerized NBDs bind GBC and diazoxide with low and high affinity, respectively, and that the enhanced stimulatory action of Q1178R and R1182Q is due to their increased affinity for ATP and ADP. Login to comment
101 Table 1 and Table S1 compare the dissociation constants, determined from saturation binding data, for the WT, Q1178R, and R1182Q aporeceptors (i.e. without nucleotides). Login to comment
105 Q1178R and R1182Q Neonatal Diabetes Mutations Potentiate Negative Allosteric Action of MgATP on GBC Binding to SUR1-To assess quantitatively the effect of MgATP on GBC binding, membranes were incubated with increasing ATP concentrations maintained constant by a regenerating system (34); the level of ATP was constant over the 30-min time period of the incubation, as determined using luciferase assays (supplemental Fig. S1). Login to comment
107 The IC50 values for MgATP are b03;850, 37, and 19 òe;M for the WT, R1182Q, and Q1178R receptors, respectively, an increase in the apparent affinity of SUR1Q1178R for ATP of b03;45-fold. Login to comment
109 Q1178R and R1182Q Receptors Have Higher Affinity for ATP4afa; than WT-All ABC proteins have Walker-type nucleotide binding sites whose physiologic substrate is MgATP. Login to comment
115 In terms of an enzyme-substrate model where hydrolysis is blocked, the results show that the mutant receptors have at least a 10-fold greater affinity for ATP4afa; , with Q1178R having a somewhat higher affinity than R1182Q (Tables 2 and S2). Login to comment
126 The parameters for WT and R1182Q receptors are given in Table 2. Login to comment
139 E, neonatal diabetes (Q1178R in red and R1182Q in green) and hyperinsulinemia (C1174F in blue) causing mutations are clustered on transmembrane helix 15 (yellow), which feeds into NBD1 (light gray). Login to comment
143 Values are means afe; S.E. SUR1 KG nM WT 0.25 afe; 0.02 Q1178R 1.0 afe; 0.1 R1182Q 0.50 afe; .15 SUR1 Nucleotide Affinities in Neonatal Diabetes 17988 JOURNAL OF BIOLOGICAL CHEMISTRY VOLUME 287ߦNUMBER 22ߦMAY 25, 2012 equation for the four-state model can be expressed as a simple binding isotherm (see supplemental material), G afd; ᐵGᐶ ᐵGᐶ af9; Kobs (Eq. 4) where Kobs, the apparent dissociation constant at a specified concentration of ATP4afa; , is given by the following: Kobs afd; betaKG ᐳᐵTᐶ af9; KTᐴ ᐳᐵTᐶ af9; betaKTᐴ (Eq. 5) Kobs values at increasing concentrations of ATP4afa; were determined by homologous competition experiments (Fig. 3, A-D) and used to estimate KT and beta. Login to comment
156 A, the curves through the data are logistic equations with IC50 values of 849 afe; 195, 37 afe; 13, and 19 afe; 7 òe;M for WT, R1182Q, and Q1178R, respectively. Login to comment
163 The allosteric and ATP4afa; dissociation constants (beta/KD) (òe;M) are 14/12,200, 6.8/1250, and 9.3/1000 for the WT, R1182Q, and Q1178R receptors, respectively. Login to comment
166 TABLE 2 KT and beta values for WT and neonatal diabetes SUR1 are shown d1e; S.E. (p values in parentheses) SUR1 beta KT òe;M WT 14 afe; 10 (0.2) 12,200 afe; 4030 (0.02) R1182Q 6.8 afe; 0.9 (b0d;0.001) 1250 afe; 258 (0.003) Q1178R 9.3 afe; 1.8 (b0d;0.001) 1000 afe; 179 (b0d;0.001) Q1178R (Kobs method) 10.5 afe; 0.8 (0.005) 846 afe; 142 (0.03) SUR1 Nucleotide Affinities in Neonatal Diabetes MAY 25, 2012ߦVOLUME 287ߦNUMBER 22 JOURNAL OF BIOLOGICAL CHEMISTRY 17989 An eight-state model that describes the linkage between the diazoxide, GBC, and nucleotide binding sites under equilibrium, non-hydrolysis conditions is given in Fig. 5. Login to comment
203 A, the curvesarebestfitstoalogisticequation.TheIC50 forQ1178Ris39afe;8òe;M.The IC50 for the averaged values of WT and R1182Q is 9.8 afe; 0.3 òe;M; the individual values are 10.1 afe; 0.5 òe;M (WT) and 9.2 afe; 0.8 òe;M (R1182Q). Login to comment
246 The same argument holds for the R1182Q substitution (see Table 2). Login to comment

[hide] Molecular genetic testing of patients with monogen... Mol Genet Metab. 2015 Mar;114(3):451-8. doi: 10.1016/j.ymgme.2014.12.304. Epub 2014 Dec 20. Bennett JT, Vasta V, Zhang M, Narayanan J, Gerrits P, Hahn SH
Molecular genetic testing of patients with monogenic diabetes and hyperinsulinism.
Mol Genet Metab. 2015 Mar;114(3):451-8. doi: 10.1016/j.ymgme.2014.12.304. Epub 2014 Dec 20., [PMID:25555642]

Abstract [show]
Genetic sequencing has become a critical part of the diagnosis of certain forms of pancreatic beta cell dysfunction. Despite great advances in the speed and cost of DNA sequencing, determining the pathogenicity of variants remains a challenge, and requires sharing of sequence and phenotypic data between laboratories. We reviewed all diabetes and hyperinsulinism-associated molecular testing done at the Seattle Children's Molecular Genetics Laboratory from 2009 to 2013. 331 probands were referred to us for molecular genetic sequencing for Neonatal Diabetes (NDM), Maturity-Onset Diabetes of the Young (MODY), or Congenital Hyperinsulinism (CHI) during this period. Reportable variants were identified in 115 (35%) patients with 91 variants in one of 6 genes: HNF1A, GCK, HNF4A, ABCC8, KCNJ11, or INS. In addition to identifying 23 novel variants, we identified unusual mechanisms of inheritance, including mosaic and digenic MODY presentations. Re-analysis of all reported variants using more recently available databases led to a change in variant interpretation from the original report in 30% of cases. These results represent a resource for molecular testing of monogenic forms of diabetes and hyperinsulinism, providing a mutation spectrum for these disorders in a large North American cohort. In addition, they highlight the importance of periodic review of molecular testing results.

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120 Gene Nucleotide Protein Pheno dbSNP Times seen Interp. LOVD ClinVar Reference ABCC8 c.1277ANG/c.3545GNA p.N426S/p.R1182Q NDM -/rs193922400 1/2 VUS/PATH -/- -/LP This report/[9] c.1433CNA p.A478D CHI - 1 PATH - - [41] c.1608TNG p.F536L NDM - 1 LP - - This report c.2422CNA p.Q808K "DM1"* rs202189540 1 LB - - This report c.2506CNT/c.4138_4140delinsCA p.R836*/p.T1380Qfs*80 CHI rs72559722/- 1/1 PATH/PATH -/- -/- [42]/this report c.3976GNA p.E1326K CHI rs200563930 1 VUS - - [8] ex 32 del p.? 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.

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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