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Pharmacologic evidence for stabilization of a nucleotide‐bound, stimulatory conformation of SUR1Q1178R, an ABCC8 neonatal diabetes mutation
Author(s) -
Ortiz David Javier,
Rüdiger Benjamin,
Bryan Joseph,
Quast Ulrich
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.527.7
Subject(s) - glibenclamide , chemistry , sulfonylurea receptor , allosteric regulation , diazoxide , agonist , binding site , mutant , biochemistry , pharmacology , stereochemistry , enzyme , endocrinology , receptor , biology , diabetes mellitus , insulin , gene
Mutations in ABCC8/SUR1 that generate hyperactive neuroendocrine‐type Kir6.2/SUR1 K ATP channels are a cause of neonatal diabetes. Analysis of one mutant, SUR1 Q1178R , is consistent with the MgATP‐dependent accumulation of a post‐hydrolytic, ADP‐bound enzymatic intermediate that stimulates channel opening. SUR1 is the target for K ATP channel inhibitors, e.g., glibenclamide, and openers, e.g., diazoxide and NCC. In the Kir6.2/SUR1 channel, the mutation potentiated the negative allosteric effect of MgATP on binding of [ 3 H]‐glibenclamide reducing the number of specific channel binding sites by ~50% whereas in wild‐type, the K D increased 4.5x. This is consistent with a greater depopulation of antagonist binding sites in the R1178 channels at steady‐state. MgATP is required for opener function and high‐affinity agonist binding. SUR1 R1178 increased the apparent number of agonist binding sites, without affecting their K i , implying these agonists interact with the stimulatory, post‐hydrolytic conformation stabilized by the R1178 substitution. The data suggest the stimulatory, post‐hydrolytic conformation could accumulate either because R1178 increases the rate of ATP hydrolysis or reduces the rate of product dissociation, and rationalize the need for a higher glibenclamide dose to reach metabolic control in ABCC8 neonatal diabetes patients. Supported by NIH DK44311(JB); DFG QU_100/4‐1(UQ).