Increased ATPase activity produced by mutations at arginine-1380 in nucleotide-binding domain 2 of ABCC8 causes neonatal diabetes

Proc Natl Acad Sci U S A. 2007 Nov 27;104(48):18988-92. doi: 10.1073/pnas.0707428104. Epub 2007 Nov 19.

Abstract

Gain-of-function mutations in the genes encoding the ATP-sensitive potassium (K(ATP)) channel subunits Kir6.2 (KCNJ11) and SUR1 (ABCC8) are a common cause of neonatal diabetes mellitus. Here we investigate the molecular mechanism by which two heterozygous mutations in the second nucleotide-binding domain (NBD2) of SUR1 (R1380L and R1380C) separately cause neonatal diabetes. SUR1 is a channel regulator that modulates the gating of the pore formed by Kir6.2. K(ATP) channel activity is inhibited by ATP binding to Kir6.2 but is stimulated by MgADP binding, or by MgATP binding and hydrolysis, at the NBDs of SUR1. Functional analysis of purified NBD2 showed that each mutation enhances MgATP hydrolysis by purified isolated fusion proteins of maltose-binding protein and NBD2. Inhibition of ATP hydrolysis by MgADP was unaffected by mutation of R1380, but inhibition by beryllium fluoride (which traps the ATPase cycle in the prehydrolytic state) was reduced. MgADP-dependent activation of K(ATP) channel activity was unaffected. These data suggest that the R1380L and R1380C mutations enhance the off-rate of P(i), thereby enhancing the hydrolytic rate. Molecular modeling studies supported this idea. Because mutant channels were inhibited less strongly by MgATP, this would increase K(ATP) currents in pancreatic beta cells, thus reducing insulin secretion and producing diabetes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Binding Cassette Transporters / antagonists & inhibitors
  • ATP-Binding Cassette Transporters / chemistry
  • ATP-Binding Cassette Transporters / genetics*
  • ATP-Binding Cassette Transporters / metabolism
  • Adenosine Diphosphate / pharmacology
  • Adenosine Triphosphate / metabolism
  • Adenosine Triphosphate / pharmacology
  • Amino Acid Substitution
  • Arginine / chemistry
  • Beryllium / pharmacology
  • Binding Sites
  • Diabetes Mellitus, Type 1 / congenital
  • Diabetes Mellitus, Type 1 / genetics*
  • Fluorides / pharmacology
  • Humans
  • Hydrolysis
  • Infant, Newborn
  • Insulin / metabolism
  • Insulin Secretion
  • Ion Channel Gating / drug effects
  • Kinetics
  • Models, Molecular
  • Mutation, Missense*
  • Point Mutation*
  • Potassium / metabolism
  • Potassium Channels / chemistry
  • Potassium Channels / genetics*
  • Potassium Channels / metabolism
  • Potassium Channels, Inwardly Rectifying / antagonists & inhibitors
  • Potassium Channels, Inwardly Rectifying / chemistry
  • Potassium Channels, Inwardly Rectifying / genetics*
  • Potassium Channels, Inwardly Rectifying / metabolism
  • Protein Structure, Tertiary / genetics
  • Receptors, Drug / antagonists & inhibitors
  • Receptors, Drug / chemistry
  • Receptors, Drug / genetics*
  • Receptors, Drug / metabolism
  • Structure-Activity Relationship
  • Sulfonylurea Receptors

Substances

  • ABCC8 protein, human
  • ATP-Binding Cassette Transporters
  • Insulin
  • Potassium Channels
  • Potassium Channels, Inwardly Rectifying
  • Receptors, Drug
  • Sulfonylurea Receptors
  • beryllium fluoride
  • Adenosine Diphosphate
  • Adenosine Triphosphate
  • Arginine
  • Beryllium
  • Fluorides
  • Potassium