C-terminus determinants for Mg2+ and polyamine block of the inward rectifier K+ channel IRK1

EMBO J. 1995 Nov 15;14(22):5532-41.

Abstract

Critical loci for ion conduction in inward rectifier K+ channels are only now being discovered. The C-terminal region of IRK1 plays a crucial role in Mg2+i blockade and single-channel K+ conductance. A negatively charged aspartate in the putative second transmembrane domain (position 172) is essential for time-dependent block by the cytoplasmic polyamines spermine and spermidine. We have now localized the C-terminus effect in IRK1 to a single, negatively charged residue (E224). Mutation of E224 to G, Q and S drastically reduced rectification. Furthermore, the IRK1 E224G mutation decreased block by Mg2+i and spermidine and, like the E224Q mutation, caused a dramatic reduction in the apparent single-channel K+ conductance. The double mutation IRK1 D172N+ E224G was markedly insensitive to spermidine block, displaying an affinity similar to ROMK1. The results are compatible with a model in which the negatively charged residue at position 224, E224, is a major determinant of pore properties in IRK1. By means of a specific interaction with the negatively charged residue at position 172, D172, E224 contributes to the formation of the binding pocket for Mg2+ and polyamines, a characteristic of strong inward rectifiers.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Magnesium / pharmacology*
  • Molecular Sequence Data
  • Mutation
  • Oocytes / metabolism
  • Polyamines / pharmacology*
  • Potassium Channel Blockers
  • Potassium Channels / genetics
  • Potassium Channels / metabolism*
  • Potassium Channels, Inwardly Rectifying*
  • Signal Transduction
  • Structure-Activity Relationship
  • Xenopus

Substances

  • Polyamines
  • Potassium Channel Blockers
  • Potassium Channels
  • Potassium Channels, Inwardly Rectifying
  • Magnesium

Grant support