New structure and function in plant K+ channels: KCO1, an outward rectifier with a steep Ca2+ dependency

EMBO J. 1997 May 15;16(10):2565-75. doi: 10.1093/emboj/16.10.2565.

Abstract

Potassium (K+) channels mediating important physiological functions are characterized by a common pore-forming (P) domain. We report the cloning and functional analysis of the first higher plant outward rectifying K+ channel (KCO1) from Arabidopsis thaliana. KCO1 belongs to a new class of 'two-pore' K+ channels recently described in human and yeast. KCO1 has four putative transmembrane segments and tandem calcium-binding EF-hand motifs. Heterologous expression of KCO1 in baculovirus-infected insect (Spodoptera frugiperda) cells resulted in outwardly rectifying, K+-selective currents elicited by depolarizing voltage pulses in whole-cell measurements. Activation of KCO1 was strongly dependent on the presence of nanomolar concentrations of cytosolic free Ca2+ [Ca2+]cyt. No K+ currents were detected when [Ca2+]cyt was adjusted to <150 nM. However, KCO1 strongly activated at increasing [Ca2+]cyt, with a saturating activity observed at approximately 300 nM [Ca2+]cyt. KCO1 single channel analysis on excised membrane patches, resulting in a single channel conductance of 64 pS, confirmed outward rectification as well as Ca2+-dependent activation. These data suggest a direct link between calcium-mediated signaling processes and K+ ion transport in higher plants. The identification of KCO1 as the first plant K+ outward channel opens a new field of structure-function studies in plant ion channels.

Publication types

  • Comparative Study

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Arabidopsis / genetics*
  • Arabidopsis Proteins
  • Baculoviridae / genetics
  • Biological Transport
  • Calcium / pharmacology*
  • Cloning, Molecular
  • Genes, Plant
  • Ion Channel Gating*
  • Models, Molecular
  • Molecular Sequence Data
  • Patch-Clamp Techniques
  • Plant Proteins / physiology*
  • Potassium / metabolism
  • Potassium Channels / classification
  • Potassium Channels / drug effects
  • Potassium Channels / physiology*
  • Potassium Channels, Tandem Pore Domain*
  • Protein Conformation
  • RNA, Messenger / biosynthesis
  • RNA, Plant / biosynthesis
  • Recombinant Proteins / metabolism
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid
  • Spodoptera / cytology

Substances

  • Arabidopsis Proteins
  • KCO1 protein, Arabidopsis
  • Plant Proteins
  • Potassium Channels
  • Potassium Channels, Tandem Pore Domain
  • RNA, Messenger
  • RNA, Plant
  • Recombinant Proteins
  • Potassium
  • Calcium

Associated data

  • GENBANK/X97323
  • GENBANK/Y07825