New structure and function in plant K+ channels: KCO1, an outward rectifier with a steep Ca2+ dependency.
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.
Czempinski
K
K
Max-Planck-Institut für Molekulare Pflanzenphysiologie, Golm, Germany.
Zimmermann
S
S
Ehrhardt
T
T
Müller-Röber
B
B
D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins; D016367:Baculoviridae / Q000235:genetics; D001692:Biological Transport; D002118:Calcium / Q000494:pharmacology*; D003001:Cloning, Molecular; D017343:Genes, Plant; D015640:Ion Channel Gating; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D010940:Plant Proteins / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D024683:Potassium Channels, Tandem Pore Domain; D011487:Protein Conformation; D012333:RNA, Messenger / Q000096:biosynthesis; D018749:RNA, Plant / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D018411:Spodoptera / Q000166:cytology
D029681:Arabidopsis Proteins; C503455:KCO1 protein, Arabidopsis; D010940:Plant Proteins; D015221:Potassium Channels; D024683:Potassium Channels, Tandem Pore Domain; D012333:RNA, Messenger; D018749:RNA, Plant; D011994:Recombinant Proteins; D011188:Potassium; D002118:Calcium