title: Modulation of the Arabidopsis KAT1 channel by an activator of protein kinase C in Xenopus laevis oocytes.
abstract: The Arabidopsis thaliana K(+) channel KAT1 has been suggested to play a key role in the regulation of the aperture of stomatal pores on the surface of plant leaves. Calcium-dependent and calcium-independent signaling pathways are involved in abscisic acid-mediated regulation of guard cell turgidity. Although the activity of the KAT1 channel is thought to be regulated by calcium-dependent protein kinases, the effect of phosphorylation on KAT1 and the phosphorylated target sites remain elusive. Because it has been proposed that the phosphorylation recognition sequence of plant calcium-dependent protein kinases resembles that of animal protein kinases C, in this study, we used the Xenopus laevis oocyte protein kinase C to identify the target sites of calcium-dependent protein kinases. KAT1 expressed in Xenopus oocytes was inhibited by the protein kinase C activator phorbol 12-myristate 13-acetate. On the basis of an in silico search, we selected S/T-X-K/R motifs facing the cytosol, as it has been reported that protein kinase C and calcium-dependent protein kinase share a common consensus sequence. Mutagenesis analyses revealed that six Ser/Thr residues were responsible for the reduction in activity after phorbol 12-myristate 13-acetate application. Simultaneous mutation of the five residues located in the carboxyl-terminus region of KAT1 led to a K(+) channel mutant that was insensitive to protein kinase C. These results indicate that, in plant cells, a kinase analogous to protein kinase C might exist that may modulate KAT1 channel activity through calcium-dependent phosphorylation at some of the pinpointed residues in the cytosolic region of KAT1.
authors.affiliation: Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Sato
authors.forename: Franco
authors.initials: F
authors.lastname: Gambale
authors.forename: Ingo
authors.initials: I
authors.lastname: Dreyer
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Uozumi
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D029681:Arabidopsis Proteins / Q000187:drug effects / Q000502:physiology*; D055724:Electrophysiological Phenomena / Q000187:drug effects; D009281:Naphthalenes / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000502:physiology*; D054730:Protein Interaction Domains and Motifs / Q000187:drug effects / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012694:Serine / Q000235:genetics / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013912:Threonine / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014982:Xenopus laevis
chemical_list: D029681:Arabidopsis Proteins; C501210:KAT1 protein, Arabidopsis; D009281:Naphthalenes; D024661:Potassium Channels, Inwardly Rectifying; D013912:Threonine; D012694:Serine; D011493:Protein Kinase C; C058819:calphostin C; D013755:Tetradecanoylphorbol Acetate