title: Immunosuppressants implicate protein phosphatase regulation of K+ channels in guard cells.
abstract: The elevation of Ca2+ levels in the cytoplasm inactivates inward-rectifying K+ channels that play a central role in regulating the apertures of stomatal pores in higher plants. However, the mechanism for the Ca(2+)-mediated inhibition of K(+)-channel function is unknown. Using patch-clamp techniques, we show that cyclophilin-cyclosporin A and FK506-binding protein-FK506 complexes, which are highly specific inhibitors of protein phosphatase 2B (calcineurin), block Ca(2+)-induced inactivation of K+ channels in Vicia faba guard cells. A constitutively active calcineurin fragment that is Ca(2+)-independent inhibits K(+)-channel activity in the absence of Ca2+. We have also identified an endogenous Ca(2+)-dependent phosphatase activity from V. faba that is inhibited by the cyclophilin-cyclosporin A and FK506-binding protein-FK506 complexes. Our findings implicate a Ca(2+)-dependent, calcineurin-like protein phosphatase in a Ca2+ signal-transduction pathway of higher plants.
authors.affiliation: Department of Chemistry, Harvard University, Cambridge, MA 02138.
authors.forename: S
authors.initials: S
authors.lastname: Luan
authors.forename: W
authors.initials: W
authors.lastname: Li
authors.forename: F
authors.initials: F
authors.lastname: Rusnak
authors.forename: S M
authors.initials: SM
authors.lastname: Assmann
authors.forename: S L
authors.initials: SL
authors.lastname: Schreiber
mesh_terms: D000591:Amino Acid Isomerases / Q000378:metabolism / Q000494:pharmacology*; D000595:Amino Acid Sequence; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism / Q000494:pharmacology*; D016572:Cyclosporine / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism; D019696:Peptidylprolyl Isomerase; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D059828:Plant Cells; D018521:Plant Physiological Phenomena; D010944:Plants / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D013379:Substrate Specificity; D016559:Tacrolimus / Q000378:metabolism / Q000494:pharmacology*; D022021:Tacrolimus Binding Proteins
chemical_list: D002352:Carrier Proteins; D010455:Peptides; D015221:Potassium Channels; D016572:Cyclosporine; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases; D000591:Amino Acid Isomerases; D022021:Tacrolimus Binding Proteins; D019696:Peptidylprolyl Isomerase; D002118:Calcium; D016559:Tacrolimus