Inward rectification of the AKT2 channel abolished by voltage-dependent phosphorylation.
The Arabidopsis K(+) channel AKT2 possesses the remarkable property that its voltage threshold for activation can be either within the physiological range (gating mode 1), or shifted towards considerably more positive voltages (gating mode 2). Gating mode 1 AKT2 channels behave as delayed K(+)-selective inward rectifiers; while gating mode 2 AKT2 channels are K(+)-selective 'open leaks' in the physiological range of membrane potential. In the present study we have investigated modulation of AKT2 current by effectors of phosphatases/kinases in COS cells and Xenopus oocytes. These experiments show that (i) dephosphorylation can result in AKT2 channel silencing; and (ii) phosphorylation by protein kinase A (PKA) favors both recruitment of silenced AKT2 channels and transition from gating mode 1 to gating mode 2. Interestingly, phosphorylation of AKT2 by PKA in COS cells and Xenopus oocytes is favored by hyperpolarization. Two PKA phosphorylation sites (S210 and S329) were pinpointed in the region of the pore inner mouth. The role of these phosphorylation sites in the switch between the two gating modes was assessed by electrophysiological characterization of mutant channels. The molecular aspects of AKT2 regulation by phosphorylation, and the possible physiological meaning of such regulation in the plant context, are discussed.
Michard
Erwan
E
Biochimie et Physiologie Moléculaire des Plantes, UMR5004 Agro.M-CNRS-INRA-UM2, Montpellier, France.
Dreyer
Ingo
I
Lacombe
Benoît
B
Sentenac
Hervé
H
Thibaud
Jean-Baptiste
JB
D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D019556:COS Cells; D002462:Cell Membrane; D002522:Chlorocebus aethiops; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015640:Ion Channel Gating; D008564:Membrane Potentials; D009865:Oocytes; D010766:Phosphorylation; D015221:Potassium Channels / Q000378:metabolism*; D011485:Protein Binding; D014982:Xenopus laevis
C097485:AKT2 protein, Arabidopsis; D029681:Arabidopsis Proteins; D015221:Potassium Channels; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases