pH-Responsive, posttranslational regulation of the Trk1 potassium transporter by the type 1-related Ppz1 phosphatase.
Intracellular pH and K+ concentrations must be tightly controlled because they affect many cellular activities, including cell growth and death. The mechanisms of homeostasis of H+ and K+ are only partially understood. In the yeast Saccharomyces cerevisiae, proton efflux is mediated by the Pma1 H+-ATPase. As this pump is electrogenic, the activity of the Trk1 and -2 K+ uptake system is crucial for sustained Pma1p operation. The coordinated activities of these two systems determine cell volume, turgor, membrane potential, and pH. Genetic evidence indicates that Trk1p is activated by the Hal4 and -5 kinases and inhibited by the Ppz1 and -2 phosphatases, which, in turn, are inhibited by their regulatory subunit, Hal3p. We show that Trk1p, present in plasma membrane "rafts", physically interacts with Ppz1p, that Trk1p is phosphorylated in vivo, and that its level of phosphorylation increases in ppz1 and -2 mutants. Interestingly, both the interaction with and inhibition of Ppz1p by Hal3p are pH dependent. These results are consistent with a model in which the Ppz1-Hal3 interaction is a sensor of intracellular pH that modulates H+ and K+ homeostasis through the regulation of Trk1p activity.
Yenush
Lynne
L
Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia CSIC, Camino de Vera s/n, 46022 Valencia, Spain. lynne@ibmcp.upv.es
Merchan
Stephanie
S
Holmes
James
J
Serrano
Ramón
R
D001692:Biological Transport; D027682:Cation Transport Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005838:Genotype; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D047468:Immunoprecipitation; D021962:Membrane Microdomains / Q000378:metabolism; D008856:Microscopy, Fluorescence; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011188:Potassium / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism
D027682:Cation Transport Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C068664:TRK1 protein, S cerevisiae; D049452:Green Fluorescent Proteins; C075119:PPZ1 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; D011188:Potassium