Key role for intracellular K+ and protein kinases Sat4/Hal4 and Hal5 in the plasma membrane stabilization of yeast nutrient transporters.
K+ transport in living cells must be tightly controlled because it affects basic physiological parameters such as turgor, membrane potential, ionic strength, and pH. In yeast, the major high-affinity K+ transporter, Trk1, is inhibited by high intracellular K+ levels and positively regulated by two redundant "halotolerance" protein kinases, Sat4/Hal4 and Hal5. Here we show that these kinases are not required for Trk1 activity; rather, they stabilize the transporter at the plasma membrane under low K+ conditions, preventing its endocytosis and vacuolar degradation. High concentrations (0.2 M) of K+, but not Na+ or sorbitol, transported by undefined low-affinity systems, maintain Trk1 at the plasma membrane in the hal4 hal5 mutant. Other nutrient transporters, such as Can1 (arginine permease), Fur4 (uracil permease), and Hxt1 (low-affinity glucose permease), are also destabilized in the hal4 hal5 mutant under low K+ conditions and, in the case of Can1, are stabilized by high K+ concentrations. Other plasma membrane proteins such as Pma1 (H+ -pumping ATPase) and Sur7 (an eisosomal protein) are not regulated by halotolerance kinases or by high K+ levels. This novel regulatory mechanism of nutrient transporters may participate in the quiescence/growth transition and could result from effects of intracellular K+ and halotolerance kinases on membrane trafficking and/or on the transporters themselves.
Pérez-Valle
Jorge
J
Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-CSIC, Camino de Vera s/n, 46022 Valencia, Spain.
Jenkins
Huw
H
Merchan
Stephanie
S
Montiel
Vera
V
Ramos
José
J
Sharma
Sukesh
S
Serrano
Ramón
R
Yenush
Lynne
L
D000222:Adaptation, Physiological; D027682:Cation Transport Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology*; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009997:Osmotic Pressure; D011188:Potassium / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D017384:Sequence Deletion; D013347:Subcellular Fractions / Q000201:enzymology; D013816:Thermodynamics; D014617:Vacuoles / Q000378:metabolism
D027682:Cation Transport Proteins; D047908:Intracellular Signaling Peptides and Proteins; D026901:Membrane Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; C068664:TRK1 protein, S cerevisiae; D011494:Protein Kinases; C522341:Hal5 protein, S cerevisiae; C072246:SAT4 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D011188:Potassium