title: Molecular analysis of the mechanism of potassium uptake through the TRK1 transporter of Saccharomyces cerevisiae.
abstract: The TRK-HKT family of K(+) transporters mediates K(+) and Na(+) uptake in fungi and plants. In this study, we have investigated the molecular mechanism involved in the movement of alkali cations through the TRK1 transporter of Saccharomyces cerevisiae. The model that best explains the activity of ScTRK1 is a cotransport of two K(+) or Rb(+), both of which bind the two binding sites of ScTRK1 with very high affinities in K(+)-starved cells. Na(+) can be transported in the same way but it exhibits a much lower affinity for the second binding site. Therefore, only at critical concentration ratios between K(+) and Na(+), or Rb(+) and Na(+), the transporter takes up Na(+) together with K(+) or Rb(+). Mutation analyses suggest that the two binding sites are located in the P fragment of the first MPM motif of the transporter, and that Gln(90) is involved in these binding sites. ScTRK1 can be in two states, medium or high affinity, and we have found that Leu(949) is involved in the oscillation of the transporter between these two states. ScTRK1 mediates active K(+) uptake. This is not Na(+)-coupled and direct coupling of ScTRK1 to a source of chemical energy seems more probable than K(+)-H(+) cotransport.
authors.affiliation: Departamento de Biotecnología, Escuela Técnica Superior de Ingenieros Agrónomos, Universidad Politécnica de Madrid, Spain.
authors.forename: Rosario
authors.initials: R
authors.lastname: Haro
authors.forename: Alonso
authors.initials: A
authors.lastname: Rodríguez-Navarro
mesh_terms: D001665:Binding Sites / Q000235:genetics; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins; D017136:Ion Transport / Q000187:drug effects; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D016296:Mutagenesis; D017354:Point Mutation; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D027682:Cation Transport Proteins; D007476:Ionophores; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D014475:Uncoupling Agents; C068664:TRK1 protein, S cerevisiae; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012964:Sodium; D012413:Rubidium; D011188:Potassium