The KlTrk1 gene encodes a low affinity transporter of the K⁺ uptake system in the budding yeast Kluyveromyces lactis

Abstract

Potassium uptake in Saccharomyces cerevisiae is mediated by at least two proteins, known as Trk1p and Trk2p. Direct involvement in cation movements has been demonstrated for Trk1p, which is the high affinity transporter. S. cerevisiae cells also show low affinity potassium uptake, perhaps mediated by Trk2p. Mutants lacking Trk1p, lose high affinity system, but when grown with moderate potassium concentrations, Trk2p seems to replace it. Mutants lacking both proteins are viable but require at least 10 mM K + in the medium to sustain growth. Here we report the cloning and characterization of a gene from Kluyveromyces lactis encoding a homologue of these two proteins. KlTrkp is a 1070 amino acid peptide that shows, overall, higher homology with Trk2p than with Trk1p, and its disruption gives rise to cells with deficient potassium transport and with an increased K + requirement for normal growth. Determination of kinetic parameters in the K. lactis wildtype and Kltrk1D strains, as well as in Sctrk1D Sctrk2D S. cerevisiae cells expressing KlTrk1, indicated that this is a low affinity component of a major potassium uptake system in K. lactis. The sequence has been deposited in GenBank under Accession No. AF136181.

Conservation and dispersion of sequence and function in fungal TRK potassium transporters: focus onCandida albicans

“…With regard to other members of the C. albicans clade (red block in Fig. 3), data on TRK‐mediated K + fluxes in K. lactis (Miranda et al , 2002) and D. hansenii (Prista et al , 2007) qualitatively resemble those for CaTrk1p and ScTRK1,2p, but do not address the quantitative impact of varying methods of starvation.…”

The yeast potassium transporter TRK2 is able to substitute for TRK1 in its biological function under low K and low pH conditions

“…pombe , other yeast species, such as Neurospora crassa (Haro et al , 1999), Debaryomyces hansenii (C. Prista, M.C. Loureiro‐Díaz and J Ramos, unpublished results), Kluyveromyces lactis (Miranda et al , 2002) and S. occidentalis (Banuelos et al , 2000) have a TRK transporter structurally closer to ScTrk2p as well as a HAK (high affinity K transporter) transporter (Rodriguez‐Navarro, 2000). The HAK transporter belongs to a family of K + transporters that seem to be better adapted to function on low potassium concentrations (Rodriguez‐Navarro, 2000).…”

“…Rb + kinetics was performed in whole cells as described Miranda et al (2002). Briefly, 50 mg cells were incubated in 10 m M MES‐TEA, pH 6.0, 50 m M glucose for 3 min at 30 °C.…”

“…Trk2p also contains four MPM segments whose identity to those of Trk1p MPM segments rises to 70–90%. The principal difference between Trk1p and Trk2p lies between the first and second MPM motifs; in Trk1p this loop is 642 amino acids long, while in Trk2p this intracellular segment is significantly shorter (326 residues) (Miranda et al , 2002).…”

Alkali-metal-cation influx and efflux systems in nonconventional yeast species

“…Kluyveromyces lactis is endowed with a TRK homologous gene whose product works as a low‐affinity K + transporter (Miranda et al , 2002). Trk transporters have been studied in two Debaryomyces species ( Debaryomyces occidentalis , former Schwanniomyces occidentalis , and Debaryomyces hansenii ), and Do Trk1 was found to be involved in the potassium uptake and in the control of the membrane potential (Banuelos et al , 2000).…”