Epitope Tagging of the Yeast K+ Carrier Trk2p Demonstrates Folding That Is Consistent with a Channel-like Structure

pH-Responsive, Posttranslational Regulation of the Trk1 Potassium Transporter by the Type 1-Related Ppz1 Phosphatase

“…These results establish Trk1p as yet another yeast transporter present in lipid rafts. Interestingly, a previous report suggested that Trk2p is also present in these microdomains, although in that case, the protein was highly overexpressed, complicating the interpretation of these data (62).…”

The TRK1 Potassium Transporter Is the Critical Effector for Killing of Candida albicans by the Cationic Protein, Histatin 5

“…These results suggest that the membrane density of Trk1p is optimal, or near maximal, with two functional alleles in wildtype C. albicans and that overexpressed protein is shunted into cytoplasmic aggregates, perhaps the vesiculotubular clusters described upon overexpression of Trk2p in Saccharomyces (49), and into a membrane complex with other proteins (the 210-kDa immunopositive band), which could still be functional (see "Discussion"). To investigate whether the membrane-bound Trk1p detected by immunoblotting represents functional protein, we examined the abilities of all four strains to carry out the normal transport processes of TRK1 protein.…”

“…Most simply, cytoplasmically localized Trk1p is likely to be sequestered within endomembranes (karmellae or vesicular-tubular clusters) (49), as a device to counter the threat of excessive membrane permeability. Then, if direct interaction between Hst 5 and Trk1p occurs as postulated above, elevated endomembranal Trk1p could also bind significant Hst 5, decreasing the free concentration available to the effector site, which is plasma membrane-localized Trk1p.…”

“…Purely on the basis of structural modeling, Durell and Guy (44) postulated that yeast TRK proteins (in S. cerevisiae and Schizosaccharomyces pombe) should form symmetric dimers or tetramers. Without such clustering, the monomers, which fold like potassium channels (49), would have unusually well conserved surface residues, exposed primarily to membrane lipids. Hetero-oligomerization of TRK proteins in Saccharomyces is also a strong possibility because of the presence of three genes/proteins of unknown function but having strong sequence homology with plant potassium-channel ␤-subunits.…”

Coordination of K + Transporters in Neurospora: TRK1 Is Scarce and Constitutive, while HAK1 Is Abundant and Highly Regulated

“…For the Trk-HKT proteins, early sequence data revealed strong similarity to K ϩ channels and led to a theoretical model (16,17) based on the bacterial potassium channel, KcsA (18). That model, which varied slightly among the bacterial, fungal, and plant homologues, has been substantiated by a variety of point mutation and sidedness studies (19)(20)(21)(22). More recently, VpTrkH, a bacterial homologue from Vibrio parahaemolyticus, has been crystallized (23), confirming the major features of the Durell and Guy model and pointing to a fundamentally channel-like permeation process for K ϩ ions.…”