ThreeCandida albicanspotassium uptake systems differ in their ability to provideSaccharomyces cerevisiae trk1trk2mutants with necessary potassium

Abstract

Yeasts usually have one or two high-affinity potassium transporters. Two complete and one interrupted gene encoding three types of putative potassium uptake system exist in Candida albicans SC5314. As high intracellular potassium is essential for many yeast cell functions, the existence of three transporters with differing transport mechanisms (Trk uniporter, Hak cation-proton symporter, Acu ATPase) may help pathogenic C. albicans cells to acquire the necessary potassium in various organs and tissues of the host. When expressed in Saccharomyces cerevisiae lacking their own potassium uptake systems, all three putative transporters were able to provide cells with the ability to grow with low amounts of potassium over a broad range of external pH. Only CaTrk1 was properly recognized and secreted to the plasma membrane. Nevertheless, even the small number of CaHak1 and mainly CaAcu1 molecules which reached the plasma membrane resulted in an improved growth of cells in low potassium concentrations, suggesting a high affinity and capacity of the transporters. A single-point mutation restored the complete CaACU1 gene, and the resulting protein not only provided cells with the necessary potassium but also improved their tolerance to toxic lithium. In contrast to its known homologues, CaAcu1 did not seem to transport sodium.

Potassium uptake systems of Candida krusei

“…Figure ). This very long loop generally varies in length among yeast Trk; it is poorly conserved and almost completely disordered except for a short (approximately 10 aa long) conserved alpha‐helix motif in the first third of L23 (Elicharova et al, ). Also, Ck Trk1 and Ck Trk2 possess this long loop with a short conserved alpha‐helix motif.…”

Cation Transporters of Candida albicans—New Targets to Fight Candidiasis?

“…C. albicans is one of the few yeast species that encodes an additional potassium transporter system—Acu1 ATPase. The gene encoding Acu1 in the canonical SC5314 strain contains a stop codon, which, if replaced, restores open reading frame (ORF) and the full-length protein of 1081 amino acid residues long can be produced [ 64 ]. It has 10 putative transmembrane segments with a long intracellular loop between segments 4 and 5, which contains an ATP-binding site ( Figure 3 C).…”

“…It has 10 putative transmembrane segments with a long intracellular loop between segments 4 and 5, which contains an ATP-binding site ( Figure 3 C). Importantly, in two-thirds of analyzed C. albicans strains, ORF encoding Acu1 seems to be unbroken [ 64 ].…”

“…It has been shown that the full-length Acu1 of C. albicans has a high affinity for potassium ions and greatly improves the tolerance to lithium ions, but it does not transport sodium ions [ 64 ]. Furthermore, it can also modulate membrane potential or pH to some extent [ 65 ].…”

Trk1-mediated potassium uptake contributes to cell-surface properties and virulence of Candida glabrata

“…C . albicans has all three types of these transporters, i.e., the Trk uniporter, Hak potassium-proton symporter and Acu potassium-influx ATPase 33 . This might be an advantage in proliferating in host niches with relatively low potassium concentrations, or in formation and rapid growth of hyphae, a process which needs a high intracellular turgor 34 .…”