Secrets of the fungus-specific potassium channel TOK family.

The tandem-pore outward-rectifying potassium (K+) channel family (TOK) is found only in fungi. Therefore, a specific role in fungus physiology can be assumed. ScTOK1 was the first TOK channel characterized in Saccharomyces cerevisiae that displayed a unique structure: two pore domains and eight transmembrane domains per subunit. ScTOK1 induces mainly outward K+ currents upon membrane depolarization, and is highly regulated. The gating model of TOK channels has evolved over the years and involves external and internal K+ concentration, potential binding sites, and membrane potential. TOK channels have also been found recently in filamentous fungi, and light has been shed on their potential role in beneficial and pathogenic interactions with host organisms. Several families of potassium (K+) channels are found in membranes of all eukaryotes, underlining the importance of K+ uptake and redistribution within and between cells and organs. Among them, TOK (tandem-pore outward-rectifying K+) channels consist of eight transmembrane domains and two pore domains per subunit organized in dimers. These channels were originally studied in yeast, but recent identifications and characterizations in filamentous fungi shed new light on this fungus-specific K+ channel family. Although their actual function in vivo is often puzzling, recent works indicate a role in cellular K+ homeostasis and even suggest a role in plant–fungus symbioses. This review aims at synthesizing the current knowledge on fungal TOK channels and discussing their potential role in yeasts and filamentous fungi. [ABSTRACT FROM AUTHOR]