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


  • Present addresses: Manuel Miranda, Department of Biological Sciences and Border Biomedical Research Center, University of Texas at El Paso, El Paso, TX 79968, USA.
    Slavena Vylkova, Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston, TX 77030, USA.

  • Editor: André Goffeau

Correspondence: Clifford Slayman, Department of Cellular and Molecular Physiology, Yale School of Medicine, New Haven, CT 06520, USA. Tel.: +1 203 785 4478; fax: +1 203 785 4951; e-mail:


TRK proteins – essential potassium (K+) transporters in fungi and bacteria, as well as in plants – are generally absent from animal cells, which makes them potential targets for selective drug action. Indeed, in the human pathogen Candida albicans, the single TRK isoform (CaTrk1p) has recently been demonstrated to be required for activity of histidine-rich salivary antimicrobial peptides (histatins). Background for a detailed molecular investigation of TRK-protein design and function is provided here in sequence analysis and quantitative functional comparison of CaTrk1p with its better-known homologues from Saccharomyces cerevisiae. Among C. albicans strains (ATCC 10261, SC5314, WO-1), the DNA sequence is essentially devoid of single nucleotide polymorphisms in regions coding for evolutionarily conserved segments of the protein, meaning the four intramembranal [membrane–pore–membrane (MPM)] segments thought to be involved directly with the conduction of K+ ions. Among 48 fungal (ascomycete) TRK homologues now described by complete sequences, clades (but not the detailed order within clades) appear conserved for all four MPM segments, independently assessed. The primary function of TRK proteins, ‘active’ transport of K+ ions, is quantitatively conserved between C. albicans and S. cerevisiae. However, the secondary function, chloride efflux channeling, is present but poorly conserved between the two species, being highly variant with respect to activation velocity, amplitude, flickering (channel-like) behavior, pH dependence, and inhibitor sensitivity.