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Updated: May 8, 2025
Measurement of Vacuolar and Cytosolic pH In Vivo in Yeast Cell Suspensions
Published on: April 19, 2013
The molecular basis of pH sensing by the human fungal pathogen Candida albicans TOK potassium channel
Rían W Manville1, Claire L Illeck1, Anthony Lewis2
1Bioelectricity Laboratory, Department of Physiology and Biophysics, School of Medicine, University of California, Irvine, Irvine, CA 92697, USA.
Abstract:
Two-pore domain, outwardly rectifying potassium (TOK) channels are exclusively expressed in fungi. Human fungal pathogen TOK channels are potential antifungal targets, but TOK channel modulation in general is poorly understood. Here, we discovered that Candida albicans TOK (CaTOK) is regulated by extracellular pH, in contrast to TOK channels from other fungal species tested. Low pH increased CaTOK channel outward currents (pKa = 6.0), hyperpolarized the voltage-dependence of TOK activation, and increased pore selectivity for K+ over Na+, shifting the reversal potential (E REV) toward E K. Mutating H144 in the S1-S2 extracellular linker partially diminished pH sensitivity, suggesting H144 forms part of the CaTOK pH sensor. Functional analysis of chimeras made with pH-insensitive Saccharomyces cerevisiae TOK and point mutants revealed that CaTOK V462 and S466 in the final transmembrane segment complete the pH-responsive elements. A tripartite network of residues thus endows CaTOK with the ability to respond functionally to changes in pH.
Insights
Two-pore domain potassium (TOK) channels in Candida albicans are regulated by extracellular pH. This pH sensitivity, mediated by specific residues, offers a potential target for antifungal drug development.
Area of Science:
- Biochemistry
- Molecular Biology
- Mycology
Background:
- Two-pore domain potassium (TOK) channels are fungal-specific.
- TOK channels are potential antifungal targets, but their modulation is not well understood.
Purpose of the Study:
- Investigate the pH regulation of the Candida albicans TOK (CaTOK) channel.
- Identify the molecular determinants of CaTOK pH sensitivity.
Main Methods:
- Electrophysiological recordings of CaTOK currents.
- Site-directed mutagenesis and chimera analysis.
- Analysis of channel selectivity and voltage-dependence.
Main Results:
- CaTOK activity is regulated by extracellular pH (pKa = 6.0), unlike other fungal TOK channels.
- Low pH increases outward currents, hyperpolarizes activation, and enhances K+ selectivity.
- Histidine 144 (H144) in the extracellular linker and residues V462/S466 in the final transmembrane segment are crucial for pH sensing.
Conclusions:
- CaTOK possesses a unique pH-sensing mechanism involving a tripartite network of residues.
- This pH sensitivity represents a novel regulatory feature of fungal TOK channels.
- Understanding CaTOK pH regulation may lead to new antifungal strategies.
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