Functional comparison of plasma-membrane Na+/H+ antiporters from two pathogenic Candida species

Abstract

<p>Abstract</p> <p>Background</p> <p>The virulence of <it>Candida </it>species depends on many environmental conditions. Extracellular pH and concentration of alkali metal cations belong among important factors. Nevertheless, the contribution of transporters mediating the exchange of alkali metal cations for protons across the plasma membrane to the cell salt tolerance and other physiological properties of various <it>Candida </it>species has not been studied so far.</p> <p>Results</p> <p>The tolerance/sensitivity of four pathogenic <it>Candida </it>species to alkali metal cations was tested and the role of one of the cation transporters in that tolerance (presumed to be the plasma-membrane Na⁺/H⁺antiporter) was studied. The genes encoding these antiporters in the most and least salt sensitive species, <it>C. dubliniensis </it>and <it>C. parapsilosis </it>respectively, were identified, cloned and functionally expressed in the plasma membranes of <it>Saccharomyces cerevisiae </it>cells lacking their own cation exporters. Both <it>Cp</it>Cnh1 and <it>Cd</it>Cnh1 antiporters had broad substrate specificity and transported Na⁺, K⁺, Li⁺, and Rb⁺. Their activity in <it>S. cerevisiae </it>cells differed; <it>Cp</it>Cnh1p provided cells with a much higher salt tolerance than the <it>Cd</it>Cnh1 antiporter. The observed difference in activity was confirmed by direct measurements of sodium and potassium efflux mediated by these antiporters.</p> <p>Conclusion</p> <p>We have cloned two genes encoding putative Na⁺/H⁺antiporters in <it>C. parapsilosis </it>and <it>C. dubliniensis</it>, and characterized the transport properties of encoded proteins. Our results show that the activity of plasma-membrane Na⁺/H⁺antiporters is one of the factors determining the tolerance of pathogenic <it>Candida </it>species to high external concentrations of alkali metal cations.</p