The Hydrophilic C-terminus of Yeast Plasma-membrane Na+/H+ Antiporters Impacts Their Ability to Transport K+.

[Display omitted] • Yeast Na+/H+ antiporters differ in cation selectivity for Li+, Na+ and/or K+. • The hydrophilic C-terminus influences the transport of particular cations. • Composition of the conserved C3 domain impacts the ability to transport K+. • Physiological functions of yeast Na+/H+ antiporters depend on their C-termini. Yeast plasma-membrane Na+/H+ antiporters (Nha/Sod) ensure the optimal intracellular level of alkali-metal cations and protons in cells. They are predicted to consist of 13 transmembrane segments (TMSs) and a large hydrophilic C-terminal cytoplasmic part with seven conserved domains. The substrate specificity, specifically the ability to recognize and transport K+ cations in addition to Na+ and Li+, differs among homologs. In this work, we reveal that the composition of the C-terminus impacts the ability of antiporters to transport particular cations. In the osmotolerant yeast Zygosaccharomyces rouxii , the Sod2-22 antiporter only efficiently exports Na+ and Li+, but not K+. The introduction of a negative charge or removal of a positive charge in one of the C-terminal conserved regions (C3) enabled Zr Sod2-22 to transport K+. The same mutations rescued the low level of activity and purely Li+ specificity of Zr Sod2-22 with the A179T mutation in TMS6, suggesting a possible interaction between this TMS and the C-terminus. The truncation or replacement of the C-terminal part of Zr Sod2-22 with the C-terminus of a K+-transporting Nha/Sod antiporter (Saccharomyces cerevisiae Nha1 or Z. rouxii Nha1) also resulted in an antiporter with the capacity to export K+. In addition, in Sc Nha1, the replacement of three positively charged arginine residues 539–541 in the C3 region with alanine caused its inability to provide cells with tolerance to Li+. All our results demonstrate that the physiological functions of yeast Nha/Sod antiporters, either in salt tolerance or in K+ homeostasis, depend on the composition of their C-terminal parts. [ABSTRACT FROM AUTHOR]