Chimeras between C. glabrata Cnh1 and S. cerevisiae Nha1 Na+/H+-antiporters are functional proteins increasing the salt tolerance of yeast cells

The transport activity and substrate specificity of two chimeras consisting of S. cerevisiae Nha1p’s N-terminal regions (either first 125 or 184 AA) and the rest of the C. glabrata Cnh1p (up to the total protein length of 946 AA) were compared with those of the two native antiporters. Both chimeric transporters were functional upon expression in S. cerevisiae cells, their presence improved the ability of cells to grow in the presence of high external concentration of K+, Na+ or Rb+ (as chlorides), but not in the presence of the smallest cation (Li+). Cation efflux confirmed the ability of chimeras to export cations and showed their significantly reduced transport capacity compared to the wild-type proteins. Despite the very high level of primary sequence identity (87 %) between the S. cerevisiae and C. glabrata plasma-membrane Na+/H+ antiporters, various parts of these proteins are not exchangeable without affecting the antiporter’s transport capacity.