A cloned prokaryotic Cd2+ P-type ATPase increases yeast sensitivity to Cd2+

CadA, the P1-type ATPase involved in Listeria monocytogenes resistance to Cd(2+), was expressed in Saccharomyces cerevisiae and did just the opposite to what was expected, as it strikingly decreased the Cd(2+) tolerance of these cells. Yeast cells expressing the non-functional mutant Asp(398)Ala could grow on selective medium containing up to 100 microM Cd(2+), whereas those expressing the functional protein could not grow in the presence of 1 microM Cd(2+). The CadA-GFP fusion protein was localized in the endoplasmic reticulum membrane, suggesting that yeast hyper-sensitivity was due to Cd(2+) accumulation in the reticulum lumen. CadA is also known to transport Zn(2+), but Zn(2+) did not protect the cells against Cd(2+) poisoning. In the presence of 10 microM Cd(2+), transformed yeasts survived by rapid loss of their expression vector.