Point mutations in Pma1 H+-ATPase of Saccharomyces cerevisiae: influence on its expression and activity.

Yeast Pma1 H+-ATPase is a key enzyme of cell metabolism generating electrochemical proton gradient across the plasma membrane, thus playing an important role in the maintenance of ion homeostasis in the cell. Using site-directed mutagenesis, we have previously replaced all 21 amino acid residues in the transmembrane segment M8 with Ala (Guerra et al. (2007) Biochim. Biophys. Acta, 1768, 2383-2392). In this work, we present new data on the role of these amino acid residues in the structure-function relationship in the enzyme and cell tolerance to heat shock. Mutations Q798A and I799A are lethal for cells regardless of expression of the enzyme in secretory vesicles or plasma membrane. The F796A mutation causes enzyme and cell sensitivity to heat shock when expressed in secretory vesicles. The I794A mutation increases temperature sensitivity of cells when the enzyme is expressed either in secretory vesicles or, to a lesser extent, in plasma membrane. The E803A mutation has no significant influence on the ATPase and cell sensitivity to heat shock; however, it causes a shift in the equilibrium between E1 and E2 conformations of the enzyme towards E1.