Structure-function relationships in membrane segment 6 of the yeast plasma membrane Pma1 H+-ATPase

► Amino acid substitutions of the conserved Asp-730 and D-739 residues led to protein misfolding. ► Mutations on the extracellular side of M6 were expressed in secretory vesicles but had a severe reduction of ATPase activity. ► Mutations of Ala-726, Ala-732 and Thr-733 decreased the coupling ratio of H+/ATP.