C-TERMINAL DELETION ANALYSIS OF PLANT PLASMA-MEMBRANE H+-ATPASE - YEAST AS A MODEL SYSTEM FOR SOLUTE TRANSPORT ACROSS THE PLANT PLASMA-MEMBRANE

The plasma membrane proton pump (H+-ATPase) energizes solute uptake by secondary transporters. Wild-type Arabidopsis plasma membrane H+-ATPase (AHA2) and truncated H+-ATPases lacking 38, 51, 61, 66, 77, 92, 96, and 104 C-terminal amino acids were produced in yeast. All AHA2 species were correctly targeted to the yeast plasma membrane and, in addition, accumulated in internal membranes. Removal of 38 C-terminal residues from AHA2 produced a high-affinity state of plant H+-ATPase with a low K-m value (0.1 mM) for ATP. Removal of an additional 12 amino acids from the C terminus resulted in a significant increase in molecular activity of the enzyme. There was a close correlation between molecular activity of the various plant H+-ATPase species and their ability to complement mutants of the endogenous yeast plasma membrane H+-ATPase (pma1). This correlation demonstrates that, at least in this heterologous host, activation of H+-ATPase is a prerequisite for proper energization of the plasma membrane.