The 14-3-3 protein interacts directly with the C-terminal region of the plant plasma membrane H(+)-ATPase.

Accumulating evidence suggests that 14-3-3 proteins are involved in the regulation of plant plasma membrane H(+)-ATPase activity. However, it is not known whether the 14-3-3 protein interacts directly or indirectly with the H(+)-ATPase. In this study, detergent-solubilized plasma membrane H(+)-ATPase isolated from fusicoccin-treated maize shoots was copurified with the 14-3-3 protein (as determined by protein gel blotting), and the H(+)-ATPase was recovered in an activated state. In the absence of fusicoccin treatment, H(+)-ATPase and the 14-3-3 protein were well separated, and the H(+)-ATPase was recovered in a nonactivated form. Trypsin treatment removed the 10-kD C-terminal region from the H(+)-ATPase as well as the 14-3-3 protein. Using the yeast two-hybrid system, we could show a direct interaction between Arabidopsis 14-3-3 GF14-phi and the last 98 C-terminal amino acids of the Arabidopsis AHA2 plasma membrane H(+)-ATPase. We propose that the 14-3-3 protein is a natural ligand of the plasma membrane H(+)-ATPase, regulating proton pumping by displacing the C-terminal autoinhibitory domain of the H(+)-ATPase.