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Maudoux, O. et al.

A plant plasma membrane H+-ATPase expressed in yeast is activated by phosphorylation at its penultimate residue and binding of 14-3-3 regulatory proteins in the absence of fusicoccin.

The Nicotiana plumbaginifolia plasma membrane H(+)-ATPase isoform PMA2, equipped with a His(6) tag, was expressed in Saccharomyces cerevisiae and purified. Unexpectedly, a fraction of the purified tagged PMA2 associated with the two yeast 14-3-3 regulatory proteins, BMH1 and BMH2. This complex was formed in vivo without treatment with fusicoccin, a fungal toxin known to stabilize the equivalent complex in plants. When gel filtration chromatography was used to separate the free ATPase from the 14-3-3.H(+)-ATPase complex, the complexed ATPase was twice as active as the free form. Trypsin treatment of the complex released a smaller complex, composed of a 14-3-3 dimer and a fragment from the PMA2 C-terminal region. The latter was identified by Edman degradation and mass spectrometry as the PMA2 C-terminal 57 residues, whose penultimate residue (Thr-955) was phosphorylated. In vitro dephosphorylation of this C-terminal fragment prevented binding of 14-3-3 proteins, even in the presence of fusicoccin. Mutation of Thr-955 to alanine, aspartate, or a stop codon prevented PMA2 from complementing the yeast H(+)-ATPase. These mutations were also introduced in an activated PMA2 mutant (Gln-14 --> Asp) characterized by a higher H(+) pumping activity. Each mutation directly modifying Thr-955 prevented 14-3-3 binding, decreased ATPase specific activity, and reduced yeast growth. We conclude that the phosphorylation of Thr-955 is required for 14-3-3 binding and that formation of the complex activates the enzyme.[1]

References

A plant plasma membrane H+-ATPase expressed in yeast is activated by phosphorylation at its penultimate residue and binding of 14-3-3 regulatory proteins in the absence of fusicoccin. Maudoux, O., Batoko, H., Oecking, C., Gevaert, K., Vandekerckhove, J., Boutry, M., Morsomme, P. J. Biol. Chem. (2000) [Pubmed]

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