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
O. Maudoux 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, J BIOL CHEM, 275(23), 2000, pp. 17762-17770
The Nicotiana plumbaginifolia plasma membrane H+ ATPase isoform PMA2, equip
ped with a His, 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 forme
d in vivo without treatment with fusicoccin, a fungal toxin known to stabil
ize the equivalent complex in plants. When gel filtration chromatography wa
s used to separate the free ATPase from the 14-3-3.H+-ATPase complex, the c
omplexed 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 fr
agment 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 dephosphorylati
on of this C-terminal fragment prevented binding of 14-3-3 proteins, even i
n 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 modi
fying 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.