14-3-3 proteins interact with a novel phosphothreonine motif (Y946pTV) at the extreme C-terminal end of the plant plasma membrane H+-ATPase molecule. Phosphorylation-independent binding of 14-3-3 protein to the YTV motif can be induced by the fungal phytotoxin fusicoccin. The molecular basis for the phosphorylation-independent interaction between 14-3-3 and H+-ATPase in the presence of fusicoccin has been investigated in more detail. Fusicoccin binds to a heteromeric receptor that involves both 14-3-3 protein and H+-ATPase. Binding of fusicoccin is dependent upon the YTV motif in the H+-ATPase and, in addition, requires residues further upstream of this motif. Apparently, 14-3-3 proteins interact with the unusual epitope in H+-ATPase via its conserved amphipathic groove. This implies that very diverse epitopes bind to a common structure in the 14-3-3 protein.

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