Diterpene Molecular Glue Stabilizes Protein–Protein Interactions of a Disordered Phosphoprotein that Controls Translational Repression

Chemical stabilization of protein-protein interactions involving intrinsically disordered phosphoproteins is an emerging yet challenging problem. Synthetic agents capable of achieving this goal are desirable for advancing understanding of the biological roles of these transient interactions and for developing new therapeutics. 12-Deoxyfusicoccin (<b>12-dFC</b>), a semisynthetic derivative of the phytotoxin fusicoccin A, exhibits significant antitumor activity in animal models while its parent compound and 12-hydroxyfusicoccin (<b>12-hFC</b>) are inactive, although the molecular mechanism underlying this differential activity has remained unclear. Here, through tandem-affinity proteomics, we identified GRB10-interacting GYF protein 2 (GIGYF2), a largely disordered scaffold protein in mRNA translational repression complexes as a 14-3-3 binding partner selectively stabilized by <b>12-dFC</b> but not <b>12-hFC</b>. Biochemical analyses revealed that <b>12-dFC</b> promotes cooperative binding of 14-3-3 to the mode-1 consensus motif KGVpS₅₄₆IP in GIGYF2, enhancing binding affinity by approximately 50-fold. This stabilization enhanced GIGYF2's translational repressor function, suppressing protein synthesis and inhibiting cell proliferation. We further demonstrated that activation of AMP-activated protein kinase (AMPK), the cellular energy sensor kinase, enhanced 14-3-3 binding to wild-type GIGYF2 but not the S546A mutant, indicating that AMPK mediates S₅₄₆ phosphorylation. Importantly, S₅₄₆ phosphorylation increased significantly under starvation conditions, suggesting a GIGYF2-regulated stress-responsive pathway that suppresses protein synthesis to conserve ATP through reversible 14-3-3 binding. These findings demonstrate that <b>12-dFC</b> is a potent molecular glue stabilizer of 14-3-3 interactions with intrinsically disordered phosphoproteins and offers a robust chemical basis for developing synthetic agents that target 14-3-3-mediated control of metabolic homeostasis.