Exploring new pharmacological perspectives of Fusicoccin, a stabilizer of 14-3-3 – target protein complex

The development of small-molecules regulating protein - protein interaction has emerged as a powerful field in pharmacology. In this scenario, 14-3-3 proteins represent a promising target, as they are an important class of adapter proteins that regulate several hundred partners, many of them described as disease-relevant proteins such as p53, Raf1, α-Synuclein and HERG channel. The fungal phytoxin Fusicoccin (FC) has shown to possess stabilizing properties on the complex formed by 14-3-3 proteins with some of their targets, including ion channels and pumps. Thus, FC is a promising tool to control cellular processes regulated by 14-3-3 proteins. To date FC action was thought to be limited to a specific subset of targets displaying the 14-3-3 binding site at their C-terminus (MODE III). The structure of the ternary 14-3-3 - target - FC complex shows that FC displays its stabilizing effect by developing an hydrophobic interaction with the C-terminal non-polar residue of the target protein. In this work, by taking advantage of our structural and functional study on the interaction between 14-3-3 and the voltage-gated inward rectifier potassium channel KAT1 of Arabidopsis thaliana, we expanded the palette of pharmacological targets of FC to a new kind of internal and C-terminal binding motifs lacking the hydrophobic residue. By solving the structure of the ternary complex, we discovered a new orientation of FC within the 14-3-3 - KAT1 complex, that accounts for the unexpected stabilizing effect of the molecule. Thus, our structural and functional work opens new perspectives in the employment of FC as a stabilizing molecule for 14-3-3 - target complexes