Direct interactions between proteins are essential for the regulation of their functions in biological pathways. Targeting the complex network of protein-protein interactions (PPIs) has now been widely recognized as an attractive means to therapeutically intervene in disease states. Even though this is a challenging endeavor and PPIs have long been regarded as ‘undruggable’ targets, the last two decades have seen an increasing number of successful examples of PPI modulators resulting in a growing interest in this field. PPI modulation requires novel approaches and the integrated efforts of multiple disciplines to be a fruitful strategy. This Perspective focuses on the hub protein 14-3-3, which has several hundred identified protein interaction partners and is therefore involved in a wide range of cellular processes and diseases. Here, we aim to provide an integrated overview of the approaches explored for the modulation of 14-3-3 PPIs and review the examples resulting from these efforts in both inhibiting and stabilizing specific 14-3-3 protein complexes by small molecules, peptide-mimetics and natural products.

Brown adipose tissue (BAT) is considered an interesting target organ for the treatment of metabolic disease due to its high metabolic capacity. Non-shivering thermogenesis, once activated, can lead to enhanced partitioning and oxidation of fuels in adipose tissues, and reduce the burden of glucose and lipids on other metabolic organs such as liver, pancreas and skeletal muscle. Sustained long-term activation of BAT may also lead to meaningful bodyweight loss. In this review, we discuss three different drug classes (the thiazolidinedione (TZD) class of PPAR agonists, 3 adrenergic receptor agonists and fibroblast growth factor 21 (FGF21) analogues) that have been proposed to regulate BAT and beige recruitment or activation, or both, and which have been tested in both rodent and human. The learnings from these classes suggest that restoration of functional BAT and beige mass as well as improved activation might be required to fully realize the metabolic potential of these tissues. Whether this can be achieved without the undesired cardiovascular side-effects exhibited by the TZD PPAR agonists and 3 adrenergic receptor agonists remains to be resolved.

Protein–protein interactions (PPIs) remain poorly explored targets for the treatment of Alzheimer’s disease. The interaction of 14‐3‐3 proteins with Tau was shown to be linked to Tau pathology. This PPI is therefore seen as a potential target for Alzheimer’s disease. When Tau is phosphorylated by PKA (Tau‐PKA), several phosphorylation sites are generated, including two known 14‐3‐3 binding sites, surrounding the phosphorylated serines 214 and 324 of Tau. The crystal structures of 14‐3‐3 in complex with peptides surrounding these Tau phosphosites show that both these motifs are anchored in the amphipathic binding groove of 14‐3‐3. However, in the absence of structural data with the full‐length Tau protein, the stoichiometry of the complex or the interface and affinity of the partners is still unclear. In this work, we addressed these points, using a broad range of biophysical techniques. The interaction of the long and disordered Tau‐PKA protein with 14‐3‐3σ is restricted to two short sequences, containing phosphorylated serines, which bind in the amphipathic binding groove of 14‐3‐3σ. Phosphorylation of Tau is fundamental for the formation of this stable complex, and the affinity of the Tau‐PKA/14‐3‐3σ interaction is in the 1–10 micromolar range. Each monomer of the 14‐3‐3σ dimer binds one of two different phosphorylated peptides of Tau‐PKA, suggesting a 14‐3‐3/Tau‐PKA stoichiometry of 2 : 1, confirmed by analytical ultracentrifugation. These results contribute to a better understanding of this PPI and provide useful insights for drug discovery projects aiming at the modulation of this interaction.