Fragment‐Based Stabilizers of Protein–Protein Interactions through Imine‐Based Tethering

A Tight Contact: The Expanding Application of Salicylaldehydes in Lysine-Targeting Covalent Drugs

The installation of aldehydes into synthetic protein ligands is an efficient strategy to engage protein lysine residues in remarkably stable imine bonds and augment the compound affinity and selectivity for their biological targets. The high frequency of lysine residues in proteins and the reversibility of the covalent ligand-protein bond support the application of aldehyde-bearing ligands, holding promises for their future use as drugs. This review highlights the increasing exploitation of salicylaldehyde modules in various classes of protein binders, aimed at the reversible-covalent engagement of lysine residues.

RGD Cyclopeptide Equipped with a Lysine-Engaging Salicylaldehyde Showing Enhanced Integrin Affinity and Cell Detachment Potency

Salicylaldehyde (SA) derivatives are emerging as useful fragments to obtain reversible-covalent inhibitors interacting with the lysine residues of the target protein. Here the SA installation at the C terminus of an integrin-binding cyclopeptide, leading to enhanced ligand affinity for the receptor as well as stronger biological activity in cultured glioblastoma cells is reported.

Molecular glues modulate protein functions by inducing protein aggregation: A promising therapeutic strategy of small molecules for disease treatment

Molecular glues can specifically induce aggregation between two or more proteins to modulate biological functions. In recent years, molecular glues have been widely used as protein degraders. In addition, however, molecular glues play a variety of vital roles, such as complex stabilization, interactome modulation and transporter inhibition, enabling challenging therapeutic targets to be druggable and offering an exciting novel approach for drug discovery. Since most molecular glues are identified serendipitously, exploration of their systematic discovery and rational design are important. In this review, representative examples of molecular glues with various physiological functions are divided into those mediating homo-dimerization, homo-polymerization and hetero-dimerization according to their aggregation modes, and we attempt to elucidate their mechanisms of action. In particular, we aim to highlight some biochemical techniques typically exploited within these representative studies and classify them in terms of three stages of molecular glue development: starting point, optimization and identification.

Reactivity and Selectivity Principles in Native Protein Bioconjugation

Are chemical methods capable of precisely engineering the native proteins? Is it possible to develop platforms that can empower the regulation of chemoselectivity, site-selectivity, modularity, protein-specificity, and site-specificity? This account delineates our research journey in the last ten years on the developments revolving around these questions. It will range from the realization of chemoselective and site-selective labeling of reactivity hotspots to modular linchpin directed modification (LDM®) platform and site-specific Gly-tag® technology. Also, we outline a few biotechnology tools, including Maspecter®, that accelerated the detailed analysis of the bioconjugates and rendered a powerful toolbox for homogeneous antibody-drug conjugates (ADCs).

Reversible Covalent Imine-Tethering for Selective Stabilization of 14-3-3 Hub Protein Interactions

The stabilization of protein complexes has emerged as a promising modality, expanding the number of entry points for novel therapeutic intervention. Targeting proteins that mediate protein–protein interactions (PPIs), such as hub proteins, is equally challenging and rewarding as they offer an intervention platform for a variety of diseases, due to their large interactome. 14-3-3 hub proteins bind phosphorylated motifs of their interaction partners in a conserved binding channel. The 14-3-3 PPI interface is consequently only diversified by its different interaction partners. Therefore, it is essential to consider, additionally to the potency, also the selectivity of stabilizer molecules. Targeting a lysine residue at the interface of the composite 14-3-3 complex, which can be targeted explicitly via aldimine-forming fragments, we studied the de novo design of PPI stabilizers under consideration of potential selectivity. By applying cooperativity analysis of ternary complex formation, we developed a reversible covalent molecular glue for the 14-3-3/Pin1 interaction. This small fragment led to a more than 250-fold stabilization of the 14-3-3/Pin1 interaction by selective interfacing with a unique tryptophan in Pin1. This study illustrates how cooperative complex formation drives selective PPI stabilization. Further, it highlights how specific interactions within a hub proteins interactome can be stabilized over other interactions with a common binding motif.