Rational optimization of a transcription factor activation domain inhibitor.

Transcription factors are among the most attractive therapeutic targets but are considered largely 'undruggable' in part due to the intrinsically disordered nature of their activation domains. Here we show that the aromatic character of the activation domain of the androgen receptor, a therapeutic target for castration-resistant prostate cancer, is key for its activity as transcription factor, allowing it to translocate to the nucleus and partition into transcriptional condensates upon activation by androgens. On the basis of our understanding of the interactions stabilizing such condensates and of the structure that the domain adopts upon condensation, we optimized the structure of a small-molecule inhibitor previously identified by phenotypic screening. The optimized compounds had more affinity for their target, inhibited androgen-receptor-dependent transcriptional programs, and had an antitumorigenic effect in models of castration-resistant prostate cancer in cells and in vivo. These results suggest that it is possible to rationally optimize, and potentially even to design, small molecules that target the activation domains of oncogenic transcription factors.

A glutamine-based single α-helix scaffold to target globular proteins.

The binding of intrinsically disordered proteins to globular ones can require the folding of motifs into α-helices. These interactions offer opportunities for therapeutic intervention but their modulation with small molecules is challenging because they bury large surfaces. Linear peptides that display the residues that are key for binding can be targeted to globular proteins when they form stable helices, which in most cases requires their chemical modification. Here we present rules to design peptides that fold into single α-helices by instead concatenating glutamine side chain to main chain hydrogen bonds recently discovered in polyglutamine helices. The resulting peptides are uncharged, contain only natural amino acids, and their sequences can be optimized to interact with specific targets. Our results provide design rules to obtain single α-helices for a wide range of applications in protein engineering and drug design.

Intrinsically disordered proteins and biomolecular condensates as drug targets.

Intrinsically disordered domains represent attractive therapeutic targets because they play key roles in cancer, as well as in neurodegenerative and infectious diseases. They are, however, considered undruggable because they do not form stable binding pockets for small molecules and, therefore, have not been prioritized in drug discovery. Under physiological solution conditions many biomedically relevant intrinsically disordered proteins undergo phase separation processes leading to the formation of mesoscopic highly dynamic assemblies, generally known as biomolecular condensates that define environments that can be quite different from the solutions surrounding them. In what follows, we review key recent findings in this area and show how biomolecular condensation can offer opportunities for modulating the activities of intrinsically disordered targets.

Toxoplasma Parasite Twisting Motion Mechanically Induces Host Cell Membrane Fission to Complete Invasion within a Protective Vacuole.

To invade cells, the parasite Toxoplasma gondii injects a multi-unit nanodevice into the target cell plasma membrane (PM). The core nanodevice, which is composed of the RhOptry Neck (RON) protein complex, connects Toxoplasma and host cell through a circular tight junction (TJ). We now report that this RON nanodevice mechanically promotes membrane scission at the TJ-PM interface, directing a physical rotation driven by the parasite twisting motion that enables the budding parasitophorous vacuole (PV) to seal and separate from the host cell PM as a bona fide subcellular Toxoplasma-loaded PV. Mechanically impairing the process induces swelling of the budding PV and death of the parasite but not host cell. Moreover, this study reveals that the parasite nanodevice functions as a molecular trigger to promote PV membrane remodeling and rapid onset of T. gondii to intracellular lifestyle.