Anti-apoptotic condensates of extremotolerance-related proteins*

Phase-separated macromolecular assemblies have long been implicated in biological tolerance to environmental stress, from prototypical stress granules to the gel-like or glassy states thought central to achieving anhydrobiosis. Many extremotolerance-associated (ExTol) proteins exhibit features like intrinsic disorder and/or repetitive sequence, which are also often hallmarks of proteins that undergo liquid-liquid phase separation. We screened a library of proteins exhibiting these features, which included many ExTol proteins but also non-ExTol and even de novo designed proteins, for their ability to protect human cells against chemically-induced apoptosis. In addition to identifying protective proteins, we observed that their anti-apoptotic effect can be enhanced by promoting phase separation through modification with inducible oligomerization domains (e.g., FKBP). One of the condensates examined, driven by a synthetic protein, exhibited Caspase-7 partitioning, thereby suggesting effector sequestration as a possible mechanism for condensate-mediated apoptosis protection.