Actinosomes: condensate-templated proteinaceous containers for engineering synthetic cells

Engineering synthetic cells has a broad appeal, from understanding living cells to designing novel biomaterials for therapeutics, biosensing, and hybrid interfaces. A key prerequisite to creating synthetic cells is a functional three-dimensional container capable of orchestrating biochemical reactions. In this study, we present an easy and effective technique to make cell-sized porous containers crafted using the interactions between biomolecular condensates and actin cytoskeleton - we coin them actinosomes. This approach uses polypeptide/nucleoside triphosphate condensates and localizes actin monomers on their surface. By triggering actin polymerization at the expense of sequestered ATP and using osmotic gradients, the condensates are structurally transformed into containers with the boundary made up of actin filaments and polylysine polymers. We show that the GTP-to-ATP ratio is a crucial parameter for forming actinosomes: insufficient ATP prevents condensate dissolution while excess ATP leads to undesired crumpling. The surface of actinosomes lacks any structural order and is porous. We show the functionality of the actinosomes by using them as bioreactors capable of protein synthesis. Actinosomes are a handy addition to the synthetic cell platform, with appealing properties like ease-of-production, inherent encapsulation capacity, and an active surface which holds the potential to trigger signaling cascades and form multicellular assemblies, with potential for medical and biotechnological applications.