Recombinant Fusion Proteins with Embedded Sensing Functions as Versatile Tools for Protocell Development.

Sensory capabilities are crucial for cells to interact with their environment. To mimic these functions in synthetic cells, we developed sensory globular protein vesicles (GPVs) made entirely of recombinant fusion proteins through self-assembly under aqueous conditions. GPVs demonstrate sensory functions via the formation of the FKBP-FRB ternary complex with the signaling molecule, rapamycin. The sensory domain of FKBP or FRB was genetically fused to a fluorescent protein and leucine zipper, which self-assemble into vesicles by forming amphiphilic building blocks through high-affinity binding to a counter leucine zipper fused to an elastin-like polypeptide (ELP) above its lower critical solution temperature. We observed intervesicle aggregation in a time- and concentration-dependent manner upon rapamycin binding, confirmed by colocalization studies and statistical analysis. This system enhances our understanding of protein vesicle functionality for sensing and offers a basis for exploring GPVs as models to replicate key cellular processes in synthetic cells.