<i>In Cellulo</i> Fabrication of Supramolecular Protein Assemblies

<i>In cellulo</i> protein assemblies, spanning protein cages, filaments, crystals, and biomolecular condensates, provide cells with modular strategies to package, organize, and regulate biomolecules and biochemical reactions. Their genetic encodability, structural diversity, and tunable material properties have also made them attractive biomaterials, where <i>in cellulo</i> fabrication has underpinned their precise assembly and broad applicability. This review surveys major classes of natural and engineered assemblies fabricated <i>in cellulo</i>, with particular emphasis on how their structure, chemistry, and material state shape functions. We compare diverse cellular reactors and outline how intracellular milieu, post-translational modifications, and folding/assembly machinery influence assembly outcomes. Engineering strategies for modifying the assemblies are summarized and mapped onto broad applications across fundamental biology, biomedicine, and nonbiological fields. Lastly, we highlight existing opportunities for engineering and designing <i>in cellulo</i> protein assemblies. Through this review, we hope to give a comprehensive overview of this exciting and rapidly growing field and share our perspective on the possible future directions.