Self-Assembly of Biofunctional Nanohybrids in Complex Morphologies Using Recombinant Proteins

There has been an increasing interest in fabricating hybrid nanomaterials for technological applications in life sciences, because of the advantage that synergy of properties from distinct materials at the nanoscale can be achieved. In particular, protein-based hybrid materials provide biocompatibility and biofunctionality, which further combine useful properties and functionalities from non-protein components such as synthetic polymers or inorganics. Protein cages, which hold hollow structures with a cavity, have received considerable attention as a versatile platform. For example, catalyst or therapeutic cargo materials can be protected by biocompatible thin protein layers with tuned properties through encapsulation into hybrids. Protein cages are engineered from natural proteins (e.g. viral capsid proteins, or artificial protein cages can be engineered to provide specific properties that could be more effective for hybrid material fabrication. In this study, we present a system that assemble protein cages and simultaneously encapsulate nanoparticles, resulting in pomegranate-like protein-nanoparticle hybrid nanomaterials. Amphiphilic recombinant protein building blocks were designed by genetic fusion of elastin-like polypeptides and hydrophilic folded protein domains. Assembly of hollow spheres that mimic vesicles are triggered by a temperature change, while weak non-covalent interactions between polystyrene nanoparticles and the proteins mediate encapsulation nanoparticles in high number densities. Our analysis on the size of hybrid protein cages and the number of encapsulated nanoparticles indicates that formation of the pomegranate-like morphology is achieved by nanoparticle-mixing coacervation followed by maturation of morphology transition. A kinetics study on the hybrid assembly supports the mechanisms of cooperative assembly through weak interactions between nanoparticle and proteins. This platform is applicable as nanoscale tools that combines biofunctionality of proteins with a range of nanoparticle agents or biocolloids such as cells. Encapsulation of fluorescence nanoparticles in functional protein cages was demonstrated in this platform, which will be extended to a wide range of applications for biosensors, bioimaging, and high-throughput screening systems.