Controlled Integration of Polymers into Viral Capsids

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Role of Surface Charge Density in Nanoparticle-Templated Assembly of Bromovirus Protein Cages

Self-assembling icosahedral protein cages have potencially useful physical and chemical characteristics for a variety of nanotechnology applications, ranging from therapeutic or diagnostic vectors to building blocks for hierarchical materials. For application-specific functional control of protein cage assemblies, a deeper understanding of the interaction between the protein cage and its payload is necessary. Protein-cage encapsulated nanoparticles, with their well-defined surface chemistry, allow for systematic control over key parameters of encapsulation such as the surface charge, hydrophobicity, and size. Independent control over these variables allows experimental testing of different assembly mechanism models. Previous studies done with Brome mosaic virus capsids and negatively charged gold nanoparticles indicated that the result of the self-assembly process depends on the diameter of the particle. However, in these experiments, the surface-ligand density was maintained at saturation levels, while the total charge and the radius of curvature remained coupled variables, making the interpretation of the observed dependence on the core size difficult. The current work furnishes evidence of a critical surface charge density for assembly through an analysis aimed at decoupling the surface charge and the core size

Designing two self-assembly mechanisms into one viral capsid protein

ELP-CP, a structural fusion protein of the thermally responsive elastin-like polypeptide (ELP) and a viral capsid protein (CP), was designed, and its assembly properties were investigated. Interestingly, this protein-based block copolymer could be self-assembled via two mechanisms into two different, well-defined nanocapsules: (1) pH-induced assembly yielded 28 nm virus-like particles, and (2) ELP-induced assembly yielded 18 nm virus-like particles. The latter were a result of the emergent properties of the fusion protein. This work shows the feasibility of creating a self-assembly system with new properties by combining two structural protein elements