The equilibrium structure of self-assembled protein nano-cages

Understanding how highly symmetric, robust, monodisperse protein cages self-assemble can have major applications in various areas of bio-nanotechnology, such as drug delivery, biomedical imaging and gene therapy. We develop a model to investigate the assembly of protein subunits into the structures with different size and symmetry. Using Monte Carlo simulation, we obtain the global minimum energy structures. Our results suggest that the physical properties of building blocks including the spontaneous curvature, flexibility and bending rigidity of coat proteins are sufficient to predict the size of the assembly products and that the symmetry and shape selectivity of nano-cages can be explained, at least in part, on a thermodynamic basis. The polymorphism of nano-cages observed in vitro assembly experiments are also discussed.