Twisted rectangular subunits self-assemble into a ferritin-like capsule

The vertices of polyhedral protein capsules are spanned by multiple capsule-forming protein subunits, thus enclosing more volume and larger cargoes than if single proteins connected vertices directly. Application of protein cage design principles to synthetic analogs would allow a given ligand to enclose a greater volume. Here, we report the self-assembly of a simple tetramine subcomponent into a tetrahedral metal-organic capsule, with each face of the capsule composed of three ligand panels. The edges of the capsule are 31.8 angstrom in length-double the distance that can be spanned by a single subcomponent. The self-assembly rules followed by this system are programmed into the tetramine-it twists out of planarity in its lowest-energy configuration, thus favoring the large capsule over a simpler cube-like architecture. Unlike other large metal-organic capsules, the cavity of this new capsule is enclosed, and the structure was observed to bind large dianionic guests.

Automated summary

The vertices of polyhedral protein capsules can be composed of multiple capsule-forming protein subunits, enabling them to enclose more volume and larger cargoes than single proteins. Applying protein cage design principles to synthetic analogs can increase their volume of encapsulation. In this study, a tetrahedral metal-organic capsule was self-assembled from a simple tetramine subcomponent, with each face composed of three ligand panels. The self-assembly rules of this system are programmed into the tetramine, favoring the formation of a large capsule over a simpler cube-like structure. Unlike other large metal-organic capsules, this new capsule has an enclosed cavity and can bind large dianionic guests.