Polymorphic In Vitro Assembly of a Bacterial Microcompartment Shell Protein

Bacterial microcompartments (BMCs) are self-assembling protein nanocages involved in metabolic compartmentalization in bacteria. They consist of hexagonal and pentagonal protein subunits that tile the facets of polyhedral shells. BMCs can assemble a variety of morphologies, making them attractive platforms for engineering synthetic biomaterials and organizing catalysis. Here, a single 99-amino-acid hexameric shell protein from the BMC of Haliangium ochraceum is shown to self-assemble in vitro into a range of nanoscale and mesoscale architectures, including flat lattice sheets, nanorolls, single-walled nanotubes, and nanospheres. The assembly morphology can be controlled by modulating the ionic strength of the assembly buffer, which influences the anisotropic interactions between subunits. These structures represent model platforms for engineered synthetic nanoreactors and provide a framework for exploring the emergent physical, mechanical, and chemical properties of protein-based crystalline materials.