UC San Diego

Proteins are nature’s chosen building blocks to create sophisticated and functional 0-, 1-, 2- and 3D assemblies that are necessary for the complexity of life. Accordingly, there is significant interest in the development of highly ordered supramolecular protein arrays that mimic or even surpass the complexity and functional versatility of those assemblies found in nature. However, due to the chemical and structural heterogeneity of proteins, the rational design of supramolecular protein architectures is challenging. In contrast, coordination polymers such as metal-organic frameworks (MOFs) benefit from a high degree of modularity, where individual components can be interchanged to produce structurally unique architectures with vastly different materials properties. Inspired by the synthetic versatility of MOFs, we developed a method for assembling protein oligomers into highly ordered frameworks, termed protein-MOFs. Akin to more conventional MOFs, the modularity of these lattices stems from the multiple interchangeable components. We engineered a protein node through the installation of outward-facing metal-binding sites at the C3 vertices of the symmetric cage-like protein, human heavy-chain ferritin. These sites coordinate a variety of transition metals with high fidelity, allowing for the formation of extended crystalline networks when connected by ditopic bridging ligands. The symmetry of the resulting crystalline lattice is dictated by the inherent symmetry of the protein, the coordination preferences of the metal, and the geometry of the bridging ligand. This modularity led to the discovery of stimuli-responsive protein-MOFs capable of dynamic crystal-to-crystal transformations. Protein-MOFs have the potential to be utilized for the construction of functional biomaterials.