Protein crystalline frameworks with controllable interpenetration directed by dual supramolecular interactions.

Protein crystalline frameworks are attractive for biomimetic and nanotechnological studies because they could augment the useful functionalities of numerous proteins through dense packing and uniform orientation. However, their formation and precise structural control is challenging. Here we present novel protein crystalline frameworks with controllable interpenetration. The homotetrameric lectin concanavalin A is crosslinked by predetermined inducing ligands containing monosaccharide and rhodamine groups connected by an oligo(ethylene oxide) spacer. Two non-covalent interactions, that is, sugar-lectin binding and the dimerization of RhB, are responsible for the framework formation. The three-dimensional structure of the framework is fully characterized by X-ray crystallographic methods. For the first time, either interpenetrating or non-interpenetrating frameworks are obtained, and they are controlled by the spacer length of the inducing ligand. Further kinetics and mechanistic investigations reveal that, in the self-assembly process, the carbohydrate-protein binding occurs first, followed by RhB dimerization. This sequence favours rapid crystallization with a high yield when an excess amount of inducing ligand is used. In short, by using well-controlled dual non-covalent interactions, fast and versatile preparation of protein crystalline framework was achieved with high crystallization ratio of the proteins, which may shed light on protein crystallization in near future.