On-Axis Alignment of Protein Nanocage Assemblies from 2D to 3D through the Aromatic Stacking Interactions of Amino Acid Residues.

Aromatic-aromatic interactions between natural aromatic amino acids Phe, Tyr, and Trp play crucial roles in protein-protein recognition and protein folding. However, the function of such interactions in the preparation of different dimensional, ordered protein superstructures has not been recognized. Herein, by a combination of the directionality of the symmetry axes of protein building blocks and the strength of the aromatic-aromatic interactions coming from a group of aromatic amino acid residues, we built an engineering strategy to construct protein superlattices. Based on this strategy, substitution of single amino acid residue Glu162 around the C4 rotation axes near the outer surface of 24-mer ferritin nanocage with Phe, Tyr, and Trp, respectively, resulted in 2D and 3D protein superlattices where protein cages are aligned along the C4 axes, imposing a fixed disposition of neighboring ferritins. The self-assembly of these superlattices is reversible, which can be tuned by external stimuli (salt concentration or pH). Moreover, these superlattices can serve as biotemplates for the fabrication of 2D and 3D inorganic nanoparticle arrays.