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 C 4 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 C 4 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.

Owing to diverse functionalities and metal binding abilities, proteins have been proven to be promising ligands in the synthesis of gold nanoclusters (Au NCs). In this work, we explored β-lactoglobulin (β-Lg), a protein byproduct generated during cheese processing, as a biotemplate for fabrication of Au NCs by a facile and green method for the first time. The as-prepared Au NCs are water soluble and highly fluorescent and exhibit high sensitivity and selectivity for Hg detection in aqueous solution. Interestingly, we found that the fluorescence of these Au NCs is stable either in a variety of complex matrixes or over a broad pH range (5.0-13.0) and therefore can be explored as a cell and animal imaging agent. More importantly, we demonstrated that the β-lactoglobulin-stabilized Au NCs (β-Lg-Au NCs) could serve as a sensor for the detection and quantification of Hg in beverages, urine, and serum with high sensitivity.

Precise manipulation of protein self-assembly by noncovalent interactions into programmed networks to mimic naturally occurring nanoarchitectures in living organisms is a challenge due to its structural heterogeneity, flexibility, and complexity. Herein, by taking advantage of both the hydrophobic forces contributed by the "GLMVG" motif, a kind of amyloidogenic motif (AM), and the high symmetry of protein nanocages, we have built an effective protein self-assembly strategy for the construction of twodimensional (2D) or three-dimensional (3D) protein nanocage arrays. According to this strategy, "GLMVG" AMs from β-amyloid 42 were grafted onto the outer surface of a 24-mer ferritin nanocage close to its C 4 symmetry channels, initially resulting in the production of subgrade 2D nanocage arrays and ultimately generating 3D highly ordered arrays with a simple cubic packing pattern as the reaction time increases. More importantly, the reversibility and the formation rate of these protein arrays can be modulated by pH. This work provides a de novo design strategy for accurate control over 2D or 3D protein selfassemblies.

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