Controlled Formation of Catalytic and Emissive Gold Nanoclusters with a Synthetic Self-Assembled Protein Toroid

Self-assembled proteins are privileged building blocks for the bottom-up organization of matter at the nanoscale. However, since most proteins are very large, they have to be produced by recombinant expression, which is less versatile and flexible than chemical synthesis. Here, we show that we can bridge the potential of proteins for nanofabrication with the simplicity and versatility of solid-phase peptide synthesis by relying on the self-assembly of the viral protein gp23.1, a small 50-residue protein that oligomerizes in solution to form a stable toroidal hexamer. We report the chemical synthesis and basic biophysical characterization of a gp23.1 mutant and show that its self-assembled hexamer templates the formation of highly monodisperse gold nanoclusters of about 1.3 nm inside its central cavity. The resulting nanoclusters show catalytic activity in cycloisomerization reactions as well as luminescence emission. This work demonstrates the versatility of this small self- assembled ring protein for a variety of nanotechnological applications.