Exploiting SpyTag/SpyCatcher Technology to Design New Artificial Catalytic Copper Proteins.

Designing artificial metal binding sites within a protein is challenging since amino acid residues need to be placed in desired positions in the final construct and the use of non-natural amino acids is difficult. The alternative approach of directing the insertion of artificial metal coordination systems presents the difficulty of grafting such site in a single desired position. Spy protein is composed of a protein component (SpyCatcher) which binds spontaneously an oligopeptide (SpyTag) with formation of an isopeptide bond. A SpyTag peptide equipped with an ATCUN (amino terminal copper and nickel) binding site is designed to bind copper(II) with high femtomolar affinity both in the absence of SpyCatcher and in the reconstituted Spy construct. The Cu ATCUN site in the reconstituted Spy protein presents a catalytic activity in reactive oxygen species production, higher than that of the SpyTag peptide alone. This method offers a novel approach for constructing artificial metalloproteins by incorporating functional metal binding sites into a peptide, which can then be clicked onto its protein counterpart. The small size and modularity of this construct make it versatile for integration into other protein systems, eventually moving the complexity from a protein to a peptide and highlighting its potential for protein design.