A Genetically Encoded Thiophenol Recruits Noble Metals for Designer Enzymes

The catalytic repertoire of nature has been expanded over the past decades by the introduction of artificial metalloenzymes. These are enzymes containing a synthetic metal complex or a non-native metal ion. However, combining noble metal catalysis and enzymes remains challenging due to the lack of suitable ligands to bind these complexes. So far, noble metal artificial metalloenzyme design mostly involves in vitro approaches of ligand anchoring, like covalent modification of a cysteine residue or via supramolecular assembly. Here, we show a facile strategy to anchor a variety of 4d and 5d-transition metal complexes via genetic incorporation of a thiophenolic metal-binding ligand. We created a methodology to efficiently incorporate 4-mercaptophenylalanine in a protein scaffold using the stop codon suppression technology. The incorporated non-canonical amino acid was capable of binding a variety of noble metal complexes. To showcase the catalytic applications of this methodology, we developed an artificial hydroaminase by binding gold ions to the thiophenol-containing protein. The benefit of in vivo incorporation of the ligand is demonstrated by the susceptibility of catalytic activity to the microenvironment around the metal site, which can be modulated by changing the position of the ligand within the protein or by mutation of residues in its proximity.