UC Berkeley

Protein modification strategies enable the assembly of complex biomaterials with diverse applications in fundamental and applied sciences. While various chemical methods are available to mediate such modifications, their success at making site-selective, well-defined protein conjugates can vary from protein to protein substrate. An exciting alternative capitalizes on natural catalysts, enzymes, which are inherently selective and efficient in their chemical transformations. Our lab has demonstrated that the enzyme, tyrosinase, can be used for the assembly of various protein conjugates. Tyrosinase oxidizes the phenol functional group to a reactive o-quinone intermediate, which modifies amine- and thiol-containing substrates. This work focuses on expanding the substrate scope and applications of tyrosinase-mediated oxidative coupling chemistry. For the first time, tyrosinase was used to conjugate cytotoxic payloads to antibody biomolecules for the assembly of complex antibody drug conjugates with improved payload linkage stability and potent cell-killing efficacy. I also demonstrate that small thiol substrates and cysteine-containing peptides, although inhibitors of tyrosinase, can be coupled to tyrosine-tagged proteins with a bacterial tyrosinase. Beyond conjugation chemistry, progress was also made towards exploring tyrosinase-mediated oxidation of various phenols and naphthols for potential applications in biocatalysis of industrial and pharmaceutical compounds. Additionally, preliminary studies were initiated to identify several active homologous bacterial tyrosinases towards phenol oxidation. Taken together, this work has expanded tyrosinase’s coupling capabilities to include difficult substrates and initiated efforts to characterize tyrosinase variants with unique enzymatic properties.