Self-assembly of the oxy-tyrosinase core and the fundamental components of phenolic hydroxylation

The enzyme tyrosinase contains two Cu-I centres, trigonally coordinated by imidazole nitrogens of six conserved histidine residues. The enzyme activates O-2 to form a mu-eta(2):eta(2)-peroxo-dicopper(II) core, which hydroxylates tyrosine to a catechol in the first committed step of melanin biosynthesis. Here, we report a family of synthetic peroxo complexes, with spectroscopic and chemical features consistent with those of oxygenated tyrosinase, formed through the self-assembly of monodentate imidazole ligands, Cu-I and O-2 at -125 degrees C. An extensively studied complex reproduces the enzymatic electrophilic oxidation of exogenous phenolic substrates to catechols in good stoichiometric yields. The self-assembly and subsequent reactivity support the intrinsic stability of the Cu2O2 core with imidazole ligation, in the absence of a polypeptide framework, and the innate capacity to effect hydroxylation of phenolic substrates. These observations suggest that a foundational role of the protein matrix is to facilitate expression of properties native to the core by bearing the entropic costs of assembly and precluding undesired oxidative degradation pathways.