Catalytic mechanism of the tyrosinase reaction toward the Tyr98 residue in the caddie protein

Abstract

Tyrosinase (EC 1.14.18.1), a copper-containing monooxygenase, catalyzes the conversion of phenol to the corresponding ortho-quinone. The Streptomyces tyrosinase is generated as a complex with a “caddie” protein that facilitates the transport of two copper ions into the active center. In our previous study, the Tyr98 residue in the caddie protein, which is accommodated in the pocket of active center of tyrosinase, has been found to be converted to a reactive quinone through the formations of the μ-η2:η2-peroxo-dicopper(II) and Cu(II)-dopasemiquinone intermediates. Until now—despite extensive studies for the tyrosinase reaction based on the crystallographic analysis, low-molecular-weight models, and computer simulations—the catalytic mechanism has been unable to be made clear at an atomic level. To make the catalytic mechanism of tyrosinase clear, in the present study, the cryo-trapped crystal structures were determined at very high resolutions (1.16–1.70 Å). The structures suggest the existence of an important step for the tyrosinase reaction that has not yet been found: that is, the hydroxylation reaction is triggered by the movement of CuA, which induces the syn-to-anti rearrangement of the copper ligands after the formation of μ-η2:η2-peroxo-dicopper(II) core. By the rearrangement, the hydroxyl group of the substrate is placed in an equatorial position, allowing the electrophilic attack to the aromatic ring by the Cu2O2 oxidant.

New tyrosinases with a broad spectrum of action against contaminants of emerging concern: Insights fromin silicoanalyses

“…This character was previously reported in some fungal tyrosinases (Mayer, 2006) and a possible route for their secretion would be through quaternary associations with "caddy-like" proteins caring their own signal peptides, such as those described in Streptomyces sp. (Matoba et al, 2018). The sequence similarity between tyrosinases of ciliates and fungi is further evidenced in our phylogenetic reconstruction (Figure 1) (Figure 1).…”

Histidine residues at the copper-binding site in human tyrosinase are essential for its catalytic activities

“…Moreover, it has been proposed that the proton of the hydroxyl group of monophenols may be removed and transferred to one of the coordinating histidine residues in the catalytic mechanism of tyrosinase 38,39 . The deprotonated substrates are bound to the active centre of tyrosinase 40 , and this may be stabilised by the interaction with the conserved histidine residues serving as a proton acceptor, even though this should be proved by compelling evidence.…”

Enzyme‐catalysed polymer cross‐linking: Biocatalytic tools for chemical biology, materials science and beyond

“…Finally, the reduced enzyme is reoxidised by molecular oxygen. [70] The o-quinone product of these reactions will react avidly and spontaneously with large or multifunctional nucleophiles to generate covalent cross-links.…”