Identification of Amino Acid Residues Responsible for C−H Activation in Type-III Copper Enzymes by Generating Tyrosinase Activity in a Catechol Oxidase

Abstract

Tyrosinases (TYRs) catalyze the hydroxylation of phenols and the oxidation of the resulting o-diphenols to o-quinones, while catechol oxidases (COs) exhibit only the latter activity. Aurone synthase (AUS) is not able to react with classical tyrosinase substrates, such as tyramine and l-tyrosine, while it can hydroxylate its natural substrate isoliquiritigenin. The structural difference of TYRs, COs, and AUS at the heart of their divergent catalytic activities is still a puzzle. Therefore, a library of 39 mutants of AUS from Coreopsis grandiflora (CgAUS) was generated and the activity studies showed that the reactivity of the three conserved histidines (HisA2, HisB1, and HisB2) is tuned by their adjacent residues (HisB1+1, HisB2+1, and waterkeeper residue) either to react as stronger bases or / and to stabilize a position permissive for substrate proton shuffling. This provides the understanding for C−H activation based on the type-III copper center to be used in future biotechnological processes.