Journal
CHEMBIOCHEM
Volume 22, Issue 7, Pages 1161-1175Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cbic.202000647
Keywords
activity controllers; gatekeeper residue; oxidases; phenolase activity; tyrosinases; waterkeeper residue
Funding
- Austrian Science Fund (FWF) [P25217, P29144, P32326]
- University of Vienna
- Austrian Science Fund (FWF) [P25217, P32326, P29144] Funding Source: Austrian Science Fund (FWF)
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The article reviews the role of amino acid residues affecting the different activities of PPOs, with the structural similarity between TYRs and COs complicating the elucidation of their modes of action on a structural basis.
Type-III copper enzymes like polyphenol oxidases (PPOs) are ubiquitous among organisms and play a significant role in the formation of pigments. PPOs comprise different enzyme groups, including tyrosinases (TYRs) and catechol oxidases (COs). TYRs catalyze the o-hydroxylation of monophenols and the oxidation of o-diphenols to the corresponding o-quinones (EC 1.14.18.1). In contrast, COs only catalyze the oxidation of o-diphenols to the corresponding o-quinones (EC 1.10.3.1). To date (August 2020), 102 PDB entries encompassing 18 different proteins from 16 organisms and several mutants have been reported, identifying key residues for tyrosinase activity. The structural similarity between TYRs and COs, especially within and around the active center, complicates the elucidation of their modes of action on a structural basis. However, mutagenesis studies illuminate residues that influence the two activities and show that crystallography on its own cannot elucidate the enzymatic activity mode. Several amino acid residues around the dicopper active center have been proposed to play an essential role in the two different activities. Herein, we critically review the role of all residues identified so far that putatively affect the two activities of PPOs.
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