Abstract
Polyphenol oxidases (PPOs) are coupled binuclear copper proteins that catalyze the oxidation of phenols. New functions of PPOs are continuously being discovered, latest with several fungal o-methoxy phenolases, which are active on lignin-derived compounds. Here, we perform a comprehensive phylogenetic analysis of PPOs from a wide taxonomic origin and define 12 PPO groups. We find that a deep gene duplication has led to two distinct PPO types. Type 1 includes PPOs from chordates and molluscs, as well as the fungal o-methoxy phenolases. Type 2 includes plant PPOs, molluscan hemocyanins, and fungal tyrosinases. Most of the type 2 proteins have a C-terminal shielding domain and a thioether bond in the copper-binding site. We also find that most ascomycetes contain high numbers of the PPO type 1 that includes the o-methoxy phenolases, which may indicate a role in the lignin conversion strategy of these fungi.