Unspecific peroxygenases: The pot of gold at the end of the rainbow?

Fungal unspecific peroxygenases (UPOs) are among the most promising biocatalysts in synthetic chemistry. The kaleido-scope of oxyfunctionalization reactions that are of industrial and environmental relevance offer UPOs the opportunity to provide solutions to many processes. However, there are important shortcomings that must first be overcome in order to convert UPOs into applied biocatalysts, which include their general poor levels of heterologous functional expression, the presence of unwanted peroxidase activity and overoxidation reactions, as well as the oxidative inactivation provoked by the co-substrate, hydrogen peroxide. The specific engineering of these proteins, and that of the reactions in which they partici -pate, is being used to tackle these principal challenges, with a view to generate a portfolio of highly active, selective and stable variants. In this review, we will discuss some of the most recent developments that will convert UPOs into true industrial biocatalysts, focusing on the different trends currently being followed in this fascinating field of research.