c Unspecific peroxygenase (UPO) represents a new type of heme-thiolate enzyme with self-sufficient mono(per)oxygenase activity and many potential applications in organic synthesis. With a view to taking advantage of these properties, we subjected the Agrocybe aegerita UPO1-encoding gene to directed evolution in Saccharomyces cerevisiae. To promote functional expression, several different signal peptides were fused to the mature protein, and the resulting products were tested. Over 9,000 clones were screened using an ad hoc dual-colorimetric assay that assessed both peroxidative and oxygen transfer activities. After 5 generations of directed evolution combined with hybrid approaches, 9 mutations were introduced that resulted in a 3,250-fold total activity improvement with no alteration in protein stability. A breakdown between secretion and catalytic activity was performed by replacing the native signal peptide of the original parental type with that of the evolved mutant; the evolved leader increased functional expression 27-fold, whereas an 18-fold improvement in the k cat /K m value for oxygen transfer activity was obtained. The evolved UPO1 was active and highly stable in the presence of organic cosolvents. Mutations in the hydrophobic core of the signal peptide contributed to enhance functional expression up to 8 mg/liter, while catalytic efficiencies for peroxidative and oxygen transfer reactions were increased by several mutations in the vicinity of the heme access channel. Overall, the directed-evolution platform described is a valuable point of departure for the development of customized UPOs with improved features and for the study of structure-function relationships.

SummaryLaccases are multicopper containing enzymes capable of performing one electron oxidation of a broad range of substrates. Using molecular oxygen as the final electron acceptor, they release only water as a by‐product, and as such, laccases are eco‐friendly, versatile biocatalysts that have generated an enormous biotechnological interest. Indeed, this group of enzymes has been used in different industrial fields for very diverse purposes, from food additive and beverage processing to biomedical diagnosis, and as cross‐linking agents for furniture construction or in the production of biofuels. Laccases have also been studied intensely in nanobiotechnology for the development of implantable biosensors and biofuel cells. Moreover, their capacity to transform complex xenobiotics makes them useful biocatalysts in enzymatic bioremediation. This review summarizes the most significant recent advances in the use of laccases and their future perspectives in biotechnology.

Thermostable laccases with a high-redox potential have been engineered through a strategy that combines directed evolution with rational approaches. The original laccase signal sequence was replaced by the α-factor prepro-leader, and the corresponding fusion gene was targeted for joint laboratory evolution with the aim of improving kinetics and secretion by Saccharomyces cerevisiae, while retaining high thermostability. After eight rounds of molecular evolution, the total laccase activity was enhanced 34,000-fold culminating in the OB-1 mutant as the last variant of the evolution process, a highly active and stable enzyme in terms of temperature, pH range, and organic cosolvents. Mutations in the hydrophobic core of the evolved α-factor prepro-leader enhanced functional expression, whereas some mutations in the mature protein improved its catalytic capacities by altering the interactions with the surrounding residues.

Peroxygenases offer attractive means to address challenges in selective oxyfunctionalisation chemistry. Despite their attractiveness, the application of peroxygenases in synthetic chemistry remains challenging due to their facile inactivation by the stoichiometric oxidant (H2O2). Often atom inefficient peroxide generation systems are required, which show little potential for large scale implementation. Here we show that visible light-driven, catalytic water oxidation can be used for in situ generation of H2O2 from water, rendering the peroxygenase catalytically active. In this way the stereoselective oxyfunctionalisation of hydrocarbons can be achieved by simply using the catalytic system, water and visible light.

Laccases are multicopper oxidoreductases considered by many in the biotechonology field as the ultimate "green catalysts". This is mainly due to their broad substrate specificity and relative autonomy (they use molecular oxygen from air as an electron acceptor and they only produce water as by-product), making them suitable for a wide array of applications: biofuel production, bioremediation, organic synthesis, pulp biobleaching, textiles, the beverage and food industries, biosensor and biofuel cell development. Since the beginning of the 21st century, specific features of bacterial and fungal laccases have been exhaustively adapted in order to reach the industrial demands for high catalytic activity and stability in conjunction with reduced production cost. Among the goals established for laccase engineering, heterologous functional expression, improved activity and thermostability, tolerance to non-natural media (organic solvents, ionic liquids, physiological fluids) and resistance to different types of inhibitors are all challenges that have been met, while obtaining a more comprehensive understanding of laccase structure-function relationships. In this review we examine the most significant advances in this exciting research area in which rational, semi-rational and directed evolution approaches have been employed to ultimately convert laccases into high value-added biocatalysts.