Two new unspecific peroxygenases from heterologous expression of fungal genes in Escherichia coli

Abstract

Unspecific peroxygenases (UPOs) constitute a new family of fungal heme-thiolate enzymes with high biotechnological interest. Although several thousand genes encoding hypothetical UPO-type proteins have been identified in sequenced fungal genomes and other databases, only a handful of UPO enzymes have been experimentally characterized to date. Therefore, gene screening and heterologous expression from genetic databases is a priority in the search for ad-hoc UPOs for oxyfunctionalization reactions of interest. Very recently, Escherichia coli production (as a soluble and active enzyme) of a previously described basidiomycete UPO has been reported. Here, we explored this convenient heterologous expression system to obtain the protein products from several putative UPO genes available. In this way, two UPOs from the ascomycetes Collariella virescens (syn. Chaetomium virescens) and Daldinia caldariorum were successfully obtained, purified, and characterized. Comparison of their kinetic constants for oxidation of model substrates revealed 7-20 fold higher catalytic efficiency of the latter enzyme oxidizing simple aromatic compounds (such as veratryl alcohol, naphthalene and benzyl alcohol). Homology molecular models of these enzymes showed three conserved and two differing residues in the distal side of the heme (the latter representing two different positions of a phenylalanine residue). Interestingly, substitution of the C. virescens UPO Phe88 by the homologous residue in the D. caldariorum UPO resulted in a F88L variant with 5-21 fold higher efficiency oxidizing the above aromatic compounds.IMPORTANCE: UPOs catalyze regio- and stereo-selective oxygenations of both aromatic and aliphatic compounds. Similar reactions were previously described for cytochrome P450 monooxygenases, but UPOs have the noteworthy biotechnological advantage of being stable enzymes only requiring H2O2 to be activated. Both characteristics are related to the extracellular nature of UPOs as secreted proteins. In the present study, the limited repertoire of UPO enzymes available for organic synthesis and other applications is expanded with the description of two new ascomycete UPOs, by Escherichia coli expression of the corresponding genes as soluble and active enzymes. Moreover, directed mutagenesis in E. coli, together with enzyme molecular models, provided relevant structural-functional information on aromatic substrate oxidation by these two new biocatalysts.