Unspecific Peroxygenases - Functional Hybrids between P450 Monooxygenases and Heme Peroxidases

Author(s): Katrin Scheibner, Martin Hofrichter

Unspecific peroxygenases (UPOs) secreted by fungi represent an intriguing enzyme type that selectively transfers peroxide-borne oxygen with high efficiency to diverse substrates including unactivated hydrocarbons. They contain a cysteine-ligated heme and catalyze hydroxylation, epoxidation, dealkylation, deacylation as well as hetero atom, halide and one-electron oxidations. Substrate spectra of UPOs resemble both those of P450 monooxygenases and heme peroxidases. Non-specific peroxygenases (UPOs, EC 1.11.2.1) belong to the heme-thiolate proteins and behave "promiscuously" with respect to demanding oxygen transfer reactions. The first UPO was discovered in 2004 in the southern field mushroom (Agrocybe aegerita), a hardwood-colonizing edible mushroom from the wider mushroom family (order Agaricales) [1]. Further enzymes of this type were found in cultures of other fungi (e.g. Marasmius rotula, Chaetomium globosum) [2,3] and the long-known chloroperoxidase (CPO, EC 1.11.1.10) turned out to be a special case of UPOs [4]. The heterologous expression of UPOs is associated with major difficulties and has so far only been successful in a few cases (e.g. in Sacharomyces, Pichia); the complex folding and the formation of disulfide bridges may play a role in this [3,6]. The crystal structures of the UPOs of A. aegerita and M. rotula have been solved and reveal a compact spherical shape dominated by ? helices and containing a heme-stabilizing magnesium and a highly conserved PCP motif. The latter ideally exposes a cysteine as proximal heme ligand towards the iron. The heme access channels of UPOs are lined with hydrophobic amino acid residues (Phe or Leu/Ile/Val) and their molecular architecture is of crucial importance for the substrate specificity of the respective enzyme [3,6].