New oxidase from Bjerkandera arthroconidial anamorph that oxidizes both phenolic and nonphenolic benzyl alcohols

Abstract

A new flavooxidase is described from a Bjerkandera arthroconidial anamorph. Its physicochemical characteristics, a monomeric enzyme containing non-covalently bound flavin adenine dinucleotide (FAD), and several catalytic properties, such as oxidation of aromatic and polyunsaturated aliphatic primary alcohols, are similar to those of Pleurotus eryngii aryl-alcohol oxidase (AAO). However, it also efficiently oxidizes phenolic benzyl and cinnamyl alcohols that are typical substrates of vanillyl-alcohol oxidase (VAO), a flavooxidase from a different family, characterized by its multimeric nature and presence of covalently-bound FAD. The enzyme also differs from P. eryngii AAO by having extremely high efficiency oxidizing chlorinated benzyl alcohols (1000-1500 s- 1 mM- 1), a feature related to the different alcohol metabolites secreted by the Pleurotus and Bjerkandera species including chloroaromatics, and higher activity on aromatic aldehydes. What is even more intriguing is the fact that, the new oxidase is optimally active at pH 6.0 on both p-anisyl and vanillyl alcohols, suggesting a mechanism for phenolic benzyl alcohol oxidation that is different from that described in VAO, which proceeds via the substrate phenolate anion formed at basic pH. Based on the above properties, and its ADP-binding motif, partially detected after N-terminus sequencing, the new enzyme is classified as a member of the GMC (glucose-methanol-choline oxidase) oxidoreductase family oxidizing both AAO and VAO substrates.