High-level expression of aryl-alcohol oxidase 2 from Pleurotus eryngii in Pichia pastoris for production of fragrances and bioactive precursors

The fungal secretome comprises various oxidative enzymes participating in the degradation of lignocellulosic biomass as a central step in carbon recycling. Among the secreted enzymes, aryl-alcohol oxidases (AAOs) are of interest for biotechnological applications including production of bio-based precursors for plastics, bioactive compounds, and flavors and fragrances. Aryl-alcohol oxidase 2 (PeAAO2) from the fungusPleurotus eryngiiwas heterologously expressed and secreted at one of the highest yields reported so far of 315 mg/l using the methylotrophic yeastPichia pastoris(recently reclassified asKomagataella phaffii). The glycosylated PeAAO2 exhibited a high stability in a broad pH range between pH 3.0 and 9.0 and high thermal stability up to 55 degrees C. Substrate screening with 41 compounds revealed that PeAAO2 oxidized typical AAO substrates likep-anisyl alcohol, veratryl alcohol, andtrans,trans-2,4-hexadienol with up to 8-fold higher activity than benzyl alcohol. Several compounds not yet reported as substrates for AAOs were oxidized by PeAAO2 as well. Among them, cumic alcohol and piperonyl alcohol were oxidized to cuminaldehyde and piperonal with high catalytic efficiencies of 84.1 and 600.2 mM(-1) s(-1), respectively. While the fragrance and flavor compound piperonal also serves as starting material for agrochemical and pharmaceutical building blocks, various positive health effects have been attributed to cuminaldehyde including anticancer, antidiabetic, and neuroprotective effects. PeAAO2 is thus a promising biocatalyst for biotechnological applications.