Aryl-alcohol oxidases: catalysis, diversity, structure-function and emerging biotechnological applications

Aryl-alcohol oxidases (AAOs) are flavin-dependent enzymes of the glucose-methanol-choline (GMC) oxidoreductase superfamily that catalyze the oxidation of a broad range of activated primary alcohols into their corresponding aldehydes, generating hydrogen peroxide. While traditionally studied in wood-decaying fungi, AAOs have recently been identified in bacteria and arthropods, revealing unexpected structural and functional diversity. These enzymes display broad substrate promiscuity, with preferences shaped by differences in active-site architecture and physicochemical properties. Structural studies across kingdoms show a conserved GMC fold with specific adaptations in substrate-binding domains. Detailed mechanistic insights-particularly from the AAO from Pleurotus eryngii-suggest a consensus hydride transfer mechanism involving conserved histidine residues, enabling both oxidase and dehydrogenase activity. To explore AAO diversity, BLAST-based mining was performed across fungal, bacterial, and arthropod genomes, leading to the identification and classification of hundreds of putative AAO sequences. These have been further grouped into distinct structural and evolutionary types based on conserved motifs and active-site architecture, revealing convergent strategies and potential functional specialization across kingdoms. Beyond their natural role in biomass degradation, AAOs hold significant biotechnological potential in green chemistry, including the synthesis of valuable aldehydes, bioplastics precursors like 2,5-furandicarboxylic acid, and applications in asymmetric synthesis. Recent advances demonstrate the feasibility of integrating AAOs into industrial biocatalytic processes and artificial cascades. This growing understanding of AAO diversity, structure-function relationships, and biotechnological applications paves the way for the development of novel sustainable biocatalysts in chemical, pharmaceutical, and material industries. KEY POINTS: Aryl-alcohol oxidases (AAOs) occur across fungi, bacteria, and arthropods, with distinct structural and functional features. Sequence similarity searches reveal diverse AAO types with distinct structural and evolutionary traits. AAOs enable green synthesis of high-value-added bio-based chemicals.