Aryl-alcohol oxidase protein sequence: a comparison with glucose oxidase and other FAD oxidoreductases

Aryl-alcohol oxidase (AAO), an FAD-dependent enzyme involved in lignin degradation, has been cloned from Pleurotus eryngii. The AAO protein is composed of 593 amino acids, 27 of which form a signal peptide. It shows 33% sequence identity with glucose oxidase from Aspergillus niger and lower homology with other oxidoreductases. The predicted secondary structures of both enzymes are very similar. For AAO, it is predicted to contain 13 putative alpha-helices and two major beta-sheets, each of the putative beta-sheets formed by six beta-strands. The ADP binding site and the signature-2 consensus sequence of the glucose-methanol-choline (GMC) oxidoreductases were also present. Moreover, residues potentially involved in catalysis and substrate binding were identified in the vicinity of the flavin ring. They include two histidines (H502 and H546) and several aromatic residues (Y78, Y92 and F501), as reported in other FAD oxidoreductases.