Vanillyl-alcohol oxidase, a tasteful biocatalyst

The covalent flavoenzyme vanillyl-alcohol oxidase (VAO) is a versatile biocatalyst. It converts a wide range of phenolic compounds by catalysing oxidation, deamination, demethylation, dehydrogenation and hydroxylation reactions. The production of natural vanillin, 4-hydroxybenzaldehyde, coniferyl alcohol and enantiomeric pure phenol derivatives is of interest for biotechnological applications. The hydroxylation of 4-alkylphenols is highly stereospecific for the (R)-isomer, whereas dehydrogenation of these substrates is specific for the cis- or trans-isomer. On the basis of crystallographic data, we suggest that the stereospecificity is related to the active site residue Asp170. Another important feature of VAO is the covalent flavin attachment. Studies from site-directed mutants suggest that the covalent flavin–protein interaction improves the catalytic performance as well as the long-term stability of VAO.