ArylAlcohol Oxidase, a Rare Auxiliary Enzyme: It’s Role in Lignin Degradation and Its Potential Applications

The 2nd most abundant biopolymer after cellulose is lignin, which has a very complex structure and its biological degradation required an enzymatic consortium of different lignin degrading enzymes like Lignin peroxidase (EC 1.11.1.14), Manganese peroxidase (EC 1.11.1.13), Versatile peroxidase (EC 1.11.1.16), Laccase (EC 1.10.3.2) etc. This enzyme required hydrogen peroxide for its action which is supplied by auxillary enzyme like aryl alcohol oxidase. Aryl alcohol oxidase belongs to glucose methanol choline (GMC) superfamily and has FAD as the cofactor. The structural aspects of the enzyme are compared using PeAAO and MtAAOas model. The mechanistic and substrate chemistry of aryl alcohol oxidase as alcohol or aldehyde oxidase is discussed in detail. The enhance activity as alcohol oxidase of ‘aryl alcohol oxidase’ using electron donating substrate, which is opposite when its aldehyde oxidase activity is considered. The application of the enzyme as an efficient dye degrading enzyme for wastewater treatment biologically, or in paper-pulp bio-bleaching, or drug design make it a hot topic of research for various industrial purpose and commercialization. Other mentionable application of the enzyme, is in the production of flavours and fragrances like vanillin, benzaldehyde, trans-2-hexanal, trans-2-cis-6-nonadienal, piperonal, perillaldehydeetc. The role of the enzyme in the synthesis of bio-based precursors like HMF, FFCA or FDCA is also discussed. HIGHLIGHTS Aryl alcohol oxidase (E C 1.1.3.7) plays a significant role in lignin degradation by supplying hydrogen peroxide to lignin degrading enzymes. It acts upon both alcoholic and aldehydic substrates and convert them to corresponding aldehyde or acids. It is secreted by white-rot and brown-rot fungi, mostly and it is a member of GMC oxidoreductase superfamily. In the enzymatic consortium for lignin degradation biologically, aryl alcohol oxidase plays the role as a versatile auxiliary enzyme. The enzyme seems, to have very wide scale industrial applications in flavors or fragrance industry or drug design or synthesis of bio-based precursor like HMF, FDCA, and FFCA etc. GRAPHICAL ABSTRACT