Prospecting ligninolytic enzymes toward lignin valorization

Abstract

The enzymatic breakdown of lignin generates a spectrum of aromatic monomers — including vanillin, guaiacol, syringaldehyde, vanillic acid, ferulic acid, and p-coumaric acid — that serve as platform chemicals for pharmaceuticals, fragrances, resins, and bio-based polymers. However, its complex and recalcitrant structure necessitates highly efficient enzymatic systems for depolymerization. This review systematically classifies ligninolytic enzymes into five functional categories: laccases, peroxidases (including manganese peroxidases, lignin peroxidases, and versatile peroxidases), cytochrome P450s, dye-decolorizing peroxidases (DyPs), and auxiliary enzymes, evaluating their distinct roles and synergies in lignin breakdown. Laccases emerge as particularly versatile biocatalysts due to their widespread occurrence, broad substrate specificity, and operational flexibility under diverse conditions. Peroxidases drive critical oxidative reactions, while DyPs represent a functionally robust peroxidase class with superior stability under extreme pH, temperature, and pressure. Complementary enzymes such as etherases and lignin-mimetic systems further expand the toolbox for lignin valorization. To overcome inherent limitations of native enzymes, protein engineering strategies were highlighted to enhance catalytic efficiency, stability, and substrate affinity. Additionally, enzyme immobilization on advanced matrices (e.g., metal-organic frameworks) is discussed as a breakthrough approach to improve reusability and reaction scalability. These integrated advancements pave the way for sustainable lignin valorization.