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In situ H2O2 generation systems are efficient for H2O2-dependent biocatalytic oxidation reactions. Here, we report that lytic polysaccharide monooxygenases (LPMOs), copper-dependent polysaccharide monooxygenases, can efficiently supply H2O2 in situ to dye-decolorizing peroxidases (DyPs) using substrate gallic acid (GA) for chitosan functionalization. The maximum grafting ratio induced by the cascade reaction was significantly higher than that achieved by a reaction with initial exogenous H2O2. The maximum grafting ratio was obtained with 12 g/L GA, 5.6 mg/L DyP, 20–30 mg/L LPMO, and pH 4.5–5.0. UV–vis, Fourier transform infrared (FT-IR), and nuclear magnetic resonance (1H NMR) spectroscopy confirmed GA grafting onto chitosan. X-ray diffraction (XRD) analysis and thermogravimetric analysis (TGA) indicated that GA–chitosan conjugates had lower thermal stability and crystallinity than chitosan. The GA–chitosan conjugates had significantly higher antioxidant activity than chitosan. This study supplies a green and high-efficiency approach to achieve an enzymatic cascade reaction for chitosan functionalization and has potential applications in H2O2-dependent biocatalytic oxidation reactions.

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