Abstract:

Directed degradation of abundant renewable lignin into small aromatic compounds is crucial for lignin valorization but challenging. The degradation of lignin in natural environments typically involves multienzyme synergy. However, the proteinaceous characteristics of lignin-degrading enzymes restrict their accessibility to certain regions of intricate lignin, resulting in the multienzyme systems being unable to fully demonstrate their effectiveness. Herein, a de novo biomimetic enzyme-nanozyme hybrid system was constructed by combining λ-MnO₂ nanozyme with laccase CotA from Bacillus subtilis, aimed at facilitating lignin degradation under mild conditions. The lignin degradation rate of the CotA + λ-MnO₂ hybrid system was determined to be 25.15%, which was much higher than those of the lignin degradation systems with only laccase CotA (15.32%) or λ-MnO₂ nanozyme (14.90%). Notably, the proportion of aromatic chemicals in the products derived from the hybrid system reached as much as 48%, which was 41.2% and 118.2% higher than those of the CotA- and λ-MnO₂-catalyzed systems, respectively. Analysis of products mapping and lignin structure changes suggested that the higher proportion of aromatic compounds in the CotA + λ-MnO₂ hybrid system was more likely to benefit from the laccase-mediated methoxylation. Moreover, electron paramagnetic resonance analysis indicated that the intensity and kind of free radicals such as •OH and •O₂^- are closely linked to the degradation rate and reaction type. This work is the inaugural application of an enzyme-nanozyme hybrid system for lignin degradation, demonstrating the potential of the synergistic interaction between enzyme and nanozyme in the directed degradation of lignin.

Key words: Lignin, Biomimetic hybrid, Valorization, Nanozyme, Natural enzyme