Insights into a photo-driven laccase coupling system for enhanced photocatalytic oxidation and biodegradation

Effective depolymerization of lignin into environmentally friendly aromatic chemicals under mild conditions is gaining interest. Fungal laccase is capable of catalyzing a wide range of reactions, but its low redox potential and preference for acidic pH limit its potential applications. Herein, we developed a laccase-methylene blue (LACMB) coupling system, combining the selectivity of enzyme catalysis with the high reactivity of photocatalysis, for the efficient degradation of lignin model compounds. Theoretical calculations indicate that the electron donor's distance to the LAC's active site T1 Cu is shortened from 29.7 to 7.3 & Aring; in the LAC-MB. In this system, MB, possessing strong interaction with T1 Cu, acts as a light absorber, enabling the rapid transfer of photogenerated electrons to T1 Cu. This significantly enhances the degradation rate of guaiacol (GUA) from 28.8 % to 91.46 %. The LAC-MB can oxidize both phenolic and non-phenolic lignin model compounds under red-LED irradiation with wide pH ranging from 3.0 to 7.0 and high-efficiency. By tuning the primary coordination sphere and the access tunnel of T1 Cu, we further revealed that enhanced binding affinity and active site accessibility for the LAC-MB complex attributed to the photocatalysis's high reactivity. Based on this, LAC variants with enhanced binding capabilities were constructed and the resulting mutant LAC-MB are characterized by higher oxygen consumption and ROS generation activated by red-LED, specifically a higher quantum yield of 1O2, demonstrating increased electron transfer and light-driven reactivity. This photo-enzyme coupling system presents a new pathway for the high-efficiency processing of lignocellulosic biomass and offers insights for designing future artificial photosynthetic systems.