Archaeal tyrosinase as a versatile biocatalyst for lignin-derived aromatic compounds valorization

Biomass-derived aromatic compounds, including those obtained from lignin (which is the most abundant aromatic biopolymer on Earth), are valuable for sustainable chemical production. Various lignin-degrading approaches have been developed to cleave recalcitrant bonds. The incorporation of biocatalysts that operate under environmentally friendly and mild conditions with high substrate specificity is considered one of the emerging strategies for lignin valorization. In this study, an archaeal tyrosinase (Tyr-CNK), derived from the marine archaeon Candidatus nitrosopumilus koreensis, is characterized as a versatile biocatalyst for lignin biodegradation and valorization, based on kinetic studies, protein structure determination, and analysis. Notably, the extremely shallow active site pocket and the unique noncanonical caddy domain, which facilitate efficient copper incorporation without obstructing the active site, collectively empower Tyr-CNK with remarkable catalytic efficiency toward various lignin model compounds, such as p-coumaric acid, 4-phenoxyphenol, 4-(benzyloxy)phenol, and guaiacyl glycerol-β-guaiacyl ether. Together with molecular docking simulations, these catalytic and structural features indicate that Tyr-CNK serves as an efficient biocatalyst for the hydroxylation and oxidative degradation of lignin-derived phenolic compounds. Given its versatility, efficiency, and structural uniqueness, Tyr-CNK demonstrates great promise for expanding the catalytic repertoire for biomass conversions and offering new opportunities in sustainable biocatalysis, enzymatic and microbial biodegradation and biomass valorization.