MelC tyrosinase-dependent enzymatic synthesis of functional melanins from phenolic monomers

Sustainable microbial bioproduction offers a promising route to synthesize high-value melanin biopolymers, yet its scalability is fundamentally limited by the high cost of the L-tyrosine precursor. Here, we aimed to overcome this economic barrier by a highly efficient, engineered microbial platform that utilizes recombinant Escherichia coli expressing MelC tyrosinase to convert diverse, cost-effective noncanonical phenolic monomers into customizable melanin-like biopolymers. Among 13 screened substrates, p-Cresol (PC) and 4-hydroxyphenylacetic acid were the most efficient precursors, yielding 2.40 g/L and 3.92 g/L, respectively. Structural analyses (Ultraviolet-visible spectroscopy, Fourier-transform infrared, Solid-state NMR, MALDI-TOF MS, scanning electron microscopy, Energy-dispersive X-ray spectroscopy, X-ray diffraction, EPR) revealed that these biopolymers possess a native eumelanin-like amorphous architecture while exhibiting partial Dimethyl sulfoxide solubility for improved processability. The synthesized eumelanin-like pigments exhibited high thermal stability (retaining > 37% mass at 800 °C) and strong antioxidant activity, with PC-melanin outperforming conventional eumelanin by twenty-fold. Most importantly, these novel substrates are effluents of industrial and agriculture waste. Thus, this strategy frames a new method for bioremediation. These customizable eumelanin-like pigments hold strong potential for demanding industrial applications, including high-temperature coatings and advanced electronics.