Engineering of melanin biopolymer by co-expression of MelC tyrosinase with CYP102G4 monooxygenase: structural composition understanding by 15 Tesla FT-ICR MS analysis

Abstract In this study, novel melanin pigments were synthesized by Escherichia coli cells co-expressing tyrosinase (MelC) and cytochrome P450 monooxygenase (CYP102G4) enzymes simultaneously. The CYP102G4 catalyzes indole C3-specific hydroxylation and generates 3-hydroxyindole (indoxyl) and 3-oxoindole. Additional supply of indole derivatives leads to much darker melanin pigmentation with higher yields (3.4 g/L) of synthesized CYP-Melanin, which showed interesting morphological and electrochemical properties. To understand the correlation between its chemical structure and functions, FT-IR, NMR, and SEM analysis were attempted. Following 15 T FT-ICR mass spectrometry analysis provided information on the chemical and molecular compositions, characteristics of the synthetic melanins, evidence of higher nitrogen content, and higher degree of unsaturation in the CYP-Melanin structure. Besides, electrical conductivity of CYP-Melanin was determined by cyclic voltammetry (CV) analysis to investigate the feasibility for the application of CYP-Melanin as electric materials.