Fig. 5

Cofactor engineering and protein engineering for high-level production of melatonin. a Metabolic engineering for cofactor SAM of COMT. The red arrow indicates the enhanced expression of the gene, and the blue cross indicates the knockout of the gene. b Alignment of the OsCOMT and AtCOMT protein sequences. c Conversion of tryptophan to NAS and melatonin by recombinant E. coli strains. d HPLC analysis of the standard and bioconversion products of the representative EcMEL8 strain. e LC–ESI–MS analysis of symbols from panel d: exact mass of compound 1[M + H]⁺[m/z](219.1), compound 2[M + H]⁺[m/z](233.0). Data are the means ± standard deviations of triplicate experiments