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Background l-Tryptophan (l-Trp) derivatives such as 5-hydroxytryptophan (5-HTP) and 5-hydroxytryptamine (5-HT), N-Acetyl-5-hydroxytryptamine and melatonin are important molecules with pharmaceutical interest. Among, 5-HT is an inhibitory neurotransmitter with proven benefits for treating the symptoms of depression. At present, 5-HT depends on plant extraction and chemical synthesis, which limits its mass production and causes environmental problems. Therefore, it is necessary to develop an efficient, green and sustainable biosynthesis method to produce 5-HT. Results Here we propose a one-pot production of 5-HT from l-Trp via two enzyme cascades for the first time. First, a chassis cell that can convert l-Trp into 5-HTP was constructed by heterologous expression of tryptophan hydroxylase from Schistosoma mansoni (SmTPH) and an artificial endogenous tetrahydrobiopterin (BH4) module. Then, dopa decarboxylase from Harminia axyridis (HaDDC), which can specifically catalyse 5-HTP to 5-HT, was used for 5-HT production. The cell factory, E. coli BL21(DE3)△tnaA/BH4/HaDDC-SmTPH, which contains SmTPH and HaDDC, was constructed for 5-HT synthesis. The highest concentration of 5-HT reached 414.5 ± 1.6 mg/L (with conversion rate of 25.9 mol%) at the optimal conditions (substrate concentration,2 g/L; induced temperature, 25℃; IPTG concentration, 0.5 mM; catalysis temperature, 30℃; catalysis time, 72 h). Conclusions This protocol provided an efficient one-pot method for converting. l-Trp into 5-HT production, which opens up possibilities for the practical biosynthesis of natural 5-HT at an industrial scale.

Additional file 1: Fig. S1. SDS-PAGE analysis of different induction temperatures on the protein expression of SmTPH. Fig. S2. SDS-PAGE of cell extracts of E.coli BL21(DE3)/pET28a-DDC. Fig. S3. Effects of different induction temperatures on the catalysis in 5-HTP of HaDDC. Fig. S4. Effects of different pH on the catalysis in 5-HTP of HaDDC. Fig. S5. Effects of different PLP concentration on the catalysis in 5-HTP of HaDDC. Fig. S6. Phylogenetic analysis of HaDDC with other DDCs. Fig. S7. Plasmids construction of SmTPH gene and HaDDC gene at different cloning sites in the pET-28a ( +). Table S1. The synthesized protein sequence applied in this study.