In vitro biosynthesis of serotonin and halogenated tryptamine through the heterologous expression of tryptophan decarboxylase

Abstract:

[Background] Tryptophan decarboxylases that catalyze tryptophan to tryptamine, have specificity to catalyze target substrate in the nature. A decarboxylase from marine Bacillus atrophaeus C89, involved in the biosynthesis of bacillamide C, is referred to as BaTDC. [Objective] We are aiming to characterize BaTDC and explore the substrate spectrum of BaTDC including halogenated tryptophans and hydroxytryptophan in order to provide new methods to produce novel and pharmaceutically vital tryptamine analogues. [Methods] A phylogenetic tree was constructed using protein sequences of several TDCs to understand the status of BaTDC in evolution. Its activity was assayed with various tryptophan derivatives and the products were detected by HPLC and UPLC-MS. [Results] Phylogenetic analysis revealed the similarity of BaTDC with that of the gut bacterium Ruminococcus gnavus. The optimum temperature and pH of the purified recombinant BaTDC enzyme was 40?45 °C and 8.0, respectively. BaTDC exhibited substrate promiscuity and catalytic efficiency with hydroxytryptophan and halogenated tryptophans including 4-fluorotryptophan, 5,6,7-chlorotryptophan and 4-bromotryptophan. [Conclusion] The study presents a comprehensive characterization of the BaTDC as a promising member of its enzyme family. BaTDC exhibits broad substrate tolerance to tryptophan derivatives, suggesting the potential of substrate-feeding approach in producing novel tryptamine analogs or complex secondary metabolite analogs through precursor-directed biosynthesis.