宽泛底物谱色氨酸脱羧酶体外合成卤代色胺衍生物和血清素

【背景】色氨酸脱羧酶在自然界有高度特异性，行使催化色氨酸为色胺的功能。一个色氨酸脱羧酶BaTDC参与南海海绵共生菌Bacillus atrophaeus C89次级代谢产物bacillamides的生物合成过程。【目的】探究BaTDC酶学特征和底物谱，建立体外合成色胺衍生物的方法。【方法】通过构建系统发育树揭示BaTDC在进化中的地位。在温度梯度和pH梯度下进行酶反应，利用不同的色氨酸衍生物为底物，通过HPLC和UPLC-MS检测酶反应过程，表征BaTDC活性。【结果】系统发育分析显示BaTDC与肠道菌Ruminococcus gnavus亲缘关系相近。纯化重组BaTDC的最适温度为40?45 °C，最适pH值为8.0。BaTDC可以催化羟代色氨酸和卤代色氨酸包括4-氟色氨酸和5,6,7-氯色氨酸及4-溴色氨酸，得到相应的卤代色胺衍生物和血清素。【结论】本研究分析了BaTDC的特性，发现BaTDC表现出宽泛的底物耐受性，可为前体喂养或定向生物合成新型药用色胺衍生物和下游复杂天然产物奠定基础。

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

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.