以Neocarazostatin为模型的细菌三环咔唑生物碱生物合成研究

For several decades, alkaloids have been one of the hottest topics in the research field of natural products due to their excellent pharmaceutical applications as well as their rich structural diversities. Neocarazostatin, the target compound in this project, belongs to the tricyclic carbazole alkaloids. It exhibits a strong inhibitory effect on the brain lipid peroxidation that is normally induced by free radicals, and it also possesses a great potential to be developed into a novel antioxidant prodrug. The chemical structures of the tricyclic carbazole alkaloids have been characterized by containing only one carbazole unit with no additional annulated rings or ring systems, which distinguishes them from other carbazole containing alkaloids. The feeding experiments showed that the precursors and building blocks for the biosynthesis of bacterial tricyclic carbazole alkaloids are significantly different from that of the other carbazole alkaloids. This finding implies that a novel enzymatic mechanism may be involved in the biosynthesis of this family of compounds in bacteria. To date, the detailed biosynthetic mechanism for tricyclic carbazole alkaloids still remains elusive. In this context, based on the identification of the biosynthetic gene cluster of Neocarazostatin A, we will set out to elucidate the novel enzymatic reactions underlying the biosynthesis of this compound, to establish a general biosynthesis model for the bacterial tricyclic carbazole alkaloids, and to generate structural analogs of Neocarazostatin via chemical biology methods. This study will also be extended to discover more novel bacterial carbazole alkaloids through genome mining.

生物碱以其良好的药用活性及丰富的化学结构一直是天然产物领域的研究热点。本项目的研究对象Neocarazostatin属于三环咔唑生物碱，对由自由基引起的脑组织过氧化症状有强烈抑制作用，具备自由基清除药物的开发潜力。化学结构上，三环咔唑生物碱显著区别于其它生物碱，其分子内只含有一个咔唑环，而不含其它稠环或单环。同位素标记实验显示，以Neocarazostatin为代表的细菌来源三环咔唑生物碱的合成前体和构造单元与其它含有咔唑结构单元的生物碱明显不同，暗示该类化合物的生物合成中可能蕴含着新型酶催化机制。时至今日，细菌三环咔唑生物碱的生物合成机理还未有报道，本项目拟在前期成功克隆Neocarazostatin A的生物合成基因簇基础上，综合运用化学生物学手段，揭示该分子生物合成途径、建立细菌三环咔唑生物碱的通用生物合成模型、尝试人工制造其结构类似物、并利用基因组挖掘技术探寻更多潜在的家族成员。

生物碱以其良好的药用活性及丰富的化学结构一直是天然产物领域的研究热点。本项目的研究对象Neocarazostatin属于三环咔唑生物碱，对由自由基引起的脑组织过氧化症状具有强烈抑制作用，极具自由基清除药物的开发潜力。化学结构上，三环咔唑生物碱显著区别于其它生物碱，其分子内只含有一个咔唑环，而不含其它稠环或单环。本项目深入开展了三环咔唑生物碱Neocarazostatin A的生物合成基因簇的克隆以及基因簇中每一个生物合成基因的功能解析，全面揭示了Neocarazostatin A中三环咔唑结构单元的组装机理，并通过同位素标记实验阐明了咔唑A环上的氧原子来源，从而表征了一组新型三环咔唑合成酶；本项目还通过基因组挖掘手段从已测序细菌中寻找到更多的三环咔唑生物碱编码基因簇，正在尝试用异源表达的方法挖掘更多新型三环咔唑生物碱。