Abstract:

Plant secondary metabolites are an important source of drug discovery and development, but their low accumulation in plants and the long growth duration of the plants make their production costly. In recent years, an alternative route, microbial synthesis, has been developed for producing plant-derived secondary metabolites, which is cost-effective and sustainable compared to routes through plant cultivation and chemical synthesis. Benzylisoquinoline alkaloids (BIAs), representatives of plant-derived alkaloids, are a family of ～2500 alkaloids, which have become attractive for microbial synthesis owing to their pharmaceutical functions and potentials in this regard. Recent advances in the elucidation of biosynthetic pathways of BIAs, together with the discovery of a variety of enzymatic tools, have facilitated the assembly of the synthetic pathways of BIAs in microbial hostssuch as Escherichia coli and Saccharomyces cerevisiae. However, most production of BIAs remains at a laboratory scale, due to the long metabolic pathway and the broad substrate spectrum of those enzymes for their microbial synthesis with various side-products generated. To date, only the production of (S)-reticuline, a major precursor of BIAs, is closed to scalable production with a titer of 4.6 g/L, which was reported by Martin’s team in 2020. This review comments the development and current status in the microbial production of BIAs and highlights critical aspects on overcoming the bottlenecks. The broad substrate spectrum of key enzymes including methyltransferases, norcoclaurine synthase and codeinone reductase for the microbial synthesis of BIAs has been demonstrated in vitro, and thus this review also summarizes the possible effect of the catalytic properties of these enzymes on the metabolic flux, indicating importance of the selection and improvement of enzyme catalytic elements. At the end, the challenges for the microbial synthesis of BIAs are highlighted, and the importance of enzyme engineering and the design of new artificial microbial synthesis pathway to address these challenges are expected for more efficient production of BIAs through microbial synthesis.

Key words: benzylisoquinoline alkaloids, microbial production, plant biosynthetic pathway, catalytic properties of enzymes, control of metabolic flux, metabolic engineering

摘要：

微生物发酵是一种经济高效、可持续的生产方式，可替代植物种植和化学合成来生产多种植物来源的药物。苄基异喹啉类生物碱作为植物来源生物碱的典型代表，具有多种重要的生理活性，已成为极具吸引力的微生物合成研究的靶标分子。随着该类生物碱天然生物合成途径逐渐被阐明以及多种酶学元件的发现，使得通过大肠杆菌和酿酒酵母等微生物宿主合成苄基异喹啉类生物碱的研究取得了重大进展。本综述着重介绍了这些进展中的突破性成果，包括苄基异喹啉类生物碱微生物合成过程中瓶颈反应的突破以及合成途径中相关酶的催化特性对代谢流的影响等，指出了微生物生产苄基异喹啉类生物碱走向工业化应用所面临的挑战，以及酶工程和新人工微生物合成途径的设计开发对克服这些挑战的重要性。

关键词: 苄基异喹啉类生物碱, 微生物合成, 植物生物合成途径, 酶学催化特性, 代谢流控制, 代谢工程