Metabolic Engineering of Escherichia coli for De Novo Biosynthesis of the Platform Chemical Pelletierine

Pelletierine is a versatile plant alkaloid having a C5N-C3 structure from which numerous chemicals can be derived. One notable derivative is huperzine A (HupA) which may alleviate the symptoms of Alzheimer's disease. Currently, industrial production of pelletierine relies primarily on chemical synthesis and plant extraction. However, chemical synthesis leads to analogues that complicate product separation, and plant extraction is constrained by limited resources. Herein, we report that pelletierine can be produced by recombinant Escherichia coli in which the engineered pelletierine biosynthesis pathway comprises four modules involving seven key genes native to E. coli, three genes from other bacteria, and three genes from plants. To overproduce pelletierine, the intrinsic l-lysine biosynthesis pathway in E. coli was simplified, and a clustered regularly interspaced short palindromic repeats (CRISPR) interference (CRISPRi) system was engineered to minimize the byproducts. Moreover, the transporter MatC was overexpressed to enhance the intracellular concentration of 3-oxoglutaryl ketide, which is another precursor of pelletierine. Based on the aforementioned manipulations, the resulting recombinant E. coli harboring the pelletierine biosynthesis pathway and CRISPRi system produced 3.40 and 8.23 mg/L pelletierine in a shake-flask and a 5 L bioreactor, respectively. This is the first report of microbial production of pelletierine, which represents a sustainable route to produce the precursor of HupA and beyond.