Biosynthesis and Heterologous Expression of Medicinally Active Natural Products
- Author(s): Liu, Joyce
- Advisor(s): Zhang, Wenjun
- et al.
Natural products have long been appreciated for their potent biological activities, and their unique scaffolds and pharmacophores have served as inspiration for many pharmaceuticals. As the structural complexity of these compounds can make their production and diversification challenging for chemical synthesis, the study and engineering of natural product biosynthetic pathways can facilitate more efficient and sustainable production of natural products and their analogues. Here, we present our findings from the biosynthetic studies of several medicinally active natural products produced by Streptomyces, which reveal some unusual pathways and enzymes. In doing this work, we also demonstrate how heterologous expression can be used to expediently determine the necessity and function of individual biosynthetic enzymes, gain insight into biosynthetic mechanisms, and produce new natural product analogues.
The compounds of focus here include the cholinesterase inhibitor physostigmine, the peptidyl epoxyketone proteasome inhibitor eponemycin, and the family of antimycin-type depsipeptides. The in vivo and in vitro characterization of physostigmine biosynthesis revealed an unexpected pathway involving an acetylation-deacetylation-dependent reaction cascade and a unique indole methyltransferase. Heterologous expression-based investigations on the biosynthesis of eponemycin then revealed an unprecedented flavin-dependent enzyme to be necessary and sufficient for the formation of the terminal epoxyketone pharmacophore in addition to indicating the involvement of a decarboxylation step. Further efforts to study the biosynthesis of antimycins likewise resulted in the in vivo reconstitution of the 3-formamidosalicylate pharmacophore, and studies on the related neoantimycins led to advances in the biosynthetic understanding and heterologous expression of this ring-expanded class of antimycin-type depsipeptides. Collectively, these biosynthetic insights not only enrich our enzymatic knowledge but can also expand our ability to perform combinatorial biosynthesis.