UBC Theses and Dissertations
Engineering flavanone biosynthesis in yeast towards the production of montbretin A Liu, Le
Plants produce a diverse range of specialized metabolites, which are an important source for new pharmaceuticals. The plant metabolite montbretin A (MbA) is a novel therapeutic for type 2 diabetes. MbA is a complex acylated flavonol glycoside found in the underground storage organs, called corms, of the ornamental plant montbretia (Crocosmia x crocosmiiflora). Large quantities of MbA are needed to treat the millions of people who would benefit from it. However, MbA cannot be extracted from montbretia corms in sufficient quantities for therapeutic use, and chemical synthesis of MbA is not viable due to the compound’s chemical complexity. Engineering a plant or microbial system for large-scale, sustainable MbA production would be a viable option. The recent elucidation of the complete MbA biosynthetic pathway provides the tools to engineer yeast (Saccharomyces cerevisiae) for heterologous MbA production. The core of MbA is the flavonol myricetin, the biosynthesis of which needs to be bioengineered in yeast. In most plants, biosynthesis of myricetin uses coumaric acid as a substrate and produces naringenin as a flavanone intermediate. However, utilizing metabolic engineering of myricetin from coumaric acid via naringenin poses a problem for the downstream bioengineering of MbA in yeast. The presence of coumaric acid would lead to formation of MbB instead of MbA, where MbB contains a coumaroyl side chain instead of the caffeoyl side chain in MbA. MbB is an undesired by-product with no known therapeutic value. To address this problem, I developed a yeast strain that uses caffeic acid (instead of coumaric acid) in the formation of myricetin via eriodictyol (instead of naringenin). I achieved the formation of eriodictyol as a precursor to myricetin at 27.3 mg * L⁻¹. Optimizing flavonoid enzyme combinations, tuning gene expression, and the addition of the chalcone isomerase-like (CHIL) protein improved eriodictyol production up to 8-fold. Overall, this work demonstrates the potential of engineering a yeast strain to produce the flavanone eriodictyol, an essential step towards scalable and sustainable production of the anti-diabetic plant metabolite MbA.
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