(469b) Production of Plant Alkaloids in Saccharomyces Cerevisiae

Natural products or compounds derived from natural products comprise most successful drug molecules. However, their discovery, synthesis, and scalable manufacture remain ad hoc, tedious, and biased. As a result, many proposed drug candidates cannot be seriously explored or tested, and the number of successful new drugs that further improve human health has stagnated. For example, the benzylisoquinoline alkaloids (BIAs) are a class of plant secondary metabolites that exhibit diverse pharmacological activities, including antiviral, antiprotozoan, and analgesic activities. However, these molecules cannot be economically produced by traditional chemical synthesis strategies; current commercial production relies on plant extraction isolation of select BIAs. As such, a microbial platform for the production of BIAs has the potential to reduce the cost and increase the scale of current production strategies, as well as expand the diversity of molecules accessible beyond those that accumulate in plants.

We are developing engineered strains of Saccharomyces cerevisiae for the production of diverse BIA molecules. In particular, I will discuss the development of yeast strains for efficient production of BIAs de novo from simple carbon and nitrogen sources. The ultimate precursor of all BIA molecules is the amino acid tyrosine and we have developed strains that can produce early BIA precursors from fed tyrosine. Under native regulation, allosteric feedback inhibition of a key enzyme in aromatic amino acid biosynthesis limits carbon flux towards tyrosine. The introduction of previously identified mutations to this enzyme alleviates this allosteric inhibition in our engineered yeast strains, thereby increasing carbon flux through aromatic amino acid biosynthesis and ultimately allowing us to engineer strains that do not require fed tyrosine for BIA production. Additional modifications to the regulation of native yeast enzymes, both in central metabolism and in aromatic amino acid biosynthesis, further improved BIA production in engineered strains, but only when made in combination with the key mutations conferring allosteric feedback resistance. These yeast strains optimized for early BIA production will provide a platform for the introduction of plant enzymes for the synthesis of more complex and diverse natural products.