1.21.3.3 medicine a Saccharomyces cerevisiae strain is engineered to express seven heterologous enzymes (Papaper somniferum norcoclaurine 6-O-methyltransferase (Ps6OMT), Papaver somniferum 3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase 2 (Ps4'OMT), Papapver somniferum coclaurine N-methyltransferase (PsCNMT), Papaver somniferum berberine bridge enzyme (PsBBE), Thalictrum flavum scoulerine 9-O-methyltransferase (TfS9OMT), Thalictrum flavum canadine synthase (TfCAS), and Arabidopsis thaliana cytochrome P450 reductase 1 (CPR)), resulting in protoberberine alkaloid production from a simple benzylisoquinoline alkaloid precursor. A number of strategies are implemented to improve flux through the pathway, including enzyme variant screening, genetic copy number variation, and culture optimization. This leads to an over 70-fold increase in canadine titer up to 1.8 mg/l. Increased canadine titers enable extension of the pathway to produce berberine, a major constituent of several traditional medicines in a microbial host. This strain is viable at pilot scale 743234 1.21.3.3 synthesis heterologous production of berberine and the optimization of the engineered biosynthetic pathway from rac-norlaudanosoline to (S)-canadine in yeast involving the recombinant berberine reductase 743234 1.21.3.3 synthesis substrate tuning by introducing a fluoro moiety at one potential reactive carbon center switches the reaction to the formation of exclusively one regioisomer with perfect enantioselectivity. The formation of 11-hydroxy-functionalized tetrahydroprotoberberines instead of the commonly formed 9-hydroxy-functionalized products from 1,2,3,4-tetrahydroisoquinolines can be successfully promoted 727325