Side Products of Recombinant Amorpha-4,11-diene Synthase and Their Effect on Microbial Artemisinin Production

Amorpha-4,11-diene synthase (ADS) is the first committed enzyme in the biosynthesis of artemisinin. Artemisinin production by biobased fermentation is considered a reliable alternative pathway. Heterologously expressed ADS has been established to generate several minor products, including structural analogues of amorpha-4,11-diene, but their fate in fermentation is still unknown. Here, using chiral analysis, we found that ADS produces one of the analogues, amorpha-4-en-11-ol, as a pair of epimers. Labeling experiments revealed that ADS mutants yielded amorphene-type sesquiterpenes, indicating the co-occurrence of initial 1,6 and 1,10 cyclization of farnesyl diphosphate in a single enzyme. Interestingly, the immediate downstream oxidase CYP71AV1 had very low affinity to the side products of the recombinant ADS, including amorpha-4-en-7-ol, which is structurally similar to amorpha-4,11-diene. Our data uncover the complex catalytic mechanism of recombinant ADS and reveal a potential negative effect of the side products of recombinant ADS on the production of the artemisinin precursor in microbes.