Engineering triterpene production in <i>Saccharomyces cerevisiae</i>–β‐amyrin synthase from <i>Artemisia annua</i>

Using a degenerate primer designed from triterpene synthase sequences, we have isolated a new gene from the medicinal plant Artemisia annua . The predicted protein is highly similar to β‐amyrin synthases (EC 5.4.99.–), sharing amino acid sequence identities of up to 86%. Expression of the gene, designated AaBAS , in Saccharomyces cerevisiae , followed by GC/MS analysis, confirmed the encoded enzyme as a β‐amyrin synthase. Through engineering the sterol pathway in S. cerevisiae , we explore strategies for increasing triterpene production, using AaBAS as a test case. By manipulation of two key enzymes in the pathway, 3‐hydroxy‐3‐methylglutaryl‐CoA reductase and lanosterol synthase, we have improved β‐amyrin production by 50%, achieving levels of 6 mg·L −1 culture. As we have observed a 12‐fold increase in squalene levels, it appears that this strain has the capacity for even higher β‐amyrin production. Options for further engineering efforts are explored.