Product profile of PEN3: the last unexamined oxidosqualene cyclase in Arabidopsis thaliana.

The triterpene product profile is reported for At5g36150 (PEN3), the last unexamined oxidosqualene cyclase in the reference plant Arabidopsis thaliana. PEN3 makes tirucalla-7,24-dien-3beta-ol ( approximately 85%) and several minor products. Also discussed are the unexpectedly facile convergent evolution of another Arabidopsis tirucalladienol synthase (LUP5), mechanistic origins of the 20S configuration, and active-site remodeling necessary to accommodate the 17alpha side chain. This work marks the first completed functional characterization of all triterpene synthases in a higher plant.