Bifunctional Triterpene/Sesquarterpene Cyclase: Tetraprenyl-β-curcumene Cyclase Is Also Squalene Cyclase in Bacillus megaterium

This study demonstrates that a tetraprenyl-β-curcumene cyclase, which was originally identified as a sesquarterpene cyclase that converts a head-to-tail type of monocycle to a pentacycle, also cyclizes a tail-to-tail type of linear squalene into a bicyclic triterpenol, 8α-hydroxypolypoda-13,17,21-triene. The 8α-hydroxypolypoda-13,17,21-triene was found to be a natural triterpene from B. megaterium. It was also demonstrated that cyclizations of both tetraprenyl-β-curcumene and squalene occurred with a purified B. megaterium TC homologue in the same reaction mixture. These results suggest that the tetraprenyl-β-curcumene cyclase is bifunctional, cyclizing both tetraprenyl-β-curcumene and squalene in vivo. This is the first report describing a bifunctional terpene cyclase, which biosynthesizes two classes of cyclic terpenes with different numbers of carbons as natural products in the organism.