A squalene synthase-like enzyme initiates production of tetraterpenoid hydrocarbons in Botryococcus braunii Race L

The green microalga Botryococcus braunii is considered a promising biofuel feedstock producer due to its prodigious accumulation of hydrocarbon oils that can be converted into fuels. B. braunii Race L produces the C 40 tetraterpenoid hydrocarbon lycopadiene via an uncharacterized biosynthetic pathway. Structural similarities suggest this pathway follows a biosynthetic mechanism analogous to that of C 30 squalene. Confirming this hypothesis, the current study identifies C 20 geranylgeranyl diphosphate (GGPP) as a precursor for lycopaoctaene biosynthesis, the first committed intermediate in the production of lycopadiene. Two squalene synthase ( SS )-like complementary DNAs are identified in race L with one encoding a true SS and the other encoding an enzyme with lycopaoctaene synthase (LOS) activity. Interestingly, LOS uses alternative C 15 and C 20 prenyl diphosphate substrates to produce combinatorial hybrid hydrocarbons, but almost exclusively uses GGPP in vivo . This discovery highlights how SS enzyme diversification results in the production of specialized tetraterpenoid oils in race L of B. braunii . The green microalga Botryococcus braunii is a promising biofuel producer due to its ability to produce large amounts of hydrocarbon oils that can be converted into fuels. Here the authors implicate lycopaoctaene synthase, a squalene synthases-like enzyme, in the first step towards the biosynthesis of the C40 tetraterpenoid hydrocarbon lycopadiene.