Non-Canonical C₁₆ Homoterpene Biosynthesis Widespread in Actinobacteria

A novel biosynthetic pathway towards the rare and underexplored non-canonical family of homoterpenes was discovered in actinobacteria through targeted genome mining and enzymatic in vitro reconstitution. The pathway comprises initial methylation-induced double bond isomerization of farnesyl diphosphate (FPP) to (2E,7E)-6-methyl-farnesyl diphosphate, catalyzed by a novel family of methyltransferases with unique dual function. The resulting linear C₁₆ double bond isomer of FPP constitutes the specific substrate for a distinct family of type I terpene cyclases, catalyzing diverse cyclization reactions. Functional characterization of nine enzyme pairs led to discovery of five unprecedented homoterpene natural products. The enzymological novelty enables the development of novel biocatalytic and genetically programmable synthetic strategies towards methylated terpenoids with potentially unique properties ("magic methyl effect").