Divergent Biosynthesis of Bridged Polycyclic Sesquiterpenoids by a Minimal Fungal Biosynthetic Gene Cluster

The bridged polycyclic sesquiterpenoids derived from
sativene,
isosativene, and longifolene have unique structures, and many chemical
synthesis approaches with at least 10 steps have been reported. However,
their biosynthetic pathway remains undescribed. A minimal biosynthetic
gene cluster (BGC), named bip, encoding a sesquiterpene
cyclase (BipA) and a cytochrome P450 (BipB) is characterized to produce
such complex sesquiterpenoids with multiple carbon skeletons based
on enzymatic assays, heterologous expression, and precursor experiments.
BipA is demonstrated as a versatile cyclase with (−)-sativene
as the dominant product and (−)-isosativene and (−)-longifolene
as minor ones. BipB is capable of hydroxylating different enantiomeric
sesquiterpenes, such as (−)-longifolene and (+)-longifolene,
at C-15 and C-14 in turn. The C-15- or both C-15- and C-14-hydroxylated
products are then further oxidized by unclustered oxidases, resulting
in a structurally diverse array of sesquiterpenoids. Bioinformatic
analysis reveals the BipB homologues as a discrete clade of fungal
sesquiterpene P450s. These findings elucidate the concise and divergent
biosynthesis of such intricate bridged polycyclic sesquiterpenoids,
offer valuable biocatalysts for biotransformation, and highlight the
distinct biosynthetic strategy employed by nature compared to chemical
synthesis.