vibralactone and 4-hydroxybenzoic-acid

Oxepinone rings represent one of structurally unusual motifs of natural products and the biosynthesis of oxepinones is not fully understood. 1,5-Seco-vibralactone (3) features an oxepinone motif and is a stable metabolite isolated from mycelial cultures of the mushroom Boreostereum vibrans. Cyclization of 3 forms vibralactone (1) whose β-lactone-fused bicyclic core originates from 4-hydroxybenzoate, yet it remains elusive how 4-hydroxybenzoate is converted to 3 especially for the oxepinone ring construction in the biosynthesis of 1. In this work, using activity-guided fractionation together with proteomic analyses, we identify an NADPH/FAD-dependent monooxygenase VibO as the key enzyme performing a crucial ring-expansive oxygenation on the phenol ring to generate the oxepin-2-one structure of 3. The crystal structure of VibO reveals that it forms a dimeric phenol hydroxylase-like architecture featured with a unique substrate-binding pocket adjacent to the bound FAD. Computational modeling and solution studies provide insight into the likely VibO active site geometry, and suggest possible involvement of a flavin-C4a-OO(H) intermediate.

Topics: Flavin-Adenine Dinucleotide; Flavins; Lactones; Mixed Function Oxygenases; Proteomics

The oxidative decarboxylation of prenyl 4-hydroxybenzoate to prenylhydroquinone has been frequently proposed for the biosynthesis of prenylated (hydro)quinone derivates (sometimes meroterpenoids), yet no corresponding genes or enzymes have so far been reported. A FAD-binding monooxygenase (VibMO1) was identified that converts prenyl 4-hydroxybenzoate into prenylhydroquinone and is likely involved in the biosynthesis of vibralactones and other meroterpenoids in the basidiomycete Boreostereum vibrans. Feeding of 3-allyl-4-hydroxybenzylalcohol, an analogue of the vibralactone pathway intermediate 3-prenyl-4-hydroxybenzylalcohol, generated 20 analogues with different scaffolds. This demonstrated divergent pathways to skeletally distinct compounds initiating from a single precursor, thus providing the first insight into a novel biosynthetic pathway for 3-substituted γ-butyrolactones from a shikimate origin.

Topics: Basidiomycota; Biosynthetic Pathways; Decarboxylation; Hydroquinones; Lactones; Mixed Function Oxygenases; Parabens