Mapping uncharted enzymatic territory: discovery of terpenoid biosynthetic pathways in mushrooms

Mushrooms are a rich source of sesquiterpenoid compounds with known antifungal, antibacterial, and cytotoxic activities. The complex structures of these sesquiterpenoids, the largest group of natural products, often prevents their economical production using traditional organic syntheses. Moreover, there have been extremely few studies into the biosynthesis of these important compounds, many of which are produced only in mushroom forming fungi (Basidiomycota). The recent explosion of genome sequencing has revealed the Basidiomycota to be particularly enriched in terpenoid synthase enzymes. However, the overwhelming number of putative sesquiterpene synthases requires a means to predict the products of sesquiterpene synthases based on primary sequence alone. Here I describe the application and refinement of such a predictive framework, valid to all Basidiomycota, to selectively identify and clone several new sesquiterpene synthases based on their initial cyclization mechanism. In addition, the clustering of biosynthetic genes in fungi has allowed rapid identification and cloning of related enzymes in terpenoid maturation, enabling selective production of new, pharmaceutically relevant fungal sesquiterpenoids in model organisms.