Neofunctionalized carbonic anhydrases in the biosynthesis of neuroactive plant alkaloids

Plants synthesize numerous alkaloids that mimic animal neurotransmitters. The diversity of alkaloid structures is achieved through the generation and tailoring of unique carbon scaffolds. However, many neuroactive alkaloids belong to a scaffold class for which no biosynthetic route or enzyme catalyst is known. By studying highly coordinated, tissue-specific gene expression in plants that produce neuroactive Lycopodium alkaloids, we identified a new enzyme class for alkaloid biosynthesis: neofunctionalized -carbonic anhydrases (CAHs). We show that three CAH-like (CAL) enzymes are involved in a cryptic biosynthetic route to a key bicyclic precursor of the Lycopodium alkaloids, and additionally, we describe a series of oxidative tailoring steps that generate the optimized acetylcholinesterase inhibition activity of huperzine A. Our findings suggest a broader involvement of CAL enzymes in specialized metabolism and provide an example for how successive scaffold tailoring steps can drive potency against a natural protein target of interest.