Resurrected Ancestral Cannabis Enzymes Unveil the Origin and Functional Evolution of Cannabinoid Synthases

Cannabinoids, such as tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA) and cannabichromenic acid (CBCA), are bioactive and medicinally relevant compounds found in the cannabis plant (Cannabis sativa L.). These three compounds are synthesised from a single precursor, cannabigerolic acid (CBGA), through regioselective reactions catalysed by different cannabinoid oxidocyclase enzymes. Despite the importance of cannabinoid oxidocyclases for determining cannabis chemotype and properties, the functional evolution and molecular mechanism of this enzyme family remain poorly understood. To address this gap, we combined ancestral sequence reconstruction and heterologous expression to resurrect and functionally characterise three ancestral cannabinoid oxidocyclases. Results showed that the ability to metabolise CBGA originated in a recent ancestor of cannabis and that early cannabinoid oxidocyclases were promiscuous enzymes producing all three THCA, CBDA and CBCA. Gene duplication and diversification later facilitated enzyme subfunctionalisation, leading to extant, highly-specialised THCA and CBDA synthases. Through rational engineering of these ancestors, we designed hybrid enzymes which allowed identifying key amino acid mutations underlying the functional evolution of cannabinoid oxidocyclases. Ancestral and hybrid enzymes also displayed unique activities and proved to be easier to produce heterologously than their extant counterparts. Overall, this study contributes to understanding the origin, evolution and molecular mechanism of cannabinoid oxidocyclases, which opens new perspectives for breeding, biotechnological and medicinal applications.