Structure and mechanism of the diterpene cyclase ent-copalyl diphosphate synthase

Two crystal structures of a three-domain class II diterpene cyclase with substrate and product analogs provide new insights into the mechanistic pathway of this enzyme and illuminate evolutionary and functional relationships within terpenoid biosynthesis more generally. The structure of ent-copalyl diphosphate synthase reveals three α-helical domains (α, β and γ), as also observed in the related diterpene cyclase taxadiene synthase. However, active sites are located at the interface of the βγ domains in ent-copalyl diphosphate synthase but exclusively in the α domain of taxadiene synthase. Modular domain architecture in plant diterpene cyclases enables the evolution of alternative active sites and chemical strategies for catalyzing isoprenoid cyclization reactions.