Ent-Copalyl Diphosphate Synthase - Bifunctionality

Bifunctionality

ent-Copalyl diphosphate synthases from fungi and mosses also have a distinct ent-kaurene synthase activity associated with the same protein molecule. The reaction catalyzed by ent-kaurene synthase is the next step in the biosynthetic pathway to gibberellins. The two types of enzymic activity are distinct, and site-directed mutagenesis to suppress the ent-kaurene synthase activity of the protein leads to build up of ent-copalyl pyrophosphate. Inhibition of ent-kaurene synthase activity, by replacing Mg2+ in the growth medium with Ni2+, has the same effect.

Higher plants typically have separate proteins for ent-copalyl diphosphate synthase and ent-kaurene synthase, although these may be associated as weakly bound dimers or enzyme complexes. Rice (Oryza sativa) has two distinct ent-copalyl diphosphate synthases, which participate in distinct metabolic pathways. Only one ent-copalyl diphosphate synthase has been isolated from a bacterial species (Streptomyces sp. strain KO-3988): it is also monofunctional.

As might be expected, the bifunctional enzymes from lower plants are larger (946–960 residues, 106–107 kDa) than the monofunctional enzymes from higher plants (800–867 residues, 90–98 kDa), although not by twice as much.