Metal-dependent enzyme symmetry guides the biosynthetic flux of terpene precursors.

Terpenoids account for more than 60% of all natural products, and their carbon skeletons originate from common isoprenoid units of different lengths such as geranyl pyrophosphate and farnesyl pyrophosphate. Here we characterize a metal-dependent, bifunctional isoprenyl diphosphate synthase from the leaf beetle Phaedon cochleariae by structural and functional analyses. Inter- and intramolecular cooperative effects in the homodimer strongly depend on the provided metal ions and regulate the biosynthetic flux of terpene precursors to either biological defence or physiological development. Strikingly, a unique chain length determination domain adapts to form geranyl or farnesyl pyrophosphate by altering enzyme symmetry and ligand affinity between both subunits. In addition, we identify an allosteric geranyl-pyrophosphate-specific binding site that shares similarity with end-product inhibition in human farnesyl pyrophosphate synthase. Our combined findings elucidate a deeply intertwined reaction mechanism in the P. cochleariae isoprenyl diphosphate synthase that integrates substrate, product and metal-ion concentrations to harness its dynamic potential.