Monoterpene cyclases: physicochemical features required for pyrophosphate binding determined from inhibition by...

Monoterpene cyclases catalyze the divalent metal ion-dependent conversion of geranyl pyrophosphate, the ubiquitous C10 intermediate of isoprenoid biosynthesis, to a variety of monoterpene skeletons, and the pyrophosphoryl moiety is a primary determinant for substrate binding by these enzymes. To determine what specific features of this functional group are critical for enzymatic recognition, inorganic pyrophosphate and a series of structurally related analogs were examined as inhibitors of geranyl pyrophosphate:(+)-alpha-pinene cyclase and geranyl pyrophosphate:(+)-bornyl pyrophosphate cyclase from sage (Salvia officinalis). Analysis of trends in the magnitude of inhibition by the analogs relative to inorganic pyrophosphate indicated that the combination of ionization state (formal charge) at the enzymatic pH optimum, ability to chelate divalent metal ions, and intramolecular flexibility is required for effective interaction with both cyclases. Only when all of these criteria are met is inhibition of cyclization comparable to that observed with inorganic pyrophosphate.