Structure of limonene synthase, a simple model for terpenoid cyclase catalysis

Abstract

The crystal structure of (4S)-limonene synthase from Mentha spicata, a metal ion-dependent monoterpene cyclase that catalyzes the coupled isomerization and cyclization of geranyl diphosphate, is reported at 2.7-Å resolution in two forms liganded to the substrate and intermediate analogs, 2-fluorogeranyl diphosphate and 2-fluorolinalyl diphosphate, respectively. The implications of these findings are described for domain interactions in the homodimer and for changes in diphosphate-metal ion coordination and substrate binding conformation in the course of the multistep reaction.crystal structure ͉ geranyl diphosphate ͉ linalyl diphosphate ͉ monoterpene cyclase ͉ monoterpene synthase

Selective Monoterpene-like Cyclization Reactions Achieved by Water Exclusion from Reactive Intermediates in a Supramolecular Catalyst

“…by water) to furnish the final products. [5][6][7] An example is the conversion of geranyl diphosphate to limonene and α-terpineol via the α-terpinyl cation, as illustrated in Scheme 1.…”

“…While limonene is obtained through a deprotonation route, capture of the α-terpinyl cation with water affords α-terpineol. 4,[5][6][7] Scheme 2. Encapsulation of 2 by host 1; spheres represent a Ga 3+ center and bisbidentate ligands are depicted as lines.…”

“…26 For example, limonene synthase is thought to bind intermediate linalyl diphosphate in a cisoid conformation, facilitating electrocyclization to an α-terpinyl cation. 7 Given the conceptual similarity between the gemdimethyl effect and certain instances of enzyme catalysis, we next examined the effect of gem-dimethyl substitution on product selectivity. The structure of 2 was varied by replacing -Me and -H β-substituents with dihydro or dimethyl substitution, affording achiral homologues 6a and 7a (Scheme 5).…”

Interception of the Enzymatic Conversion of Farnesyl Diphosphate to 5‐Epi‐Aristolochene by Using a Fluoro Substrate Analogue: 1‐Fluorogermacrene A from (2E,6Z)‐6‐Fluorofarnesyl Diphosphate

“…In fact, 2-fluorogeranyl PP exhibits apparent activesite binding constants with farnesyl PP synthase and several monoterpene synthases similar to those of the natural geranyl substrates. [9][10][11] However, the rates by which the fluoro analogues are converted to fluoro products by these enzymes [9,11] are suppressed by factors of 10 2 to 10 3 . The conversion of geranylgeranyl PP to the tricyclic diterpene taxadiene was intercepted by use of the 6-fluoro substrate variant.…”

Identification of amino acid networks governing catalysis in the closed complex of class I terpene synthases

“…Very recently, a hypothesis pointing to a possible involvement of electrostatic effects during the carbocation cascade of other terpene synthases has been proposed. These effects are thought to be mediated by the PP i anion coproduct that may be retained in the active site (21,24,(26)(27)(28)(29)(30)(31)(32).…”