3s9v | pdb_00003s9v
abietadiene synthase from Abies grandis
Structural highlights
Function[TPSDV_ABIGR] Involved in defensive oleoresin formation in conifers in response to insect attack or other injury. Involved in diterpene (C20) olefins biosynthesis. Bifunctional enzyme that catalyzes two sequential cyclizations of geranylgeranyl diphosphate (GGPP) to abietadiene. The copalyl diphosphate (CPP) intermediate diffuses freely between the 2 active sites in the enzyme. Changes in reaction pH, but not salt concentration, influence the relative proportion of the major products of the enzyme, abitadiene, levopimaradiene and neoabitadiene.[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedAbietadiene synthase from Abies grandis (AgAS) is a model system for diterpene synthase activity, catalyzing class I (ionization-initiated) and class II (protonation-initiated) cyclization reactions. Reported here is the crystal structure of AgAS at 2.3 A resolution and molecular dynamics simulations of that structure with and without active site ligands. AgAS has three domains (alpha, beta, and gamma). The class I active site is within the C-terminal alpha domain, and the class II active site is between the N-terminal gamma and beta domains. The domain organization resembles that of monofunctional diterpene synthases and is consistent with proposed evolutionary origins of terpene synthases. Molecular dynamics simulations were carried out to determine the effect of substrate binding on enzymatic structure. Although such studies of the class I active site do lead to an enclosed substrate-Mg(2+) complex similar to that observed in crystal structures of related plant enzymes, it does not enforce a single substrate conformation consistent with the known product stereochemistry. Simulations of the class II active site were more informative, with observation of a well ordered external loop migration. This "loop-in" conformation not only limits solvent access but also greatly increases the number of conformational states accessible to the substrate while destabilizing the nonproductive substrate conformation present in the "loop-out" conformation. Moreover, these conformational changes at the class II active site drive the substrate toward the proposed transition state. Docked substrate complexes were further assessed with regard to the effects of site-directed mutations on class I and II activities. Insights into diterpene cyclization from structure of bifunctional abietadiene synthase from Abies grandis.,Zhou K, Gao Y, Hoy JA, Mann FM, Honzatko RB, Peters RJ J Biol Chem. 2012 Feb 24;287(9):6840-50. Epub 2012 Jan 4. PMID:22219188[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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